Simulation of fertilizer nitrogen under cropped situations1
1982
TILLOTSON, W. R. | Wagenet, R. J.
The equations describing transient, one-dimensional transport of soil-water and nitrogen and the uptake of water and nitrogen by a growing crop are numerically approximated and integrated into a crop-environment simulation computer program. The simulation is based on an implicit finite-difference method that uses divided differences. The numerical solution allows for fluxes of water and nitrogen at the soil surface during the growing season. The lower boundary condition for water flow can simulate no flux, a unit hydraulic gradient, a constant soil-water pressure head, and a water table. Nitrogen transformations considered are enzymatic hydrolysis of urea, nitrification, and denitrification, all represented by first-order kinetics. The transformational rates are constants at present, but amendable to alteration by temperature, salinity, and water content. With the ability of this simulation to estimate water and nitrogen movement into and within the soil profile and into the crop, functional relationships can be considered in which crop growth is a function of water and nitrogen availability. The development, capabilities, and limitations of the model are presented, as well as a comparison of model predictions with field data.
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