Conservation Tillage Effects on the Potassium Status of Some Kentucky Soils

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Abstract
Changes in the soil K status occurring as a result of shifting from conventional to no‐tillage management in selected fields were evaluated in this study. The fields were on loess‐ and limestone‐derived soils in western and central Kentucky and have been under no‐tillage management for the last 6 to 16 yr. Two‐ to three‐fold increases in exchangeable and soluble K were evident in most upper surface horizons (Ap1) of soils receiving no‐tillage management, and these increases correlated well with organic matter (OM) accumulations. Adsorption of exchangeable K appeared to be favored over that of Ca and Mg with increases in OM up to a maximum value, beyond which additional OM accumulations had a negative or no effect. Notillage management resulted in a lower overall affinity for K of the exchange sites in all soils (especially the Memphis soil) apparently due to OM accumulations. Quantity/intensity plots reflecting the tillage‐shift effect on K relationships suggested that the loessial soils could reach K‐availability equilibria sooner than the limestone soils due to mineralogical and textural differences. This could mean less fertilizer‐K use on loess‐ than on limestone‐derived soils to attain maximum crop yields under no‐till management.