Seasonal variations in net ecosystem exchange of CO 2 and conservation of water use efficiency of cotton in the Mississippi Delta

Accurately quantifying the net ecosystem exchange of CO ₂ (NEE) is a critical prerequisite for developing alternative farm management strategies to enhance carbon sequestration in biological systems and reduce greenhouse gas emissions. A two-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 (EC). On a seasonal scale, NEE and evapotranspiration (ET) were 8,836 kg CO ₂ ha ^− 1 and 367 mm, respectively, in 2017, and 10,759 kg CO ₂ ha ^− 1 and 430 mm, respectively, in 2018. Harvested cotton lint yields were 1,269 and 1,569 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 were 3.5 kg lint ha ^− 1 mm ^− 1 and 3.6 kg lint ha ^− 1 mm ^− 1 , respectively, in 2017 and 2018, and WUE _NEE were 24 kg CO ₂ ha ^− 1 mm ^− 1 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.