Reducing phosphorus in dairy diets improves farm nutrient balances and decreases the risk of nonpoint pollution of surface and ground waters

Abstract

Abstract Reducing phosphorus (P) in dairy diets may result in different types of manure with different chemical composition. Application of these manures to soils may affect the soil P solubility and lead to different environmental consequences. A laboratory incubation study determined the impact of 40 dairy manures on P dynamics in two soil types, Mattapex silt loam (Aquic Hapludult) and Kalmia sandy loam (Typic Hapludult). The manures were fecal samples of lactating cows, collected from commercial dairy farms located in Northeastern and Mid-Atlantic United States, with a wide range of dietary P concentrations (from 2.9 to 5.8 g P kg−1 feed dry matter, DM). Dried and ground fecal samples were mixed with surface horizon (0–15 cm) of soils at 150 kg P ha−1 and the mixtures were incubated at 25 °C for 21 days. At the end of incubation, water soluble P (WS-P) and Mehlich-3 P (M3-P) in the soil–manure mixtures were substantially higher than the control (soil alone) but were lower than the soils receiving fertilizer KH2PO4 at 150 kg P ha−1. Similarly, the relative extractability of P in soils amended with low- and high-P manures was always lower (