Effect of poultry litter and composts on soil nitrogen and phosphorus availability and corn production

Environmental problems associated with raw manure application might be mitigated by chemically or biologically immobilizing and stabilizing soluble phosphorus (P) forms. Composting poultry litter has been suggested as a means to stabilize soluble P biologically. The objectives of this study were to assess the nutrient (N, P) value of different-age poultry litter (PL) composts relative to raw poultry litter and commercial fertilizer and determine effects of poultry litter and composts on corn (Zea mays) grain yield and nutrient uptake. The research was conducted for two years on Maryland's Eastern Shore. Six soil fertility treatments were applied annually to a Matapeake silt loam soil (Typic Hapludult): (1) a check without fertilizer, (2) NH₄NO₃ fertilizer control (168 kg N ha^-1), (3) raw poultry litter (8.9 Mg ha^-1), (4) 15-month old poultry litter compost (68.7 Mg ha^-1), (5) 4-month old poultry litter compost (59 Mg ha^-1) and (6) 1-month old poultry litter compost (64 Mg ha^-1). We monitored changes in available soil NO₃-N and P over the growing season and post harvest. We measured total aboveground biomass at tasseling and harvest and corn yield. We determined corn N and P uptake at tasseling. Patterns of available soil NO₃-N were similar between raw PL- and NH₄NO₃ fertilizer-amended soils. Little NO₃-N was released from any of the PL composts in the first year of study. The mature 15-month old compost mineralized significant NO₃-N only after the second year of application. In contrast, available soil P was highest in plots amended with 15-month old compost, followed by raw PL-amended plots. Immature composts immobilized soil P in the first year of study. Corn biomass and yields were 30% higher in fertilizer and raw PL amended plots compared to yields in compost-amended treatments. Yields in compost-amended plots were greater than those in the no-amendment control plots. Corn N and P uptake mirrored patterns of available soil NO₃-N and P. Corn P uptake was highest in plots amended with 15-month old compost and raw PL, even though other composts contained 1.5-2 times more total P than raw PL. There was a linear relationship between amount of P added and available soil P, regardless of source. The similar P availabilities from either raw or composted PL, coupled with limited crop P uptake at high soil P concentrations, suggest that raw and composted PL should be applied to soils based on crop P requirements to avoid build-up of available soil P.