J. Dairy Sci. 86:4178–4186 American Dairy Science Association, 2003. Whole-Farm Nitrogen Balance on Western Dairy Farms1

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 dair-ies in Utah and Idaho using the University of Maryland Nutrient Balancer. The average N balance, or unac-counted for N, was 81 tonnes per year for the average herd size of 466 cowswith 35.8 % of the inputs accounted for in the outputs. Themajor 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 af-fected by herd N utilization efficiency (kg feed N per kg product N), crop N utilization efficiency, and avail-ability 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. (Key words: nitrogen balance, commercial dairies, western United States) Abbreviation key: CNMP = comprehensive nutrient management plan, HNUE = herd nitrogen utilization efficiency,MNSE = manure nitrogen storage efficiency