ARS | Publication request: Dairy heifer manure management, dietary phosphorus, and soil test P effects on runoff phosphorus

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 14, 2012
Publication Date: August 8, 2012
Citation: Jokela, W.E., Coblentz, W.K., Hoffman, P.C. 2012. Dairy heifer manure management, dietary phosphorus, and soil test P effects on runoff phosphorus. Journal of Environmental Quality. https://www.agronomy.org/publications/aj.

Interpretive Summary: Manure application to cropland can contribute to runoff losses of phosphorus, which can lead to excessive algae growth in lakes and streams. We conducted a series of rainfall simulation experiments to assess the effects of phosphorus supplementation of dairy heifer diets, manure application method and rate, and soil test phosphorus on runoff phosphorus losses from two successive rains. Bedded manure from dairy heifers that were fed diets with or without supplemental phosphorus was applied on a silt loam soil packed 2 inches deep in 40 by 8-inch sheet metal pans. Manure was either surface-applied or incorporated (to simulate tillage; Experiment 1) or surface-applied at two rates (Experiment 2). Experiment 3 consisted of a similar soil without manure but with phosphorus soil test levels ranging from low to excessive. We measured runoff volume and total and dissolved phosphorus in runoff collected for 30 minutes after runoff started from simulated rain events one day and three or four days after manure application. Manure incorporation reduced total and dissolved phosphorus concentration by 85 to 90% compared to surface application. Doubling the manure rate increased the concentration of dissolved and total phosphorus an average of 60%. Phosphorus supplementation in the diet resulted in more phosphorus in manure, which led to higher concentrations of phosphorus (2 to 3 times as much in the dissolved form) in runoff. Dissolved phosphorus concentrations in runoff increased with increasing soil test phosphorus, particularly at the excessive (well above optimum) levels. Overall, concentrations of phosphorus in runoff from the second rain were 25 to 75% lower than from the first rain, suggesting that effects may diminish with time. These results show that large reductions in phosphorus runoff losses can be achieved by incorporation of manure when applying to cropland, by avoiding unnecessary dietary phosphorus supplementation, by limiting manure application rate, and by avoiding soils with excessive phosphorus when applying manure.

Technical 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 x 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-1. 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-1. 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-1) 3 or 4 d apart. Manure incorporation reduced TP and DRP concentrations and load by 85-90% compared to 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 three-fold. Concentrations of solids, TP, and DRP in runoff from Rain 2 were 25-75% 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.