Ltnnnnl, ~A & M COLLEGE. canvas. R8-103S-6m TEXAS AGRICULTURAL EXPERIMENT STATION A. B. CONNER, DIRECTOR COLLEGE STATION, BRAZOS COUNTY, TEXAS BULLETIN NO. 520 DECEMBER, 1935 ik‘ DIVISION OF CHEMISTRY BASE EXCHANGE PROPERTIES OF SOME TYPICAL TEXAS SOILS Agricumzra! X FREChBHIiCJICQEIEL~Z¢ w w» A» CEHEQE Sfiaflanéffinsfik AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS T. O. WALTON, President Base exchange properties of soils are related to the retention of compounds 0f ammonia and potassium in the soil; the basicity, buffer capacity, and degree of acidity (pH) of the soil; and the physical condition of the soil as influenced by calcium and sodium salts in the soil or in irrigation waters. The ammonium acetate method for the determination of the total exchange capacity of soils is more accurate than the Puri method of titration or the Kappen method of titration. The total exchange capacity of about 360 representative Texas soils varied from 0.7 M.E. in dune sand to 70.7 M.E. per 100 grams in a Houston black clay. Varia- tions are as large between different samples of the same soil type as variations between soils of the same physical character of dif- ferent soil series. The exchange capacities of heavy soils are much greater than those of light soils. The bases found to be present in the exchange complex are principally calcium with small quan- tities of magnesium, potassium, and sodium, and also hydrogen in acid soils. There is a relation between the exchange capacities of soils and the alumina and iron oxides dissolved by strong acids. The nitrogen, phosphoric acid, potash, lime, and basicity on an average increased with the exchange capacity of the soil up to 20 M.E., after which there was little relation between these constituents and the exchange capacity. CONTENTS Page Introduction 3 Nature of Base Exchange in Soils 6 Methods for the Estimation of Total Exchange Capacity ______________________ _- 7 The Ammonium Acetate Method 7 Method of Titration—Puri 8 Method of Titration——Kappen 8 9 Total Exchange Capacity "of Texas Soils Variations in Exchange Capacity Between Different Samples of p the Same Type 13 Relation Between Exchange Capacity and Soil Texture _________________ __ 14 Relation to Location in State 15 Relative Proportion of Bases Held by the Base-Exchange Complex ______ _- 16 Relation to Chemical Composition 19 Relation Between Exchange Capacity and Iron and Aluminum Oxide 20 Summary 21 References p 2 2 BULLETIN NO. 520 DECEMBER, 1935 BASE-EXCHANGE PROPERTIES OF SOME TYPICAL TEXAS SOILS G. S. FRAPS, CHIEF, DIVISION OF CHEMISTRY, AND .I. F. FUDGE, CHEMIST Soils have the power of taking some substances out of solution and replacing them with others. If a solution of ammonium sulphate is mixed with a soil, part of the ammonium goes out of solution, while calcium, magnesium, potassium, and sodium go into solution. This phenomenon, which has been known for over 75 years, was formerly termed “fixation,” but is now termed “base-exchange.” The bases in the soil which can be exchanged are combined with organic or inorganic acids of complex composition. As the exact composition of these acids is not known, they are termed the “base-exchange complex.” Base-exchange and the base-exchange complex are important in soils for a number of reasons. Soluble compounds of ammonia and potash, when introduced into the soils in commercial fertilizers or plant residues, by exchanging with other bases, chiefly calcium, are rendered less soluble in water. They are thereby prevented from washing out of the soil readily and are held for the use of plants. The potash held by the base- exchange complex is more available to plants than that in more stable silicates. When the bases in the base-exchange complex are replaced by hydrogen, an acid compound is formed so that the soil becomes acid. The greater the bufier capacity of the exchange complex of the soil, the greater the-resistance of the soil to acidifying influences. If an acid soil is treated with a suflicient quantity of lime, the calcium of the lime replaces the hydrogen in the base-exchange complex, and the soil is made neutral or alkaline. The base-exchange complex consists of very fine particles, most of which are so fine as to be colloidal. When the complex is saturated chiefly with calcium, the particles attract one another so as to coagulate or flocculate, and this helps the soil to be porous and crumbly or to assume a condition of good tilth. When the complex contains sufficient amounts of potassium, sodium, or sometimes hydrogen, and when the soil contains only small amounts of soluble salts, the particles repel one another and become dispersed so as to deflocculate the soil. In this condition, the particles can readily become suspended in water, and may be washed down through the soil, or washed away on its surface suspended in water. Such soil may become heavy, sticky, and not easily penetrated by water. When a soil containing particles in the deflocculated condi- tion dries out, it becomes hard and cloddy, and assumes a condition of poor tilth. In extreme cases the fine particles may fill the pores of the soil and the soil may become so hard and impervious that Water and air can hardly penetrate it and plants cannot grow upon it. Irrigation waters containing sodium salts may cause the replacement by sodium of sufiicient quantities of the calcium in the base-exchange complex to cause the dispersal of the fine particles and so bring about unfavorable changes in the physical character of the soil. This brief outline of some of the 6 BULLETIN NO. 520, TEXAS AGRICULTURAL EXPERIMENT STATION important relations of the base-exchange complex in soils will be expanded in some detail in the discussion which follows, and applied to Texas soils. NATURE OF BASE-EXCHANGE IN SOILS The portion of the soil capable of base-exchange is made up of complex inorganic and organic acids, combined with various bases, and is found in the colloidal portion of the soil. Since practically all of the soils of Texas are so low in organic matter that the organic acids can play only a very minor role in base-exchange in these soils, only the inorganic acids will be considered in the following discussion. Kelly and his coworkers (6, 10 to 15), Fraps and Fudge (7, 8), and Baver and Scarseth (4) claim that several acids occur in difierent exchange complexes. Such acids vary considerably in physicochemical properties, principally in the dissociation constant of the acid. Baver and Scarseth (4) state that soil material capable of base-exchange may originate in a number of ways, that the properties of the material will vary with the factors conditioning their development, and that the nature of the soil acids involved in base- exchange is solely a function of the kind and extent of weathering, and is independent of the parent material. Kelley, Dore, and Brown (15) found that the colloids from an old soil derived from granite and formed under conditions of intensive Weathering had a total exchange capacity of 18.3 M.E. per 100 grams. Those from a soil likewise derived from granite in a semiarid region where weathering was limited had an exchange capacity of 57.2 M.E. The colloids of older and more weathered soils therefore had a much lower exchange capacity than those of younger soils which had been subject to less intensive weathering. Pierre and Scarseth (19) found that the soil acids formed under conditions of high weathering were weaker than those of soils less highly weathered. A number of investigators (4, 8, 15, 19) have shown a relation between the acids of the exchange complex and the ratio of alumina to silica in the soil colloids. In general, soils with colloids having a low ratio of alumina to silica, as compared with soils with a high ratio, tend to be more highly buffered, to have a higher total exchange capacity, and to contain acids which are stronger. Kerr (16, 17), Vanselow (22), and others claim that the acids of the base exchange complex are monobasic. The inorganic base-exchange complex is thus shown to be made up of a number of complex alumino-silicic acids, combined with different bases or with hydrogen, and differing in strength and composition, depending upon conditions of their development. The mechanism of base exchange is simple, and is a special case of a general phenomenon in chemistry known. as metathesis, in which two different acids, combined with different bases and in contact with each other, exchange part of their bases. The reaction in the case of soils may be represented by the equation CaX2 + 2NH4o2H3o2 E >oa(o2H3o2)2 +_2NH4X. The base exchange complex (represented by X) combined with calcium reacts partly with ammonium acetate to form calcium acetate and an BASE EXCHANGE PROPERTIES TYPICAL TEXAS SOILS 7 ammonium salt of the base exchange complex. The reaction is reversible, and the direction in which it tends is determined by the relative quantities of each of the compounds present. In the equation given, the direction is to the right, since calcium complex and ammonium acetate were assumed to be the only compounds present at the start of the reaction. If the quantity of the compounds on the right side of the equation are increased, the reaction is forced to the left. At equilibrium, all four compounds are present and the reaction never goes to completion in either direction if the products of the reaction are not removed from the soil. Other salts react with the soil in the same manner as the ammonium acetate discussed above. METHODS FOR THE ESTIMATION OF‘ TOTAL EXCHANGE CAPACITY The total exchange capacity of‘ a soil may be considered as the sum of all of the bases, and also hydrogen if any, which are combined with the exchange complex of the soil. In order to express the sum as a chemical unit, the bases are usually calculated to their equivalent in combining power of hydrogen. The unit usually used is 1 milligram of hydrogen, termed 1 milliequivalent or M.E. In base-exchange work, the M.E. referred to is usually in 100 grams of soil. A number of methods have been proposed for determining the total base exchange capacities of soils. Most of them depend upon the replace- ment of all the bases, including hydrogen, by ammonia, and the estima- tion of the ammonia in the soil complex. Kelley and Brown (14) used barium hydroxide to neutralize the hydrogen, followed by ammonium chloride to replace the bases with ammonia. Pierre and Scarseth (19) used barium acetate followed by ammonium chloride, securing somewhat lower results than by the method of Kelley and Brown. Schollenberger and Dreibelbis (21) proposed the use of ammonium acetate, and it has been used by other workers. Since the excess of ammonium acetate is easily removed, the method is convenient. The ammonium acetate method was used in the work here reported. The Ammonium Acetate Method The method finally used for the determination of total exchange capacity is essentially the same as that described by Schollenberger and Dreibelbis (21) and Chapman and Kelley (6). The details of the method are as fol- lows: Ten grams of soil in a Gooch.crucible provided with a disc of filter paper were leached with 250 cc of neutral, normal ammonium acetate solution. Suction was applied to expedite the leaching, care being taken that it was not too rapid to allow complete reaction. After the ammonium acetate solution had leached through, the excess was washed out with i 95 per cent ethyl alcohol. Tests for ammonia in the washings were made with Nessler’s solution. After complete removal of the excess ammonia, the soil was transferred to 800 cc Kjeldahl flasks,_water and light mag- nesium oxide were added, and the liberated ammonia was distilled into 8 BULLETIN NO. 520, TEXAS AGRICULTURAL EXPERIMENT STATION standard hydrochloric acid. The excess acid was then titrated with standard ammonium hydroxide. In the case of calcareous soils, the calcium carbonate Was destroyed by preliminary treatment with a slight excess of hydrochloric acid. Fraps and Fudge (7) have shown that such treatment did not destroy the exchange complex. Method of Titration—Puri Two methods have been proposed for estimating the total exchange capacity from the determination of the quantity of‘ acid consumed or neutralized by the soil. These methods are much more rapid than either the ammonium acetate or the ammonium chloride method. In the Puri method (20), the carbonates in the soil are first estimated by titrating the soil with 0.5 N sulfuric acid in the presence of aluminum chloride and calcium sulfate, with bromcresol green and bromthymol blue as inside indicators. Next, to estimate total exchange capacity, hydrochloric acid equivalent to the carbonate content is added to 10 grams of soil in a 500 cc reagent bottle. Then 100 cc of 0.1 N hydrochloric acid is added and the mixture shaken. The solution is filtered and the soil Washed several times with 0.05 N hydrochloric acid and then with water. The filtrate is made up to volume and an aliquot titrated with standard sodium hydroxide, with phenolphthalein as an indicator. The Puri method was compared with the ammonium acetate method on a number of soils, with the results given in Table 1. The results by the Puri method are in most cases appreciably higher than those by the ammonium acetate method. This is probably due to the extraction by the acid of bases from other soil compounds in addition to those from the exchange complex. The method may be used for rapid approximate results but we do not consider it to be accurate. The Puri method is not adapted to the estimation of the_base exchange capacity of acid soils, since only the bases and not the hydrogen would neutralize the acid. With such soils, the results would be too low. The amounts of calcium carbonate estimated by the Puri method were compared with amounts estimated by liberating the carbon dioxide with hot dilute acetic acid, absorbing it in standard barium hydroxide, and titrating‘ the barium hydroxide with standard hydrochloric acid (7, p. 11). A comparison of the results is given in Table 1. In general, the agree- ment is fairly close, although there are notable exceptions. The method of Puri does not measure very small quantities of carbonates. In the four soils of highest carbonate content, it did not show nearly as much carbonate as was actually present. Since the method for total exchange capacity is corrected by results of the carbonate estimation, any error in the latter will cause a corresponding error in the former. The Puri method for carbonates may be considered to be a rapid approximate method. Method of Titration—Kappen In the Kappen method (9) for the estimation of total exchange capacity, 50 grams of soil is stirred or shaken with 250 cc of 0.1 N hydrochloric BASE EXCHANGE PROPERTIES TYPICAL TEXAS SOILS 9 Table 1. Comparison of three methods for estimating total exchange capacity L b Carbonates in soil Total exchange capacity a o- ratory By ab- By direct Ammonium Acid Acid num- Soil type sorption titration acetate method method ber of CO2 (Puri) method of Puri of Keppen 2610s Crockett fine sandy loam. . .° 0 26 0 4.93 9.00 3.29 29450 Amarillo fine sandy loam. . . 2.40 0 6.80 14.30 4. 20 31888 Webb fine sandy 10am. . . . . 0.12 0 8.58 12.00 5.24 31820 Amarillo fine sandy loam. . . 0.98 (J 9.15 10. 70 7.25 31802 Yahola fine sandy loam. . . . 61.10 60. 62 10.90 31.70 . . . . . . . . . . 25883 Willacy fine sandy loam. . .. 7.92 5.64 11.61 21.80 12.27 25865 Lomalto clay loam . . . . . . . . 20. 14 18. 24 13.40 28. 90 14. 44 31884 Hidalgo clay 10am . . . . . . . . . 254.80 236.00 17.59 44.00 . . . . . . . . . . 25891 Rayrnondville fine sandy loam . . . . . . . . . . . . . . . . . .. 26.80 27.76 19.12 66.90 17.42 31905 Victoria clay loam . . . . . . . . 11.00 11.26 19.22 29.20 18.30 29436 Wilson clay . . . . . . . . . . . . . . 1.04 1 . 14 20.40 25.70 17.48 31321 Amarillo silty clay loam. . . . 2.88 2.88 20.62 30.90 . . . . . . . . . . 25905 Laredo silt loam . . . . . . . . . . 317.60 301.88 20.68 28.30 . . . . . . . . . . 29434 Wilson clay . . . . . . . . . . . . . . 1 . 34 0.88 21 .00 33.10 18.64 31833 Spur fine sandy loam . . . . .. 14. 20 7.00 21.46 42.40 13.85 29426 Crockett clay loam . . . . . . . . 0.99 0 23. 36 22. 20 . . . . . . . . . . 29438 Lufkin fine sandy loam. . . . 0.05 1.26 23.90 32.10 . . . . . . . . . . 29425 Crockett clay loam . . . . . . . . 0. 79 0 25.90 23.50 . . . . . . . . . . 29365 Amarillo fine sandy loam. . . 0.11 0 30.10 8.50 24.41 26089 Catalpa clay . . . . . . . . . . . . . 118.00 115.92 35.08 43.40 . . . . . . . . . . 25967 Houston clay . . . . . . . . . . . . . 2.10 2.38 35. 78 40.00 24.93 25959 Irving clay . . . . . . . . . . . . . . . 2.00 1.88 38.22 38.10 25.82 25869 Point Isabel fine sandy loam 91.20 68. 74 38.60 52. 70 . . . . . . . . . . 26823 Lake Charles clay . . . . . . . . . 8.80 10.62 45. 10 49. 80 . . . . . . . . . . acid for one hour. The suspension is then allowed to stand overnight. The clear, supernatant liquid is decanted the next morning, and 125 cc is titrated with standard sodium hydroxide, phenolphthalein being used as the indicator. In this method, the products of the reaction are not removed by leaching with acid, so that the acid consumed represents a state of equilibrium between soil and acid, rather than the total capacity of the soil to neutralize acid. Fraps and Fudge (7) have shown that on the average under these conditions about 13 per cent of the exchange complex does not react with the acid. In the Kappen method, no attempt is made to correct for the portion of the acid which is used by the carbo- nates of the soil, nor for the portion used by soil materials other than carbonates and bases in the exchange complex. This method is therefore unsuitable for soils containing appreciable amounts of calcium carbonate. It is also unsuitable for acid soils, since only the bases will react with the acid. Results by the Kappen method on a number of soils are compared in Table 1 with the results by the ammonium acetate method. As could be expected, the results are too low. They are decidedly lower than those secured by the Puri method. We consider the Puri method better than the Kappen method, but neither method is as accurate as the ammonium acetate method. TOTAL EXCHANGE CAPACITY OF TYPICAL TEXAS SOILS The total base-exchange capacity of about 360 Texas soils was deter- mined by the ammonium acetate method already described. The type 10 BULLETIN NO. 520, TEXAS AGRICULTURAL EXPERIMENT STATION Table 2. Total exchange capacity of typical Texas soils Surface soil Subsoil Labo- ratQry T012211 TOtEIl. num- Basic- Ex- Basic- x- ber of Type Name County Depth rty change Depth ity change sur- inches per capac- inches per Qapag- fa¢e cent 1ty cent ity 5011 M.E. M.E 20196 Abilene clay loam . . . . . . . . . . Coleman . . . . 0-8 1 . 84 29. 60 8-30 . . . . . . 24.82‘ 9297 Amarillo fine sandy loam. . . . Lubbock. . . . 0-18 0. 69 11.11 . . . . . . . . . . . . . . . . . . 31331 Amarillo fine sandy loam. . . . Potter . . . . . . 0-7 0.52 8.33 7-19 0.53 9.54 31820 Amarillo fine sandy loam. . . . Potter . . . . . . 0-7 0.57 9. 15 7-12 0.25 9.201 9382 Amarillo clay loam . . . . . . . . . Lubbock. . . . 0-12 0. 74 14.91 12-24 0.93 18.90 12655 Bastrop sand . . . . . . . . . . . . . . Brazos . . . . . . . . . . . . 0. 24 3.50 . . . . . . 0.08 2.55 12653 Bastrop fine sandy loam. . . . Brazos . . . . . . . . . . . . 1. 70 11.54 . . . . . . 0.45 8.80‘ 12657 Bell clay . . . . . . . . . . . . . . . . . . Brazos . . . . . . . . . . . . 2.03 24.29 . . . . . . 1.43 26.36 21222 Bell clay . . . . . . . . . . . . . . . . . . Henderson . . 0.10 2. 2O 44.37 10-36 4.95 44.28 26079 Bell clay . . . . . . . . . . . . . . . . . . Navarro. . . . 0-7 2.61 46.36 7-19 3.59 44.08- 29523 Bowie fine sandy loam . . . . . . Van Zandt. . 0-7 0. 26 2.51 7-19 0. 24 4. 74 18538 Bowie very fine sandy loam. . Red River. . . 0-10 0. 43 4. 05 16-36 0. 89 12.69‘ 31896 Brennan fine sandy loam. . . . Frio . . . . . . . . 0-7 0.16 6.31 7-19 0.10 4.11 12590 Caddo fine sandy loam. . . . . Camp . . . . . . . . . . . . (1.45 5.48 . . . . . . 0.35 4.21 9161 Caddo fine sandy loam. . . . ; Harrison. . . . 0-8-10 0.25 3.23 10-16 0.20 5.21 21809 Cahaba fine sandy loam. . . . Henderson. . 0.—6 0.45 5.00 6-20 0,05 2.39- 26089 Catalpa clay.) . . . . . . . . . . . . Navarro. . . . 0-7 7.12 35.08 7-19 7.41 37.96- 12572 Crawford clay 10am . . . . . . .. Ellis . . . . . . . . . . . . .. 3.18 44.21 . . . . .. 3.88 43.52" 21771 Crockett fine sandy loam. . . . Henderson . . 0-10 0. 28 6. 66 10-26 0, 78 4,95 23954 Crockett fine sandy loam. . . . ' Milam . . . . . . 0-7 0. 70 12.44 7-19 1.05 24. 73 25969 Crockett fine sandy loam. . . . Navarro. . . . 0-7 0.30 7.12 7-19 0.56 16.22 26103 Crockett fine sandy loam. . . . Navarro. . . . 0-7 0. 25 4.92 7-19 0.65 14.69 12512 Crockett fine sandy loam. . . . Washington. 0-5 0. 75 15.10 5- 1.08 24.37 29533 Crockett very fine sandy loam Van Zandt. . 0-7 0. 3S 12.24 7-18 0. 30 9. 08 12667 Crockett loam . . . . . . . . . . . . . Brazos . . . . . . . . . . . . 0.40 9.96 . . . . . . 0.48 12. 25 12518 Crockett loam . . . . . . . . . . . . . Washington. . . . . . . 0.94 13. 71 . . . . . . 1.00 18.49 29427 Crockett clay loam . . . . . . . . . Brazos . . . . . . 0-7 1.22 28.85 7-19 1.92 34. 78 26099 Crockett clay loam . . . . . . . . . Navarro. . . . 0-7 1.47 31.54 7-19 1.14 22.24‘ 18234 Denton clay . . . . . . . . . . . . . . . Tarrant. . . . . 0,—8 1.23 31.80 8-36 8.93 31.02 25871 Dune sand . . . . . . . . . . . . . . .. Willacy. . . .. 0-7 0.41 .69 7-19 0.42 1.16 12576 Durant (Now Wilson) fine - sandy loam . . . . . . . . . . . . . . . Ellis . . . . . . . . 0-12 2.33 20. 27 12- . . . . . . 25.50 12531 Durant (Now Wilson) very fine sandy loam . . . . . . . .. Ellis . . . . . . . . . . . . .. 3.63 19.23 . . . . .. 5.88 20.44 12584 Durant (Now Wilson) loam. Ellis . . . . . . . . . . . . . . 1.67 29.80 . . . . . . 1.59 31.34 12574 Durant (Now Houston) clay. Ellis . . . . . . . . . . . . . . 2.98 5.93 . . . . . . 2.57 36.97 31880 Duval fine sandy loam . . . . . . Frio . . . . . . . . 0-7 0.23 7.31 7-19 0.40 8.00 31892 Duval fine sandy loam . . . . .. Frio . . . . . . . . 0-7 0.21 5.31 7-19 0.30 9.16 26083 Ellis clay . . . . . . . . . . . . . . . . . Navarro 0-7 1.56 32.58 7-19 2.27 35. 70 12582 Elis clay . . . . . . . . . . . . . . . . .. llis . . . . . . . . . . . . .. 10.9 32.52 . . . . .. 12.3 36.08 31804 Fritch fine sandy loam . . . . . . Potter . . . . . . 0-7 0. 75 11.56 7-19 0. 75 12.92‘ 18210 Frio fine sandy loam . . . . . . . . Erath . . . . . . 0-15 0.88 5.50 15-36 0.63 8. 78 29331 Frio silt loam . . . . . . . . . . . . . . Midland 0-7 8. 95 1 1 . 76 7-19 13 . 3 11 . 38 7223 Frio silty clay loam . . . . . . . . Edwards 0-12 . . . . . . 25 .30 12- 37.26 23.96 23950 Frio clay . . . . . . . . . . . . . . . . Milam . . . . . . 0-7 26.3 31.46 7-19 31. 7 30.96 26817 Guadalupe silty clay loam. . . Victoria. . . . . 0-7 18.9 19.24 7-15 19.1 16.40 20724 Hockley fine sandy loam. . . . Harris . . . . . . 0-7 0.23 4.13 7-19 0.10 3.00- 26819 Hockley fine sandy loam. . . . Victoria. . . . . 0-7 0. 14 2.70 7-19 0.45 5.96 12500 Houston loam . . . . . . . . . . . . . \Vashington. . . . . . . 0.55 8.64 . . . . . . 0.40 16.42 12498 Houston clay loam . . . . . . . . . Washington. . . . . . . 1.13 27.38 . . . . . . 1.21 . . . . . . 12568 Houston clay . . . . . . . . . . . . . . Ellis . . . . . . . . 0-12 6.96 47.79 12- 7.00 50.08 23952 Houston clay . . . . . . . . . . . . . . Milam . . . . . . 0-7 11.7 34.68 7-19 15.00 33.23 25967 Houston clay . . . . . . . . . . . . . . Navarro. . . . 0-7 1.72 35.78 7-19 1.49 16. 15 26085 Houston clay . . . . . . . . . . . . . . Navarro. . . . 0-7 3. 71 39.98 7-19 3.17 41.76 21073 Houston clay . . . . . . . . . . . . . . Rockwall. . . . 0-7 19. 7 34.54 7-19 33.5 43.14 12502 Houston black clay . . . . . . . . . Ellis . . . . . . . . . . . . . . 7.43 41.82 . . . . . . 8.41 44.53 12535 Houston black clay . . . . . . . . . Ellis . . . . . . . . . . . . . . 8.99 43.38 . . . . . . . . . . . . 43.67 ' 23956 Houston black clay . . . . . . . . . Milam . . . . . . 0-7 5.28 53.06 . . . . . . 6.95 53.28 26095 Houston black clay . . . . . . . . . Navarro . . . . 0-7 4.17 51.44 7-19 4.35 51.42" 25961 Houston black clay . . . . . . . . . Navarro. . . . 0-7 5.11 43.88 7-19 6.43 60.64 18546 Houston black clay . . . . . . . . . Red River. . . O—14 6.39 38.10 14-36 6.83 37.87 9313 Houston black clay . . . . . . . . . Lamar . . . . . . 0-6 0.26 36.62 . . . . . . . 2.00 36.56- 21069 Houston black clay . . . . . . . . . Rockwall. . . . 0-7 6.93 70. 66 7-19 7.94 . . . . . . 18226 Houston black clay . . . . . . . . . Tarrant. . . . . 0-10 5.69 47.12 10-36 17.83 39. 74 12570 Houston stony clay . . . . . . . . . Ellis} . . . . . . . . . . . . . 21.38 48.44 . . . . . . 23.08 44.13 25959 Irving clay . . . . . . . . . . . . . . . . Navarro. . . . 0-7 1.15 38.22 7-19 1.25 35.22 26075 Irving clay . . . . . . . . . . . . . . . . Navarro. . . . 0-7 1.76 36.86 7-19 1.82 37.97 20722 Katy fine sandy loam . . . . . . . Harris . . . . . . 0-7 0.35 3.48 7-19 0.08 2.32 21215 Kirvin fine sandy loam. . . . . Henderson. . 0-6 0.20 2.76 6-26 0.45 9.68- 24007 Kirvin fine sandy loam . . . . . Nacogdoches 0-7 0.59 6.03 7-19 0.54 7.05 23964 Kirvin fine sandy loam. . . . . Milam . . . . . . 0-7 0.53 10.88 7-19 1.05 26.89 18230 Kirvin fine sandy loam. . . . . Tarrant. . . .. 0-7 0.38 4.98 7-36 0.28 16.57‘ BASE EXCHANGE PROPERTIES TYPICAL TEXAS SOILS 11 Table 2. Total exchange capacity of typical Texas oils (Continued) Surface soil Subsoil Labo- ratory _ Total Total num- Basic- Ex- Basic- Ex- ber of Type Name County Depth 1W Change DEDUI ity change sur- inches per capac- inches per (japac- face cent ity cent ity soil M.E. M.E 21807 Kirvin gravelly fine sandy loam . . . . . . . . . . . . . . . . . . .. Henderson. . 0-10 0.33 4.15 10-36 0.33 10.03 24005 Kirvin clay loam . . . . . . . . . . Nacogdoches 0-7 1.15 16. 20 7-19 1.35 15.28 9347 Lake Charles clay loam. . . . . Harris . . . . . . 0-9 0.99 18.13 9-18 1.18 18.31 20720 Lake Charles clay 10am. . . . . Harris . . . . . . 0-7 0.80 18.20 7-19 1.33 21,28 20728 Lake Charles clay . . . . . . . . . . Harris . . . . . ; 0-7 1 .35 30.48 7-19 1.25 35.90 26823 Lake Charles clay . . . . . . . . . . Victoria . . . . . . . . . . . 2.52 45.23 7-19 2.39 22.46 25905 Laredo silt loam . . . . . . . . . . . Willacy. . . . . 0-7 15.30 14.98 7-19 12.5 11,45 21773 Laredo silty clay loam . . . . . . Cameron. . . . 0-15 8.09 23.00 15-30 23.14 16, 74 21775 Laredo clay loam . . . . . . . . . . Cameron. . . . 0-12 14.6 29.98 12-36 20.1 27. 88 21812 Leaf fine sandy loam . . . . . . . Henderson. . 0-10 0.23 5.41 10-36 0.80 24.38 25873 Lomalto fine sandy loam. . . . Willacy. . . . . 0-7 0.46 3.54 7-19 0.59 3,24 25865 Lomalto clay loam . . . . . . . . . Willacy. . . . . 0-7 2.07 13.40 7-19 3.52 16,88 21803 Lufkin fine sand . . . . . . . . . . . Henderson. . 0-6 0 1.66 6-36 0.20 , 75 12674 Lufkin fine sandy loam. . . . . Brazos . . . . . . 12-20 0.57 9.67 20- 0.27 5.81 29438 Lufkin fine sandy loam. . . . . Brazos . . . . . . 0-7 1.14 23.90 7-19 1.36 35. 74 29440 Lufkin fine sandy loam. . . . . Brazos . . . . . . 0-7 0.33 9.48 7-19 1.10 31.45 8836 Lufkin fine sandy loam. . . . . Franklin. . . . 0-11 0.20 8.95 11-23 0,55 21,33 21217 Lufkin fine sandy loam. . . . . Henderson. . 0-6 0.25 5.99 1-36 0.75 21.86 12520 Lufkin fine sandy loam. . . . . Washington. . . . . . . 0.94 19.44 . . . . . . 1.30 27.60 18540 Lufkin sandy clay loam. . . . . Red River. . 0-6 0.49 15. 78 6-36 0.98 20.06 12677 Lufkin clay loam . . . . . . . . . . . Brazos . . . . . . . . . . . . 1.31 27.35 6-18 1.29 29,42 31890 Miguel fine sandy loam. . . . . Frlo . . . . . . . . 0-7 0.36 8.28 7-19 1.00 19.43 20544 Miles fine sandy loam . . . . . . Coleman. . . . 0-15 0.35 7.21 15-36 1 . 10 27.67 12647 Miller fine sandy loam . . . . . . Brazos . . . . . . . . . . . . 0. 79 6. 44 . . . . . . 0. 74 11.12 29431 Miller fine sandy loam . . . . . . Brazos . . . . . . 0-7 0. 71 2.88 7-19 0. 30 2.15 12514 Miller fine sandy loam . . . . . . Washington. . . . . . . 6. 78 8.29 . . . . . . 8.40 22.57 22234 Miller silty clay loam. . . . . . Wichita. . . . . 0-7 4.38 16.76 7-19 6.89 21.34 12649 Miller clay . . . . . . . . . . . . . . . . Brazos . . . . . . . . . . . . 0.47 15.56 . . . . . . 1 .49 26.52 29429 Miller clay . . . . . . . . . . . . . . . . Brazos . . . . . . 0-7 7.62 20.30 7-19 5.57 23,10 23946 Miller clay . . . . . . . . . . . . . . . . Milarn . . . . . . 0-7 10. 9 35 . 96 7-19 1 1 . 8 36, 74 12516 Miller clay . . . . . . . . . . . . . . . . Washington. . . . . . . 10.3 28.89 . . . . . . 11.88 28,29 21224 Norfolk sand . . . . . . . . . . . . . . Henderson. . 0-6 0.10 .64 6-36 0.10 ,91 21783 Norfolk fine sand . . . . . . . . . . Cameron. . . . 0-10 0.10 1.73 10-36 0.09 1,04 12594 Norfolk fine sand . . . . . . . . . . Camp . . . . . . 0-6 0. 28 1.56 . . . . . . 0. 22 1,48 23962 Norfolk fine sand . . . . . . . . . . Milam . . . . . . 0-7 0. 23 1.24 7-19 0.18 1.06 9139 Norfolk sandy loam . . . . . . . . Tyler . . . . . . . 0-6 0.07 1.59 . . . . . . 0.05 2. 64 21785 Norfolk fine sandy loam. . . . Henderson. . 0-8 0.07 3.16 8-36 0.28 5.75 12592 Norfolk fine sandy loam. . . . Camp . . . . . . 0-12 0.27 2.63 12-24 0.23 3.03 21814 Norfolk fine sandy loam. . . . Henderson. . 0-12 0.13 2.91 12-36 0.29 8.08 25783 Nueces fine sand . . . . . . . . . . . Willacy. . . . . 0-7 0.04 2.80 7-19 0.05 2. 70 12676 Ochlockonee fine sandy loam Brazos . . . . . . . . . . . . 0.05 3. 70 . . . . . . . . . . . . . . . . . 21805 Ochlockonee very fine sandy loam . . . . . . . . . . . . . . . . . . . . Henderson. . 0-8 0.50 9.25 8-36 0. 65 10,55 22121 Orangeburg silt loam . . . . . . . Nacogdoches . . . . . . 0. 10 . . . . . . . . . . . . 0. 30 9.61 31914 Orelia fine sandy loam . . . . . . Frio . . . . . . . . 0-7 0.60 12.34 7-19 0. 74 14.24 31904 Orelia clay loam . . . . . . . . . . . Fno . . . . . . . . 0-7 . . . . . . . . . . . . 7-19 3.51 31.60 12645 Pledger clay . . . . . . . . . . . . . . . Brazos . . . . . . . . . . . . 3.01 46. 30 15-70 3.53 42.89 25869 Point Isabel fine sandy loam Wlllacy. . . . . 0-7 5.78 8. 73 7-19 6.24 10.87 25877 Point Isabel clay . . . . . . . . . .. Willacy. . . . . 0-7 13.6 17.04 7-19 17.5 19.48 31329 Potter clay loam . . . . . . . . . . . Potter . . . . . . 0-7 6. 33 18.65 7-19 26. 8 27.78 31321 Pullman silty clay loam. . . . . Potter . . . . . . 0-7 1.10 20.16 7-19 1,53 22.96 31323 Pullman silty clay loam. . . . Potter . . . . . . 0-7 1 .23 20.66 7-19 1.52 16.16 31325 Pullman silty clay loam. . . . . Potter . . . . . .' 0-7 0. 89 18.75 7-19 1.48 26.67 29317 Randall clay . . . . . . . . . . . . . . Midland. . . . 0-7 1 .43 30.08 7-19 1.35 28.02 31327 Randall clay . . . . . . . . . . . . . . . Potter . . . . . . 0-7 1.48 27.60 7-19 1.52 28.63 25891 Rayrnondville fine sandy clay loam . . . . . . . . . . . . . . . . . . .. Willacy. . . .. 0-7 2.51 19.12 7-19 4.83 19,35 25893 Rayrnondville clay loam. . . . Willacy. . . . . 0-7 4.53 23.82 7-19 2.40 21.14 29333 Reagan fine sandy loam. . . . . Midland. . . . 0-7 3.54 10.60 7-19 6.30 11.63 29335 Richfield fine sandy loam. . . Midland. . . . 0-7 0.62 9. 12 7-19 2.26 10.42 21777 Rio Grande silty clay loam. . Cameron. . . . 0-15 19.3 22.74 15-36 17. 7 13. 18 21219 Ruston fine sandy 10am. . . . . Henderson. . 0-8 0.10 1. 71 8-24 0.10 1 ,47 24009 Ruston fine sandy loam. . . . . Nacogdoches 0-7 0.40 1.88 7-19 0.33 5.52 7147 San Antonio silty clay loam Kendall. . . . . 0-10 4. 72 44.04 . . . . . . 8.66 38.26 18232 San Saba clay . . . . . . . . . . . . . Tarrant. . . . . 0-12 3.42 35.38 12-30 3.22 38.52 29311 Springer fine sand . . . . . . . . . . Midland. . . . 0-7 0.01 1.72 7-19 0.08 2.00 29315 Springer fine sandy loam. . . . Midland. . . . 0-7 0.41 5.48 7-19 0.47 9,65 29364 Springer fine sandy loam. . . . Midland. . . . 0-7 0.20 4.14 7-19 0.30 30.10 29449 Springer fine sandy loam. . . . Midland. . . . 0-7 0.45 5.20 7-19 0.46 6.80 31833 Spur fine sandy loam . . . . . . . Potter . . . . . . 0-7 1 .02 14. 20 7-19 5.19 19. 75 31806 Spur clay loam . . . . . . . . . . . . Potter . . . . . . 0-7 2.21 18.16 7-19 4.55 20.26 I2 BULLETIN NO. 520, TEXAS AGRICULTURAL EXPERIMENT STATION Table 2. Total exchange capacity of typical Texas soils (Continued) Surface soil Subsoil Labo- ratory Total Total num- Basic- Ex- Basic- Ex- ber of Type Name County Depth ity change Depth ity change sur- inches per capac- inches per capac- face cent ity cent ity soil M.E. M.E 12671 Susquehanna fine sandy loam Brazos . . . . . . . . . . 0. 37 8. 28 . . . . . . 0. 85 25 .51 12586 Susquehanna fine sandy loam Camp . . . . . . . . . . 0. 2S 4.04 . . . . . . 0.19 10.28 12596 Susquehanna fine sandy 10am Camp . . . . . . . . . . 0. 29 5 . 95 . . . . . . 0. 25 3 .08 12578 Susquehanna (now Leaf) fine sandy loam . . . . . . . . . . . Ellis . . . . . . . . . . .. 0.69 6.98 . . . . .. 0.65 10.90 18544 Susquehanna very fine sandy loam . . . . . . . . . . . . . . . Red River. . . 0-12 0.43 3. 70 12—-36 0. 78 24. 73 12598 Susquehanna gravelly loam. . Camp . . . . . . . . . . 0.51 2.32 . . . . . . 0. 25 1 .99 12588 Susquehanna stony loam. . . . Camp . . . . . . . . . . 0.19 4. 64 . . . . . . 0.20 7.46 12661 Tabor fine sandy loam . . . . . . Brazos . . . . . . . . . . 0.30 4.46 . . . . . . 0. 75 16.13 12641 Trinity fine sandy loam. . . . . Brazos . . . . . . 0-12 0. 74 6.58 12-24 0.89 18. 71 12643 Trinity clay . . . . . . . . . . . . . . . Brazos . . . . . . . . . . 2.33 39.56 . . . . . . 1.94 . . . . . . 12580 Trinity clay . . . . . . . . . . . . . . . llis . . . . . . . . . . . . 14.0 29.60 . . . . . . 13.3 27.60 21769 Trinity clay . . . . . . . . . . . . . . . Henderson. . 0-8 7.55 52. 72 8-36 6.09 51.88 23972 Trinity clay . . . . . . . . . . . . . . . Milam . . . . . . 0-7 22.4 47.29 7—19 21.4 43.42 25965 Trinity clay . . . . . . . . . . . . . . . Navarro . 0-7 5. 13 55.62 7—19 3.30 52 .45 26091 Trinity clay . . . . . . . . . . . . . . . Navarro . . . . 0-7 6.34 51.94 7—19 3. 76 50.00 26093 Trinity clay . . . . . . . . . . . . . . . Navarro . . . . 0—-7 7. 7S 53.82 7—19 7.21 51.52 21067 Trinity clay . . . . . . . . . . . . . . . Rockwall. . . . 0-7 25.9 45 .81 7—19 29. 4 43.98 12504 Trinity clay . . . . . . . . . . . . . . . Washington. . . . . 2.76 19.28 . . . . . . 3.56 25.28 22226 Vernon fine sandy loam. . . . . Wichita. . . . . 0-7 0.45 6.16 7—19 0.67 . . . . . . 25781 Victoria fine sandy loam. . . . Willacy. . . . . 0-7 1.38 15.88 7—19 1 .28 15.67 17698 Victoria fine sandy loam. . . . Brooks . . . . . . . .. 0.21 7.24 . . . . . . 4.80 7.04 25903 Victoria fine sandy loam. . . . Willacy. . . . . 0-7 0.96 4. 72 7—19 1.01 16.51 25895 Victoria fine sandy clay loam Willacy. . . . . 0-7 1.71 21.14 7—19 1.28 23.18 25885 Victoria fine sandy clay loam Willacy. . . . . 0~7 0. 71 14.37 7—19 0.94 20.25 31905 Victoria clay loam . . . . . . . . . Frio . . . . . . . . 0-7 1.70 19.22 . . . . . . . . . . . . 23.34 25887 Victoria clay loam . . . . . . . .. Willacy. . . . . 0-7 1.55 19.31 7—19 2.11 19.14 9298 Victoria clay . . . . . . . . . . . . Willacy. . . . . 0-12 7.22 72.2 . . . . . . . . . . . . . . . . . . 25881 Victoria clay . . . . . . . . . . . . . . Willacy. . . . . 0-7 1.95 24.27 7—19 2.82 24. 29 31888 Webb fine sandy loam . . . . . . Frio . . . . . . . . 0-7 0.26 8.58 7—19 0.95 18.98 25883 Willacy fine sandy loam. . . . . Willacy. . . . . 0-7 1.06 11.61 7—19 0.59 10.22 25785 Willacy fine sandy loam. . . . . Willacy. . . . . 0-7 0.93 12.92 7—19 0. 81 16.07 12679 Wilson fine sandy loam. . . . . Brazos . . . . . . . . . . 0.53 9.17 10-20 0.65 15 .31 25963 Wilson fine sandy loam. . . . . Navarro. . . . 0-7 0.23 7.52 7—19 0.36 9.66 26097 Wilson fine sandy loam. . . . . Navarro . . . . 0-7 0.31 6.40 7—19 0.34 9.04 29525 Wilson very fine sandy loam. Van Zandt. . . . . . 0.44 14.01 . . . . . . 0.90 18.09 12533 Wilson loam . . . . . . . . . . . . . . . Ellis . . . . . . . . . . . . 14.6 37.24 . . . . . . 9.95 35.89 12659 Wilson clay loam . . . . . . . . . . Brazos . . . . . . . . . . 0.90 23.43 . . . . . . 0.90 22.40 23958 Wilson clay loam . . . . . . . . . . Milam . . . . . . 0-7 1.13 19.20 7—19 1 . 18 23.54 25971 Wilson clay loam . . . . . . . . . . Navarro 0-7 0. 76 18.00 7—19 1.31 29.70 21071 Wilson clay loam . . . . . . . . . . Rockwall 0-7 1.30 26.38 7—19 1.60 38.80 12639 Wilson clay . . . . . . . . . . . . . . . Brazos . . . . . . . . . . 0.34 28.97 12-24 1.39 30.45 29436 Wilson clay . . . . . . . . . . . . . . . Brazos . . . . . . 0-7 1 . 16 20.40 7—19 1 .01 26.56 29434 Wilson clay . . . . . . . . . . . . . . . Brazos . . . . . . 0-7 1.31 27.16 7—19 1.41 29.03 26115 Wilson clay . . . . . . . . . . . . . . . Brazos . . . . . . 0-7 1.20 26.06 7—19 1.05 22.92 18542 Wilson clay . . . . . . . . . . . . . . . Red River 0—-10 1.85 46. 76 10-36 7.52 48.18 18548 Wilson clay . . . . . . . . . . . . . . . Red River 0-12 1.84 48.07 . . . . . . 1.23 49 28 21077 Wilson clay . . . . . . . . . . . . . . . Rockwall 0‘-7 2.27 53.66 7—19 1.31 . . . . . . 18205 Windthorst fine sandy loam. Erath . . . . . . 0-8 0.17 6.40 8-16 0_.88 6.22 18208 Windthorst fine sandy loam. Erath . . . . . . 0-8 0.35 2. 73 8-36 0.88 20.32 31802 Yahola fine sandy loam. . . . . Potter . . . . . . 0-7 4.50 10.90 7—19 7.04 11.85 12651 Yahola silt loam . . . . . . . . . . . Brazos . . . . . . . . . . 10.94 16.08 . . . . . . 8.40 11 .30 name, baslcity, and total exchange capacity of the surface and subsoils are given in Table 2. (M.E.) per 100 grams of soil. calcium oxide. The results are expressed as milligram equivalents One M.E. in 100 grams is equivalent to 500 parts per million of calcium carbonate, or 280 parts per million of The soils are arranged in alphabetical order according to the name of the series, and the list is believed to be representative of the various kinds of soil found in Texas. BASE EXCHANGE PROPERTIES TYPICAL TEXAS SOILS 13 The exchange capacities of the soils studied varied from 0.69 M.E. in dune sand to 70.7 M.E. in a sample of Houston black clay. In general, the sands had a low exchange capacity, the sandy loams a little higher one, the loams a still higher, and the clays the highest. The exchange complex is associated with the clay particles, so that as a rule the greater the quantity of clay particles, the higher the exchange capacity. Subsoils as a general rule had higher exchange capacities than surface soils, but this was not always the case. Some examples to the contrary to be found in Table 2 are Pullman silty clay loam, No. 31323; Abilene clay loam, No. 20196; Bastrop sand; Bell clay, No. 26079; Caddo fine sandy loam, No. 12590; Crockett fine sandy loam, N0. 21771; and others. Variations in Exchange Capacity Between Different Samples of the Same Type It is a matter of some significance to know whether there is as much variation between the exchange capacities of samples of the same soil type, taken in different localities, as there is between samples of different soil series. The variation in exchange capacity for surface soils and subsoils of samples of the same type taken from different localities is given in Table 3. Six of the types are named as fine sandy loams and four as clays. The surface soils of the Norfolk fine sandy loam had the lowest average exchange capacity and also showed the least variation. Three of the series of fine sandy loams averaged very nearly the same in exchange capacity. The difference between the highest and the average was about 5 M.E., about equal to the average exchange capacity. The Crockett fine sandy loam and the Lufkin fine sandy loam had high exchange capacities and the difierence in M.E. between the average and the highest exchange capacity was not large, although the percentage difference was about the same as for the other soils. The Wilson clay had a lower average exchange capacity than the other three clays and was also more variable. The maximum deviation of the exchange capacity of surface soils of the last three clays was about 9 to 11 M.E. from the average, while that of the Wilson clay was about 21 M.E. from the average. The subsoils of the fine sandy loams had higher average exchange capacities than the surface soils but varied approximately to the same extent. The subsoils of the clays averaged about the same as the surface soils and varied approximately to the same extent. The exchange capacities of soils of the same physical character appar- ently resemble one another closely, even though the soils are of different series; variations in samples of the same series having the same physical character are generally as large as between samples of different series. It would require averages of many more samples than were here used to ascertain if the average exchange capacity can be used as a definite characteristic of a particular series, but it is certainly not an outstanding characteristic. 14 BULLETIN NO. 520, TEXAS AGRICULTURAL EXPERIMENT STATION Table 3. Variations in total exchange capacity within soil types Total exchange capacity (M.E.) Num- Type ' befr Surface soils Subsoils Q * . sam- Low- High- Aver-I Low- High- "Aver- ples est est age Range est est age Range Norfolk fine sandy loam . . . . . .. 4 2 63 3 16 2.88 » 53 2.64 8.08 4.89 5.44 Kirvin fine sandy loam . . . . . . . 5 2 76 10 88 5.76 8.12 7.05 26.89 14.04 19.84 Susquehanna fine sandy loam. . 4 4.04 8 28 6.31 4.24 3.08 25 .51 12.44 22.43 Crockett fine sandy 10am . . . . . . 5 4.92 15 10 9. 25 10 18 14. 69 24. 73 16.99 10.04 Lufkin fine sandy loam . . . . . . . 6 5.99 23.90 12.90 17.91 5.81 31.45 23.97 25.64 Wilson clay . . . . . . . . . . . . . . . . . 6 20.40 53.66 32.90 33.26 22.92 49.28 34.40 26.36 Houston clay . . . . . . . . . . . . . . . . 5 34.54 47.79 38.55 13.25 16.15 50.084. 36.87 33.93 Houston black clay . . . . . . . . . .. 8 36 62 53 06 44 51 16 44 36 56 60 64 49 59‘ 24 08 Trinity clay . . . . . . . . . . . . . . . .. 8 19 28 55 62 44 51 36 34 25 28 52 45 43 27 27 17 Average of fine sandy loams 7.42 8.18 . . . . . . . . . . . . 14.46 16.68 Average of clays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40. 12 24.82 . . . . . . . . . . . . 41.03 27.88 Relation Between Exchange Capacity and Soil Texture The exchange capacity, as pointed out in the previous section, is more closely related to the texture than to the soil series. The classification of 187 samples of surface soil according to texture indicated by the name of the type is given in Table 4. Practically all the samples named as sand had an exchange capacity less than 5 M.E. The exchange capacity of fine sandy loams varied from about 2 to 20 M.E., but most of the samples had an exchange capacity less than 10. Only eleven of the samples examined classed as loams and silt loams; they were quite variable, the exchange capacity ranging from less than 5_ to nearly 45 M.E. _. Table 4. Relation between total exchange capacity and soil texture Fine Loams Group by exchange Sands sandy and silt Clay Clays Total capacity Number loams loams loams Number Number Number Number Number 0-S.00 . . . . . . . . . . . . . . . . . .. 8 27 2 0 0 37 5.01-10.00 . . . . . . . . . . . . . .. 0 35 2 0 1 38 10.01—15 00 . . . . . . . . . . . . . . 0 13 2 3 0 18 15.01-20.00 . . . . . . . . . . . . .. 0 4 1 14 3 22 20.01-25.00 . . . . . . . . . . . . .. 0 2 1 7 4 14 25.01-30.00 . . . . . . . . . . . . .. 0 0 1 7 6 14 30.01-35.03 . . . . . . . . . . . . .. 0 0 0 1 8 9 35.01-40.00 . . . . . . . . . . . . . . 0 0 1 0 10 11 40.01-45.00 . . . . . . . . . . . . .. 0 0 1 1 6 8 45.01 + . . . . . . . . . . . . . . . . . . 0 O 0 0 16 16 Total . . . . . . . . . . . . . . . . . 8 81 11 33 54 187 The 33 clay loams had exchange capacities varying from 1O to about 45 M.E., but most of them had an exchange capacity of 15 to 3O M.E. The soils classed as clay were also quite variable, with exchange capacities ranging from 5 to 70 M.-E., but most of them had exchange capacities exceeding 30 M.E. BASE EXCHANGE PROPERTIES TYPICAL TEXAS SOILS 15 These differences between soils of difierent textures are also brought out in Table 3 and in Table 5. In Table 5 the average exchange capacities for different series and different textures are given. The average exchange capacities of the fine sandy loams varied from 5.5 to 12.9; of the clay loams, from 16.2 to 30.2; and of the clays, from 17.0 to 44.5 M.E. Table 5. Total exchange capacity of surface soils of different series Fine sandy loams Clay loams Clays Series M. E. M. E. M. E. Frio . . . . . . . . . . . . . . . . . . . . . .. 5.50 25.30 31 46 Kirvin . . . . . . . . . . . . . . . . . . . .. 5.76 16.20 . . . . . . . . . . . . . . . . . . .. Miller . . . . . . . . . . . . . . . . . . . . . . 5.87 . . . . . . . . . . . . . . . . . . . . 25 18 Trinity . . . . . . . . . . . . . . . . . . . . . 6.58 . . . . . . . . . . . . . . . . . . . . 44 51 Wilson . . . . . . . . . . . . . . . . . . . . . 7. 70 21.75 32 9O Point Isabel . . . . . . . . . . . . . . . . 8. 73 . . . . . . . . . . . . . . . . . . . . 17 04 Crockett . . . . . . . . . . . . . . . . . . . 9.25 30.20 . . . . . . . . . . . . . . . . . . . . Victoria . . . . . . . . . . . . . . . . . . .. 11.56 19.22 24 27 Lufkin . . . . . . . . . . . . . . . . . . . .. 12.90 27.35 . . . . . . . . . . . . . . . . . . .. Average . . . . . . . . . . . . . . . . . . 8.21 23.34 29.23 Relation to Location in the State The exchange capacity of a number of soils averaged by textures as indicated by the name of the type for different soil regions is given in Table 6. There are more regular difierences between the different Table 6. Average total exchange capacity of surface soils of different soil regions Fine sandy loams Clay loams Clays Soil Region M. E. M. E. M. E. Gulf Coast Prairie . . . . . . . . . . . 3.45 18.18 37.86 East Texas Timber . . . . . . . . . . 5.38 27.35 . . . . . . . . . . . . . . . . . . . . Blackland . . . . . . . . . . . . . . . . . . 7. 84 ‘ 23.88 38. 39 Rio Grande Plains . . . . . . . . . . . 8.16 21.29 24.26 ‘ Rolling and High Plains . . . . . . 9.14 21.26 28.84 Average . . . . . . . . . . . . . . . . . w 6. 79 22.39 32.34 regions with the fine sandy loams than between those with the clay loams or clays. The groups are arranged in order according to the average exchange capacities of the fine sandy loams. This arrangement is found to be approximately related to the rainfall, since the Gulf Coast Prairie area receives the highest rainfalLthe East Texas Timber Country comes second, the Blackland Prairie ranks third, the Rio Grande Plain stands fourth, and the Rolling Plains and High Plains have the lowest rainfall. The sandy loam soils of the region with the highest rainfall have the lowest average base exchange capacity; those of the region with the lowest rainfall have the highest base exchange capacity. The base exchange complex is probably formed by weathering of the original parent material, and is decomposed and reduced in quantity by subsequent 16 BULLETIN NO. 520, TEXAS AGRICULTURAL EXPERIMENT STATION weathering. The relation of the exchange capacity to the rainfall may be due to the exchange complex either having been decomposed to a greater extent in the regions of high rainfall than in regions of low rain- fall, or having been washed down into the subsoil to a greater extent. The variations in exchange capacity may also be due to the considerable differences in the material from which the soils 0f these regions were originally derived. The soils of the Blackland Prairie and of the Rio Grande Plains, Rolling Plains, and High Plains were derived from more calcareous material than were those of the Gulf Coast Prairie and the East Texas Timber Country, and they still retain many properties derived from the original parent material. The difierences in exchange capacities between the cl-ay loams and clays from the various regions were irregular and less marked than those between the fine sandy loams. The fine sandy loams, of course, are more porous and are therefore more susceptible to the weathering action of both water and air. RELATIVE PROPORTION OF BASES HELD BY THE BASE-EXCHANGE COMPLEX The bases in the base-exchange complex of neutral soils are usually composed chiefly of calcium, though some magnesium, sodium, and potassium are also present, and sometimes small amounts of hydrogen. In an acid soil, the base exchange complex contains larger relative amounts of exchangeable hydrogen than that in a neutral soil. In a solonetz soil, the base-exchange complex contains a large proportion of sodium, which makes the soil particles run together, causes the soil to- be lumpy, and prevents the free entrance of air and Water (1, 2, 3, 14). In order to ascertain the character of the bases held by the base- exchange complex in Texas soils, analyses were made of a number of rep- resentative soils. In the noncalcareous soils, hydrogen was determined by electrometric titration of the ammonium acetate leachate with 0.1 N ammonium hydroxide. The other bases removed by ammonium acetate were determined by essentially the same method outlined by Schollen- berger and Dreibelbis (21). The soil was leached with ammonium acetate solution, and the leachate was freed of ammonium acetate, organic mat- ter, iron, and manganese. Calcium Was determined in the filtrate by precipitation as the oxalate and conversion to the sulfate, which was weighed. Magnesium was precipitated with ammonium phosphate and ignited and weighed as the pyrophosphate. Potassium and sodium were determined in another aliquot after removing the ammonium acetate by precipitation of the other bases with ammonium hydroxide, carbonate, and oxalate, and after weighing the ignited combined chlorides of po- tassium and sodium secured from the filtrate, precipitating the potassium as the chloroplatinate, and estimating the sodium by difference. An alcoholic solution of potassium chloride was used for estimating calcium and magnesium in calcareous soils, since calcium carbonate is highly soluble in ammonium acetate solution. The method was essen- tially that of Chapman and Kelley (5, 6). cent ethyl alcohol. BASE EXCHANGE PROPERTIES TYPICAL TEXAS SOILS 17 The soil was leached with two successive portions of a 0.2 N solution of potassium chloride in 63 per second portions was considered to be the exchangeable calcium. sum of the exchangeable calcium, potassium, and sodium (in M. E.) was subtracted from the total M. E. exchange capacity, and the difference was considered to be M. E. of magnesium. The difference between the calcium in the first and The Table 7. Exchangeable bases, in M. E., in some Texas soils Total Labo- Basic- Ex- Sum Mag- ratory ity change of Ca1- nes- Potas- So- Hy- Num- Soil type per capac- bases cium ium sium dium dro- ber cent ity M.E M.E. M.E. M.E. M.E. gen 23962 Norfolk fine sand . . . . . . . . . . . . . . 24 1.24 1.66 .93 . 32 . 07 . 17 . 17 24009 Ruston fine sandy loam. . . . ; . .. .40 1 .88 2.34 1.22 .39 .07 . 13 .53 12598 Susquhanna gravelly loam . . . . . . .20 2.32 3.77 1.85 .45 . 17 . 18 1.12 29431 Miller fine sandy loam . . . . . . . . . 1 . 21 2 . 8,8 4.98 3.56 . 60 . 16 . 19 .47 21785 Norfolk fine sandy loam . . . . . . . .07 3.16 3.24 1.48 .36 . 15 .26 1 .25 20724 Hockley fine sandy loam . . . . . . . .23 4.13 6.40 5.28 .65 . 19 . 10 . 18 12590 Caddo fine sandy loam . . . . . . . . .45 5.48 10.38 8.28 1.15 .36 . 17 .42 24007 Kirvin fine sandy loam . . . . . . . . .59 6.03 6.24 4.30 .94 .29 .27 .44 22226 Vernon very fine sandy loam. . . .45 6.16 7.33 5.40 1.43 .33 .17 0 31896 Brennan fine sandy loam . . . . . . . .16 6.31 7.68 4.36 1 . 14 .49 .18 1 .51 26097 Wilson fine sandy loam . . . . . . . . .31 6.40 8.18 4. 72 .98 .21 .28 1.99 25969 Crockett fine sandy 10am . . . . . . .30 7.12 6.88 4.15 1.37 .45 .32 .59 31880 Duval fine sandy loam . . . . . . . . . .23 7.31 8.14 4.88 1.17 .29 . 15 1.65 12671 Susquehanna fine sandy loam. . . .69 8.28 12.06 5.85 2.97 .31 . 29 2.64 31890 Miguel fine sandy loam . . . . . . . . . . . . . . 8. 28 11.27 5.68 2.03 .71 .27 2.58 31331 Amarillo fine sandy loam . . . . . . . .52 8.33 '8.33 5.66 '2.05 .43 . 19 0 25869 Point Isabel fine sandy loam. . . . 5 . 78 8.46 '9.08 7.50 '0 .54 1.04 0 31888 Webb fine sandy loam . . . . . . . . . .26 8.58 10.32 5.49 1 .82 .37 .87 2.27 21805 Ochlockonee very fine sandy loam . . . . . . . . . . . . . . . . . . . . . .. .50 9.25 11.53 6.86 2.53 .31 .24 1.59 29440 Lufkin fine sandy loam . . . . . . . . .33 9.48 11 . 15 6. 83 2. 13 .54 .16 1 .49 22122 Orangeburg silt loam. . -30 9.61 10.60 t ,5__.9& - 2-15 _ J54 - 4-52-. 31804 Fritch fine sandy loam. . . . . . .. .75 11 .56 15.33 10.6 2.55 . 5 . 17 1 .23 25883 Willacy fine sandy loam . . . . . . . 1.06 11 .61 '11 .61 7. 80 '2.84 .69 .28 0 25865 Lomalto clay loam . . . . . . . . . . .. 2.07 13.40 '18.93 3.9 '0 .59 14.44 0 25781 Victoria fine sandy loam . . . . . . . 1.38 15.88 '15.88 11.10 '3.20 .78 .80 0 25971 Wilson clay loam. . . . . . . . . . . . . . 76 18.00 15.45 6.28 8.10 .20 .46 .41 25891 Raymondville clay loam . . . . . . . 2.51 19.12 '19. 12 13.60 '2.39 1.96 1 . 17 0 21779 Victoria clay loam . . . . . . . . . . . . 1 .64 19.60 '22.70 19.60 '0 1.69 1.41 0 29317 Randall clay . . . . . . . . . . . . . . . . . 1 .43 30.08 '30.08 19.80 '7.47 .81 1.00 0 26099 Crockett clay loam . . . . . . . . . . . . 1 .42 31.54 '31 .54 25.00 '4.98 .62 .94 0 25967 Houston clay . . . . . . . . . . . . . . . . . 1.72 35.78 '35 78 28. 60 '4.92 . 79_ 1.47 0 23967 Miller clay . . . . . . . . . . . . . . . . . . . 9.46 35 .96 '35 96 29. 80 '2 . 94 .96 2 .26 0 26075 Irving clay . . . . . . . . . . . . . . . . . . . 1.76 36.86 '36 86 31.20 '2.69 .25 1.28 0 12643 Trinity clay . . . . . . . . . . . . . . . . . . 2.33 39.56 '39 56 30. 60 '7.32 . 76 .88 0 25961 Houston black clay . . . . . . . . . . . . 5 . 11 43 . 88 '43 . 88 38.60 '3 . 92 . 78 58 0 'Caculated Data secured by the procedures outlined on 35 representative soil types are presented in Tables 7 and 8. calcareous soils, in which magnesium was determined and not calculated, the sum of the bases in M. E. was greater than the M. E. of total ex- change capacity. greater than the quantity which was taken. up by the soil. In practically all of the non- That is, the quantity of bases going into solution was This means that the ammonium acetate solution removed bases from soil materials in addition to replacing those in the base-exchange complex. It is probable that a similar error due to solubility also occurs in the case of the soils for which the magnesium was calculated, and that the value given for magnesium in these soils is correspondingly low. 18 BULLETIN NO. 520, TEXAS AGRICULTURAL EXPERIMENT STATION Table 8. Individual exchangeable bases (M.E.) in percentage of the total bases ' Total Labo- Ex- Mag- Hy- ratory ' change Cal- nes- Po tas- So- dro- Num- Soil type capac- cium ium sium dium gen ber it per per per per per M .E. cent cent cent cent cent 1-5 23962 Norfolk fine sand . . . . . . . . . . . . . . . . . . . 1 24009 Ruston fine sandy 10am . . . . . . . . . . . . . . 1 12598 Susquehanna gravelly loam . . . . . . . . . . . 2 29431 Miller fine sandy loam . . . . . . . . . . . . . . . 2 21785 Norfolk fine sandy 10am . . . . . . . . . . . . . 3 20724 Hockley fine sandy loam . . . . . . . . . . . . . 4 12590 Caddo fine sandy 10am . . . . . . . . . . . . . . 5 24007 Kirvin fine sandy loam . . . . . . . . . . . . . . 6 22226 Vernon very fine sandy loam . . . . . . . . . 6 31896 Brennan fine sandy 10am . . . . . . . . . . . . . 6. 26097 Wilson fine sandy loam . . . . . . . . . . . . . . 6.40 73. 25969 Crockett fine sandy loam . . . . . . . . . . . . 7 31880 Duval fine sandy loam . . . . . . . . . . . . . . . 7 12671 Susquehanna fine sandy loam . . . . . . . . . 8 31890 Miguel fine sandy loam . . . . . . . . . . . . . . 8 31331 Amarillo fine sandy loam . . . . . . . . . . . . . 8 25869 Point Isabel fine sandy loam . . . . . . . . . 8 31888 Webb fine sandy loam . . . . . . . . . . . . . . . 8 21805 Ochlockonee very fine sandy loam. . . . . 9 29440 Lufkin fine sandy 10am . . . . . . . . . . . . . . 9 9 F"\—5 P‘