ABSTRACT

Evaluating the effects of management practices on soil organic matter storage has been a popular topic of study for some time. It is well documented that increases in soil organic matter improve soil physical properties, and increase the overall fertility and sustainability of the soil. Research in this area has recently been stimulated following the proposal that agricultural soils may provide a significant C sink that may aid in the mitigation of increasing atmospheric CO₂. Observed differences in lint yield and N response from a cotton performance study at the Texas A&M University experimental farm near College Station, TX prompted us to examine the effects of tillage and rotation on soil organic C (SOC) storage, soil microbial biomass C (SMBC), mineralizable C, and water-stable aggregation in these cotton cropping systems. The three tillage/rotation treatments examined included conventionally tilled continuous cotton (CT), reduced tilled continuous cotton (RT), and conventionally tilled cotton after corn rotation (CC) treatments. SOC, SMBC, and C mineralization were significantly greater under RT and CC managed plots, when compared to CT plots. SOC, SMBC, and mineralizable C were 33, 58, and 79 % greater in the top 5 cm of RT managed plots and 29, 32, and 36 % greater in the top 5 cm of CC managed plots when compared to CT plots. Tillage and rotation had little effect on water-stable aggregation and aggregation did not correlate with SOC, SMBC, or C mineralization. C mineralization provided the most sensitive indicator of management-induced change, followed by SMBC, and SOC. Increases in SOC storage were relatively modest, suggesting that potential SOC storage under cotton in this region may be limited by warm climatic conditions. However, increases in labile organic matter fractions resulting from reduced tillage and rotation could have the potential to significantly impact soil fertility in cotton cropping systems.