Changes in soil test phosphorus levels on a grazing farm in the Chesapeake Bay watershed

Authors: Sanderson, Matt; Gonet, Jeffery; Stout, Robert

Submitted to: Forage and Grazinglands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2011
Publication Date: 11/2/2011
Citation: Sanderson, M.A., Gonet, J., Stout, R. 2011. Changes in soil test phosphorus levels on a grazing farm in the Chesapeake Bay watershed. Forage and Grazinglands. doi:10.1094/FG-2011-1128-02-RS.

Interpretive Summary: Improved nutrient cycling along with less soil nutrient accumulation are perceived benefits of management-intensive grazing compared with traditional continuous stocking management and confined feeding systems. Recent efforts to develop total maximum daily loads for phosphorus (P) for the Chesapeake Bay watershed highlight grazing and pasture management as agricultural best management practices to reduce P loads. In this case study, we compiled 30 years of soil P data for a beef cattle farm in the Chesapeake Bay watershed. The dataset provided an opportunity to compare changes in soil P before and after a change from row crops and hay production to management-intensive grazing. Variation in soil test P among paddocks on the case study farm was related to cropping history, manure management, and grazing management. Soil test P levels in fields used for corn grain production decreased by 30%, fields used for hay production decreased by 26%, and permanent pastures decreased by 17% after conversion of the farm to grazing. The largest reductions in soil test P occurred on corn silage fields previously used for manure disposal. Farmers who convert cropland to pasture and adopt management-intensive grazing practices with lower inputs can stabilize or reduce soil test P levels in the long term and potentially increase profits. Graziers need to monitor soil fertility regularly and implement appropriate nutrient management practices.

Technical 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 resource 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 P levels before and after a change from row crops and hay production in the 1980s to management-intensive grazing during 1990 to 2010. Soil P data from detailed farm management records maintained since 1980 were augmented with spatially explicit soil sampling in 1999, 2004, and 2010. Pastures on fields that historically had received large amounts of manure and were used for corn silage production changed the most in soil test P (132 mg kg-1 P in 1980 to 70 mg kg-1 in 2010). Soil test P levels 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 probably resulted from less inorganic P imported for use on corn, increased off-take of P in hay and grazed forage, and perhaps redistribution of P around the farm from changes in cropping and grazing management.