Phosphorus and ammonium concentrations in surface runoff from grasslands fertilized with broiler litter.

Application of broiler (Gallus gallus domesticus) litter to grasslands can increase ammonium (NH4-N) and dissolved reactive phosphorus (DRP) concentrations in surface runoff, but it is not known for how long after a broiler litter application that these concentrations remain elevated. This long-term study was conducted to measure NH4-N and DRP in surface runoff from grasslands fertilized with broiler litter. Six 0.75-ha, fescue (Festuca arundinacea Schreb.-)bermudagrass [Cynodon dactylon (L.) Pers.] paddocks received broiler litter applications in the spring and fall of 1995-1996 and only inorganic fertilizer N in the spring of 1997-1998. Surface runoff from each paddock was measured and analyzed for NH4-N and DRP. Broiler litter increased flow-weighted NH4-N and DRP concentrations from background values of 0.5 and 0.4 mg L(-1), respectively, to values > 18 mg L(-1) in a runoff event that took place immediately after the third application. Ammonium concentrations decreased rapidly after an application and were not strongly related to time after application or runoff volume. In contrast, DRP concentrations tended to decrease more slowly, reaching values near 1 mg L(-1) by 19 mo after the last application. Dissolved reactive P concentrations decreased linearly with the natural logarithm of days after application (p<0.03), and increased linearly with the natural logarithm of runoff volume (p<0.0001).