Seasonal variations in net ecosystem exchange of CO₂ and conservation of water use efficiency of cotton in the Mississippi Delta

Abstract Accurately quantifying the net ecosystem exchange (NEE) of CO 2 is a critical prerequisite for developing alternative farm management strategies to enhance carbon sequestration in biological systems and reduce greenhouse gas emissions. A 2‐year study quantified the NEE of CO 2 from cotton ( Gossypium hirsutum L.) on silty clay in farm‐scale fields using an eddy covariance approach. On a seasonal scale, NEE and evapotranspiration were 8836 kg CO 2 ha −1 and 367 mm, respectively, in 2017, and 10,759 kg CO 2 ha −1 and 430 mm in 2018. Harvested cotton lint yields were 1269 and 1569 kg ha −1 in 2017 and 2018, respectively. The water use efficiency (WUE) for lint production (WUE lint ) and ecosystem level WUE for NEE (WUE NEE ) across the two seasons was nearly constant. WUE lint was 3.5 and 3.6 kg lint ha −1 mm −1 , respectively, in 2017 and 2018, and WUE NEE was 24 and 25 kg CO 2 ha −1 mm −1 . The NEE and WUE measured in this study can be used as a benchmark for comparing carbon sequestration potential in cotton production. However, further research is needed to understand NEE responses to long‐term climate variability and to develop climate‐smart crop‐soil management strategies.