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

Many aspects of the denitrification process in pasture ecosystems remain po orly investigated, especially as affected by application of animal manures. Denitrification can be, however, a major pathway of N loss from soil, decr easing efficiency of N fertilizers, as well as contributing to global warmi ng and ozone depletion. We quantified N loss via denitrification from tall fescue (Festuca arundinacea Schreb.) pastures following fertilization with broiler litter. Study sites were located in the Coastal Plain (Alabama), Pi edmont (Georgia), and Cumberland Plateau (Tennessee) Major Land Resource Ar eas of the southeast USA. Litter was applied to supply 70 kg of available N hs-L 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) u sing an in-situ acetylene-inhibition technique. Denitrification flux was hi ghly 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 signi ficantly; higher than those from control plots. Denitrification rates at th ese sites were not predictable by any one factor, but seemed to respond onl y to combinations of various factors such as soil temperature, soil NO3 con centration, and soil,vater content. Our results indicate that risk of N los s and atmospheric pollution due to denitrification from soils in the southe astern USA is not significantly increased by application of broiler litter at appropriate rates.