Impacts of Conservation Practices and Irrigation on Greenhouse Gas Emissions in Mid-South Cotton

Improvements in soil quality along with reductions in water pollution are linked with expanded adoption of conservation practices in US cotton, but there is little information about how these evolving systems impact greenhouse (GHG) emissions. In 2020, GHG measurements were included in the long-term cotton field study on management practices effect on water quality, soil properties and yield. The study included four system treatments: conservation and conventional production systems with and without supplemental irrigation layout in a RCB design with three replications. The conservation cropping system included a broadcast cereal rye winter cover crop, vegetative buffer strip and reduced tillage while conventional cropping treatments included winter fallow, plowed to form beds and water furrow (irrigated treatments). Both conventional and conservation system treatments were managed under irrigated and rainfed irrigation. GHG fluxes were measured using a static flux chamber technique. Sample sites in each plot were positioned at the top of the planted bed and down in the furrow between the rows (i.e. inter-row space). In all management treatments, methane fluxes were low and below the detection limit of measurements. High N₂O emissions occurred after rainfall in early summer in conventional treatments while high N₂O emissions occurred after N fertilization combined with heavy rainfall in conservation treatments. Cumulative seasonal N₂O emissions ranged from 0.15 to 5.0 kg N₂O ha^-1 season^-1 with no significant difference among tillage and irrigation treatments while total seasonal CO₂ emissions were significantly different between tillage and irrigation treatments with 34- 40% increase in emissions in the conservation irrigated treatments compared to conventional irrigated treatments. Across all treatments, lint yields were significantly higher in the irrigated compared to rainfed treatments . This study provides a first step to quantify the effects of adoption of conservation production practices on GHG emissions in Mid-south cotton.