Comparison of Eddy Covariance Evapotranspiration Measurements to DSSAT Simulation for Dryland Corn and Cotton in East-Central Texas.

Simulations of evapotranspiration (ET) that are backed up by field data are important in quantifying the contributions of agroecosystems to global hydrologic cycles. The objective of this study is to model ET using the Decision Support System for Agrotechnology Transfer (DSSAT) crop growth model and to compare the modeled ET to measurements made using eddy covariance. Two eddy covariance flux towers were established in Burleson County, TX for the 2017 and 2018 growing seasons; one planted to corn (Zea mays L.) and one to cotton (Gossypium hirsutum L.). The eddy covariance towers used an open-path 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). Standard metrological instruments (temperature and relative humidity probe, solar radiation sensors, and a rain gauge) and soil instruments (soil temperature, heat flux, and moisture content) were all installed at each site in addition to the eddy covariance instruments. Phenological data was taken biweekly via destructive sampling. 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 were compared with actual field measurement. Statistical analysis and graphing was performed using Sigma Plot 13.0. The models for corn performed adequately for both years with nRMSE less than 1.5 mm / m² / day. The cotton model outperformed the corn model with an nRMSE of 0.6 mm / m² / day for both 2017 and 2018.