Evaluation of RZWQ2 Model and Management of Poultry Litter As Corn Nitrogen Source in the Mid-Southern United States.

Knowledge on the proper time and amount of manure to be applied for optimum yield of a given crop without degradation of water quality is important for agricultural sustainability. Because of the numerous variables, computer simulation models would be valuable to partially replace expensive field experiments. The Root Zone Water Quality Model2 (RZWQM2) was calibrated and evaluated using three years (2006-2008) of field data to simulate nitrogen balance derived from broiler litter applied to a continuous corn production system. The experiment was located at the R.R. Foil Plant Science Research Center of Mississippi State University near Starkville Mississippi. Two rates of litter (9 or 18 Mg/ha) and one rate of NH4NO3-N at 202 kg/ha were applied in the fall and spring of 2006, 2007 and 2008 corn growing seasons in order to determine the right application time of litter in a corn field. The RZWQM2 was calibrated using observed data of the least stressed treatment of spring-applied 18 Mg/ha poultry litter, then was validated by the other treatments. Generally, the model was sensitive enough to respond to application at different rate and timing of both manure and NH4NO3-N. The calibrated model provided predictions for yield, biomass, soil nitrate, plant N uptake and N balance at acceptable resolution (coefficient of determination R2, the Nash-Sutcliffe modeling efficiency EF and d index were greater than 0.56). Simulated N balance reveals that only 24% of applied total N in litter becomes available to plant in the first growing season regardless of timing. Repeated application of litter in the same field increased plant N availability to 40% and 45% in the second and third years, respectively. Twenty three percent of the total N in litter applied over the three years was left in soil after harvest in the third year. Poultry litter lost 21% of its fertilizer potency when it is applied in the fall to fertilize spring-planted corn. Leaching and denitrification are the pathways of nitrogen loss. On average across the three years, fall application of 18 Mg/ha litter lost 54 kg N/ha more than spring application of the same rate, whereas application of 9 Mg/ha litter lost 59 kg N/ha regardless of the application timing. RZWQM2 is an unique, efficient and reliable tool for development of manure best management practices.