GROWTH AND NUTRITION OF PLANTS AS AFFECTED BY DECREE OF BASE SATURATION OF MONTMORILLONITIC, KAOLINITIC AND ILLITIC TYPES OF SOIL COLLOIDS By TSU SIANG- CtftL- A THESIS Submitted to the School of G-raduate 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 194b ProQuest Number: 10008281 All rights reserved INFO RM ATIO N TO ALL USERS The quality o f this reproduction is dependent upon the quality of the copy subm itted. In the unlikely event that the author did not send a com plete m anuscript and there are m issing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQ uest 10008281 Published by ProQ uest LLC (2016). C opyright of the Dissertation is held by the Author. All rights reserved. This w ork is protected against unauthorized copying under Title 17, United States Code M icroform Edition © ProQ uest LLC. ProQ uest LLC. 789 East Eisenhow er Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346 ACKNOWLEDGEMENTS The writer wishes to express his sincere appre­ ciation to Dr. L. M. Turk for assistance, advice and encouragement in the research reported in this paper and in the preparation of the manuscript. To Dr. C. E. Millar, Dr. R. L. Cook, Dr. N. S. Hall and Dr. K. Lawton, he Is also indebted for their sympathetic interest and help during the course of investigation. CONTENTS Introduction Page 1 Review of Literature 2 Experimental 5 Materials Used 5 Preparation of Colloidal Clay 6 Electrodialysis 9 Plan of Greenhouse Experiments 10 I . Bentonite-sand mixtures 11 I I . Kaolin-sand mixtures III# Fox sandy loam IV. Pure quartz sand Analytical Methods Results 14 15 19 20 21 Actual Base Status of the Treated Colloids 21 The Effect of Treatment on Soil Reactions 2? The Effect of Degree of Base Saturation on Crop Yields I. Bentonite-sand mixtures II. Kaolin-sand mixtures III. Fox sandy loam IV. Pure quartz sand 28 28 39 49 54 The Effect of Degree of Base Saturation on the Mineral Content of Planta 55 I* Bentonite-sand mixtures 55 II. Kaolln-sand mixtures 61 III. Fox sandy loam 65 The Effect of Complementary Ions on the Growth and Mineral Composition ofPlants 65 I . Bentonite- and Kaolin-sandmixtures 65 II . Fox sandy loam 73 The Effect of the Nature of Colloids on the Availability of Exchangeable Cations 77 Discussion 78 Summary and Conclusions 84 Literature cited 88 GROWTH AND NUTRITION OP PLANTS AS AFFECTED BY DEGREE OF BASE SATURATION OF MONTMORILLONITIC, KAOLINITIC AND ILLITIC TYPES OF SOIL COLLOIDS TSU SIANG CHU Exchangeable bases held on the surface of soil col­ loids have been generally considered by many soil scient­ ists and agronomists to be available to plants. Recent workers, however, have indicated that not all exchange­ able bases held on the soil colloidal surface are equally available for plant absorption. Among the factors which affect the availability of exchangeable bases to plants, the nature of colloids, the degree of base saturation, and the nature of complementary Ions are important. In a study of some chemical properties of orchard soils in relation to satisfactory and unsatisfactory grow­ th of peach trees, the writer (8) found that two groups of soils supporting trees of different growth vigor, although containing about the same amount of total exchangeable bases, varied greatly in the degree of base saturation due to the difference in their base exchange capacity. Soils supporting good growth of peach trees had a much higher degree of saturation of total as well as of individual ex­ changeable bases than those supporting poor growth of 2 peach, trees. Although, the finding is not considered as a conclusive one in the case of peach trees, it is believed that there exists a relationship between the degree of base saturation of soils and plant growth. The objectives of this investigation were to attain a better understanding of the significance of. the degree of base saturation and the nature of complementary ions in relation to the growth and composition of certain crops, and to evaluate the effect of the nature of clay minerals on the availability of exchangeable cations. REVIEW OF LITERATURE Probably one of the first investigators to study the effect of the degree of saturation on plant growth was Stoh^mann (3 6 ). Using organic colloid, he found in 1864 that the yield of matured corn plant increased with the degree of base saturation. Since then, little knowledge has been accumulated regarding the effect of degree of base saturation of soils on the^ plant growth until recently when soil workers have taken a renewed interest in this problem• During the past decade, many papers stressing the im­ portance of degree of base saturation in relation to plant growth have been reported. Thus, G-edroiz (11) and several 3 other investigators working with, soils and plant systems found that the exchangeable calcium is available for plant growth only as its degree of saturation is relatively high* Jenny and Cowan (19) found that the growth of soybean plants in Ca-H-clay suspensions was sharply reduced when the degree of calcium saturation fell below 30% of the total exchange capacity. Also working with soybean, H o m e r (l6) found that with constant amount of calcium supply, the growth of the plants, as measured by both height and weight, increased markedly when the degree of calcium saturation increased from 40 to 60%. Albrecht (l), in discussing degree of calcium saturation of clay and ni­ trogen fixation, concluded that calcium from the same ori­ ginal total supply was delivered into the plants to a much larger extent when it was on a nearly saturated clay than on one only partly saturated. Similar conclusions drawn from the results of soybean experiments have also been reached recently by Mehlich and Colwell (26) and Mehlich and Reed (27)• According to the recent report of Bower and Turk (6), naturally occurring alkali soils high in exchangeable so­ dium may not furnish an adequate supply of calcium to plants despite the presence of CaCO-^. This is in harmony with the finding of Gredroiz (ll) that soils saturated with ammonium, sodium or potassium failed to support plant grow- 4 th even when CaCO^ was added to the cultures. It has been suggested by some Investigators that the hind of complementary ions present on the colloidal sur­ faces may affect the availability of the other exchange­ able ions. Using purely chemical methods, Seatz and Winters (34) were able to prove that much more potassium was released from the exchangeable complex when the com­ plementary ion was dominantly calcium than when it was dominantly hydrogen. Previous work done by Peech (31) has also substantiated this theory by chemical analysis. The effect of the nature of complementary ion on the nutrient absorption by plants was also demonstrated by the experiments of Jenny-and Ayres (18) using excised barley roots. Their results are in general agreement with those mentioned above. However, results conflict­ ing to them have also been reported by many workers. According to Albrecht and Schroeder (2), the degree of H-ion saturation is in general a helpful factor in mobiliz­ ing calcium, magnesium and other cations into plants, al­ though it does not affect the availability of potassium. Contradictory results regarding the degree of base saturation in relation to cation availability to plants might be attributed partly to the difference in the nature of clay minerals. Elgabaly, et al. (10) found that the 5 uptake of Zn and K by barley roots was affected by the type of clay mineral. Studies by Mehlich and Golwell (26) and by Allaway (4) showed that calcium uptake by plants was greater from soils or colloids representing the organic and 1:1 lattice type than from those representing the 2:1 lattice type. Recently, working with peanuts, Mehlich and Reed (28) found that for any given level of calcium, the calcium content of the peanut shells was highest when the plants were grown in the kaolinitic-type colloid, but, on the other hand, the highest content of calcium in the plants was found in those growing in the organic-type colloid. EXPERIMENTAL Materials Used. In the present investigation, a Wyoming bentonite from the American Colloidal Company, known as !lvolclayn , was used as a source of montmorillonitic clay and a commercial kaolin, as a source of kaollnltic clay. The "volclay*', as described by the pro­ ducers, is 90% montmorillonite and in its natural state is predominantly saturated with sodium. The exchange capacity per 100 gms. of electrodialyzed bentonite, as determined by the usual ammonium acetate leaching method, was 86 m.e., and of electrodialyzed kaolin, 3*3 m.e. Besides the two exchange materials mentioned above, 6 a soil having a relatively low degree of base saturation was also sampled from a peach orchard near Benton Harbor, Michigan. The soil is classified as a Fox sandy loam. It has an exchange capacity of 9*8 m.e. per 100 grams, and is about 25$ saturated with bases. Differential thermal curves of the colloid fraction of the soil, as shown in Fig. 1, indicate the predominance of the clay mineral illite. Pure quartz sand was mixed with the bentonite and kaolin in the greenhouse experiments. Rapid chemical tests on a dilute HNO^ extract of the sand showed the absence of major cations and anions. Preparation of Colloidal Olavs. Much time was re­ quired to prepare the mineral colloids with the desired cation ratios. In the past, three methods have been used in preparing mineral colloids for such studies. In the first method, the colloids are first leached with a dilute acid, or electrodialyzed, or subjecting them to a powerful adsorbent, such as synthetic resins, and then the respective cations are introduced as hydroxides or salts in desired ratios. A serious objection to this method Is that the cations do not necessarily react with the exchange complex In the ratio In which they are added. Some of them might exist In the system as free cations and would not be adsorbed by the colloids as exchangeable cations. e.inq.ejiocTaiQ,! 8 The second method is to saturate various portions of the colloids with the desired cations and then mix these in proper proportions* It is assumed that when the col­ loids with the respective cations are mixed together there would be an interchange of cations and ultimately not only a mechanical mixture would result but also a chemical com­ plex containing the required cation ratios* However, this may not be true, because soil colloids together with their adsorbed ions, represent a Donnan■system, and the attain­ ment of a Donnan equilibrium may result in an unequal or non-homogeneous distribution of adsorbed ions. In the third method, the colloids are leached with a solution of salts mixed In definite proportions* However, due to preferential adsorption of colloids for different cations, the ratio between cations adsorbed on the surface of colloids will not be the same as that existing in the original solution. The preferential adsorption also varies with the type of colloids, temperature, nature and concen­ tration of the respective ions in leaching solution, etc* It Is, therefore, very difficult to find out either theo­ retically or empirically the concentration of salts neces­ sary to produce the desired ratio of cation mixtures. For a large scale experiment, the method Is indeed, impracti­ cable. In the present study, the preparation of colloids with 9 desired cation ratios was done by the first method* Electrodialvsis * The electrodialyzing cell used was composed of three wooden chambers of the Bradfield type (7) arranged in a parallel manner. It had an inside dimension of 12 x 10*5 x 7*25 inches, and a maximum capa­ city of about 8,500 ml. in the central compartment and 2,500 ml. in each of the side compartments. Porous por­ celain plates about 50 mm. or 0.25 inch thick were used as membranes. A perforated gold sheet having an area of 6 x 2.75 inches served as the anode and an ordinary copper wire screen having 9*5 x 6.5 inches area served as the cathode. apart. The electrodes were placed about 20-22 cm. An adjustable high resistance rheostat and an ordinary ammeter were connected in series with the cell with 220 volts, d.c., as the source of current. The rheostat was adjusted to keep the ammeter reading below 8 amperes and usually around 5* Too high temperature is soon reached with an amperage above 10. At times three such cells were connected in parallel and run simul­ taneously. By frequent renewal of the electrodialysates and stirring up of the colloidal suspension, the whole process of electrodialyzing a 3% suspension of bentonite could be completed in about 80 to 98 hours* In case of kaolin, a 8-10^ suspension was used for electrodialysis, and the whole process was completed In a much shorter time. 10 The completion of the removal of bases was Indicated by rather constant but very low current density (amperage per unit area of the electrode) and was confirmed by the phenolphthalein test on the cathode electrodialysate and pH measurement of the suspension. The unsaturated ben­ tonite and kaolin suspension thus obtained had a pH of about 3*2 and 4.5 respectively. After the electrodialysis had been completed, the flocculated suspension was removed from the cell and dried on a hot plate. The dried bentonite was ground In a steel mill to pass through a 100-mesh sieve. The pulverization of dried kaolin was affected by a wooden pestle In an open tray. Since the natural content of exchangeable bases in Fox sandy loam was low, no pretreatment for their removal was attempted. Plan of Greenhouse Experiments. G-reenhouse experi­ ments were conducted involving the growing of several different crops In four different cultural media, I.e., bentonite-sand mixture, kaolin-sand mixture, Fox sandy loam and pure quartz sand. On each of the four cultural media, two series of experiments were carried out for different purposes. In the first series of experiments, plants were grown in the cultural media having different degrees of base 11 saturation but with the 'fixed ratios between the major exchangeable bases, i.e. exchangeable calcium, magnesium and potassium. The principal purpose of this experiment was to study the effect of degree of base saturation on the growth and nutrition of plants. In the second series of experiments, the base exchange capacity of the cul­ tural media was held constant while the ratio between the major exchangeable bases varied within a certain range. The experiments were thus designed to supply information as to the mutual effect of the complementary ions on the growth and nutrition of plants. Both series of experiments were laid out in the same general pattern. G-lazed earthenware jars were employed throughout the investigation. With the exception of the experiments on peach seedlings in Fox sandy loam, which were replicated four times, all greenhouse experiments were run in triplicate. Equal rates of fertilizer appli­ cations, involving diammonium acid phosphate and ammonium nitrate, were made to all of the jars unless otherwise mentioned. Solutions of ZnSO^, FeSO^, and MnCl 2 were also added to each of the cultural jars to give con­ centrations of 2, 4, 3 and 8 p.p.m. of Zn, Fe, B and Jin respectively in the final clay-sand mixtures. All chemi­ cals used x*ere of c.p. grade. I. Bentonite-sand mixtures. From the known exchange 12 capacity of the electrodialyzed bentonite, calculations were first made as to the amount of bentonite required to give 4000 gms• mixtures of bentonite and sand with the desired base exchange capacity# For the first series of experiments, the treatments involved four levels of base exchange capacity, i.e. 2, 4, 6 and 8 m#e, per 100 gms# of the mixture, and each in combination with four degrees of total base saturation, i#e# 20, 40, 60 and 80^# For the second series of experiments, the difference between treatments was made only for the ratio between calcium, magnesium and potassium while the base exchange capacity was constant at 2 m#e. per 100 gms# for all of the treatments. A summary of the treatments for both series is given in Table I . In setting up the greenhouse experiments the desired amount of colloids was first placed into one gallon jars, and solutions of calcium acetate, magnesium nitrate and potassium sulfate added in amounts to supply 20, 40, 60 and 80^ of total base saturation with a Ca:Mg:K ratio of 75sl5il0# The colloids were maintained as thick suspen­ sions for a period of about three weeks with occasional mixing. After that, while still moist, they were tho­ roughly mixed with quartz sand to give desired levels of exchange capacity. Two crops, Eaton Oats and Rosen Rye, were grown in 13 Table I A Summary of the Treatments of the Greenhouse Experiments on Bentonite-sand Mixtures* Treatments Mean pH Series Exch. Cap*, Base saturation, % Start End m.e./lOO g. Ca Mg K Total 2 2 2 2 15 30 45 60 3 6 9 12 2 4 6 8 20 40 60 80 4*5 4.6 5*0 5.3 4.6 4.8 5.9 6.1 4 4 4 4 15 30 45 60 3 6 9 12 2 4 6 8 20 40 60 80 4.5 4*6 4.9 5.1 4.6 4.8 5.7 5.9 6 6 6 6 15 30 45 60 3 6 9 12 2 4 6 8 20 40 60 80 4.4 4.5 4.8 5.0 4.5 4.7 5 .4 6.2 8 8 8 2 2 *2 2 2 15 30 45 30 35 40 45 50 3 6 9 2 4 6 20 40 60 4.4 4.5 4.7 15 15 15 15 15 15 15 15 15 15 60 65 70 75 80 4.3 4*4 4.6 4.7 5.0 4.4 4.6 5.5 4.4 4.8 5.2 5.4 5.8 2 2 *2 2 2 40 40 40 40 40 5 10 15 20 25 15 15 15 15 15 60 65 70 75 80 4.8 5.0 4*6 4.8 4.6 5.1 5.2 5.2 5.4 5.4 I II 40 15 2 40 15 2 40 15 *2 40 15 2 40 2 15 •^Identical treatments, jars in the experiment. Crops grown Oats: June 27 to Aug• 8, 1947 Rye: Sept. 20 to Nov. 31, 1947 R ye; Sept. 20 to Nov. 31 9 1947 60 4.7 5.0 5 10 65 4.7 5.2 4.6 5.2 70 15 5.4 4.6 20 75 5.6 80 4.7 | 25 actually represented by the same 14 succession in the experiment. A moisture content of around 12.% was maintained for the growth of oats, and about (start with 3%) for that of rye. II. Kaolin-sand mixtures.— — Due to its very low exchange capacity a considerable amount of kaolin had to be used in order to afford kaolin-sand mixtures with base exchange capacities comparable to those of bentonitesand mixtures. The mixtures, being high in kaolin, were low in apparent specific gravity. As a result, each 1- gallon jar could hold only 3500 gms. of the mixture. By precisely the same way as described for preparing bentonite-sand mixtures, kaolin and pure quartz sand were mixed and treated to give two series of experiments. In the first series, the treatments involved two levels of exchange capacity, I.e., 1 and 2 m.e. per 100 gms. of mixture, each with four degrees of total base saturation, i.e., 20, 40, 60 and 80^, while the ratio of Ca:Mg:K was constant at 75:15*10. In the second series, the exchange capacity was fixed at 1 m.e. per 100 gms. for all of the treatments, while Ca:Mg:K ratio was varied as in the bentonite-sand mixtures. The fertilizer applications were the same as those for the bentonite-sand mixtures. Rosen Rye was the first crop grown in the media. During its growth period, the moisture content of the media was maintained at about "L2% for those having an 15 exchange capacity of 1 m.e. per 100 gms., and 16$ for those having an exchange capacity of 2 m.e. per 100 gms. After the rye was harvested, the contents of each jar wewe added to an equal amount of pure quartz sand and potted into 2-gallon jars in the following manner. Two thousand grams of sand was first spread on the bottom of the 2-gallon jar to facilitate drainage and aeration; then 7000 gms. of the kaolin-sand mixture was introduced; and finally an 1-inch layer of about 800 gms. sand was evenly spread over the surface. The purpose of further diluting of the mixture with sand and the manner of pot­ ting the mixture by layers was to improve the physical properties of the mixture and to prevent the formation of a surface crust. The same fertilizer applications were made as were made originally to Insure sufficient quantities of nitro­ gen, phosphorus, and minor elements. Moisture contents of the new mixtures were maintained at 10$ for the low exchange capacity series, and at 12$ for the high series. Oats were grown for a period of 70 days. Table II gives the summary of the actual plan of the greenhouse experi­ ments for kaolin-sand mixtures. III. Fox sandy loam. No sand was added to the Fox sandy loam.* The soil had a base exchange capacity of 9*8 m.e. per 100 gms., and Is about 25$ saturated with bases. 16 Table II A Summary of the Treatments o:f tlie G-reenhouse Experiments on Kaolin-sand Mixtures. Treatments Mean PH Series Exch. cap., |Base saturation, % m.e./lOO g. Ca Mg K Total I Start End Crops grown 1 1 1 1 15 30 45 60 3 6 9 12 2 4 6 8 20 40 60 80 5.1 5.8 6.5 6.8 5.4 6.1 6.6 6.9 Rye: Sept.20Nov. 31, 1947 2 2 2 2 15 30 45 60 3 6" 9 12 2 4 6 8 20 40 60 30 5.2 5.9 6.7 6.9 5.4 6.3 6.9 7.2 Oats: Dec. 19, 1947-Feb, 26,1948 1 1 *1 1 1 30 35 40 45 50 15 15 15 15 15 15 15 15 15 15 60 65 70 75 80 6*2 6*3 6.5 6.6 6.7 6*4 6.5 6.6 6.7 6.7 1 1 40 40 40 40 40 5 10 15 20 25 15 15 15 15 15 60 65 70 75 80 6.3 6.3 6.5 6.5 6.6 6.5 6.5 6.6 6.5 6.6 40 40 40 40 40 15 15 15 15 15 5 10 15 20 25 60 65 70 75 80 6.4 6.2 6.5 6.3 6.5 6.5 6.4 6.6 6.4 6.3 Jb II 1 1 1 1 1 1 Rye: Sept. 20Kov. 31, 1947 ^Identical treatments, actually represented by the same jars in the experiment. 17 The first series of experiments was run with five levels of total base saturation, I.e., 2 5 , 5 0 , 75, 100 and 150^, each having the same Ca:Mg:K ratio of 75:15:10* The second series of experiments consisted of five treatments with varying ratios between Ca:Mg:K but with a constant degree of base saturation at 50^. One of the treatments was actually a part of the first series as is noted in Table III, which gives the summarized plan of the treat­ ments • Both series were first carried out in 4-gallon glazed earthenware jars, each filled with 20 kg. of the soil* Three young peach seedlings were transplanted Into each jar, only one being retained after three weeks. A moisture content of about 15^ was maintained during the experiment. At the end of 166 days, the total length of the main shoots of peach seedlings was determined. After the removal of peach seedlings, the soil in each jar was allowed to dry and was remixed. Without additional fertilizer treatment, 9500 gm. portions of the soil from each jar were weighed into 2-gallon pots. Thus a total of eight 2-gallon pots could have been obtained from each quadruplicate of the same treatment In 4-gallon jars but only six of them were actually used for further experimental purposes. Each six of these 2-gallon pots, having the same treatment, were divided equally Into two 18 Table III A Summary of the Treatments of the Greenhouse Experiments on Fox Sandy Loam Treatments Exch. Base saturation, % Series cap., Ga Mg K Total m.e. lOOg. I II M a q r ^ Start End 9.8 18.7 3.9 1.3 24.5 6.0 *9.8 37.5 7.5 5 50 6.2 75 6.4 10 100 6.5 22.5 15 150 6.7 9.8 56.25 11.25 7.5 9.8 75 15 t VPT 9.8 112.5 *9.8 37.5 7.5 5 50 6.2 9.8 40 5 5 50 6 .2 9.8 35 5 10 50 6.3 9.8 30 10 10 50 6.2 9.8 30 5 15 50 6.1 Crops grown 6.1 In 4-gal. jars: Feach seed­ 6.0 lings,Mar. 9Aug. 21,1947 6.3 In 2-gal. jars: 6.5 Soybeans,Aug. 28-0ct.23,1947 6.5 . Proso,0ct. 23" 6.0 Nov. 27,1947 Oats, Dec. 19, 6.0 1947-Feb. 26, 1948 6.2 Tomato, Aug. 6.2 27,1947-Jan. 29,1948 6.1 ^Treatments actually represented by the same jars* 19 groups. One group was used for the growth of soybeans, proso and oats in succession and the other for the growth of tomatoes. Soybeans and proso were grown in the period from Aug. 28 to Oct. 23,1947 and from Oct. 23 to Nov. 27, 1947 respectively, with no artificial illumination of the greenhouse. Being short day plants, they all appeared dwarf in the vegetative growth and matured earlier than usual. Because of the limiting nature of the photo­ periodicity to the growth of soybeans and proso, the results were not valid for direct interpretation. No measurement for their growth rate was, therefore, attempt­ ed during the experiment. IV. Pure quartz sand. The purpose of using pure quartz sand as cultural media was to afford comparisons with treatments made on bentonite and kaolin media so that a better interpretation of the results might be ob­ tained. Rye and oats were grown in succession in 1-gallon jars, each filled with 4 Kg. of pure sand. tent of the sand was maintained at about 5$. Moisture con­ Every treat­ ment represented in the both series of bentonite-sand and kaolin-sand mixtures was also made in the pure quartz sand cultures. The rate of applications given to each treatment at the start of the sand culture experiment was only two-fifths of the actual rate received by the bento­ nite-sand mixtures, the remaining three-fifths was sup- 20 plied after the first crop was harvested. Analytical Methods. Harvested plant materials in­ cluding oats, rye, and leaves of tomato were air-dried and ground in a small Wiley Mill to pass through a 20mesh sieve* One gram portions of the oven-dried tissue were then wet-ashed at a moderate heat with a mixture comprising of 4 ml. of 70% HCIO^, 15 ml* of concentrated HNO-^ and 4 ml. of concentrated H 2SO4. (33)* was finally diluted with water to 25 ml. The extract Aliquots of this extract were taken for the analysis of calcium, magnesium and potassium. The determination of calcium was made volumetrically on the 5 nil. aliquot as oxalate, following the precedure of standard A.O.A.C. micro-method (5)* Magnesium was determined photocolorimetrically, using 520 m^u filter in 0.2 ml. aliquot by thiazol yellow method (2 9 )* which was essentially the same as ordinary titan-yellow method (3 2 ). Potassium was determined on 1 ml. aliquot by the, cobaltinitrite method using Peech’s technique (30). All pH measurements of soil and clay-sand mixtures were made potentiometrically with a Macbeth alternating current pH-meter using glass electrodes with a soil water ratio of about 1 to 2 . 21 RESULTS Actual Base Status of the Treated Colloids* In the previous sections, reference has been made to the possi­ bility that with the present method of preparing colloids, the exchange reactions between the exchangeable hydrogenion of the electrodialyzed clays and cations of the in­ troduced electrolytes are likely to be incomplete* In order to evaluate the actual status of the bases in the exchange materials, a series of laboratory experiments were carried out. To 10 gnu portions of H-bentonite in suspension, different amounts of the solutions of calcium acetate, magnesium nitrate and potassium sulfate were added ac­ cording to the calculated ratios* The systems were then allowed to stand In the laboratory, with occasional shak­ ing, for a period of at least two weeks* Analyses of calcium, magnesium and potassium were finally made on the filtrate* From that, the actual percentages of base sa­ turation were calculated* Similar experiments, using 50 gnu portions of materials, were also carried out for electrodialyzed kaolin and natural Fox sandy loam, only in the latter case the soil, after leaching with about 400 ml. alcohol, was used for analyses instead of the filtrate. 22 The results of these experiments, presented in Table I V *, indicate that some of the bases added to the colloids were not held on the colloidal surface. The portion of the bases that existed in the free form varied with the nature of colloid, and electrolyte, and the symmetry con­ centration of the electrolyte added. The higher efficien­ cy of replacement for H-ions was observed In the lower symmetry concentration of electrolytes,. It is not the purpose of this paper to involve a discussion of exchange reactions except to mention the fact that the results obtained were in general agreement with many others (1 2 ). Figures II, III and IV show exchange isotherms of calcium, magnesium and potassium with different types of soil colloids. As no similar laboratory experiment has been made for the treatments involved in the experiment series no. II of either bentonite-sand mixture or kaolinsand mixture or Fox sandy loam, the actual base status of those treatments were not precisely known. However, with aid of data shown In Table IV, It is perhaps pos­ sible to get a fairly close evaluation of them. Inasmuch as the results of the present Investigation, like many others along the same line, are likely to be qualitative in nature, the degree of base saturation referred hereafter In the tabulation of the results of greenhouse experiments will be the theoretical values 23 Table IV The Extent of Ionic Exchange Reactions of Bentonite, Kaolin and Fox Sandy Loam* Symmetry concentration,* % Mg K Ca Total PH value Actual base saturation, % (according to analyses) Ca Mg K Total Bentonite— -~Exch. cap.— -86 m.cj. per 100 gms. 2 20 14.2 3*82 3 2.7 1.6 18.5 15 30 6 4 40 4.21 26.0 5.6 3.1 34.7 45 9 6 60 4.83 40.3 7.9 5.0 53.2 60 12 8 80 5.40 48.1 9.2 6.1 63.4 15 Kaolin-- Exch. cap ^=-3 .8 m.e« per 100 gms. 12.8 2 20 2.2 1.3 5.18 16.3 3 30 6 4 40 5.86 24.3 4.5 2.3 31.1 45 9 6 60 6.41 32.3 6.4 3.7 42.4 60 12 8 80 6.72 42.9 8.0 4.8 55.7 22*5 112.5 66.6 57.5 H O 15 5.2 6.4 74.9 7.5 94.3 6.4 51.6 10 100 6.5 15 150 6.9 « 75 9.8 75 7 *5 9 11.25 o « ro H 56.25 00 Fox sandy loam-— Exch. cap.:= 9.8 m.e. per 100 gms* 6.8 3.8 34.1 50 6.2 44.7 5 37 *5 7.5 ^Symmetry concentration when expressed in terms of percentage is same as the percentage base saturation calculated according to the treatment received* Symmetry concentration, % Fig. II. The exchange isotherms of calcium in different types of soil colloids. 25 10 •/ saturation (according to analysis) 12 Base Kaolin Bentonite Fox sandy loam 9 12 Symmetry concentration, % Fig* III* IS 21 The exchange isothenns of magnesium in different types of soil colloids* io Base saturation (according to analysis) 26 ° Kaolin Bentonite 2— ♦ --- // 0 Fig# IV# 2 k 10 6 8 Symmetry concent ration 9 % Fox sandy loam 12 The exchange isotherms of potassium in different types of soil colloids. 27 indicated explicitly by the treatment according to cal­ culation, rather than the actual value indicated impli­ citly by the treatment according to chemical analysis. The Effect of Treatment on Soil Reactions. The pH of cultural media measured at the start and the end of the experiment are presented in Table I, II and III. A comparison of Table I and IV reveals that the pH values of pure bentonite suspension were different from those of bentonite-sand mixtures used for greenhouse studies. The difference Is mainly due to the presence, in the bentonite-sand mixtures, of the large amount of sand which tends to raise their pH values. The pH values of bentonite-sand mixtures were low as can be seen from Table I . Even with a total base saturation of 80%, the pH of the mixtures were still around.5*0 at the start of the experiment. The results thus indicate a rather high buffer capacity of bentonite at low pH levels which Is In general agreement with Mehlich’s findings (24, 2 5 ). There were general Increases in the pH values of the bentonite-sand media after crops had been grown on them, although the increases were slight where the degree of base saturation was low. On the other hand, noticeable pH increases were observed where the degrees of base saturation were high. No effort has been made to explore 28 the reasons for* these increases* However, it. is suspect- e& that aside from the possibly unequal absorption of NH4 -N and by plants, the decomposition of acetic acid, which is formed as a result of base exchange re­ actions between calcium acetate and acid colloid, might be one of the main reasons• The Effect of Decree of Base Saturation on Cron Yields * I* Bentonite-sand mixtures. The general growth of oats and rye as related to the total quantity of bases present in the bentonite-sand mixture is shown by the data in Table V. These results show that as the supply of exchangeable bases was increased, with a constant base exchange capacity, the yields of the crop increased. The increased yields for the increasing percentages of base saturation arrange themselves in a nearly straight line relation, as can be seen from the actual photographs of the growth conditions of the plants (Figs, V, VI, VII and VIII). A more effective comparison can be made for this relationship by reference to the graphs for the yields of oats and rye, shown in Figs. IX and X. The four-levels of degree of base saturation, which represent a variation in both the supply of exchangeable bases and the hydrogen—ion concentration--the two vari­ ables which are reciprocally related— show that the 29 Table V The Effect of Different Levels of Exchangeable Bases on Yields of Oats and Rye Plants in Bentonite-sand Mixtures. Base satu­ ration % Exchange capacityt m.e. per 100 gms,► 4 8 2 6 Y3.eld in p;rams* Rye Rye Oats Rye Oats Rye Oats Oats / 20 •53 1.58 •55 1.93 .55 1.86 .54 1.83 40 1*13 2.45 .86 2.80 .85 2.48 .77 2.40 60 1.85 3*39 1.09 3.80 •'t o• H 3.12 1.07 3.03 80 2.59 4.24 1.30 5.70 1.18 3.58 -— ------ ^Values represent average dry weights of the above­ ground portions from three replicate pot cultures. 30 Fig. V. Growth of 17-day old oats in bentonite- sand mixture showing the general plan of a part of the greenhouse experiment. Exchange capa­ city of the media varied from 2 m.e. to 8 m.e. per 100 gms. mixture. Treatments on base status-, were made to supply 2 0 , 40, 60 and 80 % satura­ tion of the exchange capacity, while Ca:Mg:K was kept constant. triplicate. Experiments were set up in 31 Fig* VI. Growth of 17-day old oats as related to degree of base saturation of the bentonite sand mixture with a base exchange capacity of 2 m.e. per 100 gms. of the mixture. (Increas­ ing saturation from left to right). 32 i*■ Fig# VII. Growth of ry© at the end of 2 months as related to degree of base saturation of the bentonite-sand mixture with exchange ca­ pacity of 2 m.e. (left four Jars) and 4 m.e. (right four Jars) per 100 gms. 33 Fig. VIII. G-rowth or rye at the end of two months as related to degree of base saturation of the bentonite-sand mixture with exchange capacity of 6 m.e. (left four jars) and 8 m.e. (right three jars) per 100 gms* CD o CV3 CO r o * CO W o cO O o I— I 'sp • CD a ca to o O • CO co o §) CO O o I I— o • o • ^ 0 S o 02 ^ CO 0 a oo tO O o • ^ 0• o Ca (X! in o L0 in o 0 CO ca (xiOTq.j:od punojcS •p • 0 P« 0 cd 0 A o q y ) ’ sui3 u T ‘ sq.00 jo ppoTX o • PQ o X of different levels of exchangeable bases on yield in bentonite-sand mixtures. )— t o*^ "cf • The effect o coo o Fig. IX. CO of oats planted 34 35 0 £ o o r P n 0 i— i o • p* 'sf4 0 • 0 >s £ S h o C\2CO P o nO i— 1 o • 0 00 0 •rH cO O O i— 1 g) r*> fi o 0 0 o • 0 0 ^ 0 * P o £ 0 X C\2{£) i — !t oo CO O i— I p cd ‘Td r“* bi> P fi 0 Fh 0 Pi P i •H o O to o 1— 1 P O • o T}f 0 • o CAi CAi C\2 CO p u n o j 3 QAoqy)*sin9 h i ‘ Jo PT^I-^ 8 9 b .I8A~ 0 t> * 0 rH £ LO (uo*tC}.,iod r— ! •• • •* • p 0 P 0 0 O 0 • 0 0 PQ o M (P P o 0 p p 0 0 ,0 bH • • bD •H ip 36 growth of both oats and rye improved with a decreasing hydrogen*ion concentration and an increasing base satura­ tion. Which of these two variables is the more signi­ ficant factor is not evident in the yield data presented. However, the fact that both oats and rye are acid-tolerant crops is well known. According to Weir (39)» oats and rye may grow normally at strongly acid soil with pH 4.8. The compilation of soil reaction preferences of plants by Spurway (35) shows oats and rye will tolerate a pH 4.5 without possibility of serious injury. Analyses of plant materials, as will be presented in the later sections, also give indications that the total amount of available bases is a more important factor in affecting the dif­ ference in growth than a variation in hydrogen-ion con­ centration. The data in Table V also show that at 20% of base saturation, oats and rye yields were approximately the same, regardless of the exchange capacity of the media. A similar situation is observed at 40 and 60% base sa­ turation levels except in the yields of oats from the 2 m.e. base exchange capacity jars, which were higher than the rest at corresponding base saturation levels. Photo­ graphs showing these facts are presented in Pigs. XI and XII. With the design of this experiment, it is possible 37 Fig* XI. Seventeen-day old oats showing, with the same low degree of base saturation, no effect on the growth by varying the base-exchange capa­ city of the bentonite-sand mixture. 38 Pig* XII* Rye crops at the end of two months showing no significant difference of the growth by varying the base exchange capa­ city of the bentonite-sand mixture* 39 to make a further comparison between treatments* Out of the 15 different treatments listed in Table V, there were actually eight different levels of total bases contained in the cultural media, viz., 0*4, 0.8, 1.2, 1.6, 2.4, 3*2, 3*6 and 4.8 m.e. bases per 100 gms. of medium* Except for the levels 0.4 and 3*6 m.e., each level was made up, in more than one way, by varying the levels of the base exchange capacity, and the degrees of saturation. Thus, for instance, treatments made up by either of 2 m.e. exchange capacity, Q0% saturation, or 4 m.e. exchange capacity, 40^ saturation, or 8 m.e. exchange capacity, 20^5 saturation, all gave the same absolute amount of bases, i.e., 1.6 m.e. per 100 gms. of the bentonite-sand mixture. However, crop yields have shown different effects from these treatments. In all cases, with the same absolute amount of bases present in the media, the highest percent­ age of saturation gave the best yields of oats and rye. Futhermore, the greater the difference of degree of satura­ tion, the greater the difference in yields. These facts, shown by the graphs in Figs. XIII and XIV, and by the photographs in Figs. XV and XVI, suggest that the growth of both oats and rye crops Is more directly related to percentage saturation than to total amount of bases. II. Kaolin-sand mixtures. Yields of oats and rye showing the effect of varying levels of bases in the 40 2.5 pi o *i~t -p p1 o p ^2.0 o p* CJD 0 i> O 1.5 w pi •H CO ra 1.0 o V) o n3 i—I CD ■tH 0 SD 0 P t 0 *5 •55 2 4 Exch* cap*: 40 20 Base sat*: 0.8 Total bases: Fig# XIII. 6 8 m.e./lOO gms* 4 8 2 6 2 4 8 46 80 60 60 20 B0 40 20 60 40 BO 40 % 2.4 3.2 4.S m.e./lOO gms. 1.2 1.6 Effect of degree of base saturation on yield of oats planted in bentonite-sand mixtures. 41 P 5- O •H -P P O P- np P P O P 4-1 00 CD > O P •rH •V 03 -P P P rH 2-P <5h O nH i—I 0 •rH I- 0 £iO P P 0 Exch* cap*: Base sat*: Total bases: Fig. XIV. 2 4 40 20 0*8 2 6 248 46 4 S 6 8 m.e./lOO gms, 60 20 80 40 20 60 40 SO 40 SO 60 * 2.4 3*2 4.S m.e./lOO gms. 1.6 1.2 Effect of degree of base saturation, on yield of rye plants in bentonite-sand mixtures 42 Fig. XV“. Seventeen-day old oats showing the growth condition is more directly related to percentage saturation than to total amount of bases in bentonite-sand mixtures. All three jars contained 1.6 m.e. of bases per 100 gms* media. 43 Fig. XVI. Rye crops at the end of two months showing the growth condition is more direct­ ly related to percentage saturation than to total amount of bases in bentonite-sand mixtures. The two jars on the left contained 1.2 m.e. bases, the three in the middle con­ tained 1.6 m.e. bases, and the two on the right contained 3*2 m.e. bases per 100 gms. media. 44 kaolin-sand mixtures are given in Table VI. The increase of percentage saturation of the kaolin-sand mixtures in this experiment did not seem to have the same effects on the yields of oats and rye as it had produced in the bentonite-sand mixtures. There were some increases in the yields as the degree of base saturation increased from 20% to 40/ at both levels of exchange capacity. But on the percentage basis the amount of Increase was slight as compared with the percentage increases of yields in the case of bentonite-sand mixtures. The yields of rye were about the same at the corresponding levels of base saturation regardless of the exchange capacity, although the yields of oats were little higher at the 2 m.e. exchange capacity series after the mixture had been diluted with sand. These facts suggest that a sufficient supply of available bases was supplied In the low saturation levels, and/or that some other factors besides the base status of the media were limiting the growth of the plants. It is evident from the data in Table II that the pH of the media is not sufficiently low to limit the growth of oats and rye. But it was noticed during the experiment that kaolin-sand mixtures exhibited poor physical pro­ perties. As water evaporated from the mixture, a very hard crust formed on the surface as if it had been 45 Table VI The Effect of Different Levels of Exchangeable Bases on Yields of Oats and Rye Plants in Kaolin-sand Mixtures, Exchange capacity, m.e. per 100 gms • Base satu­ ration 2 1 Oats Rye 4.85 H 5.06 3.23 40 5.77 3.90 6.82 « 60 5.50 3.81 6.72 4.14 80 6.03 3.72 6.35 3.98 % Oats 20 H 00 Rye • o Yield in grams* ^Values represent average dry weights of the above­ ground portions from three replicate pot cultures. 46 subjected to pressure* Furthermore, cavities developed under the surface crust which might cause damage to the roots of the crops* All these indications lead one to suspect that the base status of the kaolin-sand mixture is not the only factor affecting the growth of oats and rye* However, the general similarity of the results between the yields of rye grown on the original kaolinsand mixtures and the yields of oats grown on the diluted kaolin-sand mixtures indicate that the growth of oats and rye are more closely related to the base status than to the physical properties of the media. It was observed that a 20% saturation of bases in kaolin-sand mixtures provided a sufficient supply of available bases for fair growth of oats and rye, and a h0% saturation supplied enough available bases for maximum growth of plants under the limitation of other factors existing in the experi­ ment* A comparison of treatments between 1 m.e. and 2 m*e. exchange capacity series reveals that with the same total supply of 0*4 m.e. bases per 100 gms. of the mixture, the 40^ saturation of the 1 m.e. exchange capacity jars gave greater yields of oats and rye than the 20^ saturation of the 2 m.e. exchange capacity jars (Figs. XVII and XVIII). On the other hand, no improvement of yields of the 80^ saturation of the 1 m*e* exchange capacity jars over 47 pi o •H ti O ft Pi P Oo PiJ HD CD > O 5| HD Pi •H „2 w -p pi cd rH p^ 0 >9 N <+H o •pf * 1 rH 1 0 •rH 0 HD cd U 0 5 % Base sat.: Exch. cap.: Fig. XVII, 20 40 60 80 1 m.e./lOO gms. 20 40 60 80 2 m.e./lOO gms. The effect of different levels of exchangeable bases on yield of rye plants in kaolin-sand mixtures. 48 Sd o P u o p. d PI Pi o PH HD (D > O to S HO PJ ♦rH CO P cd o

s CD HD cd u CD $ Base sat*: Exch* cap*: Fig* XVIII* 20 40 60 80 1 nue./lOO gms* 20 40 60 80 2 m.e./lOO gms* The effect of different levels of exchangeable bases on yield of oats planted in kaolin-sand mixtures* 49 those of the 40^ of the 2 m.e. exchange capacity jars was obtained, although they all contained 0*8 m.e. total bases per 100 gms* mixture. These results again suggest that the growth of both oats and rye crops is more directly related to percentage saturation than to total amount of bases and that a 40^ saturation of bases in kaolin-sand mixture is probably all that is needed for the growth of oats and rye under the experimental con­ dition* III* Fox sandy loam.--— The general growth condition of peach seedlings as affected by the degree of base sa­ turation is shown in Fig. XIX* The average total length of the shoots of peach seedlings after 5 months of growth in the treated soil was 29*1, 41.5* 25*7» 22.3 and 23*7 cm. for the 25 ^ (untreated), 50%, 75%9 100% and 150% saturated soils respectively. As can be seen in Fig. XIX, the growth of the peach seedlings In general was not very good. was at the 50% saturation level. The best growth Peach seedlings grown in the soil with the treatments supposed to give more than 75% saturation of bases appeared very poor in growth with only few leaves remaining on the top, and, of the four replications, two failed to servive at the 150^ saturation level, and one at the 100^ saturation level. During the early stages of the experiment, It was dis — 50 I Fig* XIX* Growth of peach seedlings as Influenced by the degree of base saturation of Fox sandy loam* Treatments from left to right are: No* 1 untreated natural soil(about 25 % saturation), No* 2-- 50 % saturation, No* 5 75 % saturation, No. 4 -- 100 % saturation,No* 5— 150 % saturation* 51 covered that some of* the peach seedlings developed ab­ normalities in growth* Their leaves became curled and the seedlings began to branch out with numerous small leaves. According to Tukey and Carlson (37, 38) these abnormalities are most probably due to insufficient length of the dormancy period of the peach seed and are frequently accompanied by the dwarfing effect. Although all the abnormal peach seedlings were finally replaced by normal ones during the experiment, the general un­ successful growth did not yield dependable information as to the effect of degree of saturation on the growth of peach. Because of the unfavorable photo-periodicity, as has been mentioned before, the growth of soybean and proso crops following the peach was also not successful. Consequently, no measurement for their response to the soil treatments has been made available for the dis­ cussion. In Table VII is presented the results: of the experi­ ment on tomato and oats crops with the same treatments. A comparison of the height of the tomato plants, as affected by the various treatments, can be made by refering to Fig. XX. Differences In the yields of fruit and plant and also in t he,length of the main stalk were marked between the 50^ and 75/£ saturation levels. Above 52 Table VII Yields of Tomato and Oats Crops as Affected by the Degree of Base Saturation of Fox Sandy Loam* Base saturation ^ Tomato plant Wt. Wt. Main fruit* plant* stalk* Oats Wt. straw* cms. gms. Ca Mg K % % % % gms* 18.7 3.9 1.9 24.5 582 32*1 105 4.5 37.5 7.5 5 50 593 36.1 118 5.7 56*25 11.25 7.5 75 692 50.2 150 5.5 75 10 100 670 44.2 123 5.8 15 150 653 42.7 115 5.5 112.5 . 15 22.5 Total ' gms • *Values representing averages from three replicated pot cultures* 53 Fig* XX, Growth of tomato plants at 90 days as influenced by the degree of base satu­ ration of Fox sandy loam. left to right are: No.l Treatments from untreated natural soil(about 25 % saturation),No.2---50 % 9 No.3-- 75 % 9 No.4 --- 100 % 9 and No.5 base saturated. 150 % 54 75% saturation levels, there were slight decreases in the yield of fruit and plant materials, accompanied by more marked decreases in the length of the main stalk. The yield data of the oats show the same general trend as related to the base status, of the soil as did the tomatoes except that the difference in yields is noticeable only between 25% (untreated) and 50 % satura­ tion levels. All these facts suggest that the growth of tomato and oats increases as the degree of base saturation of the soil increases but only up to a certain saturation level. For the present soil containing dominantly illitic type of mineral colloid along with some organic colloids, this limiting level seems to be at around 50 % saturation for the oats and 75% for the tomato plant. The high critical saturation level for tomato plants as compared with that for oats has the support of the well recognized fact that in general tomatoes demand soils of higher fertility than do oats. IV. Pure sand.— --Generally speaking, the yield data of oats and rye in pure quartz sand were in the same order as those from bentonite-sand and kaolin-sand mix­ tures. They served as checks for the treatments in the bentonite-sand and kaolin-sand mixture and were not ex­ pected to give any direct information relating to the problem. Actual yield data, therefore, are not presented 55 here# The Effect of Decree of Base Saturation on the Mi­ neral Content of Plants# I. Bentonite-sand mixtures. The chemical analyses of the above-ground portions of oats and rye are summariz­ ed in Table VIII# Among the three mineral constituents, the greatest variation occurred in K. Figures XXI to XXVI show graphically the Ca, Mg and K contents of the oats and rye# The results show interesting relationships between the base status of the bentonite-sand mixture and the mineral composition of the crops# From Figs. XXI and XXII, It can be seen that the Oa content of both oats and rye increased markedly from 15 to 30% Ca saturation levels (or from 20 to h0% saturation of total bases), but showed only a little Increase from 30 to 43% Ca saturation levels (or from 40 to 60% satura­ tion of total bases). Beyond that, there was practically no increase In Ca content. This situation is similar in all cases, regardless of the exchange capacity of the media. The results Indicate that for a bentonite-sand mixture, a 15^ saturation of Ca will not supply enough available Ca to meet the requirement of oats and rye. In order to afford an ample supply of readily available Ca from the exchange complex, the saturation level of Ca for a montmorillonitic clay has to be at least above 30% 9 56 Table VIII Mineral Content of the Oven-dry Tissues of Oats and Rye as Influenced by Base Status of Bentonite-sand Mixtures. Base exchange capacity, m ♦e* per 100 gms . mixture 2 Base 4 8 M.e. per 100 gms. dry tissue sat, % 6 Ca Mg K Ca Mg Ca E Mg K Ca Mg K Oats 8.0 10.8 19.2 40 28.0 9.3 23.9 31.3 11.5 17.8 40.2 o * 3.1 13.2 14.8 4.6 12.7 8.5 14.0 41.3 7.4 16.1 5.4 10.3 CVl CVJ 20 18.2 60 52.1 20.9 37.5 33.2 19.1 36.5 38.5 13.2 30.7 42.8 18.1 29.5 80 32.3 22.6 52.3 34.5 22.0 44.7 40.2 20.3 36.0 --- > --- --- Rye 20 11.1 3.0 11.7 11.9 7.2 21.0 18.5 7.0 9.2 15.2 • K'* OJ 40 21.6 12.9 13.7 29-5 15.0 20.1 29.9 14.3 12.7 34.0 8.1 21.5 23.5 60 29.8 20.2 41.1 34.0 16.5 37.3 32.6 23.3 25.8 35.2 26.5 49.2 80 31.6 23.1 52.0 32.8 22.8 45.5 32.3 24.0 40.4 --- --- --- 57 Ca saturation Ca content m.e,/100 of oats, gms. 30 40 30 20 10 40 % Total base saturation 20 Fig. XXI. of rye, gins, SO The effect of degree of base saturation on the Ca content of oats in bentonite-sand mixtures. 30 15 40 Ca content m.e./lOO kl 0 / 30 % Ca saturation -------------- 45 60 - /s '/ s / s 20 — ----- 4 m. e. --- 6 m. e. — — -- S m. e. 10 ____________________ 40 20 SO 60 base saturation Fig. XXII. The effect of degree of base saturation on the Ca content of rye in bentonite-sand mixtures. % Total M.e. K per 100 gms. oats tissue 58 50 40 — — —— — — — 6 m. e. 8 m. e. y ✓ / / i 30 1 20 y y ' s 'S / # *«■ 10 — 40 60 80 % Total base saturation Fig* XXIII. The effect of degree of base saturation on the K content of oats in bentonite-sand mixtures. K per 100 gms. rye tissue 20 20 40 60 80 % Total base saturation Fig. XXIV. The effect of degree of base saturation on the K content of rye in bentonite-sand mixtures. 59 M.e. Mg/100 g, oats tissue % Magnesium saturation 30 20 — 10 ------- 6 m. e. - - - - - 8 m. e. 20 40 60 80 % Total base saturation Fig. XXV. The effect of degree of base saturation on the Mg content of oats in bentonite-sand mixtures. M.e. Mg/100 g. rye tissue % Magnesium saturation 30 0 20 s — ---- ■ _ — •/ 10 — — 0 20 40 60 - 4 m. e. — — ■> 6 in. e. — — 8 m. e. 80 % Total base saturation Fig. XXVI. The effect of degree of base saturation on the Mg content of rye in bentonite-sand mixtures. 60 or better 45^>, of the exchange capacity. With respect to the potassium curves shown in Figs. XXIII and XXIV, the following trend is noticeable. Generally, they all began to rise slowly at the begin­ ning, and then rather steadily throughout the remaining range of the curves. Considering the usually greater error Involved In the method of determining potassium, it Is believed that the potassium content of the plants In question was probably not significantly affected by the base status of the medium until it reached a K sa­ turation level of about of the total exchange capacity. A considerable increase of K availability to the plants from a 4^ to a 6% K-saturation level was evident from the curves. As the K-saturation level increased from 6% to 8% s the K-content of the plants increased still further, indicating a maximum availability of K has not yet been reached. The Mg-curves (Figs. XXV and XXVI) also show general Increases in the Mg content of the plant tissue as the saturation level of Mg in the medium increases. The trend is more or less like that of K rather than Ca, but the variation is within a smaller range. In comparing the yields with the mineral composition of the oats and rye, it is suggested that the marked in­ crease of Ca availability at the 40fs level of total base 61 saturation is probably the main reason, for the increase of the yields at that level. Furthermore, the Increase of yields beyond the 40^ level seems to coincide with the continuous rise of the K and Mg curves. These facts give the indications that the differences In the growth of oats and rye are more closely related to the degree of base saturation, through Its combined effects on the availability of different cations, rather than the pH values as such. Furthermore, the data reveal that the mineral con­ tents of the plants, like the yields, were more directly related to percentage saturation than to total amount of bases present In the montmorillonitic colloids. II. Kaolin-sand mixture. The effect of the varia­ tions In the level of base saturation upon the mineral content of the plants in kaolin-sand mixture is given in Table IX and Figs. XXVII, XXVIII and XXIX. There was no significant increase in the calcium content of the plants as the saturation level increased. This indicates that a 15^ level of Oa saturation supplies enough available calcium for the nutritional requirement of oats and rye. The potassium curves show that there was a general increase In the potassium content of the plants as the level of K saturation in the kaolinitic colloid increased from 2, through 4 to &% of the total base exchange capaci- 62 Table IX Mineral Content of the Oven-dry Tissues of Oats and Rye as Influenced by Base Status of Kaolin-sand Mixtures. Base exchange capacity,m.e./lOO gms. mixture Base 1 saturation % 2 M.e. per 100 gms. dry tissue Ca Mg K Ca Mg K Oats 20 38.1 10.1 5.5 45.0 13.3 H « O H 40 37.3 18.2 17.1 43.1 19.2 18.5 60 39.1 16.2 18.5 42.2 21.1 21.3 80 37.8 17.3 23.0 39.2 19.8 22.8 Rye 20 31.1 9.1 2.5 28.2 12.5 8.5 40 30.8 10.2 13.5 31.9 15.8 12 .4 60 29.2 14.0 18.7 30.5 17.3 19.6 80 29.9 15.7 19.3 34.8 16.2 18.0 63 Ca saturation %\ K, 5 %* Ho.6— Saturation of Ca,40 %\ Mg, 5 %% K, 5 %* No.7— Saturation of Ca,35 %\ Mg, 5 %* K,10 %. No.8— Saturation of Ca,30 N o .9--Saturation of Ca,30 %% Mg, Mg, 10 %% K,10 5 %\ K,15 %• 77 further Interpretation because of the design of the experiment♦ The Effect of the Nature of Colloids on the Avail­ ability of Exchangeable Cations* Since most of the relationships between the nature of mineral colloids and the effects of degree of base saturation on the growth and mineral composition of plants have alreadybeen mentioned In the previous sections, only a few remarks need to be added here to complete the picture* It has been mentioned in Table I that rye was grown on the bentonite- and kaolin-sand mixtures at the same period during the experiment. As a result, data are available for making direct comparisons between the effect of the degree of base saturation of montmorillonitlc colloids and that of kaolinitic colloid on the growth and mineral composition of the plants. In re­ ference to the data shown in Table V and Table V I , It is observed that the yields of rye were all higher in kaolinitic than In montmorillonitic media when the base saturation was below 60% level of the total exchange capacity of 2 m.e. per lOOgms. Furthermore, a com­ parison of the data in Table VIII and IX reveals that the Ca and Mg contents of the rye grown in kaolin-sand mixture were higher than that grown in bentonite-sand mixture when both were at the levels below 60^ of base 78 saturation. DISCUSSION The most outstanding fact demonstrated in this investigation is the marked influence of the nature of soil colloid upon response to increasing degree of base saturation. Yields from montmorillonitic colloid in­ creased with each increment of base saturation reaching a maximum at 80^ saturation, the highest experimental level. Growth in kaolinitic colloid increased from 20 to M-0% saturation but shows no rise beyond this point. The illitic colloid gave results which are intermediate between them. Mehlich and Colwell (26), working with soil containing montmorillonitic and kaolinitic type of colloids, have found similar results. The mineral composition data show that only within a certain range of base saturation Is the mineral com­ position of plant a function of the degree of base saturation. The ranges of Ca, Mg and K are all higher In montmorillonite than in kaolinite colloids. This fact suggests that with a given degree of base satura­ tion, more exchangeable cations are available to plants in kaolinitic colloid than In montmorillonitic colloid. Exchangeable Ca and K held by illitic colloid seem to be even less available than those held by montmorillonitic 79 colloids at the same degree of base saturation. From the structural consideration, Marshall and Krindill (2 3 ) classified montmorillonite, beidellite, nontronite, saponite, and attapulgite as colloidal electrolytes whereas the clays of the Illite and kaolin groups as non-electrolytes. Using the potentiometric titration method and conductance measurement, Marshall (22) and his coworkers (23) recently concluded that for the three cations, Nat K* and NH4 ’, the ionization of the clay "salts" follows the order: kaolin!te> montmoril­ lonite > beidellite> illite, whereas the apparent strengths of the clay "acids" as judged by their dissociation of H* are in the order: kaolinite. montmorillonite> beidellite> Illite> Adopting Marshall’s idea of cationic activity (21) in explaining the relative uptake of exchangeable bases by plants, It can be seen that the results of the present investigation coincide with the results found by Marshall and his coworkers In their laboratory studies. From the view point of practical agriculture, it iB of interest to note that In order to increase the Ca uptake by growing plants higher saturation levels of Ca and K are needed for illitic clay than for montmoril­ lonitic clay. In the case of kaolinite, the Ca uptake by plants was as great at low as at high degrees of Ca saturation and increasing amounts of K at the lower 80 degrees of K saturation resulted in a slight but gradual Increase in the uptake of K by plants. Hence on kaolini­ tic soils only a relatively small amount of lime would be necessary to react with a small percentage of the exchan­ geable hydrogen in order to give a good crop response, while on montmorillonitic and illitic soils, much larger quantities would be needed to give higher levels of Ca saturation for improving the Ca nutrition of plants. The fact that illite, according to G-rim(l3)» is one of the main constituents of the glacial materials of the United states, might partly explain the need of heavy liming in some of Michigan Soils. The advantage of localized application of fertili­ zers, particularly in montmorillonitic and illitic soils, is clearly indicated by the results. Creator uptake of exchangeable bases and better growth of plants were ob­ tained when the degree of base saturation was relatively high. Of great importance also in soil-plant relationships are the effects of complementary ions on the uptake of exchangeable bases by plants. The results of this inves­ tigation indicate that neutralizing an acid soil with Ca or Mg should render K more available. This serves as an­ other reason for the general superiority of Ca—clay over H-clay. However, excess application of K fertilizers to 81 an acid soil may prove to be undesirable, because as com­ plementary ions, K tends to inhibit the uptake of Ca by plants. Turning to the theoretical aspects, let us now review briefly some of the theories which have been offered to explain the difference in availability of various exchan­ geable bases. Explanations given by Horner (16) attri­ buted the difference to the relative energy of adsorption of different exchangeable bases on the surface of clay particles. However, no numerical value or exactly rela­ tive order of energy of adsorption was given by Horner. Jenny (17)» in his equation illustrating the quantitative relationship between the interchanging cations and the complementary ions, used oscillation volume as a measure of adsorbability. The greater the oscillation volume, the smaller the adsorbability, and consequently the great­ er the availability of the ion to the plant. Later,Jenny and Ayres(18) were able to evaluate the ratio of oscilla­ tion volumes of some of the exchangeable ions. Recently Marshall employed various methods for the measurement of cationic activity of the exchangeable bases, and used the term "cationic activity" almost synonymously as "ionic dissociation" or "availability". Cooper and his co-workers (9) have repeatedly proposed and presented evidence for the theory that the intensity 82 of* removal of cations from soil colloidal complexes is largely a function of the normal electrode potentials of the element concerned* All the theories proposed by various workers are, in reality, essentially the same but with different terminology. No satisfactory explanation has yet been advanced for the different availability of exchangeable bases because of the difference in the nature of colloids* In the following sections, the writer offers his own explanations from the theoretical point of view. The physico-chemical behavior of the surface of a colloidal particle is a function of both the geometrical and electrical properties of this surface* From the geo­ metrical viewpoint the surface may be of the convex, plane or concave type. These differences In geometric shape of colloidal particles will result in different distribution of electrostatic attractive force In the surface of the colloidal particle. Declaux (3) has calculated the dis­ tribution of ions around a spherical particle (convex field) of opposite charge. Winterkorn (40) made studies on the surface behavior of platy-shaped clays (planar surface). An analysis of the equations for the convex field shows that the Ionic concentration is very high close to the surface and falls off rapidly with increasing distance. This decrease becomes more rapid with increas- 83 Ing charge of the ions* In the case of the planar surface the concentration stays practically constant with Increas­ ing distance from the surface. For clays of different shape, these facts may account for a part of the different availability of exchangeable bases on different colloidal clays. But since the three colloids used in this experi­ ment are all platy in shape, this factor of the shape of clay minerals does not actually exist in the present case * According to Hendricks (15) there are two forces which exercise the attraction of exchangeable cations on the surface of colloidal crystals. One is the Couloumb's force due to electrostatic attraction and the other is the Van der Waals force. Van der Waals force varies pri­ marily with the nature of the ions (or molecules) which come upon the surface of a clay mineral as adsorbed par­ ticle, while Gouloumb's force varies with the nature of Ions, the crystal structure of the mineral and the dis­ tance between the crystal surface and the seat of isomorphous replacement within the crystal lattice. For certain structural reasons (14), isomorphous substitution within the crystal lattice of kaolin!te is believed to be absent. The exchangeable bases are held on the surface of kaolinite mostly through the direct replacement, by cations, of H in OH groups of the lattice surface (20). But in montmoril- 84 Ionite, a 2:1 type clay mineral, due to its structural characteristics, seats of replacement are offered to the cations. The difference in the fiorces of attraction thus created may account for at least a part of the difference in the availability of exchangeable bases on the surface of montmorillonitic and kaolinitic types of clay minerals. SUMMARY AND CONCLUSIONS This investigation was undertaken to attain by means of pot cultures a better understanding of the significance of the degree of base saturation in relation to the growth and mineral composition of certain crops. Two relatively pure mineral colloids, bentonite and kaolin, and a Fox sandy loam containing Illite were used for the studies. Bentonite and kaolin were first electro- dialyzed and then mixed with different amounts of pure quartz sand to give different levels of base exchange capacity. Treatments were made to all three cultural me­ dia for varying degrees of base saturation and also, in a separate experiment, for varying ratios between one of the three major exchangeable cations and exchangeable hydrogen. Oats and rye were grown In succession In montmorillonitic and kaolinitic media, while peach, soybean, proso, tomato and oats were grown in the Fox sandy loam. Dry weights and contents of certain mineral constituents of oats, rye 85 and tomato were determined. Yield data from the montmorillonitic media showed nearly linear relationship between the degree of base saturation and the growth of the plants. In the kaolini­ tic media the Increase of yield was only noticeable from the first Increment of bases, effects above 40^ total base saturation being insignificant. The results from Illitic soil was Intermediate between those mentioned above, I.e., the highest yield of tomato obtained at the 75^ saturation level. The yield data further indicate that the growth of plants was more closely related to the degree of base saturation than to the total supply of exchangeable bases. With the same amount of bases and at the levels below 60% base saturation, the yields of rye in the kaolinitic colloid were higher than in the montmorilloni­ tic colloids. In the montmorillonitic media, the increase of Ca uptake by the plants from the first increment of Ca was pronounced with only little effects above 30% Ca satura­ tion (or 40^ level of total base saturation). The K content of the plants was increased appreciably at only the higher levels of base saturation, while significant increases of the Mg content of the plants occurred at lower levels (i.e. below 60% base saturation level). 86 In the kaolinitic media, no appreciable change of Oa and Mg contents of the plants was noticed* This is an interesting contrast to the results obtained with the montmorillonitic media* However, there were defi­ nite increases in K content of plants with increasing increments of K at the lower levels of saturation* The higher contents of Ca and Mg in the plants were found in kaolinitic media rather than in the montmoril­ lonitic media provided that the total base saturation level was under 60 % of the exchange capacity. On the other hand, the K content of the plants from montmoril­ lonitic media was invariably higher than that from kao­ linitic media* In the Illitic soil, the most marked increase of Ca content in plants occurred when the degree of base saturation Increased from the 50 % to the 75 % level. Beyond that point, no appreciable increase was noticed. As the degree of base saturation of illitic soil in­ creased, the K and Mg percentages in the plants increased also. The effect of complementary ions on the availability of the exchangeable bases was indicated by the mineral composition of the rye grown in montmorillonitic and kao­ linitic media receiving the same treatments. The results all show that referring to H-ion as standard, the Ca-ion and Mg-Ion tended to increase the availability of exchange­ 87 able K, while the K-Ion exhibited the reverse effect on exchangeable Ca and Mg* The well recognized fact that Ca and Mg ions have the mutual repressive effect was also observed in the experiment* The study also discusses, from the theoretical point of view, some of the factors involved in determining the availability of exchangeable bases* 88 LITERATURE CITED 1. Albrecht, Wm. A. tion by legumes. 1939 Soil factors in nitrogen fixa­ Trans. 3rd Comm. Internl. Soc. Soil Sci., A: 71-84. 2. Albrecht, Wm. A. and Schroeder, R. A. 1942 Plant nu­ trition and the hydrogen ion: I. Plant nutrients used most effectively in the presence of a significant con­ centration of hydrogen ions. 3* Alexander, J. 1926 Soil Sci., 53: 313-327. Colloid chemistry, Vol.I: 515*524. Chemical Catalog Co., Inc., New Xork. 4. Allaway, W. H. 1945 Availability of replaceable cal­ cium from different types of colloids as affected by degree of calcium saturation. 5. A.O.A.C. 1935 Soil Sci., 59: 207-217. Methods of analysis, 123-124. 6. Bower, C. A. and Turk, L. M. 1946 sium deficiencies in alkali soils. Calcium and magne­ Jour. Amer. Soc. Agron., 38: 723-727. 7. Bradfield, R. 1928 An inexpensive cell for the puri­ fication of colloids by electro-dialysis. Ind. and Eng. Chem., 20: 79. 8. Chu, T. S. 1946 Some chemical studies of soils in re­ lation to satisfactory and unsatisfactory growth of peach trees. M. S. Thesis, Michigan State College. 9. Cooper, H. P., Paden, W. R. , G-armen, W. H. and Page, N. 89 R. 1948 Properties that Influence availability of calcium in the soil to plants. Soil Sci., 6 5 : 75 -9 6 . 1 0 . Elga^.y, M. M . , Jenny, H. and Overstreet, R. 1943 Effect of type of clay mineral on the uptake of zinc and potassium by barley roots. Soil Sci., 5 5 : 257- 263. 11. Gedroiz, K. K. 1931 and the plant: Exchangeable cations of the soil I. Relation of plant to certain cations fully saturating the soil exchange capacity. Soil Sci., 32: 51-63. 12* Gieseking, J. E. and Jenny, H. valent cations in base exchange. 1936 Behavior of poly­ Soil Sci., 42: 273- 280. 13. Grim, R. E. 1939 Properties of clay. 111. State Geo­ logical Survey, Circular No. 49. 14. Hendricks, S. B. 1939 Random structures of layer mi­ nerals as illustrated by cronstedite. content of kaolinite. 15. Hendricks, S. B. Possible iron Amer. Min., 24: 529-539. 1941 Base exchange of the clay mi­ neral montmorillonite for organic cations and its de­ pendence upon adsorption due to Van der Waals forces. J our. Phy s . Chem., 45 5 6 5 . 16. Horner, G. M. 1936 Relation of the degree of base saturation of a colloidal clay by calcium to the grow­ th, nodulation and composition of soybeans. Mo. Agr. 90 Exp. Sta. Res. Bui. 2 3 2 , pp. 3 6 . 17* Jenny, H. change. 1936 Simple kinetic theory of ionic ex­ I. Ions of equal valency. Jour. Phys. Chem., 40: 501-517 * 18. Jenny, H. and Ayers, A. D. 1939 The influence of the degree of saturation of soil colloids on the nu­ trient intake by roots. Soil Sci., 48: 443-359. 19* Jenny, H*, and Cowan, E. W. 1933 Uber die bedeutung der im Boden adsorbierten Rationen fur das Pflanaenwackgtum. Ztschr. Pflanzenernahr., Diingung, u. Bodenk., (A) 3 1 : 57-67. 20. Kelley, W. P. 1942 to agriculture. Modern clay research in relation Jour. Greol., 50: 307-319* 21. Marshall, C. E. 1944 Cationic activities, exchange­ able bases and uptake by plants. Soil Sci. Soc. Amer. Proc., 8 : 175-178. 22. Marshall, C. E. 1948 Ionization of Ca from soil col­ loids and its bearing on soil plant relationships. Soil Sci., 6 5 : 57-68. 23. Marshall, C. E. and Krindill, C. A. as colloidal electrolytes. 1942 The clays Jour. Phys. Chem., 46: 1077-1090. 24. Mehlich, A. to soil type. 25. Mehlich, A. 1942 Base unsaturation and pH in relation Soil Sci. Soc. Amer. Proc., 6: 150-156. 1943 The significance of percentage base saturation and pH in relation to soil differences. 26. Mehlich, A. and Colwell, W. E. 1944 Influence of nature of soil colloids and degree of base saturation on growth and nutrient uptake by cotton and soybeans. Soil Sci. Soc. Amer. Proc., 8 : 179-184. 27• Mehlich, A. and Reed, J. F. 1946 The Influence of degree of saturation, potassium level, and calcium additions on removal of calcium, magnesium, and potas­ sium. Soil Sci. Soc. Amer. Proc., 1 0 : 87*93* 28. Mehlich, A. and Reed, J. F. 1947 The Influence of type of colloid and degree of calcium saturation on fruit characteristics of peanuts. Soil Sci. Soc. Amer. Proc., 11: 201-205* 29. Mikkelsen, D. S. and Toth, S. J. 1947 Thiazol yellow for determining the magnesium content of soil extracts. Jour* Amer. Soc. Agron., 39* 165*166. 30. Peech, M. in soils. 1941 Determination of exchangeable bases Rapid micromethods. Indus, and Engin. Chem., Analyt. Ed. 13, 436-441. 31. Peech, M. and Bradfield, R. 1943 The effect of lime and magnesia on the soil potassium and on the absorp­ tion of potassium by plants. 32. Peech, M. and English, L. soil tests. 3 3 . Piper, C. S. 274. Soil Sci., 55• 37-48. 1944 Rapid microchemical Soil Sci., 57* 167*195* 1947 Soil and plant analysis, pp. 272 - The Univ. of Adelaide, Adelaide, Australia. 34. Seatz, L. F. and Winters, E* 1944 Potassium release from soils affected by exchange capacity and comple­ mentary ion. Soil Sci. Soc. Amer* Proc., 8: 150-153. 35* Spurway, C* H. plants. Mich. Agr. Expt. Sta., Special Bui. 306. 3 6 . Stohmann, F. stoffen. Soil reaction (pH) preferences of 1864 Versusche mit absorbirten Nahr- Landw. Vers. Sta., 6: 424-428. (Original not seen. Data cited by Jenny, H. and Ayers, A. D. in Soil Sci., 48: 443-459, 1939) 37 • Tukey, H. B. and Carlson, R. F. 1945 Breaking the dormancy of peach seed by treatment with thiourea. Plant Physiol., 20: 505-516. 38. Tukey, H. B. and Carlson, R* F. 1946 Morphological changes in peach seedlings following after-ripening treatments of the seeds. 39. Weir, W. W. 1936 Soil science, its principles and practice, pp. 286-28740. Winterkorn, H. F. Bot. G-az*, 106: 431-440. 1936 Lippincott Co., Chicago. Studies on the surface be­ havior of bentonite and clays. Soil Sci., 41: 25-32.