THE OLD ROTATION—1996-1999

1

The

Old Rotation
1996-1999

Agrononmy and Soils Departmental Series No. 228 Alabama Agricultural Experiment Station Luther Waters, Director Auburn University Auburn, Alabama September 2000

2

ALABAMA AGRICULTURAL EXPERIMENT STATION

Contents
page

ACKNOWLEDGMENTS OBJECTIVES ........................................................................................................................................... 4 METHODS ............................................................................................................................................. 4 1996-99 RESULTS .................................................................................................................................. 5 A New Era Begins ........................................................................................................................................ 5 Crop Yields ................................................................................................................................................... 6 Soil Quality ................................................................................................................................................... 7 CONCLUSIONS ...................................................................................................................................... 7

This research report is a periodic update on the Old Rotation. Crop yields and trends on the Old Rotation seem to reflect Alabama cotton producers’ experiences each year. The Old Rotation is an index of long-term sustainability of cotton production in Alabama.

THE OLD ROTATION—1996-1999 ACKNOWLEDGMENTS

3

The Old Rotation exists as the world’s oldest, continuous cotton plots, and the third oldest continuous field crop experiment on the same site in the United States because of the dedication and cooperation of many individual researchers and administrators at Auburn University. The support of the Alabama Agricultural Experiment Station, Dr. Luther Waters, Director, has been the main reason it has continued to exist. The help of Mr. Dennis Delaney, Extension Associate, the staff at E.V. Smith Research Center, Dr. Jim Bannon, Director, and AAES’s Research Operations on the AU campus has been necessary to plant, maintain, and harvest the plots. Most of the day-to-day work and maintenance is conducted by Mr. Charlie France, Research Technician, who has worked on these plots for more than 40 years. Many students have collected data from the plots that add to our knowledge of soil quality changes. Recently, the USDA Soil Dynamic Laboratory staff (Dr. Wayne Reeves and Mr. Jeffrey Walker) and their equipment have played a major role in converting the Old Rotation to conservation tillage. The Old Rotation and other long-term experiments in Alabama are partially supported through grower checkoff funds through the Alabama Wheat and Feed Grain Committee and the Alabama Cotton Commission.

4

ALABAMA AGRICULTURAL EXPERIMENT STATION

The Old Rotation—1996-1999

Charles C. Mitchell, Wayne Reeves, and Michael D. Hubbs

The Old Rotation experiment on the campus of Auburn University is the oldest, continuous cotton experiment in the world. The test was started in 1896 by Professor J.F. Duggar to test and demonstrate his theories that sustainable cotton production was possible on Alabama soils if growers would use crop rotation and include winter legumes (clovers and/or vetch) to protect the soil from winter erosion and provide nitrogen (N) for the summer crop. The Old Rotation was placed on the National Register of Historical Places in 1988. Since the centennial cropping year of the Old Rotation (1995), major technological modifications have been implemented in managing this experiment. These include switching to genetically modified crops, almost complete elimination of insecticide use, drastically reducing herbicide use, and switching to conservation tillage instead of conventional moldboard plowing and cultivation. This report will highlight yields and observations made during these transition years.

TABLE 1. CURRENT CROPPING SYSTEMS USED ON OLD ROTATION
Continuous cotton No legume/no fertilizer N (plots 1 & 6) Winter legumes (crimson clover and/or vetch) (plots 2, 3, & 8) 120 pounds N per acre (as ammonium nitrate) (plot 13) Cotton-corn rotation Winter legumes (plots 4 & 7) Winter legumes + 120 pounds N per acre (plots 5 & 9) Three-year rotation Cotton (winter legumes) (plots same as continuous cotton) Corn (small grain for grain) (plots same as cotton-corn rotation) Soybeans (plots 10, 11, & 12)

OBJECTIVES
The objectives today are very similar to Professor Duggar’s original objective: to determine the effect of crop rotations and winter legumes on sustainable production of cotton in the southern United States. In addition, phosphorus (P) and potassium (K) fertilizer treatments initiated in 1925 allowed early researchers to evaluate the timing of P and K applications to cotton rotation systems. Today, the site is also used as a field laboratory for researchers, students, and visitors interested in long-term, sustainable crop production systems in the southern United States. Since conversion to conservation tillage in 1997, soil quality changes are being monitored.

METHODS
The site is at the junction of the Piedmont Plateau and Gulf Coastal Plain soil physiographic regions. The soil is identified as a Pacolet sandy loam (clayey, kaolinitic, thermic Typic Hapludults). There are 13 plots on one acre of land. Each plot is 136 feet long by 21.5 feet wide with a three-foot alley between each plot. Originally, each plot was a separate treat-

ment, but today the following cropping systems are used: continuous cotton, cotton-corn rotation, and three-year rotation (Table 1). Of minor interest today is the timing of fertilizer P and K. Originally, the soil was low in both P and K and the winter legume produced more biomass (and more N) with direct P and K applications. This provided more N for the following cotton crop, resulting in higher cotton yields. Today, all soils test high in P and K, and there is no longer a differential response to the time of fertilizer application, although the treatments continue. They are as follows: (1) P & K applied prior to planting cotton (plot 8) (2) P & K applied to the winter legume in fall (plot 2) (3) P & K split, i.e. 1/2 to cotton and 1/2 to legume (plot 3) (4) P & K split between cotton and winter legumes in a cottoncorn rotation (plots 4,5,7, and 9) All plots have received a total application of 80 pounds P2O5 and 60 pounds K2O per acre per year since 1956. Fertilizer N or legume N is the only fertility variable. Lime is applied to each plot as determined by a soil test to maintain soil pH between 5.8 and 6.5. Soil samples are taken in even-numbered years. Crop varieties planted have always been those common varieties recommended and used by growers. However, since 1997, varieties planted and dates harvested have reflected new, genetically modified crops that fit well with conservation till-

Mitchell is Professor in Agronomy and Soils, Reeves is Soil Scientist with the USDA Soil Dynamics Laboratory, and Hubbs is with the NRCS Soil Quality Institute.

THE OLD ROTATION—1996-1999
age practices (Table 2). In 1999, cotton and soybean were both Roundup Ready® varieties, and corn was a Liberty Link® variety, allowing weed control using only two herbicides. All plots were managed with conventional tillage (moldboard plow, flatbed disk or chisel, field cultivate or harrow, and cultivation for weed control) from 1896 through 1996. In 1997, all plots were switched to conservation tillage (spring paratill under the row and plant using no till planter; no mechanical cultivation). A goal was to establish reseeding crimson clover in those plots planted to winter legumes. Table 3 presents the management sequence which is now used.

5
TABLE 2. CROPPING INFORMATION
ON

OLD ROTATION, 1996-99
Date planted 9/28/95 5/2/96 5/2/96 9/25/95 5/6/96 10/31/96 4/23/97 5/17/97 10/16/96 5/6/96 11/19/97 4/6/98 5/15/98 11/19/97 6/10/98 10/30/98 4/20/99 5/21/99 10/30/98 6/10/99 Date harvested 4/12/96 9/25/96 10/8/96 Not harvested 11/5/96 3/31/97 9/16/97 10/21/97 5/22/97 11/19/97 No yield taken 8/26/98 10/6/98 6/2/98 10/30/98 4/10/99 8/10/99 10/5/99 5/20/99 10/27/99

Year 1996

Crop Crimson clover Corn Cotton Rye Soybean(36”rows) after rye Crimson clover Corn (36” rows) Cotton (36” rows) Wheat Soybean drilled after wheat Crimson clover Corn (30” rows) Cotton (30” rows) Rye Soybean drilled after rye Crimson clover Corn (30” rows) Cotton (30” rows) Wheat Soybean drilled after wheat

Cultivar AU Robin Pioneer 3167 DPL 35B Wrens Abruzzi Stonewall AU Robin Pioneer 3167 DPL 35B Wakefield Hartz H-7550’(RR) AU Robin Pioneer 34A55 (LL) Paymaster 1220BG/RR Wrens Abruzzi Asgrow 6101 (RR) AU Robin Pioneer34A55 (LL) Paymaster 1220BG/RR Pioneer 2684 Asgrow 6101 (RR)

1997

1998

1999

1996-99 RESULTS
A New Era Begins Cotton yields in 1995 were the lowest recorded since a disaster year in 1946. Average yield on the five best plots was only 350 pounds lint per acre, compared to a 10-year average of 960 pounds lint per acre. Yields on the Old Rotation reflect general conditions throughout the rest of the state. Statewide average for 1995 was 409 pounds lint per acre, also a longterm record low. On the Old Rotation, low yields were a result of (1) replanting on May 10 after heavy rains damaged the first planting on April 21 and (2) uncontrollable insect pressure (bollworms and armyworms) late in the season. The near statewide disaster in 1995 prompted Alabama farmers to quickly adopt the new Bollgard® genetically modified varieties commercially available for the first time in 1996. With the boll weevil controlled by the statewide Boll Weevil Eradication Program and genetically modified varieties containing the Bt gene for bollworm resistance, 1996 opened a new era for Alabama cotton producers and for the Old Rotation. Since then, only genetically modified cotton with bollworm resistance has been planted on the Old Rotation. Interestingly, no broadcast application of insecticides has been applied to the Old Rotation since then. This contrasts with more than eight applications made annually prior to this new era. Roundup® resistant varieties were introduced in 1997 (soybean) and 1998 (cotton). In 1999, only two herbicides were used: Roundup® on cotton and soybean and Liberty® on corn, and no insecticides have been used since the 1995 season. Genetically modified crops and conservation tillage introduced a new millenium of crop production unlike anything imagined by Professor Duggar’s generation in the 1890s.

TABLE 3. CURRENT MANAGEMENT SEQUENCE USED ON OLD ROTATION
Time of year Early April Early to late April Managment activity Clip winter legumes for dry matter yield Paratill (subsoil) cotton and corn plots Broadcast appropriate fertilizers and/ or lime Strip plant corn into clover using row cleaners Strip plant cotton into mature clover us ing row cleaners and no-till planter Use Roundup® on cotton or Liberty® on corn to control emerged weeds Harvest small grain for grain Drill soybean into grain residue Apply Roundup® or Liberty® as appropriate Scout cotton and apply appropriate insecticides if necessary Harvest corn for grain Paratill and plant small grain following corn Harvest cotton Overseed with winter legumes if necessary (plots should have reseeded, and clover seedlings will be emerging at this time) Apply fall fertilizer to appropriate plots Chop cotton stalks when winter legumes are established Harvest soybean Enjoy football, hunting, and basketball Write reports Topdress small grain on plot 10, 11, or 12 with 60 lb. N/acre

Late April to early May

Late May/early June

Summer Late August October-November Early October

Late October

November-March February

6
Crop Yields Year-to-year cotton yields continue to be extremely erratic due to uncontrollable environmental factors, mainly mois-

ALABAMA AGRICULTURAL EXPERIMENT STATION

ture. As an example, annual seed cotton yields since 1896 are plotted in Figure 1. Interesting, rarely does one see two extremely bad years in a row or two extremely good years in a row. In past decades, there seemed to be a slight advanFigure 1. Yields from plot 3 (continuous cotton with winter legumes) are an example of the yield trends over the 100 years of the Old Rotation. Year-to-year yields are extremely erratic for nontage to rotating cotton with irrigated cotton. However, rarely does an exceptionally high yielding year follow another high yielding corn or other crops. During year. The same is true for low yielding years. While 1994 was one of the highest yielding years on the 1990s, this statistical record, 1995 was one of the worst. The five-year running average gives an indication of yield trends. advantage disappeared (Table 4). The highest numerical average (more than two bales per acre) was produced with a cotton-corn rotation using winter legumes plus N fertilizer (plots 5 and 9). Winter legumes (crimson clover) versus fertilizer N resulted in no differences in 10-year average cotton yields. Except for poor cotton yields in 1995 and in 1999 (hot and dry August and September), the decade of the 1990s has produced the highest cotton yields in the 104-year history of the Old Rotation (Table 5). In 1999, a record corn grain yield of 236 bushels per acre was produced on the three-year TABLE 4. CROP YIELDS ON OLD ROTATION, 1996-1999 rotation with only legume N. This was attributed to Plot Treatment 1996 1997 1998 1999 10-yr mean paratilling and residue left Cotton lint yields (pounds/acre) 1 on the soil surface, less wa1 No N 430 360 450 320 390 b ter runoff and more infiltra2 + legume 1100 1130 890 710 900 a tion, narrow rows (30-inch 3 + legume 1100 860 890 560 940 a rows), a high plant popula4&7 Cotton-corn+legume 1090 1160 870 660 970 a tion, and very high rainfall 5&9 Cotton-corn+legume+120 N 1250 1090 1010 910 1020 a 6 No N 650 250 330 320 410 b in June during silking and 8 + legume 1130 1190 860 740 950 a pollination. Paratilling and 10,11,12 3-yr rotation 1090 920 980 700 910 a a cool, dry spring were re13 +120 N 900 1250 880 840 830 a sponsible for the record Corn grain yields (bushels/acre) high wheat grain yield (79 4&7 Cotton-corn + legume 108 123 50 182 95 a bushels per acre) in 1999. 5&9 Cotton-corn + legume + 120 N 129 148 93 207 120 a The record soybean yield in 10,11,12 3-yr rotation 97 82 89 236 113 a 1996 (67 bushels per acre) Small grain (wheat and rye) yields (bushels/acre) was attributed to early 10,11,12 3-yr rotation 0 (rye) 49 (wheat) 46 (rye) 79 (wheat) 36±23 planted, full-season beans Soybean yields (bushels/acre) planted into rye stubble and 10,11,12 3-yr rotation 67 33 30 34 35±19 very favorable moisture Winter legume dry matter yields (pounds/acre) during pod fill. Due to a late All plots Average of all plots 1040 3600 No data 5540 3550 freeze in 1996, the rye crop ±220 ±110 ±990 ±1080 was not harvested for grain, 1 Cotton lint yields are calculated from seed cotton yields by assuming 38% lint. Mean values which allowed for early followed by the same letter are not statistically different at P<0.10. planting of soybean. Nor-

THE OLD ROTATION—1996-1999
mally, soybean is planted after grain harvest in late May or early June. Soil Quality Interest in sustainable agricultural systems and soil quality prompted a new look at these factors in the Old Rotation. Surprisingly, little effort has been directed over the past 100 years toward documenting the effects of the cropping systems on soil organic matter and its effect on yields. Soil organic matter was first measured on plots of the Old Rotation in 1988. Since then, measurements have been repeated. As expected, the long-term treatments have had a dramatic effect on the buildup or depletion of soil organic matter. This is reflected in the yields. Yields in 1988, 1992, and 1994 were closely correlated with soil organic matter measurements (Figure 2). In 1997, just prior to conversion to conservation tillage, additional soil physical and chemical measurements were taken to serve as a benchmark for future comparisons (Table 6). As crop rotation increased and more biomass was returned to the soil in the form of crop residue, we saw increases in soil water holding capacity, hydraulic conductivity (Ksat), respiration, total carbon (C), total N, cation exchange capacity (CEC), and water-stable aggregates. All these indicate improvements in soil quality.

7
TABLE 5. RECORD YIELDS
Crop Cotton Rank 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3
ON THE

OLD ROTATION
Plot 3 9 13 11 5 10 12 11 10 11 12 10 12 11 11 12 10 10 11 3 11 Yield1 1490 1270 1250 236 148 148 79 49 48 109 97 87 55 48 40 67 61 55 7250 6410 5790

Year 1994 1993 1997 1999 1997 1991 1999 1997 1992 1958 1937 1956 1981 1988 1979 1996 1992 1983 1981 1999 1993

Corn

Wheat (1961-present)

Oat (before1960)

Rye (1978-present)

Soybean (1957-present)

Winter legume

CONCLUSIONS
After 104 cropping years, the Old Rotation continues to document the long-term effects of crop rotation and winter legumes on sustainable cotton production in the Deep South.
Figure 2. Long-term treatments have resulted in significant differences in soil organic carbon (organic C x 1.7 = soil organic matter). These differences are reflected in soil structure, water holding capacity of the plow layer, and increased soil buffering capacity, e.g. increased cation exchange capacity, total mineralizable N, etc. Soil organic C was measured in 1988, 1992, and 1994 and regressed against plot yield relative to plot 3 (continuous cotton and winter legumes). There is a definite trend toward higher yields with increased soil organic matter.
1

Yields are measured as follows: cotton = pounds of lint per acre, corn = bushels per acre, wheat = bushels per acre, soybean = bushels per acre, winter legume = pounds dry matter per acre.

140

120

Yield relative to plot 3 (%)

100

80 1988 60 1989 1990 40 1991 1992 20 1993 1994 0 0 2 4 6 8 10 12 14 16 Soil organic C (g/kg)

8
Long-term yields suggest that winter legumes are just as effective as fertilizer N in producing optimum cotton yields. Yields are also highly correlated with soil organic matter that reflects the long-term treatments. In the past, crop rotation benefits have had a small effect on cotton yields, considering yield

ALABAMA AGRICULTURAL EXPERIMENT STATION
levels and crop value. These benefits should be enhanced under conservation tillage. Soil quality differences, e.g., aggregation and soil tilth, due to rotations and cover cropping are dramatic and are likely to increase under conservation tillage.

TABLE 6. SELECTED SOIL PHYSICAL AND CHEMICAL MEASUREMENTS MADE ON TREATMENTS FROM THE OLD ROTATION IN 1997 BEFORE CONVERSION TO CONSERVATION TILLAGE
Treatments Continuous cotton No N/no legumes + winter legumes +120 lb. N/acre Two-yr rotation + winter legumes + legumes/+120lb N/acre Three-yr rotation Treatments Bulk density g/cm3 1.66 1.66 1.73 1.68 1.62 1.65 Total C % Continuous cotton No N/no legumes + winter legumes +120 lb. N/acre Two-yr rotation + winter legumes +legumes/+120lb N/acre Three-yr rotation 0.50 d 0.84 c 0.87 c 0.85 c 1.09 b 1.27a Soil water % 7.69 c 7.47 b 9.40 bc 10.11 ab 11.67 a 11.47 a Total N % 0.02 c 0.04 ab 0.04 abc 0.05 ab 0.06 a 0.05ab Ksat inches/min 0.37 0.43 0.04 0.57 0.33 1.22 C.E.C. cmolc/kg 3.1 c 4.3 b 5.6 a 4.6 b 5.4 a 5.5 a Soil respiration lb. C/a/day 22 b 44 ab 36 ab 60 a 45 ab 60 a Water stable aggregates % 49.8 b 52.2 b 34.7 c 53.2 b 48.9 b 64.1a

Values followed by the same letter are not statistically different at P<0.10