Influence of Soil Properties and Manure Sources on Phosphorus in Runoff during Simulated Rainfall

Runoff from agricultural fields amended with animal manure or fertilizer is a source of phosphorus (P) pollution to surface waters, which can have harmful effects such as eutrophication. The objectives of this study were to evaluate the impact of soil P status and the P composition of manure sources on P in runoff and characterize the effects of manure sources on mass loss of dissolved reactive P, total dissolved P, and total P in runoff. Soil boxes set at 5% slopes received 7.5cmh(-1) of simulated rainfall for 30min. Study soils included a Kenansville loamy sand (loamy siliceous subactive thermic Arenic Hapludults, a Coastal Plain soil) and a Davidson silt loam (kaolinitic thermic Rhodic Kandiudults, a Piedmont soil). Soil test P concentrations ranged from 16 to 283mg P kg(-1). Sources of P included broiler litter, breeder manure, and breeder manure treated with three rates of aluminum sulfate (Al-2(SO4)(3)) 0, 3.9, and 7.8kg m(-2), di-ammonium phosphate (DAP), and an un-amended control. All manure sources were surface applied at 66kg P ha(-1) without incorporation. Water extractable P represented an average of 10 +/- 6% total P in manure. Runoff samples were taken over a 30-min period. Piedmont soil contained greater amounts of clay, aluminum (Al), and iron (Fe) concentrations, and higher P sorption capacities that produced significantly lower dissolved reactive P, total dissolved P, and total P losses than the Coastal Plain soil. Runoff P loss did not differ significantly for low and high STP Coastal Plain soils. Water extractable P in manures accounted for all dissolved reactive P lost in runoff with dissolved reactive P correlating strongly with water extractable P concentration (r(2)=0.9961). Overall, manures containing the highest water extractable P concentrations contributed to the largest amounts of dissolved reactive P in runoff. Manure treated with 3.9 and 7.8kg m(-2) of Al-2(SO4)(3) (alum) decreased dissolved reactive P in runoff by 29%. While this soil box runoff study represents a worst-case scenario for P loss, highly significant effects of soil properties and manure sources were obtained. Management based on these results should help ameliorate harmful effects of P in runoff.