Modeling Soil Water Redistribution during Second‐Stage Evaporation

Abstract

Calculating the dynamics of soil water content (θ) near the surface and modeling soil water evaporation (Es) are critical for many agricultural management strategies. This study was performed to develop a model to simulate soil water redistribution during second‐stage evaporation (SSE). In this model, the daily change of θ was estimated from the difference between the initial θ (θi) and air‐dry θ (θad), multiplied by a conductance coefficient (C). The C represents the fraction of the remaining soil water (θi − θad) that can be removed in 1 d during SSE and is a power function of soil depth. Testing the dependency of C and α (the slope of cumulative evaporation [Ec] vs. square root of time [t1/2]) on soil characteristics was done using theoretical and laboratory data. Then the whole model was evaluated in laboratory and field conditions by measuring θ for different soils at different depths during SSE. Linear relationships with zero intercept were found between α and drained upper limit θ (θdul) with slope and r2 = 1.19 and 0.69 and 1.39 and 0.95 for laboratory and theoretical data, respectively. Conductance coefficient and θdul were correlated with r2 > 0.9. Root mean square error (RMSE) between measured and estimated θ in the field was highest (0.014 cm3 cm−3) at depths of 3 and 6 cm and lowest (0.005 cm3 cm−3) at the 9‐cm depth. The model gave reasonable estimates of both water redistribution and Es during SSE and is expected to work well for soils for which the diffusivity theory holds.