Long-Term (20 year) Studies on the Effects of Alum Additions to Poultry Litter on Soil Test Phosphorus and Leaching.

Treating poultry litter with aluminum sulfate (alum) has been shown to reduce phosphorus (P) runoff and ammonia (NH₃) emissions.  Two 20 year studies, a paired-watershed experiment and a small plot study, were initiated in 1995 to compare the long-term effects of alum-treated litter to untreated litter on P availability, runoff and leaching. While the watershed study only had two treatments (alum-treated and untreated litter), the small plot study had 13 treatments with four replications per treatment, which included an unfertilized control, four rates of alum-treated litter, four rates of untreated litter and four rates of ammonium nitrate.  Alum-treated litter applications resulted in significantly higher Mehlich III P (M3-P) and significantly lower water extractable P (WEP) in surface soils samples, compared to untreated litter.  Subsurface (10-50 cm) soil M3-P values were 266% higher in plots fertilized with untreated litter (331 kg M3-P ha^-1) than alum-treated litter (124 kg M3-P ha^-1), indicating alum additions greatly reduced P leaching.  Total P loads in runoff were 231% higher in from untreated litter (1.87 kg ha^-1) than that fertilized with alum-treated litter (0.81 kg P ha^-1) in the paired watershed study.  This research indicates that adding alum to poultry litter provides long-term benefits to P conservation and water quality.