TNT CATTQN EXCHANGE CATACTTT AND 75 PERCENT CALCTLTM STATTT RATTCTN TN ~ RELATION Tc TNT RELEASE ANTT UPTAKE - or- EXCHANGEABLE CALCIUM AND I POTASSIUM Thesis“ {or 11190139199 of M. TS. MTcNTGAN STATECOLLEGE LuiT Armando Roma 1 1951 This is to certify That the thesis entitled The Cation Exchange Capacity and Percent Calcium Saturation in Relation to the Release and Uptake of mohangeable Ca and K presented by Luis A. Home has been accepted towards fulfillment of the requirements for 801 Masters degree in So ence TKMW Major professor Date Janna” 22, 1951 0-169 THE CATION EXCHANGE CAPACITY AND PERCENT CALCIUM SATURATION IN RELATION TO THE RELEASE AND UPTAKE OF EXCHANGEABLE CALCIUM AND POTASSIUM By LUIS ARMANDO ROMO m 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 1951 ACKNOWLEDGMENTS The author wishes to express his sincere apprecia— tion to Dr. Kirk Lawton for his wise advice and construc— tive criticism in carrying out all phases of the present investigation. He is indebted to Dr. L. M. Turk for his interest in the investigation and his criticism and suggestions in improving the presentation of materials. Sincere thanks are also due Dr. N. D. Baten for his advice pertaining to certain phases of analysis of vari- ance and Dr. Earl Erickson for his informal suggestions on the methodology of scientific research. Introduction Review of the Literature Experimental Methods Laboratory investigations Greenhouse experiment Analytical Methods Experimental Results The relationship between (H-soil) and the organic The effect of percent calcium saturation upon the adsorption of potassium added at different symmetry concentrations to soil system the The and The and CONTENTS 0 yield of sudan grass . The relationship of percent calcium satura- tion and concentration of exchangeable potassium in soils with the contents of the inorganic fraction (H-peat) with respect to cation exchange capacity . calcium and potassium in the plant . The relationship between the exchangeable forms of the Ca:K ratio in the soil and the Ca:K ratio in aerial plant tissue Discussion Summary and Conclusions . Bibliography effect of percent calcium saturation potassium treatments on plant growth . effect of percent calcium saturation potassium treatments on dry matter Page IO 10 15 22 28 28 31 33 41 52 57 59 66 72 l'lllll'l‘llIl'l Tables 1. 8. and 9. 10. to 14. 15. 16. 17. 18. LIST OF TABLES The Effect of Different Concentrations of HCl on the Cation Exchange Capacity Of $011 0 O O O O O O O O O O O O I 0 O O The Total Cation Exchange Capacity of Treatments M , M and M . . . . . . . . . l 2 3 Summary of Percent Calcium Saturation on Treatments M1, M2 and M3 . . . . . . . The Potassium Treatments on Calcium Saturation Levels in Treatments M1, M2 and M3 Respectively . . . . . . . . . . The Relation Between the Cation Exchange Capacity of Soil-Peat Mixtures and the Calculated Sums of the Exchange Capacities of the Individual Components . . . . . . . The Effect of Percent Calcium Saturation on the Adsorption of Potassium by a Hydrogen Saturated Soil . . . . . . . . . The Specific Conductivity of Soil-Water Suspension of the Soil After the First HarveSt O I O O O O O O I O O O O O 0 O O The Oven-Dry Weights of Sudan Grass Produced per Jar Expressed in Grams . . . Analysis of Variance of Sudan Grass Yields as Affected by Percent Calcium Saturation and Potassium Treatments . . . Calcium and Potassium Content in Soil After Cropping. First Crop. . . . . . . . Calcium and Potassium Content in Plant Materials. First CrOp. . . . . . . . . . Calcium and Potassium Content in Soil After Cropping. Second Crop. . . . . . . Calcium and Potassium Content in Plant Materials. Second Crop. . . . . . . . . . Page l2 l8 19 20 29 32 54 55 56 Figures I II III IV VI LIST OF FIGURES The Effect of HCl Leaching on the Cation Exchange Capacity of Soil . . . . The Cation Exchange Capacity of the Mixture of the H-Soil and the H—Peat and the Sum of the Components . . . . . . The Effect of Cation Exchange Capacity, Percent Calcium Saturation, and Potas- sium Treatments on Growth of Sudan Grass. FirSt crop. (a & b) O O O O O O O O O O The Effect of Cation Exchange Capacity, Percent Calcium Saturation, and Potas- sium Treatments on Growth of Sudan Grass. Second Crop. a & b . . . . . . . . . . c & d O O O O 0 O O O O 0 e & f . . . . . . . . . . The Yield of Sudan Grass as Affected by Percent Calcium Saturation and Potassium Treatments. Ea; First CrOp . . . . . . . b Second Crop . . . . . . The Relation Between the Ca:K Ratio of the Soil and the Ca:K Ratio of the Plant. Page 13 3o 36 37 39 44 45 58 THE CATION EXCHANGE CAPACITY AND PERCENT CALCIUM SATURATION IN RELATION TO THE RELEASE AND UPTAKE OF EXCHANGEABLE CALCIUM AND POTASSIUM Introduction Early studies in Soil Chemistry led soil scientists to suspect that certain cations in the soil were avail- able to the plant in the exchangeable form (12). This consideration resulted in a change of concepts in the realm of soil fertility and plant nutrition investigations. It was discovered that as soils were depleted of bases such as Ca, Mg, K, and Na they became acid as a result of H-saturation (17). This condition resulted in a considerable decrease in plant growth. In experiments carried out to correct this condition (12) it was soon found that the addition of the depleted cations, mainly calcium and potassium, resulted in a significant increase in plant growth. While studying the factors governing the uptake of cations from the soil it was discovered that calcium oc- curred in larger amounts than other soil cations and that it acts as a regulator of the physiological equil- ibrium of salt intake by plants (37). The percent base saturation is an important factor in the soil fertility status of a soil for it has been established, that the release and uptake of the exchange- able cations is a dependent function of the aforementioned factor (2). Ionic exchange is one of the most dynamic properties of the soil as far as determining the magnitude of ad- sorption and supply of exchangeable cations in the soil for plant growth is concerned. Many soils have a low total cation exchange capacity and therefore the amount of cations held in exchangeable form is low. Under these conditions the productive ca- pacity of the soil may be decreased considerably. A great many studies (12, 13, 51) have been made towards the general understanding of the role of exchange- able cations in soils and the mechanism of ionic exchange. In searching the literature no contribution could be found pertaining to a systematic investigation of the factors which govern the release and uptake of exchange— able calcium and potassium, as influenced by the percent calcium saturation in a soil, in which different levels of total cation exchange capacities were established with the use of peat. It is the object of this investi- gation to elucidate: (a) the relationships existing between the inorganic (H-soil) and the organic (H-peat) fractions as they affect cation exchange capacity; (b) the effect of percent calcium saturation upon the adsorption of potassium added to the soil at different symmetry concentrations; (c) the effect of percent calcium saturation on the release and uptake of calcium and potas- sium in a soil in which different levels of total cation exchange were maintained with a peat depleted of bases. Review of the Literature The application of physico-chemical methods to the study of the forms in which the cations occur in the soil system has resulted in a series of scientific findings Which clarify the mechanism of certain colloidal phenom- ena in the soil. Way (17) found in 1850 that the soil exchanged ions supplied in solution of neutral salts with those found in the soil. Later, it was postulated that the plants take up only the cations which are found in the soil in the exchangeable form (20). These findings led soil scien- tists to consider the importance of cation exchange ca- pacity in soils as one of its most dynamic properties (26). Although the mechanism of ionic exchange was at first not well understood, methods to determine the "total base exchange capacity" were prOposed and adopted (25). A'l I 'Ill‘ I'I‘Aflllll The cation exchange capacity has been found to be a constant property of a soil (12) although the magnitude of the estimated value depends upon a number of factors such as the nature of the exchange complex (37), the hydrogen ion concentration (49) and the nature, kind and concentration of the saturation cation (19, 38). It has been found (20) that plants take up the ca- tions from the soil when they are in the exchangeable form. Several factors (26) govern the equilibrium rela- tions of these cations in the exchange complex and con- sequently the ease of their availability. Among these factors, the percent base saturation has been found to be very important (2). Base unsaturated soils are in- fertile and acid due to a process of depletion of bases and replacement of those cations by H ions. Gedroiz (12, 37) conducted a number of experiments to determine the role of percent base saturation on the uptake of cations by plants. As a result he concluded that calcium is the major exchangeable cation in a nor- mal soil and that the availability of other exchange- able cations such as potassium and magnesium depends to a large extent on the percent saturation of the calcium ion. He showed that plants can not grow when the adsorbed calcium is removed from the soil, and that plants could secure potassium and magnesium from the soil where the exchangeable forms were removed by leaching, provided the calcium ion was present. Similar results have been ob- tained by other workers in carefully controlled experi— ments (1, 2). The increase in percent calcium saturation in acid soils results in an increase in the delivery of exchange- able calcium to the plant (1, 30). This is due to (a) a higher ionic activity, (b) the forces which hold the cations adsorbed by the colloid complex become smaller, and (c) the nature of the other saturating cations (19). Allaway (2) has shown that the increase in calcium saturation results in an increase in the availability of calcium and other saturating cations up to an optimum which he found to be forty percent in the case of soils containing kaolinite and eighty percent in soils con- taining montmorillonite. Jenny and Ayres (19) showed that ionic exchange be- tween the soil solution and clay surfaces is not a pre- requisite to the intake of adsorbed ions by plants. Jenny and Overstreet (20) theorized that the intake of cations is due to a process of direct contact exchange between soil colloids and root surfaces. As a result of this investigation, they concluded that the degree of base saturation of the soil is one of the governing fac- tors of the availability of adsorbed ions. The cations making up the total percent of base saturation of soils are mainly calcium, potassium, and magnesium (12). If the effect of the percent saturation of a particular cation is to be studied it has been found convenient to single it out by designating the other ions as "complimentary ions." This new concept has been very useful in studying certain soil phenomena of a physico-chemical nature. Many workers have found that the ease of replace- ment of an exchangeable cation depends upon the kind and number of complimentary ions held on the exchange sur- faces (19). If the complimentary ions are held loosely they will tend to depress the release of the other "adsorbed ion." In reference to the relation of exchangeable cal- cium to the release and fixation of potassium in the exchange complex it may be stated that there is no gen- eral agreement (#1). Under certain circumstances it has been found that the amount of exchangeable potassium varies inversely with the percent calcium saturation (21). Jenny et al. (20) found that in multiple ion systems the replacement of potassium is governed by complicated inter- actions of adsorbed and released ions. Jenny et al. (18, 19) explained the quantitative relation of the saturating exchangeable cation to the complimentary ions in the process of exchange, by means of the kinetic theory of ionic exchange. They showed that a decrease in percent base saturation reduces the amount of exchangeable cations replaced by the added cation. Furthermore, if the complimentary ions are held more tight- ly than the saturating cations in question the added ca- tions will displace more readily the saturating cations. In this case the degree of base saturation has little effect. When the ions included in exchange have equal oscillation volumes (equal adsorbability) the release of exchangeable cations is a direct function of per- cent base saturation. When the complimentary ions are held loosely as compared with the exchangeable cation, the complimentary ions will be more easily replaced than the exchangeable cation in question and therefore the percent base saturation assumes a significant role. Jenny et a1. (21) have found that in acid soils a higher degree of calcium saturation of the soil colloids results in a higher release of exchangeable potassium. Bear and Toth (6) while studying the influence of calcium on the availability of other cations came to the conclusion that deficiencies in potassium in the soil occur due to a disequilibrium of the CazK ratio. Jenny and Shade (21) state that in acid soils ad— ditions of calcium results in the liberation of potassium while in alkaline soils, where the hydroxyl ions are not excessive, additions of calcium induces fixation of po— tassium. Peach and Bradfield (41) reconciled the controver— sies by evaluating the experimental conditions under which the various results were obtained. It should be indicated here that the factors determining the avail- ability of potassium are numerous (8) although release occurs through the process of ionic exchange (20). The exchange complex of the soil is considered to be the active fraction which is capable of ionic ex- change consisting of the inorganic fractions (clay minerals) and the organic fraction made up by the end- products of the decomposition of organic matter (49). It has been found that the "humus" fraction of soils exhibits high cation exchange per unit weight. According to Mitchell (33) the organic fraction is re- Sponsible for 41 to 65 percent of the cation exchange of a mineral soil. Olson and Bray (36) found that in a humus soil the organic fraction contributed 6.8 to 43.3 percent of the total cation exchange capacity. Therefore, it is obvious that additions of organic matter to a mineral soil would result in a significant increase in the total capacity of the treated soil to hold and ex- change cations. A critical review of the literature indicates that there is no comprehensive study in which peat has been used as a source of material to increase total cation ex- change capacities of soils in making exchange studies. Jones (24) in a study on the availability of humate potassium found that the potassium held by the humate fraction was more readily exstractable than that from clay. For the proper growth of plants it is necessary to have not only an adequate supply of cations but also of certain anions such as N03" and P04-" which are indis- pensable for the prOper growth of plants (32). Truog (48) asserts that calcium plays an important role in the economy of nitrogen. Pierre and Allaway (42) found that calcium in the soil is essential for the nitrification process to take place. In acid clay soils calcium is the limiting fac- tor for the development of micro—organisms, specially nitrifying bacteria. Calcium depresses the solubility of phosphorus (A8) at pH values higher than 7. McGeorge (28) states that the alkalinity caused by additions of lime to the soil is instrumental in reducing the availability of phos— phorus. When the soil contains free calcium, the phos- phate ions will combine with calcium ions and precipi- tate as an insoluble salt provided the pH is higher than 8. 10 Experimental Methods The soil used in the investigation was a gray-brown podzolic soil low in fertility characterized by a low total cation exchange capacity, a relatively high satura- tion of hydrogen and an acid reaction. A well decomposed peat which had pH 3.9 was used to increase the total cation exchange capacity of the soil. Sudan grass was used as the indicator of the uptake of potassium and calcium from the soil. The percent calcium saturation was adjusted with calcium acetate and the potassium was supplied as potas- sium chloride. Both of these salts were chemically pure. Laboratory Investigations Preparation of the H-soil In order to carry out certain studies of the effect of calcium saturation upon the release of exchangeable calcium and potassium it was necessary to prepare a hydro- gen saturated soil. Since the soil was low in total cation exchange ca- pacity, in order to have a relatively high total exchange capacity per unit weight, it was found convenient to eliminate the sand fraction. The sand fraction ( 0.052 mm) was separated by sieving retaining the very fine sand, silt, and clay 11 fractions respectively. By this procedure it was possible to increase the total base exchange capacity by more than 100 percent. In preparing a hydrogen saturated soil a very dilute solution of HCl was used to prevent changing the nature of the exchange complex. Gedroiz (l2) and Yarusov (51), in preparing a hydrogen soil, used 0.05 N HCl as the leaching solution to remove the exchangeable bases of the soil and to saturate it with hydrogen ions. Assuming that all the exchangeable cations are not leached out, it was decided to determine the effect of different concentrations of HCl-leaching upon the ex- change capacity of the soil. It was expected that a maximum point would be found in the curve formed by plot- ting the concentrations of HCl solutions against the total cation exchange capacity. A maximum capacity was found in every case as is shown in Table l. The maximum cation exchange capacity was found in most instances where the soil was leached with 0.1 N HCl solution as shown by the curve in Figure I. On this basis the H-sat- urated soil was prepared by leaching each 10 grams of soil with 500 ml of 0.1 N HCl. The saturated system was then washed with 150 ml of COe-free water until free from chlorides. Finally it was rinsed with 10 ml of 9&6 ethyl alcohol to eliminate occluded water. The soil was air-dried and stored. This procedure was assumed to give a soil one hundred percent saturated with hydrogen. Table l 12 THE EFFECT OF DIFFERENT CONCENTRATIONS OF HCL ON THE CATION EXCHANGE CAPACITY OF SOIL* Cation 33:22:“ 2:231 8:221“! hits: grams 1 0.000 0.1126 0.0663 0.0650 9.650 2 0.025 0.1214 0.0715 1.0399 10.399 3 0.050 0.1232 0.0725 1.0559 10.559 4 0.075 0.1337 0.0787 1.1460 11.460 5 0.100 0.1421 0.0836 1.2321 12.321 6 0.125 0.1319 0.0776 1.1290 11.290 7 0.150 0.1087 0.0640 0.9320 9.320 8 0.175 0.0890 0.0524 0.7625 7.625 9 0.200 0.0860 0.0506 0.7370 7.370 10 0.225 0.0850 0.0500 0.7290 7.310 11 0.250 0.0848 0.0495 0.7210 7.210 12 0.275 0.0839 0.0494 0.7190 7.190 13 0.300 0.0836 0.0492 0.7165 7.165 *The values reported are averages of two determinations. 13 COM. .0: 02. 11;... 3.1.1102 OO Ono. o ~mo110001 I'I'Tu ‘asuvuoxa NOILVO 0v .- 111.14!!!“ .... .. II)) I l 11111 l.. -11 I! IIIIIPIII IIIIIII 721.17...II|I 1«I . o | I I \‘I IIIIIIII ll .'. IlsIlll. I-.III. (III. 1‘ [II‘IIIIIIIIIIIIJ ...I 1 .III‘111 ILIII.III... 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IIIIIIdIIAIITIIIIIIIIfiIIIIIOIIoIYQ H}.I01!III111!IIQIlollAVII.I)I. . . . . .. . . .7. . . . « 1 . 1 . .. . . . a .. . . e . .. 1 . . . . . . . 1- .~ . 7. . . 1 . . . 1 q. . w . e 7 7 1 .1 . r r 1 I 121 The air-dried fine soil was leached with 0.1 N HCl in the ratio of 50 ml of solution for each gram of soil. The soil was then leached with distilled water until free of the chlorine ion. It was finally leached with 90 per- cent alcohol in the proportion of 5 ml per gram of soil. Preparation of H-peat A well decomposed and strongly acid (pH 3.9) peat was used. Although no bases were detected by titrating the residue remaining after all the leachate was evap- orated, with 0.05 N HCl, using methyl red as indicator, it was decided to leach the air—dry peat with 0.1 N HCl in the proportion of 25 ml per gram of air—dried peat. It was then washed with distilled water until free of chlorine. Alcohol was not used in the final leaching be- cause it has been found that it produces dispersion of some organic materials (33). The effect of percent calcium saturation on the adsorption of potassium added to the soil at different symmetry concentrations was determined by saturating the hydrogen soil with calcium from O to 25, 50, 75, 100 and 125 percent with respect to the total exchange capacity. At each calcium saturation level, potassium was added to make up 0, 0.5, 1.0, 1.5, and 2.0 symmetry con- centration levels. 15 The calcium was added to the soil in Erlenmeyer flasks in a solution of calcium acetate containing 0.1 m.e. Ca per ml. The excess water was evaporated fol- lowed by the addition of potassium as KCl in a solution containing 0.1 m.e. K per ml. The liquid phase was made up to 250 ml in every case. All the Erlenmeyer flasks were shaken and left standing at room temperature for a period of 72 hours, although the reaction is instan- taneous (26, 34). Aliquots of the supernatant liquid were removed with a bent-tipped pipette, filtered through Whatman filter paper No. 42 and analyzed for potassium using the flame photometer. Adsorbed potassium is reported as the difference between the initial and final concentrations. pH de— terminations with the glass electrode were made as soon as the initial volumes were made up and at the time of removing the aliquots for analysis. Greenhouse Experiment In order to determine the effect of percent calcium saturation on the uptake of calcium and potassium by sudan grass and find the interaction effects of treat- ments upon total yields, a factorial experiment was set up in which three factors were involved: cation exchange, percent calcium saturation and potassium levels respec- tively. 16 The cation exchange level served as an independent group in which three levels of percent calcium satura- tion and three levels of potassium were combined in all possible ways in order to have three groups with nine treatments each. Four replications were used. The air-dried soil was passed through a 3 mm mechan- ical sieve for the purpose of removing stones and other coarse materials. Seven thousand grams of soil were placed in each of the one hundred and eight glazed ear- thenware two—gallon jars which were then distributed at random in three groups of thirty-six units each. The first group received no peat and was designated as Ml' Peat was added to the soil in the second group in the proportion of five grams per one hundred grams of soil in order to give the desired exchange capacity which was determined previously in samples of different soil: peat ratios. This group was called M2. Similarly the third group was treated with 15 grams of peat per 100 grams of soil to give the highest cation exchange capacity which was designated as M3. See Table 2. The peat was sieved and mixed by hand in the proper proportions with the soil. The total weight of soil and peat in each case was ad- Justed to 7,000 grams per Jar. Each one of these cation exchange capacity levels was distributed at random in four replicates of nine Jars each. 17 With each of the cation exchange capacity treatments three levels of percent calcium saturation were estab- lished by adding 1 N calcium acetate in amounts, to give levels of Cal, Ca2, Ca3, representing forty, seventy, and one hundred percent calcium saturation respectively. The summary of treatments is shown in Table 3. Finally, three levels of potassium, using 1 N potas- sium chloride, were distributed factorially in order to have each percent calcium saturation level combined with each potassium treatment in all possible combinations as listed in Table 4. K [K1 {1 {1 Cal E K2 Ca2 E K2 Ca3 E K2 [ K3 [ K3 [ K3 The contents of each jar were mixed thoroughly by hand to give a homogeneous distribution of peat, calcium, and potassium throughout the soil. Soon after the saturating solutions were added, a strong fermentation process started in all jars accompa- nied by the evolution of carbon dioxide which was most conSpicuous in the M3 group. This action should aid in keeping the calcium ion in a free state. Hypothetically, the reaction can be represented as follows: Ca(CH3000)2 + H2003 + 03 g: CH1,L + 4002 + 21120 + Ca++ The Jars were left for eight days with adequate aera- tion for the purpose of allowing time for the attainment 18 Table 2 THE TOTAL CATION EXCHANGE CAPACITY OF TREATMENTS: M1, M2, AND M 3 Peat Added Organic Cation Exchange Treatments grams/100 Matter Capacity grams soil Percent m.e./100 grams M1 0 2.71 5.83 M2 5 7.05 10.85 9.82 19.13 M3 15 SUMMARY OF PERCENT CALCIUM SATURATION ON TREATMENTS M1, M2, AND M Table 3 l9 3 Ex- Ex- Ex- Ex- Satu- Calcium change- change- change- change- able able able ration Satu- able Bases Calcium Calcium Treat- ration Calcium . ments Percent m e /100 in Soil Required Added Crams m.e./100 m.e./100 m.e./100 Grams Grams Grams Treat- ment M1 Cal 54.88 3.20 3.20 0.00 0.00 Ca3 100.00 5.83 3.20 2.63 3.08 Treat- ment M2 Cal 40.00 4.34 3.15 1.19 1.75 Ca2 70.00 7.60 3.15 4.45 4.55 Ca3 100.00 10.85 3.15 7.70 7.89 Treat- ment “3 Ca1 40.00 7.65 3.10 4.55 4.63 Ca2 70.00 13.39 3.10 10.29 10.49 Ca3 100.00 19.13 3.10 16.03 16.31 Exchangeable calcium found by previous analysis was as follows: Treatment M Treatment M 1 2 Treatment M 3 2.17 m.e./100 grams 1.46 m.e./100 grams 1.35 m.e./100 grams 20 Table 4 THE POTASSIUM TREATMENTS ON CALCIUM SATURATION LEVELS IN TREATMENTS M1, M2, AND M3 RESPECTIVELY Potassium* m.e. 100 Ca Ca Ca grams 1 2 3 K1 0.00 0.00 0.00 K2 0.32 0.32 0.92 K3 0.64 0.64 0.64 * 0.32 m.e./100 grams = 250 pounds K/2 x 106 pounds soil 6 0.64 m.e./100 grams 500 pounds K/2 x 10 pounds soil The native exchangeable potassium found in the soil by analysis was equal to 0.19 m.e./100 grams. 21 of equilibrium. The jars were watered and seeded with sudan grass. After eight days the seedlings were thinned to twelve plants per jar giving an even distribution of plants. The plants were harvested after 45 days, at which time some had started to bloom. In general the growth was scant. In level M1’ at forty percent calcium satu- ration, no yields were recorded. It was believed the poor growth was due to deficiencies in other plant nutri- ents or to an unbalance of the nutrient elements in the soil. A second experiment was set up because of the poor plant growth in the first experiment. Nitrogen and phosphorus were added to all jars. Substances which would affect the "saturation status" the least were used, i.e., nitric and orthophosphoric acids in very dilute solutions. The high degree of dilution coupled with the high buffering capacity of the soil-peat systems re- sulted in no significant change in soil environment as indicated by the pH values shown in Tables 8 and 9. The nitrate ion was added at the rate of 500 ppm, requiring 3.53 ml of HNO CP grade (1.005 gms HN03/ml) per 7,000 3 grams of soil. PhOSphorus was added at the rate of 20 ppm. It required 3.05 ml of H3P04 CP grade (1.453 gms H3P04/m1) per 7,000 grams soil. The acids were made up to 600 ml with distilled water and the two solutions were mixed thoroughly to give a homogeneous system before be- ing applied to the jars. 22 The water holding capacity was determined previously at pF 1.6 and was found to be as follows: Level M1 = 8.09%, level M2 = 23.20% and level M3 = 55.40% respective- ly. Therefore, the water saturation in the cation ex- change capacity groups was brought up to the respective water holding capacities with additional water. The jars were left for five days to allow for aeration and at- tainment of equilibrium. The jars were then seeded with sudan. After 8 days the seedlings were thinned to 12 plants per jar distributed evenly over the entire area. The plants were harvested after 50 days when they had started to bloom. Exchangeable calcium and potassium were analized in the soil after cropping. The total contents of these cations were also determined in the aerial tissues of sudan grass after the yields (oven dry tops) were re- corded. Analytical Methods All quantitative determination were made using standard procedures. The percent organic matter in the soil and in the soil-peat mixtures was determined by the method of Peech (40). The soil sample was subjected to wet oxidation using a normal solution of potassium dichromate, activated 23 by the heat of dilution of concentrated sulfuric acid, and titrated with a normal solution of fresh ferrous sulfate to reduce the dichromate ions. The cation exchange capacity of the soil and the soil-peat mixtures was determined by saturating 20 grams of soil with 250 ml of 1 N barium acetate solution (25). The systems were left overnight and filtered with suc— tion. The saturated system was rinsed first with 100 ml C0 -free water and finally 50 ml of 95% ethyl alcohol 2 until free from acetate. The adsorbed barium ions were displaced with 300 m1 of l N ammonium chloride which was sufficient to give complete displacement, as evi- denced by tests for barium carried out with ammonium carbonate and sulfuric acid. The barium was precipitated as BaS04 with 0.01 N H2804 from a hot solution which was digested for two hours. The precipitate was then washed with plenty of boiling distilled water and filtered through Whatman paper No. 40. The precipitate was ignited at constant weight with the proper precautions to prevent reduction of the sulfate ion and weighed. The number of milli- equivalents of barium recovered as the sulfate is equal to the total cation exchange capacity expressed in m.e./100 grams of soil. The cation exchange capacities of the H-soil, the H-peat, and the hydrogen saturated soil-peat mixtures 24 which were prepared in the same way as the H-soil, were determined potentiometrically (27, 39). In making these determination, 10 grams of soil were saturated with 30 m1 of l N barium chloride. These were stirred and left overnight. The exchanged hydrogen was titrated poten- tiometrically with 0.05 N barium hydroxide which was added in small aliquots at intervals of two minutes. The equivalence point was determined by extrapolation in the titration curves to pH 7.00. In exploratory experiments it was found that the time rate of addition of the standard barium hydroxide is important in the neutralization of the hydrogen ions. At the interval of two minutes per addition, the equiv- alence point found by extrapolation in the curve, gave a value which compared favorably with values obtained by the gravimetric determination of barium in the sulfate precipitate. Otherwise, smaller values were recorded invariably. The total bases were determined by leaching the soil with 400 ml 1 N ammonium acetate solution (27). The system was left overnight and filtered with suction. The leachate was evaporated and the residue treated with 10 ml of concentrated nitric acid and 4 m1 of hydro- chloric acid to oxidize residual organic matter. The bases were then dissolved in a known volume of standard hydrochloric acid and back titrated with standard sodium hydroxide. Methyl orange was used as indicator. 25 The excess of base needed to neutralize the system, after the acid had been neutralized, was considered as equal to the total bases present expressed in m.e. per 100 grams of soil. The exchangeable calcium in soils was determined by Peech's Method (40). Calcium was precipitated as the oxalate in the ammonium acetate extract which had been evaporated and taken up with diluted nitric acid. An aliquot of the extract, heated almost to boil- ing, was saturated with 5% oxalic acid and adjusted to pH 4.6 with l N ammonium hydroxide using bromecresol green as the indicator. The calcium oxalate precipitate was titrated with 0.05 N potassium permanganate in the presence of 100 ml of hot 1 N sulfuric acid. The ex- changeable calcium is reported in m.e. per 100 grams. The exchangeable potassium in soils was determined by the method proposed by Attoe and Truog (4) whereby a soil sample is treated with a 2 N solution with respect to ammonium acetate and 0.2 N with respect to magnesium acetate. The systems were stirred and left overnight. They were then filtered with suction through Whatman paper No. 42 and made up to volume with the extracting solution. The determination of potassium was made spectrophotometrically using a flame photometer cali- brated with standard solutions made up with the extract- ing solution. A standard curve was prepared covering an adequate range of concentrations. 26 In plant analyses, the ground material was treated with perchloric and sulfuric acids mixed in the propor- tions of 2:1 (43). The mixture was added to the plant material in a 450 ml beaker followed by 20 ml of nitric acid. The plant material was oxidized first at low temperature but as soon as the nitric fumes disappeared the oxidation was completed at a higher temperature. The residual sulfates were taken up in H20, filtered through Whatman paper No. 42 and made up to volume. Calcium was determined by the procedure of Piper (43) whereby an aliquot of the extract is acidified with 5 ml of hydrochloric acid and neutralized with ammonia using methyl red until a full yellow color was developed. Hydrochloric acid is added until the solution turns red followed by the addition of 10 m1 of 2.5% oxalic acid. At this point, the solution is brought up to the boiling point and 10 m1 of ammonium oxalate is added drop by drop with constant stirring. The solution is cooled and adjusted with a saturated solution of sodium acetate to pH 5 (the indicator has an orange pink color with tendency to red). If an excess of sodium acetate is added the solution is adjusted to the proper pH with acetic acid. After the solutions are allowed to stand overnight they are filtered through Whatman paper No. 42 and washed with cold water until free from chlorine. Corrections were made for the error introduced by 27 oxidation of filter paper in the titration with the stan— dard permanganate solution in the presence of hot sul— furic acid (40). The calcium is reported as m.e. per 100 grams of plant material. Total potassium in plant materials was determined by the spectrophotometric method proposed by Attoe (3) whereby a finely ground sample is digested overnight with a solution of 2 N ammonium acetate and 0.2 N mag- nesium acetate, filtered through Whatman paper No. 42 and made up to volume with the extracting solution. The apparatus was calibrated and a standard curve prepared using solutions of known concentrations covering a range from O to 100 ppm. The final results are reported as m.e. of potassium per 100 grams of plant material. The pH of the soils was measured with the glass electrode using a soil water ratio of 1:2 by volume. All results are expressed on an oven—dry weight basis. 28 Experimental Results The Relationship Between the Inorganic (H-Soil) and the Organic Fraction (H-Peat) with Respect to Cation Exchange Capacity It has been reported (27) that the cation exchange capacity of the sum of the individual cation exchange ca- pacities of the organic and inorganic fractions is not equal to the cation exchange capacity of the mixture. In other words the cation exchange capacity is not an "additive property.” In the present study it was found that the cation exchange capacity of the mixture was less than the sum of the cation exchange capacities of the components. This is illustrated by the experimental data shown in Table 5. The decrease in cation exchange capacity by mixing the two components may be due to sorption of the organ- ic fraction by the hydrogen saturated soil resulting in a decrease of the available surface. The parallelism of the curves, shown in Figure II, suggest that the rate of sorption is constant over a wide range of variation in the ratio of the cation ex- change of soilzpeat, although cation exchange decreases exponentially the larger the ratio of cation exchange capacity of soil to peat. The curves would converge in both directions if extended, and continue parallel Table 5 THE RELATION BETWEEN THE CATION EXCHANGE CAPACITY OF SOIL-PEAT MIXTURES AND THE CALCULATED SUMS OF THE EXCHANGE CAPACITIES OF THE INDIVIDUAL COMPONENTS _:= Cation Sum. Treatments Cation Cation Cation grams grams grams grams grams ' ' 95 5 11.95 11.33 3.58 14.91 3.16 90 10 14.50 10.73 7.17 17.90 1.49 85 15 16.65 10.13 10.76 20.89 0.94 80 20 19.14 9.54 14.34 23.88 0.67 75 25 22.20 8.94 17.94 26.88 0.50 70 30 24.44 8.34 21.52 29.86 0.39 Cation exchange capacity H-peat = 71.70 m.e./100 grams. Cation exchange capacity H-soil = 11.92 m.e./100 grams. I 1 1 1 4 1 ....g III I i 'lIIIII 71:1“. III‘. 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P 1 » 1|) . 1% L ..EEuoozéé .LH mmswam w>H onsmfim \. .8: 2.6.: 2.0.2 0440. .momo onomm .mm¢mw Z¢QDm mo mB30mw zo mezmze¢mme EDHmm¢BOm 92¢ AZOHefimDB¢m EbHoq¢o BzmomMm «NBHo¢mH and m>H monsmfim 38 6>H magmas o>H magmas .5... ..Eth. a 2305! ii 653:9 .momo ozoomm .mmame zamsm mo mezomu zo mezmzeamme amemaeom 62a .ZOHaambeam szoqao ezmommm .weHoamao mezamoxm 20HaH mossmfim 39 m>H mpsmfim tn 8&2 .03.: is: 2.6.2 ‘Iwué 11“.“11| - AJA“‘1V,\ Ala 2.6.2 , I. ‘4 .4. ,. 2.171 K“ as”.: 6\ A... (new? _ .gt ... 5 - I /.\ .momo 9200mm .mmH ass m>H mopswfim 40 At M3, a tall scant growth occurred at 403 cal- cium saturation which may be attributed in part to a good supply of nitrogen. Again the maximum growth oc- curred at 706 calcium saturation. As is illustrated in Figure IVb, the addition of potassium at the K2 level influenced growth significantly over no potassium. With the M1 group the maximum growth corresponded to 100% calcium saturation while in the M2 and M3 treatments the best growth occurred with 703 cal— cium saturation. In the second crop, as was shown in the first crop, potassium did not affect growth as influenced by vary- ing the percent calcium saturation. This is proved by the evidence given in Figures IVd, IVe, IVf, whereby the percent calcium treatments were held constant and the potassium levels were varied within each of the cation exchange capacity groups. This, again indicates that the effect of potassium on the growth of sudan grass is less than the effect of percent calcium saturation. 41 The Effect of Percent Calcium Saturation and Potassium Treatments on Dry Matter Yield of Sudan Grass The yields obtained in the first and second crops are reported in Tables 8 and 9 and in Figures Va and Vb. The effect of percent calcium saturation upon dry Hatter yield of sudan grass has been determined quanti- tatively by finding the relation of average yields and the analysis of variance. In general yields were higher for the second than for the first crop. It is worthy to indicate here the relation of the cation exchange capacity level with percent base satura- tion as affecting yield. In the second cr0p, group Ml, an increase in yield was obtained by increasing the per— cent calcium saturation. In group M2 the trend was somewhat similar to M1 although maximum yield was ob- tained with 70% calcium saturation. In group M3 yields decreased with an increase in percent calcium saturation (Figure Vb). The effect of potassium on yield was somewhat variable but in general, higher yields were associated with the K2 level (250 pounds of potassium per acre). In order to determine the validity of these results an eXperiment, using a factorial design, was set up and the results analyzed statistically (9). 42 Ca3 Treatment Ca2 Treatment Table 8 EXPRESSED IN GRAMS First Crop, Ml level THE OVEN-DRY WEIGHT OF SUDAN GRASS PRODUCED PER JAR Cal Treatment tions Rep- lica- 2 0.. First Crop, M2 level 0.70 1.60 1.00 1.10 2.50 3.20 0.90 1.80 3.50 1.90 3.20 2.50 0 1.20 1.00 0 0.40 1.70 0 1.00 1.30 0 0.90 1.90 0 4 5 5 l 0 0 O 1.40 1.80 3.80 1.40 1.50 1.60 3.30 1.70 50 70 30 60 2 1 1 l 1 2 3 4 pH Start End 0.70 1.10 0.90 1.50 1.30 0.80 1.30 1.10 1.00 0.90 1.00 1.00 First Crop, M3 level .00 1.60 1.60 1.30 602 1.70 2.00 1.40 2.80 3.30 2.40 3.90 1. R25 .44 The pH measurements were made on composite samples drawn from the jars of the same treatments. 43 1010 1070 0.85 1.95 1.10 1.20 1.80 1.20 1.70 2.57 1.60 1.90 Ca3 Treatment Ca2 Treatment Table 9 EXPRESSED IN GRAMS Second Crop, M1 level Second Crop, M2 level Second Crop, M3 level 0.21 0.25 0.20 0.20 0.18 0.22 0.20 0.60 0.20 0.15 0.35 0.18 THE OVEN-DRY WEIGHT OF SUDAN GRASS PRODUCED PER JAR Cal Treatment tions 1 2 3 4 pH Start End Rep- lica- .30 8.60 7.00 7.15 6.40 6.10 7.40 7 6.6010.00 6.95 7.10 6.70 1 2 3 4 pH Start End drawn from four Jars of the same treatment. * The pH measurements were made on composite samples ‘1141 1141 I411] ‘3§‘-fi1jii!lll #1 1111 11‘ 7. .....7 7.. 7. ._.. . 7 M . 9 .. n 1 .1 . .7.1 9119 . . . 1.... 7 17 ..7 v . 7 .. . 1.. .u... . 7 .771 . n l... . . 1 7 . . . . 70.1.1W17 . 7 . . 7 Iololllvr 101-1 l11‘l111q1 .n 1101 1.1 0 I111! 111. 111.19... 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A 7 1 . . .L .. ... . .1. .. 7 7.. .7 . 7 .. ... .... . 7 . .7 7... q .. . .. . . . . ._ _ .. . .7 . . ,. . .-. . . . . 7 , .. . . . . 7 P'nl'11'rr10‘1- Ill 1 I-IIIIIOV}. nl'rllhtttllil 10h ‘lrlrlhlbllllb. l11|11111t1»1.£1'tttl§| vr’$l.ll P » 7? .r 11 1! . 0|? b [111..." ‘I! ll.‘.u{'r 1'1! 01*:unt'ln‘t. 1". 1.411.“.1; 5 7 .16 1 1.. .11 .7 1 . J1 H 0 A71 1 . . l I J; .1 .77 1 7.1 n 7‘ '1 A. u. . .9 ..07 a. 7 . 0 . .17. .7 1 .. . u Lv 11.1 a. ‘0 1 . . 6. 77+ :1 o p 11% ‘71. 11 ‘~‘+. 9 l1. 1.71 1 . 77L- 1 J.... V ' m 1111+? 1.1L 01‘ 91-9 o‘ +- 1“ '31". 1‘1 - L.7A 46 The analysis of variance of the yields of sudan grass are reported in Tables 10, ll, 12, 13 and 14. As has been pointed out, each cation exchange level constituted an independent group; M1, M2, and M3 both in the first and second crop. In each group there were 9 treatments which, for the purpose of analysis of variance, gave 8 combinations. Each treatment was associated with a single degree of freedom. The error term statistically associated with each treatment has 3 degrees of freedom. In a preliminary analysis of variance each of the 8 error terms were calculated. Since it was suspected that they may not be statistically different from each other a test of homogeneity was carried out. After running Bartlett's test (5), as it is illustrated by Snedecor (46), it was found that there was no evidence of heterogeneity in the various error term mean squares. Therefore, all treat— ments were tested for significance using the pooled er— ror term as the experimental error. Besides the mean squares calculated for each treat- ment comparison as shown in the respective tables, mean squares, associated with other treatment comparisons, were calculated and are liSted in Tables 10, ll, l2, l3 and 14. Table 10 47 ANALYSIS OF VARIANCE OF SUDAN GRASS YIELDS AS AFFECTED BY PERCENT CALCIUM SATURATION AND POTASSIUM TREATMENTS Source of Variation D.F. S.S. M.S. F Tests Unit M2, First Crop Total 35 26.41 Replications 3 0.24 (Ca3-Cal) 1 6.10 6.10 13.86** (Ca3-Cal+20a2) 1 1.84 1.84 4.18 (KB-Kl) 1 3.01 3.01 6.84* (K3+Kl-2K2) 1 1.10 1.10 2.50 (Ca3-Cal)(K3-Kl) 1 0.30 0.30 0.68 (Ca3+Cal-20a2)(K3-Kl) 1 0.28 0.28 0.64 (Ca3-Cal)(K3+Kl-2K2) 1 2.26 2.26 5.14* (Ca3+Ca1—2Ca2)(K3+K1- -2K 1 0.80 0.80 1.82 Experimental Error 24 10.48 0.44 Other Comparisons (Ca2-Cal) 1 0.00 0.00 — (Ca3-Ca2) 1 5.80 5.80 13.18** (Kg-K1) 1 0.00 0.00 — (KB-K2) 1 3.05 3.05 6.85* (Caz-Cal)(K2-K1) 1 0.16 0.16 0.36 (Ca2-Cal)(K3-K2) 1 1.32 1.32 3.00 (Ca3-Ca2)(K2- K1) 1 0.20 0.20 0.45 (Ca H—Ca2)(K -K2) 1 2.18 4.95 4.95* AVERAGE YIELD VALUES - GRAMS PER JAR Cal Ca2 Ca3 Kl 1.15 1.77 0.60 1.17 K2 2.27 2.50 0.88 1.88 K3 2.55 1.62 1.48 1.88 1.99 1.96 0.98 Table 11 48 ANALYSIS OF VARIANCE OF SUDAN GRASS YIELDS AS AFFECTED BY PERCENT CALCIUM SATURATION AND POTASSIUM TREATMENTS m __=_ Source of variation D.F. S.S. M.S. F Tests Unit M3, First Crop Total 35 24.91 Replications 3 1.85 (Ca3-Cal) 1 13.65 13.65 44.03** (Ca3+Cal-2Ca2) l 0.66 0.66 2.13 (KB-K1) 1 0.71 0.71 2.29 (K3+Kl-2K2) 1 0.15 0.15 0.48 (Ca3-Cal)(K3-Kl) 1 0.36 0.36 1.16 (Ca3+Ca1-2Ca2)(K3-K1) 1 0.05 0.05 0.16 (Ca3-Cal)(K3+Kl-2K2) 1 0.08 0.08 0.26 (Ca3+Cal-2Ca2)(K3+Kl-2K2 ) 1 0.04 0.04 0.13 Experimental Error 24 7.36 0.31 Other Comparisons (Caz-Cal) 1 6.51 6.51 21.00** (Ca3-Ca2) 1 1.31 1.31 4.22 (Ka-Kl) 1 0.07 0.07 0.02 (KB-K2) 1 0.57 0.57 1.84 (Ca2-Cal)(K2-K1) 1 0.28 0.28 0.90 (Ca 2-Ca1)(K3-K2) l 0.00 0.00 - (Ca 32—0a2)(K -K1) 1 0.00 0.00 - (Gag-Ca2)(E§ -K2) 1 0.01 0.01 0.03 AVERAGE YIELD VALUES - GRAMS PER JAR Cal Ca2 0&3; K1 2.50 1.10 0.66 1.41 K2 2.12 1.25 0.75 0.75 K3 1.77 0.93 0.50 1.06 2.13 1.09 0.62 Table 12 49 ANALYSIS OF VARIANCE OF SUDAN GRASS YIELDS AS AFFECTED BY PERCENT CALCIUM SATURATION AND POTASSIUM TREATMENTS Source of Variation D.F. S.S. M.S. F Tests Unit M1, Second Crop Total 35 14.85 Replications 3 0.80 (Ca3—Cal) 1 10.10 10.10 132.89** (Ca3-Cal—2Ca2) 1 1.49 1.49 19.60** (K3-K1) 1 0.17 0.17 2.24 (K3+K1-2K2) 1 0.01 0.01 0.13 (Ca3-Ca1)(K3-Kl) 1 0.19 0.19 2.50 (Ca3+Cal-2Ca2)(K3-Kl) 1 0.19 0.19 2.50 (Ca3-Cal)(K3+Kl—2K2) 1 0.04 0.04 0.53 (Ca3+Cal—20a2)(K3+K1—2K2) 1 0.03 0.03 0.39 Experimental Error 24 1.83 0.076 Other Comparisons (Ca2-Cal) 1 0.30 0.30 3.39 (Ca3-Cal) 1 7.04 7.04 92.63** (K2-Kl) 1 0.04 0.04 0.52 (KB—K2) 1 0.04 0.04 0.52 (Caz-Ca1)(K2—Kl) 1 0.00 0.00 - (Ca3-Ca2)(K3-K2) 1 0.00 0.00 — (Ca3-Ca2)(K2-Kl) 1 0.28 0.28 3.68 (Ca3-Ca2)£E:-K2) 1 0.02 0.02 0.26 AVERAGE YIELD VALUES - GRAMS PER JAR Cal Ca2 Ca3 Kl 0.20 0.47 1.85 0.84 K2 0.35 0.54 1.40 0.76 K3 0.20 0.41 1.41 0.68 0.25 0.47 1.55 Table 13 50 ANALYSIS OF VARIANCE OF SUDAN GRASS YIELDS AS AFFECTED BY PERCENT CALCIUM SATURATION AND POTASSIUM TREATMENTS Source of Variation D.F. S.S. M.S. F Tests Unit M2, Second Crop Total 35 177.29 Replications 3 1.29 (CaB-Cal) 1 63.20 63.20 38.07** (Ca3+Cal-2Ca2) 1 26.14 26.14 15.75** (K3-Kl) 1 23.52 23.52 14.17** (K3+K1-2K2) 1 3.90 3.90 2.35 (Ca3-Cal)(K3-Kl) 1 12.27 12.27 7.39* (Ca3+Ca1—2Ca2)(K3-Kl) 1 7.05 7.05 4.25 (Ca3—Cal)(K3—Kl—2K2) 1 0.09 0.09 0.05 (Ca3+Cal-2Ca2)(K3+Kl-2K 1 0.06 0.06 0.04 Experimental Error 24 39.77 1.66 Other Comparisons (Caz-Cal) 1 1.96 1.96 2.36 (Ca3-Ca2) 1 1.04 1.04 1.25 (Xe-Kl) 1 21.90 21.90 13.40** (K3-K2) 1 0.53 0.53 0.36 (Ca2-0a1)(K2-Kl) l 0.06 0.06 0.07 (Cae-Ca1)(K3-K2) 1 0.02 0.02 0.01 (Ca3-Ca2)(K2-Kl) 1 0.36 0.36 0.43 (CaB-Ca2)(K§-K2) 1 1.56 1.56 1.87 AVERAGE YIELD VALUES - GRAMS PER JAR Cal Ca2 Ca3 Kl 0.86 4.65 2.31 2.58 K2 2.02 5.45 5.37 4.29 K3 1.89 5.03 6.81 4.58 1.59 5.02 4.83 Table 14 51 ANALYSIS OF VARIANCE OF SUDAN GRASS YIELDS AS AFFECTED BY PERCENT CALCIUM SATURATION AND POTASSIUM TREATMENTS Source of Variation D.F. S.S. M.S. F Tests Unit M3, Second Crop Total 35 51.28 Replications 3 6.45 (CaB-Cal) 1 6.88 6.88 8.29** (Ca3+Cal-2Ca2) 1 0.12 0.12 0.14 (K3-Kl) 1 2.25 2.25 2.71 (K3+Kl—2K2) 1 13.72 13.72 16.53** (Ca3-Cal)(K3-Kl) 1 0.08 0.08 0.09 (Ca3-Cal)(K3+Kl-2K2) 1 1.36 1.36 1.64 (Ca3+Cal-2Ca2)(K3-Kl) 1 0.25 0.25 0.30 (Ca3+Cal-2Ca2)(K3+K1-2K2) 1 0.35 0.35 0.42 Experimental Error 24 19.82 0.83 Other Comparisons (Caz-Cal) l 70.50 70.50 43.46** (Ca3—Ca2) l 0.21 0.21 0.13 (K2~Kl) 1 0.11 0.11 0.13 (K3-K2) 1 0.04 0.04 - (Caz-Cal)(K2-Kl) 1 0.07 0.07 0.04 (Ca2-Cal)(K3—K2) 1 0.08 0.08 0.06 (Ca3-Ca2)(K2-Kl) l 4.79 4.79 2.88 (Ca3-Ca2)(K3-K2) 1 3.75 3.75 2.26 AVERAGE YIELD VALUES - GRAMS PER JAR Cal Ca2 Ca3 Kl 6.66 5.80 5.40 5.95 K2 7.91 7.30 7.50 7.50 K3 7.25 6.76 5.71 5.71 7.27 6.62 6.20 52 The significance of the effect of the treatments were determined by means of the F tests at the 5 and 1 percent levels of probability. They are shown with one and two asterisks reSpectively. An interpretation of the analysis of variance will be presented under "discussion." The Relationship of Percent Calcium Saturation and Concentration of Exchangeable Potassium in Soils with the Contents of Calcium and Potassium in the Plant The results of analysis for the calcium and potas- sium content in the soil after cropping and the plant materials are reported in Tables 15, 16, 17, and 18 for both the first and second crops. The contents of exchangeable calcium and potassium in the soil increased in accordance with the initial saturation concentrations (Tables 15 and 17). In the plant materials the analysis of calcium and potassium reveal that the contents of these two cations have a relationship with the percent calcium satura- tion and the content of exchangeable potassium in the soil. An examination of the data shown in Tables 16 and 18 reveals the fact that an increase in percent calcium saturation in the soil decreases the calcium uptake by the plants except in case of M1 group. The potassium content in the plant material increased as the concentration of exchangeable potassium in the soil is raised. 53 Table 15 CALCIUM AND POTASSIUM CONTENT IN SOIL AFTER CROPPING FIRST CROP Treatment Ca, K, Ca Weight Ca, m'e‘ Weight K, ”'9' Sat— K Sample ppm E88 Sample ppm Egg gig; level grams grams Ml level: Cation exchange capacity 5.83 m.e./100 grams. 1 25.00 228 1.144 20.00 3 0.054 Cal 2 25.00 96 0.480 20.00 20 0.333 3 25.00 154 0.772 20.00 38 0.655 Ca2 2 25:00 335 1:676 20:00 23 0:310 3 25.00 314 1.568 20.00 61 0.780 II’ 25.00 . . . Ca3 2 25.00 478 2.392 20.00 34 0.435 3 25.00 595 2.976 20.00 61 0.7 0 M2 level: Cation exchange capacity 10.85 m.e./100 grams. 1 25.00 578 2.388 20.00 54 0.690 Ca1 2 25.00 500 2.500 20.00 53 0.678 2 .00 4 6 2.180 20.00 66 0.844 1 O 3. O O Caz 2 25.00 829 4.144 20.00 41 0.524 3 25.00 4.0 2 20.00 78 0.9 7 :1 25.00 818’ 5.4%8““20700“‘I§“UTI%6 Ca3 2 25.00 1089 4.889 20.00 0.486 3 25.00 1042 5.208 20.00 0 1.020 M3 level: Cation exchange capacity 19.13 m.e./100 grams. 1 25.00 1009 5.049 20.00 7 0.090 Cal 2 25.00 978 4.890 20.00 142 1.816 %_r 25.00 1248 6.240 20.00 212 2.711 25.00 1509 *7.544 20.00 7* 0.090 Ca2 2 25.00 109 5.498 20.00 44 0.56% 3 25.00 149 7.468 20.00 #91 1.93 I? 25.007 2163 ‘10.816’ 20.00 53 0.680 Ca3 2 25.00 1861 9.302 20.00 79 1.015 3 25.00 2094 10.471 20.00 100 1.287 Table 16 54 CALCIUM AND POTASSIUM CONTENT IN PLANT MATERIALS FIRST CROP W Treatment Ca, K, Ca Sample Calcium méi‘ Sample P2233” 36:. Sat- K Weight* Percent 9 Weight* ura- level 100 Percent 100 t ion grams grams Ml level: Total cation exch. capacity 5.83 m.e./100 gms 1 - _ _ _ - 031 ’g‘ : : ' : : : 1 1.00 '0. 720 36.40 0.50 1.40 35. 09 Ca2 2 1.00 0.722 36.10 0.50 1.52 8. 88 3 1.00 0.460 23.00 0.50 1.92 9.11 ‘1.00 0.568 28.42 0.50 1.28 32.74 Ca3 2 1.00 0.526 26. 0.50 1. 64 41.95 3 1.00 0.368 18. 0 0.50 l. 82 46.55 M2 level: Total cation exch. capacity 10.85 m.e./100 gms 1 1.00 0.938 46. 90 0.50 1.38 35.30 Ca1 2 1.00 0.864 0.50 2.20 56.27 __3 1.00 0.774 %670 0.50 . 59. 4 *1.00 0.9061.§0 0.50 1. 3 . Ca2 2 1.00 0.836 0.50 1.76 45.02 3 1.00 0.692 4.60 0. 0 1.60 40. 2 1 1.00 0.658 . . . 2 .5 Ca3 2 1.00 0.830 41.50 0.50 1.14 22.16 3 1.00 0.622 31.10 0.50 1.34 M3 level: Total cation exch. capacity 19.13 m.e./100 gms 1 1.50 0.761 57.53 0.50 1.08 27.02 Cal 2 1.50 0.647 48.66 0.50 1.88 48.10 3 1.50 0.52 .20 0.50 1.90 48.60 1 1.50 0. 9. .5 . 2 . Ca2 2 1.50 0.625 46.93 0.50 1.40 35.81 3 1.50 0.217 17.00 0.50 1:38 5. 6 1 1.50 0.417 31.33 0.50 1.30 .2 Ca3 ,2 1.50 0.522 39.20 0.50 1.24 31.72 3 1.50 0.358 26.87 0.50 1.88 48.10 The sample weights reported are the equivalents to the aliquot used in the analysis. 55 Table 17 CALCIUM AND POTASSIUM CONTENT IN SOIL AFTER CROPPING SECOND CROP Treatment Ca, K, Ca Weight Ca, még' Weight K, mg?“ Sat— K Sample ppm p Sample ppm p ura— level 100 100 tion grams grams Ml level: Cation exchange capacity 5.83 m.e./100 grams. l 20.00 140 0.700 20.00 038 Cal 2 20.00 163 0.815 20.00 30 0. 3 0 § 20.00 272 1.%gg 20.00 5 20.00 660 ‘3. 20.00 Ca2 2 20.00 544 2.720 20.00 23 0.319 _g 20.00 606 .0 0 20.00 56 0. 716 20100 1136 5. ‘08 820.00 4 0. 051 Ca3 2 20.00 9 2 4.660 20.00 20 0.256 3 20.00 12 1 6.405 20.00 55 0.709 M2 level: Cation exchange capacity 10.85 m.e./100 grams. 1 20.00 606 3.030 20.00 30 0.380 Cal 2 20.00 611 3.105 20.00 2? 0. 371 3 20.00 637 .18 20.00 4 0.561 1 20.00 11 6 5.. 5 Ca2 2 20.00 1320 6. 600 20.00 22 0.281 3 20.00 1 44 6. 720 20.00 50 0.6 T— 20000 O 0 C63 2 20.00 1591 7.955 20.00 18 0.2 0 3 20.00 2019 10.095 20.00 46 0.5 8 M3 level: Cation exchange capacity 19.13 m.e./100 grams. 1 20.00 1087 5.435 20.00 .29 0.371 Cal 2 20.00 ‘ 994 4.970 20.00 2 0.026 3% 20.00 100% 5.04% 20.00 g 0.0g8 20.00 19 9. 2 . . Ca2 2 20.00 1700 8.500 20.00 11 0.141 37 20.00 1911 9.555 20.00 32 0.40 20.00 1599 7.495 20.00 . Ca3 2 20.00 2175 10.875 20.00 56 0.716 3 20.00 2524 12.620 20.00 110 1.408 Table 18 56 CALCIUM AND POTASSIUM CONTENT IN PLANT MATERIALS SECOND CROP Treatment 08, K, Ca Sample Calcium méi' Sample ngfiz- méi. Sat- K Weight* Percent E00 Weight* P t 100 ura— level ercen grams grams tion Ml level: Total cation exch. capacity 5.83 m.e./100 gms 1 0.40 1.400 28.00 0.18 0.78 19.95 Cal 2 0.40 1.165 2 .30 0.05 1.00 25.57 3 1.00 1.730 .50 0.30 1.70 43.48 iI* 0.50 *1.088 5 .40 0.50’ 0.66 16.88 Ca2 2 1.50 0.517 38.83 0.50 1.58 40.41 3 1.20 0.596 .72 0. 0 1.97 50.39 1.20 0.768 . 9 . .2 . 9 Ca3 2 1.20 0.809 48.54 0.50 1.52 38.88 3 1.20 0.681 40.78 0.50 1.56 39.90 M2 level: Total cation exch. capacity 10.85 m.e./100 gms 1 1.00 1.088 54.40 0.50 1.46 37.34 Cal 2 1.20 0.815 49.19 0.50 2.16 55.25 3 1.50 0.667 50.4 0.50 2.20 56.27 I‘ 2.50 0. . 0.50 1.44“":36780 Ca2 2 2.50 0.412 51.26 0.50 2.28 58.32 3 2.50 0.192 24.80 0.50 2.52 64. 6 1 1.00 0.660 33.00 0.50 1.2 . Ca3 2 2.00 0.485 48.46 0.50 1.82 46.55 3 2.00 0.222 27.20 0.50 2.20 56.27 M3 level: Total cation exch. capacity 19.13 m.e./100 gms 1 2.50 0.492 61.82 0.50 1.02 26.10 Ca1 2 2.50 0.347 43.49 0.50 2.48 63.43 3 2.50 0.094 11.80 0.50 2.84 72.64 1 2.50 ‘0.281 35.10 0.50 1.14 29.16 Ca2 2 2.50 0.630 78.80 0.50 1.74 44.51 3 2.50 0.094 11.80 0.50 1.80 46.04 :I‘ 2.50 ‘0.243 30.44* 0.50 1.86 . Ca3 2 2.50 0.315 39.46 0.50 2.20 56.27 3 2.50 0.157 19.57 0.50 2.24 57.30 The Relationship Between the Exchangeable Forms of the Ca:K Ratio in the Soil and the Ca:K Ratio in the Aerial Plant Tissue The Ca:K ratios in soils and in the plant materials, in terms of m.e., were calculated from the results re- ported in Tables 15, l6, l7, and 18. The relation of the CazK ratios is shown in a scatter diagram in Figure VI. A preliminary correlation analysis gave a coefficient of r = +0.18 which is not significant although it suggests that there is a trend which is di- reCtly proportional. 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I . ‘1 ... 1. .1 «A x .1... ... 1 j 1 r . .. .V L 4 . . 1 LH .. v-r v v .. 0 ' . .0 . .. . .L, V , . . o 0.1; . .. . ”tj A w . _ f. ‘1. -11 1 1;! 1-119! 4 411 . . v p. . . Dali ‘ C1 . o . w .1. .4. 1 fl .1. e v Y. A ... +11 0 r1. 4 _. 7.. 3 . e. . ., J 1.-.. . . .740. o .. HJ&O.f44 c T.,.J . v..... o.._ . . L 144 141] 1 1 . ~ ..u I. e o... v .1 . .10 V We 0. 7| 0 T. A «I 1 o 4 V¢ . .. fl P. Y. . . 0 1 C I . m .. ”Iliunlb!’ ....I". 1-...-.“ -’~- . - .44 , f ' .4 *- . A..-‘ AI “- O-Innnn- a .lnn .I An- ..- ---- 59 Discussion For the most part the results obtained in this in— vestigation confirm current hypotheses and theories rela- tive to cation exchange and the effect of degree of calcium saturation on the release and uptake of exchange- able calcium and potassium by plants. The complexity of the problem of plant nutrition is clearly indicated. The non—additive effect of the organic and inorganic fractions on the cation exchange capacity of the soil is due to adsorption, although it cannot be stated which is the adsorbent and which is the adsorbate. It may well be a process of "mutual sorption." Obviously the extent of mutuality is not the same as shown by the curves in Figure II which do not correSpond to those of an equilateral hyperbole where the distance from a given point in the coordinates is the same as the correspond- ing points in the curve. The nature of the curves indi— cate that the peat is playing a major role in the effect of "mutual sorption" as is revealed by the measurements of cation exchange (Table 5). The process of "mutual sorption" which may involve a mechanism of molecular orientation and polar adsorp- tion, resulting in a decrease in the specific surface, would cause a decrease in cation exchange capacity. The explanations offered are hypothetical and need to be 60 tested further under varying conditions. Similar sug- gestions have been proposed by other workers (27). It was found that the higher the percent calcium saturation the greater the adsorption of potassium (from KCl) irrespective of symmetry concentration of potassium added. These results are in agreement with those reported by Peech and Bradfield (41) who showed that potassium supplied as a neutral salt replaces calcium more easily than hydrogen from the exchange complex and that the adsorption of potassium from solu- tion increased with an increase in the percent calcium saturation. This cation exchange reaction is in turn dependent upon the energy of adsorption of the cations involved (12). The growth of plants, in general, increases with an increase in percent calcium saturation (8) as is shown in Figure IIIa. However, when the total concen- tration of salts in solution exceeded a certain value, 100 x 10"5 Ohms'l, as determined by conductivity mea- surements the growth of sudan grass decreased consider- ably. This indicates that some of the plant nutrients are taken directly from the soil solution (42). If such is the case, then the concentration of salts near the root membranes becomes an important factor in the uptake of cations. It is apparent that the significance of os- mosis and Donnan equilibrium cannot be overlooked (32). 61 At 40 percent calcium saturation no growth was re- corded in group M1. The scant growth obtained in the M3 group, even at 40 percent calcium saturation, may have been due to additional nitrogen released by the peat. There is also the possibility that more potassium was released where peat was added (24) as shown in Figures IIIa, IVa, IVc, IVe. In the second crop it is of interest to note that in the M1 group, maximum growth occurred at 100 percent calcium saturation while in groups M2 and M3 best growth occurred at 70% calcium saturation. The fact that maximum growth occurred at 70% calcium saturation in groups M2 and M suggests that other factors such as 3 the supply of nitrogen, phosphorus, or probably minor elements resulted in an improvement in fertility (28, 48). In other words, sudan grass made its best growth at 70% calcium saturation when the other nutrient ele- ments in the soil were properly balanced. These re- sults are in accord with those obtained by Allaway (2). Potassium additions did not have an appreciable effect upon the growth of sudan grass (Figures IIIb and IVd). This may be explained on the basis of "selective adsorption” of this plant species. Any plant may ex- hibit "selective adsorption" (10). In view of these results sudan grass is a poor indicator of potassium deficiencies in soils. 62 As shown in Figure Va the dry matter yield of sudan varied with changes in percent calcium saturation al- though the effect varied in each one of the independent groups. I According to Figure Va, and the analysis of variance data presented in Tables 10 and 11, it is observed that in group M2 there is a highly significant difference among the calcium saturation treatments. The response is, Cal) Ca but Ca g Ca . The best yield 2‘ 3 2 1 corresponds to 40% calcium saturation. Ca2 ) Ca In case of the potassium treatments K1 < K2 9: K3. The best being K and K levels. 2 3 In group M3 (Table 11) the difference in response to the various percent calcium saturation treatments is highly significant in most cases. Cal) Ca2 and Ca3, but Ca2 g Ca3. The maximum yield is associated with 403 calcium saturation. The yield reSponse to potassium is not significant 1 = K2 = K In the second crop at the M1 level (Table 12) the at any level. K percent calcium saturation affected the yield of sudan 2' l - Cae. The maximum yield corresponds to 100% calcium saturation. grass significantly, Cal ( Ca3; Ca2 ( Ca3 but Ca The response of yield to potassium treatments is not significant at any level. It means K g K 3'K 1 2 3° 63 In group M2 (Table 13) the yield response to per- cent calcium saturation is highly significant only in the comparison of the extreme levels, i.e., Ca3‘> Ca1 ; Ca but Ca and Ca g Ca . The maximum yield cor- 2 l 3 2 responded to 1005 calcium saturation. As is shown by the response curves the potassium treatments affected yield significantly: K3 ) K1; K2 ) Kl; but K3 g K2. The highest yield was obtained with K3 level. In group M3 (Table 14) the yield response to cal- cium saturation is highly significant for the comparison Ca3 < Cal; Ca2 < Cal; but Ca3 2’ 0212 therefore the best yield corresponds to treatments Cal, i.e., 40% calcium saturation. The reSponse to potassium is not significant at any level. Essentially, Kl g'K2 g’K3. Thus, in the first crop maximum yields were ob- tained at 40 percent calcium saturation but were not affected by the potassium treatments. In the second crop, the best yields correspond to 100 percent calcium saturation except in group M which 3 equaled those with 40 percent calcium saturation. Again, the potassium treatments did not affect yields signifi- cantly. The significance of either the (K3 + Kl - 2K2) or (Ca3 + Cal — 2Ca2) comparisons means that the response curves of potassium and calcium deviate considerably 64 from a straight line. The significance of (Ca3 - Cal) (K3 + Kl - 2K2) indicates that the quantities which are the products of these two expressions vary over the replications by an amount which is not due to chance. Finally, the non—significance of the interaction of the quadratic reSponse of calcium and the linear Iresponse of potassium would mean that the experimental values obtained do not differ by quantities different from those which are due to chance. The results showing that there is a relationship between the percent calcium saturation and potassium content in the soil with the content of calcium and potassium in the aerial plant tissues is important and shows that the concentration of the exchangeable cations in the soil colloids, other factors being equal, in- fluences the chemical composition of the plant tissues. The fact that an increase in percent calcium saturation in the soil correSponds to a decrease in calcium uptake is not due necessarily to a direct effect of percent calcium saturation. Rather this effect may be due to an antagonistic effect of potassium (10), the ionic activity of which is enhanced significantly by the increase in percent calcium saturation (29) resulting in a relatively higher availability of potassium. These results are in accordance with the theory that the uptake of cations by plants may take place by a process of contact exchange (20) in which the adsorption of the exchangeable cations in question plays an important role (12). An additional support to these findings are the interpretations offered by Peech and Bradfield (41) who state that the hydrolytic release of potassium at a given percent of potassium saturation will increase rapidly with.an increase in percent calcium saturation. The study of the relationships of the Ca:K ratios in soils with the Ca:K ratios in plants has received a considerable amount of investigation (6, 30, 42) to determine if a definite relationship exists. So far, a definite relationship has not been found. A correlation analysis of the soil Ca:K ratios versus the Ca:K ratios in the plants was made from the analytical data obtained from the first crop (Table 15). A positive correlation was found (r = +0.46) which is significant at the 5% level. When the analytical results shown in Table 17 were included with those calculated from Table 15, a statistical analysis failed to give a significant posi- tive correlation. The failure to find a significant correlation does not mean that there is no relation at all, for it is found that perhaps a trend may exist (Figure VI). In general, when calcium is higher than potassium in the soil, potassium will be dominant in the plant. This is attributed to a characteristic of ionic selec- tivity by the plants (10). This is why the Ca:K ratios 66 in the soil has little relationship to the Ca:K ratios in plants. Similar results have been reported by other workers (6, 30). The fact that there is not a close relationship between yields and the Ca:K ratio in soils is in agree— ment with results reported by other workers (6). How- ever, it was observed in the studies herein reported that yield decreases where the Ca:K ratios are above 30 and no yield was recorded when ratios were below 2. The wean of the soil Ca:K ratios associated with the highest yields was 15.70. Bear and Toth (6) found that a Ca:K ratio of 13 gave the greatest yield of alfalfa. These results would indicate that each plant species does not give maximum yield at the same Ca:K ratio in the soil even though the other factors of growth are at an Opti- mum 0 Summary and Conclusions This investigation was carried out with the purpose of studying the effect of cation exchange capacity and percent calcium saturation on the release and uptake of calcium and potassium and the effect of these factors on growth and yield of sudan grass. The methods of investigation used embraced two phases: chemical investigations and greenhouse experi- ments. 67 The laboratory studies were made to determine the relationship existing between the individual cation ex- change capacities of the organic and inorganic frac- tions and the cation exchange capacity of their mixture. It was found that the property of cation exchange capa- city is not additive:i the cation exchange capacity of the mixture is less than the cation exchange capacity of the individual components. In a laboratory experiment a hydrogen saturated soil was treated with calcium at various percentage saturation levels with respect to cation exchange ca- pacity and potassium added from potassium chloride at different symmetry concentrations. It was found that the adsorption of potassium through exchange depends on percent calcium saturation although above 75p calcium saturation no significant variations in adsorption were noticed. In the greenhouse experiment gray—brown podzolic soil low in cation exchange capacity, acid in reaction, and low in fertility was used. Three cation exchange capacity levels were main— tained with peat. In each one of the three groups three calcium saturation levels were established cor— reSponding to 40, 70, 100 percent. Potassium was added in amounts correSponding to O, 250, and 500 pounds per acre to the jars in order to have each one of the calcium saturation levels treated with potassium at all levels and in all combinations with the calcium saturation treatments. The effect of percent calcium saturation upon growth was found to depend on the levels of cation ex— change capacity. In the first crop the M1 group (C.E.C.* = 5.83 m.e./100 grams) at 40 percent calcium saturation gave no growth. At 70 and 100 percent cal- cium saturation levels growth was practically the same. In M2 group (C.E.C. = 10.85 m.e./100 grams) at 40 and 70 percent calcium saturation growth was similar and higher than that corresponding to 100 percent cal- cium saturation. In group M3 (C.E.C. = 19.13 m.e./100 grams) a de— crease in growth corresponds to an increase in percent calcium saturation. Potassium treatments did not seem to have a notice- able effect upon growth. In the second crop, group Ml growth was directly related to percent calcium saturation while in group M2 and M3 the maximum growth occurred at 70 percent calcium saturation. Again, potassium did not affect growth noticeably. On the basis of these results it may be stated that * C.E.C. refers to cation exchange capacity. sudan grass is a poor indicator of the effect of potassium on growth. Yield data from the M , M , and M groups in both 1 2 3 crops indicate that the effect of percent calcium satu- ration on yields depends on the cation exchange capacity of the soil. I In the first crop, M1 group, the yield at 40 percent calcium saturation is zero while at 70 and 100 percent calcium saturation the yield was almost the same. Potassium treatments at K2 and K3 levels increased yield over Kl level. In the M3 group a decrease in yield resulted as percent calcium saturation was increased. Yields did not respond to potassium additions. In the second crop, yields were higher than in the first crOp as a result of the improvement in the supply of N,P, and probably minor elements. In group Ml yields at 40 percent calcium saturation were almost zero but increased with an increase in per- cent calcium saturation. Potassium had no effect on yield. At 40 and 70 percent calcium saturations, in the M2 group, the yields were higher than at 100 percent calcium saturation. An increase in yield was obtained as the supply of potassium increased. 70 In group M3, yield decreased as the percent calcium saturation was increased. The reSponse of yield to potassium was significant at the K2 level. In K1 and K3 levels, yields were sim- ilar. The conclusions presented, on the effect of percent calcium saturation and potassium treatments, on yields are drawn from interpretations based on the analysis of variance. The analytical results, of calcium and potassium content of the soil and aerial plant tissues, indicate that as percent calcium saturation was increased in the soil, calcium uptake by the plants decreases. The contents of potassium in plant tissues, within the limits of concentrations used, increased with an increase of exchangeable potassium in soils. The Ca:K ratio in the soil varied from 1.44 to 34.59 while the Ca:K ratio in aerial sudan grass tissues ranged from 0.26 to 2.36. The maximum yields of sudan grass were associated with a mean in soil Ca:K ratios of 15.76. Significant decreases in yield were recorded whenever the Ca:K ratio in soil was less than 2 or exceeded 30. No significant correlation was found between the soil Ca:K ratios and the Ca:K ratios of the plants. 71 The theoretical aspects of the problem are presented in the "Review of the Literature," and the discussion, presented in each section, is based on the results ob— tained in the experiments reported. 10. ll. 72 Bibliography Albrecht, W. A. 1940 Adsorbed ions on the colloidal complex and plant nutrition. Soil Sci. Soc. Am. Proc. 5: 8-16. Allaway, W. H. 1947 Availability of replaceable calcium from different types of colloids as affected by degree of calcium saturation. Soil Sci. 59: 207-217. Attoe, 0. J. 1947 Rapid photometric determination of potassium and sodium in plant tissue. Soil Sci. Soc. Am. Proc. 12: 131-134. Attoe, O. J., and Truog, E. 1946 Rapid photo- metric determination of exchangeable potassium and sodium. Soil Sci. Soc. Am. Proc. 11: 221-226. Bartlett, M. S. 1937 Properties of sufficiency and statistical tests. Proc. Royal Soc. London Series A, 160: 273. Bear, E. Firman, and Toth, Stephen. 1948 Influence of calcium on the availability of other soil cations. Soil Sci. 65: 69-74. Bradfield, Richard. 1943 Calcium in the soil: physico—chemical relations. Soil Sci. Soc. Am. PI'OC. 6: 8‘15. Chu, T. S., and Turk, L. M. 1949 Growth and nu— trition of plants as affected by degree of base saturation of different types of clay miflerals. Mich. Agr. Expt. Sta. Tech. Bull. 21 . Cochran, William and Cox, Gertrude. 1950 Exper- imental Designs. John Wiley and Sons, Inc. New York. pp. 122-152. Collander, Runar. 1941 Selective absorption of cations by higher plants. Plant Phys., 16: 691-720. Fieger, E. H., and Simpson, J. E. 1938 Studies of hydrolysis effects upon soil colloids: 1 Hydrolysis of various colloids with water as the hydrolyzing medium. Soil Sci. Soc. Am. Proc. 3: 94-99. l2. 13. 14. 150 l6. 17. 18. 19. 20. 21. 22. 23. 73 Gedroiz, K. 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Sweden. pp. 154~164. 50. Wood, L. K., and DeTurk, E. E. 1942 Absorption of potassium in soils. Soil Sci. Soc. Am. Proc. 5: 152—156. 51. Yarusov, S. S. 1937 Mobility of exchangeable cations. Soil Sci. 43: 285—303. ‘6 Mn It} 1 38 PW}. W” "w; r021 13 58 “vmigfié U1: L — "—-‘ee-~---... MIC‘3HIGAN STATE UNIVERSITY LIBRAR 3!!!!3 3!!! 3!!! 3!!! MN!!!