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Availability of Nonexchangeable Soil Potassium to Plants as Affected by Added Potassium and Ammonium¹

ABSTRACT

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.

¹ Journal Paper No. J-3899 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Project No. 1234. Presented before Div. II, Soil Science Society of America, Lafayette, Ind., Aug. 5, 1958. This work was supported in part by the American Potash Institute.

² Former Graduate Assistant, now Soil Scientist, Southern Piedmont Soil Conservation Field Station, Agricultural Research Service, USDA, Watkinsville, Ga., and Professor of Soils, respectively.

Received for publication June 27, 1960. Accepted for publication August 1, 1960.