MODELING NITROUS-OXIDE EMISSIONS FROM AGRICULTURE - A FLORIDA CASE-STUDY

The DNDC (Denitrification-Decomposition) model is shown to simulate emissions of nitrous oxide (N2O), changes in soil nitrate, and nitrogen mineralization rates consistent with field measurements at three agricultural sites in Florida. As a case study of the potential policy relevance of a process-oriented biogeochemical model, we estimated N2O emissions to the atmosphere from all agricultural lands in Florida, a state with significant agriculture on both organic and mineral soils. Nine landscape classes (3 soil classes x 3 annual rainfall classes) were coupled with county-based data on crops (5 major crops + pasture + fallow), fertilization, irrigation, and representative areas, to generate 86 model scenarios. Annual simulations were run for each case, and county and state emissions were tabulated. Total N2O emissions from Florida's agricultural lands were estimated to be 0.024 Tg N2O-N y-1. Emissions were unevenly distributed with approximately 50 percent of the N2O being emitted from soils in six (of 68) Florida counties. Organic soils, while occupying only 9% of the total agricultural land area and receiving no nitrogen fertilizer additions, accounted for 38% of the state's total N2O flux. Sensitivity studies suggest that the most effective means for mitigating N2O emissions would involve a combination of measures including reductions in drainage of organic soils, injection of fertilizers to soil depths of 10 cm or greater, and increased attention to precision irrigation. Biogeochemical modeling will be critical to developing an integrated framework for assessing policies for reducing N2O emissions from agricultural systems.