Reducing phosphorus runoff through diet modification and treatment of manure with aluminum amendments

Phosphorus (P) runoff from fields fertilized with animal manure may contribute to eutrophication of surface waters. Ammonia (NH 3) emissions from manure decreases animal production and can contribute to acid rain. The objectives of this study were to determine if dietary manipulation and/or addition of aluminum amendments to swine manure and poultry litter could reduce P runoff and NH3 volatilization. In order to meet these objectives three experiments were conducted. In the first two studies animals were grown with low P diets and aluminum amendments were added to the manure which was collected and used for rainfall simulation studies on small plots cropped to tall fescue. In the first study swine were fed either a normal or phytase diet, and manure pits for each pen were treated with liquid AlCl3 at 0, 0.25, 0.50 or 0.75% by volume. High levels of AlCl 3 reduced NH3 volatilization by as much as 52%, while phytase reduced NH3 volatilization by as much as 25% compared to the normal diet without AlCl3. Phosphorus runoff was reduced by as much as 42% using AlCl3, and increased by 25% when phytase was used without AlCl3. When both treatments were used together, NH3 volatilization was reduced by 59% and P runoff was reduced by 57%. In the second study, broilers were fed either normal, phytase, high available P (HAP) corn or HAP corn + phytase diets, and litter was treated with alum [Al 2(SO4)3·14H20] at 0 or 10% by weight between flocks. Phytase, HAP corn and alum reduced P runoff by as much as 42%, 26% and 57% respectively. Using phytase, HAP corn and alum together reduced P runoff by 66% compared to normal litter. A laboratory study using manure from all of these treatments confirmed results from runoff studies. Swine manure from phytase diets consistently increased P availability upon addition to soil. Results from this study indicate that animal producers should consider the use of both dietary manipulation and manure amendments to reduce potential nutrient losses associated with NH3 volatilization and P runoff.