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Potassium Supplying Power of Iowa Soils at Their "Minimal" Levels of Exchangeable Potassium¹

ABSTRACT

The plant removal of native K from seven surface soils and seven subsoils from Iowa was studied at their "minimal" levels of exchangeable K. The "minimal" levels of exchangeable K were directly related to the percentages of <2 µ clay present in the surface soil samples. Plant uptake of nonexchangeable K was a linear function of time of cropping for all the soils and was highly correlated with the "minimal" level of exchangeable K. In the 758-day cropping period, an average of about 24 times as much K was removed by the plants as was present as exchangeable K in the soils at their "minimal" exchangeable K levels. Long-term K supplying powers of the soils used were highly correlated with their "minimal" levels of exchangeable K.

¹ Journal Paper no. 5957 of the Iowa Agr. & Home Econ. Exp. Sta., Ames, Project no. 1190.

² Research Associate and Professor of Soils, respectively.

Received for publication May 13, 1968. Accepted for publication July 22, 1968.