Technical Abstract: Phosphorus (P) runoff from animal manure is perceived as the biggest environmental problem caused by animal agriculture. Research has shown that alum additions to poultry litter result in significantly lower ammonia volatilization and phosphorus runoff, however, the long-term effects of this practice on P runoff are unknown. The objective of this study was to compare the long-term effects of alum-treated litter to normal poultry litter and ammonium nitrate on P availability in soils, P uptake by plants and P runoff. Two ten year studies were conducted; one using 52 small plots, the other using paired watersheds. Results from the small plot study showed that using alum-treated litter results in much lower soluble P in the soil, but may slightly increase Mehlich III P in soils. We hypothesized that the increase in Mehlich III P at the surface with alum-treated litter was due to more leaching from normal litter. During year 7 soil samples were taken from various depths and analyzed for water extractable and Mehlich III P. These data did show alum additions help prevent P leaching. The results from the paired watershed study showed that P runoff was 340% greater with normal litter contents were slightly lower in plants fertilized with alum-treated litter than normal litter, however, P uptake was not affected since forage growth was greater with alum. Results from the paired watershed study showed P runoff was approximately 340% higher for normal litter than alum-treated litter. Cumulative P runoff was highly correlated to the cumulative amount of soluble P applied, but not to cumulative total P applied or soil test P. This research indicates that alum additions to litter is long-term solution to reducing P runoff and leaching from poultry litter.