Spears R A, Kohn R A, Young A J
Animal, Dairy, and Veterinary Sciences Department, 4815 Old Main Hill, Utah State University, Logan 84322-4815, USA.
J Dairy Sci. 2003 Dec;86(12):4178-86. doi: 10.3168/jds.S0022-0302(03)74033-8.
Environmental legislation has made it necessary for livestock producers to be able to quantify and adjust the N balance on their farms. Whole-farm N balance and efficiencies were computed for 41 commercial dairies in Utah and Idaho using the University of Maryland Nutrient Balancer. The average N balance, or unaccounted for N, was 81 tonnes per year for the average herd size of 466 cows with 35.8% of the inputs accounted for in the outputs. The major inputs for farms that grew crops (n = 23, herd size = 284 total cows) were imported feed (57.4% of all inputs) and nitrogen fixation (30% of inputs). The major outputs were animal products (primarily milk and some meat, 80% of outputs). For farms that grew no crops (n = 18, herd size = 700 total cows), 98% of the inputs were from imported feed. Of the outputs, 57% of the N was in animal products and 42.9% in manure and compost. Whole-farm balance per product for those farms that grew crops was most affected by herd N utilization efficiency (kg feed N per kg product N), crop N utilization efficiency, and availability of manure N applied to crops, while manure N storage efficiency was of lesser importance. For farms that grew no crops, whole-farm N balance per product was most affected by herd N utilization efficiency and manure N storage efficiency. Maximizing conversion of feed N to product N was the best way to reduce whole-farm N balance.
环境法规要求牲畜养殖者能够量化并调整其农场的氮平衡。利用马里兰大学养分平衡器，计算了犹他州和爱达荷州41个商业化奶牛场的全农场氮平衡和效率。对于平均牛群规模为466头奶牛的养殖场，平均氮平衡（即未核算的氮）为每年81吨，产出占投入的35.8%。种植作物的农场（n = 23，牛群总规模 = 284头奶牛）的主要投入是进口饲料（占所有投入的57.4%）和固氮（占投入的30%）。主要产出是动物产品（主要是牛奶和一些肉类，占产出的80%）。对于不种植作物的农场（n = 18，牛群总规模 = 700头奶牛），98%的投入来自进口饲料。在产出中，57%的氮存在于动物产品中，42.9%存在于粪便和堆肥中。对于种植作物的农场，每产品的全农场平衡受牛群氮利用效率（每千克产品氮的饲料氮千克数）、作物氮利用效率以及施用于作物的粪便氮的可用性影响最大，而粪便氮储存效率的重要性较低。对于不种植作物的农场，每产品的全农场氮平衡受牛群氮利用效率和粪便氮储存效率影响最大。将饲料氮转化为产品氮最大化是减少全农场氮平衡的最佳方法。
