THE EFFECT OF SPRING AND WINTER KILLED COVER CROPS ON SOIL PHYSICAL PROPERTIES AND SOIL ORGANIC CARBON

Maintaining soil organic carbon (SOC) and healthy soil physical structure in agroecosystems is crucial to sustainable production. To assess medium term impacts of cover crops on soil health in the top 90 cm, we conducted a field experiment in central Kentucky with varying levels of winter cover: spring and winter kill cover crops, weedy and bare winter fallows. After eight years of cover crop use, some soil physical properties improved: 35% greater mean weight aggregate diameter at 0-30 cm with spring kill covers and 5.2% more C held within large aggregates for both cover crop treatments compared to winter fallow. Nine years of annual cropping resulted in a 70% decline in particulate organic matter across treatments compared to reference sod. In all treatments except spring kill, mineral associated organic matter (MAOM) C stocks were lower than the original land use at 0-10 cm. Total SOC stocks remained the same across treatments and sod. At 0-10 cm, cover crop roots had a positive effect on soil structure through various mechanisms, and cover crop shoots had a positive effect on MAOM C stocks. Our findings suggest that winter cover management with more C inputs improves some soil health indicators, with variable results.