Water quality implications of dairy slurry applied to cut pastures in the northeast USA

Abstract. Nitrate nitrogen (NO₃-N) leaching from animal production systems in the northeast USA is a major non-point source of pollution in the Chesapeake Bay. We conducted a study to measure NO₃-N leaching from dairy slurry applied to orchardgrass ( Dactylis glomerata L., cv. Pennlate) using large drainage lysimeters to measure the direct impact of four rates of slurry (urine and faeces) N application (0, 168, 336, 672 kg N ha^?1 yr^?1) on NO₃-N leaching on three soil types. We then used experimentally-based relationships developed earlier between stocking density and NO₃-N leaching loss and leachate NO₃-N concentration to estimate the added impact of animal grazing. Nitrate N leaching losses from only dairy slurry applied at the 0, 158, 336, and 672 kg N ha^?1 yr^?1 rates were 5.85, 8.26, 8.83, and 12.1 kg N ha^?1 yr^?1, respectively with corresponding NO₃-N concentrations of 1.60, 2.30, 2.46, and 3.48 mg l^?1. These NO₃-N concentrations met the 10 mg l^?1 US EPA drinking water standard. However, when a scenario was constructed to include the effect of NO₃-N leaching caused by animal grazing, the NO₃-N drinking water standard was calculated to be exceeded.