ASSESSMENT, SELECTION, AND TARGETING BEST MANAGEMENT PRACTICES TO MINIMIZE THE IMPACTS OF MANURES AND PHOSPHORUS ON SURFACE WATER QUALITY

Authors: Sharpley, Andrew; Kleinman, Peter; Weld, Jennifer

Submitted to: New Zealand Journal of Agricultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2004
Publication Date: 12/15/2004
Citation: Sharpley, A.N., Kleinman, P.J.A., Weld, J.L. 2004. Assessment, selection, and targeting best management practices to minimize the impacts of manures and phosphorus on surface water quality. New Zealand Journal of Agricultural Research. 47:461-477.

Interpretive Summary: Phosphorus is an essential nutrient for crop and animal production, which when transferred from land to fresh water, can accelerate eutrophication - the increased growth of undesirable algae and aquatic weeds leading to oxygen shortages caused by their death and decomposition. Recent assessments of water quality status have identified eutrophication as one of the most ubiquitous water quality impairment in the U.S., Europe, and Australasia. The intensification of farming systems has resulted in local accumulations of phosphorus in some agricultural watersheds with related increases in the loss of phosphorus in runoff. In most cases, continual land application of manure at rates exceeding crop phosphorus removal is the main cause of phosphorus runoff. To alleviate related water quality impairments, conservation measures (i.e., Best Management Practices) to control phosphorus losses are now a requirement of farm nutrient planning. These measures include balancing phosphorus imports and exports, improved livestock feed management, chemical and physical treatment of manures, appropriate rate, method, and timing of land application based upon regular soil and manure testing, adequate manure storage and transport infrastructure, and composting. Conservation practices are also available to reduce runoff and erosion via practices such as conservation tillage, contour plowing, and vegetative filter strips. Ultimately, system-level changes in farm and regional phosphorus balances are required to check the effects of long-term localized phosphorus accumulations. Even when nutrient balances are maintained, phosphorus transfers from land to water are possible. Because manure contains high concentrations of nutrients in ratios inconsistent with crop demands, prudent land application of manure requires a holistic approach to phosphorus management. We demonstrate that tools such as the Phosphorus Index elucidate opportunities for improved management of land applied manure.

Technical Abstract: Phosphorus (P), an essential nutrient in crop and livestock agriculture, can accelerate freshwater eutrophication. Intensification of farming systems has resulted in local accumulations of P in some agricultural watersheds with related increases in P runoff. In most cases, continual land application of manure at rates exceeding crop P removal is the proximate cause of P runoff. To mitigate associated water quality impairments, P-based agricultural Best Management Practices (BMPs) are now a requirement of farm nutrient planning. This planning involves the selection, timing, and implementation of source and transport BMPs at field, farm, and watershed scales. Source measures include balancing P imports and exports, improved livestock feed management, chemical and physical treatment of manures, appropriate rate, method, and timing of land application based upon regular soil and manure testing, adequate manure storage and transport infrastructure, and composting. Transport measures aim to reduce runoff and erosion via practices such as conservation tillage, contour plowing, and vegetative filter strips. To be effective, these measures must be carefully selected and targeted to areas at greatest risk to P loss. This vulnerability can be identified and ranked by P Indices, which account for source and transport factors controlling P loss. We demonstrate that the P index can provide flexible yet reliable manure management and provide farmers with options to minimize the risk of P loss from several farms in Pennsylvania, U.S. Overall, a comprehensive and holistic approach to manure management can decrease P transfers from land to water.