title: Diet modification to reduce phosphorus surpluses: a mass balance approach.
abstract: Diet modification to reduce phosphorus (P) concentrations in manures has been developed in response to environmental concerns over P losses from animal agriculture to surface waters. We used USDA-NASS statistics on animal numbers and crop production to calculate county scale mass balances for manure P production, P removed in harvested portion of crops, and the potential effects of diet modification. Although spreading manure evenly over all crop acreage within a county is unlikely to occur, these calculations give a good indication as to the impact diet modification to reduce P can have at a regional or national scale. There was a high degree of regional variability in manure P surpluses (e.g., with the large crop acreages in the grain belt leading to large P offtake in crops preventing most P surpluses). In 89% of counties, there was a deficit of manure P relative to crop P removal; therefore there was a manure P surplus in 11% of counties. Diet modification decreased the percentage of states with a manure P surplus from 11 to 8%, a decrease of approximately 27%. Diet modification decreased the percentage of counties with the greatest surpluses of manure P (>30 kg ha(-1)) from 3% of all counties to 1%. Diet modification to decrease manure P is an important part of strategies to alleviate environmental concerns associated with surplus manure P in many areas, but additional strategies to deal with manure P surpluses are needed in some areas.
authors.affiliation: Department of Crop and Soil Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, USA. rmaguire@vt.edu
authors.forename: R O
authors.initials: RO
authors.lastname: Maguire
authors.forename: D A
authors.initials: DA
authors.lastname: Crouse
authors.forename: S C
authors.initials: SC
authors.lastname: Hodges
mesh_terms: D000383:Agriculture; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D005247:Feeding Behavior; D008372:Manure; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism*; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry; D014481:United States; D014876:Water Pollution / Q000517:prevention & control*
chemical_list: D008372:Manure; D012989:Soil Pollutants; D010758:Phosphorus