Evapotranspiration, Gross Primary Production and Water-Use Efficiency Estimates of Cotton and Corn in East-Central Texas Using Eddy Covariance and Remote Sensing.

Accurate simulations of evapotranspiration (ET) and gross primary production (GPP) are important in quantifying the contributions of agroecosystems in global carbon and hydrologic cycles. The objective of this study was to model ET, GPP and water use efficiency (WUE) using a plant growth simulation and satellite remote sensing. Net ecosystem CO₂ exchange (NEE) and ET measurements were made using eddy covariance flux towers established in two near-by fields in Burleson County, TX in the 2017 growing season; one planted to corn (Zea mays L.) and one to cotton (Gossypium hirsutum L.). These measurements were made using an open-path eddy covariance system consisting of a CSAT-3A sonic anemometer (Campbell Scientific Inc., Logan, UT, USA) and LI-7500A infrared gas analyzer (LI-COR Biosciences, Lincoln, NE, USA). Using the eddy covariance method, half-hourly fluxes of latent heat fluxes (LE) and NEE were calculated as the covariance between fluctuations from the mean vertical wind speed and corresponding fluctuations of water vapor and CO₂ concentrations. Half-hourly LE and NEE values were converted to ET and GPP respectively. WUE was estimated in terms of net CO₂ uptake per unit water lost by regressing daily ET against daily GPP. Supporting meteorological and plant phenological data were also collected from these fields. The DSSAT- Cropping System Models (CSM) for cotton (CROPGRO plant growth module) and corn (CERES-Maize Plant Growth Module) were calibrated using plant phenological data. After calibration, model simulations of ET and GPP were compared with actual field measurements of ET and estimated GPP from NEE. ET and GPP were also modeled using Landsat satellite data. Final results from this project will be presented at the meeting.