Stout W L, Delahoy J E, Muller L D, Saporito L S
The United States Department of Agriculture/Agricultural Research Service, University Park, PA 16802, USA.
ScientificWorldJournal. 2001 Oct 9;1 Suppl 2:887-91. doi: 10.1100/tsw.2001.253.
Substantial amounts of nitrate nitrogen NO3-N can leach from intensively grazed pasture in the northeast U.S. where there is about 30 cm of groundwater recharge, annually. Management options for reducing NO3-N leaching were evaluated for this environment using the Cornell Net Carbohydrate and Protein System Model and a recently developed nitrogen leaching index. Management options utilizing energy supplementation of grazing dairy cows could improve nitrogen efficiency within the cow, but would not necessarily reduce NO3-N leaching at the pasture scale if stocking rate was not controlled. The management option of using white clover to supply nitrogen to the pasture decreased NO3-N leaching, but produced less dry matter yield, which in turn reduced stocking rate. The economic returns of reducing NO3-N with these options need to be evaluated in light of milk prices and commodity and fertilizer nitrogen costs. At current prices and costs, the economic benefit from the energy supplementation options is substantial.
在美国东北部，每年有大约30厘米的地下水补给，大量的硝态氮（NO3-N）会从过度放牧的牧场中淋溶出来。利用康奈尔净碳水化合物和蛋白质系统模型以及最近开发的氮淋溶指数，对这种环境下减少NO3-N淋溶的管理方案进行了评估。利用能量补充放牧奶牛的管理方案可以提高奶牛体内的氮效率，但如果不放牧率不受控制，不一定能在牧场规模上减少NO3-N淋溶。利用白三叶为牧场提供氮素的管理方案减少了NO3-N淋溶，但干物质产量较低，进而降低了放牧率。需要根据牛奶价格以及商品和化肥氮成本来评估这些方案减少NO3-N的经济效益。按照当前的价格和成本，能量补充方案的经济效益相当可观。
