How Changes in Management Impact Size Distribution and Stability of Soil Aggregates

Within agricultural soils, the active layer (top 5cm) is by far the most dynamic in response to management practices. Tillage events break apart the structure of the soil, weakening soil aggregates and reduce their resilience to mechanical and hydrological forces. During storm events, raindrops impact the soil surface, dislodging soil fractions that can be swept up and transported across the landscape by overland flow. These erosion processes can become amplified without the presence of surface residue cover or cover crops, which absorb raindrop energy and break up flowpath connectivity. Therefore, looking the distribution and stability of aggregate size fractions within the active layer may indicative to changes in management or dynamicity of landscape processes.

In this rare study we capture changes in soil aggregate dynamics during the conversion of long-term conventional tillage systems to reduced till w/ cover crop systems. We implemented a 50m x 50m grid where topsoil samples were collected. Soil samples were air dried and broken into 9 size fractions to determine dry size distribution, and then analyzed for water stable aggregates, and stability against raindrops using kinetic energy supplied by rainfall simulator. Results found a 20% increase in dry mean weight diameter upon conversion to cover crops as well as a 5% increase in stability. LiDAR data was used to determine flowpath networks within the fields and overlaying the sampling grid uncovered landscape processes impacting aggregate dynamics. Data from this study is currently being used to build upon a hillslope transport model to simulate size fraction redistribution in intensely managed landscapes.