Whole-Farm Phosphorus Management in West Virginia Beef Cattle Operations

Demand for animal proteins is increasing worldwide, spurring an increase in forage based agricultural production. Forage based agriculture utilizes grass and legume crops from areas which are not suited for row-crop production to feed ruminant animals. These systems provide increased animal proteins to consumer markets, while using minimal amounts of cereal crops that would otherwise be used for human consumption. However, forage based agriculture does not come without a risk of environmental degradation. The US EPA determined that agriculture non-point source (NPS) pollution is among the top three causes of phosphorus (P) related surface water impairment and accounts for an estimated 38% of land degradation worldwide. A lack of conservation planning is the largest cause of P impairment. In an effort to improve operation management, USDA NRCS is providing cost assistance for comprehensive nutrient management plans (CNMP), heavy use area protection (HUAP), and waste storage facilities (WSF). During the initial planning process for all of these practices, assumptions are made for manure P concentration based on engineering book values, which were been reported to have errors from 20 to 100% of analysis values. Current categorizations are based either on herd size or gross farm profit rather than distinguishing management characteristics. A new categorization system has been developed using dry-lot feeding as the distinguishing characteristic. Twelve cow-calf operations in West Virginia, with 16 different WSFs, collectively, were sampled. Four of the 12 operations did not dry-lot feed and were considered to be basic operations; all others were considered complex. To determine if these categories were different, a nutrient mass balance (NMB) was calculated for five of the operations. Basic operations (n=3) had a mean phosphorus use efficiency of 0.02 kg P/kg animal produced, while complex operations (n=2) had a mean use efficiency of 0.11 kg P/ kg animal produced. Based on this new categorization system, manure P book value and manure P analysis were compared. For basic operations (n=4) mean book value manure P concentration was 0.74 kg P/MT, was statistically different (p \u3c0.01) than the actual mean analysis of 1.19 kg P/MT, a difference of 61%. Complex operations (n=12) mean book value P concentration was 0.78 kg P/MT, also different from the actual mean analysis (p \u3c0.01) of 1.95 kg P/MT, a difference of 145%. It is suggested that future HUAP and WSF structures be sized based on the proposed categorization method and resulted manure P concentrations