Water quality implications of nitrate leaching from intensively grazed pasture swards in the northeast US

Abstract

High density animal production systems, such as management intensive grazing (MIG), can have a negative effect on water quality. Learning to manage such systems to minimize water quality impacts is essential for the environmental and economic sustainability of these types of animal production systems. Management intensive grazing is a grazing system in which animals at a high stocking density are rotated through several paddocks at short time intervals (12–24 h) so that animal performance is maximized. Although MIG has the potential to increase dairy farm profitability in the northeast US, recent work in this region has shown that a substantial amount of N applied as fertilizer is leached below the root zone of orchardgrass ( Dactyls glomerata L., (cv.) ‘Pennlate’) managed as an intensive pasture. How much N is leached from other forage species managed as intensive pasture under the climatic conditions of the northeast US is not known. A field study was conducted using large drainage lysimeters to measure NO 3–N leaching loss from six pasture swards: orchardgrass + N, orchardgrass + alfalfa ( Medicago sativa L., (cv.) Alfagraze), orchardgrass + Ladino type white clover ( Trifolium repens L.), Ryegrass ( Lolium perrene L, (cv.) Citadel) + N, ryegrass + alfalfa, and ryegrass + white clover. The study site was located in central Pennsylvania on a Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalf). Nitrate–N leaching losses were most consistent under N fertilized swards where the amount of N could be adjusted for yearly weather conditions. In a drought year, NO 3–N leaching increased dramatically in swards containing alfalfa or white clover. Sward type and stocking density need to be taken into consideration when developing an animal production system that will be both environmentally and economically sustainable.