Effects of alum and aluminum chloride on phosphorus runoff from swine manure

Phosphorus (P) runoff from fields fertilized with swine (Sus scrofa domesti cus) manure may contribute to eutrophication. The objective of this study w as to evaluate the effect of aluminum sulfate (alum) and aluminum chloride applications to swine manure on P runoff from small plots cropped to tall f escue (Festuca arundinacea Shreb.). There were six treatments in this study : (i) unfertilized control plots, (ii) untreated manure, (iii) manure with alum at 215 mg Al L-1, (iv) manure with aluminum chloride at 215 mg Al L-1, (v) manure with alum at 430 mg Al L-1, and (vi) manure with aluminum chlor ide at 430 mg Al L-1. Manure application rates were equivalent to approxima tely 125 kg N ha(-1). Alum and aluminum chloride additions lowered soluble reactive phosphorus (SRP) levels from about 130 mg P L-1 to approximately 3 0 mg P L-1 at low rates. At high rates, SRP levels in swine manure were aro und 1 mg P L-1. Soluble reactive P concentrations in runoff were 5.50, 3.66 , 3.00, 0.87, 0.87, and 0.55 mg P L-1, for normal manure, low alum, low alu minum chloride, high alum, high aluminum chloride, and unfertilized control plots, respectively. Hence, high alum and aluminum chloride reduced SRP co ncentrations in runoff by 84% and were not statistically different from SRP concentrations in runoff from unfertilized control plots. These data indic ate that treating swine manure,vith alum or aluminum chloride could result in significant reductions in nonpoint-source P runoff.