RELEASE OF NITROGEN AND PHOSPHORUS FROM POULTRY LITTER

In areas of intensive poultry production, large amounts of litter prod uced are often applied as fertilizer to local agricultural land. To as sess the agronomic and water quality implications of poultry litter ap plications, we quantified the effects of recurring, simulated rainfall (5 x 50-min rainfalls of 2.54 cm h(-1)) alternated with different dry ing temperatures (4, 20, 30, and 35 degrees C for 1 h) on the release of dissolved N and dissolved P from two types of poultry litter (pine bark shavings-and wheat straw-based). Amounts of litter leached were e quivalent 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 we re released by the end of five rainfalls (averaged for the two types o f poultry litter, and for all drying temperatures). Although the patte rn of N and P release from litter was similar for all drying periods, the magnitude of losses was a function of drying temperature. The aver age portion of total N present in the litters released as NH4-N during five rainfalls decreased from 22% for litter dried at 4 degrees C to 18% for litter dried at 35 degrees 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 degrees C to 10% at 35 degrees 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 s uggested that the timing of poultry Litter application should coincide with active periods of crop growth to combine maximum agronomic produ ctivity with minimum edge-of-field losses of N and P to surface and gr oundwaters. As much as 60% of the N and 40% of the P released during t he five rainfalls was lost during the first rainfall. This initial rap id N and P release stresses the importance of avoiding litter applicat ions during periods of heavy rainfall.