Energy balance simulation for surface soil and residue temperatures with incomplete cover

Knowledge of the effects that crop residue architecture has on exchange processes at the soil surface can extend the applicability of soil and,vater balance modules. Our objectives were to evaluate the feasibility of using a numerically reduced soil-residue energy boundary condition module, compatible with the USDA-ARS Root Zone Water Quality Model, and to compare the accuracy of calculated values against measurements. We developed a Penman-type energy balance module, PENFLUX, which solves for surface temperatures of a soil slab and a single flat residue layer, adjusting for aerodynamic resistances of standing residue stems. It provides surface boundary conditions for simulations of energy transfer in a one-dimensional soil profile. PENFLUX simplifies iterative solutions by simplifying radiation, convection, and soil heat algorithms. We collected hourly radiation data; air, soil, and residue temperatures; and wind profile data after wheat harvest on a level Nunn clay loam soil (fine, smectitic, mesic Aridic Argiustoll) (1997 soil series reclassification). Model parameterization avoided fitting model calculations to measurements, as inputs were measured at the site or referenced from literature. PENFLUX calculations exhibited a low degree of random error for dry soil and residue conditions, though systematic bins in surface soil temperature and negative bias in nighttime net irradiance reduced predictive efficiency. Error propagated from surface soil temperature probably contributes to the negative bins in net radiation. The reasonable predictive accuracy of PENFLUX for dry soil conditions demonstrates the feasibility of a numerically simplified model of soil-residue energy exchanges, and justifies further evaluation against a range of residue architectures and environmental conditions.