Release of Nitrogen and Phosphorus from Poultry Litter

In areas of intensive poultry production, large amounts of litter produced are often applied as fertilizer to local agricultural land. To assess the agronomic and water quality implications of poultry litter applications, we quantified the effects of recurring, simulated rainfall (5 × 50-min rainfalls of 2.54 cm h⁻¹) alternated with different drying temperatures (4, 20, 30, and 35°C for 1 h) on the release of dissolved N and dissolved P from two types of poultry litter (pine bark shavingsand wheat straw-based). Amounts of litter leached were equivalent to a 10 Mg ha⁻¹ application, containing an average of 360 kg N ha⁻¹ and 158 kg P ha⁻¹. A total of 74 kg ha⁻¹ NH₄-N, which accounted for >95% of the dissolved N, and 14 kg ha⁻¹ inorganic P were released by the end of five rainfalls (averaged for the two types of poultry litter, and for all drying temperatures). Although the pattern of N and P release from litter was similar for all drying periods, the magnitude of losses was a function of drying temperature. The average portion of total N present in the litters released as NH₄-N during five rainfalls decreased from 22% for litter dried at 4°C to 18% for litter dried at 3S°C. This decrease was attributed to an increase in N volatilization at the higher temperature. Conversely, the portion of litter P released as dissolved inorganic P, increased from 8% at 4°C to 10% at 35°C. Thus, the influence of drying temperature on the release of N and P should be considered when determining the optimum timing of poultry litter application. It is suggested that the timing of poultry litter application should coincide with active periods of crop growth to combine maximum agronomic productivity with minimum edge-of-field losses of N and P to surface and groundwaters. As much as 60% of the N and 40% of the P released during the five rainfalls was lost during the first rainfall. This initial rapid N and P release stresses the importance of avoiding litter applications during periods of heavy rainfall.