Denitrification from fescue pastures in the southeastern USA fertilized with broiler litter

Many aspects of the denitrification process in pasture ecosystems remain poorly investigated, especially as affected by application of animal manures. Denitrification can be, however, a major pathway of N loss from soil, decreasing efficiency of N fertilizers, as well as contributing to global warming and ozone depletion. We quantified N loss via denitrification from tall rescue (Festuca arundinacea Schreb.) pastures following fertilization with broiler litter. Study sites were located in the Coastal Plain (Alabama), Piedmont (Georgia), and Cumberland Plateau (Tennessee) Major Land Resource Areas of the southeast USA. Litter was applied to supply 70 kg of available N ha^-1 based on equations developed by the USDA and the USEPA. Measurements were taken every 2 wk during the course of 2 yr (1995-1996 and 1996-1997) using an in-situ acetylene-inhibition technique. Denitrification flux was highly variable, ranging from -20 to 2500 mg N gas m^-2 h^-1. Total losses of N gas were all <6 kg ha^-1 during 150 d after application, representing a loss of <5% of total N applied. Losses from treated plots were not significantly higher than those from control plots. Denitrification rates at these sites were not predictable by any one factor, but seemed to respond only to combinations of various factors such as soil temperature, soil NO₃ concentration, and soil water content. Our results indicate that risk of N loss and atmospheric pollution due to denitrification from soils in the southeastern USA is not significantly increased by application of broiler litter at appropriate rates.