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Potassium Status of Some Alluvial Soils in Kentucky¹

ABSTRACT

Six alluvial soils from Kentucky were intensively cropped to ‘Midland’ bermudagrass (Cynodon dactylon L. Pers.) to determine K availability in each soil. Potassium removal by the bermudagrass was compared to exchangeable K, to labile K estimated from Beckett quantity/intensity plots and to Gapon coefficients before and after cropping. Exchangeable K was not a good measure of uptake (r = 0.61 not significant), but labile K determined on soils before cropping and the Gapon coefficient after cropping gave highly significant linear correlations with K removed by bermudagrass. Exchangeable K after cropping changed an average of only 23 ppm K in the soils, but availability of K to plants was lowered drastically in all soils. This study shows that exchangeable K is an insensitive measurement of K availability to plants. Exchangeable K is a useable measurement only because wide ranges are used in determining classes of availability in soil testing.

¹ Contribution from the Dep. of Agronomy, Univ. of Kentucky, Lexington. This paper (no. 76-3-51) is published with the approval of the Director of the Kentucky Agric. Exp. Stn.

² Former Graduate Assistant, now Assistant Professor of Agronomy, Virginia Polytechnic Instit. and State Univ., Blackstone, and Professor of Agronomy, respectively.

Received for publication April 9, 1976. Accepted for publication June 24, 1976.