Conservation tillage effects on the potassium status of some Kentucky soils.

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. Contribution from the Dep. of Agronomy, Univ. of Kentucky, Lexington. Published with the approval of the Director of the Kentucky Agric. Exp. Stn. as Journal Article no. 89-3-142.