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

High density animal production systems, such as management intensive grazin g (MIG), can have a negative effect on water quality. Learning to manage su ch systems to minimize water quality impacts is essential for the environme ntal and economic sustainability of these types of animal production system s. Management intensive grazing is a grazing system in which animals at a h igh stocking density are rotated through several paddocks at short time int ervals (12-24 h) so that animal performance is maximized. Although MIG has the potential to increase dairy farm profitability in the northeast US, rec ent work in this region has shown that a substantial amount of N applied as fertilizer is leached below the root zone of orchardgrass (Dactyls glomera ta L., (cv.) 'Pennlate') managed as an intensive pasture. How much N is lea ched from other forage species managed as intensive pasture under the clima tic conditions of the northeast US is not known. A field study was conducte d using large drainage lysimeters to measure NO3-N leaching loss from six p asture swards: orchardgrass + N, orchardgrass + alfalfa (Medicago sativa L. , (cv.) Alfagraze), orchardgrass + Ladino type white clover (Trifolium repe ns L.), Ryegrass (Lolium perrene L, (cv.) Citadel) + N, ryegrass + alfalfa, and ryegrass + white clover. The study site was located in central Pennsyl vania on a Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalf). Nitrate-N leaching losses were most consistent under N fertilized swards wh ere the amount of N could be adjusted for yearly weather conditions. In a d rought year, NO3-N leaching increased dramatically in swards containing alf alfa or white clover. Sward type and stocking density need to be taken into consideration when developing an animal production system that will be bot h environmentally and economically sustainable. (C) 2000 Published by Elsev ier Science B.V. All rights reserved.