Reduction of Phosphorus in Runoff from Field‐Applied Poultry Litter Using Chemical Amendments

Abstract

Field applications of poultry litter at rates to meet forage N requirements normally result in an over‐application 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 (Al₂ (SO₄)₃ · 14H₂O) and ferrous sulfate (FeSO₄ · 7H₂O), 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.