SIMULATION OF DENITRIFICATION LOSSES OF NITRATE FERTILIZER APPLIED TO UNCROPPED, CROPPED, AND MANURE-AMENDED FIELD PLOTS

Abstract

We simulated losses of nitrate fertilizer via denitrification, using a mathematical model that included transport and plant uptake of water and nitrogen in soil. The denitrification rate was considered to be a function of nitrate concentration, water-extractable organic carbon concentration, degree of soil-water saturation, and temperature. Water-extractable organic carbon concentrations were calculated from initial amounts of soil carbon and additions of plant residues or animal manure. We assumed that the consumption of added carbon in the soil system would occur in two or three stages and assigned different rate coefficients for each stage and carbon source. A Q10 value of 2 was used in correcting the rate coefficients for denitrification and carbon consumption at two temperatures. Model simulations for denitrification were compared with measured N2 and N2O gas fluxes at the soil surface during nitrate leaching in field plots of Yolo soil maintained at different soil-water contents and soil temperatures and that received various carbon additions and irrigation frequencies. We found reasonable agreement between measured rates and total amounts of denitrification and those calculated by the model using a single denitrification rate coefficient for all cropped field plots and another rate coefficient for all uncropped field plots.