title: Whole-farm nitrogen balance on western dairy farms.
abstract: 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.
authors.affiliation: Animal, Dairy, and Veterinary Sciences Department, 4815 Old Main Hill, Utah State University, Logan 84322-4815, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Spears
authors.forename: R A
authors.initials: RA
authors.lastname: Kohn
authors.forename: A J
authors.initials: AJ
authors.lastname: Young
mesh_terms: D000383:Agriculture; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002417:Cattle; D003612:Dairying; D004787:Environmental Pollution; D005308:Fertilizers; D007061:Idaho; D008372:Manure; D008460:Meat; D008892:Milk / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D009586:Nitrogen Fixation; D014589:Utah
chemical_list: D005308:Fertilizers; D008372:Manure; D009584:Nitrogen