B-1090 December 1969 Fixation and Supply By Soilr Wit]? Mixed Clay Zllineralr i UNIVERSITY a1 Experiment Station Acting Director, College Station, Texas Summary‘ Studies were made on three agriculturally important soils of South Texas and Northern Mexico to determine their potassium (K)-supplying power, the influence of cropping on fixation of K and the response of grain sorghum to fertilizer K. Under greenhouse conditions, Laredo si l supplied 3.29 me K/me of exchangeable K Potassium Fixation and Supply By Soils Wit/o [Ilixed Clay THE POTASSIUM STATUS OF sous of the Midwest, North- east and Southeast United States has been investigated. Little work has been done, however, on soils of the Southwest. Soils of the West and Southwest are generally quite high in K, and responses are not usually obtained from the addition of K fertilizers. Since the Southwest is rapidly becoming one of the most important agricultural areas of the U.S., more knowledge concerning the K supply- ing power of these soils is desirable. Previous work by Hipp and Thomas (3) pointed out the importance of clay type in the assessment of K avail- ability in certain soils of Texas. Fraps and Fudge (2), investigating the chemical properties of some Texas soils, found many of them to be quite high in total and “active” K. Laws (5) found that no crop response to applied K was obtained in several soils of Central Texas. To obtain additional information regarding the K status of soils of the Southwest, greenhouse and laboratory experiments were conducted on three soils common to South Texas and Northern Mexico. MATERIALS AND METHODS Soil was collected from the surface 15 cm of three soils that are of agricultural importance in South Texas and Northern Mexico. Description of the chemical proper- ties of the soils is given in Table 1. The soils were from cropped areas which had not received K fertilizers recently. The soils were allowed to air dry. Then they were crushed to pass through a 2mm screen. Four plastic pots were filled with 3000 g of each of the three soils. A sample to the plants while Cameron clay supplied me/ me of exchangeable K. The capacity f‘ soils to fix K increased with increasing rel by cropping. The increase in fixation was ‘ be partially due to the removal of fixed K byl Grain sorghum growth on any of the so increased by the additionofy K fertilizer after *- of each soil was retained for K determinatio = was extracted from the air-dry soils with at monium acetate at pH 7.0 and K deter ' with a Techtron Atomic Absorption Spe f Each of the pots was cropped with grain 7 nine successive crops. varied from five to 20, but each pot had the of plants for any one crop period. The plants The number of pl Bill f with distilled water throughout the experiment; were grown from 3O to 52 days, but plants of I all pots were allowed to grow the same length ~- crop was harvested at the end of the growth ~- ting the entire plant at soil level. The plants distilled water and dried at 70° C. Then the, were recorded. The whole plants were dry lined by Chapman and Pratt (1), and K dd made by atomic absorption. _ determine the me K / 100 grams removed fr. by each crop. After each crop was harvested, I each pot was remixed, and a 100-g sample a removed for exchangeable K determinatio l I were fertilized with Nitrogen. (N), ~~.__A Iron (Fe) and Zinc (Zn) as required after Q period, but none of the pots received K fe ' end of the ninth crop, K was added (as ‘a replications of each soil at the rate of 0.1.1; then one more crop of grain sorghum was ‘I termine whether a response to applied K co after removal of K by nine crops of sorgh n- *Assistant professor, Texas A&M University Agri ~ and Extension Center at Weslaco. Calculations if TABLE 1. CHEMICAL PROPERTIES OF THE SOILS USED IN THE STUDY Safurafed "Ia/loo 9mm Predominant Soil paste pH K Mg Na Ca CEC clay mineral (approximate) Cameron clay 8.2 2.1 5.3 1.2 29.4 38 Montmorillonite Laredo silt Ioam 8.2 0.7 4.2 1.3 15.8 22 Mica Willclcy fine sandy Ioam 7.9 1.2 3.1 0.7 11.0 16 Mica §= 1348-0700:: .. r= -0.954 Q w om 0 l|.||6"Q.555X g f""0.893 O ° . O r} - O 860 0.2 0.4 0.6 0.8 l.0 l.2 f applied K was determined for each soil The 100-g sample removed after each if used for this purpose, and the fixation u ed as described by jackson (4), except l ere subjected to six cycles of wetting and ULTS AND DISCUSSION hip between K removal _by the plants eK isushown in Figure _1._ Theslope of i equation can be regarded as an indication supplying power for that soil. The slopes soils are different in their capacity to i ~ ing plants. Laredo has a relatively flat *1 indicating that for each milliequivalent " Kr extractable with ammonium acetate, ome available to plants. Similarly, Wil- ' 1.81 me K/me of exchangeable K. The i, b in Table 1 is not necessarily an indication "g rate of these soils. The soil with pre- tmorillonitic clay (Cameron) has a much I ‘—0.700) indicating that non-exchangeable iFexchangeabIe at a less rapid rate than in L. 1 primarily micaceous clay minerals. All the expected to have smaller b values under because of the numerous wetting and drying “- between yearly cropping periods. Also, L would possibly decrease the b value. lei K/me exchangeable K. o Cameron 0 Willocy A Laredo v °' ' e ‘n J o o Figure 1. Relationship be- . v o J tylveen Ib<1 removed ancll ex- A AA ' c angea e K on 3 SO15. ; ~ ' 3 ‘. A y e . _“ J ~\ I i; §'0.727'0.304X ‘ 1.4 I.6 Me K/IOO g removed by plants The data in Figure 2 indicate that the capacity of all three soils to fix K increased with cropping. The constants for K fixation and release were similar on Laredo si l ie.; exchangeable K decreased at a rate of 0.504 me/me re- moved, and fixation increased at the rate of 0.336 me/me removed. Exchangeable K decreased in Cameron soil at 0.700 me / me K removed, but the fixation due to the nine cropping periods was only 0.240 me fixed / me removed. These data suggest that a considerable amount of fixed K was utilized by plants grown on Laredo si 1, ‘but as small amount of fixed K was utilized by plants grown on Cameron clay. If the sequence of weathering on these soils is Illite—>Montmorillonite, these data suggest that the use of fixed K by plants proceeds at a faster rate than the decrease in K fixing capacity brought about by the weather- ing process. TABLE 2. POTASSIUM CONTENT OF GRAIN SORGHUM PLANTS GROWN ON THREE TEXAS SOILS i Crop Percent potassium in whole plant number Cameron Laredo Willacy 1 3.46 2.91 3.28 2 2.52 2.28 2.55 3 2.45 2.10 2.17 4 2.31 1.98 1.88 5 2.07 2.00 1.71 o 2.15 1.98 1.85 7 2.26 2.06 2.13 8 2.35 2.13 2.08 9 2.25 1.88 1.95 0 Cameron 0 Willa cy L4 ' A Laredo |.2 . §=oe3 s-aasex a E I0- g 0.8- 9=o.1|s+o.24ox g o r= o. e64 v x 0.6- 4 Q _ i re . nfluence f K5 2 0'4‘ Q Y: o’ ferigiiuvalzon tIhe K fixixfg ca- I ' f: o, 6 pacity of 3 soils. I 0.2- Me K/IOQQ removed by plants The K content of grain sorghum plants grown on each soil is indicated in Table 2. There was a sharp decrease in g K content of the plants after the first crop of sorghum, but then the decline was gradual until the sixth crop when an increase occurred in K content of plants grown on all the soils. The fluctuations in K con- tent of the plants were attributed to the unequal age and number of plants per pot at each cutting and seasonal temperature and light fluctuations in the greenhouse during the experimental period. The influence of K fertilizer on growth of grain sorghum in each of the soils after nine crops is shown in Table 3. From these data it can be concluded that the level of exchangeable K is high enough after nine succes- sive crops of sorghum to preclude an increase in plant growth from added K. ' These studies indicate that the soils of South Texas and Northern Mexico with a mixed clay mineralogy have TABLE 3. INFLUENCE OF POTASSIUM FERTILIZER ON GROWTH OF GRAIN SORGHUM AFTER NINE SUCCESSIVE CROPS Grams per plant 0 potassium 0.1 me K/IOO grams Cameron 2.50 2.44 WiIIacy 2.59 2.50 Laredo 2.19 2.25 0.2 0.4 0.6 as 1.0 |.2 1.4 l.6 a high capacity for supplying K to plants, and a’ to applied K on the soils described as well as V’ soils of the area is not likely for several years. studies indicate that the fixing capacity of all __ is increased by cropping, but the increase is not i, for all the soils. The increase in fixing attributed to removal of fixed K by plants. LITERATURE CITED 1. Chapman, H. D. and P. F. Pratt. 1961. _ analysis for soils, plants and waters. Univ; Div. of Agri. Sci. 2. Fraps, G. S. and I. F. Fudge. 1937. Ch -l position of soils of Texas. Tex. Agri. Exp, 549. a 3. Hipp, B. W. and G. W. Thomas. 1967. v of soil clay type on potassium availability. . Exp. Sta. M.P. 829. ' 4. Jackson, M. L. 1958. Soil chemical analysg Hall. Englewood Cliffs, N. I. L 5. Laws, W. D. 1962. Potassium status of -I soils as related to crop yield and plant -Y_ Soil Sci. 94:230-234. ‘ *3.