Soil Structure and Carbon Pools in Agroecosystems and Mixed-Grass Ecosystems.

Carbon sequestration and aggregation have long been recognized as important indicators of soil productivity for sustainable agriculture. The current low levels of C sequestration and aggregate stability in cropland soils have increased interest in enhancing organic matter with no-till systems and the Conservation Reserve Program (CRP).  The objective of this research was to evaluate the impact of agroecosystems and mixed-grass ecosystems in Western Kentucky on soil C pools and aggregation.  The agroecosystems included corn-soybean cropping systems with no-till (NT) and conventional tillage (CT), CT- tobacco cropping systems, organic vegetable farming systems, CRP land and garden prairie.  Macro-aggregates and aggregate stability were higher in NT systems compared to CT at the depth of 7.5 cm, but there is no significant difference at the lower depth.  An increase in soil C and particulate organic matter (POM) generally followed the improvement in aggregate stability.  NT and organic farming systems had greater aggregation and C sequestration at the soil surface, but garden prairie and CRP had higher macro-aggregates below the surface.  Improved soil management practices are still needed to sequester C and enhance macro-aggregates and aggregate stability in agroecosystems in Western Kentucky.