Simultaneous calibration of evapotranspiration and crop yield in agronomic system modeling using the APEX model

Authors: TALEBIZADEH, MANSOUR - Orise Fellow; Moriasi, Daniel; Gowda, Prasanna; Steiner, Jean; Tadesse, Haile; Nelson, Amanda; Starks, Patrick

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2018
Publication Date: 7/3/2018
Citation: Talebizadeh, M., Moriasi, D.N., Gowda, P., Steiner, J.L., Tadesse, H.K., Nelson, A.M., Starks, P.J. 2018. Simultaneous calibration of evapotranspiration and crop yield in agronomic system modeling using the APEX model. Agricultural Water Management. 208: 299-306. https://doi.org/10.1016/j.agwat.2018.06.043.
DOI: https://doi.org/10.1016/j.agwat.2018.06.043

Interpretive Summary: Accurate estimation of evapotranspiration (ET) is important for adopting cost-effective actions for managing water and land resources particularly in semi-arid conditions. This study presents an objective approach on utilizing annual observed ET and crop yield data for estimating representative ET and crop growth Agricultural Policy/Environmental eXtender (APEX) model parameters. Measured ET and crop yield data from Bushland, Texas were used in this study. The results indicated a substantial improvement for both ET and crop yield predictions. The prediction improved by 18% on monthly time scale. The errors for crop yield predictions were also reduced from 43% to 16% using the proposed parameter estimation method, when it was tested for simulation of an agricultural field, managed as dry land with semi-arid conditions. The presented approach (which can be extended to other USDA-ARS hydrologic and water quality models like Soil and Water Assuagement Tool (SWAT)) can assist in realistic crop yield predictions which in turn determine the economic feasibility of a specific cropping system in a region.

Technical Abstract: Evapotranspiration (ET) is a major outgoing source of water in an agronomic systems. Reliable estimation of ET is very important especially in semi-arid condition where ET prediction is instrumental in cost-effective management of scarce water resources and crop production. In addition to the role of climate variables, the actual ET is influenced by crop characteristics during the growing season. Therefore, accounting for the interaction between crop growth and actual ET can significantly impact the performance of models. In this study an efficient calibration approach is presented for simultaneous calibration of ET and crop growth parameters for the Agricultural Policy/Environmental eXtender (APEX) model. The proposed approach involves development of an objective function based on a compounded time series comprising of scaled annual ET and crop yield data. An efficient search algorithm based on DiffeRential Evolution Adaptive Metropolis (DREAM) algorithm was implemented in R language to find the parameter values that minimizes the defined objective function. The simultaneous calibration approach which utilized annual data improved ET prediction for annual as well as finer time scales (25% in RMSE reduction for 3-month, 18% for monthly, 17% for 2-week, 19% for weekly, 17% for, 3-day and 13% for daily time scales). The average of absolute relative error for crop yield predictions were also reduced from 43% to 16% for the calibrated model. The simulated leaf area index (LAI) for the calibrated model (i.e. calibrated using annual ET and crop yield data) were also consistent with the measured LAI values, confirming the validity of the calibrated parameter values.