REDUCTION OF PHOSPHORUS IN RUNOFF FROM FIELD-APPLIED POULTRY LITTER USING CHEMICAL AMENDMENTS

Field applications of poultry litter at rates to meet forage N requirements normally result in an over-appiication of P. Chemical amendments have the potential to reduce the solubility of manure P through precipitation and/or adsorption reactions. This study was conducted to determine the effects of two chemical amendments, alum (Al-2 (SO4)(3).14H(2)O) and ferrous sulfate (FeSO4.7H(2)O), on P concentrations and load in runoff and to evaluate the effects of amended litter on forage production. Litter was broadcast applied to fescue (Festuca arundinacea Schreb.) plots at 11.2 Mg ha(-1) alone and in combination with alum or ferrous sulfate (1:5 amendment/litter). Rainfall simulators were used to produce three runoff events at 2, 9, and 16 d after litter application. Alum reduced the P concentrations in runoff by 87 and 63% of that from litter alone for the first and second runoff events, respectively, whereas ferrous sulfate decreased runoff P concentration by 77 and 48%, respectively. Both chemical amendments resulted in significant reductions (P < 0.05) in total P load for the first runoff event. Litter application significantly increased fescue yields, with total forage yield having the greatest response to alum-amended litter. Mean forage yield with alum amended litter was 2358 kg ha(-1), compared with a mean yield of 1847 kg ha(-1) with litter alone. This was probably due to decreased NH3 volatilization with the alum treatment. The combination of decreased P loss and increased forage yields suggest that alum-amended Litter has substantial promise for use as an environmental and economic management tool in the poultry industry.