Performance evaluation of AquaCrop in simulating soil water storage, yield, and water productivity of rainfed soybeans (Glycine max L. merr) in Ile-Ife, Nigeria

Abstract

In this study, experiments were carried out for two seasons at the teaching and research farms, Obafemi Awolowo, Nigeria to evaluate the performance of FAO AquaCrop version 5.0 in simulating canopy cover, soil water storage, above ground biomass, evapotranspiration, grain yield and water productivity of soybeans (TGX 1448 2E) under rainfed conditions. The Experimental treatments consisted of conventional and six water conservation practices: Tied ridges; Mulching; Bund; Tied ridges plus mulch; Tied ridges plus bund and Bund plus mulch. The experimental treatments were arranged in randomised complete block design with four replicates. The 2012 and 2011 data sets were used for calibration and validation respectively. The performance of AquaCrop was tested using the regression coefficient (b), coefficient of determination (R2), Root mean square error (RMSE), Normalised root mean square error (NRMSE), Nash and Sutcliffe efficiency coefficient (EF), Willmott’s index of agreement (d-index) and percentage bias (PBIAS). AquaCrop simulated canopy cover adequately for the two seasons, 0.95 ≤ b ≤ 0.99; R2 ≥ 0.95 and RMSE ≤ 11.6%. The model captured well the variability in soil water storage with 0.95 ≤ b ≤ 1.01; R2 ≥ 0.74 and RMSE ≤ 10.2 mm. AquaCrop simulated evapotranspiration with R2 = 0.66 and RMSE = 64.6 mm. The model simulated dry above ground biomass with RMSE ≤ 0.25 t ha−1 and d-index ≥ 0.98. Grain yield was simulated with b = 1.01; R2 = 0.99; RMSE of 0.03 t ha−1d-index = 1.00 and the maximum deviation between the simulated and predicted grain yields is 3%. The water productivity was simulated with R2 = 0.78 and RMSE = 0.08 kg m-3. Considering the overall performance, the AquaCrop model is adequate in simulating canopy cover, dry above ground biomass and grain yield. However, it has low aptitude in simulating evapotranspiration and water productivity of rainfed soybeans under soil surfaces management practices.