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.
This study was an attempt to predict potential long‐term mineralogical transformation trends in soils under continuous no‐tillage management using the in situ soil solution composition as a sensitive index of changes occurring in the soil system. Mineralogical and soil solution compositions of surface and subsurface horizons of a catena of loess‐derived soils (Memphis, Grenada, Calloway) under continuous (16 yr) no‐till (NT) and conventional‐till (CT) management suggested a shift in weathering patterns as a result of the differential tillage management. This shift was evident primarily as a buffer effect of the NT management on drainage characteristics. Interstitial soil solutions of surface NT horizons were generally two to three times higher in Si and K than respective surface CT horizons. The elevated soluble Si and K concentrations maintained in the NT horizons correlated well with increases in organic matter content. The Si‐enrichment of the NT‐solutions combined with the reduced Al3+ activities, due to increased complexation, appeared to favor a hydroxyinterlayered vermiculite/vermiculite metastable state over the hydroxyinterlayered vermiculite/kaolinite of the CT system. This slowdown of the weathering process under continuous NT management should have important implications on K equilibria of these soils.
To test the hypothesis that K content of Iowa soils was related to soil development, samples from the B horizon of selected sites were obtained from loess‐derived prairie soils at several locations within the state. Samples were also obtained from Nebraska and Illinois loess soils to relate the Iowa study to the midwestern prairie region. Total K in clay from the B horizons decreased progressively from west to east. This was explained on the basis of concurrent increase in average annual precipitation from west to east across the area. No consistent relationships between total K content and standard indexes of profile development were obtained. However, K was highly correlated with depth to the B horizon. Although montmorillonite was the dominant clay mineral in all samples, there was relatively more illite in samples of higher K content and from sites receiving lesser amounts of annual precipitation. Studies of K released to sodium tetraphenyl boron (NaTPB) on Iowa soils reflect the trends in total K content found in the B horizons.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.