NITROGEN MINERALIZATION RATES AND PHOSPHORUS AVAILABILITY OF COMPOSTED AND UNCOMPOSTED POULTRY LITTER

Abstract

Production of large numbers of chickens (Gallus gallus domesticus) in the Chesapeake Bay watershed has resulted in application of large quantities of poultry litter and manure to agricultural land. Poultry litter has been applied to land based on N concentration in litter and on crop requirements for nitrogen. Consequently, phosphorus has been applied (in poultry litter) at rates that exceed crop uptake. Excess nutrient applications combined with nutrient movement by erosion and leaching threaten the health of the Chesapeake Bay. The incubation study reports N and P availability from poultry litter in a controlled environment. The effect of source and application rate of poultry litter (composted (CPL) or fresh (FPL)), on N mineralization and availability of P in 3 soil types was determined. Fresh and composted litter from 2 sources (Dorchester County, Maryland on the Delmarva peninsula and Moorefield, West Virginia) were used. Two rates of litter application were based on nitrogen requirements of peach trees and N concentrations in litter. The soils were representative of the Delmarva peninsula and eastern WV. N mineralization (percent total organic N converted to inorganic (NH₄-N and NO₃-N) nitrogen) rates were higher for fresh litter (range of 32 to 72%) than composted litter (range of -6 to 10%). The N mineralization rate from fresh litter from the Delmarva peninsula was consistently lower than the fresh litter from Moorefield, WV. Since the C:N ratios were similar for the 2 fresh litters, causes for the source effects in N mineralization are unknown, but may be due to differences of uric acid, bedding materials, and feed content. N mineralization rates of fresh litter were lowest in clay and higher in sand and silt. N mineralization rates in composted litter from both sources were not significantly different within each soil type (7 to 10% in sand, 1 to 8% in silt and -6 to 3% in clay). This result is striking since the length of time that the litter was composted and the source materials (litter and carbon added) at the two composting facilities were completely different. N mineralization rates of fresh and composted litter were not affected by application rates. The high application rate was the equivalent of 270 lb of N per acre and the low application rate was 50% that amount. Water soluble phosphorus (WSP) extracted was similar in soils amended with composted litter from WV and fresh litter from both sources. Double acid soluble phosphorus (DAP) was similar in soils amended with WV fresh litter and composted litter from both sources. These results suggest that WSP and DAP availability was not affected by the composting process in WV and was therefore as available in composted poultry litter as in fresh poultry litter. Nutrient management practices by growers who apply large amounts of composted litter to provide adequate nitrogen for crop growth and yields may need to consider P availability to comply with legislation of non-point (agricultural) sources of nutrients.