Spatially distributed hydrologic-biophysical modeling: applications in precision agriculture

Precision agriculture is a knowledge-intensive practice. Successful implementation both requires and generates detailed, spatially and temporally distributed data on topography, on soil characteristics, including textural and hydraulic properties, moisture and nutrient status, and on crop yield. In order to make effective use of spatially variable rates of application, knowledge of the localized influences of landscape position, in-canopy microclimate and soil characteristics on crop productivity is required. In addition, a capability to predict soil moisture conditions is useful for assessing field trafficability, thereby preventing or minimizing soil compaction and loss of structure, and knowledge of in-canopy moisture is useful in predicting susceptibility to pests and disease. We describe the development and preliminary evaluation of a terrain-driven distributed parameter hydrologic-biophysical model (IBIS-AFS) intended to provide the basis for a decision support system for precision agriculture in the Upper Midwest. The model is based on the Integrated Biosphere Simulator - IBIS (Foley, et al., 1996), which simulates land surface biophysics, balances and one-dimensional fluxes of energy, water, carbon and nitrogen; and vegetation dynamics. Important enhancements in IBIS-AFS include routines to simulate overland flow processes via diffusive wave routing and detailed ecophysiological models of important field crops (maize, soybeans). Model performance is evaluated using detailed field data from two midwestern locations.