DRAINMOD-N, A NITROGEN MODEL FOR ARTIFICIALLY DRAINED SOILS

DRAINMOD-N, a quasi two-dimensional model that simulates the movement and fate of nitrogen in shallow water table soils with artificial drai nage, is described. Results of sensitivity analyses are presented and model predictions are compared with results from VS2DNT a more complex , two-dimensional model. The nitrogen transport component is based on an explicit solution to the advective-dispersive-reactive (ADR) equati on. Nitrate-nitrogen is the main N pool considered. Functional relatio nships are used to quantify rainfall deposition, fertilizer dissolutio n, net mineralization, denitrification, plant uptake, and surface runo ff and subsurface drainage losses. A sensitivity analysis showed DRAIN MOD-N predictions are most sensitive to the standard rate coefficients for denitrification and mineralization and nitrogen content in rainfa ll. Simulated daily water table depths were within 0.121 m, cumulative subsurface drainage rates were within 0.016 m, and cumulative surface runoff rates were within 0.003 m, of those predicted by VS2DNT for a 250-day period. DRAINMOD-N predictions for NO3-N losses in subsurface drainage water only differed from VS2DNT predictions by less than 2.6 kg ha(-1). DRAINMOD-N predictions for denitrification were within 8%, for plant uptake were within 15%, and for net mineralization were with in 26%, of those simulated by VS2DNT.