RESEARCH REPORT SERIES NO. 4 RESEARCH REPORT 1986 SOYBEANS \ ALABAMA AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY DAVID H. TEEM. ACTING DIRECTOR AUBURN UNIVERSITY. ALABAMA MAY 1986 r ., FOREWORD This publication was developed to provide an update of the many aspects of soybean research underway at the Alabama Agricultural Experiment Station. Although results of individ- ual soybean projects have been reported in various Experi- ment Station publications, not since Bulletin 415 was pub- lished in 1971 has a single publication summarized all phases of soybean research underway. Some of the studies reported date back several years, but the findings are such that they are still applicable today. Thus, these reports were included to make the publication representative of Auburn's soybean research program. We trust this information will be useful to soybean growers and to Alabama's total soybean industry Preparation of this comprehensive report was truly a team effort, with 34 individuals representing four subject matter areas and the outlying units of the Alabama Agricultural Ex- periment Station (AAES), the Alabama Cooperative Exten- sion Service (ACES), and Agricultural Research Service, U.S. Department of Agriculture (USDA). The contributors are: J. L. Stallings, Associate Professor of Agricultural Economics and Rural Sociology, AAES James R. Hurst, Economist-Crops Marketing, ACES David B. Weaver, Assistant Professor of Agronomy and Soils, AAES G.V Granade, former Research Associate of Agronomy and Soils, AAES R. Rodriguez-Kabana, Professor of Botany, Plant Pathology, and Microbiology, AAES B. H. Cosper, Research Associate of Agronomy and Soils, AAES D.L. Thurlow, Associate Professor of Agronomy and Soils, AAES C.B. Elkins, Adjunct Associate Professor of Agronomy and Soils, USDA A.E. Hiltbold, Professor of Agronomy and Soils, AAES Clyde E. Evans, Professor of Agronomy and Soils, AAES J.T. Touchton, Associate Professor of Agronomy and Soils, AAES J.T. Cope, Jr., Professor Emeritus of Agronomy and Soils, AAES C.C. King, Jr., Professor of Agronomy and Soils, AAES J.A. Pitts, Superintendent, Chilton Area Horticulture Sub- station (formerly Superintendent, Brewton Experiment Field), AAES C. H. Burmester, Research Associate of Agronomy and Soils, AAES Fred Adams, Professor Emeritus of Agronomy and Soils, AAES John W Odom, Assistant Professor of Agronomy and Soils, AAES R. Harold Walker, Associate Professor of Agronomy and Soils, AAES James R. Harris, Graduate Assistant of Agronomy and Soils, AAES Ted Whitwell, former Weed Scientist, AAES and ACES T.P. Mack, Assistant Professor of Zoology-Entomology, AAES C.B. Backman, Lab Technician II of Zoology-Entomology, AAES J.D. Harper, Professor ofZoology-Entomology, AAES Paul A. Backman, Professor of Botany, Plant Pathology, and Microbiology, AAES Mark A. Crawford, Research Associate of Botany, Plant Pa- thology, and Microbiology, AAES Mack Hammond, former Graduate Assistant of Botany, Plant Pathology, and Microbiology, AAES D.G. Robertson, Research Associate of Botany, Plant Pa- thology, and Microbiology, AAES C. E Weaver, Research Associate of Botany, Plant Pathology, and Microbiology, AAES P S. King, Lab Technician III of Botany, Plant Pathology, and Microbiology, AAES E. L. Snoddy, Lab Technician II of Botany, Plant Pathology, and Microbiology, AAES Curt M. Peterson, Professor of Botany, Plant Pathology, and Microbiology, AAES Michael W Folsom, Graduate Assistant of Botany, Plant Pa- thology, and Microbiology, AAES Roland R. Dute, Assistant Professor of Botany, Plant Pathol- ogy, and Microbiology, AAES Larry W Dalrymple, Lab Technician III of Botany, Plant Pa- thology, and Microbiology, AAES David H. Teem Acting Director Alabama Agricultural Experiment Station Auburn University CONTENTS Page FOREWORD .................................................................. 3 INTRODUCTION ... ............... ................................. ......... 5 Status of Alabama's Soybean Industry ..................................... 5 International Trade in Soybeans ......... ............................... 6 Alabama's Soybean Marketing System ..................................... 7 VARIETY DEVELOPMENT ........................................................ 9 Evaluation and Improvement of Soybean Varieties ............................. 9 CULTURAL PRACTICES .................. ...................................... 11 Effect of In-row Chisel at Planting on Yield and Growth of Soybeans ............................................... 11 Tillage Systems for Full-season and Double-cropped Soybeans................... 12 Crop Rotations .......... ....................................... 14 Soybean Row Spacing.................. ........ ................. 15 Planting Date Effects on Soybean Growth and Yield ............................ 17 Effect of Depth of Planting on Stand of Soybeans ........................... .. 19 Soil Fertility Requirements for Soybeans ................................... 20 Soybean Inoculation and Nitrogen Fixation ...................................... 22 PEST CONTROL ............... 27 Soybean Weed Control .......... ................................... 27 Management of Soybean Insects.......... .............................. 32 Biological Control of Soybean Insect Pests.................................35 Interrelationships of Soybean Cultivars and Environment to Disease Development and Fungicide Performance ............................. 37 A Common Sense Timing System for the Application of Foliar Fungicides ...................... ........................... 39 Aerial Applications of Fungicides to Soybeans ............. ...................... 39 Reducing Losses from Soybean Stem Canker ................................ 40 Nematode Problems in Soybeans ......................................... 40 PHYSIOLOGICAL DEVELOPMENT .......... ........................................ 44 Flower and Pod Abscission of Soybeans................ .................... 44 FIRST PRINTING 5M, MAY 1986 Information contained in this report is available to all persons without regard to race, color, sex, or national origin. INTRODUCTION Status of Alabama's Soybean Industry Thousands of acres J.L. Stallings 3,000 Acreage of soybeans has dramatically increased in Ala- bama in the last 20 years after being a relatively minor crop in earlier years. The increase started slowly after 1960, then 2,500 increased generally at an increasing rate until peak acreage was reached in 1979, figure 1. Along with this increased acreage has come a shift in lo- 2,000 cation of soybean production, figure 2. In 1959, which was before the start of the general increase, soybean acreage in Alabama was concentrated mostly in Baldwin County in the Gulf Coast Region, with only scattered acreage in the rest of 1,500 the State. By 1969, however, while the Gulf Coast Region was still important, new acreage concentrations were starting to develop in the Black Belt and Limestone Valley regions. 1,000 These regions continued to increase acreage during the next 10 years, but by 1979, the peak acreage year, important new production regions had developed in the Wiregrass, Sand500 Mountain, Upper Coastal Plains, and Lower Coastal Plains regions. The dramatic increase in acreage of soybeans in the last 2001 1 1 years probably resulted from a variety of reasons, including 06 7 15 0 increasing prices and value, profitability relative to alterna- 1960 '65 '70 '75 '80 '85 tive enterprises, increasing use with wheat in double crop- ping, and adaptability of soybeans to a wider range of soil FIG. 1. Harvested acres of soybeans in Alabama, 1960-85. FIG. 2. Harvested acres of soybeans in Alabama, by counties, 1959, 1969, and 1979. [5] 1979 1959 1969 + = less than 500 acresI dot = 500 harvested acres types than for some other row crops. However, the trend in average yields in Alabama has remained approximately level to slightly downward in recent years, a phenomenon of in- creasing concern. There are needs and opportunities for dra- matic breakthroughs in soybean yields. International Trade in Soybeans J.L. Stallings International trade is the dominant economic factor in the U.S. soybean economy. Between 50 and 60 percent of all U.S. soybeans have been exported in recent years. This means that more than 1 of every 2 acres of U.S. soybeans is dependent upon export markets. Because of the fungible na- ture of every bushel of soybeans (i.e.-i bushel of soybeans is approximately equal to every other bushel), the same is true of Alabama, regardless of the bushels actually exported from the State. Over the last 5 years, the United States has exported an average of 55.3 percent of total soybean produc- tion. Thus, Alabama's export share is that proportion of the State output. The value of Alabama's export share increased to a high of 203.6 million dollars in 1979-80. WHOLE SOYBEAN PRODUCTION AND TRADE The United States is by far the most important producer of soybeans in the world, accounting for an average of 63.9 per- cent (nearly two-thirds) of world production in the 5 years from 1977 to 1981. Only three other countries, individually, averaged over 1 percent or more of world production during these years: Brazil, with 16.3 percent; the Peoples Republic of China, 9.5 percent; and Argentina, 4.0 percent. Given the already large U.S. share of world exports, the prospects for increasing the United States' sale of whole beans by obtaining a bigger share of the existing market would seem to be somewhat limited. More promising is the potential for sales to an expanding total market. Such expan- sion may occur with or without U. S. encouragement as coun- tries become more affluent and develop livestock feeding in- dustries. There may be somewhat greater potential for expansion of the world market share in exports of soybean meal and soybean oil, where the United States does not now control as large a proportion of the market. There is also the question of whether exports of whole beans should be expanded at the expense of exports of meal and oil. Conventional economic and political wisdom would hold that, from the United States' perspective, the more of the manufacturing process that can be done in the United States using domestic labor, the better. The process of con- verting beans to meal and oil before export presumably would result in more employment in the United States and the export of a higher value product per unit of weight. SOYBEAN CAKE AND MEAL PRODUCTION AND TRADE Soybean meal production does not necessarily take place in the countries where the soybeans are produced. For in- stance, while the four largest producers of soybeans ac- counted for an average of 93.7 percent of world production during 1977-81, these countries accounted for only 66.8 per- cent of meal production. Many important users of soybean meal prefer to import whole beans and produce their own meal and oil. Some of these countries in turn export meal and, especially, oil in competition with the United States. Notable among these are the countries of the European Eco- nomic Community (EEC). While the United States dominated world production of soybean meal with an average of 40.7 percent during 1977-81, the domination was not nearly as great as with soybean pro- duction (63.9 percent) and whole soybean exports (81.7 per- cent). Brazil is the only other important producer of both soy- beans and soybean meal competing with the United States in the export of soybean meal. The United States is the world's largest producer of soy- beans and soybean meal, but it is not the dominant exporter of meal. Over the period 1977-81, Brazil averaged slightly more meal exports than the United States, with 36.8 percent of the world total. One of the reasons for Brazil's leadership in meal exports is that the United States utilized domestically an average of 72.2 percent of its total meal supply for these years. U.S. meal exports, therefore, are more of a residual market after domestic needs are met than is the case in Bra- zil. This condition applies to Alabama as well. With its large poultry industry, Alabama uses virtually all soybean meal produced within the State. During this same period, Brazil used domestically only 25.6 percent of its production of meal, leaving a larger absolute amount for export. While the EEC produces much of the meal it uses from imports of whole beans, it is also the world's principal im- porter of soybean meal. The EEC accounted for 52.7 percent of all world imports of soybean meal during 1977-81. The Communist bloc countries of Europe have also become im- portant importers as they have increasingly developed more livestock feeding, accounting for 22.7 percent of meal im- ports during 1977-81. European countries together account for about three-fourths of the world's meal imports. As with world imports, the EEC and the Communist countries of Europe (including Yugoslavia) took the largest amounts of U.S. exports of soybean meal, 49.8 and 20.2 per- cent, respectively, during 1977-81. When all of Europe is in- cluded, about three-fourths of U. S. trade in soybean meal is accounted for. Only Canada, Japan, and Mexico are other im- portant customers for U.S. soybean meal. -SOYBEAN OIL PRODUCTION AND TRADE As with world meal production, the United States and Bra- zil dominated world soybean oil production (41.5 and 16.7 percent, respectively, during 1977-81). Only these two coun- tries produced enough oil from their own beans to have a sig- nificant amount to export. Most other important producers of oil, excepting the Peoples Republic of China, produce it from imported beans. Relatively few countries of the world export important amounts of soybean oil, but a great many import at least some. While importers of oil are many of the same countries that export whole beans and meal, the important importers [6] of oil comprise a different set of customers than for beans and meal. Important exporters of oil are the United States, Brazil, and Argentina, as with beans and meal. However, some of the European countries that import whole beans and do their own crushing to obtain the meal have a surplus of oil for ex- port. Among these are the Netherlands, Spain, West Ger- many, France, Belgium, and Luxemburg. India has consistently accounted for a large percentage of the world's imports of soybean oil to meet the needs of its large population. Unlike the Peoples Republic of China, which produces most of what it uses, India consistently does not produce enough edible oils for its domestic needs and should be a good customer for edible oils for many years. Over the past 5 years, the United States has contributed an average of 41.9 percent of India's imports of soybean oil. A large number of countries import important amounts of soybean oil, but none is as important as India. However, over 37 percent of the soybean oil imported is accounted for by countries other than the top 10. Much of this total is to third world countries, especially in Africa, which is exported under the PL 480 (Food for Peace Program) program as a form of foreign aid. While none of these countries beyond the top 10 is a significant importer individually, together they are a sub- stantial outlet for sales of soybean oil. A current problem hindering their growth is the large third-world debt which limits their purchasing power in the world market since most of their hard currency must go to service their debts. U.S. exports of soybean oil have generally followed the same pattern as the more important importers of the world, with a few exceptions. India was the most important cus- tomer for soybean oil during 1977-81, averaging 25.2 percent of U.S. exports, while Pakistan was second with 14 percent. The United States has supplied over 62 percent of Pakistan's total imports over the last 5 years. After India and Pakistan, a large number of countries take an important share of U.S. exports of oil, but no other coun- try dominates. There is also an important amount of exports beyond the top 10 accounting for over 26 percent of U. S. ex- ports. Most of this is in shipments under PL 480 as a form of foreign aid, and represents a small amount to each of a large number of countries. Alabama's Soybean Marketing System James R. Hurst Alabama's soybean marketing system consists of some 75 country elevators, two processing plants, and one export el- evator located throughout the major producing areas of the State, table 1. Most country elevators which buy soybeans and grain from local producers for shipment to export mar- kets or to domestic processors are owned by or deal exclu- sively with one of the major cooperatives or private export firms. Almost all Alabama-produced soybeans are shipped by country elevators either to domestic processing plants in Decatur and Guntersville or to Mobile for export. Alabama has few terminals or sub-terminal elevators because shipping directly to processors or exporters is more economical than is transfer through terminal elevators. Also, increased farm storage and development of highways have caused more soy- beans to move. directly from farms to processors and export- ers. Such direct shipments result in improved prices to farm- ers. The State had approximately 75 million bushels of grain and soybean storage capacity in 1979, 2.9 times the 1969 ca- pacity. On-farm storage accounted for 35 million bushels and commercial storage (including soybean processing plants and export elevators) for 40 million bushels in 1979. The effective handling capacity of the commerical market- ing system is about 160 million bushels annually. The system is adequate to handle the annual volume but is congested during harvest season, when a majority of the soybean crop is marketed. .Most soybean producers have an adequate number of al- ternative marketing facilities within reasonable trucking dis- tance to assure receiving a competitive price. Geographical price differentials within Alabama over the period 1977 to 1981 ranged from about 10? to 50?. Cash soy- bean prices at country elevators were generally higher in the southern part of the State in the fall and winter months and higher in the northern part during the summer months just before harvest. With the decreasing export demand in the 1980's, geographical price differentials are becoming less sig- nificant. Locational price differences can be explained largely by the fact that export demand peaks during the fall and winter, while domestic processor demand peaks in summer. When prices at more distant terminal markets are high enough to more than offset the additional transportation costs, produc- ers may find it profitable to sell at the more distant markets. Producers who market their soybeans uniformly through- out a marketing year may find it profitable to make some sales to distant markets based on current market differentials. However, when adjusted for transportation costs, geograph- ical price differentials are not as significant as seasonal price differentials. This leads to the conclusion that where to sell has not offered as much opportunity for increasing profit as when to sell in recent years. [7] TABLE 1. ELEVATORS SERVING ALABAMA SOYBEAN PRODUCERS, 1984 Firm Phone Storage Firm Phone Storage number capacity number capacity Bu. Bu. Gold Kist, Inc., Summerdale .............. 989-6257 318,000 Section Gin & Grain, Section .............. 228-4238 125,000 L. Irwin & Son, Foley .................... 943-8067 115,000 Scott Brothers Grain Elev., Detroit ........ 273-7161 90,000 Louis Dreyfus Corp. Robertsdale .......... 947-5002 150,000 Lauderdale County Coop., Florence ........ 764-8441 272,000 E.G. Manci, Loxley ...................... 964-5031 40,000 Lawrence Co. Exchange, Inc., Moulton..... 974-9213 100,000 W.J. Nelson Co., Fairhope ................ 928-8225 16,000 Wheeler Grain Co., Hillsboro ............. 637-2772 400,000 Fitzpatrick Grain, Fitzpatrick ............. 738-4747 92,000 Gold Kist Soy Elev., Athens............... 232-8776 80,000 Quality Seed & Fertilizer, Fitzpatrick....... 277-5400 100,000 Limestone Farmers' Coop., Athens......... 232-5500 150,000 Lapeyrouse Grain Corp., Greenville........ 382-6631 160,000 Wheeler Grainery, Athens .... ........... 729-1772 400,000 Cherokee Farmers Coop., Centre .......... 927-3135 30,000 Central Ala. Grain Elev., Hurtsboro ........ 485-3203 290,000 Cherokee Milling, Centre ................ 927-5192 30,000 J. D. Ray Co., Tuskegee .................. 727-1260 50,000 Farmer's Grain-Leesburg, Inc., Leesburg... 526-8118 70,000 Gold Kist Grain, Huntsville ............... 539-0425 51,000 Central Grain & Feed Supply, Maplesville .. 366-2672 52,000 Madison County Coop., Meridianville ...... 828-0744 47,000 Colbert Farmers Co-op, Tuscumbia ........ 383-6462 95,000 Demopolis Grain Corp. (Lapeyrouse), Colbert Farmers Co-op, Leighton .......... 446-8170 70,000 Demopolis............................. 289-1440 380,000 Farmer Home Gin Co., Leighton ........... 446-8330 32,000 Fincher Farm Supply, Inc., Hackleburg ..... 935-3137 45,000 Darby Grain Elevator, Inc., Evergreen 578-1420 250,000 McRae Brothers, Hamilton ................ 921-2639 150,000 Anderson's Grain, Andalusia .............. 223-6541 100,000 Cargill, Inc., Guntersville ................. 582-5719 575,000 Zorn Brothers, Inc., Florala ............... 858-3297 155,000 Central Soya of Ala., Inc., Guntersville ..... 582-3223 240,000 Brantley Gin Co., Brantley ............... 527-3208 30,000 Continental Grain-Processing Div., Gold Kist, Inc., Browns .................. 628-6240 250,000 Guntersville..............582-5664 3,200,000 R.W. Kirk and Son, Orrville. .............. 996-8301 280,000 Great Combine, Guntersville .............. 582-6206 110,000 Selma Grain Corp., Selma ................ 874-6676 302,000 Ala. State Docks Public Grain Elev., Mobile 690-6063 3,200,000 M.B. Bell, Jr., Grain Co., Sylvania ......... 638-3666 120,000 Lapeyrouse Grain Corp., Mobile. .......... 476-3592 1,000,000 DeKalb Farmers Coop., Inc., Rainsville..... 683-2569 170,000 Lapeyrouse Grain of St. Elmo, St. Elmo .... 957-2177 45,000 Great Combine, Inc., Crossville ............ 528-7165 75,000 Farmers Coop Market, Frisco City ......... 267-3175 15,000 Seed Processors, Inc., Wetumpka...........567-4710 88,000 Lapeyrouse Grain Corp. of Ala., Claiborne . 258-2494 427,000 Atmore Truckers Assoc., Inc., Atmore ...... 368-2191 32,000 Montgomery Grain Corp. (Lapeyrouse), Frank Currie Gin Co., McCullough ......... 577-6411 30,000 Montgomery .......................... 263-5541 594,000 Escambia Farm & Seed Co., Inc., Atmore... 368-1340 300,000 AFC Marketing Ser., Inc., Decatur ........ 353-2961 375,000 Lapeyrouse Grain Corp., Atmore ........... 368-4539 85,000 Bunge Grain, Inc., Decatur ............... .350-4550 7,500,000 Fayette Grain & Feed Co., Fayette ........ 932-6732 47,000 Uniontown Grain Elev., Uniontown ........ 628-6726 250,000 Farmer's Supply & Mkt. Assn., Russellville 332-3273 64,000 Lapeyrouse Grain, Aliceville ............... 455-2271 312,000 Brooks Grain Co., Inc., Samson ............ 898-7194 250,000 Tom Soya Grain, Aliceville ................ 373-8761 140,000 Geneva Grain Co., Inc., Geneva ............ 684-2188 468,000 Pike Farmers Coop., Troy ................ 566-1834 45,000 Harrell Milling Co., Inc., Hartford .......... 588-2261 400,000 Central Ala. Grain, Inc., Hurtsboro ........ 485-3203 292,000 Hartford Farm Coop., Inc., Hartford ....... 588-2992 135,000 Chattahoochee Valley Grain, Phenix City .... 298-1498 426,000 AFC Marketing Ser., Demopolis ............ 289-1100 1,000,000 Gold Kist, Inc., Pell City .................. 884-2415 42,000 Columbia Grain (Lapeyrouse), Columbia .... 696-4414 579,000 Talladega Coop Grain Elev., Talladega ...... 362-2716 80,000 I.E. Airheart & Sons, Scottsboro............574-2011 171,000 Tuscaloosa Grain Corp. (Lapeyrouse), Jackson Farmers Co-op, Scottsboro..........574-1688 85,000 Northport ............................ 345-3727 572,000 Jackson Farmers Co-op, Stevenson .......... 437-8829 11,000 Gold Kist, Inc., Jasper .................... 387-1436 165,000 Pisgah Gin Co., Pisgah ................... .451-3255 25,000 Gold Kist Elev., Camden ................. .682-4632 183,000 [8] VARIETY DEVELOPMENT Evaluation and Improvement of Soybean Varieties David B. Weaver, G.V. Granade, R. Rodriguez-Kabana, and B.H. Cosper Varietal selection is an integral part of any soybean man- agement program. Not only do soybean varieties differ in yield potential, but frequently these differences occur be- cause of other important agronomic and pest resistance char- acteristics. A variety that may be best at one location may re- spond poorly at another because of differences in rainfall, soil fertility, pest population, and a host of other variables that shape the environment in which the plants are growing. Var- ietal selection is complicated even further by the number of varieties available for production in Alabama. In 1971 there were only 15 varieties available for production. In contrast, the 1983 Experiment Station variety tests included 103 vari- eties. VARIETY DEVELOPMENT In 1981, a soybean breeding project was initiated to de- velop improved soybean varieties especially adapted to Ala- bama growing conditions. The primary objective is to develop varieties with higher yield potential that are better able to re- sist attack by some of Alabama's major pests, including soy- bean cyst nematodes, root-knot nematodes, and stem canker. Over 4,000 experimental lines have been evaluated so far. Several of these have shown good agronomic potential and will be yield tested at several locations across Alabama. Other experimental lines are currently in various stages of de- velopment. Experimental lines are being grown year- round-at the Plant Breeding Unit in Tallassee during the summer and in winter nurseries in Belize, Central America, and in the greenhouse at Auburn during the winter. CURRENT VARIETIES Seed yields for selected varieties are summarized for the years 1981-83 for five soybean production areas in Alabama, table 2. Analysis of variety tests conducted since 1976 re- vealed that variety recommendations are best made on the basis of five major areas: the Baldwin-Mobile county (Gulf Coast) area, the Black Belt area, and the remainder of the State divided into north, central, and south areas. Three years is considered to be the minimum time necessary for testing and comparing varieties, because some years may fa- vor certain varieties while the same variety may do poorly in other years. Some newer varieties (released since 1980) are probably suitable for production in one or more areas but have not had sufficient testing time to be included in the com- parisons. Some of the new public varieties, Foster, Kirby, Johnston, and Jeff, have been compared to older, more established va- rieties, tables 3 and 4. These new public varieties have not been sufficiently tested in Alabama variety tests to appear on the recommended list, and seed of some of these varieties may still be limited. Also reported in the tables are reactions to a number of pests that are frequently a problem in Ala- bama. For many varieties, large differences in reaction to these pests are much more important than small differences in yield. Jeff, for example, yielded about 3 bushels per acre less than Tracy-M or Centennial over a 3-year period at the Tennessee Valley Substation, table 3. However, Centennial and Tracy-M are susceptible to race 4 of the soybean cyst nematode and would be expected to yield poorly in fields in- fested with this pest.Jeff is resistant and should perform nor- mally under race 4 cyst nematode infested conditions. Special pest problems that have recently been evaluated in Alabama Agricultural Experiment Station trials are covered in the fol- lowing paragraphs. TABLE 2. PERFORMANCE OF SELECTED SOYBEAN VARIETIES, 1981-83 Seed yield per acre Variety North Alabama Central South Alabama Variety Early planted Late planted Alabama Early planted Late planted Bu. Bu. Bu. Bu. Bu. Bu. Bu. Early Bedford.................... 36.3 34.3 13.4 46.4 Deltapine 105 ............... . 42.6 39.5 25.8 40.9 29.7 24.3 Essex...................... 34.8 38.9 Forrest..................... 38.8 38.7 24.8 34.2 24.9 15.3 35.2 Medium Centennial ................. 32.6 33.6 24.1 41.1 30.0 17.1 40.6 Coker l56.................. 36.5 37.3 24.5 45.2 19.1 22.6 42.8 Davis...................... 33.5 35.8 24.9 44.7 33.6 24.9 43.8 Tracy-M.................... 34.4 34.7 24.8 37.5 25.3 20.9 41.2 Late Braxton .................... 33.5 35.2 25.6 46.3 33.4 27.1 46.1 Cobb ...................... 48.7 39.9 18.4 42.9 Foster ..................... 21.2 45.5 13.0 41.8 GaSoy 17 ................... 23.8 47.3 34.4 18.1 46.1 Hartz 7126 ................. 26.9 40.4 15.4 Ransom .................... 23.1 43.1 30.5 21.0 43.7 W right ..................... 24.4 45.0 32.5 23.0 46.0 L.S.D. (.05) ................ 6.2 4.2 8.1 9.9 7.5 5.3 9.8 [9] TABLE 3. MATURITY GROUP VI COOPERATIVE UNIFORM SOYBEAN TEST, TENNESSEE VALLEY SUBSTATION, 1981-83 Variety Yield/acre M.i.' M.a. SCN-3 SCN-4 S.C. Bu. Centennial....... 36.4 R 2 S R S MR Tracy-M ......... 36.4 S S S S R Jeff ............. 33.0 R S R R S 'M.i. = Meloidogyne incognita (cotton root-knot nematode); M.a. = M. arenaria (peanut root-knot nematode); SCN = soybean cyst nematode (race 3 and 4); S.C. = stem canker. 2 R = resistant, MR = moderately resistant, and S susceptible. TABLE 4. MATURITY GROUP VIII COOPERATIVE UNIFORM SOYBEAN TEST, GULF COAST SUBSTATION AND TALLASSEE, 1981-83 Variety Yield/acre M.i.' M.a. SCN-3 SCN-4 S.C. Bu. Hutton.......... 31.6 R 2 S S S S Cobb............ 33.9 R S S S MR Foster........... 33.6 R S R S MR Kirby ........... 33.4 R R R S MR Johnston.......... 34.9 S S S S MR IM.i. = Meloidogyne incognita (cotton root-knot nematode); M.a. = M. arenaria (peanut root-knot nematode); SCN = soybean cyst nematode (race 3 and 4); S.C. = stem canker. 2 R = resistant, MR = moderately resistant, and S = susceptible. Root-knot nematodes. Several root-knot resistant or root- knot susceptible varieties were compared for yield perfor- mance on a field in Baldwin County, Alabama, that was se- verely infested with the cotton root-knot nematode, table 5. Two tests were conducted-one during 1982 and 1983 and one during 1983 only. Varieties that are susceptible to the cot- ton root-knot nematode were included in the tests for com- parison purposes. Results confirm that nematode resistance is highly specific. Coker 317 has good resistance to soybean cyst nematode, but this resistance did not prevent damage by the cotton root-knot nematode. Under high levels of root-knot nematode infestation, such as those occurring in this field, even root-knot resistant varieties offer little protection. With the Environmental Protection Agency's recent elimination of EDB, an effective and economical soil fumigant, nematode resistant varieties will be a key control practice for many TABLE 5. SEED YIELDS OF SOYBEAN VARIETIES GROWN WITHOUT CONTROL FOR ROOT-KNOT NEMATODES, BALDWIN COUNTY, ALABAMA Cultivar Yield/acre Bu. Test 1 (1982-83) Foster ............................................. 21.1 Coker 317' ............................................. 9.9 Ransom ............................................... 10.5 Braxton ............................................ 15.4 GK 49 .. . 10.3 A 7372 11.2 Test 2 (1983 only) Kirby. ... 35.4 Foster ................................................. 26.1 Coker 317' .......................................... 19.0 Ransom ' ............................................... 14.5 Johnston' .............................................. 8.5 Cobb...............................................8.5 'Susceptible to root-knot nematode. All other varieties are resistant. TABLE 6. STEM CANKER AND IRON CHLOROSIS RATINGS FOR SELECTED SOYBEAN VARIETIES Variety Stem canker rating' Iron chlorosis rating B ay .................. 1.0 2 Bedford.............. 3.0 2 Deltapine 105 ......... 2.7 2 Deltapine 345......... 2.5 1 Essex..............M 2 Forrest................ 2.7 3 Agratech 67........... 2.3 2 Centennial ........... 1.3 3 Coker 156 ............ 2.0 2 D avis ....... ......... 1.1 2 Jeff .................. 3.0 2 Lee 74 ............... 2.7 2 Tracy-M .............. 1.0 2 Agripro AP 70 ....... 2.3 2 Braxton .............. 1.0 1 Coker 237............ 3.3 1 Duocrop ............. 2.7 2 GaSoy 17 ............. 2.0 2 Govan ........... 2.3 2 Ransom ......... ....... 2.3 2 Wilstar 790 ........... 3.3 2 W right ............... 2.0 3 Cobb ................. 2.3 2 Coker 488 .............. 2.0 2 Foster ......... 2.0 3 Hutton.................. 4.0 1 Kirby . ................. 2.7 3 'Stem canker and iron chlorosis are rated on a scale of 1 to 5, with 1 = growers. Based on results of these tests, Kirby and Foster (new releases by the USDA and University of Florida) offer the best chance for success in soybean fields infested with the root-knot nematode. Braxton also offers some resistance in a variety with slightly earlier maturity. These tests were con- ducted under extreme conditions and yield losses will prob- ably not be so severe under more normal infestation levels. Stem canker. Much attention has been paid to varietal re- sponse to infection by stem canker (Diaporthe phaseolorum var. caulivora), first diagnosed in Alabama in 1977. Initial ob- servations and research quickly discovered that a few vari- eties were extremely and uniformly susceptible to stem canker, and two or three varieties were resistant. The major- ity of varieties lie somewhere between these two extremes. Average disease ratings from several experiments for many adapted varieties are presented in table 6. Any variety with a rating of 4 or higher is considered to be extremely suscep- tible and unsuited for planting under any circumstances. Va- rieties with a rating of 2 to 3 are considered to be somewhat susceptible. Those few varieties with a rating less than 2 are considered to be resistant, but it would be inadvisable to plant only those varieties in view of the other pests that may be present. Tracy-M and Braxton, for example, have no resis- tance to the soybean cyst nematode. Other characteristics. Also included in table 6 is an iron chlorosis susceptibility rating. Iron chlorosis is caused by the unavailability of iron in certain high pH soils, and some va- rieties are better able to extract iron at low soil levels than others. This condition is usually not apparent except during periods of dry weather, but can cause significant yield loss. See color plate numbers I and 2, page 24. [10] CULTURAL PRACTICES Effect of In-row Chisel at Planting on Yield and Growth of Full-season Soybeans D.L. Thurlow, C.B. Elkins, and A.E. Hiltbold Sandy surface soils, such as those in the Coastal Plains of Alabama, are highly susceptible to traffic and tillage compac- tions. Wheel traffic of tractors and combines often compacts the plow layers, and disks and plows can create severe com- paction at the bottom of the tillage zone, which is referred to as a disk, plow, or tillage pan. These compacted layers often prevent proper root development and prevent roots from reaching available moisture in the subsoil horizons. Tillage pans are present in almost all soils, but they do not restrict root development in all soils. During 1974 and 1975, a study was conducted at the Wire- TABLE 7. EFFECT OF PLANTING DATE AND IN-ROW CHISELING ON SOYBEAN YIELD AND PLANT HEIGHT, WIREGRASS SUBSTATION, 1974-75 Soil Yield/acre Plant height preparation Variety 1974 1975 Av. 1974 1975 Av. Bu. Bu. Bu. In. In. In. Early Planting Date' Chisel Forrest 45 27 36 28 24 26 Chisel McNair 600 47 34 41 30 25 28 Chisel Bragg 45 29 37 33 29 31 Av. 38 28 Conventional Forrest 30 25 28 23 21 22 Conventional McNair 600 36 36 36 21 24 23 Conventional Bragg 33 27 30 27 28 28 Av. 31 24 Late Planting Date Chisel McNair 600 44 31 38 30 37 34 Chisel Bragg 54 27 41 35 31 33 Av. 40 34 Conventional McNair 600 33 30 32 25 23 24 Conventional Bragg 39 25 32 31 26 29 Av. 32 27 'Planting dates were May 10 and May 30 for 1974 and May 22 and June 3 for 1975. grass Substation to determine the effects of in-row subsoil- ing, conventional tilled soil, and planting date on growth and yields of Forrest, McNair 600, and Bragg soybean varieties. The conventional treatment seedbed was prepared by turn- ing soil 9 inches, disking, and rotary tilling (prior to planting). The chisel treatment was prepared with a 2-inch subsoil shank run to a depth of 14 inches and the soil bedded over the chisel opening. There was a yield increase to chiseling under the row with all varieties at both planting dates in 1974. However, yields were not different due to chiseling in 1975. There was a plant- ing date interaction on yield of McNair 600 and Bragg in 1974 in that McNair 600 produced a higher yield for May 11 plant- ing but was lower in yield than Bragg for the May 30 planting, table 7. All varieties responded with increased plant height at both planting dates and in both years where the subsoil chisel was used. From 1977 through 1981, research was done at nine loca- tions in Alabama to determine if disrupting the tillage pans with an in-row subsoiler at planting, in both conventional and no-tillage cropping systems, would improve soybean plant growth and yields. The conventional tillage treatment consisted of either chis- eling or turning soils 8-10 inches deep and then disking, ro- tary tilling, or using a combination seedbed conditioner to prepare a seedbed. The no-tillage treatment was planted into a killed stand of small grain or old crop residue with only a double disk opener planter. The in-row subsoil treatments were planted with a Brown Harden Super Seeder?. Subsoil depth was 12-14 inches. Essex soybeans were planted in the three northern Ala- bama locations and Ransom soybeans were planted in the six southern Alabama locations. All plantings were made for full season production using a 36-inch row width. The yield and growth of soybeans are reported as relative yield and plant height in relation to the conventional tillage treatment, tables 8 and 9. TABLE 8. RELATIVE PLANT HEIGHT OF SOYBEANS AS AFFECTED BY PREPLANT SOIL PREPARATION AND IN-ROW SUBSOILING ON SEVEN SOILS IN ALABAMA' Relative plant height by location Tillage Tennessee Sand Prattville Monroeville WiregrassGulf treatment Valley Mountain Tallassee Experiment Experiment Substationrgr Coast Substation Substation (1977-81) Field Field (1978) Substation (1978-79) (1977-78) (1977-81) (1977&79) (1978) Conventional tillage .......... 100 100 100 100 100 100 100 Conventional tillage plus in-row subsoiling ...... 100 101 107 100 102 125 103 No-tillage .................. 97 101 82 71 87 71 76 No-tillage plus in-row subsoiling .......... 102 109 107 94 100 118 94 Av. plant height for conventional tillage, inches ............. 26 25 31 31 33 23 37 'Soil types: Tennessee Valley Substation, Decatur clay; Sand Mountain Substation, Hartsells fine sandy loam; Tallassee, Cahaba fine sandy loam; Prattville Field, Lucedale fine sandy loam; Monroeville Field, Lucedale fine sandy loam; Gulf Coast Substation, Malbis fine sandy loam; Wiregrass Substation, Dothan fine sandy loam. [11] TABLE 9. RELATIVE YIELD OF SOYBEANS AS AFFECTED BY PREPLANT SOIL PREPARATION AND IN-ROW SUBSOILING ON EIGHT SOILS IN ALABAMA Tennessee Sand Upper Prattville Monroeville Wiregrass Gulf Tillage Valley Mountain oastal Tallassee Experiment Experiment Substationregrass Coast Tillage Valley Mountain Plain Substatio treatment Substation Substation bstation (1980-81) Field Field Substation (1978-79) (1977-79) (197879) (1978-81) (1977-79) (1978-80) (1978-79) Conventional tillage ................... 100 100 100 100 Conventional tillage plus in-row subsoiling ................... . 113 92 106 115 105 99 156 98 No-tillage ........................... 114 71 87 84 66 85 85 79 No-tillage plus in-row subsoiling ................... . 116 87 91 100 104 105 152 100 Av. yield for conventional tillage, bushels per acre .................... 37.4 33.9 28.8 28.4 19.5 37.1 15.6 33.9 When compared to the conventional tillage treatment, no- tillage without subsoiling resulted in reduced soybean yields and plant growth on all Coastal Plains and River Terrace soils. The use of the in-row subsoiler with the conventional tillage system at planting increased yields over the conventional til- lage system at Tallassee and the Wiregrass Substation. The Tallassee soil had a strong plow pan and the Wiregrass soil developed a compact layer in the lower plow layer during the herbicide incorporation with rotary tiller and disk. Yields of soybeans under the no-tillage system with the in- row subsoiler were equal to those grown on the conventional system with and without the in-row subsoiler except at the Sand Mountain Substation. There the highest yields were from conventional tillage. The most noticeable effect of tillage treatments on vegetative growth was reduced plant height in the no-tillage treatment at Tallassee, Prattville Field, Mon- roeville Field, Wiregrass Substation, and Gulf Coast Substa- tion. At the Tennessee Valley Substation, all plots produced good growth and yield with all tillage systems. The results of these studies suggest that for full season soy- beans, yields from no-tillage systems may be comparable to or higher than yields from conventional tillage systems pro- vided an in-row subsoiler is used on Coastal Plains and River Terrace soils. See color plate number 3. Tillage Systems for Full-season and Double-cropped Soybeans J.T. Touchton, D.L. Thurlow, C.B. Elkins, and G.V. Granade During the past few years, many tillage studies have been conducted in Alabama and the Southeast. The conclusion to be drawn from these studies is that the most economical til- lage system will vary among soils, years, row widths, crop- ping systems, and varieties. Because of the many factors that can affect yield responses to tillage, it is impossible to pre- scribe a single optimum tillage system. FULL-SEASON SOYBEANS AND TILLAGE From 1977 through 1981, studies were conducted at eight locations in Alabama to compare the effects of conventional tillage, no tillage, and no tillage with in-row subsoiling on yield of full-season soybeans. No-tillage was planting into a killed stand of small grain (or old crop residue) with a double- disk opener planter. The in-row subsoiling was with a Brown Harden Super Seeder? to a depth of 12-14 inches. Essex va- riety was planted in the northern half of the State and Ran- som in the southern half. All plantings were made for full-sea- son production using a 36-inch row width. No-tillage without subsoiling resulted in lower soybean yields and less plant growth on all Coastal Plains and River Terrace soils, table 10. Yields under no-tillage with the in-row subsoiler were equal to the conventional system, except at the Sand Mountain Substation where the highest yield was with conventional tillage. The most visible effect of tillage treat- ments was shorter plants in the no-tillage treatment at several sites. At the Tennessee Valley Substation, all tillage treat- ments produced equally good yields. In summary, yields of full-season soybeans under no-til- lage were equal to or higher than yields under conventional tillage provided an in-row subsoiler was used on Coastal Plains and River Terrace soils. DOUBLE-CROPPED SOYBEANS AND TILLAGE From 1981 through 1983, two studies were conducted at five locations to compare the effects of tillage systems on yields of double-cropped wheat and soybeans. One study consisted of tillage prior to planting wheat (wheat tillage) and the other consisted of tillage prior to planting soybeans (soy- bean tillage). Wheat Tillage The tillage systems for wheat consisted of no-till, disk, chisel plow-disk, chisel plow-drag, turn-disk, and turn-drag. At Brewton, Monroeville, and Prattville fields, a drag bar was used for the drag treatment, but a roterra was used at the other locations. After wheat harvest, no-till soybeans were planted without a subsoiler on one-half of the plots and with an in-row subsoiler on the other half. The soybean variety was either Bragg or Braxton. For both wheat and soybeans there were no yield differ- ences among the deep tillage treatments (chisel-disk, chisel- drag, turn-disk, and turn-drag). Because of this, they will be collectively referred to as "deep tillage." Wheat yields were highly dependent on tillage, table 11. No-till produced considerably lower wheat yields than deep tillage at all locations. Disk tillage resulted in lower yields than deep tillage at Wiregrass Substation, Brewton Field, and Prattville Field. [12] TABLE 10. RELATIVE YIELD AND PLANT HEIGHT OF SOYBEANS AS AFFECTED BY PREPLANT SOIL PREPARATION AND IN-ROW SUBSOILING' Relative yield and plant height by location' Tillage Tennessee Sand Upper Plant Prattville Monroeville Wiregrass Gulf Tae Valley Mountain Coastal Breeding Experiment Experiment Wiregrass Coast treatment Valley Mountain Plain Unit ExperimSubstation Substation Substation Substation (1977-i) Field Field Substation (1978-79) (1977-79) (1978-79) (190-81) (1978-81) (1977-79) (1978-80) (1978-79) Yield Ht. Yield Ht. Yield Ht. Yield Ht. Yield Ht. Yield Ht. Yield Ht. Yield Ht. Conventional tillage. ............... 100 100 100 100 100 N/A 3 100 100 100 100 100 100 100 100 100 100 No-tillage .............. 114 97 71 101 87 N/A 84 82 66 71 85 87 85 71 79 76 No-tillage plus in-row subsoiling ...... 116 102 87 109 91 N/A 100 102 104 94 105 100 152 118 100 94 Yield (bu./acre) and plant height (in.) for conventional tillage .... 37.4 26 33.9 25 28.8 N/A 28.4 31 19.5 31 37.1 33 15.6 23 33.9 37 'Soil types: Tennessee Valley Substation, Decatur clay; Sand Mountain Substation, Hartsells fine sandy loam; Upper Coastal Plain Substation, Savannah fine sandy loam; Prattville, Lucedale fine sandy loam; Monroeville, Lucedale fine sandy loam; Gulf Coast Substation, Malbis fine sandy loam; Wiregrass Substation, Dothan fine sandy loam; Tallassee, Cahaba fine sandy loam. 2Relative yields (Yield) and relative plant heights (Ht.) were calculated by dividing yield and plant height of "conventional tillage" into yield and plant height of each tillage treatment. 3N/A-plant height not available at this substation. TABLE 11. WHEAT GRAIN YIELD AS AFFECTED BY TILLAGE PRIOR TO PLANTING WHEAT Wheat yield/acre by tillage Location' Soil Variety No-till Disk Deep 2 Bu. Bu. Bu. Wiregrass Substation Dothan fsl Coker 747 34 41 50 Brewton Experiment Field Benndale sl Coker 747 20 25 35 Monroeville Experiment Field Lucedale scl Coker 747 44 52 54 Prattville Experiment Field Bama sl Coker 747 29 40 48 Black Belt Substation Sumpter c McNair 1003 32 40 39 Gulf Coast Substation Malbis fsl Coker 762 49 55 55 'Yields are averaged over 3 years (1981-83), except Gulf Coast Substation data are for only 2 years (1982 & 1983). 2 Deep tillage is an average of four tillage systems: chisel-disk, chisel-drag, turn-disk, and turn-drag. In-row subsoiling of soybeans ahead of wheat did not affect wheat yields during the first 2 years of the test. In the third year, however, wheat following subsoiled soybeans out- yielded other tillage treatments at the Wiregrass Substation, Gulf Coast Substation, and Monroeville Field, table 12. This result illustrates the need for occasional deep tillage on some soils. Soybean yields were not particularly affected by the tillage system used for wheat, table 13. However, the need for sub- soiling soybeans was sometimes highly dependent on the pre- vious wheat tillage. On the soils at the Monroeville Field, Black Belt Substa- tion, and Gulf Coast Substation, soybean yields were not af- fected by wheat tillage nor by subsoiling of soybeans. The most economical tillage system for these soils probably would be to disk prior to wheat and no-till soybeans without in-row subsoiling. Row widths, however, might make a difference. TABLE 12. WHEAT YIELDS IN 1983 AS AFFECTED BY PLANTING METHODS FOR SOYBEANS AND TILLAGE PRIOR TO SOYBEANS LSubsoiled Wheat yield/acre, by tillage Location soybeans No-till Disk Deep Bu. Bu. Bu. Wiregrass Substation No 21 32 46 Yes 30 46 52 Monroeville Field No 41 44 46 Yes 45 47 51 Gulf Coast Substation No 49 48 53 Yes 51 59 59 Wide-row plantings of soybeans (30 to 36 inches) would prob- ably need to be subsoiled because subsoiling generally re- sults in larger plants. Large plants are required to close the canopy in wide rows but not in narrow rows. On the soils at the Wiregrass Substation and the Brewton Experiment Field, in-row subsoiling of soybeans resulted in higher yields unless the soil had been deep tilled for wheat. If wheat is no-tilled or if the soil is disked for wheat, in-row subsoiling is needed for soybeans, even if planted in narrow TABLE 13. YIELD OF NO-TILLAGE SOYBEANS AS AFFECTED BY TILLAGE PRIOR TO PLANTING WHEAT AND IN-ROW SUBSOILING FOR SOYBEANS LocationS Subsoiling Soybean yield/acre, by wheat Location' soybeans ottillage p soybeans No-till Disk Deep Bu. Bu. Bu. Wiregrass Substation No 40 41 44 Yes 43 45 44 Brewton Experiment Field No 30 36 44 Yes 46 49 49 Monroeville Experiment No 35 36 36 Field Yes 37 37 37 Prattville Experiment Field No 28 25 28 Yes 31 29 31 Black Belt Substation No 35 30 32 Gulf Coast Substation No 49 47 51 Yes 52 49 50 'Data include 1 year at Black Belt Substation, 2 years at Gulf Coast Sub- station, and 3 years at other locations. 2 Deep tillage is average of four tillage systems: chisel-drag, chisel-disk, turn-drag, and turn-disk. [13] TABLE 14. YIELD OF DOUBLE-CROPPED SOYBEANS AS AFFECTED BY TILLAGE PRIOR TO PLANTING SOYBEANS Soybean yield/acre, by location' Tillage Wiregrass Brewton Monroeville Prattville Black Gulf Substation Experiment Experiment Experiment Belt Coast Field Field Field Substation Substation Bu. Bu. Bu. Bu. Bu. Bu. No-till .................. 39 24 18 29 16 48 No-till2................... .. 43 39 22 29 22 44 Disk .................... 40 22 23 29 28 46 Deep................... 42 32 24 29 27 51 FLSD(0.10)............. . 2 4 3 NS 4 5 'Yields are averaged over 2 years at the Black Belt and Gulf Coast substations and 3 years at other locations. Deep tillage yields are averages of four systems: chisel-disk, chisel-drag, turn-disk, and turn-drag. 2Planted with an in-row subsoiler. rows. If the soil is deep tilled for wheat, however, there is no need for in-row subsoiling. The most economical tillage sys- tem would appear to be deep tillage for wheat and no-till for soybeans-with soybeans planted in narrow rows. On the soil at the Prattville Experiment Field, soybean yields were not affected by tillage for wheat, but there was a consistent yield increase (3 to 4 bushels per acre) with in-row subsoiling. Since deep tillage resulted in consistently higher wheat yields, the most economical tillage system for this soil would be deep tillage for wheat and in-row subsoiling for soy- beans. Soybean Tillage This study ws was conducted at the same locations as the wheat tillage study. Tillage treatments prior to planting soy- beans were no-till, no-till plus in-row subsoiling, disk, chisel plow-disk, chisel plow-drag, turn-disk, and turn-drag. The soil was disked each year prior to planting wheat. Soybean yields for all deep tillage systems were the same, so yields for all deep tillages are averaged. However, yield dif- ferences were found among the other tillage systems, table 14, except at the Prattville Experiment Field. Wheat yields were not affected by tillage for soybeans, so the spring tillage sys- tem can be selected based on what is best for soybeans. TABLE 15. SOYBEAN YIELDS IN 1983 AS AFFECTED BY TILLAGE AND IN-ROW SUBSOILING ON A NORFOLK FSL Yield/acre, by tillage Variety Conventional No-till No-till subsoil Bu. Bu. Bu. Maturity Group V Bay ..................... 23 19 20 Bedford ................. 27 23 22 Coker 355 ............... . 28 26 21 Forrest.................. 32 26 16 Maturity Group VI Centennial ............... 35 33 29 Coker 156 ............... . 37 33 29 Davis................... 35 33 27 Tracy-M................. 24 23 20 Maturity Group VII Braxton ................. . 35 36 37 Coker 237............... 35 37 34 Ransom ................. 35 36 31 Wright .................. 33 35 32 Maturity Group VIII Cobb ................... . 30 35 36 Coker 338 ............... . 27 31 29 Coker 488 ............... . 35 36 35 Hutton .................. 21 27 27 On soils at the Prattville Experiment Field and the Gulf Coast Substation, no-till without subsoiling would be most economical. On soils at the Wiregrass Substation and Brew- ton Experiment Field, no-till with in-row subsoiling would be most economical. Disk tillage would be best for the Black Belt Substation soil and either disk tillage or no-till with in- row subsoiling would be best on soil at the Monroeville Ex- periment Field. VARIETY-TILLAGE TEST When comparing data on tillage systems, responses to til- lage can be affected by variables that cannot be included or controlled. An example is variety responses. In most tests conducted on tillage systems, a single variety has been used. In a recent tillage-variety experiment at the E.V. Smith Re- search Center, yields of different varieties of soybeans were affected differently by the different tillage systems, table 15. For example, Forrest yielded best under conventional tillage and did poorly under no-till culture unless it was in-row sub- soiled; Braxton yielded the same under all tillage systems; Hutton yielded best under no-till culture and in-row subsoil- ing did not matter. Results of this 1-year variety-tillage experiment illustrate the difficulty of making tillage recommendations. The data are interpreted as meaning that a specific tillage system will not always result in higher yields than some other system. See color plate number 4. Crop Rotations J.T Touchton, D.L. Thurlow, and J.T Cope, Jr. For many years, rotations involving legumes were standard practice in most agricultural systems. During the past few decades, however, there has been a movement toward contin- uous cropping or monoculture, with commercial fertilizers, insecticides, fungicides, and herbicides substituted for the beneficial effects of crop rotation. However, long-term contin- uous cropping can result in problems that cannot be econom- ically solved with commercial products, and crop rotations are needed for economical yields. Currently, the primary interest in soybean-grain crop ro- tations is to control nematodes and stem canker in soybeans. [14] TABLE 16. CORN GRAIN YIELDS AS AFFECTED BY PREVIOUS CROPS AND APPLIED NITROGEN Yield/acre, by N rate/acre Previous crop None 60 lb. 120 lb. 240 lb. Bu. Bu. Bu. Bu. Black Belt Substation, 1981-82 Soybeans ..... 70 102 134 152 Sorghum ..... 26 71 122 135 Sand Mountain Substation, 1981-82 Soybeans ..... 24 92 113 111 Sorghum ..... 14 81 100 110 Tennessee Valley Substation, 1981-82 Soybeans ..... 89 112 121 120 Sorghum ..... 44 93 118 123 was corn-wheat-soybeans. Yield differences between the two rotations varied among locations, table 17. At three of the six locations (Brewton Experiment Field, Monroeville Experi- ment Field, and Wiregrass Substation), the corn-wheat-soy- bean rotation resulted in 7- and 5-bushel-per-acre higher corn and soybean yields, respectively, than the soybean-corn rotation. At the Prattville Experiment Field, the three-crop rotation increased soybean yields by 3 bushels per acre per year. At the Sand Mountain Substation, the three-crop rota- tion decreased soybean yields by 2 bushels per acre per year, but it increased corn yields by 12 bushels; in addition, wheat yields averaged 46 bushels per acre. Only at the Tennessee TABLE 17. YIELDS OF CORN, WHEAT, AND SOYBEANS FROM THREE-CROP AND TWO-CROP ROTATIONS AT Six ALABAMA LOCATIONS, 1968-78 Cropping Brewton Monroeville Prattville Wiregrass Sand Tennessee sequenceExperiment Experiment Experiment SubstationMountain Valley sequence Field Field Field Sustation Substation Substation Bu. Bu. Bu. Bu. Bu. Bu. 3-crop rotation Corn.................... 97 89 77 100 131 103 Wheat .................. 24 26 39 40 46 45 Soybeans ................ 39 39 39 32 38 29 2-crop rotation Corn.................... 93 83 78 86 119 109 Soybeans................ 34 34 36 30 40 41 Crop rotations are probably valid methods of controlling these pests, but an added benefit is that grain crop rotations with soybeans will also increase the profitability of grain crop production. In 1980, studies were established at the Sand Mountain, Black Belt, and Tennessee Valley substations to determine the effect of soybean crops on yield and nitrogen fertilizer re- quirements of corn that follows in the rotation. Corn was planted behind either soybeans or grain sorghum. The soy- beans, but not grain sorghum, would provide N and a rota- tional effect on corn. Various N rates were applied to the grain sorghum and to the corn. Corn yields from these rotations are listed in table 16. When comparing corn yield responses to N rates, it is ob- vious, especially at the low N rates, that soybeans were sup- plying 30 to 60 pounds of N per acre to corn. Lowering N fertilizer requirements was not the only ben- efit of rotating corn with soybeans. In two of the six tests (Black Belt Substation, 1981, and Sand Mountain Substation, 1982) there was also a rotational effect. For example, corn yields in both of these years leveled off at the 120-pound-per- acre N rate regardless of the previous crop, but corn yields following soybeans averaged 22 bushels per acre higher than when following grain sorghum. Similar rotational effects were obtained by following soybeans with grain sorghum. Two- vs. Three-crop Rotations Long-term rotation studies have been conducted at several locations since 1929. From 1968 to 1978, these studies were in two-crop and three-crop rotation comparisons. The two- crop rotation was corn-soybeans, and the three-crop rotation Valley Substation was the economical advantage of a three- vs. a two-crop rotation questionable. At that location, the 7- year average wheat yield was good (45 bushels per acre), but the wheat resulted in a 5-bushel-per-acre-per-year corn yield reduction and a 12-bushel-per-acre-per-year soybean yield reduction. See color plate number 5. Soybean Row Spacing D.L. Thurlow Soybeans grown in Alabama prior to 1965 were planted in 38- to 42-inch rows with the same equipment used for cotton and corn. A survey conducted by the National Soybean Crop Improvement Council indicated that 27 percent of the 1969 soybean crop in Alabama was planted in rows closer than 33 inches and 8 percent in rows closer than 26 inches. Most research on row spacing in the Southeast prior to 1960 had not shown any advantage to narrow rows. This was due to the soybean varieties then available, and to the fact that most research was conducted with planting dates that fa- vored maximum vegetation growth. However, many soybean fields planted in wide rows and double cropped after small grain fail to develop a closed soybean canopy. To study the effect of row spacing on plant growth and seed yield, field tests were conducted at three Alabama locations with full season varieties from maturity groups VI, VII, and VIII for northern, central, and southern locations, respec- [15] Yield /acre, bu. 55 - 50 45 40 35 - 30 - Z Two-year data (1968 and 1970), planted June 18. 25 - A Three-year data (1969-70 and 1974), planted May 2-10. 0 Four-year data (1968-69) and (1972-73), planted May 24 to June5. S Two-year data (1981 and 1982), variety Essex, planted June 10. O Two-year data (1981 and 1982), variety Tracy-M, planted June 10. 0I I I I I I 13 18 24 30 36 42 Row width, inches FIG. 3. Soybean yields as affected by row spacing and planting date, Tennessee Valley Substation. tively: Tennessee Valley Substation, 1968 to 1970, 1972 to 1973, and 1981 to 1982, figure 3; Black Belt Substation, 1968 to 1970, figure 4; and Gulf Coast Substation, 1968 to 1970, figure 5. These tests included row widths of 7 to 42 inches in 1968, 13 to 42 inches from 1968 to 1973, and 14 to 35 inches from 1981 to 1982. All row width tests at each location in 1968 and 1969 were planted to the same seeding rate, 1 bushel per acre, which was approximately 10 plants per foot of row in 36- inch row spacing. Later tests were conducted with more than one seeding rate, and yields are reported as average of all seeding rates for each row spacing used. The tests in north Alabama, figure 3, during 1982 and 1983 were conducted us- ing the short, early variety Essex and taller, full season Tracy- M. The planting dates at each location were selected so they either favored maximum potential growth of the soybean plant (early plantings) or were delayed by 3-4 weeks so that the soybean plants were limited in growth because shorter days induced early flowering. Soybean yields in north Alabama tests were not affected by row spacing during the 3 years plantings were made in early May, figure 3. However, when plantings were made in late May and early June, yield was increased as the row spacing was narrowed, figure 3. The highest soybean yields were ob- tained at 18- to 24-inch spacing. The greatest increase in yields due to row spacing was for the late June planting, fig- ure 3, with the highest yield from 13-inch spacing. In 1981 and 1982, Essex and Tracy-M cultivars were used to study the effect of row spacing on short and tall soybean varieties, figure 3. The shorter cultivar, Essex, produced the highest yield with little lodging. However, much of the lower yield of Tracy-M as compared to Essex was due to lodging. Lodging of Tracy-M increased when plant population was in- creased, but despite lodging problems the highest yield was obtained from the highest plant population, three plants per square foot of area. Yield/acre, bu. 35 30 - 25 20 15 ? Three-year data (1968-70) at Black Belt Substation, planted May 3-20. 10 - Three-year data (1968-70)at Black Belt Substation planted June 15-21. 13 18 24 30 36 42 Row width, inches FIG. 4. Soybean yields as affected by row spacing and planting date, Black Belt Substation. In central Alabama on a Eutaw clay soil at the Black Belt Substation, Bragg soybean yields were higher for row width narrower than 42 inches for 2 of the 4 years for plantings in mid-May and 2 of the 3 years for late June plantings, figure 4. In southern Alabama on a Malbis fine sandy loam soil at the Gulf Coast Substation, the effect of row spacing for early and late plantings shows that a delayed planting yield loss in con- ventional row widths of 36 inches can be overcome by nar- rowing row width to 13 to 18 inches, figure 5. In late May and early June plantings, yields were increased by narrow row spacing only 50 percent of the time, figure 5. However, when plantings were made in late June, soybean yields were in- Yield/acre,bu. 50 45 40 35 30 25 6 Planted early, May 27- June 9. ? Planted late, June 23-30. 13 18 24 30 36 42 Row width, inches FIG. 5. Soybean yields as affected by row spacing and planting date, 3-year average, Gulf Coast Substation. [16] creased all 4 years with 13-inch row spacings versus 36- to 42- inch spacing, figure 5. Soybean row spacing research in the Southeast does not show much advantage for narrow row spacing over the con- ventional row width of 36-40 inches for early plantings. Since there was not a decrease in yield by planting early in narrow rows and with the increased advantage in yield from narrow rows versus wide row spacing for late planted soybeans, it would be a good production practice to narrow row spacings provided other cultural practices such as weed and insect control are not hindered. See color plate number 6. Planting Date Effect on Soybean Growth and Yield D.L. Thurlow Planting date is one of the most important management practices in soybean production. Soybean varieties differ in growth habit, flowering date, and maturity Much of this var- iability in growth is due to sensitivity to day length. Because every soybean variety has a different day length response, getting maximum growth and yield requires that time of planting be based on calendar date and soil temperature for each location. In north Alabama, soil temperature and cli- matic conditions are generally favorable for planting soybeans in early May when the day length is such that the full season varieties will grow and produce adequate plant height before flowering. In central and southern Alabama, however, the soil temperature and other climatic conditions are generally fa- vorable for planting soybeans 4 to 6 weeks before the day lengths reach the stage that will allow full season varieties to make sufficient plant growth for maximum yields. The large acreage produced by most farmers has forced them to utilize more and more of this available planting period without re- alizing the effect it may have on the final growth and yield of soybeans. The Maturity Group VII varieties, which are considered full season and best adapted for central Alabama, flower be- fore adequate growth is made if grown with day lengths of less than 14.5 hours. At the Black Belt Substation, the long days of June and early July (greater than 15 hours) prevent flowering of Maturity Group VII and VIII varieties. The shorter days of late July and August will cause these varieties to stop vegetative growth and initiate flowering and pod de- velopment. If these varieties are planted in mid- to late June, adequate plant growth will not be obtained and yields will be lowered. To better evaluate this effect of early and late planting on growth and bean yield of soybeans in Alabama, studies were conducted with single cropped soybeans for several years at the Brewton and Prattville experiment fields and the Black Belt and Sand Mountain substations. Planting dates and va- rieties used are listed in tables 18-24. The soybeans were grown with conventional tillage management practices using row widths of 36 inches and seeding rates of 12 seed per foot of row TABLE 18. PLANT HEIGHT OF SOYBEAN VARIETIES AS AFFECTED BY PLANTING DATE DURING 1974-78 WHEN GROWN AT BLACK BELT SUBSTATION Maturity Plant height, by planting date group and Apr. Apr. May June June variety 15' 262 16 33 22 In. In. In. In. In. Group V Essex .......... 16 19 20 23 22 Group VI Davis......... 28 32 32 32 28 Group VII Bragg........... 26 32 37 36 31 Group VIII Hutton.......... 25 30 35 33 28 Mean ............ 24 28 31 31 27 'No planting 1978. 2 No planting 1977. 3 No planting 1974. TABLE 19. PLANT HEIGHT OF DIFFERENT SOYBEAN VARIETIES PLANTED AT VARIOUS DATES, BREWTON EXPERIMENT FIELD, 1981-82 Maturity Plant height, by planting date group and Apr. Apr. May May June June Av. variety 14 28 12 26 8 23 In. In. In. In. In. In. In. Group VI Coker 156..........23 26 29 28 29 22 26 Davis .............. 30 29 34 36 32 28 31 Group VII Braxton ............ 30 30 36 36 36 28 32 Ransom ............ 23 22 31 33 35 26 28 Group VIII Foster............. 30 30 36 36 35 29 33 Hutton............. 26 27 33 33 34 28 31 Mean................ 26 27 33 34 33 27 Data on the effect of planting date on plant height at the Black Belt Substation and Brewton Experiment Field show that the maximum growth was different for each variety, ta- bles 18 and 19. Bragg and Hutton produced maximum plant height and seed yield with the mid-May planting. The plant height of Davis was similar from late April through early June plantings. A very early variety, Essex, showed little effect of planting date on plant height. However, maximum yields for Essex were obtained for mid-May planting. TABLE 20. YIELD OF DIFFERENT SOYBEAN VARIETIES PLANTED AT VARIOUS DATES, BREWTON EXPERIMENT FIELD, 1981-82 Maturity Yield/acre', by planting date group and Apr. Apr. May May June June variety 14 28 12 26 8 23 Bu. Bu. Bu. Bu. Bu. Bu. Group VI Coker 156 ........ 48 54 52 48 37 23 Davis ............ 49 52 50 51 39 34 Average ........ .. 48 53 51 50 38 29 Group VII Braxton .......... 44 48 51 53 44 33 Ransom .......... 41 45 50 56 44 31 Average .... 42 47 51 54 44 32 Group VIII Foster ........... 48 50 50 56 41 31 Hutton ........... 47 47 46 49 40 24 Average .......... 48 49 48 53 40 27 'Computed on basis of 13 percent moisture. [17] A similar study at the Brewton Field using two varieties each from maturity groups VI, VII, and VIII indicated max- imum plant height was obtained for plantings from early May to early June, table 19. The least effect of planting date on plant height was again with varieties from Maturity Group VI. TABLE 21. YIELD OF DIFFERENT SOYBEAN VARIETIES PLANTED AT VARIOUS DATES, BLACK BELT SUBSTATION, 1970-78 Maturity Average yield'/acre, by planting date group and Apr. Apr. May June June variety 14 17 14 6 28 Bu. Bu. Bu. Bu. -Bu. 4-year average (1970-73) Group V Dare............ 36.6 35.2 35.2 30.2 18.7 Group VI Davis ........... 36.5 39.7 37.1 32.2 24.8 Group VII Bragg ........... 29.7 30.6 32.3 28.5 24.0 Group VIII Hampton 266 .... 23.1 22.0 22.6 24.4 21.4 Average ........... 31.5 31.9 31.8 28.9 22.2 5-year average (1974-78) Group V Essex ........... 21.2 23.9 32.0 26.2 22.3 Group VI Davis ........... 35.7 33.8 34.3 29.4 26.8 Group VII Bragg ........... 27.1 29.5 31.8 29.2 26.0 Group VIII Hutton .......... 27.2 28.2 32.8 28.5 25.6 Average ........... 27.8 28.9 32.7 28.3 25.1 'All yields reported as 13 percent moisture. TABLE 22. LONG-TIME YIELDS OF SOYBEANS AS AFFECTED BY PLANTING DATES AT SAND MOUNTAIN SUBSTATION, CROSSVILLE, ALABAMA Maturit14-year' average yield/acre, by group and No. of planting date variety varieties 2 May May June 5v25 20 Bu. Bu. Bu. Group V (early) ......... .1-5 38.0 33.2 (-.23) 3 29.7 (-.13) 3 Group VI (full stage) ..... 3-7 36.0 33.1 (-.15) 29.4 (-.14) Group VII (late)......... 1-2 36.9 34.5 (-.11) 30.7 (-.15) Group VIII (very late).... 1 2 36.0 32.5 (-.17) 30.6(-.07) Average ............... 6-14 36.8 33.3 (-.17) 30.1 (-.12) 114-year average includes 1967-71 and 1973-81 yields. 2Number of varieties in each maturity group used each year to compute average yield for each planting date. aAverage yield loss (bushels per acre per day) from previous planting date. The effect of planting date on yield of full-season soybeans, tables 20 and 21, followed closely with early plant growth (height from tables 18 and 19) unless late season moisture was limiting. The late May plantings at the Brewton Field, table 20, gave the highest average yield for all Group VII and VIII varieties for the 2 years, 54 and 53 bushels per acre, respec- tively. Late April and early May planting yields were lower, but not as low as early June plantings which dropped to 44 and 40 bushels and late June plantings, which were 32 and 27 bushels per acre. The varieties Coker 156 and Davis pro- duced maximum yields in the late April plantings, with only slightly lower yield for May plantings. Similarly at the Black Belt Substation, the highest average yield across all maturity groups was the mid-May plantings when Essex was the Group V entry during 1974-78. However, when Dare was the Group V entry during 1970-73, the average yields for early plantings were similar. This interaction of the maturity Group V and VI varieties Dare and Davis, table 21, with planting date was similar to Coker 156 and Davis at the Brew- ton Field. The data from the Black Belt Substation and Brew- ton Field, tables 20 and 21, indicate that early varieties (Coker 156 and Davis) are best when planted early (mid-,.pril through mid-May) in central and southern Alabama. How- ever, this may not be true of all varieties of these maturity groups as is indicated by the effect of planting date on yield of Essex, table 21. Summary data from date of planting variety tests from1967 through 1981 show yield losses when planting was delayed from optimum dates of May 5, May 15, and late May in north- ern, central, and southern Alabama locations, respectively, tables 22, 23,and 24. The yields of Group V varieties in north Alabama, table 23, were reduced the greatest (0.23 bushel per day) when plant- ing was delayed from May 5 to May 25, with a further reduc- tion of 0.13 bushel per day when delayed to June 20. The Group VIII varieties made lowest yield from early plantings, but yield was the least affected by delayed planting, with only a reduction of 0.12 bushel per acre per day when planting was delayed from May 5 to June 20. In central Alabama at two locations, there was an interac- tion with planting date and maturity groups, table 23. On a Lucedale fine sandy loam soil at the Prattville Field, the very early varieties of Maturity Group V had a 10-year average of greater than 33 bushels per acre when planted in early May. The yields of these varieties decreased by 0.16 bushel per acre per day when plantings were delayed to the middle of June. TABLE 23. LONG-TIME YIELDS OF SOYBEANS AS AFFECTED BY PLANTING DATES AT Two CENTRAL ALABAMA LOCATIONS Yield/acre, by location and planting date Maturity No. of Prattville Field, 10-yr. av.1 Black Belt Substation, 14-yr. av. 2 group varieties 3 May June May June June 15 19 22 5 26 Bu. Bu. Bu. Bu. Bu. Group V (very early) ...... 1-4 33.3 27.8 (-.16) 4 30.8 25.4 (-.39)4 17.0 (-.40) Group VI (early) .......... 4-7 31.4 27.5 (-.11) 34.0 28.0 (-.43) 20.3 (-.38) Group VII (full season) .... 2-5 29.3 28.5 (-.02) 31.8 28.1 (-.26) 20.4 (-.23) Group VIII (late) ......... 2-4 29.4 29.7 (+ .01) 28.2 25.5 (-.19) 20.7 (-.23) Average ................. . 9-17 30.7 28.1 (-.07) 31.2 26.5 (-.34) 19.6 (-.33) 'Ten-year average (1970-79). 2 Fourteen-year averages (1967-68 and 1970-81). 3 Number of varieties in each maturity group used each year to compute yields for each planting date. 4 Average yield loss (bushels per acre per day) from previous planting date. [18] TABLE 24. LONG-TIME YIELDS OF SOYBEANS AS AFFECTED BY PLANTING DATE AT BREWTON FIELD, BREWTON, ALABAMA Ten-year' average yield/ Maturity No. of acre, by planting date group varieties "2 May June 29 26 Bu. Bu. Group V (very early) ......... 1-4 33.8 25.0 (-.31) 3 Group VI (early) ............. 4-7 35.9 28.7 (-.26) Group VII (full season) ....... 3-6 39.4 30.3 (-.33) Group VIII (full season)....... 2-5 40.6 32.8 (-.28) Average.. .................. 10-19 37.4 29.2(-.31) 'Ten-year average (1971-79 and 1981). 2 Number of varieties from each maturity group used each year to com- pute average yields for each planting date. 3 Average yield loss (bushels per acre per day) from previous planting date. The full and late season varieties were the lowest yielding at the early plantings, but their yields did not change with de- layed plantings. The Prattville Field location usually has good distribution of rainfall during the growing season until the period from mid-August to mid-September. This period is usually short on rainfall, resulting in lower yields for late ma- turing soybean varieties that are usually starting to fill the pods during this period. Without this moisture stress period, the full season varieties would be expected to react similar to results in southern Alabama, table 24, where moisture is usu- ally not as limiting for yield. The highest yielding varieties from the Black Belt Substa- tion on Sumter and Vaiden clay soils over a 14-year period were the early Group VI varieties, table 23. At this location, delayed planting of Group V or VI varieties from mid-May to late June decreased soybean yields by approximately 0.4 bushel per acre per day. For the same period, the full and late season varieties yields were decreased 0.3 and 0.2 bushel per acre per day, respectively. In south Alabama at the Brewton Field on a Lucedale fine sandy loam there was an average yield loss of 0.3 bushel per acre per day when planting was delayed from late May to late June. The highest yielding varieties for the late May planting were those in maturity Group VIII. However, the greatest yield loss due to delayed planting was Group VII varieties, which had a 0.33 bushel per acre per day loss in yield. See color plate numbers 7 and 8. Effect of Depth of Planting on Stand of Soybeans D.L. Thurlow, 0.C. King, Jr., and J.A. Pitts The optimum stand for maximum seed yield of soybeans ranges from two to four seeds per square foot of area. The best seeding rate for a given location will depend on the variety used and time of planting. Soil texture, moisture, and condition of the seedbed are other factors that affect stand. Without proper seed and soil contact so that moisture can be transferred into the seed to assure rapid germination, soybean stands are certain to be poor. Soil moisture at planting time and rain within 2 weeks after TABLE 25. EFFECT OF THREE PLANTING DEPTHS ON AVERAGE PERCENTAGE EMERGENCE OF SOYBEAN SEEDLINGS FROM FIVE DIFFERENT PLANTINGS ON THREE DIFFERENT SOILS. 2 5 2 2 2 2 1 No.' of Range of germination Field emergence entries Standard Vigor by planting depth test test 5/8 in. 1 1/4 in. 1 7/8 in. Pct. Pct. Pct. Pct. Pct. ........ 92-94 82-86 72 82 69 ..... 87-91 68-77 65 77 65 ..... 82-86 64-76 64 72 62 ........ 80-81 53-58 61 70 63 ........ 76-78 58-62 60 71 57 ........ 71-75 47-53 53 70 55 ........ 68 50 50 64 50 'Sixteen lots of seed of varying laboratory germinations determined by Alabama State Department of Agriculture Seed Laboratory. 2 Percent of 100 seeds that had emerged by 14-21 days after planting. These figures are average field emergence of five test locations. planting may affect stand, as was the case in 1977 and 1978 when extremely low rainfall was recorded during May. Field emergence of only 67 percent was obtained for the 48 varieties and lines planted at 13 Experiment Station locations around the State in 1977. To get the desired stand of 6 to 11 plants per foot of row in 36-inch rows at 67 percent emergence would require planting 10 to 16 seed per foot of row. In 36-inch rows, this translates into 50 to 80 pounds of medium size seed per acre. Increasing field emergence to 80 percent could reduce seed requirements and cost by 20 percent. Planting soybean seed at the correct depth can help overcome some of the stand problems resulting from adverse soil and environmental conditions. To determine the effect of planting depth on field emergence and final stand of soybeans, field tests were conducted in northern, central, and southern Alabama in 1977 and 1978. In 1977, 16 seed lots varying in germination from 68 to 94 percent were planted; in 1978, two seed lots of Bragg soybeans (83 and 93 percent germination) were used on the same three soils. One hundred seeds were planted in 12-foot rows using three planting depths. Planting dates were May 9 and June 21, 1977, and June 10, 1978, at the Tennessee Valley Substation, June 1 and 7, 1977, and June 1 and 13 and July 6, 1978, at the E.V. Smith Research Center, and July 12, 1977, and July 21, 1978, at the Gulf Coast Substation. Soil moisture was good at all locations at time of planting, but tillage done to freshen the seedbed caused loss of moisture at all locations each year. Moisture was found to be particularly critical at the shallow planting depth each year but adequate for emergence at deeper depths. When rainfall occurred within 2 to 4 days after planting, crusting of soil lowered emergence from the deepest planting depth of 17/s or 21/4 inches. The average field emergence in 1977 was greater than 80 percent when high vigor seed were planted at 114-inch depth, but near 70 percent emergence when planted either shallower or deeper, table 25. These data also show that field emergence decreased as lower quality seed were used. Despite drought conditions in 1978, seedling emergence from the 11-inch planting depth ranged from 79 to 95 percent for seed lots of 83 and 93 percent germination, table 26. Emergence from the deepest depth, 2 inches, and [19] TABLE 26. EFFECT OF THREE PLANTING DEPTHS ON PERCENTAGE EMERGENCE OF SOYBEAN SEEDLINGS, Two SEED LOTS, FIVE PLANTINGS Location and Seed Emergence by planting date date of planting lot' 3/4 in. 11/2 in. 2 1/4 in. Pct. Pct. Pct. Tennessee Valley Substation June 10 .................. A 81 88 83 B 58 80 74 E.V. Smith Research Center June 1 ................... A 93 83 69 B 80 80 49 June 13 ................. A 87 95 49 B 86 94 53 July 6 ................... A 90 95 60 B 74 88 66 Gulf Coast Substation July 30 ................... A 60 87 74 B 72 79 65 'Lot A had 93 percent germination and lot B had 83 percent germination in laboratory tests. shallow depth was similar but generally lower than from the 11/2-inch depth at the Tennessee Valley and Gulf Coast substations. However, at the E.V. Smith Research Center emergence from the 21/4-inch depth was poorer than from the 3/4-inch depth. Poorer emergence from the 3/4-inch depth in 1978 was due to lack of rainfall for 15 and 8 days after planting, respectively, at the Gulf Coast and Tennessee Valley substations. Planting conditions for the June 1 and 13 plantings at the E.V. Smith Research Center in 1978 were excellent as rain occurred 1 day after planting. Where soil moisture was good (June 1 and 13, 1978, plantings at the E.V. Smith Research Center and July 27, 1977, planting at the Gulf Coast Substation), there was no difference in emergence from shallow (5/8- or 3/4-inch) and middle (11/4- to 12-inch) planting depth. However, the emergence at the deeper planting depth of 17/s and 21/4 inches was poor at these locations due to crusting of surface soil. At all locations and for both years, the intermediate planting depths (11/4 or 11/2 inches) produced stands which were equal to or better than stands obtained from the shallow (5- or 3/4-inch) or deep (17/8- or 2'/2-inch) planting depths. The shallow planting depth resulted in stands equal to the intermediate planting depth only when the soil moisture was excellent at planting or rains came soon thereafter. The deeper planting depth resulted in poorer stands than did the intermediate planting depth in practically every case. Thus, it appears that the most reliable planting depth for soybeans is 11/4 to 1/2 inches. Additionally, when using seed with high vigor and germination, correct planting depth would mean that fewer seed per acre would be required to obtain comparable stands. Soil Fertility liequirements for Soybeans Clyde E. Evans, O.H. Burmester, Fred Adams, J.T Cope, Jr., and John Odom The principal soil fertility factors to be considered in grow- ing soybeans are liming and phosphorus (P) and potassium (K) fertilization. The requirements for these are readily de- termined by soil testing. Soil samples tested from soybean fields during the 3 years 1982-84 showed 32 percent of them required lime. About 60 percent of the fields needed phosphorus and potassium and about 40 percent needed no fertilizer. PHOSPHORUS AND POTASSIUM During 1977-82, experiments were conducted at six loca- tions to evaluate soil-test fertilizer recommendations for phosphorus and potassium. Objectives of these experiments were to: 1. Evaluate P and K recommendations based on current soil test ratings. 2. Compare annual applications of P and K with biennial applications. 3. Compare broadcast versus row applications of fertilizers at double or triple the recommended rates of P and K. The cropping system was a soybean-corn rotation. All ex- cept one location had soils "medium" or "high" in P and K. Yields given in table 27 (averages of all years except the se- vere drought years) show that good yields of soybeans were made without fertilizer applications at all locations even on soils testing "medium." Fertilizer rates had no effect on yields. A series of experiments with potassium fertilize-" was con- ducted at several substations or experiment fields dufing 1979-82. On three sites quite low in soil-test K, good re- sponses to fertilizer K were realized, table 28. Three other locations were "medium" in soil test K, and these showed only small increases from K fertilizer. Maximum yield was achieved with either 30 or 60 pounds per acre of fertilizer K 2 0. For a soil that tests "low," the soil testing lab recom- mends 80 pounds per acre of K 2 0 and for a soil that tests "me- dium," 40 pounds per acre. Long-term soil fertility experiments with N, P, and K at six locations in Alabama included soybeans in recent years. The check (zero) treatment for P 2 0 5 has not received P fertilizer since 1957 and the check treatment for K 2 0 has not received K fertilizer since 1929. One treatment received 30 pounds N per acre. There was no increase in soybean yields from nitrogen fer- tilizer. Five of the locations were "low" in P with soil fertility indexes of 60 or 70 and one location was "high" in P One of the soils testing "low" responded to 60 pounds P 2 0 5 per acre, three responded to either 20 or 40 pounds P 2 0 5 , and P fer- tilizer did not increase yields at the other, table 29. Soybean yields were not affected by P fertilizer on the soil testing "high." Soil-test K was "medium" at all locations except for the Prattville Experiment Field where it was high in 1980-82. Five of the soils responded to either 20 or 40 pounds K. 2 0 per acre, but there was no response from K fertilizer at the Pratt- ville Experiment Field. The data presented in tables 27-29 make it clear that soil- test fertilizer recommendations based on soil-test values are more than adequate to give maximum soybean yields. For phosphorus, it appears that a soil-fertility index of about 60 or 70 is the dividing line between yield response or no response [20] TABLE 27. YIELD OF SOYBEANS AS AFFECTED BY SOIL TEST LEVEL AND P OR K FERTILIZER, 1977-82 P rating Per acre yield K rating Per acre yield Location and index Without With and ex Without With P P K K Bu. Bu. Bu. Bu. Gulf Coast Substation ........ H110 39 38 M 80 38 38 Monroeville Experiment Field H130 33 32 H 90 33 32 Brewton Experiment Field.... H 140 36 38 M 80 36 38 Sand Mountain Substation .... M 90 40 40 M 80 40 40 Black Belt Substation......... L 60 39 40 VH 160 40 40 Tennessee Valley Substation .. M 90 28 29 H 100 29 29 TABLE 28. EFFECT OF POTASSIUM FERTILIZER ON SOYBEAN YIELDS, 1979-82 Per acre yield by location Lb. K 2 0/ Sand Brewton Monroeville Prattville Tennessee acre Mountain Experiment Substation Experiment Experiment Valley Substation Field Field Substation Bu. Bu. Bu. Bu. Bu. Bu. 0 ..................... 18 16 29 23 24 45 30 ..................... 39 37 32 37 29 49 60 ..................... 48 38 33 39 29 50 120...................... 47 38 31 41 28 50 Soil test K for no K treatment Rating/index L 30 L 60 M 80 L 60 M 70 M 70 TABLE 29. EFFECT OF P AND K ON SOYBEAN YIELDS AT Six LOCATIONS, 3-YEAR AVERAGE Fertilizer Yield per acre rate, Sand Brewton Prattville Monroeville Upper Coastal Tennessee lb./acre Mountain Experiment Experiment Experiment Plain Substation Valley Substation Field Field Field Substation Bu. Bu. Bu. Bu. Bu. Bu. PHOSPHORUS P 2 0 5 0................... 28 32 32 23 32 48 20................... 33 36 32 27 37 48 40................... 38 38 31 27 38 48 60................... 37 41 32 27 39 48 100................... 37 40 31 29 37 48 Soil test P ............... L70 L70 H 170 L70 L70 L70 POTASSIUM K 2 0 0................... 31 33 32 24 34 46 20................... 34 36 31 25 35 47 40................... 37 40 31 27 35 48 60................... 38 41 32 27 37 50 80................... 40 37 33 28 38 51 100................... 37 40 31 29 37 48 Soil test K ............... M 70 M 80 H 90 M 70 M 80 M 80 to P fertilizer. There may or may not be a response to fertil- izer P at "medium" P (Index 80-100). For potassium, soils with a "medium" K fertility (Index 70-80) showed a yield re- sponse to 20 to 40 pounds per acre of K 2 0. Thus, the rec- ommended rate of 40 pounds per acre of K 2 0 for a "medium" soil-test is adequate to give maximum economic yields of soy- beans. For a "low" soil-test K (Index 10-60), soybeans re- sponded to 30 or 60 pounds K 2 0 per acre. Therefore, the rec- ommended rate of 80 pounds K 2 0 for a "low" soil-test K is adequate. LIMING A total of 53 lime experiments with soybeans on farmers' fields was harvested during the years 1975-80. Twenty-one of these were located on Highland Rim soils, 14 on Tennessee Valley soils, and 18 on Appalachian Plateau soils. The great- est yield responses to liming in individual tests were 9 bush- els per acre on Highland Rim soils, 22 bushels on Tennessee Valley soils, and 12 bushels on Appalachian Plateau soils. The soil pH below which a yield response to liming is ex- pected is called the "critical" pH. There are always some ex- ceptions, of course, and there is considerable variation in the data. The critical pH for liming Highland Rim soils for soy- beans appears to be about 5.2. The critical pH for liming Tennessee Valley and Appala- chian Plateau soils for soybeans appears to be about 5.4. The current lime recommendation for soybeans calls for liming Tennessee Valley soils when pH is below 5.6 and lim- ing other soils when they are below pH 5.8. This provides a [21] margin of safety in that lime is recommended before the soil becomes acid enough to reduce yields. MICRONUTRIENTS Although the seven micronutrients are as important in plant nutrition as the primary and secondary nutrients, they are needed in much smaller quantities and most Alabama soils contain adequate amounts for soybeans. In some cases, however, molybdenum (Mo) and manganese (Mn) are defi- cient for soybeans in Alabama. Molybdenum deficiency is rare and occurs only on very acid soils. Liming to the proper soil pH range corrects the deficiency without the use of Mo fertilizer. Use of Mo fertilizer will also correct the deficiency, but will not correct other problems associated with very low pH. Manganese is high in almost all Alabama soils. However, soybeans grown on sandy soils with intermittent high water tables, high organic content, and near-neutral pH may show Mn deficiency. This condition has been observed only in the extreme southwestern area of the State and is likely to occur in low, poorly drained spots of fields. Where this occurs, 10 pounds per acre of Mn each year in a fertilizer will correct the problem. It can also be applied as a foliar application. Symptoms for cyst nematode damage are similar to those for Mn deficiency on soybeans. Some legumes require a higher level of soil boron (B) than most other crops for maximum seed yields. To determine if soybeans was among the group of legumes requiring higher- than-normal boron, several experiments have been con- ducted on coarse-textured soils where boron deficiency is most likely to occur. Since lime applications are known to reduce the availabil- ity of soil B to plants, experiments included both limed and unlimed plots. Boron fertilizer failed to affect soybean yields any year at any test site, suggesting that boron deficiency is unlikely to be a problem for soybean production in Alabama. See color plate numbers 9 and 10. Soybean Inoculation and Nitrogen Fixation A.E. Hiltbold and D.L. Thurlow As a member of the plant family of legumes, soybeans uti- lize atmospheric nitrogen to produce high yields without the necessity of applying commercial nitrogen. By a process called nitrogen fixation, root bacteria (rhizobia) that grow in soybean roots are able to convert atmospheric nitrogen into organic forms that are utilized by the plant to produce pro- tein. In Alabama, soybeans obtain about three-fourths of their total nitrogen from the atmosphere and about one- fourth from the soil, table 30. Soybeans grown on Alabama soils obtain only about 65 pounds of nitrogen per acre from soil organic matter, crop residues, and carryover fertilizer. This soil-derived nitrogen accounts for production of only 14 to 15 bushels per acre of soybeans. Plant nitrogen derived from the atmosphere, how- ever, amounts to about 190 pounds per acre. This, along with TABLE 30. YIELD AND NITROGEN FIXATION BY LEE SOYBEANS IN 1984 Soybean Atmospheric N 2 fixed Location yield/ Total N/ Pct. of acre acre plant N Bu. Lb. Pct. Gulf Coast Substation ......... 55 202 75 Brewton Field .............. 57 182 70 Black Belt Substation 1 ....... 43 186 76 Black Belt Substation 2 ....... 42 112 66 Prattville Field .............. 44 180 80 Plant Breeding Unit .......... 59 173 67 E.V. Smith Research Center .. 61 213 80 Sand Mountain Substation 58 221 75 Tennessee Valley Substation.. 55 218 79 AVERAGE ................. 53 188 74 soil nitrogen, is adequate for the crop to produce an average of 53 bushels per acre, table 30. EFFECTIVENESS OF INOCULANTS Not all rhizobia are alike. Those that form nodules on clo- ver, for example, do not nodulate peanut or soybean. Soy- beans are nodulated only by the rhizobia Rhizobiumjaponi- cum, which is not native to the United States. This means that soils planted to soybeans for the first time are not likely to contain R. japonicum although they may have rhizobia for other legumes. First plantings require application of R. ja- r 0 Nodules per plant 10 20 30 40 50 60 Nitragin S-166 Nitragin S-66 Nitragin S-247 Nitragin S-247 Nitrogin S- 178 Nitrogin S-356 Rudy-Patrick 309 Nitragin S-347 Nitragin S-343 Nitragin Granular S-681- TCI Nitro Fix Urbana 196 Rudy-Patrick 268 Triple Noctin L 185 Nitragin Nitro Mo S-343 Control Nitragin Protreat 2 S-269 Rudy-Patrick 326 _Legume Aid H71088 Molynoctin 893 Nitragin ProTreot3 S-337 Hy Rhize frozen 90344 Control Setre L205 Nitragin ProTreot 3 S-269 Rudy- Patrick granular 358 Dormal + Mo 922 Triple Noctin L 381 Unico H7398 Triple Noctin L 4310 Nitragin ProTreat 3 S-334 Setre L205 Unico H7718 Legume Aid granular Dormal+Mo 928 Control Dormal + Mo 924 Legume Aid frozen 7904 Unico H7718 Dormal + Mo 918 Dormal granular CD-7 I I I I I I ? o 10 20 30 40 50 60 70 Nodules per plant FIG. 6. Number of nodules per plant at bloom time in 1979 after ap- plication of commercial soybean inoculants at planting. Products within a vertical line do not differ (95 percent confidence level). [22] --- (3-f xa:n ic~ pi IE tin 10 -r in ~ in ~ In ( in i in i in ~ Bar in i lin ~ t~ r IVU 1 i! an i j ne~i-Iti-2j-25- 1' S-J~riclS-3 5-3 70 I 1 ponicum with the seed to ensure nodulation and avoid nitro- gen deficiency and low yield. The inoculant industry cultures rhizobia and markets a va- riety of products for application on the seed or into the furrow with the seed at planting. Powdered peat is the conventional carrier for bacteria, but clay, vermiculite, and oil carriers are also used for application on soybean seed. Granular peat or corn cob carriers are used for in-furrow application. Frozen, concentrated cultures are available that may be diluted and sprayed in the furrow at planting. Some inoculants have seed- treatment chemicals such as fungicide or molybdate salts mixed with the bacteria or packaged separately for applica- tion with bacteria. Soybean inoculants offered for sale in Alabama during 1975-79 were evaluated for effectiveness. The number of vi- able rhizobia in each inoculant was determined by bacterial plate count and by nodulation of soybeans in the plant dilu- tion technique. Inoculants were also compared in green- house pot experiments and in field experiments where each inoculant was applied according to the manufacturer's in- structions. Experiment sites with essentially no R. japonicum in the soil were selected to make the nodulation and yield of soybeans dependent on the applied inoculants. Results showed a wide range of effectiveness among commercial in- oculants. Some products contained more than a billion rhi- zobia per gram of inoculant, while others contained a thou- sand or less per gram when purchased. When applied as recommended to soybeans in the field, some inoculants pro- duced abundant nodules, while other inoculants produced none, figure 6. Those that provided one hundred thousand to one million R. japonicum cells per seed produced superior nodulation, while those that supplied one thousand or less per seed were useless. Similarly, inoculants that produced abundant nodulation increased soybean grain yields, while yield was poor with those providing few rhizobia and no no- dulation. Nodules/ plant 25 20 15 10- 5 Teo 'n L I Fungicide SNo fungicide ControlSeed FIG. 7. Number of nodules per plant at bloom stage after application of inoculant on the seed or into the furrow with seed treated or not treated with captan fungicide. Furrow Rhizobia/gram of soil, thousands 17000 , 100 10 1- winter soybean cotton legumes residues Feb. May July Sept. Nov. Jan. FIG. 8. Numbers of Rhizobium japonicum in soil following the soy- bean crop and during the growth of cotton and winter legumes, 1980- 82. Some products performed poorly despite apparently ade- quate viability of the inoculant. This was the case where fun- gicide was added to the seed with the inoculant at planting. Captan and other fungicides for seedling disease control are not compatible with R. japonicum when both are placed on the seed. Research at the Wiregrass Substation in 1980 de- termined the effectiveness of inoculant applied on the seed compared to in-furrow application somewhat separated from the seed. Powdered peat with sticker was used for the seed- applied rhizobia, while a granular inoculant was applied in the furrow. Another variable was application of captan to the seed at the recommended rate for seedling disease control. Soybean plants were dug at bloom stage and their nodulation determined. Where captan was applied on the seed with rhi- zobia, the inoculant failed, figure 7. Separating the bacteria from the fungicide-treated seed, however, as with the gran- ular in-furrow inoculant, avoided toxicity to the rhizobia and resulted in good nodulation. When soils are planted to soybeans for the first time, early and effective inoculation can be obtained with either seed- or soil-applied inoculant supplying one hundred thousand or more R. japonicum cells per seed. An evaluation of 118 com- mercial inoculants showed that peat-based inoculants were the most viable and effective. Clay- and oil-based products performed poorly; the latter contained fungicide and/or mo- lybdate. If seed quality or planting condition dictate the use of fungicide, then a granular inoculant has distinct advantage over a seed-applied inoculant. However, granular inoculants are more expensive and require application equipment on the planter. Soils that have previously produced good crops of soybeans will have established populations of R. japonicum throughout the root zone so that fungicide toxicity to seed-ap- plied rhizobia is of no concern. Response to any inoculant is unlikely under these conditions. Soybean rhizobia survive in soil following the soybean crop, but their populations decrease. In a soybean-cotton- [23] 2 i" . YI~ "l~f-~U, I- i. z -e 4 - B ~1 Ij P ~ ; 9:'C (1) Four-row varietal plots at the Plant Breed- ing Unit, Tallassee, are a part of the extensive variety development program underway. (2) USDA uniform and preliminary tests screen large numbers of experimental varieties for (left) and 14 inches (right) were compared in this Tennessee Valley Substation planting, as well as at locations in other Alabama regions. (7) Effect of planting date on growth of Brax- their potential value. (3) Deeper rooting of plants at left is the result of in-row subsoiling as compared to conventional tillage. (4) TUrn- disk preparation for wheat ahead of no-till soybeans was one of the tillage systems tried ton soybeans, a Group VII variety, at Tennes- see Valley Substation. (8) Effect of planting date on growth of Hutton soybeans, a Group VIII variety, at Tennessee Valley Substation. for double-crop production of soybeans. (5) Rotating soybeans with grain crops not only helps control nematodes and stem canker in soybeans, but it also increases profitability of grain production. (6) Row widths of 42 inches .,.* ,.a1 ' .,1 (9) Effect of low phosphorus on soybeans is evident in the plot in foreground. (10) Plants in foreground show symptoms of potassium deficiency. (11) Soybean plants with root nod- 9 a, -: 4 4 jrrp ules at 3 weeks after planting. (12) Growth of sicklepod and cocklebur was suppressed by 12-inch rows (shown) and 6-inch rows, as compared with 18- and 36-inch rows. (13) Chlorimurm (a part of the herbicide Canopy) applied preemergence at 1 ounce active in- gredient per acre provided excellent control of sicklepod at the Black Belt Substation (14) Controlled droplet applicator delivers low vol- ume (1 quart to 10 gallons per acre) and pro- duces spray particles in the 200-micron range. a 'L.~a~'a - a ~ .'-~ ' ~ i'U aA.. -c~r; :Wa 4.' r- ~r AA NNWvip -1 r - ;-; ; L c. j J" +; i~ ~i .> w r, x- 4", V w~I g (15) The soybean looper, Pseudoplusia inclu- dens, is a voracious soybean foliage feeder (photo courtesy J. French). (16) The velvet- bean caterpillar, Anticarsia gemmatalis, is a serious soybean pest in the southern region of Alabama (photo courtesy J. French). (17) The threecornered alfalfa hopper, Spissisti- lus festinus, helps spread soybean diseases and also slows sugar flow from leaf petioles to developing seed (photo courtesy J. French). (18) Leaf petiole girdled by threecor- 27 ,. , f 16~ ): .1 1 ; ' & ~ - :a F'i c/:' ~U " // F-4K v low (26) Response of varieties growing on nema- tode infested soil. (27) Nematode damage to soybeans in a Baldwin County field infested with cyst and root-knot nematodes. (28) Vari- ety comparisons in nematode infested field on same farm as field shown in 27. (29) Ter- 4 minal raceme of a field-grown Braxton soy- bean plant with developing flowers produced at approximately 18 nodes. Pod development is occurring at basal nodes, whereas open flowers are still present at the raceme tip. (30) Terminal raceme from a field-grown Bragg soybean plant with one developing pod re- maining at a basal node and open flowers present at the tip. Many flowers have ab- scised from intervening nodes. (31) Terminal raceme from a field-grown Bragg soybean plant in which all flowers or pods have ab- scised at all nodes. (32) Terminal racemes from field-grown Bragg soybean plants at )N H20 harvest. Racemes were treated during flow- ering as follows: CON (untreated), H 2 0 potassium hydroxide solution), BAP (sprayed with a solution of 6-benzylamino- purine, a plant growth regulator). Note the large numbers of pods on the BAP-treated ra- )H 10 3 M BAP cemes compared to other treatments. 1* ~i~ k.ST 1K; -- 32 K a ~21 nered alfalfa hoppers. (19) Nabids are abundant natu- ral enemies of many soy- bean insect pests. (20) The green lynx spider, an effec- tive predator, is one of many species of spiders that contribute to pest reg- ulation in Alabama soy- bean fields. (21) Tachinid flies are effective parasi- toids of most major lepi- dopterous pests in the soy- bean ecosystem. (22) Nomuraea rileyi, a fungal pathogen of nearly all lepi- dopterous larvae attacking soybeans, causes high lev- els of mortality in some years, particularly late in the growing season. (23) Erynia (Entomophthora) gammae is a fungal para- site which at times causes dramatic levels of mortality in populations of the soy- bean looper. (24) Symp- toms of stem canker on soybean leaf. (25) Severe stem canker lesion on soy- bean stem. :~- ~lii! -'7"; .: :~" t; corn rotation experiment at Auburn, one million or more R. japonicum cells per gram of soil were found during the winter after the soybean crop, figure 8. Populations decreased sharply into the following season under cotton. In the crop- ping sequence of soybeans-cotton-corn, the number of R. ja- ponicum in the soil declined each year until soybeans were replanted in the rotation. The die-off of R. japonicum was most extreme in strongly acidic soil, compared to soil main- tained at favorable pH with liming. In soil at pH 5 or below, populations of R. japonicurn essentially disappeared in the year after soybeans. Therefore, strongly acidic soils need (1) liming to correct the acidity limitation of both soybean host and rhizobia, and (2) application of an effective inoculantwith the seed. Other situations where seed inoculation may be ad- vantageous include fields that have not been planted to soy- beans within 5 years or where previous inoculations failed. Recent evidence in Alabama and elsewhere suggests soybean yields may respond to application of superior strains of R. ja- ponicum, even in soils well supplied with soybean rhizobia. EFFECT OF N FERTILIZER Nitrogen in the form of ammonium and nitrate (normal fer- tilizer forms) is readily used by legume plants, but these chemically combined sources of nitrogen interfere with nod- ule development and nitrogen-fixing activity of existing nod- ules. This may occur in soils well supplied with decomposa- ble organic matter or with fertilizer nitrogen carryover from a prior crop. An experiment in central Alabama showed as lit- tle as 40 pounds per acre of fertilizer nitrogen applied at planting reduced nodulation of soybeans at bloom stage, ta- ble 31. Furthermore, fertilizer nitrogen did not increase yield TABLE 31. EFFECTS OF SEED INOCULATION AND FERTILIZER NITROGEN ON NODULATION AND YIELD OF SOYBEANS, 1975 Treatment Nodules per plant Soybean at bloom stage yield/acre No. Bu. None .............. 2.9 c 25.2 b, Seed inoculation................... 25.7 a 31.3 a Seed inoculation plus 40 lb./acre N ... 10.3 b 29.6 a 'Values bearing the same letter within a column do not differ (95% con- fidence level, Duncan's multiple range test). over that obtained with seed inoculation alone. This is the usual result; fertilizer nitrogen can be utilized by soybeans, but nitrogen fixation is reduced by an equivalent amount. Where soybeans are well inoculated, fertilizer nitrogen is un- necessary and costly On the other hand, where soybeans are poorly inoculated, it may be possible to avoid crop failure with applied nitrogen. The extent to which soybean yield can be salvaged decreases with advancing stage of development. Inoculation failure is shown by lack of root nodules, pale green foliage, and slow growth. Fertilizer nitrogen applied prebloom may substitute partially for lack of fixation. How- ever, an effectively fixing soybean crop derives 150 to 200 pounds of nitrogen per acre from the atmosphere, equivalent to a fertilizer application of 300 to 400 pounds per acre. EFFECT OF MOLYBDENUM Molybdenum, a nutrient element required by plants in only trace amounts, plays a special role in nitrogen-fixing plants as a constituent of the enzyme that reacts with atmo- spheric nitrogen. Molybdenum deficiency, therefore, limits the nitrogen nutrition of soybeans. Soils contain small amounts of molybdenum and its availability is related to soil acidity Molybdenum deficiency may be encountered when soils become more acid than about pH 5.5. Conversely, lim- ing strongly acidic soils increases molybdenum availability and avoids deficiency Where soybeans are planted in soils below pH 5.5, application of molybdenum to the seed may in- crease yields. As little as 1 ounce of sodium molybdate (Na 2 MoO 4 ) dissolved in a small amount of water to moisten a bushel of seed at planting time will supply this nutrient ele- ment. This practice has not been found to interfere with seed- applied rhizobia. However, molybdenum is not a satisfactory substitute for lime on strongly acid soils. In many instances, infertility of strongly acid soils is not corrected by adding mo- lybdenum. In these situations, liming improves yield by re- ducing toxic aluminum, increasing calcium levels, and im- proving molybdenum availability. See color plate number 11. [26] PEST CONTROL Soybean Weed Control R. Harold Walker, James R. Harris, and Ted Whitwell Weeds continue to be a major pest problem for Alabama soybean producers. The complexity of the problem is com- pounded by the variety and nature of the weeds in soybean fields. Many annual weeds and grasses, and a few persistent perennials such as johnsongrass and nutsedges, are severe problems. The complexity of the problem is further dramatized by changes that take place in the soybean-field ecosystem. These changes were slow when hand-hoeing and cultivation removed weeds mechanically. However, the introduction and use of herbicides accelerated changes in the ecosystem. When a field is consistently treated with the same or similar herbicides for a number of years, some obvious and pre- dictable changes occur. Annual weeds best controlled by these herbicide(s) begin to lose their dominance in the weed population and begin to disappear. Taking their place will be annual and/or perennial species that are less susceptible to herbicides in general. Today, weed species that are most troublesome in Ala- bama soybean fields include sicklepod, annual morningglo- ries, cocklebur, and johnsongrass. Other species that pose similar concerns include Florida beggarweed, bristly star- bur, Texas panicum, pigweeds, nutsedges, and prickly sida. Consequently, research efforts are directed toward these problems. CULTURAL AND MECHANICAL METHODS Competitive Capacity of Soybeans One of the least appreciated aspects of the soybean plant is its capacity to smother weeds that emerge during the first few weeks after soybean planting. If weeds are effectively controlled the first 4 to 6 weeks after soybean planting, the soybean canopy will effectively suppress weeds during the remainder of the growing season. Cooperative research be- tween the Alabama and Georgia Experiment Stations shows soybeans maintained free of sicklepod for 4 weeks after TABLE 32. EFFECT OF SICKLEPOD-FREE PERIOD ON SOYBEAN YIELD Free of Soybean yield/acre2 sicklepod' Headland Headland Plains Headland Plains Bu. Bu. Bu. Bu. Bu. None ............. 27b 29c lc 24b 33b 4 weeks...........34a 51a 49a 28a 57a All season........ 37a 51a 50a 28a 55a 'Indicates number of weeks after planting that soybeans were kept free of weeds and then allowed to reinfest naturally. 2 Means within columns followed by the same letter are not statistically different. Data are summed over three row spacings, 8, 16, and 32 inches. emergence produced yields equal to those kept free of sick- lepod all season, table 32. In three of the five trials, only 2 weeks of weed-free maintenance was required to produce yields equal to season-long maintenance. Soybean row spacing influences the time required for weed-free maintenance. The sooner the soybean canopy shades the ground, the shorter time required for weed con- trol inputs. In research at the Wiregrass Substation, soy- beans were planted in rows spaced 6, 12, 18, and 36 inches and the same number of sicklepod or cocklebur plants were allowed to grow with the soybeans for 17 weeks. Data taken at 17 weeks show that as row spacing became narrower, weight of sicklepod and cocklebur decreased, indicating more competition from the soybeans, table 33. Both sickle- pod and cocklebur produced about as much weight in the non-irrigated treatments as they did in the irrigated, indi- cating their capacity to effectively compete for water. TABLE 33. EFFECT OF SOYBEAN Row SPACING ON SICKLEPOD AND COCKLEBUR FRESH WEIGHT, WIREGRASS SUBSTATION Fresh weight/acre Ro sinches Non-irrigated Irrigated Sicklepod Cocklebur Sicklepod Cocklebur Lb. Lb. Lb. Lb. 6 ............. 1,850 4,610 830 2,940 12 ............. 4,175 7,370 2,760 9,765 18 ............. . 4,650 12,520 6,500 13,290 36............. 5,150 13,649 8,930 14,700 Mechanical Control Some weeds, such as bristly starbur, were adequately controlled with cultivation in research at the Wiregrass Sub- station. Treflan? does not control this weed, but Treflan plus one cultivation provided bristly starbur control and soybean yields equal to the best preemergence applied her- bicide (metribuzin). Early planting allowed soybeans to gain a competitive advantage over the bristly starbur and thus cultivation was adequate. Tillage, Herbicides, and Crop Rotation Tillage, weed control, and crop rotation are important fac- tors in any soybean production system. Integrating these components into a system in order to identify the value of each was the objective of other research. Comparisons in- cluded conventional tillage versus no-till; "standard" versus "intense" weed control inputs; and continuous soybeans versus soybean/corn rotation. Sicklepod was the weed stud- ied in this research. Sicklepod control, sicklepod seed in the soil, and crop yield were measured along with calculating net returns to land and management. Several trends are ap- parent from data in tables 34 and 35: (1) No-till, although planted approximately 1 month later, compared favorably with conventional tillage for sicklepod control, soybean yield, and net returns; (2) "intense" weed control provided [27] TABLE 34. SICKLEPOD CONTROL AND SOYBEAN YIELD IN RESPONSE TO WEED MANAGEMENT SYSTEMS, TALLASSEE, ALABAMA Results, by years' Treatment 1979 1980 1981 1982 Sicklepod Soybean Sicklepod Soybean Sicklepod Soybean Sicklepod Soybean control yield/acre control yield/acre control yield/acre control yield/acre Pct. Bu. Pct. Bu. Pct. Bu. Pct. Bu. Tilled 1. Continuous soybeans, "standard" weed control ............. ....... ....... 96 b 35a 52 b 11bc 77b 23d 60c 10c 2. Continuous soybeans 3 , "intense" weed control ............. .............. 98 a 24c ed 98 a 16ab 98a 28abc 97a 29a 3. Soybean/corn rotation, "standard" weed control ....................... 97 ab 32 ab 40b 79b 30ab 66c - 4. Soybean/corn rotation 3 , "intense" weed control ............................ 98 a 24 cd 93a - 98a 32a 92ab No-till 5. Continuous soybeans, "standard" weed control................. 98 a 24 a-d 86 a 11 bc 72 b 21 d 86 b 28 a 6. Continuous soybeans 3, "intense" weed control........................... 86b 23d 99a 14abc 94a 25bcd 97a 28a 7. Soybean/corn rotation, "standard" weed control....................... 98 a 25 bcd 85 a 79 b 26 bcd 83 b 8. Soybean/corn rotation 3 , "intense" weed control............................ 25 bcd 92 a - 94a 26 bcd 88 ab 'Mean values with the same letter are not statistically different. 2 Corn was planted in 1980 and 1982 in the rotation. 3Soybean yields were reduced as a result of injury from postemergence-directed herbicides during 1979. TABLE 35. NET RETURNS TO LAND AND MANAGEMENT FROM SOYBEANS AS A RESULT OF WEED MANAGEMENT SYSTEMS, TALLASSEE, ALABAMA Treatment 2 Net return/acre' 1979 1980 1981 1982 Dol. Dol. Dol. Dol. Tilled 1. Continuous soybeans, 72a -64a 6bc -71c "standard" weed control .... 2. Continuous soybeans, -26efg -62a ic 5b "intense" weed control ..... 3. Soybean/corn rotation 2 , 55ab 46a "standard" weed control .... 4. Soybean/corn rotation, -30fg 21abc "intense" weed control ..... No-till 5. Continuous soybeans, 45abc -53a 6bc 49a "standard" weed control .... 6. Continuous soybeans 3 -6def -45a 15bc 30ab "intense" weed control ..... 7. Soybean/corn rotation, 23bcd - 34ab - "standard" weed control .... 8. Soybean/corn rotation, 13cde - 21abc - "intense" weed control ..... 'Mean values with the same letter are not statistically different. 2 Corn was planted in 1980 and 1982 in the rotation. 3Soybean yields were reduced as a result of injury from postemergence- directed herbicides during 1979. reduced sicklepod seed in the soil 40 to 50 percent, but net returns to land and management were frequently unaccept- able; (3) "standard" weed control provided fair sicklepod control, reasonable soybean yields, and more acceptable net returns, although sicklepod seed in the soil increased about 10 percent; and (4) the soybean/corn rotation began to show a positive trend in the third year. CHEMICAL METHODS Johnsongrass and Annual Grasses Several of the new herbicides that can be applied over the top proved to be effective for johnsongrass control in soy- beans. They performed well at low rates when applied fol- lowing Treflan preplant, or at higher rates when Treflan was not applied preplant. Smaller grass was generally easier to control, particularly with Verdict? and Fusilade?. This also indicates that not all grass species are equally susceptible to each of the herbicides. Other susceptible grasses include Texas panicum, goosegrass, broadleaf signalgrass, and ber- mudagrass. There also is evidence that tank-mixing these new postemergence grass herbicides with other herbicides, such as Basagran?, Blazer?, and Dyanap?, will reduce grass control. At the Wiregrass Substation, mixing Tackle? (same as Blazer) and Whip? reduced crabgrass control as com- pared to Whip alone, and the same type antagonism oc- curred with Assure? plus Tackle. Sicklepod This weed continues to be one of the most troublesome in soybean production in Alabama and other Southern States. Lexone?/Sencor? still provide the most effective preemerg- ence control, but preemergence Lasso?, Dual?, and Ver- nam? also suppress sicklepod. Postemergence treatment with Lorox?, 2,4-DB, Lexone/Sencor, and Toxaphene?, along with appropriate cultural practices, provided effective sicklepod control in research at two locations, table 36. Consistent control of sicklepod and better soybean yields were evident with the more intensive control systems (treat- ments 3, 4, 9, 10, and 11) for both row spacings. With ex- cellent growing conditions in 1979, however, less weed con- trol inputs (numbers 1, 2, 7, and 8) provided good results, indicating the increased competitiveness of the soybeans. Where growing conditions were poor in 1978 and 1980, the less intensive control systems tended to give better per- formance when used with the 10-inch row spacing (treat- ments 1 and 2 versus 7 and 8). The narrow rows better com- pensated for the poorer soybean growth. Likewise, where no sicklepod control was applied (treatment 6 versus 13) soy- [28] TABLE 36. INFLUENCE OF ROW SPACING AND HERBICIDES ON SICKLEPOD CONTROL IN SOYBEANS Tennessee Valley Substation Control systems-treatment Planting 1978 1979 1980 Gulf Coast Sub., 1980 number and lb. active/acre dates' Sicklepod Soybean Sicklepod Soybean Sicklepod Soybean Sicklepod Soybean control yield control yield control yield control yield Pct. Bu. Pct. Bu. Pct. Bu. Pct. Bu. 30-inch rows 1. Tolban + Sencor-PPI (3/4 + 3/8) .... May 23 30 66 66 3 16 June/July - 30 24 59 7 48 23 2. Lasso + Sencor-PRE (21/2 + 3/8) .... May 15 30 95 64 0 16 June/July - - 20 25 82 12 56 24 3. Lasso + Sencor-PRE cultivate; Lorox + Butyrac 200-PDS (21/2 + 3/8; 1/2 May 98 42 100 62 93 28 - - + 1/4) ....................... June/July - 87 32 100 13 97 34 4. Tolban + Vernam-PPI cultivate; May - - 98 62 89 31 - - Sencor PDS (1/2 + 21/2; 3/8)......... June/July - - 95 192 95 13 95 32 5. Hand hoed check .................. May 100 29 98 65 92 23 - - June/July - 60 27 90 11 98 34 6. Non-treated check ................. May 0 25 0 56 3 10 - - June/July - - 0 17 0 3 0 17 10-inch rows 7. Tolban + Sencor-PPI (3/4 + 3/8) .... May 92 37 80 59 18 21 June/July - - 70 29 81 11 59 29 8. Lasso + Sencor-PRE (2/2 + 3/8) .... May 96 33 100 60 12 24 - - June/July - 56 30 98 11 64 28 9. Lasso + Sencor-PRE; Toxaphene May - 100 62 92 31 - - POT (2/2 + 3/8; 3; 3)................June/July - - 100 31 100 10 97 39 10. Tolban-PPI; Toxaphene-POT May - - - 62 25 - - (3/4; 3; 3) ......................... June/July - - - - 96 9 90 32 11. Lasso-PRE; Toxaphene-POT (3; 3; 3) May - - - 64 23 - June/July - - - - 100 7 94 32 12. Hand hoed check.................. May 98 35 91 56 98 33 June/July - 100 28 96 6 98 35 13. Non-treated check ................. May 38 33 41 64 8 16 June/July - - 0 26 9 5 0 25 1 Essex soybeans planted first week of May and Lee 74 planted last week in June at Tennessee Valley Substation. Ransom soybeans planted first week in July at Gulf Coast Substation. Soybean seeding rate was same for both row spacings, 130,000 plants per acre. 2 Low yield due to injury from Sencor post-directed. TABLE 37. INFLUENCE OF SELECTED SICKLEPOD CONTROL SYSTEMS ON NET RETURNS To LAND AND MANAGEMENT Net returns to land and management/acre Control systems-treatment Planting Tennessee Valley Gulf number and lb. active/acre dates Sub. Coast Sub. 1979 1980 1980 Dol. Dol. Dol. 30-inch rows 1. Tolban + Sencor-PPI May 345 13 - (3/4 + 3/8) ............... June/July 65 -59 62 2. Lasso + Sencor-PRE May 326 7 (2/ + 3/8) ............... June/July 70 -26 65 3. Lasso + Sencor-PRE culti- May 306 86 vate; Lorox + 2,4-DB-PDS June/July 105 -27 129 4. Tolban + Vernam-PPI culti- vate; Sencor-PDS (1/2 + 21/2; May 306 105 3/8) ..................... June/July 14 -22 114 6. Non-treated check ......... May 28 -17 - June/July 30 -70 35 10-inch rows 7. Tolban + Sencor-PPI May 253 36 (3/4 + 3/8).................June/July 69 -27 80 8. Lasso + Sencor-PRE May 228 65 (2/2 + 3/8)............... June/July 76 -26 68 9. Lasso + Sencor-PRE Toxa- May 256 95 - phene-POT (2/a + 3/8; 3;3) June/July 74 -50 128 13. Non-treated check ......... May 294 15 - June/July 55 -69 55 beans in 10-inch rows yielded more. Where plots were hand hoed (5 versus 12), 10-inch rows influenced yield less. Net returns to land and management calculated for some of the sicklepod control systems for 1979 and 1980, table 37, reflect the same trends as soybean yields given in table 36. There is a need to replace Toxaphene with another her- bicide that can be applied postemergence over the top of soybeans for sicklepod control. Classic? and Scepter? show good potential. Annual Morningglories It is common to find morningglories and sicklepod in the same field. Morningglory control with existing preemergence herbicides is generally poor, although suppression does occur with Vernam, Dyanap, and occasionally with Treflan and Sur- flan?. Conversely, some postemergence herbicides have pro- vided acceptable control. Blazer applied postemergence over the top has been the most consistent. Lorox + 2,4-DB ap- plied postemergence directed has been an effective treat- ment. With sicklepod and morningglories in the same field, the narrower row patterns (18-inch and twin 9-inch) generally produced higher yields than 36-inch rows with all levels of weed control, table 38. Also, Surflan + Lexone applied pre- [29] TABLE 38. SICKLEPOD AND MORNINGGLORY CONTROL AS AFFECTED BY ROW PATTERNS, HERBICIDES, AND CULTIVATION, GULF COAST SUBSTATION Control Treatment Row Morningglory Sicklepod Soybean Early Late Early Late Pct. Pct. Pct. Pct. Bu. Hoed check 36 in. 100 95 99 95 55 18 in. 99 95 100 95 59 Twin 9-in. 100 88 100 94 62 1 cultivation 36-in. 50 25 70 45 44 18-in. 33 9 67 24 45 Twin 9-in. 36 13 56 20 49 Surflan + Lexone 36-in. 25 8 45 15 40 18-in. 38 24 81 51 50 Twin 9-in. 24 15 60 24 54 Surflan + Lexone 36-in. 58 45 89 63 50 + 1 cultivation 18-in. 50 38 92 74 58 Twin 9-in. 56 36 82 42 58 Surflan + Lexone; 36-in. 96 88 99 95 55 Toxaphene; and 18-in. 99 95 99 95 58 Toxaphene + Blazer Twin 9-in. 98 94 99 95 67 emergence and Toxaphene + Blazer applied postemergence over the top provided highest weed control and soybean yields. Classic and Scepter show good potential for control of this weed complex. Cocklebur Common cocklebur is the most competitive weed species in soybeans. In 4 years of research at the Black Belt Substa- tion, Basagran, Dyanap, and 2,4-DB were applied in various combinations both with and without cultivation. One, two, and three cultivations were also included without herbicides. Basagran and Dyanap were applied postemergence over the TABLE 39. EARLY SEASON COMMON COCKLEBUR CONTROL AS AFFECTED BY CULTIVATION AND/OR HERBICIDES Early cocklebur control system Rate/acre 1979 1980 1981 1982 4-yr. av. Pints Pct. Pct. Pct. Pct. Pct. 1. Basagran; 1 cultivation 12 80 85 85 92 86 2. Basagran; Basagran 12; 12 89 84 98 91 91 3. Dyanap; 1 cultivation 4 85 80 71 93 82 4. Dyanap; Dyanap 4; 4 76 66 73 86 75 5. Basagran; 1 cultivation + 2,4-DB 12, 0.8 88 88 95 92 91 6. Basagran; 2,4-DB; 2,4-DB 12; 0.8; 0.8 89 69 86 80 86 7. Dyanap; 1 cultivation + 2,4-DB 6; 0.8 83 85 81 89 85 8. Dyanap; 2,4-DB; 2,4-DB 6; 0.8; 0.8 78 60 80 79 74 9. Dyanap; Basagran 6; 1 76 66 97 85 81 10. Basagran; Dyanap 1 /2; 6 89 80 94 90 88 11. Dyanap; 1 cultivation; Basagran 6; 1 81 87 98 87 88 12. Basagran; 1 cultivation; Dyanap 1 ;6 73 90 96 94 88 13. 1 cultivation - 53 54 45 71 56 14. 2 cultivations - 53 64 35 82 59 15. 3 cultivations - 44 69 48 87 62 16. Hoed check - 100 100 99 92 98 'The first cultivation and application of Basagran and Dyanap were ap- plied 22 days after planting. The second cultivation, the second application of Basagran and Dyanap, and the first postemergence directed application of 2,4-DB were applied 38 days after planting. The third cultivation and the second application of 2,4-DB were applied 59 days after planting. TABLE 40. LATE SEASON COMMON COCKLEBUR CONTROL AS AFFECTED BY CULTIVATION AND/OR HERBICIDES Control Late cocklebur control system Rate/acre 1979 1980 1981 1982 4-yr. av. Pints Pct. Pct. Pct. Pct. Pct. 1. Basagran; I cultivation 1V2 61 73 79 82 74 2. Basagran; Basagran 1'/2; 12 98 85 99 86 92 3. Dyanap; 1 cultivation 4 66 70 68 85 72 4. Dyanap; Dyanap 4; 4 91 65 73 85 79 5. Basagran; 1 cultivation + 2,4-DB 1/, 0.8 97 85 93 88 91 6. Basagran; 2,4-DB; 2,4-DB 1/; 0.8; 0.8 97 75 86 85 86 7. Dyanap; 1 cultivation + 2,4-DB 6; 0.8 95 76 83 73 82 8. Dyanap; 2,4-DB; 2,4-DB 6; 0.8; 0.8 97 60 82 64 76 9. Dyanap; Basagran 6; 1'/2 94 59 99 76 82 10. Basagran; Dyanap 1/2, 6 94 81 96 76 87 11. Dyanap; 1 cultivation; Basagran 6; 1V 95 91 99 87 93 12. Basagran; 1 cultivation; Dyanap 12; 6 90 90 99 89 92 13. 1 cultivation 35 38 45 38 39 14. 2 cultivations 66 54 45 46 53 15. 3 cultivations 65 56 66 63 63 16. Hoed check 100 100 98 93 98 'The first cultivation and application of Basagran and Dyanap were ap- plied 22 days after planting. The second cultivation, the second application of Basagran and Dyanap, and the first postemergence directed application of 2,4-DB were applied 38 days after planting. The third cultivation and the second application of 2,4-DB were applied 59 days after planting. top and 2,4-DB was directed underneath the soybean can- opy. One to three cultivations alone failed to provide adequate cocklebur control, tables 39 and 40, or soybean yields, table 41. Two or three cultivations were no better than one, for this heavy clay soil. One cultivation plus herbicide(s) or herbicides alone pro- vided good to excellent early and late season cocklebur con- trol, tables 39 and 40. However, little or no differences in soy- TABLE 41. SOYBEAN YIELD AS AFFECTED BY CULTIVATION AND/OR HERBICIDES FOR COMMON COCKLEBUR CONTROL ControSoybean yield/acre sysControem Rate/acre 1979 1980 1981 1982 4-yr. Pints Bu. Bu. Bu. Bu. Bu. 1. Basagran; 1 cultivation 1V2 33 6 27 37 26 2. Basagran; Basagran 12; 11/2 36 8 30 37 28 3. Dyanap; 1 cultivation 4 35 5 24 37 25 4. Dyanap; Dyanap 4; 4 35 6 20 28 22 5. Basagran; 1 cultivation + 2,4-DB 12; 0.8 37 7 29 38 28 6. Basagran; 2,4-DB; 2,4-DB 1'/2; 0.8; 0.8 36 8 27 38 27 7. Dyanap; 1 cultivation + 2,4-DB 6; 0.8 36 7 26 32 25 8. Dyanap; 2,4-DB; 2,4-DB 6; 0.8; 0.8 36 8 19 31 24 9. Dyanap; Basagran 6; 1'/2 33 7 31 34 26 10. Basagran; Dyanap 12; 6 38 5 30 27 25 11. Dyanap; 1 cultivation; Basagran 6; 1 36 8 31 32 27 12. Basagran; 1 cultivation; Dyanap 1 ; 6 34 6 31 30 25 13. 1 cultivation - 27 8 14 32 20 14. 2 cultivations - 33 7 13 30 21 15. 3 cultivations - 30 5 14 32 20 16. Hoed check - 39 8 33 38 30 'The first cultivation and application of Basagran and Dyanap were ap- plied 22 days after planting. The second cultivation, the second application of Basagran and Dyanap, and the first postemergence directed application of 2,4-DB were applied 38 days after planting. The third cultivation and the second application of 2,4-DB were applied 59 days after planting. [30] bean yields were evident for treatments producing cocklebur control ranging from 72 to 93 percent for the 4 -year period, table 41. Choosing the "best" system becomes a bit more involved when yield differences are few. If only cost is considered, then Dyanap at 4 pints per acre plus one cultivation was the least expensive treatment at approximately $10 per acre ($5 for chemical, $2 for application, and $3 for one cultivation). This treatment was categorized as providing good early season and fair late season cocklebur control, table 42. Since late season cocklebur control averaged 72 percent, it is logical to assume that cocklebur seed were returned to the soil. What effect these additional weed seeds will have on future cocklebur problems is not known. TABLE 42. EARLY AND LATE SEASON COMMON COCKLEBUR CONTROL AVERAGED OVER FOUR YEARS AND CATEGORIZED INTO CONTROL GROUPS COCKLEBUR CONTROL, EARLY COCKLEBUR CONTROL, LATE Excellent (90's percent) Excellent (90's percent) Basagran; i cultivation + 2,4-DB Basagran; 1 cultivation + 2,4-DB Basagran; Basagran Basagran; Basagran Hoed check Basagran; 1 cultivation; Dyanap Good (80's percent) Dyanap; 1 cultivation; Basagran Dyanap; Basagran Hoed check Dyanap; 1 cultivation Good (80's percent) Dyanap; 1 cultivation + 2,4-DB Dyanap, Basagran Basagran; 1 cultivation Dyanap; 1 cultivation + 2,4-DB Basagran; 2,4-DB; 2,4-DB Basagran; 2,4-DB; 2,4-DB Basagran; Dyanap Basagran; Dyanap Dyanap; 1 cultivation; Basagran Fair (70's percent) Basagran; 1 cultivation; Dyanap Dyanap; 1 cultivation Fair (70's percent) Basagran; 1 cultivation Dyanap; 2,4-DB; 2,4-DB Dyanap; 2,4-DB; 2,4-DB Dyanap; Dyanap Dyanap; Dyanap Poor (65 percent) Poor (65 percent) 1. Cultivation 1. Cultivation 2. Cultivation 2. Cultivation 3. Cultivation 3. Cultivation The most expensive treatment was two applications of Bas- agran at 1 /pints per acre per application ($28.50 for chem- ical and $4 for application). However, late season cocklebur control averaged 92 peaged percent for the 4-year period. One would assume that few cocklebur seeds were returned to the soil and if this continued for a few years, cocklebur infestation would probably decline. Since this was not measured, it is difficult to assess the value of the added chemical expense. Perhaps one compromise is the treatment that contained Bas- agran at 1Y2 pints per acre applied postemergence over the top plus one cultivation and 2,4-DB directed underneath the soybean canopy during the cultivation process. This treat- ment cost approximately $19 per acre, but it produced excel- lent cocklebur control for all years and had soybean yields equal to the hoed check. Both Classic and Scepter have provided excellent control of cocklebur, sicklepod, and annual morningglories. HERBICIDE APPLICATION Controlled Droplet Applicator Vs. Conventional Nozzles There have been reports that the use of the controlled droplet application (CDA) system for herbicide and other pes- ticide application will allow rate reductions. However, data have been insufficient to adequately prove or disprove these claims. Research to investigate the effectiveness of the CDA and soybean oil carrier as compared to conventional hydraulic boom (CHB) application of herbicides and soybean oil for weed control in soybeans was begun in 1983 at the Black Belt Substation, E.V Smith Research Center, Prattville Experi- ment Field, and Tennessee Valley Substation. Five methods of application were evaluated: (1) Conventional: CHB equipped with 11002 flat fan tips, water used as a carrier at 16 gallons per acre. (2) Low volume conventional: CHB equipped with 800067 (730039 at Tennessee Valley); water plus soybean oil concen- trate (1 quart/per acre) used as carrier in a total volume of 4 gallons per acre. (3) Low volume conventional: Same as method 2 except soy- bean oil concentrate increased to 2 quarts per acre. (4) Controlled droplet applicator: CDA operated at 1,650 revolutions per minute (RPM) equipped with 4916/20 orifices (RPM at Tennessee Valley was 3,700). Water plus soybean oil concentrate (1 quart per acre) used as carrier in a total volume of 2 gallons per acre. (5) Controlled droplet applicator: Same as method 4 except soybean oil concentrate increased to 2 quarts per acre. All plots received Lasso 4E + Lexone 75 df applied pree- mergence (PRE) and Basagran 4 + Blazer 2L applied post- emergence over the top (POT) at normal (X) and half normal (1/2 X) rates. This provided for four rate combinations: (1) X PRE + X POT; (2) 1/2 X PRE + X POT; (3) X PRE + 1/2 X POT; (4) 1/2 X PRE + 1/2 X POT. Data collection for each location wasipercent weed control by species, soybean injury, fresh weight of weeds, and soy- bean yields for both cultivated and uncultivated rows. Sev- eral conclusions can be made: 1. Low volume (2 to 5 gallons per acre) herbicide applica- tion is viable. Additional refinement is, however, needed. 2. The more costly CDA applicator is no better than low volume conventional application. 3. Few weed control advantages have been shown for using soybean oil as the herbicide carrier versus water. Conversely, mixing problems have been encountered with oils and her- bicides that are not oil soluble (dry and water soluble formu- lations). 4. Where a surfactant and/or adjuvant is needed, soybean oil has worked as well as petroleum base oils. 5. The full rate of herbicides is not always needed. How- ever, when and how much to reduce rates must be decided by each individual producer. Variables such as weed density, soil types, weed species susceptibility, stage of growth, and weather conditions must be included in the decision process. Herbicide label directions must also be considered for prod- uct guarantees to be valid. See color plate numbers 12, 13, and 14. [31] Management of Soybean Insects T.P Mack and C.B. Backman Insects attacking soybeans have generally increased in economic importance as the acreage of soybeans has in- creased in Alabama. Insects reduce yields by eating foliage, damaging pods and/or seeds, boring or girdling plant parts, transmitting diseases, and reducing the soybean plant's abil- ity to fix nitrogen. Soybeans are attacked by more than 100 species of arthropod pests worldwide, 17 of which are pests of soybean in Alabama, table 43. Many of these are capable of becoming economically important pests if populations of their natural control agents are disrupted by unnecessary pesticide applications. TABLE 43. INSECTS OF ECONOMIC IMPORTANCE ON ALABAMA SOYBEANS Scientific name Common name Pest status 1 Heliothis virescens (Fabricius) Tobacco budworm rare Heliothis zea (Boddie) Podworm often Spodoptera exigua Hubner Beet armyworm rare Spodoptera frugiperda (J.E. Smith) Fall armyworm rare Spodoptera ornithogalli (Guenee) Yellowstriped armyworm rare Feltia subterranea (Fabricius) Granulate cutworm rare Plathypena scabra (Fabricius) Green cloverworm rare Anticarsia gemmatalis Hubner Velvetbean caterpillar often Pseudoplusia includens (Walker) Soybean looper annual Trichoplusia ni (Hubner) Cabbage looper rare Elasmopalpus lignosellus (Zeller) Lesser cornstalk borer occasional2 Spissistilusfestinus (Say) Threecornered alfalfa hopper often Nezara viridula Linnaeus Southern green stinkbug occasional Acrosternum hilare (Say) Green stinkbug occasional Euschistus servus (Say) Brown stinkbug occasional Epilachna varivestis Mulsant Mexican bean beetle rare Cerotoma trifurcata (Forster) Bean leaf beetle occasional 'Refers to how often the insect requires a pest management action to pre- vent economic damage. 2 True status of this pest in Alabama is uncertain due to lack of good data. DISTRIBUTION OF SOYBEAN INSECT PESTS IN ALABAMA The abundance and damage potential of most soybean in- sect pests varies with location in Alabama. In a recent U. S. Department of Agriculture sponsored meeting with Alabama soybean researchers, three distinct soybean insect regions were identified, figure 9. The top six soybean insect pests were then ranked according to the amount of economic losses they cause annually, table 44. Podworms, which feed directly on developing soybean pods, ranked as the most important TABLE 44. EcoNoMIC RANKING OF SOYBEAN INSECT PESTS IN ALABAMA' Insect Ranking Northern Central Southern State Podworm .................... 12 1 1 1 Soybeanlooper ............... 2 1 3 2 Green stinkbug ................ 3 3 2 3 Threecornered alfalfa hopper .... x 3 23 33 43 Velvetbean caterpillar ......... . x 3 2 5 Lesser cornstalk borer ........... x x 4 6 'From a 1983 USDA sponsored survey. 2 Numbers indicate rank, with a rank of"" being highest. An "x" indi- cates that a pest is not an important soybean insect pest in that region. 3 New information indicates that threecornered alfalfa hoppers are a more serious soybean insect pest than this table indicates. Southern FIG. 9. Northern, central, and southern Alabama insect regions as determined in a 1983 USDA survey. statewide. Soybean loopers, which are foliar feeders, were considered in the central region to be as damaging as pod- worms, and overall were ranked as the second most impor- tant soybean insect pest in the state. Threecornered alfalfa hoppers were ranked as the fourth most damaging soybean insect pest statewide. However, new information on these stem, branch, and leaf petiole girdling insects indicates they may rank third or even second among the most damaging in- sect pests. Velvetbean caterpillars ranked fifth in statewide importance, but second in importance in the southern re- gion. These foliar feeding insects are probably the most im- portant soybean insect for the Alabama counties that border Florida. Researchers in Florida rate the velvetbean caterpil- lar as the number one soybean insect pest in that state. MANAGEMENT OF SOYBEAN INSECTS Pest management is the utilization of all available tech- niques to manage pest populations and avoid adverse ecolog- ical and social consequences. This technique is an effective method of reducing insects losses in soybeans, but is em- ployed in less than 40 percent of all of the soybeans grown in [32] INSECT REGIONS IN ALABAMA TABLE 45. SOYBEAN PEST MANAGEMENT PRACTICES FOR FOLIAR FEEDING INSECTS AND THEIR USAGE IN ALABAMA' Percent of planted acres Northern Central Southern State Corn earworm early planting 1 1 2 1 Foliar and podfeeders scouting 35 35 35 35 Velvetbean caterpillar early planting 0 2 4 2 'From 1983 USDA sponsored survey. Alabama, table 45. A cornerstone of pest management is the concept of an economic injury level-the population level of a pest that can be tolerated without significant economic loss. Since pest management practices (e.g. pesticides, biological control, etc.) are used only when the cost of control is less than or equal to the crop loss from the pest, unnecessary pes- ticide applications are prevented. This can save substantial sums of money. For example, a cotton insect pest manage- ment program in Texas increased grower net profits by more than 50 percent in a 2-year study. Soybean pest management systems in other states have saved growers money, so insect pest management in Alabama should too. Two major insects are being intensively studied in Alabama pest management research: the threecornered alfalfa hopper and the soybean looper. The threecornered alfalfa hopper is a small, green treehopper that feeds on alfalfa, tomatoes, wheat, barley, oats, clover, cowpeas, soybeans, sunflower, johnsongrass, bermudagrass, cocklebur, and vetch. It feeds by using its piercing-sucking mouthparts to puncture stems, branches, or leaf petioles. Small hopper nymphs feed ran- domly, while larger nymphs make a continuous series of punc- tures around the circumference of a stem. This characteristic THREECORNERED ALFALFA HOPPER SOYBEAN SEEDLING DAMAGE FIG. 10. Ways in which threecornered alfalfa hopper damage affects soybean seedlings. (Drawing by PR Mitchell.) damage is called a girdle. Early season girdling of main stems causes lodging, breakage, and plant mortality A large nymph can completely girdle a main stem in less than 24 hours. Threecornered alfalfa hopper damage can affect seedling soy- bean plant growth in many ways, figure 10. For example, this pest aids in the transmission of at least two soybean diseases, stem blight (Diaporthe phaseolorum) and sclerotial blight (Sclerotium rolfsii), by injuring the plant and thus providing a favorable avenue of entrance for the fungi. Stem canker (Diaporthe phaseolorum var. caulivora) infection may also be increased by threecornered alfalfa hopper injury. Stem canker is extremely closely related to stem blight, the inci- dence of which has been shown to increase with threecor- nered alfalfa hopper damage. The disease augmentation ef- fect of threecornered alfalfa hopper feeding means that a much lower population can cause economic damage because of the combined injury and disease effects. Threecornered alfalfa hopper feeding shifts from the base of the main stem to the upper part of the main stem, THREECORNERED ALFALFA HOPPER SOYBEAN VEGETATIVE DAMAGE I FIG. 11. Types of soybean vegetative damage done by three- cornered alfalfa hopper. (Drawing by P. Mitchell.) [33] v I Pdecreased increasedN2 disease fixation ain st girdliI FIG. 12. Types of reproductive damage done to soybean by three- cornered alfalfa hopper. (Drawing by P. Mitchell.) branches, and leaf petioles as a soybean plant increases in height and the main stem hardens. This vegetative feeding, figure 11, reduces yields by decreasing the flow of sugars pro- duced in the leaves to the roots and to the growing tip of the plant. However, the most serious damage occurs when a plant is blossoming and actively producing seeds. Threecornered alfalfa hoppers girdle leaf petioles at this time. A single pe- tiole can be girdled many times. This "late season" damage has been considered unimpor- tant until very recently. Results from a 2-year study indicate that threecornered alfalfa hopper feeding can reduce soy- bean stem, pod, and seed dry weights. Yield losses from 16 hoppers per row-foot were 48 percent in 1982 and 45 percent in 1983. Petiole girdling probably physically reduced the flow of sugars to the pods, figure 12. In a number of studies the flow of sugars from a leaf to a seed has been drastically re- duced by physically girdling the petiole. Threecornered al- falfa hopper girdling might be viewed as a "kink" in the leaf petiole "pipeline" to the pods and seeds. Two other reasons make threecornered alfalfa hopper re- search especially important for Alabama. First, the three- cornered alfalfa hopper overwinters on pine trees, which means that Alabama can support a larger overwintering pop- ulation than some other states, and second, the abundance of threecornered alfalfa hoppers has increased in conservation tillage regimes. Therefore, as conservation tillage use for soy- beans increases in Alabama, yield losses from hopper feeding and diseases augmented by the threecornered alfalfa hoppers may proportionally increase. Threecornered Alfalfa Hopper Control Management of threecornered alfalfa hopper populations is being viewed in the context of total pest management. Thus, any control measure used on threecornered alfalfa hoppers must impact minimally on other organisms in the ecosystem. For this reason, host plant resistance is being examined. Some of the current Group VI and VII soybean varieties were evaluated for their resistance to threecornered alfalfa hopper injury in a large plot field study. Tracy-M and Davis had lower threecornered alfalfa hopper populations than did Braxton, Bragg, Coker 237, Wright, or GA Soy 17. Fifty-six experimen- tal genotypes were also screened for resistance to threecor- nered alfalfa hoppers. A number of the genotypes had lower nymphal populations than some of the standard varieties. Chemical control of threecornered alfalfa hoppers has been examined in a number of studies. Lannate?, Ammo?, Am- bush@, Sevino, Cymbush?, and Orthene? all reduced three- cornered alfalfa hopper populations 3 days postspray in a small plot test conducted at Selma, table 46. A large plot test indicated that Lannate (0.2 pound active per acre) was the most effective insecticide tested because it reduced the threecornered alfalfa hopper population without drastically reducing big-eyed bug or nabid populations. Big-eyed bugs and nabids are extremely important insect natural enemies in soybeans. A nabid, for example, is capable of killing more than 40 small podworms per day. Podworms are most inju- rious to soybeans at early podfill. If an insecticide spray for threecornered alfalfa hoppers is applied just prior to the im- migration of podworm adults, then a podworm outbreak could be generated by the destruction of natural enemies TABLE 46. MEAN NUMBER OF LARGE THREECORNERED ALFALFA HOPPERS ON SOYBEANS AT SELMA, 19821 Large threecornered alfalfa hoppers/ Treatment, pounds 6 row ft. active/acre Postspray Prespray 1 day 3 days 7 days No. No. No. No. Scout 3E, 0.13 .............. 5.88 ab 0.75 ab 0.25 b 0 c S3206 2.3, E 0.1 ............. 2.5 b .38 b .38 b 0.13 c Orthene 75 WP, 0.66 ........ 5.00 ab 1.3 a .75b 1.00 be Cymbush 3E, 0.06.......... 4.13 ab 2.00 ab 1.00 b .63 c Pounce 3.2E, 0.10 ........... 3.88 ab 2.13 ab .88 b 1.13 abc Ambush 2E, 0.10 ........... 3.38 63a .b 1.13b .75c Lannate 1.8E 0.45 ........... . 3.5 ab .25 b .13 b .25 c Super-tin 4L ............... 2.5b 2.ab 3.63a 3.25a by the same letter are not significantly different at the 5 % level according to a DMRT. [34] such as nabids and big-eyed bugs. Thus, it is important to conserve natural enemies of insect pests. Soybean Looper Control The soybean looper is often a late season pest of soybeans in the Southeast and is capable of causing severe damage to soybeans. It is a foliar feeding insect that reduces soybean yields by eating leaves needed to produce the sugars used by the plant to grow viable seeds. Soybean looper larval popu- lation outbreaks are usually rapid, going from less than one larva per shake-cloth to more than 30 in less than 7 days. It is a migratory insect that overwinters in Florida. The soybean looper is routinely exposed to as many as 100 insecticide ap- plications per year in Florida because of loopers attacking chrysanthemums. Circumstantial evidence indicates that these applications contributed to the current Lannate resis- tance found in some looper populations. If this is true, resis- tance to the new pyrethroids, such as Ambush, Pounce, and Ammo, may rapidly occur. A study was begun to examine the egg laying rate of adult female soybean loopers over a range of temperatures. This in- formation was needed because, assuming that a large popu- lation of looper larvae originated from a large number of eggs, the number of eggs laid could be used to estimate larval populations. The total number of soybean looper eggs varied with temperature, figure 13, with most eggs being laid at 78E Soybean loopers laid eggs at their fastest rate from 78 to 85 0 E Therefore, a large number of loopers could be de- posited in a short time if temperatures ranged from 78 to 85 0 F at night when loopers lay eggs. This would be especially true if warm night temperatures coincided with a large num- ber of immigrating adults. These results suggest that an es- timate of the adult looper population size coupled with tem- perature may prove helpful in forecasting looper outbreaks, and thus give soybean growers a warning before economic losses occur. In chemical control studies, Ambush was the most effec- tive compound against soybean loopers. It was more effective Total eggs over lifetime, number 280 - Regression line FIG. 13. Effect of temperature on total number of eggs laid by soy- bean looper over a lifetime. than Ammo or Cymbush in reducing small and medium sized loopers in 1982-85 field tests. Ambush, as well as Lannate- Ambush (0.225 + 0.05 pound active per acre) and Lorsban- Ambush (0.5 + 0.05 pound active per acre) mixtures, effec- tively reduced looper populations in 1983. See color plate numbers 15, 16,17, 18, and 19. Biological Control of Soybean Insect Pests J.D. Harper A wide spectrum of parasites, predators, and pathogens af- fects populations of insect pests of soybeans. While the ex- tent of pest control by these natural enemies is hard to quan- tify, it is clear that they contribute significantly to the maintenance of pest populations below economically damag- ing levels in most fields in most years. Occasionally, unusual weather conditions, high immigration rates of pest species into fields, or other factors result in an imbalance between the natural enemies and pest species. Under these condi- tions, the pests are able to cause economic damage to the soy- bean crop. All too often, the factor which causes this imbal- ance is the misuse of pesticides. Every soybean field has its own complex of predaceous in- sects and spiders. The most common of these are big-eyed bugs, damsel bugs, minute pirate bugs, spined soldier bugs (predaceous stink bugs), ground beetles, earwigs, and sev- eral species of spiders. While the extent of pest control by each of these predators is hard to quantify, predators contrib- ute significantly to the maintenance of pest populations below economic injury levels. Parasites, principally small to minute wasps and tachinid flies which resemble rather hairy or spiny houseflies, also aid in maintaintaining pest populations below economic injury lev- els. Parasites lay their eggs in or on the eggs or larvae of pest species and develop in the living hosts. When the parasites' larval development is complete, they emerge from their hosts, generally killing the hosts in the process. Most pest insects in soybeans also suffer from one or more diseases. These are caused by viruses, protozoa, fungi, and bacteria. Nematodes parasitize pest species, causing disease- like symptoms as well. At times, mass die-offs of pests occur as these pathogens spread through pest populations. Partic- ularly well known to growers are the fungi Nomuraea rileyi and Entomophthora gammae. Nomuraea is most frequently seen in late season. It infests most species of lepidopterous caterpillars which feed on soybean. It causes the familiar white cadavers which are seen sticking to leaves and stalks of soybean plants. Entomophthora gammae infects soybean and cabbage loopers, causing the caterpillars to hang from leaves as shriveled yellow or brown larvae. Entomophthora gammae is generally important in late August and September. Nuclear polyhedrosis viruses also infect the soybean podworm in Ala- bama, and others are known from the velvetbean caterpillar and soybean looper, as well as from less frequent pests such as the various armyworms and the cabbage looper. Natural enemies are generally utilized in one of three [35] 160 65 70 75 80 Temperoture, *F 85 90 95 ways-through conservation, augmentation, or introduction. Conservation involves management practices which have minimal impact on beneficial organisms. Augmentation of natural enemies implies release of parasites or pathogens to increase the levels of beneficials which cannot multiply fast enough to control increasing pest populations. Introduction is the practice of releasing natural enemies into a field where they do not already occur. SURVEY FOR NATURAL ENEMIES For several seasons, collections of lepidopterous caterpil- lars have been made at several locations through the central and southern regions of Alabama. Many species of parasites, predators, and pathogens have been recorded in these sur- veys to determine what natural enemies are present. Five species of parasitic wasps and five species of flies make up the majority of parasites associated with larvae of green clover- worm, soybean podworm, soybean looper, and velvetbean caterpillar. Most of these parasites are not host specific, but attack two or more of these pests. Parasitism rates are usually from 5 to 20 percent, but in some fields in late summer, par- asitism of the soybean looper reached 75-80 percent. All dis- ease agents mentioned previously have been found in the Ala- bama surveys. Rates of infection have varied with host species, location in the State, and time of year, and have ranged from less than 5 to greater than 95 percent. MICROBIAL PESTICIDES Products based on the bacterium Bacillus thuringiensis are ideally suited to soybean pest management programs be- cause of their selectivity. They kill only their target pests and do not harm beneficials. Results of several studies on the use of B. thuringiensis as a selective microbial insecticide for green cloverworm, soybean looper, velvetbean caterpillar, and soybean podworm show it is (1) highly effective against both green cloverworm and velvetbean caterpillar at low rates, tables 47, 48, and 49, (2) effective against soybean looper at higher rates, table 49, and (3) not effective against podworms at the dosages tested, table 49. The improved commercial formulations of this bacterium used today are more concentrated and more easily handled than similar products available a decade ago. TABLE 47. CONTROL OF VELVETBEAN CATERPILLAR WITH DIFFERENT RATES OF DIPEL (ACTIVE INGREDIENT = BACILLUS THURINGIENSIS) FOLLOWING AUGUST 27 AND SEPTEMBER 10, 1980, APPLICATIONS ON REPLICATED FIELD PLOTS, GULF COAST SUBSTATION Treatment, Medium + large larvae/3 ft. of row Yield/acre active/acre 9/9 9/16 9/23 No. No. No. Bu. Dipel, 0.25 lb ........ 3.8a' 0.5a 7.3a 33.1a Dipel, 0.50 lb........ . 2.3a 1.0a 6.3a 29.4a Dipel, 0.75 lb ............. 1.5a 1.8a 6.0a 31.4a Lannate, 0.45 lb...... 4.5a 3.8a 1.8a 30.3a Untreated........... 13.5b 58.3b 18.9b 19.0b 'Means in the same column followed by the same letter do not differ sig- test). A second microbially derived pesticide currently under in- vestigation is Thuringiensin, a toxin produced by certain va- rieties of B. thuringiensis. Laboratory research to date has demonstrated that this material is capable of killing soybean podworms at very low dosages. Use of these materials illus- trates the introduction type of approach to biological control. Neither material occurs naturally in the field nor multiplies under field conditions. TABLE 48. VELVETBEAN CATERPILLAR CONTROL WITH THURICIDE (ACTIVE INGREDIENT = BACILLUS THURINGIENSIs) APPLIED OCTOBER 3, BLACK BELT SUBSTATION, 1979 Medium and large larvae Treatment, at days post-treatment active/acre 2 5 No. No. Thuricide HP, 0.5 lb................... 55.Oa i 9.7a Thuricide HP, 0.5 lb. + Gustol, 1.0 lb.' .... 61.Oa 9.0a Untreated .............................. 87.7a 63.7b 'Means in the same column followed by the same letter do not differ sig- nificantly at the 0.5 level of probability (Duncan's new multiple range test). 2Gustol is a commercial feeding stimulant. ROLE AND DYNAMICS OF INSECT PATHOGENS Nomuraea rileyi has been tested for its insecticidal prop- erties through introductions as a sprayed preparation of fun- gal spores. Results suggest that this method of utilization will not provide adequate control of the lepidopterous pest com- plex with the strain chosen for use. A second set of experi- ments was conducted to try to augment the natural popula- tion of Nomuraea which normally infects a low level of host larvae in early summer, creating inocula for a growing level of infection through the summer. Heavy incidence normally occurs in late summer, often too late to be of economic help to the grower. A test of the theory that an early application of infectious fungal spores might initiate an earlier buildup sug- gests that this management approach warrants further test- ing. Identification of the optimal strain of Nomuraea appears critical to the future success of this project. The incidence of the fungus, Entomophthora gammae, in soybean loopers has been monitored for several years. Findings make it obvious that under the right conditions, this fungus can decimate looper populations. Evidence indicates that E. gammae de- velops best at low night temperatures of 68-72'F and during periods when relative humidity remains above 95 percent for several hours. These conditions occur nightly during mid- to late summer in most central Alabama soybeans. These factors alone, however, do not provide all the conditions necessary for a fungal outbreak in host populations. FOREIGN EXPLORATION FOR AN INTRODUCTION OF EXOTIC NATURAL ENEMIES A final avenue of research on biological control has been the exploration for natural enemies which occur in other countries but not in the Southeastern United States. These natural enemies are imported and held in Federal quarantine facilities until they are determined to be safe for release in [36] TABLE 49. EFFECT OF DIPEL AGAINST GREEN CLOVERWORM, SOYBEAN LOOPER, AND SOYBEAN PODWORM, MATERIALS APPLIED 8/19 AND AGAIN 8/31, TALLASSEE, ALABAMA, 1982 Mean no. of larvae/3 feet of row ingredient/ ace Green cloverworm Medium + large soybean loopers Podworms 8/24 8/27 8/24 8/27 9/3 9/7 8/24 8/27 No. No. No. No. No. No. No. No. Dipel, 0.50 lb. ....................... 0.8 1.2 7.5 18.3 6.4 5.4 15.0 15.0 Dipel, 0.75lb. ........................ 0 .2 2.3 7.0 4.4 2.2 27.5 10.0 Lannate, 0.45lb. ...................... .2 .2 5.0 6.7 5.5 4.8 2.5 5.0 Untreated ........................... 6.2 4.5 10.6 19.7 9.8 12.2 22.5 20.0 this country. Several parasites have been collected in Ecua- dor, one of which has now been established in Florida and may eventually be released in Alabama. Still being examined as potential release agents are several pathogens collected in Ecuador, as well as pathogens collected by other scientists in Argentina, Brazil, and Central America. See color plate numbers 20, 21, 22, and 23. Interrelationships of Soybean Cultivars and Environment to Disease Development and Fungicide Performance Paul A. Backman and Mark A. Crawford The most frequently observed foliage, stem, or pod path- ogens on soybeans grown in the Southeast are Septoria gly- cines (cause of brown spot), Cercospora sojina (cause of frog- eye leafspot), Peronospora manshurica (cause of downy mildew), Diaporthe phaseolorum var. sojae (cause of pod and stem blight), D. phaseolorum var. caulivora (cause of stem canker), and Colletotrichum dematium (cause of anthrac- nose). Several other fungal diseases and some bacterial and viral diseases affect soybeans in the area, but they are erratic in occurrence and distribution. Loss estimates for all soybean diseases vary greatly, due to the subjective bases employed in assessment and wide differences in disease severity Development of appropriate fungicidal treatments for the control of soybean diseases requires the following informa- tion: what fungi cause significant yield and seed quality losses; what environmental conditions predispose plants to infection; and what fungicides will control the damaging pathogens? Thirty-three tests were conducted statewide in Alabama to determine the response of various soybean cultivars to fun- gicides. As the soybeans approached early pod set (R 3 ), fun- gicides were applied, followed by a second application 14-18 days later (Rs, early pod-fill). R-ratings refer to the reproduc- tive stages of the soybean plant. All fungicides were applied with a high-clearance ground sprayer operating at 90 p.s.i. and delivering 25 g.p.a. through hollow-cone type nozzles. Three nozzles were positioned over the row, i.e. one above the top and one on each side. All tests were arranged in ran- domized complete block or split-plot designs with five to eight replications. Only the results from the untreated con- trol plots and plots treated with Benlate? 50 WP (8 ounces per acre per application) will be presented. These results are related to prevailing weather conditions during the bloom to pod-fill periods as recorded by nearby stations operated by the U.S. National Weather Service. Two tests were conducted to determine the principal path- ogens of soybeans and their relative pathogenic potentials. Cultivars evaluated were Forrest, Davis, Bragg, and Hutton, representing maturity groupings V, VI, VII, and VIII, re- spectively. For Alabama conditions, maturity groups V and VI are considered early-maturing, and groups VII and VIII late-maturing cultivars. Differences in severity of the various diseases were achieved through differential susceptibilities of the cultivars, and by treatment of the cultivars with fun- gicides. Cultivars were planted at different times to coordi- nate bloom occurrence (R 1 ) on the same date (_ 2 days) for each cultivar. This allowed cultivars from different maturity groupings to be evaluated following treatment with fungi- cides under the same environmental conditions, and at the same developmental stage. Fungicides used were Benlate 50 WP (0.5 pound per acre at each application), Du-Ter 47 WP? (fentin hydroxide, 0.5 pound per acre per application), and Mertect 340 F? thiabendazole, 42.3% flowable (6 fluid ounces per acre at each application). Fungicides were applied as described for the statewide tests to four-row split plots with cultivars the whole plot. Treatment x cultivar combina- tions were replicated eight times at each of the two locations. Samples for foliar disease estimation were obtained as fol- lows: (1) approximately 15 trifoliolate leaves, including pe- tioles, were picked about one-third of the way down the plant at intervals throughout the length of the two middle rows of each plot; and (2) at harvest, combine trash was randomly bagged from each plot to include representative samples of stems and pods. Bases for the severity ratings of the various diseases and damage were: (1) Brown spot, frogeye leafspot, and downy mildew-le- sion frequency on trifoliolate samples. (2) Anthracnose and pod and stem blight-severity on dried stem samples after harvest. (3) Senescence-relative state of decline when control plots were 50 percent defoliated (on 1-5 scale, where 1 = full green and 5 = dead). Severity of each of the diseases present was recorded for each cultivar x treatment and related to environmental con- ditions occurring during the spray period. Disease ratings were made on a 1-5 rating scheme where 1 = no symptoms, 2 = scattered infection, 3 = moderate infection (most leaves, stems, or pods multiply infected), and 4 and 5 = in- creasingly severe levels of infection. Ratings were estimated [37] to the one-tenth unit. In trials involving several cultivars sprayed during the bloom to pod-fill periods (coordinated bloom studies), foliar disease ratings were made as each cul- tivar approached senescence, and reflected the performance of the fungicide at a similar physiological state (pre-senes- cence) for each cultivar. However, it should be noted that early-maturing cultivars reached senescence sooner after treatment than did the late-maturing cultivars. Yields for both statewide and coordinated bloom tests were obtained by harvesting the center two rows of the four-row plots. The ends of the plots were trimmed off before harvest to eliminate any edge effect. The yields reported reflect ac- tual seed yields after harvesting with a two-row combine. On a multi-year, multi-location basis, soybean yield re- sponses to two fungicides were erratic, varying from actual losses to 40 percent increases. When the 33 tests were eval- uated for response to benomyl, it was clear that the largest increase occurred in tests conducted in wet locations with 5 or more days of rainfall in the 3 weeks immediately after bloom initiation. Any day with >2.0 mm of rain was consid- ered "wet." Yields of both early and late maturing cultivars were increased (4.5-5.6 bushels per acre) by benomyl in "wet" environments, but were not increased in "dry" envi- ronments. Soybean cultivars from the coordinated bloom test at the Black Belt Substation predominantly were infected with brown spot and anthracr:ose. Levels of anthracnose were sim- ilar for all cultivars. Yield differences between fungicide treatments were related to control of these two pathogens. The yield of cultivar Forrest plants, however, was severely re- duced by drought. Benlate was effective against both brown spot and anthracnose, while Du-Ter 47 WP was effective pri- marily against anthracnose and Mertect 340 F was not effec- tive against either organism. In coordinated bloom studies at Tallassee, Alabama, an- thracnose and frogeye leafspot most frequently were ob- served at severe levels. Even though relative disease severi- ties (anthracnose-frogeye) were similar to the severities of the brownspot-anthracnose complex observed at the Black Belt Substation, yield responses to fungicide treatments were only 50-60 percent of those observed in the early study. Plants of cultivar Davis were resistant to C. sojina (cause offrogeye), but still responded at 70-80 percent of the increased yield of cultivars with both frogeye and anthracnose. Mertect was again ineffective against anthracnose at this location. Yield improvements following thiabendazole treatment must there- fore be related to control of frogeye. In both coordinated bloom studies, neither downy mildew nor pod and stem blight responded to fungicidal treatment. Downy mildew developed before treatment, and did not seem to increase after bloom. Pod and stem blight appeared to develop well after pod fill and thus could not affect yield. No stem canker was observed. Observations on these dis- eases, therefore, are not reported here. Delayed senescence was found to be a good indicator for reduction in total disease. In both coordinated bloom tests, delay in the onset of senescence was typically related to in- creased yield and disease control. These data indicate that for significant yield increases to occur in response to benomyl, soybeans must be under pe- riods of recurrent rainfall from bloom to pod-fill. These "wet" periods would correspond to infection periods for the prin- cipal foliar pathogens. Untreated controls in the 21 "wet" tests had much higher levels of disease than did the untreated controls in the "dry" tests. The 5 wet-dry scheme, as de- scribed, appeared to be a good predictor for the efficacy of Benlate. As modified for the two-spray program recom- mended in Alabama, farmers are advised to make the first ap- plication of 8 ounces per acre benomyl 50 WP at R 3 if 2-3 wet days have occurred since bloom. If these wet conditions have not been met by 1 week after R 3 , the application is omitted. A second application of Benlate at the same rate is made only if 2 additional wet days occur during the 10-day period follow- ing the first application. Use of this prediction system would have eliminated at least one-third of the benomyl applications made in the 33-test study. Of the results recorded, only 2 of the 12 dry tests treated with benomyl had yields at least 6 percent greater than the nontreated control. Of the six low- est-yielding wet tests treated with benomyl, all had yield im- provements of 6-10 percent over the control; the other 15 wet tests yielded considerably higher. A complete treatment of t he "common sense" system for timing of fungicide applica- tions to soybeans can be found in the following section. Reports that late-maturing cultivars sprayed with fungi- cides do not respond with yield increases as great as early- maturing cultivars are partially confirmed. However, it was noted that early-maturing cultivars usually proceed from bloom to pod-fill during the wetter late July through August period. The lower yield response of later cultivars to fungi- cides may merely be a reflection f few infection periods oc- curring during September, rather than disease tolerance. Coordinated bloom studies allowed evaluation of the dam- age potential of each of several soybean diseases. Levels of disease achieved through fungicidal application and cultivar resistance served as the basis for damage determinations. Yields from each cultivar served as the integrating factor for total disease damage, and reflected the cumulative disease load. Data from the Black Belt Substation revealed brown spot to be as damaging to yield as anthracnose. This can be deduced by comparing the yield responses of Hutton (low brown spot) and Davis (high brown spot) to Benlate treat- ment, when each had about equal levels of anthracnose (frog- eye levels were negligible). The Davis soybeans responded with a 31 percent yield increase; yield of Hutton increased 8.2 percent. Only Hutton soybeans showed increased yields after treatment with Du-Ter, primarily because this fungicide was very active against anthracnose but poor against brown spot. Since Hutton had high levels only of anthracnose, treatment with Du-Ter was effective. Yields from the Tallassee tests indicate that anthracnose af- fected yield more than did frogeye leafspot. This is apparent when comparing yield response of Davis (very little frogeye) to benomyl, with that of Forrest, Bragg, and Hutton cultivars (high levels of frogeye). Only low levels of brown spot were found in this test. Yield increased primarily in response to anthracnose control rather than to the control of frogeye leaf- spot. Comparisons of yields from the Black Belt Substation test [38] with those from the Tallassee test indicate that the greater percentage yield increases following fungicide treatment at the Black Belt were due to high levels of brown spot on the cultivars that exhibited highest yield responses. Results of these tests indicate that, in order of damage po- tential, anthracnose is slightly more damaging than brown spot, and frogeye is least damaging. In these tests, the foliar fungi C. sojina, S. glycines, and C. truncatum all apparently invaded between bloom and pod-fill. Pod and stem blight de- velops much later, probably in late pod-fill, with little yield loss. Yield reductions from these organisms were probably due to reduced photosynthetic capability because of prema- ture senescence, resulting in smaller seed. Hormone-like ac- tivity has been ascribed to Benlate in previous studies. How- ever, these data indicated no kinetin-like activity when Benlate was applied to soybeans. In the 33 statewide tests reported, anthracnose was dom- inant in every test, with recorded yield increases from con- trolling the disease. Brown spot occurred more sporadically, but yields were also improved where it was controlled. Ben- late gave superior control of both pathogens, while Du-Ter was effective against anthracnose. Mertect at the rates em- ployed was ineffective against these pathogens, but showed good activity against frogeye leafspot. Results of the Alabama tests indicate that using foliar fungicides only when wet con- ditions favor disease development should prevent many un- necessary applications and improve the economic return of fungicides when used in soybeans. A Common Sense Timing System for the Application of Foliar Fungicides Paul A. Backman, Mark A. Crawford, and Mack Hammond As early as 1977, research in Alabama indicated fungicides applied to control leaf and stem diseases in soybeans were not beneficial during dry periods. The northern portion of the State is much drier than the Gulf region during the summer months, and less frequent periods of rainfall in that region re- duce severity of soybean diseases. This weather pattern was taken into consideration in designing a cost-effective system for the application of fungicides to soybeans. Tests were conducted throughout the northern region of Alabama to evaluate a system for the timing of fungicide ap- plications based on local (on-farm) weather conditions. This timing system was compared to the standard program (sprays, regardless of weather, at early pod set and 14 to 18 days later) and to unsprayed soybeans. Beginning at early bloom (first bloom), any day with 1/10 in. of rain or extended periods of fog and dew was considered wet. When 3 to 4 wet days had been recorded, an application of Benlate at 8 ounces per acre was made using a high clearance sprayer. This ap- plication usually occurred during early pod set, but occasion- ally was made during bloom. The second application was made 14-20 days after the first, if 3 to 4 more wet days oc- curred when the count was begun 10 days after the first ap- plication. During periods of especially wet weather, the in- terval was shortened to as little as 10 days to compensate for frequent disease infection periods and washing-off of the fun- gicide. All spray trials were replicated six times and results are reported as treatment means. Data from the meteorological timing system indicated sev- eral advantages over the standard spray program. The num- ber of fungicide applications was reduced an average of 40 percent, while the frequency of nonprofitable fungicide ap- plications was reduced to zero for the meteorological system from 60 percent for the standard program. However, disease control was slightly inferior to the standard program. The economic data indicated that not only was the number of lo- cations with! non-economic return on fungicide investment reduced where the meteorological timing system was used, but all locations gave a positive dollar return above cost. The ratio of increased crop value to cost of control was very pos- itive for the meteorological program ($3.03 per $1.00), but only marginally beneficial for the standard program ($1.19 per $1.00). These data indicate that foliar diseases can cause substan- tial losses in soybeans but, in the drier regions of Alabama, control measures cannot be utilized routinely at standardized times with the expectation of reasonable return on invest- ment. The meteorological timing system described for appli- cation of benomyl, based on the probability of damaging lev- els of disease developing, reduced total pesticide application by 35 percent, yet gave a greater dollar return per acre in all six experiments. A portion of the success of this experiment can be related to the systemic nature of benomyl, which allows for removal of established infections. Further, actual weather rather than predicted weather was utilized. Should contact fungicides be employed (e.g. Bravo 500?), sprays would have to be applied before infection periods as protectants, and predicted weather would have to be utilized. Aerial Applications of Fungicides to Soybeans Paul A. Backman, B.H. Cosper, and Mark Crawford Research relating to efficiency of application of aerially ap- plied fungicides has been conducted in Alabama since 1978, with emphasis given to improving the delivery of fungicides to the crop surface. Fungicides applied to soybeans in a water carrier were compared to those in water plus spray oil,and water plus the viscoelastic agent Nalcotrol?. The percent of fungicide reaching the foliage was determined. Data gath- ered show that when small droplets were produced, the ben- efits of this tank additive were lost. The spray volume per acre in which fungicides should be delivered by airplanes was also evaluated. Results indicated that rates of delivery as low as 2.3 gallons per acre may effectively deliver the fungicide to the crop. Low volumes were particularly effective under con- ditions of high humidity (Marion, Alabama, test), but higher spray volumes generally improved deposition. [39] Reducing Losses from Soybean Stem Canker Paul A. Backman, Mark A. Crawford, and Mack Hammond Soybean stem canker, a disease caused by the fungus Dia- porthe phaseolorum var. caulivora, has been found in soy- beans grown from Canada to the Gulf of Mexico. However, until recently severe losses from this disease had not been ob- served in Alabama. In 1977, several thousand acres of soy- beans in Montgomery County were infected with this fungus and severe crop losses occurred. During the 1980 and 1981 seasons, stem canker occurred throughout the Black Belt counties of central Alabama, as well as in several river bottom areas adjacent to this zone. During the 1982 season, stem canker was found in the Tennessee Valley and the mountain valleys of northeast Alabama. Symptoms of the disease are small reddish-black lesions originating typically in the leaf axils, becoming black, sunken, and elongate on the stem. As the disease becomes se- vere, plants typically show chlorosis (yellowing) between leaf veins, followed by death of the interveinal tissue and chlo- rosis near the veins. In advanced stages of the disease, the plant dies, usually retaining the dead leaves. Whole fields have frequently been destroyed as a result of this disease. Research from several regions of the country indicates that the stem canker fungus can be seed-borne, and that this is an important means of long c&stance movement for the infesta- tion of new fields. A second means of spread is on equipment containing infested crop debris or soil. Once established, the fungus lives from year to year on crop debris. One or two in- fected plants in a field during the first year can lead to total devastation during the second year, if susceptible cultivars are grown. Infection of the soybean plant seems to occur early in the growing season. Data from central Alabama indicate that soy- beans planted after June 15 develop little or no stem canker symptoms, regardless of how susceptible the variety may be. The disease cycle begins in the early spring with the de- velopment of the spores within the fungus fruiting body (per- ithecium), figure 14. These perithecia develop on plant debris from the previous crop. In about mid-April, the spores are mature and are exuded out of the perithecial neck, in a sticky mass. This spore mass is not easily wind-borne, but when it rains, the impacting rain droplets can be carried by wind for considerable distances. Spore formation and dispersal con- tinue until early June, when the spore production of perithe- cia appears to reduce greatly In years such as 1984, when spore development is delayed by unfavorable environment, infections still occur, but too late to cause disease. Spores that are carried to young soybean plants apparently infect the leaves. Like almost all foliar pathogens, the stem canker fungus requires an extended period of free moisture for the infection process to occur. Usually this moisture would be provided by the rain that carried the spore to the soybean plant. Typically the young plant has not passed beyond the 5- or 6-leaf stage before almost all spore production steps have occurred. Reports in the literature indicate that if the first six leaves are removed anytime before bloom, the plants never FIG. 14. Life cycle of Diaporthe phaseolorum f. sp. caulivora (cause of stem canker). Solid lines indicate known developmental path- ways, while a broken line indicates one requiring verification; "X" in- dicates no apparent function. develop canker. Further, fungicide sprays made during this early vegetative period can prevent disease development. Following infection, the fungus remains in the leaf tissue until about the bloom stage of soybean development. At this time it appears to grow into the stem producing the symp- toms described earlier. Research on fungicidal control of stem canker has contin- ued since 1980. Data from a test conducted in 1983 evaluating Benlate? 50WP for control of stem canker under various ap- plication schedules indicate that only the spray program that included a treatment at the V 2 (2-leaf) stage reduced stem canker and increased yield. If a V 2 spray is used, subsequent fungicide applications enhance control, even when these later sprays do not themselves affect disease level. Evaluation of these data and data from other states indicates that fungicides must be applied during the vegetative growth stages, timed to coincide with spore release and infection, to be effective. Furthermore, these applications will show improved control if fungicides are also applied at later dates. Other points that are indicated include (1) highly susceptible and susceptible varieties (e. g. J-77-339, Hutton, and Bragg) require too many fungicide applications to economically control the disease; (2) for varieties showing some resistance (e.g. S-69-96 and Davis), fungicides show excellent yield improvements; (3) timing is critical, while application rates are less important; (4) banded applications over the top of young plants have been highly successful, and (5) Benlate gives good control, but other fungicides such as Bravo applied early can also control the disease. See color plate numbers 24 and 25. Nematode Problems in Soybeans R. Rodriguez-Kabana, D.G. Robertson, C.F Weaver, PS. King, E.L. Snoddy, and D.B. Weaver The soybean is a legume species with a wide range of sus- ceptibility to plant parasitic nematodes. Virtually all major [40] genera of plant nematodes successfully parasitize the crop. The root-knot nematodes (Meloidogyne arenaria, M. incog- nita, and M. javanica) and the cyst nematode (Heterodera glycines) cause the most economic damage. A complicating factor in nematode damage to soybeans is that there is great variation in ability to parasitize soybean within the same nematode species. Because of this, several races of cyst nem- atodes are recognized and it is known that there are races within each root-knot nematode species. Various other nematode species, such as lesion (Pratylenchus), stubby (Paratrichodorus), sting (Belonolaimus), spiral (Helicotylen- chus), lance (Hoplolaimus), and reniform (Rotylenchulus reniformis), attack and cause injury to soybeans, generally to a lesser degree than the root-knot and cyst nematodes. OCCURRENCE OF NEMATODES IN ALABAMA SOYBEAN FIELDS All of the nematode species and genera mentioned have been recorded in Alabama soybean fields. However, of most frequent occurrence are the root-knot, the cyst, the lesion, and the stubby root nematodes. The species most frequently encountered in the State and also the most difficult to manage are the soybean cyst nematode and the root-knot nematodes. Survey results indicate that simultaneous occurrence of root- knot and cyst nematodes in Alabama soybean fields is on the increase. The magnitude of the nematode problem in Ala- bama is illustrated by results from a 1983 unbiased survey of soybean fields in the State. Of the total soybean acreage in the survey, 45.6 percent was infested to some level with cyst, root-knot, or combinations of cyst and root-knot nematodes: 12.4 percent of the acreage was heavily infested with the cyst nematode, 4.4 percent was severely infested with root-knot nematodes, and 4.0 percent had both cyst and root-knot nem- atodes. The degree of infestation by nematodes varied among regions of the state, figure 15. In Baldwin County, 90.2 per- cent of the 101 fields surveyed in November 1983 were heavily infested with cyst or root-knot nematodes and 33.6 percent had mixed populations of cyst and root-knot nematodes. Root-knot + cyst nematodes Madison County Root-knot + cyst nemotodes Root-knot nematodes *0. Limestone County Madison County Root-knot nemotodes Cyst nematodes * s o * . "* S Limestone County Madison County Cyst nematodes Lowndes County Montgomery County Root-knot + cyst nematodes Lowndes County Montgomery County Root-knot nematodes Lowndes County Montgomery County Cyst nematodes Baldwin County Baldwin County FIG. 15. Distribution of root-knot and cyst nematodes in soybean fields in representative counties in Alabama, from a survey conducted in No- vember 1983. (Open dots mean no nematodes and black dots indicate the presence of nematodes; for root-knot nematodes in Baldwin County, the size of the black dot is directly related to the severity of infestation.) [41] Baldwin County ,,,,, L, ~,, YIELD LOSSES Yield losses to plant parasitic nematodes depend on the nematode species and races present in a given field and the soybean variety planted in the field. Nematodes other than root-knot or cyst nematodes rarely cause yield losses greater than 10-15 percent in Alabama. However, losses sustained from attacks by root-knot or cyst nematodes can be as much as 70-80 percent. Research for several years has attempted to quantify precisely the relation between soybean yields and numbers of root-knot or cyst nematodes in soil. This work, for example, has indicated that losses for Ransom soybean to a species of root-knot nematodes (M. arenaria) are in the range of 4-10 pounds per acre per larva of the nematode found in 100 cubic centimeters of soil (nematode infestation is best es- timated 4-6 weeks before harvest). Similar studies have been conducted for other soybean cultivars and for the cyst nema- tode and other root-knot nematodes. The results show sub- stantial yield losses to these nematodes. The calculated soy- bean yield loss to the nematode for the State in 1983 was 11.72 million bushels. METHODS OF CONTROL Traditional methods of controlling plant parasitic nema- todes rely on the development of resistant varieties, the use of effective nematicides, and rotation with non-host crops. Plant breeding efforts to develop resistant cultivars are dis- cussed in another section of this publication. Currently, there are no commercially available soybean cultivars with com- bined resistance to all important root-knot nematodes and with resistance to the major races of the cyst nematode. TABLE 50. YIELD RESPONSES OF SELECTED SOYBEAN VARIETIES TO APPLICATIONS OF EDB' IN A FIELD INFESTED WITH MELOIDOGYNE INCOGNITA AND HETERODERA GLYCINES, NEAR ELBERTA, ALABAMA, 1982 Yield per acre acre Yield Variety No EDB With EDB increase Bu. Bu. Bu. Pct. Coker 317 ...... 1 33 32 2,825 Ransom ........ 5 37 32 654 GK49 ......... 6 28 22 394 Braxton ........ 8 33 25 304 RA701......... ... 8 30 22 280 A7372......... 6 28 22 374 Foster ......... 12 37 25 206 IEDB was applied as Soilbrom? 90 at planting time at a rate of 2 gallons per acre. TABLE 51. YIELD RESPONSES OF SELECTED SOYBEAN VARIETIES TO APPLICATIONS OF EDB' IN A FIELD INFESTED WITH MELOIDOGYNE INCOGNITA AND HETERODERA GLYCINES, NEAR ELBERTA, ALABAMA, 1983 Yield per acre Gain/acre Yield Variety No EDB With EDB increase Bu. Bu. Bu. Pct. Coker 317 ...... 19 50 31 162 Ransom ........ 9 40 32 373 GK49 ......... 14 41 27 187 Braxton ........ 9 36 27 321 RA701 .......... 21 46 25 115 Kirby.......... 35 55 20 57 Foster ......... 26 51 25 96 'EDB was applied as Soilbrom? 90 at planting time at a rate of 2 gallons per acre. There are, however, soybean varieties (e.g. Kirby, Foster, LeFlore) that are capable of delivering relatively high yields in fields with extreme levels of infestation by both root-knot and cyst nematodes. Tables 50 and 51 illustrate the range of variability in yield performance of selected soybean cultivars in a field infested with root-knot (M. incognita) and cyst (race 3) nematodes. These results show that it is possible to develop soybean cultivars that can tolerate heavy nematode infesta- tions and still deliver acceptable yields. However, all cultivars suffered substantial yield losses. NEMATICIDES The use of nematicides in soybeans received a great deal of attention in the research. Nematicides can be classified as either fumigants or nonfumigants. Fumigant nematicides are those that are injected into the soil where they vaporize and move through the soil. Fumigants are the oldest nematicides and among the most effective; however, two of the best per- forming of these, EDB and DBCP, are no longer available for use by farmers. A third fumigant, 1,3-dichloropropene (Te- LSD (P=0.05) 60- EDB 55- 50 - 1,3-D 45 40 0 I 2 3 4 5 6 7 Gol./ocre FIG. 16. Although Telone II is still available for use as a nematicide, high rates are required and it has not performed as well as EDB. [42] Yield/ocre,bu. 65 k r ~1 ~ Larvae/gram of fresh root Root-knot nematode 400 (Meloidogyne incognito) Kirby soybeans 300 Magnum (Thiodicorb) 200- LSD (P= 0.05) 100- GUS 6015 Standok (Aldoxycarb) 0- I I I I 0 I 2 3 Active ingredient, lb./ 00 lb. seed FIG. 17. Seed treatment with new systemic nematicides has shown great promise in greenhouse tests. lone? II), is still available for use, but rates of 3-5 gallons per acre are required to obtain maximal yield response and has not performed as well as EDB in any of the trials, figure 16. Non-fumigant nematicides (Furadan?, Nemacur?, Temik?) are most commonly used in granular formulations. In the Alabama research, they performed best when applied at planting time in narrow (4- to 8-inch) bands or in the fur- row. Multi-year studies on the performance of these nemati- cides have shown that their use can result in significant yield increases, table 52; however, much of their performance de- pends on the level of nematode infestation and on the correct choice of cultivar. A new area of nematicide research in soybeans currently TABLE 52. COMPARATIVE EFFECT OF NEMATICIDES APPLIED TO SOYBEAN FIELDS INFESTED WITH SOYBEAN CYST AND ROOT-KNOT NEMATODES ON PRODUCTION Treatment' and Per acre increase rate/acre 1980 1981 1982 1983 4-year average Bu. Bu. Bu. Bu. Bu. Nemacur? 15G (phenamiphos), 8 7 4 10 7 Temik? 15G (aldicarb), 7 6 8 11 8 13 lb . .. . .................... Furadan 10G (carbofuran), 2 0 - 2 1 20 lb ......... Soilbrom? 90 (EDB), 2 gal ........ 11 25 17 22 19 'Granular nematicides applied in 7- to 8-inch band and scratched in top 2 inches of soil. Fumigant injected 8 inches deep. underway is the use of seed treatments. New systemic ne- maticides have been developed that can be used for seed treatments without injury to the resulting soybean plants. These treatments have shown great promise under green- house conditions for reducing root-knot and cyst nematodes, figure 17. Such a treatment has important advantages of re- duced cost, safety, and delivery of an effective material where it is needed, around the developing seedling roots. THE FUTURE Nematode problems in soybeans in Alabama will continue to increase, especially from the soybean cyst nematode. These problems will have to be addressed within a pest man- agement system. Cropping systems will have to be identified that are economical and will result in low populations of plant parasitic nematodes. Ongoing research in several areas of the State is seeking to identify cropping systems that will permit sustained soybean yields and keep nematode numbers low. Also, the information gathered from these studies is cur- rently being integrated into computer management models to deliver the information directly to producers. Within the next 5 years there are likely to be many high yielding soybean va- rieties with increased levels of tolerance to nematodes that can be integrated within production systems to reduce the costs of production. See color plate numbers 26, 27, and 28. [43] PHYSIOLOGICAL DEVELOPMENT Flower and Pod Abscission of Soybean Curt M. Peterson, Michael W. Folsom, Roland R. Dute, and Larry M. Dalrymple There are many different factors limiting soybean yields in Alabama, including environmental and biological stresses. One major factor causing a decreased yield potential and con- tributing to a yield barrier is the abscission of large numbers of flowers and pods before seed maturity Since the number of pods produced by a plant ultimately contributes to yield, substantial increases in productivity could be attained by re- ducing the number of flowers and pods lost, thereby increas- ing pod set. Although considerable research, both nationally and worldwide, has been performed in the last 30 years to de- termine the causes of abscission in soybean and other grain legumes, the primary factor(s) responsible for this problem are still unknown. Research has been in progress at Auburn since 1975 in an attempt to determine the extent and causes of abscission occurring in Maturity Group VII and VIII soy- bean cultivars grown in Alabama. A diagrammatic representation of the typical growth habit FIG. 18. Diagram of a typical field-grown soybean plant at harvest, having a determinate growth habit with many lateral or axillary branches. TABLE 53. STAGES OF REPRODUCTIVE DEVELOPMENT FOR BRAGG SOYBEAN PLANTS GROWN IN FIELD PLOTS AT THE AGRONOMY FARM, AUBURN, ALABAMA, DURING SUMMER Developmental Reproductive characteristics stages Abscised bud Developing flower prior to complete expansion of petals; before pollination and fertilization. Abscised flower Open flower; pollination completed; fertilized ovules present. Abscised immature Flower having withered and/or discolored petals; pod zygotes to proembryos present in ovules; no visible elongation of the pistil into a pod. Abscised pod Visible elongation and/or enlargement of the pod; seeds at different stages of development. Mature pod The pod present on racemes at final harvest usually with one or more seeds present. of Bragg soybean plants at harvest is illustrated in figure 18. The plants used for this study were grown in nonirrigated field plots with 40-inch row spaces and about 8 seeds per foot of row at the Agronomy Farm at Auburn. Each main stem and all axillary branches consist of nodes and internodes. A node is a place on a stem where one leaf and one or more axillary branches or flowering racemes (flower clusters) may form. A typical plant produces an average of 19 mainstenr nodes, 36 axillary branch nodes, and 10 subaxillary branch :nodes for a total number of 65 vegetative nodes. Flowers are borne on racemes which potentially can be produced at all nodes on the plant, figure 18. Frequently, two racemes are produced at higher mainstem nodes where axil- lary branches do not develop. In addition, a terminal raceme is produced at the tip of the mainstem and each axillary branch. Flowering proceeds rapidly so that within a few days flowers appear at most mainstem nodes and older nodes on axillary branches. The process then continues for a 4- to 6- week period with most flowers forming during a 2- to 3-week period. Pollination and fertilization (seed set) frequently oc- cur 1 to 2 days before flowers open. Pods develop slowly for Abscissions/ 200 100 o Pod TotalBud FIG. 19. The average number of bud, flower, and pod abscissions and total abscissions per plant for field-grown Bragg soybean plants. [44] 4- Terminal Raceme Branch Branch Main Stem Flower Number/ plant, average D Potential flowers formed Moture pods 200- 100 - 0 FIG. 20. The average number of poten- tial flowers and mature pods formed on field-grown Bragg soybean plants. Number/ plant, average Main stem Grams Axillary branches 200- -200 150- -150 100- - 100 50 - - 50 0 /A0 Potential Mature Seeds Seed pods pods weight Percent of control - Noncompocted soil (control) ' Compacted soil I formed pods seeds FIG. 21. The average number of potential pods, FIG. 22. The total number of flowers, pods, and mature pods, seeds, and total seed weight pro- seeds produced on Bragg soybean plants duced on the main stem and axillary (lateral) grown in noncompacted and compacted (hard- branches of field-grown Bragg soybean plants. pan present) soil. the first few days following fertilization, rapid elongation be- gins on the fifth day, and full pod length is attained after about 15 to 20 days. During a typical growing season, abscission was observed and recorded at several different stages of flower and pod de- velopment, table 53. Few of the abscissions were unopened flowers or buds, figure 19. Almost one-half of the potential pods abscised at flowering. In addition, a large number of pods at various stages of development abscised during pod enlargement and seed filling More than three-fourths of the flowers or pods formed on Bragg soybean plants abscised before seed maturity, figure 20. Although typical Bragg soybean plants growing under nonirrigated conditions produced an average of 341 total flow- ers during one growing season on all racemes, only an average of 72 mature pods were present on plants at final harvest. Flowers or pods abscised from all racemes on both the mainstem and axillary branches. However, abscissions were disproportionately greater from racemes at lower mainstem nodes and on branches. Thus, the final number of seeds and seed weight produced on branches were similar to that ob- served on the mainstem, figure 21. The extent of abscission during a growing season may be affected by environmental factors. One such factor is drought stress, which can be caused by a lack of rainfall or the pres- ence of a hardpan of compacted soil. A hardpan limits the size of a root system by restricting root penetration into deeper soil layers where stored water reserves might be avail- able. The resulting drought stress leads, in turn, to a de- crease in total flower production per plant, and to an increase in flower and pod abscission, resulting in fewer seeds per plant, figure 22. However, drought stress is not the only factor which causes abscission, because even in a year with ample soil moisture during flowering, abscission still may exceed 70 percent in Bragg soybean. A study of abscission from terminal racemes of Bragg soy- bean plants during one growing season showed that more than 75 percent of the abscissions occurred during a 14-day period when flowering reached its peak in mid-August, fig- ure 23. Most abscissions were either open flowers or flowers having withered petals. This indicated that there is a critical period during early pod development when most abscissions occur. This period coincides with fertilization and early em- bryogenesis. The number of nodes or sites on terminal racemes where individual flowers are attached varies with the cultivar and growing conditions. Flower development proceeds from the base to the tip of each raceme, figure 24, so that pods may be developing at basal nodes when buds or unopened flowers are present at the raceme tip. Occasionally, racemes may be ob- Abscis percer 100 - 90- 80 70 60 50 40 30- 20- I0 0- 3sions, Abscissions, it number Number 1200 S...*- - .. -- _ I100 -1000 -900 SkPercent - 800 -700 - 600 4 -500 -400 -300 -200 - O0 IO 20 30 40 50 60 70 80 90 100 Days FIG. 23. The percent abscission (shedding) and number of abscis- sions observed on terminal racemes of field-grown Bragg soybean plants during the 1977 growing season. [45] r _ ~~ r ~ r 1I~U~III~1 ~r~UU ~UVUe~~~l Ula~llS. uu u FIG. 24. Diagram of a terminal raceme (flower cluster) formed at the tip of the main stem of soybean plants having a determinate growth habit. Individual flowers are attached to the main stalk (peduncle) of the raceme at regular intervals (nodes). The oldest flower or pod is attached at node 1, with younger flowers or pods produced at re- maining nodes. served where pods and flowers are forming at all nodes oi a raceme and no abseissions are present, color plate no. 29. Usually, however, one or more pods are observed developing at the raceme base with many abseissions occurring at inter- vening nodes between these pods and )buds or flowers at the tip, color plate no. 30. More al)seissions occur froim nodes at the tip of a raceme than from nodes at the base, and in some eases all flowers al)scise from a raeeme, color plate no. 31. Ilistological observations of soyb)ean flowers, made to de- termiine stages of ovule (immature seed) development asso- ciated with abscission, revealed that large amounts of starch are deposited in the ovudle, figure 25. The starch that accu- mulates in the central cell of the embrvo sac within each ovule is formed in packets, and completely fills this cell prior FIG. 25. Ovule (immature seed) from a soybean flower. The elon- gated structure in the center is an embryo sac (ES) within which the embryo will form following fertilization. Large numbers of starch packets (SP) are visible in the central cell of the embryo sac. ': A ~ yr 4 >4K :2 4 S 4 4 ~ M Wi * M' W I sy. , 7 -~ 4 >.2~ FIG. 26. Electron micrograph showing wall ingrowths (WI) extending into the cytoplasm of the central cell. Numerous subcellular organ- elles [e.g., mitochondria (M) and lipid bodies (L)] are closely asso- ciated with these wall ingrowths. FIG. 27 Diagram of the micropylar end of an embryo sac from a soy- bean ovule showing the three cells of the egg apparatus [egg cell (E) and two synergids (S)] and numerous wall ingrowths (WI) extending along the lateral walls of the central cell (CC). Flower of node I Bract Peduncle of I 'S FI 28 ogtdnlscino/ oba vl.Afriie g E FIG. 28.b Longidnl section of latobea ovue fertlzed gE ,ih visiblethe microcared ofithe2mry sac. Fsewarch pck-o\h etse (P) remuan inrtevlrenta ieedo central cell ofteeby a Cmare cetto gue 5.) el o'h g pprts igr 7 toughrtileatioii. (:ilitIl 5' ,ll Tlti15 \vITS igof tlls ha notidl~' been detI~( ermnsetion ofrcel they ae beenrx~ ss o at ielxe crease short distance tr-ansfer of nutrients. P1 ior- to ferltiliza- tion, stai-ch b~egins5 to dlisapp1ear fr~om the central cell. l~x tile timle the fertilized egg (Z\ gote) has foimd ilielmaux of, the stai eh packets hav e dIisappeared, figure 28. Diii-ng the pr-oeinbir o stage 4 to 16 cells), starch complotei disappears aind enidosper-ili nuclei are ev ident ill the Central cell. figure- 29. \lost of the embry o sacs inl oxvules fr~om albscised flowercis contain procnmhrx os sirr-otintlet by fr~ec-nulcleai endospermIl (a mi1tritix e tissue), illustrating that hoth pollination and fe(r- tilizaltioi) had occurred. The presence of proemlbrx os inl (I iles of ahscised flox'.ers idicates thact ab sci ss ion) is not dute to i natdequ t ate po011liat ionIi lack d x i alle plllen, or failInre of fer t flizat i ii. TIhe larg~e ac- cii liii Lat loll of star-ch present inl ahscised flowvers and their T ABh~ 54. NI kSill ITS OFi'i SIED , iH RACEMESi ANT) Pill P'ol) ANT) AS I ITS(.FE Si I I) I l ith FtiiSNT R AT Sit, AN)D PI) oiI Fio T~i)-(;l \ BRA(;(; SIOITI-AN P1, SNiS Lt I-i BEiT SIFT (IToijfOTTT SIISA 0fl )11 SIf s 1()-:3 \1 BA P SOi IUION 'I~~ ~ I (('ITt TId No11 1.33 16.17 Cr ol(oP pa pd Pvr Pei (.\Io Gols Gl ams 2. 66 0.21 0.29 2.03 2.29 .21 ox iles and emllryo( sacs stigge'sts tllat neither is a lack of' as- Silidiates tii fixed cari-toii ( luttiients ') a mnajor- cause o' ab- sc ision. Ifloxx t'x ( ab~scissioni Couli d he the resiilt of sollme (eents that lead to a Cessatiton of, elrx 0 andI eldosperiii (IC x clopillelit. (;rox ~th regtulato~rs haxve ])cell xxvidly imp~licatedl inl the Conl- trol III alscissioii lof flox'.ers ani xyoutng frulits of m1ans different species tof plants. A cx tokinin, 6 (Bxlinnprn AP), is a case inl poiint. BAP treatimeints \ver-e appliedl oidyl to terminal r-acenles rather than xx htle plants to determine xx hethier ab- scissio)In itlix idllal ract'iil(s coutldI he affected. Experi- meints xx'ere perf'ormed oxver fotir diflerent gr-oxx'ing seasons o)0 terminal racemnes of' field grlxx n Br-agg, Braxton, Lee, anld 'Iracx l so~x blean p~lants. D~epending o10 the stage of' repro- dutctive dexvelopimeiit, the conicenltratitoi of HAP used, and thle (exteint of 'i'.ater str-ess at the time tof treatmnit. BA~P canl sig- nificantlx increase pod set onl terminal r-acemles. Inl one ex- per-iiiient, teiminal raceimes of' Bragg so\X beain plants xxer spr-ax ed to xx etliess xxithl It)-:3 MI HAP ex erx\' other dlax from 112 (one floxxer at exverx node onl treated plants) tintil 11.5 )illitlptlt f ,ill). This BA~P treatiment re'sultedI inl a 2.54011( increase iii the total Ilii ill lei 1)1,i latutre 1podsl pre sent oni ten iiii tal i acem cs. color p~late no. :32. Mlore than a I 2-fold increase in seeds xx as obserx ed f'or the BA P x erstis the conitroll treatment, table 54. \Vilel the uiiliher of, seeds per- -ceillle aind ax eragl' seed wxeight per raemie ,vere sublstantially inicreased. the ntiinh1er of' seeds per po11( remained tinaffected byx thec treatm(ents. Ib' eoxer, the axverage seedl xxeight per podl xxas redutcedl 27 p~ercent byx the BAP treatmnent xx heni ctmIpared tto thle contrl treatment. This redtiction inl seed xxeight x-was miore than ofl set byx the 12 1(11( increase inl ntumber (If'seets. Although BA P can sigitifilcaitlx decrecase floxx er and( po0d( shedding fr-oml teriiinal racemles of, field gr-ox'. soxheanls. it has a dlelete'riouts eflect till lt'af expanlsion. Young leaxves that artc expoIsedl to the sprax fail to expand normallx and( appear- xxvi iikled. Othecr changes ill shoot mo~rphology also haxe heenl oblserxved. Conisoeuetly the priomotixve eflect thlat HAP has oHI flower ad io reteintlion is priall ofic b thle negatixve efletcts it has oil shoot tip) dev elopm~ient including leaf expanl sion . This (lailage to the leax es becotmes a inai'or p)robllem x\,]henl entire plants alre treatetd xxith BA~P iii an attempt tto inl- cr ease toltal pod and seetd x 'ldl. Attan intent ofl anv sutistantial inicrease inl seed xieltls of soxybeans ill the fulture xx ill depend inl lar-ge measuire on suic- cess in) iundeirstandting the phy sioltogical and anatomical pro- cesses lInn itintg x icld. See color plate numbers 29, 30, 31, and 32. FIG. 29. Longitudinal section of a soybean ovule containing a proem- bryo (PE). Starch packets are completely absent in the central cell. An endosperm nucleus (arrow) is visible next to the proembryo. Alabama s Agricuitural Experiment Station System AUBURN UNIVERSITY With an agricul- tural research unit in even major soil area, Auburn University serves the needs o)f field crop, livestock, forestry, and hor- ticultural producers in each region in Alabant. Every citi- zen ()f the State has a stake in this research program, since any advantage from newV and more econom- ical xways (of produc- ing and handling farm products di- rectly benefits the consuming public. @ Main Agricultural Experiment Station, Auburn. -z E. V. Smith Research Center, Shorter. 1. Tennessee Valley Substation, Belle Mina. 2. Sand Mountain Substation, Crossville. 3. North Alabama Horticulture Substation, Cullman. 4. Upper Coastal Plain Substation, Winfield. 5. Forestry Unit, Fayette County. 6. Chilton Area Horticulture Substation, Clanton. 7. Forestry Unit, Coosa County. 8. Piedmont Substation, Camp Hill. 9. Plant Breeding Unit, Tallassee. 10. Forestry Unit, Autauga County. 11. Prattville Experiment Field, Prattville. 12. Black Belt Substation, Marion Junction. 13. The Turnipseed-lkenberry Place, Union Springs. 14. Lower Coastal Plain Substation, Camden. 15. Forestry Unit, Barbour County. 16. Monroeville Experiment Field, Monroeville. 17. Wiregrass Substation, Headland. 18. Brewton Experiment Field, Brewton. 19. Solon Dixon Forestry Education Center, Covington and Escambia counties. 20. Ornamental Horticulture Substation, Spring Hill. 21. Gulf Coast Substation, Fairhope. b i .~.kFi I, (to) " 1