Long-Term Effects of Alum-Treated Poultry Litter, Normal Litter and Ammonium Nitrate On Phosphorus Runoff and Leaching.

Previous studies have shown that additions of aluminum sulfate (alum) to poultry litter reduces ammonia emissions, lowers pathogen numbers in litter, reduces phosphorus (P) solubility in litter, and lowers P runoff from fields fertilized with litter.  Lower ammonia levels in poultry houses and reduced pathogens result in improved bird performance and reduced energy costs, as a result of lower ventilation requirements, making this best management practice (BMP) cost effective.  Two 20-year studies were initiated in the mid 1990’s to evaluate the long-term effects of alum-treated litter on P runoff, soil chemistry and crop growth.  The first study was a paired watershed experiment which was located on a broiler/beef farm in NW Arkansas.  The second study was a small plot study using 13 treatments with four replications per treatment, which included four rates of alum-treated litter, four rates of normal litter, four rates of ammonium nitrate and an unfertilized control.   Results from the watershed study showed alum reduced P loads in runoff by about 75% compared to normal litter.  Results from the small plot study indicated that P leaching was also dramatically reduced with alum.  After 13 years the Mehlich III extractable P (M3-P) at the 0-5 cm depth in plots receiving four tons of normal litter/acre annually was 317 mg P/kg, whereas the M3-P level in plots receiving the identical rate of alum-treated litter was 625 mg P/kg.  Extraction of soil samples with depth in these plots showed this was due to P leaching from normal litter.  Even though M3-P was higher in the surface soil with alum-treated litter, water extractable P and P runoff were both significantly lower when litter was treated with alum. These long-term studies provide further evidence that this is one of the few cost effective and sustainable BMPs that not only improves air, soil and water quality, but also improves poultry production and crop growth.