Evaluating Cattle Manure Application Strategies on Phosphorus and Nitrogen Losses from a Florida Spodosol

Repeated application of cattle (Bos taurus) manure to agricultural areas often results in soil P accumulation, which may pose risks to surface waters. We evaluated seven different application strategies on P and N losses from an established bahiagrass (Paspalum notatum Flugge) pasture: control (no N applied); two N sources [manure alone or manure plus ammonium nitrate (AN) (50/50% combination)]; two application frequencies (single or split); and two N rates (200 and 400 kg N ha(-1)). Shallow groundwater P was monitored using piezometers installed at 60 cm (shallow wells) and 120 cm (deep wells). Surface runoff collectors were used to monitor runoff N and P from naturally occurring rainfall events. Soil samples were analyzed for Mehlich-1 P and KCI-extractable NH4-N and NO3-N concentrations. Application of manure in combination with AN suppressed leachate P, but no effect was observed on leachate NO3-N concentrations in the shallow wells. Application of manure alone or in combination with AN did not affect P and N concentrations in the deep wells. Applying manure plus AN resulted in approximately 50% reduction in runoff N and P loads than treatments receiving manure alone. Manure applied alone or in combination with AN increased soil test P in upper soil horizons relative to control plots. Conversely, application of either manure or manure plus AN had no effect on soil NH4-N and NO3-N concentrations. Results demonstrate that combining manure application with inorganic N fertilizer represents an environmentally sound application strategy to reduce soil P and N accumulation and subsequent risks of nutrient transport.