A STUDY OP THE EFFECT OF MINERAL PHOSPHATES UPON THE ORGANIC PHOSPHORUS CONTENT OF ORGANIC SOILS By Wade Wiley McCall AN ABSTRACT 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 DOCTOR OF PHILOSOPHY Department of Soil Science 1953 Approved _ ProQ uest Number: 10008378 All rights reserved INFORM ATION TO ALL USERS The quality o f this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete m anuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10008378 Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 4 8 1 0 6 -1 3 4 6 Wade Wiley McCall abs trac t A Study of the Effect of Mineral Phosphates Upon the Organic Phosphorus Content of Organic Soils Laboratory studies were conducted to investigate the effect of mineral phosphates upon the organic phosphorus content of eight organic soils. Soil types represented were Carlisle Muck, Everglades Peat, Houghton Muck, Istopoka Peat and Rifle Peat, obtained in Michigan and two from Florida, applied to each soil at the following rates: Six of the samples were Monocalcium phosphate was 100, 200 , *400, 800 and 1600 pounds of ^2^5 Per acre* Unphosphated samples were left as controls To determine if mineralization was as extensive as shown by soil analyses available phosphorus and soluble nitrogen were determined before and after a four—month incubation period. The effect of sterilization, tem­ perature and moisture upon the mineralization of organic phosphorus in Houghton Muck was also determined. Samples were incubated for a period of four months and the amount of organic phosphorus determined, by the method of Pearson, at the end of two, three and four months. No ‘‘fixation" of mineral phosphate as organic phosphorus occurred, but mineralization of the original organic phosphorus did occur. In general the greater the amount of monocalcium phosphate added the more rapid was this rate of mineralization over a period of four months. Generally the rate of mineralization was rapid the first two months and somewhat slower during the last two months. The percentage increase in available phosphorus after four months Wade Wiley McCall incubation ranged from 37.6 to 421 percent. The percentage increase of soluble nitrogen after four months incubation ranged from 21,4 to 143*5 percent. Temperature and moisture were shown to be two factors affecting mineralization of organic phosphorus. The mineralization of organic phosphorus continued after the soil was sterilized with mercuric chloride. A STUDY OP THE EFFECT OP MINERAL PHOSPHATES UPON THE ORGANIC PHOSPHORUS CONTENT OF ORGANIC SOILS By Wade Wiley McCall 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 DOCTOR OP PHILOSOPHY Department of Soil Science 1953 ACKNOWLEDGEMENT The author expresses his sincere appreciation to Dr. J. P. Davis, under whose guidance and unfailing interest this investigation was undertaken and whose suggestions were instrumental in bringing this thesis to a conclusion. He is also indebted to Dr. L. M. Turk and Dr. K. Lawton for their interest and help in the progress of the laboratory analysis. Grateful acknowledgement is also due Dr. C. M. Harrison for his guidance and help, and to Dr. R. L. Cook for his guidance and help and for reviewing the manuscript, and to his fellow graduate students for their helpful suggestions and assistance. Wade Wiley McCall candidate for the degree of Doctor of Philosophy Final examination, November 2k, 1953. 10:00 A,M., 210 Agriculture Hall Dissertation: A Study of the Effect of Mineral Phosphates Upon the Organic Phosphorus Content of Organic Soils Outline of Studies Major subject: Minor subject: Soil Fertility Farm Crops Biographical Items Bora, August 13, 1920, Day, Florida Undergraduate Studies, University of Florida, 1938-A2 Graduate Studies, University of Florida, 1946-^7, Michigan State College, 1951-53 Experience: Member United States Army, 19^2—A6, Assistant Pro­ fessor of Soils, University of Florida, 19k6-$l, Graduate Assistant, Michigan State College, 1951—53 Member of Alpha Zeta, Phi Beta Kappa, Society of the Sigma Xi TABLE OF CONTENTS PAGE INTRODUCTION............................................... 1 REVIEW OF LITERATURE........................................ 2 EXPERIMENTAL PROCEDURE...................................... 6 METHODS OF CHEMICAL ANALYSIS................................. 9 Organic Phosphorus........... 9 Soluble Nitrogen......... . .................. ♦ .......... 10 Available Phosphorus . . ......... 11 Adsorbed phosphorus • • • • • • . . . . ............... . . Acid soluble and adsorbed phosphorus...................... 11 11 DISCUSSION OF EXPERIMENTAL RESULTS........................... 12 SUMMARY ............................................ 20 LITERATURE CITED............................................ 2k APPENDIX: A ........................................... 26 B ............................................... 35 LIST OF TABLES The Soil Type, Location and Some Chemical Properties of Eight Organic Soils . . . . . . . . .................. The Average Results of Four Months Incubation Upon the Organic Phosphorus Content of Eight Organic Soils • • • • 13 The Results of Four Months Incubation Upon the Organic Phosphorus Content of Soil 6 . . . . . ............... 15 The Effect of Four Months Incubation Upon the Available Phosphorus Content of Eight Organic Soils ............. 17 The Effect of Four Months Incubation Upon the Total Soluble Nitrogen Content of Eight Organic Soils . . . . ....... 18 The Effect of Different Treatments Upon the Mineralization of Organic Phosphorus in Two Samples of Soil 7 ....... 19 The Effect of Superphosphate Upon the Organic Phosphorus Content of a Michigan Organic S o i l ....... .......... 27 The Results of Four Months Incubation Upon the Organic Phosphorus Content of Soil 1 . . . .................. 28 The Results of Four Months Incubation Upon the Organic Phosphorus Content of Soil 2 . « • • • ............... 29 The Results of Four Months Incubation Upon the Organic Phosphorus Content of Soil 3 . . . . . . . . . . . . . . 30 The Results of Four Months Incubation Upon the Organic Phosphorus Content of Soil k . . . . . . . . . . . . . . 31 The Results of Four Months Incubation Upon the Organic Phosphorus Content of Soil 5 • • • • • • • • • • • • • • 32 The Results of Four Months Incubation Upon the Organic Phosphorus Content of Soil 7 . • • * • • • • • • • • • • 33 The Rasults of Four Months Incubation Upon the Organic Phosphorus Content of Soil 8 3k LIST OF FIGURES FIGURE PAGE 1. The Effect of CaH^CPO^g, Applied, at Different Bates, Upon the Mineralization of Organic Phosphorus in Soil 1 . . . • 36 2. The Effect of CaH^(P0j^)2 , Applied at Different Rates, Upon the Mineralization of Organic Phosphorus in Soil 2 . . . . 37 3. The Effect of CaH^CPO^g, Applied at Different Rates, Upon the Mineralization of Organic Phosphorus in Soil 3 • * • . 38 h. The Effect of CaE^CPO^g, Applied at Different Rates, Upon the Mineralization of Organic Phosphorus in Soil h . . . . 39 5. The Effect of CaHj^CPO^g, Applied at Different Rates, Upon the Mineralization of Organic Phosphorus in Soil 5 • • * . ho 6. The Effect of CaHj^CPOj^, Applied at Different Rates, Upon the Mineralization of Organic Phosphorus in Soil 6 • . . . hi 7. The Effect of CaH/^POjif^* Applied at Different Rates, Upon the Mineralization of Organic Phosphorus in Soil 7 . . • . h2 8. The Effect of CaH^CPOij^* Applied at Different Rates, Upon the Mineralization of Organic Phosphorus in Soil 8 . . . • h3 INTRODUCTION Although much research has been devoted to organic phosphorus conpounds, relatively little information is available regarding the influence of mineral phosphates upon the organic phosphorus of organic soils.'1’ Preliminary work on an organic soil of Michigan indicated that the addition of 2200 pounds of PgO^ per acre, as super­ phosphate, over a period of eleven years did not appreciably change the organic phosphorus content from that of the soil in the virgin condition (See Table VII, Appendix page 27). This investigation was planned to study the effect of mineral phosphate upon the organic phosphorus content of organic soils. ^ Organic soils are those with more than 20 percent organic matter, one foot or more in thickness and formed under conditions of poor drainage. REVIEW OF LITERATURE The first work on soil organic phosphorus dates hack 110 years to experiments in Europe, when Mulder (15)^ was unable to prepare phos­ phorus-free fractions of soil organic matter. The accumulation of knowledge concerning the methods of determination, amount, forms, trans­ formations and importance of organic phosphorus has been traced by many authors, the most recent and comprehensive to date being that of Black and Goring (5 ). Since the beginning of soil organic phosphorus studies there has been essentially only one general procedure for determining this impor­ tant constitutient of the soil. It was arrived at by determination of the inorganic and total phosphorus before and after treatments designed to change organic phosphorus to inorganic forms, the amount of organic phosphorus being determined by difference. was used in this work. The method of Pearson (l6,21) However, the procedure of Metha (ik) may prove more adaptable to this type of work. The amount of organic phosphorus varies within wide limits in different soils. Most of the organic phosphorus is found in the surface soil (5 ) and decreases gradually with depth. Soils derived from recent sediments or having pronounced horizon differentiation may present irregularities. The organic phosphorus constitutes from 30 to 85 per­ cent (5,6,10,12) of the total soil phosphorus whereas in organic soils it may amount to 75 to 85 percent of the total (10). 2 Humbers in parentheses refer to literature cited 3 Plant and animal tissue is the source of soil organic phosphorus, which should he the same form as that found in these tissues. Bower (6 ,7 ) stated that there are four forms of organic phosphorus present in the soil; nucleic acids, phytin and its derivatives, inisitol phosphate and the phospholipids which are present to a limited extent hut do not seem to he very important. Black and Goring (5 ) listed five forms of organic phosphorus in the soil; phospholipids, nucleic acid, inisitol phosphates, m''metabolic11 phosphates and phosphoproteins. In investiga­ tions of the organic phosphorus compounds in the soil, attention has heen limited to the first three groups. Dyer and Wrenshall (12) men­ tioned five organic phosphorus compounds which may he found in soils; phospholipids, nucleic acid, sugar phosphates and related compounds, phosphoproteins and phytin and its derivatives. . The availability of the different forms of organic phosphorus varies greatly (5,6,7,12,13,18). The unavailability of organic phosphorus is most likely a result, in part, of the formation of insoluble salts with polyvalent ions (5 ,13) and, in part, of adsorption by clays or organic constituents of the soil (5,7»l8). Doughty (ll) found that soluble phosphates become "fixedH by iron and aluminum in an acid peat soil. Bertramson OW reported indications that phosphorus nutrition in plants is in the organic realm and the utilization of organic phosphorus depends upon the ease with which it can be converted to inorganic forms. He further stated that the availability of organic phosphorus is in part a biological phenomenon. In most experiments it was found that the organic phosphorus was of k little significance in plant nutrition until it was mineralized. Black and Goring (5 ) reported two types of evidence that mineralization takes place. The first is Based upon changes in soils as a result of long continued treatment, Pearson, et al (l?) and Thompson and Black (22) noted that the content of organic phosphorus is usually lower in culti­ vated soils than in comparable virgin soils. The other type of evidence is Based upon laboratory experiments conducted over a relatively short period of time. Bower (7) discovered that where there was an increase in inorganic phosphorus, a corresponding decrease in organic phosphorus was noted. Pearson, et al (17) found that the organic phosphorus was incompletely mineralized in a period of one month. Thompson and Black (22 ) stated that all of the soil organic phosphorus was mineralized in a period of seven days at 150° C. The rate of mineralization of organic phosphorus depends upon several factors. Thompson and Black (22) found that it was correlated positively with the amounts of organic carhon and nitrogen in the soil. They also found that the pH of the soil, the type of organic phosphorus and the kind of soil affected rate of mineralization. Pearson, et al (l?) noted that increases in pH increased the rate of mineralization of organic phosphorus, microbiological fixation decreased the rate and the presence of lignin possibly reduced it. Dyer and Wrenshall (13) stated that the liming of acid soils might Be expected to hasten the avail­ ability of organic phosphorus for the plant. Barbarian and Bonner (3) noted that at 25° C organic phosphorus failed to form in the potato. However, Bower (7), Thompson and Black (22) discovered that mineralization 5 increased with increasing temperature especially above 25° to 30° C. Thompson and Black (22) stated also that the hot sun increased the soluble phosphorus content of the soil. Rogers (19) showed that toluene was an effective sterilization agent in stopping evolution of COg from the soil. found that plant roots produced several enzymes. Many workers have Rogers (19) determined that soils produced enzymes which caused dephosphorylation of organic phosphorus compounds. He found that catalysts in the soil were effective in mineralization of the soil organic phosphorus after effective steril­ ization with toluene. These data suggest that the conversion of organic phosphorus to mineral forms is not entirely a function of microbiological activity in the soil. EXPERIMENTAL PROCEDURE Eight surface soil samples of virgin organic soil were used in this study. Six were from Michigan and two were from Florida. The location of these soils as well as some of their chemical properties are given in Table I. The soils were air dried, passed through a two millimeter sieve and the moisture content determined. The pH was determined with the glass electrode and organic phosphorus was deter­ mined by the method of Pearson (15)# One hundred gram samples were incubated for four months after they received monocalcium phosphate at rates equivalent to 100, 200, hOO, 800 and 1600 pounds of Pg0^ per acre. Unphosphated samples were incubated for the same period of time for controls. During incubation the samples were maintained at approximate moisture equivalent and at a temperature of 80° F. Samples were analyzed for organic phosphorus at the end of two, three and four months. At the end of four months the available inorganic phosphorus and the soluble nitrogen content were determined on samples that had received hOO pounds of P2O5 per acre. The results of all determinations are reported in Tables II through V inclusive. In the second phase of the study, two samples of soil 7 (Houghton Muck) were used. Sample 7A had been stored in a moist condition for four months while sample 7B was obtained from the field in a frozen condition. These soils were prepared as were those in the first phase of the experiment. An application of 400 pounds of ^2^5 Per acre was 7 (0 THE SOIL TYPE, LOCATION AND SOME CHEMICAL PROPERTIES OP EIGHT ORGANIC SOILS •P O P h $ s11 IS u ^2 Pi O CM ♦ VA o VO 'A O Ov VO va CA CM -d ' CA vO O O CM A - CO CO *A CA • vo H VO •S' VA O S CO CA P *3 S Eh w s CM 1] p ?H o, O o CM CA vO CA O CM CA O CO CA O -3- -3CM oP •H *3 o o p o -H CO W) p A -P - <3 a .P O o o cfl oo Hi VO VA CA CA 'A CM * A - VA VO f t o f t o ft o *5? s C8 .P o a O 3 3 3 CA CM o o p o ■i-9 p o CO o o a O O 8 3 Pi e*fl PI a ** • P CD *H ft 0CDp> • *3 •ri ft • • • o o o o o o 3 o f t f t (8 O p o +9 p •H rH O p o p ■H i—1 o -H rH <0 •g g +* P CD f t CO *» <0 i—1 ft PCD w a •rt ft ft H i ■g ■5i p PM CM CA -= t- VA » M PM -H «s a) ft iCD -t to •H f t *9> tH o«3 ft VO 00 P o 1-i CD CO —1 ■ 8 made to each sample except the control* These samples were Incubated for four months with the following treatments: (l) sterilization, (2 ) con­ stant temperature of 45° F*, (3) constant temperature of 55° » (4) temperature of 80° F., (5) constant moisture at 30 percent, (6 ) constant moisture at moisture equivalent, and (7 ) constant moisture at saturation. All samples except those in treatments 2 and 3 were held at room tempera­ ture, and all treatments except those in treatments 5 aad 7 were held at moisture equivalent. All sanples were kept moist with distilled water except those in treatment 1 , which were moistened with 1 :10,000 solution of mercuric chloride. Results of this experiment are given in Table VI. In this procedure one percent variation in transmission on the colorimeter, when applied to the standard curve, resulted in a difference of 20 ppm on a soil basis and possibly accounted for, in part, the variability in the results obtained* METHODS OF CHEMICAL A&ALYSIS Organi c Phosphorus Weigh out 0.5 grams of organic soil and place in a small "beaker. Add 20 ml. of 0.1 H hydrochloric acid to each and let stand for several minutes. Place on a hot plate for five minutes. Filter through phos­ phorus free filter paper and wash with small portions of 0.1 F hydro­ chloric acid until free of calcium. Make this acid filtrate to volume in a 200 ml. volumetric flask and save. Transfer the acid washed soil with the filter paper to a 500 ml. Erlenmeyer flask graduated at 400 ml.. Add 200 to 300 ml. of 0.5 ^ ammonium hydroxide and shake thor­ oughly until the filter paper is shredded. Rinse stopper and the sides of the flask and make up to volume with 0*5 N ammonium hydroxide. Fit flask with a "bunsen stopper and digest at 90° C. for 18 hours. Cool flask to room temperature in running water hath and add five grams of ammonium chloride, adjust to 400 ml. mark, and shake thoroughly, and allow to stand until suspended material settles out. Decant through phosphorus-free filter paper and discard the filtrate as long as suspended material can "be observed. Place a 10 ml. aliquot of the clear filtrate in each of two thoroughly weathered 100 ml. beakers and add five ml. of the acid extract. One aliquot is used for the determina­ tion of the total phosphorus and one for the determination of the inorganic phosphorus. For inorganic phosphorus determination add four ml. of 1*0 H sulfuric acid and 0.025 grams of carbon black to one of the aliquots and swirl to mix thoroughly. Filter, rinse the beaker and 10 wash the paper five times with small portions of w&ter (do not fill the funnel more than one-half full). Dilute the decolorised filtrate to 40 ml* with water, add one drop of p-nitrophenol and add 1:1 ammonium hydroxide dropwise until the solution turns yellow* Then add 1.0 S' sulfuric acid drop hy drop until the color disappears. ammonium molybdate and adjust volume to 50 ml.. Add 2 ml. of To develop the color add three drops of stannous chloride and let stand for 40 minutes. Then read the percent light transmission on a photoelectric colorimeter, using a red (650 filter. Compare with standards which have "been made and treated the same as the samples (except add 0.12 grams of ammonium chloride to each 50 ml* standard) * For total phosphorus deter­ mination evaporate the second aliquot to dryness with one ml. of 10 percent magnesium nitrate (phosphorus—free)* Ignite in muffle furnace at 600° C until white ash is formed. Dissolve in four ml* of 1.0 IT sulfuric acid and dilute to 40 ml. with water. ceed as "before. Adjust acidity and pro­ Organic phosphorus is calculated as the difference between the total phosphorus and the inorganic phosphorus. Soluble Nitrogen Transfer 25 grams of soil to a 500 ml. flask and add 300 ml. of four percent potassium chloride. Shake at intervals and let stand over­ night. Filter off 200 ml. of liquid and place in an 800 ml. Kjeldahl flask. Make alkaline with six to eight ml. of concentrated sodium hydroxide solution. Distill into 25 ml. of four percent boric acid solution and continue distillation until 25 ml. remains in the Kjeldahl flask. To determine the ammonia add three drops of bronw-phenol—blue to 11 the boric acid — sulfuric acid* distillate solution and titrate using standardized Calculate the amount of ammonia present* For the nitrate nitrogen determination make the solution left in the Kjeldahl flask up to approximately the original volume with distilled water. Add one gram of Devarda*s alloy* percent boric acid solution* Distill slowly into a four Add indicator and titrate as before* Calculate the amount of nitrates* Then calculate the milligrams of soluble nitrogen in 100 grams of air dry soil* Available Phosphorus Adsorbed phosphorus* Weigh one gram of air dried soil into a glass container and add 10 ml. of extracting solution (0*03 IT IT HCl). Stopper and shake for one minute * filter through phosphorus- free filter paper. Then add six drops of ammonium molybdate—hydrochloric acid solution and three drops of stannous chloride — solution. and 0*025 hydrochloric acid After five or six minutes read on a photoelectric colorimeter using a red (650 m^O filter and compare with known standards. Acid soluble and adsorbed phosphorus. Weigh one gram of air dried soil into a glass container and add 10 ml. of extracting solution (0*03 IT KK^jP and 0.1 H HCl). Stopper and shake for forty seconds and filter through phosphorus-free filter paper. Then develop color and proceed as above* The acid soluble and adsorbed phosphorus minus the adsorbed phos­ phorus gives the acid soluble phosphorus. The available phosphorus is the sum of the acid soluble and adsorbed phosphorus. DISCUSSIOH OF EXPERIMENTAL RESULTS The eight organic soils used in this study varied in organic phos­ phorus content from 320 to 700 ppm and in percentage of phosphorus in organic form from 3^.3 to 66*7 percent* A direct relationship was found to exist between the amount of total phosphorus and soil organic phosphorus* In general the higher the total phosphorus the higher was the organic phosphorus content* Soils 5 a*id 7 were exceptions* Ho relationship was found to exist between the actual amount of organic phosphorus present and the percent of the total phosphorus in organic form in these eight soils* The effect of mineral phosphates on the level of organic phosphorus varied between soils, but the trend was the same in all soils. In order to avoid repetition the data from the eight soils were averaged and are presented in Table II. The data from all eight soils are presented separately in tables and graphs which are found in the appendix. The results of the incubation for a specific soil, number 6, are shown in Table III. In general the data are similar to those obtained by averag­ ing the results of incubation for the eight soils (Table II). In soil 6 mineralization was very rapid during the first two months in all samples except the two with the highest rates of phosphorus application. In these samples only 30 and 22 percent, respectively, of the organic phosphorus had been mineralized by the end of the second month. 13 TABLE II THE AVERAGE RESULTS OP POUR MOUTHS INCUBATION UPON THE ORGANIC PHOSPHORUS CONTENT OP EIGHT ORGANIC SOILS1 Monocalciunt phosphate strolled Pounds PoQ^ T>er acre organic phosphorus 2 months 3 months 4 months None 2M2 2*5 152 100 335 237 150 200 236 1U0 1*0 *00 2*0 177 135 800 372 100 35 1600 300 100 25 The average original organic phosphorus con­ tent of these soils was 515 PP®. 14 During the third month the rate of mineralization was slow or at a standstill in three of the samples and was rapid in the other three. It continued at a rapid rate, as shown by Table III, in the samples treated at the 100, the 800 and the 1600 pound rates of PgO^. At the end of four months, mineralization was complete in two samples, where 100 and 1600 pounds respectively of were added. The other samples all contained less than 50 PP® of organic phosphorus ex­ cept the control which contained 100 ppm* The data in Table II indicate that in these eight organic soils none of the added monecalcium phosphate was converted or "fixed11 as organic phosphorus but that the addition of the phosphate actuallycaused an apparent mineralization of the organic phosphorus of the soil. In general the greater the amount of monocalcium phosphate added the more rapid was the rate of mineralization over a period of four months. During the firBt two months approximately one-half of the organic phos­ phorus was mineralized. Except in the case of the control sample, mineral* ization continued at a rapid rate during the third month. The rate Increased again in the control, during the fourth month, but decreased slightly in all the remaining samples. The rate of mineralization was not the same as that reported (5*7,13*17.19) for organic phosphorus compounds added to the soil or for organic phosphorus compounds in the laboratory. The data show that the soil organic phosphorus behaves differently from organic phosphorus of other sources. There was an increase, as shown in Table IV in available phosphorus (acid soluble plus adsorbed) in all/soils except 7 and 8. This increase ^ 15 TABLE III THE RESULTS OF FOUR MONTHS INCUBATION UPON THE ORGANIC PHOSPHORUS CONTENT OF SOIL 61 Monocalcium phosphate armMed Pounds Per acre organic phosphorus 2 months 3 months 4 months None 220 200 100 100 220 100 0 200 120 140 20 4oo 20 20 40 800 380 300 20 1600 420 40 0 i The original organic phosphorus content of this soil was 540 ppm. 16 ranged from 37.6 to 421 percent of that present "before incubation. In soils 7 and 8 there was an increase in acid soluble phosphorus but a decrease in adsorbed phosphorus resulting in essentially no effect upon the sum of the two forms. In soils which were within the pH range of 4*0 to 5.0 inclusive the greatest increase in available phosphorus occurred. Those soils below this range showed less increase and in those above 5*1 there was no increase. The amount of adsorbed phosphorus decreased and the acid soluble phosphorus increased in the soils with pH above and below the range 4.0 to 5»1* Table V shows there was an increase in total soluble nitrogen in all eight soils during four months incubation. varied from 21.4 to 143.5 percent. The percentage Increase There was an increase in the soluble ammonia in all soils except soil 6 . The soluble nitrates increased in soils 5* 6 and 7 , decreased in soils 2 , 3 a»d 4 and remained unchanged in soils 1 and 8 , Nitrates increased in the pH range of 5*0 to 6.3 and decreased in the range 4.0 to 5*0- There is no apparent relationship between the percent increase in soluble nitrogen and the actual decrease in organic phosphorus content, however, the increase in soluble nitrogen suggests that mineralization of the organic phosphorus did take place as shown by the soil analyses. This conclusionis further strengthened by the data presented in Table IV which show an increase in available phosphorus in most of these soils. The method of handling soil samples previous to and during incuba­ tion exerted an influence upon the rate of mineralization of organic phosphorus as shown in Table VI. These data show that saturation slowed 17 TABLE IV THE EFFECT OF FOUR MOUTHS IHCUBATIOH UPOH THE AVAILABLE PHOSPHORUS1 COUTEUT OF EIGHT ORGAUIC SOILS Soil nusiber PPM of extracted nhos'ohorus Acid soluble Total Adsorbed pH Before After2 Before After^ Before After^ 1 3.6 bo 575 233 65 273 6bO 2 fc.o 9b b57 58 335 152 792 3 A .2 108 k50 85 255 193 705 A ^.7 510 880 500 510 1010 1390 5 5.0 21 192 50 155 71 3^7 6 5.1 32 310 225 210 257 520 7 6.3 12 120 150 bj 162 163 8 7.2 66 195 150 18 216 2lA ^ Analyses “by procedure of Bray and Kurtz (8), ^ These soils incubated for four months with ^00 pounds P2O5 P®r acre* 18 H o H©P d oo 00 © «H hp 40 d g &s H H +s H o soluble © PP vO Vi^ • CM 00 V\ ♦ CM oM C CM CO VO • CM ONI C"\ CO M V HP CO rH h *rt -1u ■P O © +» •H (0 d © u o rt u & cT CM CM 0 GO •H © 9H <0 H •rH rH d rH *H O VO rH CM p©q rH O • OV • 8i• CM C M -4 O • i—1 rH• CO o• CM 0to01 00 • VoO• rH s xs h» £ 90 +> d § <0 •H d rH O ‘H i i ° 0 a cfl 0o +<3 d GO © 0 rH to CO IH > *Q •H do 0 *o © rH •H rH d rH »H HIh H©P «l} © fH O © VO -4 ov • 3-♦ rH C^\ Q VO rH rH o VO * tr\ CM C M CM • CM & O no -4 • CO o CM cn O vO CM -3F • vo• rH PP W ft rH CM OV 1 1 1 © applied at dif­ ferent rates, upon the mineralization of organic ohosphorus in soil 6, kz 700 Parts Per Million of Organic Phosphorus 600 500 400 o 500 o rounds P^O per acre 100 200 100 © -- 400 rt --- 800 A 1600 1 2 3 Months of Incubation 4 Fig. 7. The effect of GaH^PO^Jp, applied at dif­ ferent rates, upon the mineralization of organic phosphorus in soil 7. 43 700 r Parts Per Million of Organic Phospboru 600 300 300 .. 200 Pounds P20 per acre 100 X 200 o 400 v --- 800 A --- 1600 1 2 4 Months of Incubation Fig. 8. The effect of C a H ^ P O ^ p , applied at dif­ ferent rates, upon the mineralization of organic phosphorus in soil 8.