Dynamics of CO2 Exchange in US Mid-South Cotton Production

The dynamics of CO₂ exchange are important in cotton production as (1) indicators of plant growth and development and (2) key determinants of the climate impact of cotton production. When integrated over a season, CO₂ dynamics can also inform about the potential for cotton fields to perform a carbon sequestering role through soil carbon storage. Enriched soil carbon content could then both increase field fertility and enable cotton production to be a part of the climate change mitigation solution. Research has shown that irrigation intensity significantly affects CO₂ emissions from clay-soil cotton fields, as more frequent irrigation stimulates soil respiration. Irrigation also provides a key input to enhance photosynthetic carbon uptake and plant and root growth.

In this study we measure CO₂ flux dynamics over a cotton production field in the U.S. Mid-South with silt loam soils. An eddy covariance system quantified 30-minute CO₂ fluxes by coupling high frequency (20 Hz) measurements of 3D wind speed, H₂O and CO₂ gas concentration. This system took measurements alongside a suite of canopy development, soil, and weather sensors used to interpret changes in flux magnitude and behavior. Three growing seasons were measured (2016-18). Initial analysis shows greatest photosynthetic uptake of CO₂ during the first week of flowering. Periods immediately following rainfall with wetter soil moisture conditions induced higher initial canopy quantum efficiency, (defined as the initial slope between photosynthetic uptake and incoming solar radiation). Soil moisture and irrigation timing seem to play a limited role in governing the dynamics of soil respiration of CO₂. Knowledge on dynamics of CO₂ exchange together with the crop water needs provides possibilities for climate-smart agricultural management.