Modeling Corn Surface Resistance to Estimate Actual Water Use

摘要

In a global scenario of climate change, water scarcity, and population growth it is imperative to optimize crop water management. One way is by calibrating a physically-based crop evapotranspiration (ET) model, in the so-called one-step approach; as opposed to the two step approach that uses reference evapotranspiration a crop coefficients. The Penman-Monteith (1965) ET model uses a surface resistance (r_s) term. This variable describes the resistance (stomatal, leaf, and canopy) to crop water transpiration and water evaporation from the soil surface. If the crop is not transpiring at a potential rate, the r_s resistance depends on the water status of the soil and vegetation. The stomatal resistance is influenced by climate and by water availability. However, this influence is different from crop to crop. The resistance increases when the crop is stressed and when the soil water availability limits ET. In this study, surface resistance was parameterized, for grain corn grown in Iowa, considering plant response to soil, plant, and environmental conditions, and not just to a well-watered and uniform corn surface. The independent variables that yielded a larger correlation with r_s were: net radiation, photosynthetic active radiation, crop height, leaf area index, percent cover, albedo, an advection function, canopy temperature, and surface aerodynamic resistance. These variables were used to obtain "r_s" models (linear, logarithmic, and exponential) which were evaluated with ET values derived from eddy covariance data. The applicability of the parameterized corn "r_s" models is discussed in contrast with "r_s" models developed for other crops.