Availability of Nonexchangeable Soil Potassium to Plants as Affected by Added Potassium and Ammonium
1961
Welch, L. F. | Scott, A. D.
Undried Marshall and Clarion surface and subsoil samples were cropped in the greenhouse (short-term cropping) to determine the effect of NH₄ and K additions on the availability of nonexchangeable soil K to corn plants. When 0, 10, 25, 50 and 100 mg. of NH₄ was added to 100 g. of soil, the corn absorbed 21.8, 16.4, 11.6, 4.96 and 0.12 mg. of nonexchangeable K from the Marshall surface soil and 5.19, 4.74, 3.55, 0.91 and −1.44 mg. from the Clarion surface soil. This reduction in the uptake of non-exchangeable K by plants was due to the blocking effect of NH₄ on the release of K, and was not an effect of NH₄ on the absorption of available K. Similar results were obtained with the Marshall subsoil. The Clarion subsoil, however, did not release K even in the absence of added NH₄. K additions also reduced the release of nonexchangeable soil K. When NH₄ and K were both added, the order of addition proved to be important because NH₄ also blocked the release of added K that was fixed by the soil.
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