Impact of Chemical Amendment of Dairy Cattle Slurry on Soil Phosphorus Dynamics Following Application to Five Soils

A 9-month incubation study was conducted to investigate the effectiveness of amending dairy cattle slurry with either alum, lime, poly-aluminum chloride (PAC), or ferric chloride (FeCl₃) in reducing water-extractable P (WEP) levels in five soils (four mineral and one organic). Alum, lime, and PAC were the most effective amendments in decreasing WEP (compared to a slurry-control) for the four mineral soils (by an average of 47% at the end the 9-month incubation period). In comparison, FeCl₃ increased WEP (compared to the slurry-control) by an average of 35% at the end the study. None of the amendments examined effectively reduced WEP of the organic soil. No amendment reduced soil-test P [(Morgan's P (P_m) and Mehlich 3 P (M3P)] compared to the soil-only treatment. Alum maintained the greatest levels of M3P across the four mineral soils with the least risk of P loss to overlying water.