Abstract

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.