title: Dairy heifer manure management, dietary phosphorus, and soil test P effects on runoff phosphorus.
abstract: Manure application to cropland can contribute to runoff losses of P and eutrophication of surface waters. We conducted a series of three rainfall simulation experiments to assess the effects of dairy heifer dietary P, manure application method, application rate, and soil test P on runoff P losses from two successive simulated rainfall events. Bedded manure (18-21% solids) from dairy heifers fed diets with or without supplemental P was applied on a silt loam soil packed into 1- by 0.2-m sheet metal pans. Manure was either surface-applied or incorporated (Experiment 1) or surface-applied at two rates (Experiment 2) to supply 26 to 63 kg P ha. Experiment 3 evaluated runoff P from four similar nonmanured soils with average Bray P1-extractable P levels of 11, 29, 51, and 75 mg kg. We measured runoff quantity, total P (TP), dissolved reactive P (DRP), and total and volatile solids in runoff collected for 30 min after runoff initiation from two simulated rain events (70 mm h) 3 or 4 d apart. Manure incorporation reduced TP and DRP concentrations and load by 85 to 90% compared with surface application. Doubling the manure rate increased runoff DRP and TP concentrations an average of 36%. In the same experiment, P diet supplementation increased water-extractable P in manure by 100% and increased runoff DRP concentration threefold. Concentrations of solids, TP, and DRP in runoff from Rain 2 were 25 to 75% lower than from Rain 1 in Experiments 1 and 2. Runoff DRP from nonmanured soils increased quadratically with increasing soil test P. 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 managing soils to prevent excessive soil test P levels.
authors.affiliation: USDA-ARS, Dairy Forage Research Center, Marshfield, WI, USA. bill.jokela@ars.usda.gov
authors.forename: William E
authors.initials: WE
authors.lastname: Jokela
authors.forename: Wayne K
authors.initials: WK
authors.lastname: Coblentz
authors.forename: Patrick C
authors.initials: PC
authors.lastname: Hoffman
mesh_terms: D000818:Animals; D002417:Cattle; D004032:Diet; D005260:Female; D008372:Manure; D010758:Phosphorus / Q000032:analysis*; D011891:Rain; D012987:Soil / Q000032:analysis; D014876:Water Pollution / Q000032:analysis*
chemical_list: D008372:Manure; D012987:Soil; D010758:Phosphorus