Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2006
Publication Date: 1/1/2007
Citation: Moore Jr, P.A., Edwards, D.R. 2007. Long-term effects of poultry litter, alum-treated litter and ammonium nitrate on phosphorus availability in soils. Journal of Environmental Quality. 36:163-174. Interpretive Summary: Phosphorus runoff from animal manure, such as poultry litter, is perceived as the biggest environmental problem caused by animal agriculture. Treating poultry litter with alum has been shown to both decrease phosphorus runoff and reduce ammonia emissions. The objective of this study was to compare the long-term effects of alum-treated litter to normal poultry litter and ammonium nitrate. Two ten year studies were conducted; one using 52 small plots, the other using paired watersheds. The 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 than alum-treated litter. Phosphorus runoff was highly correlated to the amount of soluble P applied. This research, along with other long-term studies conducted on this practice, indicate that this is a long term, sustainable solution to the P runoff problem.
Technical Abstract: Several studies have shown that alum (Al2(SO4)3.14H2O) additions to poultry litter result in significantly lower ammonia (NH3) volatilization and phosphorus (P) runoff than from untreated litter. However, the long-term effects of fertilizing with alum-treated litter on P availability in soils were heretofore unknown. The objectives of this study were to evaluate the long-term effects of normal poultry litter, alum-treated litter and ammonium nitrate (NH4NO3) on P availability in soils, P leaching, P runoff and P uptake by tall fescue. Two long-term studies were initiated in 1995; a small plot study and a paired watershed study. In the small plot study 13 fertilizer treatments (unfertilized control, four rates of normal litter, four rates of alum-treated litter and four rates of NH4NO3) were broadcast applied to small plots cropped to tall fescue (Festuca arundinacea Schreb.) annually in the spring. Poultry litter application rates were 0, 2.24, 4.49, 6.73, and 8.98 Mg ha**-1 (0, 1, 2, 3, and 4 tons acre**-1); NH4NO3 rates were 65, 130, 195 and 260 kg N ha**-1. Mehlich III and water extractable P (WEP) in surface soil samples (0-5 cm) were monitored throughout the ten year period. In the paired watershed experiment, two watersheds (0.405 ha) were constructed in 1994 using earthern berms. Both watersheds were equipped with flumes and automatic water samplers. Results of the small plot study showed that while WEP in surface soil samples was significantly higher in soils fertilized with normal poultry litter, Mehlich III tended to be higher in soils fertilized with alum-treated litter after about six years. We hypothesized that this was due to higher P leaching from normal litter, hence, during year seven soil samples were taken from 0-5, 5-10, 10-20, 20-30, 30-40, and 40-50 cm and analyzed for WEP and Mehlich III. The results showed that Mehlich III P was only higher in the surface 0-5 cm for the soils fertilized with alum-treated litter; at the lower depths it was much higher in the soils receiving normal litter, indicating alum reduces P leaching. Tall fescue P 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.