Plant Uptake and Chemical Extractions for Evaluating Potassium Release Characteristics of Soils
1969
Conyers, E. S. | McLean, E. O.
Five soils were treated with K at rates of 269, 134, and 0 kg/ha and were diluted 6:4, 3:7, and 1:9 with sand. Potassium was extracted from samples of the soils and soil-sand mixtures by various methods. The treated soils were then sequentially cropped in a growth chamber to German millet (Setaria italica stramineofructa) (one cutting) and alfalfa (Medicago sativa) (four cuttings). After cropping, K was again extracted from samples of the soils and mixtures. The soils differed greatly in amounts of K released to the plants and to the various extracting solutions. Amounts of K removed by NH₄OAc, HNO₃, HCl, and NaBPh₄ from soils prior to cropping generally correlated better with amounts of K uptake than did amounts of K removed by other extractants. When all soils, K additions, and soil dilutions were combined, energy of exchange (ΔF) values were poorly correlated with K uptake because of greater than proportional release of K in soil-sand mixtures. Both the plants and chemical extractants removed more K from soil-sand mixtures than that calculated on the basis of proportions of the soil in the mixtures. Cropping considerably reduced the amounts of exchangeable and boiling HNO₃ releasable K and caused ΔF values to become more negative.
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