DRAINMOD−N II is a field−scale, process−based model that was developed to simulate nitrogen dynamics and turnover in the soil−water−plant system under different management practices and soil and environmental conditions. It is an enhanced version of the nitrogen (N) simulation model, DRAINMOD−N, that simulates a more complete N cycle, adds a carbon (C) cycle, and operates at different levels of complexity.

 

Processes considered in the model include atmospheric deposition, application of mineral N fertilizers including urea and anhydrous ammonia (NH3), soil amendment with organic N (ON) sources including plant residues and animal waste, plant uptake, organic C (OC) decomposition and associated N mineralization/immobilization, nitrification, denitrification, NH3 volatilization, and N losses via subsurface drainage and surface runoff. Nitrogen pools considered in the model are nitrate−nitrogen (NO3−N), ammoniacal nitrogen (NHx−N) and ON. DRAINMOD−N II includes a submodel that simulates C dynamics in the soil−plant system using a C cycle similar to that of the CENTURY model.

 

A simplified approach is used to simulate temporal changes in soil pH; consequently, the model determines the composition of the NHx−N pool and, if necessary, changes its operation mode. DRAINMOD−N II simulates N reactive transport using a finite difference solution to a multiphase form of the one−dimensional advection− dispersion−reaction equation.

 

Model output includes daily concentrations of NO3−N and NHx−N in soil solution and drain flow, daily OC content of the top 20 cm soil layer, and cumulative rates of simulated N processes.