Exchangeable K levels for maximum crop yields on soils of different cation exchange capacities

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Abstract
Wide differences in levels of exchangeable K considered adequate for maximum yields in different States [USA] are probably a consequence of the acceptance of either a single 200 pp2m rate for 95-98% sufficiency suggested by Bray, or a variable level based on a percentage of the soil cation exchange capacity (CEC) proposed by Bear. It now appears that sufficiency levels should vary with soil CEC, but not merely as a simple percentage of it. Moreover, the relationship in practice is complicated by such factors as leaching of K from coarse textured soils, and fixation of added K in, and release of native K from, non-exchangeable forms in soils high in micaceous clay content. Since these influences occur widely in Ohio soils, the need for new field studies was recognized and implemented. Laboratory and growth chamber studies relating K sufficiency to energies of exchange were examined. A new procedure used by the Ohio Soil Testing Laboratory for providing K sufficiency based on soil CEC and crop yield and composition is described.

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