Changes in Soil Test Phosphorus Levels on a Grazing Farm in the Chesapeake Bay Watershed

Abstract

Improved nutrient cycling and reduced soil nutrient accumulation are perceived benefits of management-intensive grazing. Some management-intensive practices, such as increased stocking rates, rapid rotations, and supplemental feeding, could affect the soil through nutrient additions and the concentration of grazing animals. In this case study of a beef cattle farm in the Chesapeake Bay watershed, we compared changes in soil test P levels resulting from a land use change (row crops and hay in the 1980s to management-intensive grazing from 1990 to 2010). Soil test P data from farm records maintained since 1980 were augmented with spatially explicit soil sampling in 1999, 2004, and 2010. Pastures on fields that had historically received manure and were used for corn silage production changed the most in soil test P (median of 132 mg/kg P in 1980 to 70 mg/kg in 2010). Median soil test P in fields used for corn grain production in the 1980s decreased by 30%, fields used for hay production decreased by 26%, and permanent pastures decreased by 17%. The decreases in soil test P may have resulted from less inorganic P imported for use on corn, redistribution of P around the farm, and fixation of P in the soil.