Evapotranspiration Modeling of Partial Canopy/Residue-covered Fields

Knowledge of soil evaporation (E) and crop transpiration (T), collectively referred to as evapotranspiration (ET), is central to water budget analysis and modeling of agricultural cropping systems. The double layer Shuttleworth-Wallace (S-W) model provides the potential of modeling ET for the entire range of canopy cover. This model is extended herein to include the effects of surface crop residues on soil evaporation by explicitly specifying a partially covered soil area and partitioning evaporation between the bare and residue-covered areas. Although the extended S-W model is physically based, simplifying assumptions are made for the sake of functionality. Model derivation and potential uses are discussed. The main drawback to the model’s field application is parameter estimation. In this article, the concepts of soil and residue evaporative resistances are explored leading to proposed methods for estimating these difficult-to-determine parameters. An immediate use of the model is in predicting daily E and T rates in system-wide agricultural simulation models.