Water-stable aggregation among untilled and intensively tilled soils with similar contents of aggregating agents in central Ohio, USA

Abstract

Organic carbon (OC), permanganate-oxidizable carbon (POXC), and autoclaved citrate-extractable (ACE) proteins are utilized as soil quality indicators due in part to their positive relationships with water-stable aggregation (WSA). Tillage-induced losses of WSA are oftentimes attributed to decreases in these soil constituents. The objective of the present study was to explain differences in WSA existing between tilled and untilled cropland soils through comparing the soils in terms of these and other aggregating agents. We examined WSA and a suite of related properties on conventional tillage (CT) and no-tillage (NT) soils of an Epiaqualf-Argiaquoll association along a low-relief hillslope in central Ohio, USA. Overall, WSA was strongly correlated (r > 0.7, P < 0.05) with OC, POXC, and ACE proteins, but when concentrations were similar between NT and CT soils for these constituents, most notably at the toeslope position, WSA was consistently greater for the NT soil. Statistically controlling for the effect of these individual WSA covariates did not change this result. Results suggest that heightened WSA for the NT vs. the CT soil may be due to the greater water repellency of the former when other aggregating agents are equivalent between tillage regimes. These findings suggest that soil quality evaluators should measure WSA directly rather than rely on inferences based on organic constituents, especially when working with CT soils from poorly drained, depositional landscape positions.