Tillage-induced surface soil roughness controls the chemistry and physics of eroded particles at early erosion stage

Abstract

Intensive row crop agriculture on loess mantled hillslopes in the upper Midwest, USA, accelerates soil erosion and the loss of organic matter by increasing soil aggregate breakdown, changing surface roughness patterns, and leaving soil exposed to rainfall and wind for much of the year. There is a knowledge gap, however, in relating how the dynamics of soil erosion on hillslopes control landscape heterogeneity in terms of particle size, surface soil organic chemistry and reactivity. Simulated rainfall experiments on intensively managed hillslopes in the Clear Creek, IA watershed, USA, revealed that tillage-induced, oriented roughness controls the amount and organic geochemistry of soil particles mobilized downhill. The average discharge rate of mobilized sediment was nearly 30-fold higher when the tillage orientation was parallel to the runoff direction compared to when the tillage orientation (i.e. contour tillage) was perpendicular to the runoff direction. Mobilized particles under contour tillage were higher in organic carbon (OC) content and were relatively less decomposed, based on lignin chemistry, compared to analogous particles under the parallel tillage orientation. Contour tillage increased deposition of denser particles within the furrows and increased the release of the finer, lighter, and organic-rich material during over-spilling and contour breach. Our findings have important implications for understanding how the interaction of tillage practices and event-based erosion influences the spatial heterogeneity of soil geochemistry and potentially soil health across agricultural landscapes as well as understanding what controls the geochemical signature of soil erosion into streams.