Ag System Models to Explore Management Effects on Crop Water Productivity.

Process models of Agricultural systems, calibrated and tested against available experimental data, are a powerful tool to extend experimental results to explore effects of different soils, climates, and management practices on crop water productivity. We summarize here some recent case studies of the use of system models to expand the knowledge of management effects on crop water productivity at full to deficit or limited irrigation levels. We show a potential to enhance water productivity in corn by growth-stage based irrigation, choosing the proper irrigation interval and amount applied at each interval with respect to initial soil water content, and nitrogen level. Nitrogen level greatly affected the water productivity. Circular planting of sorghum and cotton on a variable topography can increase soil water storage and dryland production. Models have also been used to study the effect of crop cultivar characteristics, crop rotations, no-tillage and surface residues, planting density, and sowing time on water use efficiency. Currently, there is an interest in comparing the effect of subsurface drip versus surface drip irrigation on the water use efficiency. Models have helped design large scale irrigation systems for optimal productivity. Models have been applied to explore the effect of single versus mixed cropping at different levels and climate scenarios on dryland water productivity on smallholder farms in Sub-Saharan Africa. These modeling studies provide opportunities to enhance crop water productivity.