A STUDY or THE UTILIZATION BI OATS or PHOSPHORUS FROM THE son AND FROM VARIOUS PHOSPHA'I'IG FERTILIZERS _ AS MEASURED BY TRACER TECHNIQUES by WALLACE B. BRAMMELL, JR. A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Soil Science 1952 THESIS “ ~ / .. / p r' ‘:‘ a: /E4'" r, "v‘ "' 5.1, .1,’ ACKNOWLEDGMENT The author wishes to express his sincere appreciation for the assistance and advice given him by Dr. Kirk Lawton during the course of this investigation and in the prepara- tion of the manuscript. He is also indebted to Dr. L. M. Turk for his criticism of the manuscript. The writer gratefully acknowledges the advice and assist- ance of Dr. A. E. Erickson in the radioisotope measurement procedure. *7 He also extends his sincere thanks to Professor L. S. Robertson, Jr. for his assistance with the field-plot work. The various phoSphate fertilizers tagged with radio- active phosphorus were supplied by the Bureau of Plant Indus- try, Soils, and Agricultural Engineering of the United States Department of Agriculture. l“f“-‘{\‘L‘4 L) ’1. .‘ a ~.,' _. If 1” ii TABLE OF CONTENTS LIST OF TABLES O 0 O O O O O O O O O O O O O 0 0 LIST OF FIGUIES O O O O O O O O O O O O O O O O I. II. III. IV. VI. VII. VIII. IX. IN].1 RODUCTION O O O O O O O O O O O 0 O O 0 REVIEW OF LITERATURE . . . . . . . . . . . EXPERIMENTAL MATERIALS . . . . . . . . . . AeSOileeeeeeeeeeoeeeeoe BePhosphatGSeeeeeeeeeeeeee EXPERINENTAL I‘dETHODS O O O O O O O O O O O A. Field-plot Experiment . . B. Laboratory Investigations . . . . . . 10 Plant material 0 e e e e e e e e e 2. 8011 O O O O O O O O O O O O 0 O O 3. Phosphates . . . . . . . . . . . . RESULTS 0 O 0 O O O O 0 O O O O O O 0 O O A. Yield 0 O O 0 O O O O O 0 O 0 B. Phosphorus Utilization by the Plant . 1. Total phosphorus . . . . . . . . . 2. PhOSphorus from fertilizer . . . . 5. Phosphorus from soil . . . . . . . 4. 5. 6. Fraction of plant phosphorus derived from fertilizer . . . . . Fraction of applied phosphorus recovered by crop. . . . . . . Summary of statistical evaluations of phosphorus utilization . . . C. Laboratory Experiments with Phosphates l. 2. Fixation Stlldies e e e e e e e e e SOlubility Studies 0 e e e e e e 0 DISCUSSION 0 O O O O O O O O O O O O O O 0 SUMMARY MMNCES O O O O O O O O O O O O O O O 0 APPENDIX 0 O O O O O O O O O O O O O O O 0 iii Page iv vi 10 10 10 Table I. II. III. IV. V. VI. VII. VIII. IX. XI. XII. XIII. XIV. XV. LIST OF TABLES Page Some Physical and Chemical PrOperties of the Soils Used in this Experiment . . . . . 11 Some Physical and Chemical Properties of the Phosphatic Fertilizers Used in this Experiment 0 e e e e e e e e e e e e e o 15 Particle Size Distribution of the Phos- phates O O O O O O O O O O O I O O O O O O O O 14 Yields of Total Dry Matter from Radio- active Plots at Each Sampling Period . . . . . 52 Yields of Total Dry Matter from Non- Radioactive Plots at Harvest . . . . . . . . . 35 Concentration of Total Phosphorus in Dry Plant Material in Percent . . . . . . . . 35 Concentration of Tbtal Phosphorus in Dry Plant Material in Pounds per Acre . . . . . . 57 Concentration of Fertilizer Phosphorus in Dry Plant Material in Percent . . . . . . . 42 Concentration of Fertilizer Phosphorus in Dry Plant Material in Pounds per Acre . . . 44 Concentration of Soil Phosphorus in Dry Plant Material in Percent . . . . . . . . . . 49 Concentration of 8011 Phosphorus in Dry Plant Material in Pounds per Acre . . . . . . 51 Percent of Plant Phosphorus Derived from Fertilizer e e e e e e e e e e e e e e e 56 Percent of Applied Phosphorus Recovered by Crop e e e e e e e e e e e e e e e e e e e 65 Summary of Statistical Evaluations of Phosphorus Utilization as Measured by Several Criteria 0 e e e e e e e e e e e o e e 67 Fixation of the Various PhOSphates by Brookston Soil as Measured by the Spurway Reserve Extraction Method . . . . . . 75 iv Table XVI. XVII. LIST OF TABLES (continued) Page Extraction of Phosphorus from the Various Phosphates by the Spurway Reserve Method . . . 75 Comparison of Solubility of the Phosphates in Different Solvents as Measured by Phos- phorus Content of the Solutions . . . . . . . . 79 LIST OF FIGURES Figure l. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Statistical Arrangement of the Experi- mental Plats e e e e e e e e e e e e e e o e The Effect of Source of Fertilizer Phos- phate on the Total Phosphorus Composition Of the Oat Plant 0 e e e e e e e e e e e e 0 Rate of Uptake of Phosphorus by the Crop as Related to the Source of Fertilizer Phosphate e e e e e e e e e e e e e o e e e The Effect of Source of Fertilizer Phosphate on the Fertilizer Phosphorus Composition of the Oat Plant . . . . . . . . . . . . . . Rate of Uptake of Fertilizer Phosphorus by the CrOp as Related to the Source of Fertilizer Phosphate e e e e e e e e e e e e The Effect of Source of Fertilizer Phos- phate on the Soil Phosphorus Content of the Cat Plant e e e e e e e e e e e e e e 0 Rate of Uptake of Soil Phosphorus by the Cr0p as Related to the Source of Ferti- lizer Phosphate e e e e e e e e e e e e e 0 Relationship Between Source of Fertilizer Phosphate and Percent of Plant Phosphorus Derived from Fertilizer . . . . . . . . . . Composition of Plant Material and Plant Phosphorus with Respect to Source of Fert- ilizer Phosphate and Age of the Plant . . . Phosphorus Content of the Oat Crop with Respect to Source of Fertilizer Phosphate and Age Of the Plant 0 e e e e e e e e e e 0 Relationship Between Source of Fertilizer Phosphate and Percent of Applied Phosphorus Recovered by the Crop e o e e e e e e e e 0 vi Page 16 56 38 43 45 50 52 57 59 60 65 INTRODUCTION Phosphorus is applied to soils in any of a number of materials ranging from the manures to highly concentrated commercial fertilizers. The availability to plants of the phosphorus in these is known to vary. It is of considerable economic importance to both fertilizer producer and farmer to have an evaluation of the relative availability to crepe of the phosphorus in the various fertilizer materials. The radioactive isotOpe of phosphorus, P32, has offered a new approach to this problem. Radioactive phosphorus was first used in soil and fert- ilizer studies around 1937. However, no really intensive investigations were possible prior to the present post war period because inadequate amounts of P52 were available. Following the war, relatively large quantities of P52, pro- duced by the atomic pile, became available for experimentation with growing plants. Since 1946, when the first cooperative study using P32 tagged phosphate fertilizers was organized.by the_New York and North Carolina Agricultural Experiment Sta- tions and the Division of Soils, Fertilizer, and Irrigation of the'United States Department of Agriculture, cOOperative work with.radioactive phosphorus has expanded tremendously. At the present time many of the state agricultural experiment stations are participating, especially on a regional basis. Other agencies supporting these cOOperative field experiments are the Fertilizer Industry Committee on Radioactive and Tag- ged Element Research, the Atomic Energy Commission, and the Bureau of Plant Industry, Soils, and Agricultural Engineering. The Regional Soil Research Committees are responsible for the overall planning and coordination of the work in each.land- grant college region. This is accomplished for the most part, in regional phosphorus work conferences held each fall. Before the advent of tracer methods, evaluation of the availability of various phosphatic materials depended wholly upon measurements of yield differences and.upon comparisons of the total phosphorus content of plants grown on fertilized and unfertilized soils abnormally low in content of soil phos- phorus. It was necessary to confine fertilizer availability studies to the relatively infertile soils in order to obtain yield differences sufficiently large to be significant. The validity of applying results obtained on these soils to more fertile soils was, therefore, cpen to question. The use of radioactive phosphorus makes it possible to measure more exp actly fertilizer phosphorus uptake on the more fertile soils, and thereby evaluate the relative availability of phosphate materials under conditions of higher fertility. The use of the radioactive tracer technique to measure phosphorus availability differences is based on the assumption that the rate and amount of phosphorus uptake from the ferti- lizer by the plant is a measure of the availability of the fertilizer phosphorus. This assumption is considered valid whether there is a yield response or not. That is, the tracer technique is considered a somewhat more sensitive method of measuring availability than the yield measurement, although the final test of the value of a phosphorus compound as a fert- ilizer material should be made under conditions of yield response. The availability of different phosphorus compounds to plants is usually measured by: (a) the percentage of plant phosphorus derived from the fertilizer. (b) the percentage recovery of the fertilizer phosphorus applied. (c) the yield response attributable to differences in the phosphate carriers. Using radioactive phosphorus, it is now possible to measure the percentage of plant phosphorus derived from the fertilizer. This overcomes the main weakness of the earlier work on phos- phorus availability, which lay in the fact that it was impos- sible to tell what portion of the phosphorus absorbed by plants was derived from the fertilizer applied at planting time. Knowing the percentage of phosphorus derived from the fertili- zer, the yield, and the amount of fertilizer applied to the soil, the percentage recovery of fertilizer phosphorus may be calculated. The yield response is determined in the usual way. For a comprehensive discussion of the basic concepts involved in soil and fertilizer studies with radioactive phosphorus, reference may be made to an article by Hendricks and.Dean (5) and to a book by Kamen (7). The work reported herein was part of a state-federal co- Operative project undertaken in Michigan in the Spring of 1950. The primary purpose of this research was to study the utilization by the cat plant of phosphorus derived from dif- ferent radioactive phosphatic fertilizers and from the soil. To this end, a field plot experiment was laid out in which the six phosphates under investigation were drilled with the cats. Plant samples were taken at intervals during the sea- son and were analyzed for content of total phosphorus and radioactive phosphorus. From the weights of the individual samples, an estimate of yield at the various sampling periods was obtained. From these analytical data, calculations were made which furnished the information desired regarding phos- phorus utilization. For the purpose of better characterizing the soil and the phosphates used, several physical and chemi- cal tests were made on them in the laboratory. There were two secondary purposes of this study. The first was to attempt to explain the differences found in the availability, as measured by the plant, of phosphorus in the various phosphatic materials. The second was to evaluate the relative effectiveness of the various criteria which may'be used in measuring availability differences. REVIEW OF LITERATURE In the past the recovery of phosphate fertilizer by‘a crop has generally been determined.by a comparison of the uptake of phosphorus by the fertilized and unfertilized craps. The extra phosphorus in the fertilized crop has been taken as the quantity comdng from the fertilizer. One of the main weaknesses of the method is the assumption that the phosphorus taken up by the plant was the same phosphorus add- ed in a specific fertilizer treatment. The addition of phos- phorus stimulates plant growth and hence it has been considered possible that the increased growth.of the fertilized crop will use more soil phosphorus that the unfertilized crap. If this occurs, the increased amount taken up by the fertilized crop would not represent the amount of phosphorus which came from the applied fertilizer. In an experiment conducted by Spinks and Barber (16) to test this possibility, the recovery of applied phosphorus as measured by the tracer method was compared with.the recovery as measured by the "difference" method. It was found that results obtained by the latter method were in error by almost forty percent. It was further found that for light applications more soil phosphorus may be taken up, but for very heavy appli- cations, there may be less. The authors conclude that while the extent of the error'may vary with the soil and the season, the old "difference" method of determining fertilizer uptake is unsound and can lead to large errors. Results of a very different nature were obtained by White, Fried, and Ohlrogge (21). They calculated the percent utilization of applied phosphorus by the two methods and found a very close correlation. In view of the questionable validity of the results of earlier investigations of phosphorus uptake by plants, this review of the literature is confined to the recent work in- volving tracer technique. As previously mentioned, most of the work on the utilization of phosphorus employing tracer technique has been done since 1946. The greater part of this work was of the cooperative type described in the introduction. 0f the relatively large number of these cooperative experiments that have been undertaken since that time, very few have been published. Instead, the data have been made available to the cooperators in the form of compilations, summaries and pro- gress reports. It is from these sources that most of the following information was obtained. This review is concerned only with those experiments which involved comparison of sources of phosphorus on oats. All of these were field-plot experiments. In Wisconsin, Starostka, Jackson, and Attoe (19) found that ordinary superphosphate was the most effective source for oats, followed in order of decreasing effectiveness by calcium.metaphosphate, alpha-tricalcium phosphate, and dical- cium phosphate. Jackson, et al. (6), working in Wisconsin, found that the six phosphates compared ranked as follows in order of decreasing yield response: calcium.metaphosphate, ordinary superphosphate, monoammonium phosphate : ammoniated super- phosphate = alpha-tricalcium.phosphate, dicalcium phosphate. The various phosphates ranked as follows in order of de- creasing average percentage of total plant phosphorus derived from.the fertilizer: monoammmnium phosphate, ordinary super- phosphate 8 ammoniated superphosphate, alpha-tricalcium phosphate - dicalcium phosphate, calcium metaphosphate. Kaufman, Marriott, and Jackson (8), also working in Wisconsin found ordinary superphosphate was far more available to the plant, especially in the early part of the growing season, than calcium metaphosphate, fused tricalcium phos- phate, or dicalcium phosphate. Ammoniated superphosphate was slightly more available than ordinary superphosphate. The nitric acid process dicalcium phosphate was nearly as available as the ordinary superphosphate but much.more avail- able than dicalcium phosphate with nitrogen or ordinary super- phosphate with no nitrogen added. Ammonium.phosphate proved to be the most available form of phosphate carrier. The order of availability was summarized as follows: Ammon- ammon- superphos. nitric super- ca-meta- ium iated mixed with phos- phos. phos. phos- > super 2 amm. nit- Z phate > without’Fugedhtri- hos. rate n ni- ca - os. phate P grggen Dica .phos. (0-12-12)(+ nitrogen) In a group of experiments in Iowa, Black (1) determined the relative availabilities of various phosphates on four different soil types. 0n Clarion loam and Monona silt loam, ordinary superphosphate and calcium metaphosphate were found to be more available than dicalcium phosphate and alpha-tri- calcium phosphate. On Marshall silt loam, however, ordinary superphosphate and dicalcium phosphate were superior to calcium metaphosphate and alpha-tricalcium phosphate. The order of availability on Seymour silt loam was also different from that on the Clarion and Monona soils. Here, the materials ranked as follows in decreasing order of availability: di- calcium.phosphate, alpha-tricalcium phosphate, ordinary super- phosphate, calcium.metaphosphate. Pesek (12) compared these same phosphates on three other Iowa soils and reported that in all cases ordinary superphos- phate was the most effective source and fused tricalcium.the least effective as measured by yield of total dry matter and ‘uptake of fertilizer phosphorus at the boot and hard dough stages. Ca1cium.metaphosphate and dicalcium phosphate were intermediate. The effectiveness of calcium.metaphosphate was greater than that of dicalcium phosphate in the experiments on calcareous Ida silt loam and acid Grundy silt loam but was smaller than that of dicalcium.phosphate in the experiment on acid Seymour silt loam. The relative differences between fertilizers as measured in final yield were generally smaller and of a lower level of significance than were the differences in yield of total dry matter and.uptake of fertilizer phos- phorus at the boot and hard dough stages. In another experiment by Pesek (13) the following year, various phosphate materials were compared. The order of decreasing availability found was nitric phosphate (12-52-0), concentrated superphosphate, nitric phosphate (17-22-0), calcium metaphosphate (-40 mesh), calcium metaphosphate (-10 mesh), dicalcium phosphate. Stanford and Nelson (18), also working in Iowa, found that ordinary superphosphate was more available than calcium metaphosphate, dicalcium.phosphate, and alpha-tricalcium phosphate. Lawton, Kawin, and Robertson (9) in an experiment in Michigan compared six different phosphates and found the following order of decreasing availability: ammonium phos- phate, ammoniated superphosphate, ordinary superphosphate, dicalcium phosphate, calcium.metaphosphate, fused tricalcium phosphate. - 10.. EXPERIMENTAL MATERIALS A. Soil The soil used in this experiment was a Brockston clay loam (yellow subsoil phase), a type well-suited to the growth of oats when artificially drained. The Brookston series is described by Veatch (20) as loams and clay loams, with dark-colored plow soil, underlain by wet, mottled gritty clay to depths of several feet. The organic matter content and fertility are high; the clay is highly retentive and is generally moist or wet. These soils are non-acid or only slightly so; the carbonates may be leached out to depths of thirty inches or more. They are found on level plains and in valleys, and are wet or semi- swampy. The original vegetation was hardwood forests con- sisting of elm, soft maple, ash, shagbark, hickory, basswood, swamp white oak, etc. These soils have high value for hay, corn, small grains, beets, beans, and alfalfa when artificial- ly drained. Several of the physical and chemical prOperties of this soil are presented in Table I. B. Phosphates The six phosphatic fertilizers used in this experiment were materials supplied by the United States Department of Agriculture, Beltsville, Maryland. The kinds used were ordinary superphosphate, calcium metaphosphate, dicalcium -11- TABLE I S HE PHYSICAL AND CHEMICAL PROPERTIES OF THE SOIL USED IN THIS EXPERIMENT PrOperty Value Mechanical analysis (hydrometer) greater than 50 microns 44.5 % 5 to so microns 24.3 % 2 to 5 microns 5.3 % less than 2 microns 26.0 % Organic matter content 6.1 % Cation exchange capacity 24.80 m.e. per 100 gms. Exchangeable calcium 18.14 m.e. per 100 gms. Exchangeable magnesium 4.29 m.e. per 100 gms. ,Exchangeable potassium 0.46 m.e. per 100 gms. Calcium: magnesium ratio 4.2:1 pH (glass electrode) 6.58 Available phosphorus Spurway, reserve method 137 lbs. P per acre-6 in. Bray, total available 190 lbs. P (per acre-6 in. phosphate, ammonium phosphate, alpha-tricalcium phosphate, and ammoniated superphosphate. Each of these was furnished in both the radioactive and the non-radioactive form. Except for the presence of the radioactive isotOpe of phosphorus, P32, each radioactive phosphate was identical with the corres- ponding non-radioactive phosphate. The specific activity of each radioactive phosphate was reported as 0.2 millicuries per gram of P205. The pile date for each.material was April 5, 1950. Data relative to certain physical and chemical character- istics of the various phosphates, furnished by the labora- tories of the Bureau of Plant Industry, Soils, and Agricultural Engineering, are given in Table II. 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"H ouwoummum memos ommfie museums moment mAMAWAHAo m.e.mAe m .m .m..HAo o.o.m.HAe . o.m.m..H.Ae I I on M. M. .m .HAe I on 8 A. q a A A al. .0 o o mAH o o «AH .o.z .o.z M. o mAH o n mAH . eeo.omua see.eoua oo.Hnm om.Hum *eo. omum sen. oou m mm\o one. oum. o.H one ououm .euH .mUM1H oue .I:_I .m.mum .ouH. oneuH o JAo one ..mum.m .m...o.m-H m. ammo. .HAo ..o. .er I o JAo I. .m-mumnH .m....m. ..m HAo m. m. m. HAo o .o M.HAe M .M .HAo o .M .o.HAm o. m .M.MAo o. o. m .m.HAe M. M. M. MAe M.o.MAH J. HAN oAH M .M. M. MAe M. M. MAH eeo.oHnm *eo.mo.m .Moo.oum weso.snm *eo.oH-m wee.ooum m\o Aucooaomv Apoooaoav A. M\.mgqv Aucooaomv A. M\.monv Apoooaomv sumo done he .paom Scan pcon cH pcoHa 2H pcmHa :H pceHM nH onHossm oonopooon ooeHnoo A HHom m HHoo m .onom A .pth .onom A ogon Hm Mm Qmm9m4m5 md BZdflm ado HEB Mm ZOHBMNHHHBD mDmommwomm mo mZOHBMDH¢>M_Q¢UHBmHBHx memes -59- highest "F" value and reveals the greatest number of avail- ability differences. The most commonly used criterion for determining relative availability, the percent of the plant phosphorus which.was derived from the fertilizer, is seen to be of slightly less value at all sampling periods, as indicated by the consistently lower "F" values. By the former criterion, availability dif- ferences are revealed at the first three sampling periods which were not detected by the latter method: On June 2, ammonium phosphate was found to be more available than ammoniated super- phosphate at the five percent level; on June 22, ammonium phosphate was seen to be more available than ordinary superphos- phate at the five percent level and ordinary superphosphate more available than dicalcium phosphate at the one percent level; and on July 4, ammoniated superphosphate was found to be more available than ordinary superphosphate at the one percent level. Another frequently used measure of fertilizer phosphorus availability is the percent of applied phOSphorus recovered by the crOp. Comparison of this data in Table XIV with that for the two previously mentioned criteria shows that at the first two sampling periods this criterion is the least discriminating of the three. At the third and fourth sampling periods the three criteria were of about equal effectiveness. The "F” values for the pounds of fertilizer phosphorus per acre are the same as those for percent recovery because the -70- latter are based on treatment values of the former criterion divided by a constant--the pounds of phosphorus applied per acre. The former criterion, therefore, is as effective as the latter in availability comparisons. On soils which give a yield response to phosphorus appli- cations, comparison of yields obtained.with different phos- phatic materials is a good method of evaluating their availa- bility. In this experiment, however, as previously mentioned, there were no yield differences attributable to fertilizer phosphorus because of the high level of native phosphorus in the soil. Inspection of the data in Table XIV for the total phos- phorus in the plant shows that the "F" values are relatively very low, and there are considerably fewer significant treat- ment differences than were revealed by the criteria having the highest "F" values. Therefore, it is apparent that the amount of total phosphorus in the plant would not be an adequate measure of fertilizer phosphorus availability. The percent of fertilizer phosphorus in the plant tissue and the percent of the plant phosphorus which.were derived from the fertilizer were shown above to be the best criteria for evaluating the relative availability of fertilizer phos- phorus. It is worthwhile to observe how their "F" values decrease steadily throughout the growing season. This trend shows that the availability differences become progressively less pronounced with time. In fact, comparison of the treatment -71- differences for the various sampling dates shows that in several instances they have disappeared altogether by the last sampling date if not before this time. It is interesting to speculate on availability relation- ships which might have existed prior to the first sampling date. As indicated by the increasing "F" values, the avail- ability differences became progressively greater between July 25 and June 2 with decreasing age of the plant. If the period of 43 days between planting and the first sampling (June 2) is considered, it is probable that the availability differences were very large during the first few days after seedling emergence. This is significant in view of the well- recognized need of young plants for an adequate supply of quickly soluble phosphate after the reserve in the seed has been used up. At this critical stage, it is possible that the less available phosphates might not be able to meet this need on soils deficient in available native phosphorus. C. Laboratory experiments with phosphates Fixation studies. The laboratory extraction procedures used in this experiment to determine the level of available phosphorus in the soil have been found by other workers to correlate well with yield and response measurements. It would appear, therefore, that these procedures could also be used to measure the capacity of soils to fix fertilizer phosphorus in unavailable form. .-J r *"Y" ov r'. -72- The reserve extraction method of Spurway and Lawton (17) was used in the present study in an attempt to learn whether the various phosphates differ in the degree of fixation which occurs when they are added to the soil. In addition to the 60 pound rate, fixation was also studied at a 360 pound rate. This higher level was chosen arbitrarily as it was thought that this would more nearly represent the condition existing with band application in the field. The results are presented in Table XV. It should be noted that the values given do not represent percent fixation but rather percent unrecovered phosphorus. This distinction is made as a close study of the data leads to the conclusion that these figures include not only fixed phosphorus but also some undissolved fertilizer phosphorus not recovered by the extractant. There are several reasons for believing this to be true. First, inspection of the data shows that in every instance the percent of unrecovered phosphorus is greater at the 360 pound rate than at the 60 pound rate. If the figures repre- sented only the phosphorus actually fixed, those for the higher rate of application would be expected to be the same as, or even lower than, the corresponding ones at the lower rate. Second, the data show that in general the percent of unrecover- ed phosphorus is highest for those phosphates having the lowest percentage of their total P205 content in the water-soluble form and vice versa. (see Table II, page 13) This is the reverse of what would be expected if fixation only were involved. -75- TABLE XV FIXATION OF THE VARIOUS PHOSPHATES BY BROOKSTON SOIL AS MEASURED BY THE SPURWAY RESERVE EXTRACTION METHOD Percent phosphorus not recovered when applied at the rate of Source of 60 pounds 360 pounds _ n _ n phosphate P205/A 6 P20 A 6 Ordinary superphosphate 46.7 57.0 Calcium metaphosphate 46.7 93.9 Dicalcium phosphate 33.4 50.6 Ammonium phosphate 41.7 44.7 Alpha-tricalcium phosphate 58.4 65.0 Ammoniated superphosphate 33.4 36.6 -74- Since dissolution has to occur before fixation can take place, the more slowly available materials, such as calcium metaphosphate and alpha-tricalcium phosphate would be ex- pected to become fixed less rapidly than the highly available forms such as ammonium phosphate and ammoniated superphosphate. Phosphorus fixation is thought to be due to physical, chemical, and biological processes which cause the applied phosphorus to become unavailable to plants. Since dissolution of the phosphorus has to occur before these processes can operate, any undissolved phosphorus would not be subject to fixation and could not be considered as fixed even though it would be unavailable to the plant at that time. Therefore, in order to get a "true" measure of fixation it is necessary that the extracting solution recover all of the undissolved phosphorus in addition to any other portion of the phosphorus which was not fixed. Since the data of Table XV indicated that the extractant had not removed all of the undissolved phosphorus, an experiment was set up to check on its ability to do so. The results are given in Table XVI. Inspection of the data in Table XVI shows that all of the phosphorus from phosphates equivalent to the amounts ap- plied at the 360 pound rate in the fixation experiment was not recovered by the extracting solution. The percent recovery was especially low from alpha-tricalcium phosphate and calcium metaphosphate, only about 55 percent of the phosphorus having been recovered from the former material and about seven percent -75- TABLE XVI EXTRACTION OF PHOSPHORUS FROM THE VARIOUS PHOSPHATES BY THE SPURWAY RESERVE METHOD Percent recovery of phosphorus Whole Whole Whole 200-270 phos. phos. phos. mesh stirred stirred stirred stirred 1 min. 1 min. 30 min. 1 min. Source of gravity vacuum vacuum vacuum phosphate filt. filt. filt. filt. Ordinary superphosphate 71.2 87.9 92.0 76.8 Calcium metaphosphate 6.62 7.16 7.16 5.63 Dicalcium phosphate 91.6 96.1 100.0 96.2 Ammonium phosphate 106.8 90.0 81.8 63.5 Alpha-tricalcium phosphate 5208 57.2 88.0 80.9 Ammoniated superphosphate 81.0 79.7 88.0 76.8 from the latter. Since in the fixation experiment a part of the unrecovered phosphorus shown in Table XV was probably truly fixed, the combined quantities of undissolved and un- fixed phosphorus subject to removel by the extracting solution were most likely considerably lower in some cases than the amount initially applied. Therefore, the percent recovery of this smaller remaining fraction might have been somewhat higher than is indicated in Table XVI. Nevertheless, it appears unlikely that the recovery was complete in any case in view of the previously discussed evidence in Table XV. It will be noted in Table XVI that the extractions were carried out under four different sets of conditions. In the first procedure, the whole (unscreened) material was stirred with the extractant for one minute and filtered by gravity. This was the standard procedure used in the fixation experi- ments. Since the amount of fertilizer and the volume of ex- tractant were three times as large as in the fixation experi- ments, it was felt that the longer filtration time required might give erroneously high recovery values. To test this possibility, the extraction was repeated on another set of samples, followed by vacuum filtration. For some reason, the recovery was higher rather than lower in most cases, but the difference was not very large. In the third set of extractions, the object was to deter- mine the effect of longer extraction time on the percent recovery. It was found that thirty minutes extraction gave a -77.. considerable increase in recovery with all materials but ammonium phosphate and calcium metaphosphate. The former material showed a decrease in recovery, probably attribu- table to experimental error, and the latter only a slight increase. Even this long extraction, however, failed to completely recover all of the phosphorus. The one exception to this was dicalcium phosphate, from which the recovery was apparently complete. In the fourth set of extractions, the phosphates were screened to obtain fractions of equal particle size. The purpose was to eliminate the particle size variable in order to attempt to evaluate the effect of inherent solubility of the various materials on the percent recovery. Comparison of these results with those for the second set of extractions in which.the unscreened.material was used shows that the results are quite inconsistent. This may have been due to a difference in the phosphorus content of the fine particle size fraction as compared with that of the unscreened material. The incomplete recovery evidenced by the data of Table XVI furnishes the third reason for believing that the figures in Table XV include undissolved phosphorus in addition to fixed phosphorus. Since it isn't possible to determine how much of the unrecovered phosphorus in Table XV was actually fixed, it is impossible to evaluate differences in the degree of fixation of the various phosphatic materials. -78- On the basis of the relatively high recovery values for ammonium phosphate and ammoniated superphosphate shown in Table XVI and the fact that the percent of unrecovered phos- phorus at the two rates agreed rather closely as shown in Table XV, it appears likely that these values in Table XV for the two ammoniated phosphates represent the approximate amount of actual fixation. Therefore, it is probable that the percent fixation for the less soluble materials was somewhat lower than 35 percent. Solubility studies. The purpose of these studies was to determine the relative solubility of the different phosphatic fertilizers in water and carbonic acid. As previously des- cribed in the section on experimental procedures, phosphates were added to the flasks on an equivalent total P205 basis in amounts estimated to be sufficient to give saturated solutions. This was done in an attempt to simulate conditions which may exist in the field in close proximity to the bands of fertili- zer. The relative solubility of the different materials was determined by measuring the phosphorus concentration of the solutions and comparing the values obtained. The results are shown in Table XVII. The most significant point brought out by these data is that the phosphate materials fall into two distinctly different groups on the basis of solubility in water and carbonic acid. Ordinary superphosphate, ammonium phosphate, and ammoniated superphosphate were highly soluble while calcium metaphosphate -79- TABLE XVII COMPARISON OF SOLUBILITY OF THE PHOSPHATES IN DIFFERENT SOLVENTS AS MEASURED BY PHOSPHORUS CONTENT OF THE SOLUTIONS elemental phosphorus Source of Carbonic phosphate Water (A) Water (B)* Acid** Ordinary superphosphate 22,500 40,000 57,500 Calcium metaphosphate 28.0 67.5 155 Dicalcium phosphate 150 160 520 Ammonium phosphate 56,000 48,000 56,000 Alpha-tricalcium phosphate 18.4 18.4 89.6 Ammoniated superphosphate 10,400 14,400 14,000 e 50 percent more phosphate added to solution (A) ##002 bubbled through solution (B) for 10 minutes -80- dicalcium phosphate, and alpha-tricalcium phosphate were only slightly soluble. The order of decreasing solubility in the highly soluble group was ammonium phosphate, ordinary superphosphate, ammoniated superphosphate; in the slightly soluble group it was dicalcium phosphate,calcium metaphosphate, alpha-tricalcium phosphate. Comparison of these results with the data for water- soluble phosphorus in Table II (page 15) shows that the order of solubility is the same in both cases as would be expected. -81.. DISCUSSION It was shown in Table V that there were no significant differences either in the total dry matter yields or in the grain yields produced by the various phosphate materials. In Table IV, the data showed that the only significant differences between fertilizers in dry matter yields produced occurred at the third sampling period. This almost complete lack of dif- ferential yield response to the various phosphates was undoubt- edly due to the high level of available native phosphorus in the soil. This, as may be seen in Table I, amounted to 157 pounds of elemental phosphorus per acre as determined by the Spurway reserve method. With this test, according to workers at the Michigan Experiment Station, the critical level on slightly acid heavy-textured soils such as was used in this experiment is believed to be about 70 pounds per acre. Soils containing less than this amount of acid extractable phosphorus can be expected to respond to fertilization, while those con- taining more usually do not. Table I also gives the available phosphorus content of the soil as measured by Bray's method for measuring "total available" phosphorus. This is seen to be equal to 190 pounds of elemental phosphorus per acre. Data reported by Bray (5) indicate that a soil containing 54-61 pounds per acre of "total available" phosphorus should be capable of a yield equal to 98 -82.. percent of that possible with adequate phosphate. This means that if the soil contained more than 61 pounds per acre, little or no response to phosphorus fertilization could be expected. Since the soil used in this experiment was found to contain levels of available phosphorus two to three times higher than the critical amounts indicated above, it is obvious that yield differences due to differential utiliza- tion of phosphorus from the various fertilizers would not be expected. The significant differences noted in yields at the third sampling period were, therefore, probably due di- rectly to the extra nitrogen supplied by the two phosphates containing ammonia rather than to the phosphorus they contain- ed. Furthermore, an additional indication that the effect was due to ammonia is that ammonium phosphate, containing 7.6 percent NHs, gave a higher yield than ammoniated superphosphate, containing 4.15 percent. As mentioned above, more fertilizer ammonia was supplied to the plants fertilized with the ammonium phosphate and ammoniated superphosphate than to plants receiving the other phosphate materials. This was due to the fact that no allowance was made for the ammonia contained in the ammoniated phosphates when applying supplemental nitrogen to the plots, ammonium sulfate being applied in equal quantities to all plots. Ap- parently because of this extra ammonia, the two ammoniated phosphates gave significantly higher yields at the third sampling period. It seems possible, also, that the higher -85- availability and greater utilization of phosphorus from these materials was at least partly due to the combined direct and indirect effects of the extra ammonia. Such an indirect ef- fect might be to increase the solubility of the phosphate and thereby increase its availability; and.a direct effect would well be upon yield and thereby upon degree of utilization, because of the nutrient effect of the extra nitrogen. Consideration of the above thoughts leads to the question of whether the amount of ammonium sulfate applied to the plots fertilized with the ammoniated phosphates should have been re- duced sufficiently to give equal ammonia levels for all plots. At first glance, it might seem that this would obviously be the proper procedure, and in accord with the scientific method of eliminating all the variables but one. Apparently this is the line of reasoning of some workers, at least, on this ques- tion.) In some of the work on comparison of sources which was reviewed in which the ammoniated forms were studied, the authors stated that they had.made due allowance for the ammonia in the ammoniated materials and had reduced the application of supple- mental ammonia accordingly. In the majority of the reports, it was not stated whether this had been done. In support of the procedure followed in this experiment, it seems to the author that it would be both illogical and inconsistent to equalize the ammonia applications. The ammo- nium ion is an integral part of the fertilizer as much as is the calcium ion, the sulfate ion, and any of the other ions -84- present in the different materials. No attempt is, or should be, made to equalize the amounts of these other ions to pro- duce the equivalent of fertilizers differing only in the availability of the phosphate ion because the availability would be changed in so doing. If the ammonia applications were equalized, the effect would be that of comparing only a part of the ammoniated phOSphates with the other materials as the influence of the ammonia in the ammoniated.materials on availability and utilization would be removed, or rather, masked. In a comparison of sources, the purpose is to compare the effect of the entire phosphate fertilizer on yield and utilization, not just the effect of some specific part of the material. 0n the basis of the above reasoning the procedure followed seems justified. I With regard to the data of Table XII for the percent of plant phosphorus derived from the fertilizer, it will be ob- served that the values decreased continuously during the growing season. It is of interest to consider the factors which might have caused this trend. The percent of fertilizer-derived phosphorus in the plant at any given time would depend on the relative rates of uptake of soil-derived and fertilizer-derived phosphorus which exist- ed prior to that time. Therefore, the factors determining the percent of fertilizer phosphorus in the plant would be those affecting the rate of uptake from both the fertilizer and the soil. -85- Several factors which would affect the rate of uptake from the fertilizer are the following: 1. Amount of fertilizer applied. 2. Availability of the material. 5. Degree of fixation. 4. Total area of functional root surfaces per unit quantity of fertilizer. 5. Amount of available phosphorus in the soil. Several factors affecting the rate of uptake of soil phosphorus are: 1. Amount of available phosphorus in the soil 2. Total area of functional root surfaces per unit volume of soil 5. Total volume of soil from which the roots are ab- sorbing. All of the above-mentioned factors are dynamic and in general would Operate in the following way to cause a more or less continuous decrease in the percent of fertilizer-derived phosphorus in the plant. Early in the season the root system of the plant is small and is more or less restricted to the fertilizer zone. Because of this, the prOportion of fertili- zer phosphorus taken up by the plant is relatively very high. Also, at this time relatively little fixation has taken place. As plant growth progresses the root system expands and in- creasing amounts of soil phosphorus become accessible to the plant and are absorbed. Since there is a limit to the total amount of phosphorus which the plant will absorb in a given length.of time, an increase in the amount of soil phosphorus absorbed would cause a proportional depression in the absorp- tion of phosphorus from the fertilizer. This would lead to a -86- progressive decrease in the percent of the plant phosphorus which was derived from fertilizer. The degree of phosphorus fixation has been shown to be a function of time, several months sometimes being required for the maximum to be attained. This, together with the fact that the quantity of phosphorus remaining in the fertilizer is inversely related to the amount which has been absorbed from it, means that as the season progresses a continuously decreasing amount of fertilizer phosphorus will be available for plant use. This, also, would operate to cause a progres- sive decrease in the percent of the plant phosphorus which was derived from the fertilizer. The effects of the above-mentioned factors in Operation are well-illustrated by the data in Tables IX and XI and by Figures 5 and 7. Comparison of the data in Table IX with those in Table XI shows that the absorption of phosphorus from the soil by the plant proceeded at a much faster rate than from the fertilizer. This, as previously mentioned, caused the progressive decrease in the percent of the plant phosphorus derived from the fertilizer. The primary objective of this investigation was to obtain quantitative information regarding the utilization of phos- phorus derived from the soil and from various phosphatic fert- ilizers. A secondary objective was to attempt to explain the differences found in the availability and degree of uptake of phosphorus from these fertilizers. Only a very limited amount -87.. of experimental data was obtained for this latter purpose as extensive investigation of the reasons for the differences observed was beyond the scope of this experiment. Experimen- tal data were obtained relating to solubility studies and fixation studies. As will be shown below, the solubility results seem to correlate rather well with availability data. The fixation data, however, for reasons previously discussed, are of no value for this purpose. Because of the lack of other data to help explain the availability differences ob- served, several hypotheses will be offered later which.may be of some value. As may be observed in Table XIV, availability relation- ships fluctuated considerably during the season. This is, of course, to be expected because of the wide differences in the composition and properties of the various phosphates, and the fact that the availability of the phosphorus in a fertilizer is not a fixed quantity but changes continuously after it is applied to the soil. 0n the whole, however, the availability relationships in this experiment were sufficiently constant to permit generalized ranking as to order of availability. The phosphatic materials were found to rank in order of decreasing availability as follows: ammonium phosphate - smmon iated superphosphate > ordinary superphosphate > dicalcium phosphate - alpha-tricalcium phosphate 3 calcium metaphosphate. Ammonium phosphate, ammoniated superphosphate, and ordinary superphosphate were found to be highly available, while dicalcium .. 88- phosphate, alpha-tricalcium phosphate, and calcium metaphos- phate presented a much lower availability. phosphates were of equal availability statistically. The last three There was, however, a definite trend below the level of signifi- cance toward decreasing availability in the order given a- bove. As the season progressed, the availability differences between all the materials became less and less pronounced. From a study of the data of Table II and XVII, it was shown previously that on the basis of water-solubility, the phosphates may be divided into two groups. Ammonium phos- phate, ordinary superphosphate, and ammoniated superphosphate, listed in order of decreasing water-solubility, were all highly soluble; dicalcium phosphate, calcium metaphosphate, and alpha-tricalcium phosphate, in decreasing order, were all only slightly soluble. To facilitate comparison of the relationship between water-solubility and availability,the materials are classi- fied below on the basis of decreasing solubility and availa- bility. Water-solubility High Low Ammonium Dicalcium phosphate phosphate Ordinary Calcium superphosphate metaphosphate Ammoniated Alpha-tricalcium superphosphate phosphate Availability High Low Ammonium Dicalcium phosphate phosphate Ammoniated Alpha-tricalcium superphosphate phosphate Ordinary Calcium superphosphate metaphosphate -89... It may readily be seen from the above classification that, as a group, the phosphates with the high water-solubili- ty were also the most available as measured by the plant. Likewise, the group which were only slightly water-soluble were the least available. It appears, therefore, that there is a definite positive correlation between water-solubility and availability in a broad way in this experiment. It might appear that this would be expected in this, and any similar, experiment. Jackson, et al. (6), working with corn and cats in Wisconsin, obtained results in which the order of relative availability of these materials was quite similar to that reported here. On the other hand, Starostka, Jackson, and Attoe (19), also in Wisconsin, work- ing with the same crOps and fertilizers the previous year found calcium metaphosphate to have the highest availability to the plant. Apparently, the degree of water-solubility of a phosphate material is not a dependable criterion for pre- dicting its availability to the plant. Although in this experiment good correlation was found between water-solubility and availability as measured by the plant when the materials were compared as groups, the corre- lation for individual fertilizers was not so good. For example, inspection of the above classification shows that ammoniated superphosphate (42.8% 320-301.), the least soluble material in the high solubility group, was more available than the more -90- soluble ordinary superphosphate (86.2% H20-sol.). A possible explanation for this situation is that the water-soluble fraction of the ordinary superphosphate is super-available leading to excessive fixation. Yet, if this is so, it is difficult to explain why the even more highly water-soluble ammonium phosphate (100% H20-sol.) was also found to be the most available. Since the phosphate materials studied also contain wide- ly differing amounts Of the citrate-soluble and citrate- insoluble fractions which may become available to the plant at varying rates during the season, it seems unreasonable to expect a consistent correlation between water-soluble phosphorus and availability, except, perhaps, early in the season. If, as is commonly believed, the -H2PO4 ion is the only phosphate ion which plants utilize, the relative availability Of a phosphate fertilizer would apparently depend upOn the rate at which it was able to furnish.this ion in optimum amounts, consistent with fixation effects and plant require- ments, throughout the growing season. There are a number of dynamic factors Operating simultaneously in the soil which would affect the rate of conversion of the various phosphate ions to the -H2P04 ion, as well as affecting the rate Of fix- ation. Therefore, explanation of availability and utilization differences Observed in any particular experiment would appear to be very difficult in view of the complex interrelationships involved in the soil and the extreme difficulty of experimentally evaluating the individual factors involved. SUNHJA BY 1. The data from this experiment show that there were dis— tinct differences in the percent utilization of phosphorus by cats from the six different phosphate materials studied. Oat plants receiving ammonium phosphate and ammoniated super- phosphate had the highest percent absorption from the phos- phate applied, while oats receiving calcium metaphosphate and alpha-tricalcium phosphate showed the lowest percent ab- sorption. The percent utilization values Obtained using ordinary superphosphate and dicalcium phosphate were inter- mediate with the latter source giving a somewhat lower utilization figure. 2. Availability relationships were determined from the utilization values obtained during the growing season. The relative availability of a phosphate material, as measured by the plant, was found to fluctuate somewhat during the sea- son. However, in general the materials were found to rank in decreasing order of availability as follows: ammonium phosphate :- ammoniated superphosphate> ordinary superphosphate) dicalcium phosphate = alpha-tricalcium phosphate = calcium metaphosphate. Ammoniated phosphate and ammoniated super- phosphate were more available than dicalcium phosphate, alpha- tricalcium phosphate, and calcium metaphosphate at the one -92- percent level of significance, and were more available than ordinary superphosphate at the five percent level on the whole. Ordinary superphosphate was more available than dicalcium phosphate, alpha-tricalcium phosphate, and calcium metaphosphate at the five percent level in general. The last three phosphates were of equal availability statistically. There was, however, a definite trend below the level Of significance toward decreasing availability in the order given above. 5. The percent recovery of applied phosphorus was very low. At the last sampling period, 11 days before harvest, the highest recovery was from ammonium phosphate and the lowest from calcium metaphosphate. These recovery values were 16.1 and 5.4 percent respectively. 4. There was a continuous decrease in the phosphorus composi- tion Of the plant during the growing season. The total phosphorus composition decreased from a high of 0.70 percent to a low of 0.25 percent, the fertilizer-derived phosphorus from 0.59 percent to 0.16 percent, and the soil-derived phos- phorus from 0.51 percent to 0.20 percent. 5. Statistically significant differences between the various phosphate materials were found with regard to their effect on the percent composition and rate of uptake of total, fertilizer, and soil phosphorus by the cat plant. 6. There was a pronounced inverse relationship early in the growing season between the rates of uptake of phosphorus from the fertilizer and from the soil. The relatively rapid up- take from the more available phosphates caused a correspond- ingly slower uptake from the soil. Conversely, the relatively slow uptake from the less available phosphates permitted a correspondingly greater rate of uptake from the soil. During the latter part Of the season the rate Of uptake Of phosphorus from the fertilizer had no effect on the rate Of uptake Of soil phosphorus. A similar pronounced inverse relationship also was found early in the season between percent Of fertili- zer-derived and sOil-derived phosphorus in the plant. This inverse relationship persisted throughout the season, but below the level Of significance during the latter part of the season. 7. At the first sampling date, 45 days after planting, 55.8 percent of the phosphorus in the plant was found to be ferti- lizer-derived for those plants receivingammonium phosphate, the most available material. At this time, only 15.8 percent Of the plant phosphorus was fertilizer-derived for those plants receiving calcium.metaphosphate, the least available material. The percentage values for all of the phosphates declined steadily during the growing season, and at the last sampling date, 11 days before harvest, the values for ammonium phosphate and calcium metaphosphate were only 17.7 and 6.9 percent respectively. Percentage values for the other phosphates were intermediate at all sampling dates. Significant differences existed throughout the season between the more available -94- materials and those less available with regard to the percent of plant phosphorus derived from the fertilizer. 8. Grain yields for the various treatments were not signi- ficantly different. Total dry matter yields differed signi- ficantly only at the third sampling period, at which time the yield with ammonium phosphate was higher than that produced by either calcium metaphosphate, dicalcium phosphate, or alpha- tricalcium phosphate. The yield with ammoniated superphosphate was higher than that produced by dicalcium phosphate. In all cases, the yield differences were significant at the five percent level. There were indications that the differential yield responses Observed were caused by the direct effect of the extra nitrogen supplied by the two ammoniated phosphates, rather than by the phosphorus in these materials. One reason for believeing this to be true is that the level of native phosphorus in the soil was so very high, yield response to fertilizer phosphorus would not be expected. 9. Differences in yield response and phosphorus utilization obtained with the different materials were used as criteria for evaluating phosphate availability differences. It was found that certain criteria were much.more effective than others in revealing availability differences. The percent of fertilizer-derived phosphorus in the plant (percent of the total dry matter) was shown to be the best criterion, being slightly more effective than the percent Of the total plant -95- phosphorus which was derived from the fertilizer, the most commonly used criterion. ‘Yield values and the percent total phosphorus in the plant were found to be the least effective criteria. It was suggested that under conditions Of yield response, the percent recovery Of applied phosphate would probably be the most effective criterion. 10. Differences in availability to the plant Of phosphorus from the various phosphates became progressively less pro- nounced during the growing season. ll.- Phosphorus availability as measured by plant utilization data appeared to be positively correlated, in a broad way, with water-solubility Of the phosphates. Ammonium phosphate, ammoniated superphosphate, and ordinary superphosphate, shown by utilization data to be the most available, were also found to have the highest water solubility. Dicalcium phosphate, alpha-tricalcium phosphate, and calcium metaphosphate, shown to be the least available, were found to have the lowest water solubility. This correlation existed only when the materials were compared as high.and low solubility groups. There was apparently little correlation of availability with water solu- bility for individual phosphates. 1. 2. 5. 4. 5. 6. 7. 8. -96- REFERENCES Black, C. A., 1949. Source of phosphate experiments on oats using P52. Mimeo. Compilation Of Field Fertilizer Experiments Using RadiOphosphorus. Phos- phorus Subcommittee for the North Central Region Of the Phosphorus Work Group Of the Nat'l. Soil and Fert. Comm. pp. 49-54. Bouyoucos, G. J., 1956. Directions for making mechanical analysis of soils by the hydrometer method. Soil Sci. 42:225-250. Bray, R. H., 1948. Correlation of soil tests with crop response to added fertilizers and with fertilizer re- quirement. Diagnostic Techniques for Soils and Crops. American Potash Institute, Washington, D. C. pp. 55-86. Handbook Of Operating Instructions for the Auto Scalar. Tracerlab, Inc., 55 Oliver St., Boston, Mass. Hendricks, S. B. and Dean, L. A., 1948. Basic concepts of soil and fertilizer studies with radioactive phos- phorus. Soil Sci. Soc. Amer. Proc. 12:98-100. Jackson, M. L., et al., 1950. Phosphorus utilization by oats and corn as influenced by carrier compound and placement, measured with P32. Mimeo. Compilation of Field Fertilizer Experiments Using Radiophosphorus. Phosphorus Subcommittee for the North Central Region of the Phosphorus Work Group of the Nat'l. Soil and Fert. Comm. pp. 55—44. Kamen, M. D., 1948. Radioactive Tracers in Biology, ed. 1. Academic Press, Inc., New YOrk. pp. 1-126 and 184-2000 Kaufman, h., Marriott, L. F., and Jackson, M. L., 1951. Forms Of phosphorus in soils and their transformation, movement and utilization by various crOps. Compilation Of Phosphate Fertilizer Experiments in the North Central Region. Phosphorus Subcommittee of the North Central Region. pp. 64-70. 10. 11. 12. 15. 14. 15. 16. 17. -97- Lawton, K., Kawin, B., and Robertson, L. S., 1951. Source Of phosphate experiment on oats using radio— active phosphorus. Compilation of Phosphate Ferti- lizer Experiments in the North Central Region. Phosphorus Subcommittee Of the North Central Region. pp. 74-770 Peech, M. and Dean, L. A., 1945. Methods for preparing soil samples, and determining the readily-soluble phos- phorus, pH, and organic carbon. Methods Of Soil Analysis for Soil Fertility Investigations. Committee on Uniform Methods Of Soil Analysis. Division of Soil and Fertili- zer Investigations, Bureau of Plant Industry, Soils, and Agricultural Engineering, Beltsville, Md. pp. 7-8. Peech, M., et al., 1945. Determination Of exchangeable cations and exchange capacity. Methods of Soil Analysis for Soil Fertility Investigations. Committee on Uniform Methods Of Soil Analysis. Division Of Soil and Fertili- zer Investigations, Bureau Of Plant Industry, Soils, and Agricultural Engineering, Beltsville, Md. pp. 9-11. Pesek, J. T., 1950. The relative efficiency of various phosphate fertilizer materials and Of two methods Of placement for cats. Mimeo. Compilation of Field Fert- ilizer Experiments Using Radiophosphorus. Phosphorus Subcommittee for the North Central Region of the Phos- phorus Work Group of the Nat'l. Soil and Fert. Comm. pp. 55-600 , 1951. The relative efficiency Of various phosphate fertilizer materials for oats. Compilation Of Phosphate Fertilizer Experiments in the North Central Region. Phosphorus Subcommittee Of the North Central Region. pp. 59-65. Piper, C. S., 1944._ Soil and Plant Analysis, ed. 1. Inter- science Publishers, Inc., New YOrk. pp. 168-176. , pp. 272-274. Spinks, J. W. T. and Barber, S. A., 1948. Study Of ferti- lizer uptake using radioactive phosphorus: II. Sci. Agr. 28:79-87. Spurway, C. H. and Lawton, K., 1949. Soil testing; a practical system Of soil diagnosis. Mich. Agr. Exp. Sta. Tech. Bull. 152 revised. p. 15. 18. 19. 20. 21. -98— Stanford, G. and Nelson, L. B., 1949. Utilization Of phosphorus from various fertilizer materials: III. Oats and alfalfa in Iowa. Soil Sci. 68: 157-161. Starostka, R. W., Jackson, M. L., and Attoe, O. J., 1949. Phosphorus utilization by oats and corn from different phosphate fertilizer compounds tagged with P52. Mimeo. Compilation of Field Fertilizer Experiments Using Radio- phosphorus. Phosphorus Subcommittee for the North Cen- tral Region of the Phosphorus Work Group of the Nat'l. Soil and Fert. Comm. pp. 15-24. Veatch, J. 0., 1941. Agricultural land classification and land types of Michigan. Mich. Agr. Exp. Sta. Spec. Bull. 251. p. 24. White, J. L., Fried,M., and Ohlrogge, A. J., 1949. A study of the utilization Of phosphorus in green manure crOps by the succeeding crop, using radioactive phos- phorus. Agron. J. 41:174-175. -99- APPENDIX e e u u I. 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