BULLETIN No. 268JUE14 JUNE 1949 PHOSPHORUS STUDIES with VEGETABLE CROPS on DIFFERENT SOILS FORY TE ADVANCEMENT t u AND ARTS~ c AGRICULTURAL of the ALABAMA M. J. FUNCHESS, Director EXPERIMENT POLYTECHNIC STATION INSTITUTE AUBURN, ALABAMA CONTENTS PAGE REVIEW OF LITERATURE....................... .... 3 3 LITERATURE RELATING TO PHOSPHORUS FOR VEGETABLE CROPS...................-............... .. LITERATURE RELATING TO SOIL PHOSPHORUS.............4 LITERATURE DEALING WITH PRINCIPLES UNDERLYING PHOSPHORUS ABSORPTION, RETENTION, AND AVAILABILITY .................... GENERAL METHODS AND PROCEDURES... 5 ... 6 METHODS USED IN PREPARING AND FILLING FIELD BINS WITH SOIL.......................................6 METHODS OF HANDLING CROPS ...... .......... 6 RATES AND METHODS OF APPLYING FERTILIZERS.........7 RESIDUAL PHOSPHORUS YIELD RECORDS............ STUDIES.............7 .......... 7 LABORATORY PROCEDURES:............_7 .................... METHODS OF STATISTICAL ANALYSIS.. PRESENTATION OF DATA....... 8 8 CHARACTERISTICS OF THE .. SOILS USE .............. 8 RELATIVE RESPONSE OFVEGETABLE CROPS TO PHOSPHORUS, NITROGEN, AND POTASH ............... 11 STUDIES DEALING PRIMARILY WITH PHOSPHORUS REQUIREMENTS AND ABSORPTION.......12 CROP RESPONSES TO PHOSPHORUS APPLICATIONS. EFFECTS OF ADDED MATERIALS ON PHOSPHORUS AVAILABILITY.... - 21 .. 30 32 ..... . STUDIES OF RESIDUAL PHOSPHORUS.......... CHANGES IN SOIL PHOSPHORUS DURING THE INVESTIGATIONS............................................................. DISCUSSION 39 44 . ................ .......................................... ......... ... DIFFERENCES IN PHOSPHORUS ABSORPTION BY PLANTS...44 DIFFERENCES IN PHOSPHORUS ABSORPTION AS AFFECTED BY SOIL PROPERTIES.................................. PHOSPHORUS UTILIZATION EFFICIENCY AS AFFECTED BY RATES OF PHOSPHORUS APPLICATION ON DIFFERENT SOILS ......................................... YIELDS OF DIFFERENT RELATED TO OTHER AVAILABILITY VEGETABLE FACTORS CROPS AS 46 47 48 49 50 OF RESIDUAL PHOSPHORUS .......................... . SUMMARY APPENDIX ............................................................................... CITED. LITERATURE ......3 5 ........... ........ .................................. ............... 57 First Printing, 3M PHOSPHORUS STUDIES with VEGETABLE CROPS on DIFFERENT SOILS L.M. WARE, Horticulturist W. A. JOHNSON, Laboratory Technician of phosphorus studies reported in this bulletin are a part of a larger study dealing with the requirements of important vegetable crops for nitrogen, phosphorus, and potash on representative soils of the State. In its broader aspects, the purpose of the experiment was to obtain data by which vegetables might be classified according to their requirements for and responses to these three major elements. An earlier but brief report has been made on the needs and response of vegetable crops to nitrogen (45). Experiments were designed to permit classification of important vegetable crops according to their requirements and feeding capacity for and response to phosphorus on soils differing in physical and chemical properties. REVIEW OF LITERATURE While the volume of literature on the general subject of phosphorus is large, the literature on the more restricted subject of phosphorus as applied to vegetable crops is less extensive. Review of literature does not reveal any investigation directed primarily at a classification of vegetable crops according to their requirements and feeding capacity for, response to, and general behavior toward phosphorus. LITERATURE RELATING TO PHOSPHORUS FOR VEGETABLE CROPS RESULTS Much work has been done in the several states and by the United States Department of Agriculture on fertilizers for vegetable crops. Most of the investigations were concerned with a limited number of crops, usually grown on one soil type. Results of these studies could not be used to classify vegetables according to their phosphorus requirements and needs. Where systematic 4 ALABAMA AGRICULTURAL EXPERIMENT STATION studies of phosphorus were made, only a limited number of crops were used. Lloyd and Strubinger (22) working with 25 vegetable crops found only a few crops that gave much response to phosphorus. Mack (23) in his studies on applications of phosphorus, nitrogen, potash, and organic materials obtained greatest response from phosphorus applied to cabbage, tomatoes, and potatoes. Cooper and Watts (10) in a study of fertilizer needs of five crops reported that phosphorus gave largest increases on one soil and increases on a second soil equal to nitrogen. Zimmerley (46) at the Virginia Truck Crop Experiment Station made rather detailed studies of the effect of artificially regulated soil acidity on plant growth and composition of vegetable crops when fertilized with medium and high rates of phosphorus. Greatest response resulted from use of the larger amount of phosphorus with lettuce and beans at all soil reactions and with beets and carrots at reaction below 5.4 pH. Comin and Bushnell (9) in Ohio found that phosphorus gave increases in yields of cabbage, cucumbers, and tomatoes, either when applied alone or used as a supplement to other fertilizers. Parker (28), working with tomatoes at the Virginia Truck Experiment Station, found that 40 and 80 pounds of PsOs per acre gave significant increases in yields while 100 pounds gave a slight increase in yield over that produced with 80 pounds of PsOs. Zimmerley and Brown (47) found that potatoes did not give an increase in yield with more than 96 pounds of P205. LITERATURE RELATING TO SOIL PHOSPHORUS It has been pointed out by many investigators that phosphorus constitutes one of the most important elements in soil fertility. Some investigators have stated that conservation of phosphates is the most crucial, most important, and most far-reaching with respect to the Nation's future of any of the conservation problems. The work of Truog (40, 41), Gile (16), Ford (15), Spurway (88, 89), Scarseth and Tidmore (35, 36, 37), Davis (11, 12), and others has shown the nature of phosphorus retention in soil and the chemical basis for differences in availability of phosphorus on different soils. Ford (15) and Plummer (32) found that lime reduces the rate of phosphorus fixation into relatively insoluble phosphates, and that the application of lime increased the effi- PHOSPHORUS STUDIES with VEGETABLE CROPS 5 ciency of phosphatic fertilizers. Ensminger and Cope (13) found that there was some movement of phosphorus into the subsoil on sodium nitrate plots that had been limed. Gile (16) reported that the efficiency of superphosphate had a tendency to be highest at a pH 4.5 to 5.0 and lowest in the neighborhood of neutrality with soils that had a depressing effect on phosphorus. Scarseth and Tidmore (35) found that the efficiency of phosphorus decreased with the time of contact with the soil. They (36) also found that the phosphorus-fixing capacity of soil colloids varied inversely with the silica-sesquioxide ratio of the colloid. A number of workers have shown that the application of phosphorus to the soil builds up a reserve of this element, which is available to crops in later years. This has been shown by the work of Anderson and others (3) with tobacco in Connecticut, by Bryant (5) with citrus in Florida, by Hester (20) with tomatoes in Virginia and New Jersey, by Chapman (8) with citrus fruits in California, by Ware, Brown, and Yates (44) with potatoes in Alabama, and by Volk (43) with cotton in Alabama. LITERATURE DEALING WITH PRINCIPLES UNDERLYING PHOSPHORUS ABSORPTION, RETENTION, AND AVAILABILITY Many investigators (25, 34, 35, 36, 37) have shown that phosphorus is retained largely by the clay fraction of the soil, and that the chemical composition and characters of the colloids present determined the amount and nature of fixation and availability of phosphorus. Mattson (24) has offered a basic explanation for fixation of phosphorus and other materials in the soil. According to this explanation, phosphorus combines with base materials in the soil, consisting of iron, aluminum, calcium, magnesium, and to a less extent of sodium and potassium. On the other hand, phosphates will replace or be replaced by humates, silicates, and similar acidoid soil constituents. Several workers (13, 27, 29, 32, 33, 38) have shown that the amount and nature of phosphorus fixation in soil is influenced by acidity of the soil and the proportion of bases, consisting of the iron or aluminum on the one hand or of calcium on the other. They also showed that, as acidity of the soil is reduced by liming, the proportion of calcium in the exchange complex is increased. The result is an increase in amount of calcium phosphates formed. Pierre (31), and Albrecht and Schroeder (1) pointed out the higher ratio of iron and aluminum to silica in the colloids of the 6 ALABAMA AGRICULTURAL EXPERIMENT STATION red and yellow soils of the Southeastern States. This fact is used to explain the relatively low availability of phosphorus in these soils. GENERAL METHODS AND PROCEDURES The investigation included laboratory, greenhouse, and field studies, which were started in 1933. Soil properties were studied and plant analyses were made in the laboratory, and limited experiments were carried on in the greenhouse. The principal studies were conducted in field bins. METHODS USED IN PREPARING AND FILLING FIELD BINS WITH SOIL The soils were selected to represent wide differences as possible in physical and chemical properties, and to represent the several agricultural regions of the State. Norfolk, Eutaw, and Cecil soils were the three used in the more extensive field-bin studies. The Norfolk was a sandy loam soil of the Coastal Plain Region, the Eutaw a heavy clay soil of the Black Belt Region, and the Cecil a sandy clay soil of the Piedmont Region. Less extensive studies were conducted on a Decatur clay soil of the Tennessee Valley Region, a Hartsells sandy loam soil of the Appalachian Region, an Oktibbeha clay soil of the Black Belt Region, and a Chesterfield sandy loam of the Coastal Plain-Piedmont transition. The field bins were small field plots separated by concrete walls. The soils in the bins representing the series and types were selected by soil technicians. The soils were brought in and placed in the concrete bins to a depth of 8 inches on a clay subsoil of the Coastal Plain-Piedmont transition. The soils were equally distributed and composited in each bin throughout each complete series. METHODS OF HANDLING CROPS In the more extensive field bins composed of the Norfolk, Eutaw, and Cecil soils, there were five sets of bins. The number permitted five vegetable crops each season (spring, summer, and fall) to be grown in succession each year on each soil. Each crop was grown for a period of 2 to 4 years. The crops were rotated from one set of bins to another. PHOSPHORUS STUDIES with VEGETABLE CROPS 7 RATES AND METHODS OF APPLYING FERTILIZERS Rates of phosphorus applications on the Norfolk sandy loam soil consisted of 0, 40, 80, 120, and 160 pounds per acre per year of P205, whereas the rates used on the Cecil and Eutaw soils were double those applied to the Norfolk soil. One-third of the annual application was added to each of the three successive crops grown. During the first year, two-thirds of an annual application was added during the summer prior to the first crop grown in the fall and one-third added at planting time. The fertilizer was drilled in the rows, and the position of the rows remained approximately the same throughout the experiment. Lime was added as one treatment in conjunction with the high rate of phosphorus. Phosphorus application rates used on the Decatur soil were the same as those on the Cecil and Eutaw soils, whereas the rates used on the Hartsells soil were the same as those used on the Norfolk sandy loam. Nitrogen and potash at the rate of 90 pounds of N and 45 pounds of KuO per acre, were applied to each crop for each rate of phosphorus applied. RESIDUAL PHOSPHORUS STUDIES At the end of 9 years, four sets of bins for each of the soils were used in a phosphorus residual study. One-half of the bins received a phosphorus-maintenance application and one-half received no further application of phosphorus. Rates used in the phosphorus-maintenance application during the period of the residual study consisted of one-half of the rates used in the preceding 9-year period. The residual studies extended over a 5-year period. YIELD RECORDS Crop yields were taken by harvest periods. Both tops and roots of those crops having enlarged roots or tubers were weighed. In the case of such crops as beans, the weights of both pods and vines were taken. However, the fibrous roots were not weighed. LABORATORY PROCEDURES Laboratory studies consisted of physical and chemical determinations of soil properties, of dilute acid-soluble phosphorus in the soil, and of total phosphorus in plant tissue. 8 ALABAMA AGRICULTURAL EXPERIMENT STATION Soil texture was studied by the Bouyoucos hydrometer method (4). Some of the data on chemical properties of the soils were supplied by the soils laboratory of the Alabama Agricultural Experiment Station and by the laboratory of the Bureau of Plant Industry, Soils, and Agricultural Engineering, United States Department of Agriculture. Phosphorus-fixing properties of the principal soils used were determined in the laboratory by measuring the amount of phosphorus fixed by the three soils over a period of 4 weeks. Samples were taken from the zero phosphorus plots. Different amounts of superphosphate at the rates of P2O5 used in the principal studies were added and mixed with the soil. Soil moisture was then brought up to levels similar to those of field conditions and maintained. The amounts of dilute acid-soluble phosphorus were determined at the end of 1, 7, and 28 days. Dilute acid-soluble phosphorus in the soil was determined by Truog's modified method (42). These determinations were made annually. Total phosphorus in crops was determined by the method of Fiske and Subbarow (14) modified to include organic phosphorus. METHODS OF STATISTICAL ANALYSIS Analysis of variance, least significant difference between phosphorus rates, coefficient of variation of the experiment and an equation for second degree polynomials were computed for each set of yield data. In a number of comparisons Student's paring method was used in obtaining odds for significance. In making the analysis of variance on crop yields, the zero rate of phosphorus in all instances has been omitted. Therefore, values for "F", high enough for significance means that differences exist between the several rates of phosphorus applications above the zero rate. PRESENTATION OF DATA CHARACTERISTICS OF THE SOILS USED The textural and chemical nature of the soils used in the principal studies, and their phosphorus-absorbing capacities and phosphorus-fixing properties are given in Tables 1, 2, and 3. PHYSICAL PROPERTIES. The physical properties of the three PHOSPHORUS STUDIES with VEGETABLE CROPS 9 TABLE 1. PHYSICAL PROPERTIES OF PRINCIPAL SOILS USED Percentages in several textural separates Clay Soil Class Satand Pet. 75.8 25.2 53.2 Silt Pet. 13.8 22.0 15.8 Coarser Finer texture texture Pt. t. 3.6 6.8 3.6 49.2 1.4 29.6 Total Pt. 10.4 52.8 31.0 Colloids Pet. 13.2 58.8 38.8 Norfolk sandy loam Eutaw clay Cecil sandy clay principal soils used in this study, as determined by the hydrometer method of Bouyoucos (4), are given in Table 1. The soils are very different from each other in their physical make-up, as shown by their wide differences in percentages of sand, silt, and colloids. CHEMICAL PROPERTIES OF THE SOILS. The total anion-exchange capacity in terms of P20z, amount of exchangeable phosphorus present, and percentage of phosphorus saturation of the three untreated soils are given in Table 2. The Eutaw soil had a total anion-exchange capacity of about 2.4 times that of the Cecil soil and about 6 times that of the Norfolk soil. While the Eutaw soil had about 50 per cent more exchangeable phosphorus in the untreated soil than the other two soils, this larger amount represented only 4.5 per cent of the anion-exchange capacity of the Eutaw, as compared to 5.8 per cent of the Cecil and 19 per cent of the Norfolk. TABLE 2. PHOSPHORUS-EXCHANGE CAPACITY OF THE SOIL USED 1 Soil class Amount per acre Anion-exchangeExchangeable capacity P 2 06 P2 0 5 Phosphorus saturation Pounds Pounds Per Cent Norfolk sandy loam 3,477 675 19.0 Eutaw clay 21,514 971 4.5 Cecil sandy clay 9,045 522 5.8 1 Data from analysis by Bureau of Plant Industry, Soils, and Agricultural Engineering, cooperating with Alabama Agricultural Experiment Station. PHOSPHORUS FIXATION. A detailed study was made of the apparent fixation of phosphorus by periods for each soil at each rate of phosphorus application. According to the Truog method, there was present as dilute acid-soluble phosphorus 36 pounds per acre of P205 in the Norfolk soil where no phosphorus was added. When 40 pounds of 10 ALABAMA AGRICULTURAL EXPERIMENT STATION P205O was added, theoretically there should have been 76 pounds of readily available phosphorus. The Truog method accounted for only 66 pounds at the end of one day. Apparently 10 pounds, or 25 per cent of the amount added, had been fixed within 24 hours. At the end of 7 days, 16 pounds or 40 per cent apparently had been fixed, and, at the end of 28 days, 22 pounds or 55 per cent. Data on phosphorus fixation are given in Table 3. It is pointed out that at the end of 4 weeks approximately 54 per cent of the phosphorus added to the Norfolk soil at all rates of application of phosphorus had apparently been fixed; about 62 per cent and 70 per cent of that added to the Eutaw and Cecil soils, respectively, had been fixed. In the Cecil soil apparently 48 per cent of the amount added at the 80-pound application rate of P20s had been fixed within one day, as indicated by the Truog method. The other soils did not indicate as high a phosphorusfixing capacity in such a short period. TABLE 3. EFFECTS OF TIME, DIFFERENT SOILS, AND INCREASES IN APPLICATIONS ON FIXATION OF PHOSPHORUS Dilute acid-soluble P 2 0 5 found and apparent fixation by periods P 2 0 5 per acre 1 day after application a)0 Amount applied o a P 2 0 5 per acre 7 days after application P 0 5 per acre 28 days after application 2 per acreob Lb. Lb. e Pfe i wO n oe r,- .4 o O . w Lb. Per cent Lb. 36 60 82 102 128 20 68 90 144 170 Lb. Per cent Lb. 36 54 74 90 110 20 48 74 110 158 24 42 82 96 138 Lb. Per cent Norfolk soil 0 36 40 66 92 80 120 110 160 142 Eutaw soil 30 0 80 82 160 146 240 216 320 270 Cecil soil 0 26 80 68 160 140 240 174 320 266 10 24 46 54 28 44 54 80 25 30 38 34 35 28 16 34 54 68 32 90 116 170 40 43 45 43 40 56 48 53 22 42 66 86 52 106 150 182 62 102 168 206 55 53 55 54 65 66 63 57 78 64 70 64 23 25 28 66 83 42 48 104 65 29 84 146 60 38 122 204 64 25 Fl .Y! 144 C~ ru 'Amount found by Truog method. 2 3Amount "fixed" according to Truog method. Percentage "fixed" of that applied. 38 46 92 80*, PHOSPHORUS STUDIES with VEGETABLE CROPS 11 RELATIVE RESPONSE OF VEGETABLE CROPS TO PHOSPHORUS, NITROGEN, AND POTASH Since the use of commercial fertilizers began in the South, phosphorus, nitrogen, and potash have been the three principle elements supplied in what has been termed a complete fertilizer. Of the total plant food in a complete fertilizer, phosphorus has made up a larger proportion than either of the other two. This has been true also for the country as a whole. Indication of the relative importance of the three elements is shown in the comparison of average relative yields of a large number of crops on several soils in the larger experiment, of which the phosphorus studies were a part. The relative yields for each rate of application of phosphorus, nitrogen, and potash are given in percentage of the yield from the maximum application. The total yield in pounds of all vegetables at each rate in a given series was used as a basis for calculting the percentage of the maximum. The data are presented in Tables 4, 5, and 6. TABLE 4. RESPONSE OF VEGETABLE CROPS ON DIFFERENT SOILS TO INCREASES IN PHOSPHORUS APPLICATIONS Pz0 5 applied per acre per year 1 Norfolk Yield in percentage of maximum rate Eutaw and 2 Cecil soil2 Eutaw soil 2 Norfolk soil Cecil Per cent Per cent Per cent Pounds Pounds 8 31 14 0 0 75 72 80 73 40 92 89 91 160 80 98 98 100 240 120 100 100 100 320 160 One-third of annual application applied to each of 3 crops. 2 Average of 26 different vegetable crops on each soil. RESPONSE OF VEGETABLE CROPS ON DIFFERENT SOILS TO INCREASES IN NITROGEN APPLICATIONS TABLE 5. Nitrogen (N) applied per acre 1 Yield in percentage of the maximum rate Norfolk soil2 Hartsells soil2 Decatur soils Per cent Per cent Per cent Pounds 40 33 27 0 65 62 58 30 81 81 79 60 93 95 93 90 100 100 100 120 1Amount per acre to each of 3 crops per year. .Number of vegetable crops on Norfolk 27, on the Hartsells 11, and on the Decatur 12. 12 TABLE 6. ALABAMA AGRICULTURAL EXPERIMENT STATION RESPONSE OF VEGETABLE CROPS ON DIFFERENT SOILS TO INCREASES IN POTASH APPLICATIONS Potash (K 20) per acre per year' Pounds 0 45 90 135 Yield i'n percentage of the maximum rate Norfolk soil2 Per cent 85 117 94 100 Cecil soil2 Per cent 89 99 103 100 Decatur soil2 Per cent 82 93 95 100 Hartsells soil 2 Per cent 82 92 101 100 'One-third of annual application applied to each of 3 crops. 2 Average of 25 different crops on Norfolk and Cecil, 12 on Decatur, and 11 on Hartsells soil. It is evident from these data that crop yields on soils not previously fertilized, or fertilized at low rates, are more completely limited by the absence of phosphorus, nitrogen, and potash in the order named. The results, however, show that maximum yields of vegetable crops are more quickly reached by relatively small applications of phosphorus than of nitrogen. STUDIES DEALING PRIMARILY WITH PHOSPHORUS REQUIREMENTS AND ABSORPTION PHOSPHORUS REQUIREMENTS OF DIFFERENT VEGETABLE CROPS ON DIFFERENT SOILS. Phosphorus content of the crop from the phosphorus rate producing the highest yield was taken to indicate the phosphorus requirement of that crop for maximum production. In determining the phosphorus content of the crop, the whole plant minus the fibrous roots was analyzed. Where the weights represented fruits, pods, roots, or tubers, in addition to the vines, separate analyses were made of the separate parts and a total weighted average was obtained. The results represent the average of 4 years for most of the crops. In Table 7, the data are expressed as pounds per acre of P 2 05 absorbed. The crops are arranged in order of decreasing magnitude of phosphorus requirement or phosphorus absorption. Significance should not be attached to small differences between crops. The object is to permit grouping into five broad classes -very high, high, medium, low, and very low-phosphorus requirements. In determining the amounts of phosphorus absorbed by crops, the average yield for all record years and the average analysis for 2 to 4 years were used. PHOSPHORUS STUDIES with VEGETABLE CROPS 13 TABLE 7. PHOSPHORUS ARRANGED ABSORBED AT MAXIMUM IN ORDER OF MAGNITUDE PRODUCTION, Vegetables Amount of P 2 0 5 per acre absorbed by different vegetables on different soils Norfolk soil Eutaw soil Cecil soil Average Pounds 39.90 32.67 26.03 21.73 33.44 30.37 23.25 21.08 20.83 25.06 17.26 18.55 13.78 15.74 14.88 12.38 15.20 10.16 10.63 8.24 6.93 7.66 7.15 6.63 4.22 17.75 Pounds 74.66 42.90 44.93 45.53 30.72 26.21 34.82 33.15 29.89 24.53 29.08 22.10 19.96 19.46 17.20 17.71 17.61 15.64 7.19 12.31 10.66 10.46 10.11 6.70 8.19 24.47 Pounds 48.49 38.46 37.23 30.18 31.42 32.22 29.67 24.86 27.74 20.69 23.52 12.83 17.39 14.73 15.18 13.93 11.13 16.89 20.96 13.76 11.65 8.66 6.50 10.17 6.13 20.98 Pounds 54.35 38.01 36.06 32.48 31.86 29.60 29.25 26.36 26.15 23.43 23.29 17.83 17.04 16.64 15.75 14.67 14.65 14.23 12.93 11.44 9.75 8.93 7.92 7.83 6.18 21.07 Turnips Chinese Cabbage Collards Tendergreen Squash Sweetpotatoes Cabbage Okra Carrot Lima Beans Pepper Eggplant N. Z. Spinach Tomato Potato Kale Beans Beets Swiss Chard English Peas Endive Onion Radish Lettuce, spring Lettuce, fall AVERAGE The average P2O contained in the 25 crops on the three soils was 21.07 pounds per acre. The average ranged from 6.18 pounds per acre in fall lettuce to 54.35 pounds in turnips. Therefore, there was a wide difference in the phosphorus absorbed by different vegetables in producing the maximum yield under conditions of the experiment. Turnips was the only crop in the group having a very high phosphorus requirement. Chinese cabbage, collards, tendergreen, squash, sweetpotatoes, and cabbage, were in the group having a high phosphorus requirement. Onions, endive, radish, and lettuce were in the group that had a very low phosphorus requirement. Other vegetables were in intermediate groups. While the phosphorus requirement of the individual vegetables differed to some extent on the three soils, the 14 ALABAMA AGRICULTURAL EXPERIMENT STATION range was not wide. Usually the highest phosphate requirement was found on the soil producing the highest yield. PHOSPHORUS FEEDING CAPACITY OF DIFFERENT VEGETABLE CROPS ON DIFFERENT SOILS. By phosphorus-feeding capacity is meant the ability of a crop to absorb phosphorus from the natural supply in the soil or from phosphorus in less readily available forms. Phosphorus-feeding capacity of a given crop, as measured in this study, is indicated by the amount of phosphorus absorbed by the plant on plots receiving no phosphorus. The amounts of P2O absorbed by the different crops from the zero-phosphorus treatment are given in Table 8. TABLE 8. PHOSPHORUS ABSORBED WITHOUT PHOSPHORUS APPLICATION, ARRANGED IN ORDER OF MAGNITUDE Amount of P 2 0, per acre absorbed by different vegetables on different soils Norfolk soil Eutawr soil Cecil soil If: Average Pounds Pounds Pounds Pounds Sweetpotatoes 20.57 26.21 9.67 18.82 Lima Beans 25.06 15.70 9.40 16.72 Okra 15.84 13.70 4.75 11.43 Potatoes 9.54 5.77 3.22 6.48 Turnips 14.62 2.60 .74 5.99 Carrots 7.05 2.80 7.84 5.90 Beans 7.76 5.13 1.67 4.85 Pepper 5.06 6.92 2.14 4.71 Cabbage 7.47 1.07 2.24 3.59 Eggplant 5.19 3.81 1.43 3.48 Squash 6.14 .26 2.48 2.96 3.63 Tomato, spring 2.60 .30 2.18 Chinese Cabbage 4.19 .67 .97 1.94 English Peas 1.52 2.94 1.26 1.91 Tendergreens .12 4.80 .15 1.69 Radish 2.04 .71 .37 1.04 New Zealand Spinach 2.61 .24 .19 1.01 Onion .76 1.01 .47 .75 1.81 Collards .23 .19 .74 Beets 1.48 .19 .31 .66 Lettuce, fall .44 .71 .39 .51 Lettuce, spring .70 .43 .48 .30 Endive .28 .10 .78 .39 Swiss Chard .48 .34 .23 .35 Kale .41 .20 .08 .23 149.45 TOTAL 42.40 103.63 98.51 AVERAGE 5.98 4.15 1.70 3.84 Vegetables ---, PHOSPHORUS STUDIES with VEGETABLE CROPS 15 It will be noted that there was a very wide difference in the amount of phosphorus absorbed by the different crops and a very wide difference in the amount of phosphorus taken up by the same vegetable on the different soils. This indicates a difference both in the phosphorus-feeding capacity of the different crops and in the availability of the phosphorus in the three soils. It is pointed out that the three soils had received little or no phosphorus for many years before being placed in the field bins. The Cecil was a virgin soil and had never received any commercial phosphorus, while the Eutaw and Norfolk soils were from abandoned fields that had received no phosphorus for many years and then only in small amounts. Two crops, lima beans and sweetpotatoes, are outstanding in their ability to absorb less readily available phosphorus from soil. These crops absorbed an average of about 18 pounds per acre of P205 from the soils. These were in marked contrast to endive, chard, lettuce, kale, or beets, which absorbed an average of about one-half pound each per acre of P205. The two crops in the first group, therefore, were able to absorb approximately 36 times as much phosphorus as the crops in the other group. As to relative phosphorus-feeding capacities of the other vegetables, okra was high; beans, cabbage, carrots, eggplant, peppers, potatoes, squash, tomatoes, and turnips were medium; Chinese cabbage, English peas, collards, onions, radishes, spinach, tendergreen, and beets were low; and lettuce, endive, Swiss chard,and kale were very low. PHOSPHORUS-ABSORPTION EFFICIENCY OF DIFFERENT VEGETABLE CROPS. It is obvious that one crop might have a high-phos- phorus requirement with either a high-, medium-, or low-phosphorus-feeding capacity. Another crop might have a low-phosphorus requirement with either a high-, medium-, or low-feeding capacity, while still another might have a medium-phosphorus requirement with either a low-, medium-, or high-phosphorusfeeding power. To provide a convenient means of expressing relative efficiency of a crop to obtain its phosphorus needs from less available phosphorus of the soil, the term "absorption efficiency" is used and expressed as the absorption-efficiency index. This index is the reciprocal ratio of phosphorus absorbed at the rate giving greatest plant weight to phosphorus absorbed at the zero rate. Use of the reciprocal for index value means that the higher the 16 ALABAMA AGRICULTURAL EXPERIMENT STATION index, the higher the ability of plant to obtain its phosphorus needs without phosphorus applications. The average phosphorus absorption-efficiency indices are given in Table 9 for different vegetable crops on the three soils. The range is from 1.6 to 71.0. Influence of the several factors in determining efficiency index is illustrated by collards and lima beans. The collard had a relatively high phosphorus requirement, an average of 36.06 pounds of P2O per acre on the three soils. The crop had a very lowphosphorus-feeding capacity, only 0.74 pounds of PsO per acre. Its phosphorus absorption efficiency, therefore, was very low. Lima beans had a medium-phosphorus requirement, 23.43 pounds TABLE 9. PHOSPHORUS ABSORPTION EFFICIENCY OF DIFFERENT VEGETABLES Absorption At zero At phosphorus rate efficiency Vegetable giving maximum phosphorus index 2 rate plant growth TL_. __1Pounds Pounds 71 16.72 23.43 Lima Beans 64 29.60 18.82 Sweetpotato 43 26.36 11.43 Okra 15.75 39 6.18 Potato 33 4.85 14.65 Beans, Snap 23 26.15 5.90 Carrot 20 23.29 4.71 Pepper 20 17.83 3.48 Eggplant 13 16.64 2.18 Tomato, spring 13 7.92 1.04 Radish 12 29.25 3.59 Cabbage 11 54.35 5.99 Turnip 9 31.86 2.96 Squash 8 8.93 .75 Onion 8 6.18 .51 Lettuce, fall 6 7.83 .48 Lettuce, spring 17.04 6 1.01 N. Z. Spinach 1.69 32.48 5 Tendergreen 5 38.01 1.94 Chinese Cabbage 5 14.23 .66 Beets 4 9.75 .39 Endive 3 12.93 .35 Swiss Chard 2 .74 36.06 Collards 1.6 .23 14.67 Kale i ~LI~IL-L L L 1 Average of 2 to 4 years on each of 3 soils. SReciprocal ratio P 2 0 5 absorbed at phosphorus rate giving maximum plant growth to P 2 0 5 absorbed at zero-phosphorus rate. Amount P 0 5 per acre absorbed1 2 PHOSPHORUS STUDIES with VEGETABLE CROPS 17 of P20 per acre being absorbed by this crop when it made its greatest plant growth. The phosphorus-feeding capacity, however, of the lima bean was high, 16.72 pounds per acre of P20 5 being absorbed without the addition of a phosphatic fertilizer. This crop, therefore, had a very high absorption-efficiency index. Under conditions of this experiment, sweetpotatoes and lima beans had very high absorption-efficiency index values. Okra, potatoes, and beans had high efficiency indices, while kale and collards had very low absorption-efficiency values. The indices of the other crops were intermediate. Results from studies conducted preliminary to this investigation by Whitten' showed that (1) there were large differences in the amount of phosphorus contained in seed or vegetative parts used for propagation, (2) that this larger quantity of phosphorus gave larger root development in cultures lacking phosphorus, and (3) that these larger root systems absorbed more phosphorus on soils low in phosphorus than plants having small root systems. The data in Table 9 indicate that phosphorus-absorption capacity may be related to such quantitative factors as the rootabsorption area as well as the qualitative factors of root absorption and chemical requirements (lime usually) of the plant as advanced by Truog (40). PHOSPHORUS ABSORPTION BY DIFFERENT VEGETABLES AT DIFRATES OF PHOSPHORUS APPLICATIONS. Amounts of FERENT phosphorus absorbed by each vegetable on each of the three soils when receiving each of the five treatments are given in Appendix Table I. The crops in the table are arranged in order of the magnitude of total phosphorus absorbed on all soils for all phosphorus rates. No important significance is attached to the order other than to indicate the general relationship of each crop in respect to phosphorus absorption. Data reveal large differences in amounts of phosphorus absorbed by the different crops, in amounts absorbed on different soils by the same crops, and in the relative amounts absorbed by different crops when receiving different rates of phosphorus. Considering all rates of phosphorus applications on all three soils, turnips, sweetpotatoes, and lima beans absorbed large 1 Whitten, T. P. The interrelation of phosphorus reserves in seeds, root development, phosphorus absorption, and plant growth. Unpublished thesis. Alabama Polytechnic Institute Library, 1935. 18 ALABAMA AGRICULTURAL EXPERIMENT' STATION quantities of phosphorus. Lettuce, endive, and onions absorbed relatively small quantities. The amounts absorbed by the first group ranged from 8 to 10 times those absorbed by the second group. The amount of phosphorus absorbed by beans and beets might be used to illustrate differences in absorption by different crops on different soils. At the rate of 160 pounds of P 20s per acre, beans absorbed 15.2 pounds per acre of phosphorus on Norfolk soil:. but only 8.4 pounds on Cecil soil. At the same phosphorus application rate, beets absorbed only 10.2 pounds per acre of P205 on the Norfolk soil but 12.9 pounds on the Cecil soil. Phosphorus absorption of sweetpotatoes and lima beans illustrate the differences between crops in the relative amounts absorbed at different rates of application. On Cecil soil with no phosphorus added, absorption by sweetpotatoes was only 9.7 pounds per acre of P20s and by lima beans 9.4 pounds. When 160 pounds per acre of PsOs was applied to Cecil soil, sweetpotatoes absorbed 27.6 pounds, while lima beans absorbed 16.4 pounds. Thus, sweetpotatoes on Cecil soil treated with 160 pounds per acre of P205, absorbed 185 per cent more phosphorus than they did on the same soil but with no phosphorus added. On the other hand, the increased absorption of phosphorus by lima beans under identical conditions was only 74 per cent. PHOSPHORUS UTILIZATION EFFICIENCY OF DIFFERENT VEGETABLE CROPS. The term utilization efficiency is expressed as the percentage of phosphorus absorbed by the plant in relation to the amount applied. In Table 10 are given the relative utilization efficiencies of different vegetable crops when supplied different amounts of phosphorus on different soils. Data in the table reveal that there are (1) wide ranges in the utilization efficiency of different crops on the same soils, (2) wide differences in efficiency of the same crops on different soils, and (3) consistent differences in utilization efficiencies when different amounts of phosphorus are added. It may be observed, for example, that relative utilization efficiencies of the different crops on Norfolk soil ranged from a low of 14 per cent for lettuce or 16 per cent for endive to 238 per cent for turnips when fertilized at 40 pounds per acre of P20O on an annual basis. Although not as extreme, similar differences occurred at the other phosphorus rates and on the other soils. PHOSPHORUS STUDIES with VEGETABLE" CROPS 19 It may be noted also that the utilization efficiency of phosphorus absorption was consistently lower for higher phosphorus applications (Table 10). For example, the decrease of cabbage on Norfolk soil was from 105 to 79 to 58 to 47 per cent as the annual applications of P 8OS were increased from 40 to 160 pounds per acre. On Eutaw soil, the utilization efficiency of cabbage decreased from 76 to 33 per cent, and on the Cecil soil, from 50 to 28 per cent as the rates were increased from 80 to 320 pounds per acre of P20s. Since a number of vegetable crops have a high-phosphorusabsorption capacity, it is obvious that these crops might absorb more phosphorus than had been supplied, especially at a low rate of phosphorus application. The data show that this is true with several crops: At the annual rate of 40 pounds per acre, turnips absorbed 31.7 pounds of P2O. on the Norfolk soil. This was 2.38 times as much phosphorus as its share (13.3 pounds) of the annual rate. There are many factors that have a part in the final utilization efficiency of a crop. The final results involve interplay of phosphorus requirements, phosphorus-feeding power, and residual phosphorus from previous crops. The collard offers a good illustration of the interplay of these factors. At the lowest rate of phosphorus application, it had a utilization efficiency of 117 per cent on the Norfolk soil, 112 per cent on the Eutaw soil, and 72 per cent on the Cecil soil. This crop had a very low phosphorusfeeding capacity, as represented by an absorption of 0.74 pounds of P2O5 from the zero-phosphorus treatment on the three soils. It had a high-phosphorus requirement, as represented by 36.06 pounds per acre of PO; absorbed for the treatment giving maximum plant growth. Its phosphorus absorption index was very low; yet given a very small application of phosphorus, the crop absorbed 17 per cent more phosphorus than it received for its one-third of an annual application. In the case of turnips, the amount of phosphorus absorbed was 138 per cent more than was supplied at the low rate of application. The phosphorus absorbed in excess of that supplied might come from the soil's natural phosphorus reserves or from unused portions of phosphorus applied to other crops in the rotation. The extent to which a crop might use the natural phosphorus of soil when presumably the more available phosphorus supplied from superphosphate is present has basic implications. It seems evident that when low-phosphorus applications are given, certain TABLE 10. EFFICIENCY OF PHOSPHORUS UTILIZATION BY DIFFERENT VEGETABLE CROPS ON DIFFERENT SOILS FERTILIZED AT DIFFERENT RATES OF PHOSPHORUS i r 1 I r I J I Percentage of P2 O5 absorbed of that applied to different soils at different rates Pounds of P2 0, per acre Pounds of P2 0 5 per acre Pounds of P205 per acre applied to Cecil soil' applied to Eutaw soil' applied to Norfolk soil' Vegetables 320 80 160 240 320 40 80 120 160 80 160 240 Pct. Pct. Pct. Pct. Pct. Pct. Pct. Pct. Pct. Pct. Pot. Pot. 54 48 131 69 55 103 73 77 189 152 95 244 Sweetpotatoes 61 49 84 61 102 117 93 75 157 95 238 123 Turnip 33 56 48 40 72 46 96 62 82 61 141 110 Chinese Cabbage 35 58 47 72 59 42 112 79 65 47 86 117 Collards 38 29 66 46 57 43 72 41 105 81 62 111 Tendergreen 38 30 31 59 47 53 41 42 93 79 52 152 Okra 24 19 54 31 23 46 29 48 81 94 62 195 Lima Beans 28 40 30 33 50 36 76 51 58 47 105 79 Cabbage 29 33 34 40 29 30 34 48 64 63 87 94 Squash 34 26 41 37 34 28 65 41 52 41 85 62 Carrot 27 22 52 30 27 37 31 31 60 51 43 86 Pepper 12 12 17 22 23 28 28 35 63 45 101 65 Eggplant 14 27 22 43 25 21 32 50 32 26. 43 63 N. Z. Spinach 18 15 23 16 25 26 24 47 35 30 77 48 Tomatoes, spring 10 12 23 16 21 17 26 29 42 46 36 89 Beans 16 14 18 16 26 26 19 36 34 28 46 83 Potatoes 15 13 26 20 21 17 28 25 23 32 30 32 Kale 16 24 19 25 17 15 18 16 19 24 20 38 Beets 13 16 23 20 12 19 15 33 18 15 21 29 English Pea 20 18 24 23 7 8 8 6 20 29 31 30 Swiss Chard 6 12 8 20 12 9 19 13 28 18 42 24 Radish 11 14 11 11 12 10 15 13 19 17 16 16 Endive 9 10 11 11 11 10 12 12 14 17 16 16 Onion 9 10 11 6 10 8 8 7 12 18 23 22 Lettuce, spring 6 8 7 9 10 8 9 8 12 9 11 14 Lettuce, fall 25 20 31 24 40 38 30 58 43 34 57 87 AVERAGE 2 -- T tIlL bVI VU YU ~U VO LO LO urrlrl e 'Annual rates per acre. --- a C n z -4 CA, -I 2 from total phosphorus absorbed at the differents rates. 0 z PHOSPHORUS STUDIES with VEGETABLE CROPS 21 crops continue to absorb phosphorus from the reserve supply of the soil. Furthermore, it seems likely that the application of a small amount of phosphorus supplies certain crops with enough phosphorus to enable them to absorb phosphorus from the less available supplies through mass root-soil relations made possible by increased root growth. CROP RESPONSES TO PHOSPHORUS APPLICATIONS The data reported thus far have dealt with various phases of phosphorus absorption and with differences in phosphorus requirements and feeding capacities of different crops. This phase of the study deals with the response of different vegetable crops to applications of phosphorus as expressed in yields of plant parts normally used for food. YIELD OF DIFFERENT CROPS FROM PHOSPHORUS INCREMENTS. Yields of 26 vegetable crops at five rates of phosphorus applications on each of three soils are given in Appendix Table 2. Since these are the basic data from which a number of other tables are derived, they are analyzed in some detail statistically. In Appendix Table 3 are given the "F" value for differences in yield between different rates of phosphorus applications and the coefficient of variation for each set of data consisting of the yields of each crop on each soil for the years involved. The least significant difference between treatments for each set of data is presented in Appendix Table 4. Three other sets of statistics derived from Appendix Table 2 are presented in Appendix Table 6. In this table are given the rates of phosphorus applications theoretically required for maximum yields, the theoretical rate for zero yields, and slope of the lines between the yield at the zero and the yield at the theoretical maximum rate of phosphorus application. These data were derived from equations for second degree polynomials, which were computed for each set of data.2 The data in Appendix Table 2 are expressed in Table 11 as "relative yields," i. e. yield of each crop from each rate of phosphorus application as percentage of the yield at maximum rate. The yields of any two vegetables or groups of vegetables at any of the lower rates of application may be compared in terms of the yields at the highest rate. 2 Equations are available in mimeograph form upon request. TABLE 11. RELATIVE YIELDS OF DIFFERENT VEGETABLES ON DIFFERENT SOILS FROM DIFFERENT PHOSPHORUS APPLICATIONS Relative yields from pounds of Relative yields from pounds of 1 Vegetable 0 P205 per Pct. acre applied to Norfolk soil 160 120 80 40 Pet. Pct. Pct. P2 05 per acre applied to Eutaw soil. 320 240 160 80 0 Pct. Pet. Pct. Relative yields from pounds of Pct. Pet. Pet. Pct. P2 0 5 per acre applied to Cecil soil 320 240 160 80 0 Pct. Pet. Pct. Average number crops Pct. Sweetpotatoes Lima Beans Okra Radish Turnip Tendergreen Tomatoes, spr. English Peas N. Z. Spinach Chinese Cabbage Potatoes Carrots Collards Cabbage Beets Pepper Eggplant Beans Squash Kale Onions Endive Swiss Chard Tomatoes, sum. Lettuce, spr. Lettuce, fall 102 89 99 100 101 94 99 100 87 111 80 100 100 107 95 100 97 87 96 100 115 112 90 100 92 96 74 100 90 65 98 100 70 86 97 100 98 69 104 100 90 96 100 75 60 83 102 100 71 94 102 100 74 98 100 100 90 99 76 100 82 73 117 100 96 90 100 75 81 92 100 70 91 88 100 50 52 79 98 100 47 79 89 100 71 98 100 36 50 85 100 100 42 73 85 100 52 83 95 100 77 95 53 100 69 90 97 100 31 AVERAGE rll ~ 'Yield at each rate of phosphorus application 94 104 81 39 44 34 29 25 23 17 57 33 10 40 16 32 11 38 13 5 18 4 6 23 9 13 57 98 100 109 97 94 98 100 94 97 100 94 100 72 48 84 95 79 100 88 107 82 112 31 72 81 55 110 100 110 9 11 96 89 97 95 106 100 100 2 93 103 85 79 8 103 83 101 100 1 80 1 92 92 100 116 4 92 30 61 98 105 100 102 100 100 15 98 94 36 72 97 100 106 93 83 2 1 103 128 93 76 100 95 87 3 4 110, 110 86 23 59 86 98 100 32 84 92 63 95 100 14 88 35 70 83 51 98 100 97 91 1 76 96 1 73 99 100 92 94 92 4 8 76 65 96 100 75 94 98 46 3 2 56 98 100 76 56 24 86 94 64 10 72 83 64 81 101 100 50 9 3 87 56 92 44 67 19 100 77 7 92 62 100 87 7 85 99 0 52 94 2 100 93 55 70 80 2 88 90 93 100 102 18 79 41 44 78 9 53 9 84 89 100 1 71 80 32 93 '100 6 45 74 51 63 3 86 6 39 102 100 71 4 47 71 66 4 32 88 100 54 60 77 5 32 8 56 100 45 37 87 92 7 73 68 20 97 100 84 63 10 87 96 in relation to yield of the maximum phosphorus rate. 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 C) C C rn rn z -4 0 z PHOSPHORUS STUDIES with VEGETABLE CROPS 23 Figures 1 to 5 graphically illustrate the response of different crops in yields to increments of phosphorus and certain factors that affect the nature of the response. Figures 1 to 3 are based on data from field bins, while Figures 4 and 5 are based on data from greenhouse experiments. The data in Table 11 and Figures 1 to 5 reveal great differences in the yield response of different vegetables to different rates of phosphorus on different soils under different conditions. For example, the relative yields of a number of crops on Norfolk soil receiving 40 pounds per acre of PsO5 were nearly as high as the yields of the maximum rates, whereas the relative yields of several other crops were below 50 per cent. Sweetpotatoes produced about as much on Norfolk and on the Eutaw soils without added phosphorus as they did from any amount applied. The yield of lima beans on the Norfolk at the lowest rate used was practically the same as that from the highest rate. Another observation of importance is the effect of soil type on the nature of the yield response and the corresponding yield curve. Lima beans, for example, on the Norfolk soil with no additional phosphorus gave relative yields as high as those from the highest application. On the other hand, the relative yield from the zero-phosphorus rate was 79 per cent on the Eutaw and 48 per cent on the Cecil soil. From the 80-pound rate of P205, the relative yield was 95 per cent on the Eutaw soil but only 72 per cent on the Cecil soil. The yields of sweetpotatoes on Norfolk and Eutaw soils were as high from the no-phosphorus treatment as from any of the amounts of phosphorus applied, but the yield on the Cecil at the zero-phosphorus rate was only 57 per cent as high as the maximum rate. For the five rates of phosphorus application ranging from zero to 160 pounds per acre of P205, the average relative yields of 26 crops were 31, 69, 90, 97, and 100 per cent on the Norfolk. The average relative yields from applications ranging from 0 to 320 pounds per acre were 20, 68, 84, 97, and 100 per cent on the Eutaw soil and 10, 63, 87, 96, and 100 per cent on the Cecil soil. Figures 1 to 5 illustrate the different types of curve and some of the factors affecting the type of curve. The relative yield curves for sweetpotatoes are given in Figure 3. On the Norfolk and Eutaw soils, the curves are straight and horizontal, whereas on the Cecil the curve is slightly convex. When crops give as high yields from no phosphorus as from different rates of phosphorus, straight line horizontal curves result. 24 ALABAMA AGRICULTURAL EXPERIMENT STATION 24 ALABAMA AGRICULTURAL EXPERIMENT STATION Rlaktive yields 1.00- I .80, .60 .40 .20 80 Eutaw 5oilI Y =,O'794 +.Z91ZX )-.O 45X2~ 160 240 3520 0 80 160 5 240 320 Poundsof P20 added per acre per year FIGURE 1. Relative yields of lettuce grown on different soils receiving different rates of average) in experiments conducted in field bins. Treatment consisted of phosphorus repeated applications of phosphorus. (4-year 'PHOSPHORUS STUDIES with VEGETABLE PHOSPHORUS STUDIES with VEGETABLE CROPS CROPS 25 25 Relative yields Pounds of PzO iadded per acre per year FIGURE 2. Relative yields of collards grown on different soils receiving different rates of phosphorus (4-year average) in experiments conducted in field bins. Treatment consisted of repeated applications of phosphorus. 26 ALABAMA AGRICULTURAL EXPERIMENT STATION 1.00" .80 Relative yields .60f .40 Norfolk Y=.9 Soil -. 0029X2 __ _ .20 10 40 80 58Z2 + .013GX 120 IGC R~elative yields LOO0T .801[ F SolI Z40 32C .40 .20,F 0 80 [Eutcaw Y =.9940-.o3GX+..OlXZ i i 160 Relaitive yields 1.00 .80 .60 AO 20 80 _ _ Cecil Soil z59 .1 Z3+ . i 338)(-.0607)(X Pounds Of' P O0dded per acre per year 2 5 160 w 240 3Z.0 s FIGURE 3. Relative yields of sweetpotatoes grown on different soils receiving different rates 4 of phosphorus ( -year average) in experiments conducted in field bins. Treatment consisted of repeated applications of phosphorus. PHOSPHORUS STUDIES with VEGETABLE CROPS PHOSPHORUS STUDIES with VEGETABLE CROPS 27 27 Pounds of P0 4.. Relative dded per dere FIGURE yields of, lettuce grown on different soils receiving different rates of phosphorus in experiments conducted in pots in the greenhouse. Treatment. consisted of one application of phosphorus mixed with all soil in the pot. Relative 1.40 F 1.80 AO Ce ~(acY=.lGa+.3776 "20 Lc (10Y=.25 G +.209X .0395 +-.2852X- X-.o4osXZ - .015X 2 0(c)Y= ' 40 0I .0195)(1 320 - Pounds of FPO GO 5 ctddectd per acre FIGURE 5. Relative yields of mustard grown on different soils receiving different rates of phosphorus in experiments conducted in pots in the greenhouse. application of phosphorus mixed with all soil in the pot. Treatment consisted of one 28 ALABAMA AGRICULTURAL EXPERIMENT STATION When crops make low yields without phosphorus but relatively high yields at low rates of application, highly convex curves result (Figure 2). Crops that give somewhat uniform increases for increases in phosphorus application give inclined, flat, or straight line curves (Figure 1). When crops give low increases in yield for low rates of application and high yield only from high applications, the curves are concave. No crop grown over a period of years in field bins gave concave curves. A number of factors affect the convexity and concavity of curves. The effects of a number of factors are shown in Figures 4 and 5. Data in these graphs are from greenhouse experiments. The phosphorus was mixed with all the soil in the pots and only one application of phosphorus was given. The curve for relative yield of lettuce on Norfolk soil (Figure 4) is convex, on Oktibbeha soil almost straight, and on Cecil soil concave. The curve for the relative yield of mustard on Norfolk soil is highly convex and on Oktibbeha and Cecil soils slightly convex (Figure 5). Figures 4 and 5 along with Figures 1 to 3 and the data in Tables 1, 2, 3, 7, 8, and 11 indicate that relative yield curves are more convex or less concave when crops absorb relatively low amounts of phosphorus at the zero rate and make high relative yields from low rates of phosphorus applications, when soils have low phosphorus-fixing capacity, and when phosphorus is applied repeatedly to the same soil and applied to a limited zone. RELATIVE CAPACITY OF DIFFERENT VEGETABLE CROPS TO MAKE SATISFACTORY YIELDS AT LOW-PHOSPHORUS APPLICATIONS. In areas of highly specialized vegetable production, heavy applications of phosphorus are made. The amounts applied are often much in excess of phosphorus needs of the crops grown, and continued use of heavy applications results in accumulation of high or excessive amounts of phosphorus (3, 5, 7, 8, 30, 43, 44). The situation is often quite different in many gardens and truck patches on farms where the rate of fertilization used is for field crops rather than vegetable crops. Hence, satisfactory production often depends upon the ability of the crop to grow with relatively small phosphorus applications. In Table 12, the relative yields of different crops on different soils are given for the smallest phosphorus application made. The rates on an annual basis were 40 pounds of P202 per acre on Norfolk soil and 80 pounds on the two clay soils. Yield at the maximum phosphorus application is used as 100 per cent. The PHOSPHORUS STUDIES with VEGETABLE CROPS 29 TABLE 12. RELATIVE YIELDS OF DIFFERENT CROPS ON DIFFERENT SOILS AT LOW RATES OF PHOSPHORUS APPLICATIONS Vegetable Yield of lowest phosphorus rate in percentage of yield at highest rate on different soils Norfolk soil Eutaw soil Per cent 94 96 95 83 85 83 81 98 76 92 76 83 56 76 59 55 56 70 62 46 45 41 53 37 Cecil soil Per cent 94 89 72 80 79 93 72 72 86 61 73 50 72 65 63 70 44 51 52 56 51 44 32 45 Sweetpotatoes Radish: Lima Beans Tendergreen Turnip N; Z. Spinach Okra English Peas C. Cabbage Tomato, spring Collards Eggplant Pepper Cabbage Potato Kale Beans Carrot Squash Beets Swiss Chard Onion Endive Lettuce, fall Lettuce, spring Per cent 99 95 101 90 87 70 87 65 69 74 71 75 73 74 75 52 70 60 50 76 50 47 36 53 52 32 32 relative yields ranged from a low of 32 to a high of 101 per cent. Sweetpotatoes, lime beans, collards, turnips, tendergreen, tomatoes, and okra are crops that produced between 70 and 100 per cent of the maximum yields from the lowest rate of phosphorus applied. Such response undoubtedly is one of the reasons why these crops are grown more commonly than other vegetables on farms in the Southeastern States. EFFECTS OF PHOSPHORUS RATES ON EARLINESS OF MATURITY. Effects of phosphorus on earliness of maturity has been recognized by plant physiologists for many years. In Table 13 are presented early and medium-early yields of a number of crops, as expressed by percentages of total yields. Phosphorus had a decided effect on earliness with most crops. The most pronounced 30 TABLE 13. ALABAMA AGRICULTURAL EXPERIMENT STATION EFFECTS OF PHOSPHORUS RATES ON EARLINESS OF MATURITY Percentage of total yield of early and medium-early harvests on different soils at different rates of phosphorus Vegetable Pounds P 2 0s per acre applied to Norfolk soil 0 40 80 120 160 Pounds P 208 per acre applied to Eutaw soil 0 80 160 240 320 Pounds PiO5 per acre applied to Cecil soil 0 80 160 240 320 a1 b1 L. Beans a b Tomatoesa b English a Peas b Squash a b Tomatoesa b Pepper a b Okra a b Eggplant a b Beans % 7 39 22 73 6 32 68 7 30 3 15 23 56 14 44 0 15 % 14 44 26 76 21 50 67 15 77 6 29 25 57 11 44 8 51 % 21 59 28 75 26 51 57 31 77 4 34 28 61 16 49 16 68 % 27 66 29 76 26 65 47 28 78 8 35 28 63 12 49 15 67 % 30 67 29 78 27 60 47 24 79 8 35 31 64 14 46 16 62 % 21 66 21 74 2 36 76 14 45 3 19 14 51 18 54 0 25 % 24 75 34 86 20 54 % 31 78 33 89 15 53 % 30 79 38 89 18 55 % 32 82 33 89 15 52 % % 5 56 14 57 0 19 14 62 11 61 11 37 60 14 64 3 32 27 58 12 44 4 41 % 23 72 15 70 10 52 60 19 81 4 32 21 58 16 50 12 57 % 20 71 15 71 8 30 60 19 83 2 32 24 60 14 46 17 58 % 23 73 15 73 7 37 58 17 77 3 31 25 64 17 55 20 59 46 38 39 29 33 35 74 82 85 8 1311 45 47 50 24 28 23 63 70 72 16 .19 22 50 54 60 13 18 21 60 61 71 35 78 32 0 80 100 9 0 49 13 30 7 88 31 21 11 56 46 16 0 70 25 1a = early; b = early + medium-early. difference occurred between no phosphorus and the low rate of phosphorus, although usually the increase in the percentage harvested as early or medium-early continued with each increment. Crops giving little response in total yield from phosphorus applications showed little effects of phosphorus on earliness. English peas proved to be the exception. On all three soils, English peas gave a higher percentage of early and medium-early harvest with the no-phosphorus treatment than with any rate of phosphorus. EFFECTS OF ADDED MATERIALS ON PHOSPHORUS AVAILABILITY EFFECTS OF LIME. Much work has been done on the influence of lime on availability of phosphorus and on factors responsible for increased availability. Parker and Tidmore (27) found much higher phosphorus in the soil solution on limed soil from plots in long continued experiments in Alabama, Illinois, Ohio, and Kentucky. Salter and Barnes (33) reported that liming of soils not receiving phosphorus gave response about as great as adding phosphate without lime. Investigators have attributed this to a PHOSPHORUS STUDIES with VEGETABLE CROPS 31 reduction in soil acidity and an increase in the calcium ions in proportion to the iron and aluminum ions. At high acidity, more iron and aluminum salts are in solution. They unite with the phosphate present giving highly insoluble iron and aluminum phosphates. When lime is added, acidity is reduced, calcium ions are increased, and the more soluble calcium phosphates are formed. Included in this experiment was one treatment containing lime. The phosphorus application to each soil in this treatment was at the maximum rate. A comparison of dilute acid-soluble phosphorus in the maximum-phosphorus rate with and without lime is given in Table 14. The data show that there was a significant increase in the amount of dilute acid-soluble phosphorus on limed plots. TABLE 14. DILUTE ACID-SOLUBLE PHOSPHORUS IN SOILS AS AFFECTED BY LIME P 2 05 on limed and unlimed plots 1 Amount in phosphorus mainAmount in phosphorus Soil type tenance plots 2 Without With DifferOdds residual plots 2 Without With DifferOdds lime lime ence p.p.m. p.p.m. p.p.m. Norfolk 120 189 69 3 434:1 lime lime p.p.m.p.p.m. 114 173 ence p.p.m. 59 3 999:1 Eutaw Cecil 262 204 300 280 38 76 60:1 73:1 188 159 237 254 49 95 29:1 999:1 1Comparison based on limed and unlimed plots receiving annually during first 9 years 160 pounds per acre P 2 0 5 on the Norfolk and 320 pounds on the Eutaw and Cecil. 2 Phosphorus maintenance plots received from the 10th through the 14th years one-half of the phosphorus rates of the first 9 years; the residual plots received no phosphorus after the 9th year. 3 Odds as determined by Student's method using the phosphorus in limed and unlimed plots for each of the 5 years as pairs. EFFECTS OF ORGANIC MATTER ON THE DILUTE ACID-SOLUBLE A number of investigators have pointed out that one of the many effects of organic matter is the increase in availability of phosphorus. Hester and Shelton (19) showed that a Norfolk fine sandy loam low in phosphorus and containing 3 per cent organic matter gave as high yields of lima beans as the same soil with three times as much phosphorus but containing only 1 per cent organic matter. The effect of organic matter on phosphorus availability was investigated in the residual phosphorus study. Grain sorghum was grown in the summer and turned under on one-half of both PHOSPHORUS. 32 ALABAMA AGRICULTURAL EXPERIMENT STATION TALE 15. DILUTE ACID-SOLUBLE PHOSPHORUS IN SOILS OF RESIDUAL PLOTS AS AFFECTED BY ORGANIC MATTER Rates of Dilute acid-soluble P 2 0~ on plots receiving and Pa05 not receiving a green manure crop applied No organic Organic '? per acre 1 matter added matter added Difference Odds Pounds Norfolk soil 0 40 80 120 160 Eutaw soil 0 80 160 240 320 Cecil soil 0 80 160 240 320 p.p.m. 26 39 65 87 120 12 34 76 132 202 8 22 55 102 161 p.p'm, 26 40 64 89 130 13 37 89 145 224 9 25 63 107 181 p.p.. 0 1 -1 2 10 1 3 13 13 22 1 3 8 5 20 NS NS NS NS NS NS NS 216:1 57:1 57:1 NS NS NS NS NS Av. amount of green sorghum turned per a. per yr. Pounds 7,991 10,895 14,294 15,669 12,657 14,218 18,101 18,718 20,223 19,379 4,611 9,558 16,181 17,190 17,373 1 Amount of phosphorus applied per acre per year for 9 years of the first period; determinations for readily available phosphorus represent the average of the 5 years on residual phosphorus plots by use of Student's method with plots receiving and not receiving organic matter each year as pairs. Organic matter consists of crops of sorghum grown and turned under. 2 the phosphorus-residual and phosphorus-maintenance plots. The amounts of dilute acid-soluble phosphorus on each of three soils of the residual plots during the period of the study are given in Table 15. The organic material supplied in amounts and by methods employed in this experiment affected the amount of dilute acidsoluble phosphorus little or none in the Norfolk and the Cecil soils. There was a small but significant increase in the indicated amount in the Eutaw soil. STUDIES OF RESIDUAL PHOSPHORUS AVAILABILITY OF RESIDUAL PHOSPHORUS AS MEASURED BY CROP YIELDS. In areas devoted to intensive production of commercial truck crops, liberal applications of fertilizers containing high percentages of phosphorus are added. It is known that phos- PHOSPHORUS STUDIES with VEGETABLE CROPS 33 phorus added to the soil becomes "fixed" and, therefore, is not readily lost by leaching. It is also known that while the added phosphorus thus fixed is less readily available to crops, much of it may be used by plants. It is still further known that crops remove only a portion of the phosphorus supplied. Hester (20), Bryan (5), Chapman (8), Hawkins (18), and Bushnell (7) have shown that high amounts of phosphorus do accumulate in the soil and are available later for use. Data presented here provide considerable information on the subject of phosphate accumulation and its later availability to crops. Although the phosphorus rates used in the experiment were not as high as those reported in some commercial vegetableproducing areas, there was a considerable accumulation over a 9-year period. This accumulated supply affected yields for an additional 5-year period, the harvested amounts varying with the rates applied and with type of soil. The index crops used were Irish potatoes in the spring and turnips in the fall. Actual and relative yields of turnips are given in Table 16. The data are for each of the 5 years of the second period on each of the three soils. In expressing relative yields, the yields of plots on the three soils receiving the highest phosphorus-maintenance application are used as reference plots (100 per cent). Yields from all other plots are expressed as the percentages of yields of the corresponding reference plots. Plots referred to as phosphorus-maintenance plots received each year during the residual study one-half as much P20 5 as was applied during the first period. The amounts of phosphorus applied to the lighter Norfolk soil at maintenance rates were 0, 20, 40, 60, and 80 pounds of P2Os per acre per year divided equally between the spring and fall crops. The maintenance rates applied to the two clay soils were double those used on the Norfolk soil. Because of fluctuation in yields by years, the relative yields show the value of residual phosphorus better than the actual yields. The relative yields of turnips on each soil by years are given in Figure 6. On the Cecil and Eutaw plots that received 240 and 320 pounds per acre of P2O for the 9 years of the first period, relative yields of residual plots during the second period were within 10 per cent of the reference plot even at the end of 5 years. On plots that had previously received 160 pounds per acre of 34 ALABAMA AGRICULTURAL EXPERIMENT STATION 34 ALABAMA AGRIUTRLEPRMN TTO TABLE 16. ACTUAL AND RELATIVE YIELDS OF TURNIPS FROM RESIDUAL AND PHOSPHORUS MAINTENANCE APPLICATIONS P2 0 5 per acre Yields per acre by applied for 9 years 2 1946 Lb. 1947 Lb. Relative yields by years3 years'1948 Lb. o 40 80 120 160 Lb. 1944 Lb. 473' 8,391 13,171 15,008 15,494 1945 Lb. 1943 Pet. 1944 1945 1946 1947 Pet. Pct. 3 54 85 97 100 7 26 52 76 78 1 56 79 94 1 [00 3 33 61 87 81 Pet. Pct. 5 0.2 53 31 85 79 99 92 100 100 i i t E Norfolk soil Maintenance application of 8,006 14,028 11,635 14,714 0 phosphorus'1 0 0 40 4,263 80 10,803 120 11,744 160 14,432 Eutaw soil 589 1,600 64 0 22,343 17,133' 9,357 54 31,629 27,392 23,629 95 37,344 31,962 27,219 79 89,795 32,294 29,734 100 Residual phosphorus 1 1,043 999 870 147 0 3,994 13,241 4,115 1,965 29 7,981 24,397 12,979 7,917 73 11,756 34,810 23,251 18,098 80 12,134' 32,378 27,283 20,294 98 3 13 40 72 84 0.4 7 27 61 68 0.1 51 100 110 100 0 154 80 18,842 160382,653 240 34,503 320 .37,139 0 80 160 240 320 Cecil 0 80 160 240 269 12,141 29,939 34,752 35,788 soil Maintenance application of phosphorus 1,408 320 1,466 64 0.4 5 0.7 4 17,907 34,400 31,974 19,296 51 61 84 79 23,878 40,947 39,501 37,325 88 81 1L00 97 26,848 38,809 39,526 41,350 93 91 95 97 29,478 40,941 40,640 100 100 1L00 100 Residual phosphorus 684 448 1,587 1 288 0.7 2 4 11,411 18,438 14,541 11,782 33 39 45 36 23,719 32,742 31,437 31,347 81 80 80 77 26,170 42,988 38,502 35,488 05 95 94 89 29,690 39,488 42,752 43,149 96 101 96 105 37,491 31 84 95 115 0.7 Maintenance application of phosphorus 0 0 77 115 0 0 0.2 0.3 0 52 65 5,709 12,653, 25,479 21,587 12,294 86 62 39 14,080 17,875 29,670 .32,672 29,843 128 93 101 94 95 13,991 19,744 31,046 33,798 82,218 128 102 97 108 105 31,322 100 100 100 100 100 320 10,970 19,335 29,517 Residual phosphorus 0 0 205 13 326 6 0 1 0 0.9 0 30 1 13 5 80 1,709 2,445 8,756 1,843 403 16 160. 10,656 15,910 2.7,981 24,378 15,942 97 82 51 70 95 93 114 90 96 240 11,750 18,016 33,504 31,059 29,965 107 320 11,475 20,364 32,096 32,653 30,125 105 105 109 94 96 6 34,688 1 Rates applied annually for 9 years; no further application was made on the residual plots; and of original rates were applied to phosphorusmaintenance plots. 2 Yield of roots and tops. 1/2 received highest phosphorus application for 9 years and highest maintenance application for residual period. 3 Relative yield in percentage of the yield of the reference plot, which PHOSPHORUS STUDIES with VEGETABLE :CROPS 35 R~elaive yields. NorfolIk. Soil ________ _______ Lu.tctw SooI. Cecl Sol1 (80 Pound 1.0 ('loPoursd- rate p o) (80 Pound-rate P~o ) 6 -rate V ? 0 .80 40P- -'4 ' .404 .20 1.00 oo 4 -eII d b .80. .60 .20 120 Pou.nds 240 Pounds 240 Pounds 0 .80 .60 .40 .0 .20 "s IGO Pounds ________________. 520 Pounids 4th 5th 2nd 3rd .1.320 4th 5th Pounds 4+h 5+h '1st 2nd 3rd 2nd 3rd Yecars FIGURE 6. Relative yields by years of turnips from residual phosphorus. Phosphorus was applied for 9 years at indicated rates. Yields from residual phosphorus were measured from the 10th through the 14th year., Maintenance rates for the residual period were one-half of the -rates used in the first period. 36 ALABAMA AGRICULTURAL EXPERIMENT STATION POs, the relative yields of the residual plots averaged about 83 per cent as high as the reference plots on Norfolk and Eutaw soils, and about 91 per cent on the Cecil soil for 3 years after phosphorus applications were discontinued. By the fifth year, yields of the residual plots on the Norfolk and Cecil soils had dropped to 68 and 51 per cent, respectively. On residual plots that received lower rates of phosphorus during the first period, the decline in relative yields was more rapid. By the fifth year, the relative yields of the plots previously receiving 80 pounds of P205 per acre dropped from 73 to 27 per cent on Norfolk soil, and from 16 to 1 per cent on Cecil soil. On the other hand, there was practically no decline on the Eutaw soil. AVAILABILITY OF RESIDUAL PHOSPHORUS AS MEASURED BY CHEMICAL METHODS. Indicated amounts of readily available or dilute acid-soluble phosphorus in soils from previous phosphorus applications are given in Table 17 and the indicated relative amounts are shown in Figure 7. The dilute acid-soluble phosphorus during the residual period follows very closely the amounts of phosphorus added during the first period. Consistently, these amounts were higher in plots previously receiving higher applications of phosphorus during the first period. The amounts, likewise, were consistently higher on the plots receiving the phosphorus-maintenance applications during the residual period than companion plots receiving no phosphorus. There was very little loss in the amounts of dilute acid-soluble phosphorus in either of the three soils during the 5 years of the residual study. This was true at the low rates as well as at the high rates of phosphorus application and on soils rated high as well as on those rated low in phosphorus-fixing properties. These data and those on yields in the residual phosphorus studies give quantitative data on the amount and availability of phosphorus added to three soils. The retention of phosphorus often considered as a problem in phosphorus fertilization appears to be a favorable factor in fertilization of vegetable crops. While a relatively low percentage of the phosphorus added is used, nevertheless it is securely held by the soil for use at a later date. Data on this phase of the study and on relative yields from different rates of phosphorus application would indicate that vegetable crops might make maximum or near-maximum yields PHOSPHORUS STUDIES with VEGETABLE CROPS 37 IRelative- Amounts-3P 20 'Eu~ta~w Soli 1Pond (8OPound-rafePOs) 0steP) -- Mantenince 1PO. w --- Residual P2.0r NrokSoil 1.0 Cecil (8OPownd-rtie'o Si 5) .Go .2 "00 80Pounds .80 160 Pounds 160 Pounds .60 .40 .2 op- - - i !. 00 12 1 0Pounds -- 00\ 240 Pounds 2-40 Fbunds .80I .6q AO .201 .oo z .80 160 Pounds,'f 520 Pounds 520 Pounds 14 40. ----- ------ ---- .60 AO .20.1 01s 2nd 3rd yecars 4th 5th aI ! 1 e 1 1 e e t 1 2~nd 3rd 41h 5h 2nd. 3rd 4th .5th FIGURE 7. Relative amounts of dilute acid-soluble P205 by years from residual phosphorus. Phosphorus was applied for 9 years at indicated rates. Determinations for available P2O5 were made each year from the 10th through the 14th year. Maintenance rates of the residual period were one-half of the rates used in the first period. 38 ALABAMA AGRICULTURAL EXPERIMENT STATION TABLE 17. ACTUAL AND RELATIVE AMOUNTS OF DILUTE ACID-SOLUBLE PHOSPHORUS FROM RESIDUAL AND PHOSPHORUS MAINTENANCE APPLICATIONS P2 0 5 Amounts of P 2 0 5 per acre per acre by years 2 applied 9years11943 1944 1945 1946 1947 Lb. p.p.m. p.p.m. p.p.m. p.p.m. p.p.m. soil 19 33 48 81 103 22 34 49 76 99 Relative amounts of phosphorus by years 3 1943 Pct. 1944 Pet. 1945 Pct. 1946 Pet. 1947 Pct. Norfolk 0 40 80 120 160 0 40 80 120 160 Maintenance application of phosphate 20 22 25 25 32 18 38 44 41 43 32 35 70 71 46 54 58 57 88 78 83 90 81 106 108 108 146 132 100 100 22 37 49 78 100 28 34 55 81 105 Residual phosphorus 25 31 21 45 36 33 77 65 48 83 74 95 96 136 129 1 23 41 53 76 100 26 31 51 75 97 17 28 48 73 100 17 31 53 65 93 24 32 54 67 100 23 27 49 63 98 1 20 34 46 72 92 Eutaw soil 10 0 80 34 70 160 240 144 320 218 0 80 160 240 320 7 28 64 127 194 Maintenance application of phosphorus 10 4 4 13 10 19 16 12 38 45 34 39 93 32 32 100 122 100 66 61 164 214 164 191 293; 245 100 100 314 236 11 31 68 149 187 10 28 75 114 182 Residual 16 40 84 132 212 phosphorus 3 9 28 13 29 61 58 101 89 164 4 10 22 48 60 4 16 42 70 100 4 12 32 48 77 6 15 42 73 100 6 14 29 45 72 4 14 38 67 100 4 11 25 41 67 Cecil soil 0 5 80 22 160 72 99 240 320 172 0 80 160 240 320 3 20 51 108 163 Maintenance application of phosphorus 4 3 4 8 9 7 9 15 14 31 13 30 31 25 36 39 74 79 42 71 82 59 63 129 57 135 126 117 100 100 220 100 199 212 218 7 21 49 114 166 10 25 59 108 173 Residual 7 21 45 84 141 phosphorus 8 2 22 12 30 48 81 63 95 152 3 11 25 57 83 5 12 28 51 82 4 12 34 58 100 3 10 21 39 64 4 14 36 59 100 4 10 22 37 69 1Rates applied annually for 9 years; no further application was made of original rates were applied to phosphoruson the residual plots; and maintenance plots. 2As determined by Truog's improved methods. 3 Relative amount of phosphorus in percentage of the amount in the reference plots which received highest phosphorus applications for 9 years and highest maintenance applications for residual period. /2 PHOSPHORUS STUDIES with VEGETABLE CROPS 39 on much less phosphorus than is now applied on land used continuously for vegetable crops. The data also indicate that on soils heavily fertilized with phosphorus, applications may be withheld for a few years without serious loss in yield. CHANGES IN THE REQUIRED RATES OF PHOSPHORUS AFTER REPEATED APPLICATIONS. On a soil fertilized for the first time, only the phosphorus applied at that time plus the naturally available phosphorus of the soil is available to the crop. After phosphorus has been applied a few years, crops will draw on the residual phosphorus in addition to that added currently. To obtain some measure of the change in phosphorus requirements of crops, the relative yields of a number of crops fertilized at different rates were averaged for each of the first 4 years. The crops for each period compared were identical. The results are presented in Figure 8. The spread between the curves serves as a measure of the effects of residual phosphorus. The average relative yield of 15 crops was about as high or higher on the Eutaw soil and almost as high on the Cecil soil at the 160-pound rate of PsOs by the fourth year as it was at the 240- and the 320-pound rates for the first and second years. The 80-pound rate of P205 on the Norfolk soil by the 4th year was giving a relative yield about as high as or higher than the 120- and 160-pound rates the first and second years. These data suggest the advisability that current phosphorus applications be based on past applications to a given soil. CHANGES IN SOIL PHOSPHORUS DURING THE INVESTIGATION To obtain data on changes in soil phosphorus during the experiment, one of the five sets or sections of bins was chosen for detailed study. On this section, tabulations were made of all phosphorus added by fertilizers and all phosphorus absorbed and removed by harvested crops at each of the five rates of phosphorus application for the first 9 years. All plant residues from these crops remained on the plots. The data for phosphorus absorbed account only for the phosphorus in harvested crops, for which records of yield and phosphorus content were obtained. The actual amount absorbed, therefore, was in excess of the determined amounts to the extent of the crops grown but not recorded. (See footnote 3. Table 18). An analysis was made in 1945 of the three soils in each rate 40 ALABAMA AGRICULTURAL EXPERIMENT STATION 40 ALABAMA AGRICULTURAL EXPERIMENT STATION lRelcative nA . yields AO znd KNorfolk Soil .20 0 40 3rd yr.._......v 4th yr.-......Y= 80 .3208 .4194X- .OG3GXZ 3652,+.4646X- .0764XZ $20 Itdc+ivi v ~e -1 F 1.00 .0 " 3rd 80 E Cecil Soil ist r_._Y 2ndyr._._,. ® isz+ s+ .5388X .075 7X2 .5ZGGX -. 0764X)@ 2 + .Go26% -. o9G4X z 4th yr.._.... P= .0952 160 240 320 Pouinds of P OS cadded per acre 2 FIGURE 8. Average relative yields by years af 15 vegetable craps grown for the first 4 years on different sails receiving different rates of phosphorus. PHOSPHORUS STUDIES with VEGETABLE CROPS 41 TABLE 18. PHOSPHORUS ADDITIONS AND REMOVALS FOR THE 9-YEAR PERIOD, 1933-1942 Amt. P205 added, absorbed, and removed from phosphorus applications at different rates per acre 1 0 lb. 40 lb. 80 lb. 120 lb. 1601b. Norfolk soil P 20 5 added 1933-1942 2, lb. per acre P 2 O absorbed by harvested crops 3, lb. per acre PO 5 removed from plots, lb. per acre Net additions, P 2 0 5, lb. per acre Absorbed by harvested crops, per cent Removed by harvested crops, per cent Eutaw soil P20 5 added 1933:-1942 2, lb. per acre P20 5 absorbed by harvested crops 3, lb. per acre P2 05 removed from plots, lb. per acre Net additions, P 2 0 5, lb. per acre Absorbed by harvested crops, per cent Removed by harvested crops, per cent Cecil soil Pe0 5 added 1933-1942 2, lb. per acre PO0 absorbed by harvested crops 3, lb. 5 per acre POs removed from plots, lb. per acre Net additions, P 2 0 5 , lb. per acre Absorbed by harvested crops, per cent Removed by harvested crops, per cent 0 93 59 -59 360 720 1080 1440 Item 191 296 125 214 235 506 53.0 41.1 34.7 29.7 347 359 257 262 823 1178 32.1 24.9 23.8 18.1 0 lb. 80 lb. 160 lb. 240 b. 320 b. 0 56 24 -24 720 1440 2160 2880 230 333 420 461 161 247 314 343 559 1193 1846 2537 31.9 23.1 19.4 16.0 22.4 17.2 14.5 11.9 720 1440 2160 2880 0 21 10 -10 190 310 366 483 137 231 267 297 583 1209 1893 2583 26.3 21.5 16.9 16.8 19.0 16.0 12.4 10.3 1 Data obtained from section B of the bins. 2 Period from fall 1933 through summer 1942. 3 Does not include phosphorus absorbed by one crop of eggplant destroyed by disease, one crop of Chinese cabbage killed by unexpected hard freeze, and one fall potato crop failure due to stand; all residues from these crops remained on the plots. treatment to determine total and exchangeable phosphorus. Prior to 1945 the equivalent of 10 annual applications of phosphorus had been made. From the data, balance sheets were prepared. These data are presented in Tables 18, 19, and 20. PHOSPHORUS ADDITIONS AND REMOVALS. In Table 18 are given the total amounts of phosphorus added from fertilizers and removed by crops. The amounts of phosphorus absorbed by the harvested crops are also given. The net additions, as given, represent the difference between the amounts of phosphorus added by fertilizer and the amounts removed from plots. The removals of P2O from the bins of Norfolk soil were 59, 42 ALABAMA' AGRICULTURAL EXPERIMENT STATION TABLE 19. PHOSPHORUS ADDED, REMOVED, LEFT IN SOIL, AND AMOUNT FOUND BY ANALYSIS 1 Phosphorus (P 2 0 5 ) applied per acre ' Calculated amount in original soil 3 Amount added 1933-44 Pounds 0 400 800 1,200 1,600 0 800 1,600 2,400 3,200 0 800 1,600 2,400 3,200 P 0 5 per P20 5 in soil plus amount added 2 acre Removed by plants 1933-44 Pounds 66 150 253 300 307 34 183 285 352 390 11 149 249 292 326 Amount theoretically in soil Pounds 1,145 1,461 1,758 2,111 2,504 1,178 1,829 2,527 3,260 4,022 1,742 2,404 3,104 3,861 4,627 Amount found by analysis 1945 4 Pounds 1,145 1,330 1,803 2,078 2,405 1,178 1,646 2,190 2,958 3,582 1,742 2,144 2,628 3,051 3,899 Pounds Norfolk soil 0 1,211 40 1,211 80 1,211 120 1,211 160 1,211 Eutaw soil 0 80 160 240 320 Cecil soil 0 80 160 240 320 1,212 1,212 1,212 1,212 1,212 1,753 1,753 1,753 1,753 1,753 Pounds 1,211 1,611 2,011 2,411 2,811 1,212 2,012 2,812 3,612 4,412 1,753 2,553 3,353 4,153 4,953 1 Data obtained from soil in section B of bins. 2 This amount of P 2 0 5 was applied each year for the first 9 years and one-half this amount was applied each year for the last 2 years. Ninety pounds of N and 45 pounds K 20 per acre per crop were used with all rates of P 2 Os. 3 Caluculated from final analysis data by adding amount removed by plants. 4 Data from analysis by Department of Agronomy and Soils, Alabama Agricultural Experiment Station. 125, 214, 257, and 262 pounds per acre for the 40-pound increments ranging from 0 to 160 pounds per acre. Removals from the Eutaw soil were 24, 161, 247, 314, and 343 pounds, and from the Cecil soil 10, 137, 231, 267, and 297 pounds per acre for 80pound increments ranging from 0 to 320 pounds per acre. It will be noted that the amounts of phosphorus removed from the plots receiving no phosphorus were 59 pounds per acre from Norfolk soil, 24 pounds from Eutaw soil, and 10 pounds from Cecil soil. These data give a fair indication of relative availability of natural phosphorus in the three soils. When all additions and removals of phosphorus from the bins are taken into account, the net additions on the Norfolk ranged from -59 pounds per acre of PgOn on the no-phosphorus plots to PHOSPHORUS STUDIES with VEGETABLE CROPS 43 1,178 pounds on the plots receiving 160 pounds per acre of P205; on the Eutaw soil, the range was from -24 to 2,537 pounds, and on the Cecil from -- 10 to 2,583 pounds per acre of P2 0 5. Under conditions of the experiment that included adverse weather, disease, and crop failure, the removals expressed as percentage of the phosphorus added to the Norfolk soil ranged from 34.7 to 18.1 per cent as the rates increased from 40 to 160 pounds per acre of P2OS. The percentage removals from the Eutaw soil ranged from 22.4 to 11.9 per cent, and from the Cecil soil 19.0 to 10.3 per cent as the rate increased from 80 to 320 pounds per acre. These data show, as do those presented earlier, that only a small part of the phosphorus added to the soil actually is removed in the used portions of the crops. They also show a decrease in the percentage of phosphorus used as the rates of phosphorus application increase. TABLE 20. EXCHANGEABLE PHOSPHORUS, PERCENTAGE OF PHOSPHORUS SATURATION, AND ANION-EXCHANGE CAPACITY AS SHOWN BY ANALYSIS, 19451 P 20 5 applied Exchangeable phosphorus P per per acre 2 Pounds Per year Total amount (1933-44) 100g P 2 0 5 per acre Phosphorus capacity ca acity saturation P205 per Anionexchange P per acre Pounds 0400 800 1,200 1,600 0 800 1,600 2,400 3,200 0 800 1,600 2,400 3,200 Millimol 0.38 0.48 0.61 0.69 0.85 0.72 0.73 1.18 1.64 2.00 0.35 0.55 0.87 1.15 1.38 Pounds 675 853 1,083 1,225 1,509 971 985 1,592 2,213 2,698 522 820 1,297 1,715 2,058 Per cent 19 25 31 35 44 4.5 4.6 7.4 10.3 12.5 5.8 9.1 14.4 19.0 22.8 Pounds 3,477 3,477 3,477 3,477 3,477 21,514 21,514 21,514 21,514 Norfolk soil 0 40 80 120 160 Eutaw soil 0 80 160 240 320 Cecil soil 0 80 160 240 320 9,045 9,045 9,045 9,045 9,045 1Data from analysis by USDA Bureau of Plant Industry, Soils, and Agricultural Engineering. 2 This amount of P 2 0 5 was applied each year for the first 9 years and one-half of this amount was applied each year for the last 2 years. Ninety 0 pounds of N and 45 pounds KO per acre per crop were used with all rates of P 205. 2 44 ALABAMA AGRICULTURAL EXPERIMENT STATION The study of phosphorus additions and removals indicates that repeated applications of phosphorus for a number of years result in additions far in excess of removals. Investigations have universally shown that this surplus phosphorus is held by the soil. In 1945, total phosphorus determinations were made. In Table 19 data are given showing the total amounts of phosphorus added and removed during the period 1933-44, the amounts theoretically remaining at the end of the period, and the amounts found by analysis. On plots receiving the highest phosphorus rate, the Norfolk was found to have 2,405 pounds per acre of P2 0 5 , as compared with the theoretical amount of 2,504 pounds; the Eutaw, 3,582 pounds as compared with 4,022 pounds; and the Cecil, 3,899 pounds as compared with 4,627 pounds. Theoretical and indicated amounts showed about the same relationship for the other rates of application. It is pointed out that the plots were enclosed by concrete walls as boundaries, which prevented run-off of a large portion of muddy water during heavy rains. This partially accounts for the relatively high recovery of phosphorus at the end of the period. PHOSPHORUS BALANCE SHEET. EXCHANGEABLE SATURATION. PHOSPHORUS AND DEGREE OF PHOSPHORUS In Table 20 are given the amounts of exchangeable phosphorus in the three soils after they had received the equivalent of 10 annual applications of phosphorus. The total anionexchange capacity in terms of P205 for each soil and the percentage of phosphorus saturation are given. The Norfolk soil after receiving 10 applications of 160 pounds per acre of P2O had reached a phosphorus saturation of 44 per cent. Phosphorus saturation of the Eutaw soil after 10 applications of 320 pounds per acre of P20 was 12.5 per cent, and of the Cecil soil 22.8 per cent. The percentage of saturation ranged from 19 per cent to 44 per cent on the Norfolk, from 4.5 to 12.5 on the Eutaw, and from 5.8 to 22.8 on the Cecil soil. sO DISCUSSION DIFFERENCES IN PHOSPHORUS ABSORPTION BY PLANTS The data resulting from this study show that great differences do exist among vegetables in regard to their ability or capacity PHOSPHORUS STUDIES with VEGETABLE CROPS 45 to absorb phosphorus from soil in which there is only a limited amount readily available. These differences are striking. Data in Table 8 show an average absorption of P205 on three soils by the different vegetables, ranging from 0.23 pounds per acre for kale to 18.82 pounds for sweetpotatoes. Lieleland and others (21) found that Aiken clay loam soil near Paradise in the Sierra foothills had a very low amount of available phosphorus and a very high phosphorus-fixing capacity, which was about 10 times that of other apparently similar soils in California. While six different fruits showed no phosphorus response, the yield of such crops as cucumbers was increased 13.3 times and that of squash 29.4 times by the application of phosphorus. The explanation offered by Truog (41) would attribute the differences largely to qualitative factors related to the chemistry of the material needed and used by the plant in its metabolism, in addition to the liberation of carbon dioxide by the roots. According to his explanation, plants absorbing large quantities of calcium had relatively high phosphorus-feeding power. Unpublished results from work preliminary to the study at the Alabama Station showed that large quantities of phosphorus in the seed or vegetative parts used in propagation gave larger root development in cultures lacking phosphorus, and that these larger root systems absorbed more phosphorus on soils low in phosphorus than plants with less phosphorus in the propagating parts. Lima beans (Table 8) on soils receiving no phosphorus absorbed 16.72 pounds of P2O per acre under conditions where turnips absorbed 5.99 pounds and collards absorbed only 0.74 pounds. This comparison indicates that there are strong qualitative differences in the ability of crops to absorb phosphorus. Yet, the fact that turnips having a low phosphorus-absorbing power and a very high phosphorus requirement can develop a large root system with a very small application of phosphorus, absorb several times the amount applied, and make near-maximum yields would indicate that size of the root system is a factor to consider in the ability of a crop to absorb the required amount of phosphorus for full production. The significant contribution of this study is the establishment of the facts that vegetable crops do differ greatly in their ability to absorb phosphorus, and that they may be grouped according to their capacities to absorb this element. 46 ALABAMA AGRICULTURAL EXPERIMENT STATION DIFFERENCES IN PHOSPHORUS ABSORPTION AS AFFECTED BY SOIL PROPERTIES The three soils used in this experiment varied greatly in properties and characteristics, as shown in Tables 1 and 2. The extent of differences in availability of phosphorus contained in the soils selected for use in this investigation may be seen from the data in Table 8. The total amount of phosphorus absorbed annually by the 25 crops on the Norfolk soil was equivalent to 149.45 pounds per acre of P205, on the Eutaw soil 103.63 pounds, and on the Cecil soil 42.40 pounds. The Norfolk soil had a lower colloid content and could not absorb as much phosphorus as the Cecil soil; yet, it had more exchangeable phosphorus and a much higher percentage of its total anion-exchange capacity as exchangeable phosphorus than the Cecil soil. It, therefore, gave up over three times as much phosphorus to the crops grown than the Cecil soil. Although the percentage of phosphorus saturation in the Eutaw soil was somewhat smaller that that in the Cecil soil, indicating that the phosphorus might be more tightly held, this soil with about 67 per cent more exchangeable phosphorus released 103.63 pounds or twice as much as the Cecil soil. The amounts absorbed by the same crops on soils receiving enough phosphorus to give maximum yield were quite different than the amounts absorbed on the same soils receiving no phosphorus. The amounts removed annually by 25 crops fertilized at rates to give maximum production were equivalent to 444 pounds per acre of P2O0 on the Norfolk, 612 pounds on the Eutaw, and 525 pounds on the Cecil soil, Table 7. The Cecil had thus released more phosphorus than the Norfolk soil. There was usually an average of 30 to 40 per cent more exchangeable phosphorus in the Cecil than in the Norfolk soil at maximum crop-production levels, although the percentage of phosphorus saturation was still much lower on the Cecil than on the Norfolk soil. Data from the investigation reveal that differences exist in the ability of different crops to absorb phosphorus from different soils, as shown in Table 8. Many investigators (2, 17, 21, 26, 31) found that plants vary in capacity to obtain less readily available phosphorus from the soil. Where no phosphorus was added, turnips absorbed 14.62 pounds per acre of P20O on the Norfolk soil, but absorbed only 0.74 pounds on the Cecil. Carrots by PHOSPHORUS STUDIES with VEGETABLE CROPS 47 contrast absorbed only 7.05 pounds per acre of P209 on the Norfolk soil but absorbed 2.8 pounds on the Cecil soil. The carrot, therefore, had absorbed only one-half as much phosphorus as the turnip on the Norfolk but 4 times as much on the Cecil soil. In the order of phosphorus absorbed, turnips would rank 4th on the Norfolk but 11th on the Cecil soil, while carrots would rank 8th on the Norfolk soil and 5th on the Cecil. PHOSPHORUS UTILIZATION EFFICIENCY AS AFFECTED BY RATES OF PHOSPHORUS APPLICATION ON DIFFERENT SOILS The total amount of phosphorus absorbed per acre annually by 25 crops increased on each soil as the amount of phosphorus applied was increased (Appendix Table I). The percentage of phosphorus added that was absorbed, however, decreased on each soil as the amount of phosphorus applied increased (Tables 10, 18, 19, 20). It is obvious that the principle of diminishing returns applies to the absorption of phosphorus and its use by the plant. To the grower this fact is of economic importance. As the rates of phosphorus increase, the total amount of phosphorus, the amount of exchangeable phosphorus, and the percentage of phosphorus in exchangeable form in the soil increases (Table 20). These factors all tend to increase the amount of phosphorus available to plants. Plants, however, are inherently able to use only so much phosphorus. There develops, therefore, a quantity of phosphorus in the soil in excess of plant needs. While yields may continue to increase because of this excess amount of phosphorus, increases are made at increasingly higher costs and at increasingly lower efficiency from a standpoint of phosphorus utilization by the plant. At the lowest rate of phosphorus application, especially on the Norfolk soil, there was a high percentage of utilization. This was 87 per cent for the 25 crops, and a number of crops absorbed considerably more phosphorus than was applied. Many plants on soils with a low-fixation capacity may make extremely efficient use of the phosphorus when applied at low rates, but this efficiency in utilization is greatly reduced at higher rates of phosphorus application (Table 10). The average percentage of phosphorus absorbed of that added on the Norfolk soil decreased from 87 to 34 per cent as the amount applied increased from 40 to 160 pounds per acre of P20. The decrease on the Eutaw soil was from 58 to 24 per cent, and on the Cecil soil from 48 ALABAMA AGRICULTURAL EXPERIMENT STATION 40 to 20 per cent. These decreases have a definite bearing on the cost of production per unit under light and heavy applications of phosphorus. Two additional points should be made with reference to diminishing returns from phosphorus at high rates of application. One applies to the plant's performance; both points apply to the economics of production. The points may be illustrated by data in Table 11 and Appendix Table 1. Potatoes may be used as an example. As the phosphorus was increased on Norfolk soil, relative yields increased from 75 to 90 to 96 to 100 per cent. The increases in phosphorus application were in the ratio of 1 : 2 : 3 : 4. The relative increases in yield were 20, 28, and 33 per cent. For an increase in phosphorus application of 300 per cent, there was an increase in yield of 33 per cent. In addition to the very great difference in increased rates of phosphorus application and crop yields, there is a difference due to what amounts to a luxury consumption of phosphorus by plants receiving high rates of phosphorus. The work of Wright 3, conducted with vegetable crops as preliminary to this investigation, showed a higher percentage of phosphorus in plants grown at higher phosphorus rates. Thus, plants grown at higher rates of phosphorus not only gave increases in yields far below increases in the phosphorus applied but required increased amounts of phosphorus for each pound of yield made. YIELDS OF DIFFERENT VEGETABLE CROPS AS RELATED TO OTHER FACTORS The data in Table 8 and Appendix Table 1, and in Table 11 and Appendix Table 2 show a close relationship between the capacity of crops to absorb phosphorus and the actual and relative yields made. Crops absorbing high amounts of phosphorus from no-phosphorus or from low-phosphorus applications made high yields without phosphorus and with small applications of phosphorus. Relative yields of these crops were also correspondingly high at the zero- and low-phosphorus rates. Crops shown in Table 8 and Appendix Table 1 are arranged in order of phosphorus absorption; in Table 11 they are, likewise, arranged 3 phosphorus, soluble plant phosphorus, and growth of different vegetable crops on different soil types. Unpublished thesis, Ala. Poly. Inst. Library, 1932. Wright, Lawrence. A study of the relationship between available soil PHOSPHORUS STUDIES with VEGETABLE CROPS 49 PHOSPHORUS STUDIES with VEGETABLE CROPS 4 generally in order of relative yields made at zero- and low-phosphorus rates. The orders are very similar. As would also be expected, the amount of phosphorus absorbed and the relative yieldsat corresponding phosphorus rates were both highest on the Norfolk soil and lowest on the Cecil soil. The relationship of phosphorus-absorption capacity and yields is natural, since crops with high phosphorus-absorption capacities absorb more phosphorus, which in turn is converted into greater yields. AVAILABILITY OF RESIDUAL PHOSPHORUS Data presented in Tables 18 and 19 show quantitatively the additions, removals, theoretical accumulation, and actual accumulation of phosphorus on different soils where different amounts of phosphorus had been added over a period of 9 to 11 years. In Table 17 and Figure 7 are given quantitative data on the indicated availability of accumulated phosphorus by chemical tests. Data on the availability of accumulated phosphorus to plants are given in Table 16 and Figure 6. Figure 8 shows relative yields of crops from first and later applications of different rates of phosphorus. These data show that large quantities of phosphorus are added to the soil in excess of what is used by crops and that the excess phosphorus accumulates and is later available to crops for a period of years. They also show that the rates of fertilizer application may be reduced on land that has grown truck crops for a number of years and that has received repeated applications of high rates of phosphorus. Economy and conservation in the use of phosphorus may be effected by greatly reducing the amount of phosphorus applied on land that has received large applications over previous years, and by reducing moderately, after several applications, the amount applied to land not previously used for production of truck crops. The fixation of phosphorus by soils, a factor considered a few years ago as wasteful of phosphorus, may yet prove a factor in its conservation provided erosion can be controlled. 50 ALABAMA AGRICULTURAL EXPERIMENT STATION SUMMARY Experiments reported in this publication measured differences among vegetable crops in their phosphorus requirement, phosphorus - absorption capacity, phosphorus - absorption and phosphorus-utilization efficiencies, and response to increased applications of phosphorus on Norfolk sandy loam, Eutaw clay, and Cecil sandy clay soils. The phosphorus requirement of different crops for maximum production ranged from 6.18 pounds per acre of P2O5 for fall lettuce to 54.35 pounds for turnips. The phosphorus-feeding capacity of different crops, as measured by the amount of phosphorus absorbed with no phosphorus added, ranged from a low of 0.23 pounds per acre of P 2 O for 5 kale to a high of 18.82 pounds for sweetpotatoes. The phosphorus-absorption efficiency of different crops, as measured by the reciprocal ratio of P2O5 absorbed at the phosphorus rate giving maximum yield to the P20s absorbed at the zero-phosphorus rate, ranged from a low of 1.6 for kale to a high of 71 for lima beans. The phosphorus utilization efficiency of different crops was measured by the percentage of phosphorus absorbed of the phosphorus added. This efficiency ranged from a low of 6 per cent for fall lettuce grown on the Cecil soil and fertilized at the highest phosphorus rate to a high of 244 per cent for sweetpotatoes grown on the Norfolk soil and fertilized at the lowest phosphorus rate. The percentage of phosphorus absorbed of that added was highest on the Norfolk and lowest on the Cecil soil. Percentages absorbed on each soil were highest at the lowest rate of phosphorus application and were lowest at the highest application rate. The average absorption percentage of 25 crops ranged from 87 to 34 per cent on the Norfolk soil, from 58 to 24 per cent on the Eutaw soil, and from 40 to 20 on the Cecil soil. Vegetable crops varied greatly in relative yields obtained from different rates of phosphorus applications expressed in percentage of the yield from the highest rates. Two crops, the sweet- PHOSPHORUS STUDIES with VEGETABLE CROPS 51 potato and the lima bean, gave yields about as high without phosphorus and from low rates of applications as from the highest rates used. Relative yields of a number of crops were 90 per cent as high from the lowest application as from the highest applications, whereas relative yields of others were only 50 per cent as high. The type of response of a given crop was affected by type of soil. Average relative yields of 26 different vegetable crops grown without phosphorus on the Norfolk sandy loam were 31 per cent, on the Eutaw clay 20 per cent, and on the Cecil clay 10 per cent of the average yields from the highest rates used. Average relative yields of the 26 crops from an application of 80-pounds per acre of PsO were: 90 per cent on the Norfolk soil, 68 per cent on the Eutaw soil, and 63 per cent on the Cecil soil. The p. p. m. of dilute acid-soluble phosphorus, as determined by chemical test, were increased on the three soils by the addition of lime but only on one soil by the addition of organic matter. Repeated applications of different rates of phosphorus over a period of 9 years resulted in accumulation of large quantities of phosphorus in the soil. Chemical tests indicated that considerable quantities of accumulated phosphorus were in a readily available form. The yield of turnips as an index crop showed that sufficient quantities of readily available phosphorus accumulated from the higher rates of applications of phosphorus during the first 9 years to give maximum or near-maximum yields over the next 5 years. Based on average relative yields of 15 different vegetables, the Norfolk soil produced about as much by the fourth year from repeated applications of 80 and 120 pounds per acre of P~2~ as it did from 160 pounds per acre the first year. Relative yields on the Eutaw and Cecil soils, likewise, were about as high from four annual applications of 160 pounds per acre of P2O5 as those from 240 and 320 pounds per acre the first year. Analysis of soil for total phosphorus after the equivalent of 10 annual applications accounted in a large measure for phosphorus additions, phosphorus removals, and original soil phosphorus. Analyses accounted for 96 per cent of the phosphorus in the Norfolk soil, 89 per cent in the Eutaw soil, and 84 per cent in the 52 ALABAMA AGRICULTURAL EXPERIMENT STATION Cecil soil in the plots receiving the highest phosphorus applications. After the equivalent of 10 annual applications of phosphorus at the highest rates had been made, the phosphorus saturation percentages of total anion-exchange capacity for the three soils were: Norfolk, 44 per cent; Eutaw, 12.5 per cent; and Cecil, 22.8 per cent. PHOSPHORUS STUDIES with VEGETABLE CROPS 53 LITERATURE CITED 54 ALABAMA AGRICULTURAL EXPERIMENT STATION (1) ALBRECHT, W. A. AND SCHROEDER, R. A. Colloidal clay culture for refined control of nutritional experiments with vegetables. Proc. Amer. Soc. Hort. Sci. 37: 689-692. 1939. ALWAY, F. J., SHAW, W. M., AND METHLEY, W. J. Phosphoric acid (2) content of crops grown upon peat soils as an index of the fertilization received or required. Jour. Agr. Res. 33: 701-740. 1926. (3) ANDERSON, P. J., MORGAN, M. F., AND NELSON, N. T. The phosphorus requirements of old tobacco soils. Conn. Agr. Expt. Sta.-Tobacco Sta. Bul. 7. 1927. BouYoucos, G. J. A comparison of the hydrometer method and the pipette method of making mechanical analysis of soils, with new directions. Jour. Amer. Soc. Agron. 22: 747-751. 1930. BRYAN, O. C. The accumulation and availability of phosphorus in old citrus grove soils. Soil Sci. 36: 245-259. 1933. BROWN, B. E. AND OTHERS. Field comparisons of colloidal phosphate and superphosphate as sources of phosphorus in potato fertilizers. Amer. Potato Jour. 21: 241-249. 1944. BUSHNELL, J. Possibility of reducing the proportion of phosphate in fertilizers applied to sandy soils. Amer. Potato Jour. 20: 153-155. 1943. CHAPMAN, H. D. The phosphate of Southern California soils in relation to citrus fertilization. Cal. Agr. Expt. Sta. Bul. 571. 1934. CoMIN, DONALD AND BUSHNELL, J. Fertilizer for early cabbage, to- (4) (5) (6) (7) (8) (9) matoes, cucumbers, and sweet corn. 1928. Ohio Agr. Expt. Sta. Bul. 420. (10) COOPER, J. R. AND WATTS, V. M. Fertilizers for Irish potatoes, sweetpotatoes, tomatoes, muskmelons, and watermelons. Ark. Agr. Expt. Sta. Bul. 333. 1936. (11) DAVIS, F. L. Retention of phosphates by soils: III. Nature of phosphate retention of Virgin Hammond very fine sandy loam treated with Ca (OH) 2 and H'3PO 4 . Soil Sci. 60: 481-489. 1945. .Retention of phosphates by soils: IV. Solubility of phosphate retained by Virgin Hammond very fine sandy loam treated with Ca (OH) 2 and H3PO. Soil Sci. 61: 179-190. 1946. (12) (13) ENSMINGER, L. E. AND COPE, J. T., JR., Effect of soil reaction on the efficiency of various phosphates for cotton and loss of phosphorus by erosion. Jour. Amer. Soc. Agron. 39: 1-11. 1947. (14) (15) FISKE, C. H. AND SUBBAROW, Y. The Colormetic determination of phosphorus. Jour. Biol. Chem. 66: 375-400. 1925. FORD, M. C. The distribution, availability, and nature of the phosphates in certain Kentucky soils. Jour. Amer. Soc. of Agron. 24: 395-410. 1932. PHOSPHORUS STUDIES with. VEGETABLE CROPS 55 (16) GILE, PHILIP L. The effect of different colloidal soil materials on the efficiency of superphosphate. USDA Technical Bul. 371. 1933. HARTWELL, BURT L. AND DAMON, S. C. The degree of response of different crops to various phosphate carriers. R. I. Agr. Expt. Sta. Bul. 209. 1927. (17) (18) HAWKINS, A. Nutrient status of soils in commercial potato producin areas of the Atlantic and Gulf Coast: III. Plant responses to fertilization. Soil Sci. Soc. of Amer. Proc. 10: 252-256. 1945. (19) HESTER, J. B. AND SHELTON, F. A. Soil organic matter investigations upon Coastal Plain soils. Va. Truck Expt. Sta. Bul. 94. 1937. (20) . Phosphate fertilization on long-continued vegetable crop soils. Fertilizer Review 22, No. 2, pp 10-11, March-April, 1947. (21) LIELELAND, OMOND, BROWN, J. G., AND CONRAD, J. P. The phosphate nutrition of fruit trees: III. Comparison of fruit trees and field crop responses on a phosphate deficient soil. Proc. Amer. Soc. Hort. Sci. 40: 1-7. 1942. LLOYD, J. W. AND STRUBINGER, L. H. Fertilizing twenty-five kinds of vegetables. Ill. Agr, Expt. Sta. Bul. 346. 1930 Expt. Sta. Bul. 210. 1927. (22) (23) MACK, W. B. Fertilization of truck crops in rotation. Penn. Agr. (24) MATTSON, SANTE. Laws of soil colloidal behavior: and exchange. Soil Sci. 31: 311-331. 1931. V. Ion adsorption Soil (25) MIDGLEY, A. R. Phosphate fixation in soils-A critical review. Sci. Soc. Amer. Proc. 5: 24-30. 1940. in a varietal trial of corn. Jour. Amer. Soc. Agron. 25: 1933. (26) MOOERS, C. A. The influence of soil productivity on the order of yield 796-800. (27) PARKER, F. W. AND TIDMORE, J. W. The influence of lime and phosphatic fertilizers on the phosphorus content of the soil solution and of soil extracts. Soil Sci. 21: 425-441. 1926. of tomatoes. Va. Truck Expt. Sta. Bul. 80. 1933. (28) PARKER, M. M. The effect of different fertilizer ratios on the yield (29) , HESTER, J. B., AND CAROLUS, R. L. The effect of soil conditions on the growth and composition of certain vegetable crop plants as influenced by soil reaction. Proc. Amer. Soc. of Hort. Sci. 30: 452-457. 1933. (30) PEECH, M. Nutrient status of soils in commercial potato producing areas of the Atlantic and Gulf Coast: Part II. Chemical data on the soils. Soil Sci. Soc. Amer. Proc. 10: 245-251. 1945. (31) PIERRE, W. H. Phosphorus deficiency and soil fertility. U. S. Yearbook of Agriculture, 1938: 377-396. 1938. 56 ALABAMA AGRICULTURAL EXPERIMENT STATION (32) PLUMMER, J. K. The effects of liming on the availability of soil potassium, phosphorus, and sulphur. Jour. Amer. Soc. Agron. 13: 162-171. 1921. (33) SALTER, ROBERT M. AND BARNES, E. E. The efficiency of soil and fertilizer phosphorus as affected by soil reaction. Ohio Expt. Sta. Bul. 553. 1935. (34) ROSZMAN, C. A. Retention of Phosphorus by soil colloids. Soil Sci. 24: 465-474. 1927. (35) SCARSETH, G. D. AND TIDMORE, J. W. The fixation of phosphates by clay soils. Jour. of Amer. Soc. Agron. 26: 152-162. 1934. (36) (37) (38) (39) . The fixation of phosphates by soil colloids. Jour. of Amer. Soc. Agron. 26: 138-151. 1934. SCARSETH, G. D. The mechanism of phosphate retention by natural alumino-silicate colloids. Jour. Amer. Soc. Agron. 27: 596-616. 1935. SPURWAY, C. H. Some factors influencing the solubility of phosphorus in soil-acid-phosphate mixtures. Soil Sci. 19: 399-405. 1925. . The effect of the nature of the exchangeable bases upon the retention of anions by soils. Jour. Amer. Soc. Agron. 18: 497-515. 1926. (40) TRUOG, E. The utilization of phosphorus for agricultural crops including a new theory regarding feeding power of plants. Wisc. Agr. Expt. Sta. Res. Bul. 41. 1916. (41) The feeding power of plants. Sci. 56: 294-298. 1922. . The determination of the readily available phosphorus of soils. Jour. Amer. Soc. Agron. 22: 874-882. 1930. (42) (43) VOLK, G. W. Response to residual phosphorus of cotton in continuous culture. Amer. Soc. of Agron. 37: (44) WARE, L. M., BROWN, 330-340. 1945. Residual effects of OTTo, AND YATES, HAROLD. phosphorus on Irish potatoes in South Alabama. Hort. Sci. 41: 265-269. 1942. (45) (46) Proc. Amer. Soc. AND JOHNSON, W. A. Nitrogen requirements of different groups of vegetables. Proc. Amer. Soc. Hort. Sci. 44: 343-345. 1944. ZIMMERLEY, H. H. The effects of heavy applications of phosphorus on the interrelation of soil reaction, growth, and partial chemical composition of lettuce, beets, carrots, and snap beans. Va. Truck Expt. Sta. Bul. 73. 1930. (47) AND BROWN, B. E. Fertilizer ratios of ammonia, phosphoric acid, and potash for potatoes. Va. Truck Expt. Sta. Bul. 77. 1931. PHOSPHORUS STUDIES with VEGETABLE CROPS 57 APPENDIX APPENDIX TABLE 1. ABSORPTION OF PHOSPHORUS BY DIFFERENT CROPS ON DIFFERENT SOILS RECEIVING DIFFERENT RATES OF PHOSPHORUS Vegetable ege e Turnips Sweetpotatoes Collards Chinese Cabbage Tendergreen Okra Lima Beans Cabbage Squash Carrot Pepper Eggplant N. Z. Spinach Tomatoes, spr. Potatoes Beans Kale Beets English Peas Swiss Chard Radish Endive Onion Lettuce, spr. Lettuce, fall ,, Total P 2 O absorbed per acre by different crops on different soils receivir ig different rates of phosphorus 5 Pounds of P 2 Os per acre applied Pounds of P 0 5 per acre applied 0 per Pounds of PNorfolk acre applied to 2 5 soil to Eutaw soil to Cecil soil 0 40 80 120 160 0 80 160 240 320 80 160 240 320 0 Lb. Lb. Lb. Lb. Lb. Lb. Lb. Lb. Lb. Lb. Lb. Lb. Lb. Lb. Lb. Lb. 14.6 31.7 32.9 38.0 39.9 2.6 41.9 62.2 .7 27.2 44.8 48.5 52.3 74.7 64.8 20.6 24.4 30.4 28.4 30.9 26.2 37.9 41.2 43.8 44.2 9.7 26.1 27.6 32.2 38.4 1.8 15.6 23.0 26.0 25.1 .2 .2 19.1 31.1 37.8 37.2 29.9 42.1 47.0 44.9 4.2 18.8 29.4 32.7 32.3 1.0 25.5 35.0 32.9 37.1 29.8 38.5 42.9 .7 19.3 4.8 14.8 21.7 21.7 22.0 .1 27.9 38.5 45.5 46.1 .2 17.6 24.3 30.2 30.6 15.8 20.2 21.1 20.6 22.2 13.7 24.8 28.0 33.0 24.9 30.3 32.5 33.2 4.6 15.8 25.1 26.0 25.1 24.7 25.6 15.7 21.7 24.5 23.1 24.5 14.5 16.4 19.1 20.7 9.4 7.5 14.0 21.2 1.1 13.4 21.4 24.4 29.7 23.3 25.1 2.2 20.4 27.5 28.9 34.8 6.1 12.5 23.1 25.8 33.4 2.5 12.9 15.8 26.8 30.7 .3 9.0 21.3 26.3 31.4 7.1 11.3 16.6 20.8 22.0 7.8 17.3 22.0 27.0 29.9 2.8 10.8 19.8 27.4 27.7 2.1 13.8 16.0 21.6 23.5 5.1 11.4 13.7 17.3 16.6 6.9 16.0 19.8 24.7 29.1 5.2 13.5 17.3 17.9 18.6 1.4 6.1 8.8 10.0 12.8 3.8 16.8 14.8 22.1 23.1 2.6 8.4 11.5 12.9 13.8 .2 13.3 17.0 20.0 22.8 15.2 .2 11.5 14.4 17.4 16.2 12.1 14.7 .3 6.6 3.6 10.3 12.7 14.1 15.7 2.6 12.5 13.8 19.5 17.5 9.5 11.0 12.2 13.7 14.9 5.8 9.6 13.9 15.3 17.2 3.2 6.9 9.4 12.6 15.2 7.8 1.7 6.1 8.4 9.9 11.1 11.9 12.0 14.2 15.2 5.1 11.2 13.7 17.1 17.6 .4 4.3 8.6 11.8 12.4 .2 7.5 13.1 16.5 17.7 .1 6.8 10.4 12.31 13.9 1.5 5.0 6.4 8.1 10.2 .2 4.9 8.7 13.5 15.6 .3 6.6 12.9 14.9 16.9 1.5 3.9 5.7 7.4 8.2 2.9 8.7 10.2 12.3 13.2 1.3 6.1 10.4 12.5 13.8 .3 6.5 12.5 .5 4.1 8.1 11.5 14.3 21.0 10.6 .2 2.2 3.4 6.5 7.2 2.0 5.6 6.4 7.2 7.1 .7 7.5 10.1 9.7 9.3 .4 5.2 6.4 6.1 6.5 .3 2.2 4.4 6.5 6.9 .8 5.0 7.9 9.2 10.7 .1 3.0 7.7 9.1 11.7 .8 2.2 4.6 6.2 7.7 1.0 3.2 6.5 9.1 10.5 5.5 8.7 9.4 .5 2.8 .7 3.0 5.9 7.4 6.6 .3 2.1 3.7 6.2 6.7 .4 2.7 5.7 7.5 10.2 .4 1.9 2.9 3.7 4.2 .7 3.3 4.8 7.7 8.2 .4 2.5 4.1 5.4 6.1 149.5 288.1 376.9 424.6 447.2 103.6 383.9 495.8 596.2 622.3 42.4 265.8 406.2 491.6 539.0 2 .OO .- g C -- 4 C '.O 10 rn rn rn Z -4 -4 CA' -4 APPENDIX TABLE 2. YIELDS OF DIFFERENT CROPS ON DIFFERENT SOILS RECEIVING DIFFERENT RATES OF PHOSPHORUS APPLICATIONS 0 o .0 7O Mean yields per acre on different soils receiving different amounts of phosphorus Vegetable Pounds of P2 Os per acre applied to Norfolk soil 0 72 Beans, bu. 213 Beans, Lima, bu. 1,815 Beets, lb. 10,860 Cabbage, lb. 6,028 Carrots, lb. Chinese Cabbage, lb. 6,184 1,549 Collards, lb. 2,230 Eggplant, lb. 392 Endive, lb. 591 English Peas, lb. 410 Kale, lb. 756 Lettuce, spr., lb. 536 Lettuce, fall, lb. 4,471 N. Z. Spinach, lb. 3,669 Okra, lb. 1,205 Onions, lb. 5,257 Pepper, lb. 93 Potatoes, bu. 2,617 Radish, lb. 2,374 Squash, lb. 469 Sweetpotatoes, bu. 807 Swiss Chard, lb. 4,149 Tendergreen, lb. Tomatoes, spr., lb. 6,988 Tomatoes, sum., lb. 3,367 13,648 Turnips, lb. 1 o Pounds of P 2 0 5 per acre applied to Eutaw soil 1 0 53 167 286 2,860 8,346 1,489 256 2,333 1,568 1,301 251 3931 725 511 3,587 1,856 7,387 79 1,042 1,096 453 560 142 5,552 1,020 3,438 80 152 200 7,829 27,000 16,441 31,223 20,445 20,824 9,369 3,532 6,182 3,023 3,598 24,216 5,252 4,368 17,090 148 9,138 10,280 428 3,983 17,457 17,071 7,022 36,225 160 211 211 12,662 32,520 19,620 36,002 24,505 20,133 14,763 3,609 8,951 5,009 5,365 27,341 5,312 8,365 19,600 216 10,502 14,118 440 5,543 19,521 18,641 12,889 42,529 240 250 205 15,969 33,120 22,383 38,908 25,978 25,269 15,599 3,679 10,377 8,253 8,316 31,047 5,693 9,789 23,104 245 10,483 16,464 444 8,195 21,421 21,592 18,401 45,108 320 273 211 16,948 35,400 23,559 41,146 26,908 24,940 17,538 3,599 11,169 9,349 9,611 29,244 6,482 10,581 30,405 251 9,524 16,650 453 8,781 21,134 18,625 18,110 42,583 40 132 207 8,445 20,080 10,825 24,943 10,613 15,745 3,360 1,553 4,178 4,227 2,236 13,370 3,937 3,145 12,009 123 6,404 9,284 495 7,158 10,921 17,548 6,268 27,224 80 153 193 9,912 26,820 14,999 35,347 13,970 20,104 6,668 2,153 6,420 6,820 3,273 16,300 5,039 5,236 13,501 147 6,772 16,832 511 12,288 13,903 21,867 10,862 30,359 120 175 203 10,958 27,360 18,464 37,685 15,164 18,882 9,228 2,354 7,889 7,787 4,014 18,396 3,596 5,962 19,224 158 7,234 16,355 447 14,403 13,514 22,977 12,647 29,985 160 190 205 11,066 27,260 18,166 36,203 14,929 20,868 9,398 2,405 8,079 8,169 4,246 19,027 4,520 6,665 16,490 164 6,736 18,542 500 14,447 12,096 23,815 14,912 31,152 Pounds of P205 per acre applied to Cecil soil 1 0 80 160 240 320 10 96 447 1,280 3,234 962 172 519 181 571 132 755 506 261 1,443 876 2,015 45 573 8 227 643 161 634 455 835 66 145 9,352 19,380 11,671 26,731 14,098 9,229 4,831 2,780 5,939 4,309 3,103 16,415 3,386 4,067 14,639 123 6,025 6,661 376 10,559 12,246 10,684 5,728 26,858 98 170 16,322 27,500 20,005 34,087 18,755 11,846 10,690 3,780 7,324 8,192 5,027 18,172 5,245 7,243 17,511 165 6,523 11,124 392 15,380 14,148 17,180 8,613 31,672 136 190 16,316 28,880 22,300 34,118 19,247 16,020 11,979 3,640 7,705 10,444 6,386 22,575 4,994 9,481 19,318 180 6,400 12,063 436 17,905 15,746 18,408 8,009 35,106 148 201 16,624 30,020 22,809 31,077 19,441 18,409 14,987 3,887 8,525 13,599 6,914 17,584 4,676 9,306 20,467 196 6,733 12,806 399 20,738 15,308 17,576 12,084 34,207 -4 C m ,- m 0 In Pounds of P20 5 per acre per year, 1/3 to each of 3 crops. 60 ALABAMA AGRICULTURAL EXPERIMENT STATION 60 ALABAMA AGCUTRLEPIMNSAIO APPENDIX TABLE 3. STATISTICAL VALUES ON CROP YIELDS "F" values for differences in yields between rates of phosphorus applications Vegetable on different soils' Coefficient of variation _ Norfolk soil Bean Beans, Lima Beets Cabbage C. Cabbage Carrots Chard Collards Eggplant Endive Kale Lettuce, spr. Lettuce, fall Okra Onion Peas, English Pepper Potato Radish Spinach, N. Z. Squash Sweetpotato Eutaw soil 195** 6.0 84.6** 7.41 142.00** 144.6** 20.5* Norfolk soil Pct. 7.06 36** 43** 245** 4.28 . .94 15.34 59.12** 26* 36.88** 8.40 22.12* 10.93 5.69 7.28 68.82** 6.14 79.0** 1.32 107.0** Cecil soil 20.43 2 17.79 14.96 11.81 39.48 2 22.312 22.48 2 Eutaw soil Pct. 9.14 10.61 7.30 3.72 10.56 13.96 5.75 22.89 12.90 20.45 12.52 10.64 Cecil soil Pct. 15.40 9.18 11.52 5.78 9.40 20.49 10.22 44.25 2 2 2 9.0* 1.99 14.3* 1.35 23.46* 4.90 65.5** 3.77 61.61** 481.56** 19.3* 2.65 .70 13.15* 11.97* 19.20* 14.6* 604** 76.5** 12.7* 52** 22.84* 10.29 29.87 2 5.71 5.32 10.47 28.62'2 3.61 172.0** 14.0* 5.94 10.58 18.72 13.80 15.34 8.25 467.7** 4.59 6.26 43.89** 529.4** 17.0* 3.88 2.23 3.20 12.93 32.792 2 4.69 21.46 2 5.76 16.54 23.23* 1.06 4.83 2.30 2.1 4.09 37.3** 2.3 31.00** 14.29 18.88 .59 25.64 .97 15.95 8.65 25.46 2 16.18 7.24 18.80 32.44'2 17.72 34.92** 10.59* 17.48 Tendergreen Tomato, sum. Tomato, spr. Turnip 1 *Significant .44 16.19* .73 42.26** 5.6 1.47 84.9** 1.60 11.21* 57.95** 11.25 12.52 14.98 22.59 4.51 12.68 7.47 13.55 19.98 7.82 14.46 8.59 21.00 29.13 6.84 2 2 2Fiue at .05 degree level; **significant at .01 degree level considered too high for high confidence except when "F" values are highly significant. PHOSPHORUS STUDIES with VEGETABLE CROPS APPENDIX TABLE 4. STATISTICAL DATA ON CROP YIELDS 61 Vegetable Unit per acre Bushels Bushels Pounds Pounds Pounds Pounds Pounds Pounds Pounds Pou~tds Least significant difference between treatmients for different crops on different soils - 5 per cent level Norfolk soil Eutaw soil 38.28 31.61 2,320 3,482 1,605 8,844* 7,193 3,820 10,390* 3,591 2,578 534 567 8,789* 1,569 1,875 326 6,998* 52.53 1,468 7,465 70 2,165 9,952* 3,765 7,209 confidence in data. Cecil soil 26.31 7.18 3,128 3,558 2,800 1,877 Beans Beans, Lima Beets Cabbage Carrots Chard Chinese Cabbage Collards Eggplant Endive Kale Lettuce, spr. Lettuce, fall N. Z. Spinach Okra Onion Peas, English Pepper Potatoes Radish Squash Sweetpotatoes Tendergreen Tomatoes, spr. Tomatoes, -sum. Turnips *Differences Pounds Pounds Pounds Pounds Pounds Pounds Pounds Pounds Bushels Pounids Pounds Bushels Pounds Pounds Pounds Pounds 10.14 12.70 594 5,786 1,331 3,406 2,196 3,079 7,194 1,572 4,173 2,310 519. 5,222* 652316 819 5,772* 20.91 1,487 3,112 85 4,260 .6,198* 2,699 5,033 6,579 2,512 8,372* 2,192 1,360 2,436 1,590 10,433* 1,956 493 173 3,061 26.09 1,851 3,809 93 650 12,072* 3,528 2,158 too large to establish high 62 ALABAMA AGRICULTURAL EXPERIMENT STATION APPENDIX TABLE 5. STATISTICAL DATA FOR YIELDS OF TURNIPS IN RESIDUAL PHOSPHORUS PLOTS Soils"F" Statistical values for drop yields by year on different soils 1 values- Least significant Coefficient of difference difference between variation between treatments at .05 treatments 2 level Per Cent Pounds per acre Norfolk 1943 43773 14.40 1.063 12.25 11,5973,750 1944 1945 1946 1947 Eutaw 1943 1944 1945 1946 1947 Cecil 1943 1944 12.92 13.90 25.323 10.82 20.86 10.28 9,018 7,258 10,349 3 12.60 7.61 8.78 6.97 12.70 11.91 23.88 12.49 28.34 14.60 8,794 4,250 7,494 5,747 9,651 18.39. 24.413 10.62 4.73 4,371 6,797 9,990 5,523 9,126-1 1945 1946 1947 10.54. 15.91 10.26 .15.03 13.67 51.00 1'Data for yields in residual and phosphorus-maintenance plots used in determining statistical value. "F" values required -for significance at -.01 level = 7.00 and at .05 level 12 3.79. = 3Figures considered unsatisfactory for high confidence. APPENDIX TABLE 6. THEORETICAL RATE OF PHOSPHORUS APPLICATION FOR MAXIMUM YIELDS, FOR ZERO YIELDS, AND SLOPE OF LINE FROM YIELD AT ZERO RATE TO THEORETICAL MAXIMUM RATE FOR DIFFERENT VEGETABLE CROPS ON DIFFERENT SOILS' Phosphorus rate per acre Phosphorus rate per for zero yield for maximum yield Vegetable Norfolk Eutaw Norfolk Eutaw Cecil soil soil soil soil soil Lb. Lb. Lb. Lb. Lb. 164 40 336 49 392 Beans 344* 92 -283' 232 no pt. Beans, Lima 14 124 248 -4 320 Beets 35 124 240 18 248 Cabbage 32 160 304 288 -79 Carrots 12 120 -14 216 248 Chinese Cabbage -8 120 240 -9 240 Collards 11 120 248 384* 22 Eggplants 296 424* - 1 17 184 Endive 21 136 240 60 216 English Peas -4 108 288 256 -6 Kale -8 148 856* 848* Lettuce, spr. -7 352* 12 160 22 816* Lettuce, fall 21 216 10 136 232 N. Z. Spinach _171* 112 400* 232 -224* Okra 18 180 376* 320 31 Onions 136 27 960* 256 Pepper -103 312 160 296 85 62 Potato 112 216 31 224 18 Radish 144 264 10 13 248 Squash 112 92 -640* 224 no pt. Sweetpotatoes 140 416* 320 - 4 14 Swiss Chard 108 232 232 -- 21 10 Tendergreen 128 248 Tomatoes, spr. 224 -26 42 120 224 232 43 15 Turnips 'Results based on annual applications of phosphorus (P2O5), with three crops Figures considered unsatisfactory for high confidence. -i acre Cecil soil - Slope of line between yield at zero rate and yield at maximum rate Norfolk Eutaw Cecil soil soil soil Pet. 14 -3 27 21 18 30 31 29 23 22 26 25 22 22 5 19 22 Lb. 14 --141* -4 -9 - - 20 8 7 12 .4 25 11 14 131 38 11 22 - - -6 - Pet. 19 7 25 30 16 30 33 28 24 25 26 15 15 35 8 19 10 Pct. 20 12 33 31 24 41 34 20 20 28 29 15 21 .44 28 24 18 20 38 33 28 25 -3 .4 -2 18 -111* 19 23 28 -- 10 -8 31 35 35 34 29 -5 22 18 35 35 -9 being grown per year on same area. 46 21 11 24 24 27