SIMULATION OF NITROGEN DYNAMICS AND LEACHING FROM ARABLE SOILS

The LEACHM model was evaluated using data from a field experiment conducted in Lancaster County, Pennsylvania, U.S.A. Many of the parameter input values were the means of determinations for soil samples from the field site. Measured nitrogen (N) uptake and nitrate (NO3-N) storage in the soil profile, as well as mineralization and nitrification rates were higher in 1987 than in 1988. The measured N removal by crops was taken as the simulated N uptake. A reasonably good agreement between simulated and measured values was obtained for NO3-N storage. However, higher rate constants had to be used for 1987 than for 1988 in order to match simulated with measured storage. The simulated soil solution NO3-N concentrations at 1.2-m depth agreed quite well with those measured in porous cup water samples, except for the highest ammonium nitrate treatment. In general, the simulation results indicated that the LEACHM model described the nitrogen dynamics fairly well.