Soil health system impacts on soil hydraulic functions in southern Minnesota

Abstract

Soil health management systems use agricultural practices incorporating living roots, persistent surface cover, diverse crop rotations, and minimal soil disturbance. These systems are widely believed to improve soil hydraulic functions. However, intense rainfall can cause physical slaking of aggregates, loss of surface pores, and reduced hydraulic functions. Soil health management systems correlate with stable aggregates and large soil pores, but it is not clear how these properties change with rainfall in fine-textured soil profiles in southern Minnesota, United States. Therefore, quantifying the hydraulic function of these systems is important as climate change intensifies growing season rainfall. Here, we investigated soil health system’s volumetric soil water content and aggregates’ response to rainfall. During 2021 and 2022, we collected data from five tillage and cover crop treatments in replicated plots at the Southern Research and Outreach Center in Waseca, MN, and paired conventional and soil health systems at three long-term on-farm sites (≥5 years, clay loam and silt loam soils). We monitored volumetric soil water content and soil aggregates within 24 hours before and 24 and 72 hours after select rainfall events. Across all locations, drier conditions led to greater rainfall capture. Differences in response to rain were found between the paired farm treatments. Generally, conventional sites had 5-20% more small aggregates following rain than soil health sites, but this effect was inconsistent across all locations. Soil health systems generally retained 10-30% more large water-stable aggregates than conventional systems in response to rain. Based on soil water retention curves, soil health treatments trended 2.5-12.5% more macroporosity than conventional systems, likely contributing to the water capture. At the farms, greater microporosity and connectivity led to 0.25-2 cm/hr greater unsaturated hydraulic conductivity relative to soil health sites, validating the greater macroporosity results we found in the soil health sites. Despite long-term treatment history at SROC, there was no unsaturated hydraulic conductivity difference, though trends showed a positive relationship with increased disturbance, like rip/chisel. Soil health indicators were higher for the soil health system of one on-farm site, where soil health practices included 30 years of long-term no-till and cover crops compared to moldboard plowing. This research indicates the importance of holistically incorporating soil health practices into field systems for achieving soil functions.