Reducing Phosphorus Runoff from Swine Manure with Dietary Phytase and Aluminum Chloride

Phosphorus (P) runoff from fields fertilized with swine ( Sus scrofa ) manure has been implicated in eutrophication. Dietary modification and manure amendments have been identified as best management practices to reduce P runoff from manure. This study was conducted to compare the effects of dietary modification and aluminum chloride (AlCl 3 ) manure amendments on reducing P in swine manure and runoff. Twenty‐four pens of nursery swine were fed either a normal diet or a phytase‐amended diet. Each pen was connected to a separate manure pit, which was treated with AlCl 3 to give final concentrations in the liquid manure of 0 (control), 0.25, 0.50, or 0.75% (v/v). Manure was collected and applied to plots cropped with tall fescue ( Festuca arundinacea Schreb.), and simulated rainfall was applied at 50 mm h −1 , sufficient to generate a minimum of 30 min of continuous runoff. Samples of manure and runoff were analyzed for P and Al concentrations. Phytase reduced manure soluble reactive phosphorus (SRP) by 17%, while AlCl 3 reduced manure SRP by as much as 73% compared with normal manure. Phosphorus runoff was reduced from 5.7 to 2.6 mg P L −1 (a 53% reduction) using AlCl 3 The mean SRP concentration in runoff from phytase diets without AlCl 3 was 7.1 mg P L −1 during the first rainfall simulation. When phytase and AlCl 3 were used together, both manure SRP and P runoff were reduced more than if either treatment were used without the benefit of the other. Use of AlCl 3 did not increase soluble Al in manure or Al lost in runoff. Results from this study indicate that producers should use dietary manipulation with phytase and AlCl 3 manure amendments to reduce potential P losses from fields fertilized with swine manure.