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Release of Nonexchangeable Soil Potassium During Short Periods of Cropping and Sodium Tetraphenylboron Extraction¹

ABSTRACT

Undried soils were cropped in the greenhouse to determine the short-term release of nonexchangeable K under intensive cropping conditions. Using corn root mats with plants intact, it was found that 218, 59, 50 and –1 ppm. nonexchangeable K was released in 10 days by Marshall surface and subsoil and Clarion surface and subsoil samples, respectively, that had received no NH₄ or K additions. It was concluded that this short-term cropping method could be used to study factors that affect the availability of nonexchangeable soil K to plants.

Nonexchangeable K was also extracted from the undried soils by two chemical methods that tend to reduce the blocking effect of replaced K. Single extractions with a NaOAc-NaBPh₄ solution removed more nonexchangeable K than five successive NaCl-HCl extractions or 5-day cropping periods. The corn plants and the NaCl-HCl solution, however, continued to remove K when the extraction period was increased whereas the NaOAc-NaBPh₄ solution did not.

¹ Journal Paper No. J-3901 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Project No. 1234. This work was supported in part by the American Potash Institute.

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

Received for publication June 24, 1960. Accepted for publication August 8, 1960.