Evaluating Various Water Stress Calculations in RZWQM and RZ‐SHAW for Corn and Soybean Production

Abstract

Better understanding of water stress calculation is needed to improve crop production simulation. In this study, the Root Zone Water Quality Model (RZWQM) and RZWQM‐SHAW (Simultaneous Heat And Water) (RZ‐SHAW) Hybrid Model were evaluated for simulating corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] growth and water use under a range of water conditions in the Central Great Plains. In both models, a water stress index (WSI) was calculated as a nonlinear form of the ratio between actual transpiration (AT) and potential transpiration (PT) [WSI = (AT/PT)α, 0 < α < 1]. Evapotranspiration (ET) was calculated using the Shuttleworth–Wallace approach on a daily basis (ETSW‐DAY) in RZWQM and using either the Shuttleworth–Wallace approach on hourly basis (ETSW‐HR) or the SHAW approach (ETSHAW) in RZ‐SHAW. Results showed that RZWQM using ETSW‐DAY provided similar simulation for both corn and soybean production as RZ‐SHAW using the ETSW‐HR option, given that the same plant parameters were used. However, RZ‐SHAW with ETSHAW provided less accurate simulations for corn and soybean growth. This study demonstrated that, when RZ‐SHAW is used for plant simulation, AT and PT should be calculated the same way as in RZWQM to preserve the plant parameters. Otherwise, recalibration of plant growth parameters is needed. This study also showed that the α value varied from crop to crop and among ET calculations. Based on the results, it is suggested to use α = 0.75 for corn and α = 0.5 for soybean in RZ‐SHAW with the ETSW‐HR option.