Predicting soybean evapotranspiration and crop water productivity for a tropical environment using the CSM-CROPGRO-Soybean model

Abstract

Prediction of crop yield, evapotranspiration, and crop water productivity are essential aspects for water management and the sustainable intensification of agriculture. The goal of this study was to evaluate the Cropping System Model (CSM)-CROPGRO-Soybean model for simulating evapotranspiration and crop water productivity of soybean grown in a tropical environment. Energy balance evapotranspiration was measured daily using a Bowen Ratio Energy Balance (BREB) system for irrigated experiments that were conducted in Piracicaba, SP, Brazil, during the 2016-2017 and 2017-2018 growing seasons. Evapotranspiration was simulated with the CROPGRO-Soybean model using either the Priestley–Taylor or the FAO-56 Penman–Monteith method for potential ET combined with either the Ritchie-Two-Stage or the Suleiman–Ritchie soil water evaporation methods. The model provided good predictions of daily (D-statistic > 0.7) and cumulative evapotranspiration (RMSE ranged from 8 to 64 mm). FAO-56 Penman–Monteith with the Ritchie-Two-Stage method provided a better fit than the Priestley–Taylor with Suleiman–Ritchie when compared with measured data. Simulated crop water productivity agreed well with observed, but with a systematic underprediction (variation between simulated and measured ranged from -2.2 to -16.8 %). Simulation of long-term scenarios was conducted for different tropical environments, i.e., Piracicaba and Teresina, with soil tillage and water management practices. The results demonstrated that the implementation of no-tillage can increase 0.1 kg/m3 (11%) crop water productivity for grain. This study also showed that when irrigation was triggered at more than 60% of available soil water, irrigation did not result in an increase in yield despite an increase in water supply.