ARS | Publication request: Dairy heifer diets, manure management, and runoff phosphorus

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 19, 2011
Publication Date: January 10, 2012
Citation: Jokela, W.E., Coblentz, W.K., Hoffman, P.C. 2012. Dairy heifer diets, manure management, and runoff phosphorus. Meeting Proceedings. Vol 51.

Technical Abstract: Manure application to cropland can contribute to runoff losses of phosphorus and eutrophication of surface waters. We conducted a series of three rainfall simulation experiments to assess the effects of dairy heifer diet P, manure incorporation, application rate, and soil test P on runoff P losses from two successive rains. Bedded manure (18-21% solids) from dairy heifers offered diets with or without supplemental P was applied on a silt loam soil packed into 40 x 8-inch sheet metal pans. Manure was either surface-applied or incorporated (Experiment 1) or surface-applied at two rates (Experiment 2). Applied manure supplied a range of 75 to 180 lb P2O5 per acre for various manure P-level and application-rate combinations. Experiment 3 consisted of four similar soils without manure with Bray P1-extractable P levels of 11, 29, 51, and 75 ppm. We measured runoff volume, total and dissolved P, and solids in runoff collected for 30 min after runoff initiation from rain events one day and three or four days after manure application. Manure incorporation reduced total and dissolved P concentration and load by 85 to 90% compared to surface application. Doubling the rate of surface-applied manure increased runoff dissolved and total P concentrations an average of 60%. Phosphorus supplementation resulted in more water-extractable P in manure and 25 to 100% higher concentrations of dissolved P in runoff from surface-applied manure. Runoff dissolved P increased with increasing soil test P, particularly at the excessive (above optimum) levels. Overall, concentrations of total solids and total and dissolved P in runoff from Rain 2 were 25 to 75% lower than from Rain 1. These results show that large reductions in P runoff losses can be achieved by incorporation of manure, avoiding unnecessary diet P supplementation, limiting manure application rate, and avoiding soils with excessive P.