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 CO₂ 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 CO₂ 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 CO₂ ha⁻¹ and 367 mm, respectively, in 2017, and 10,759 kg CO₂ 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 CO₂ 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.