|Powell, J Mark|
Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2001
Publication Date: N/A
Citation: Interpretive Summary: The survival of many dairy operations increasingly depends on the farmers' ability to comply with environmental regulations, especially those associated with phosphorus (P) management. Very little information exists on how feeding practices affect other system components (crops and soils) and the overall impact of livestock numbers on nutrient cycling under farmer conditions. A survey of 98 representative dairy farms in Wisconsin showed that approximately 50% of the farms, or those having stocking densities of less than 1.07 cows per hectare were self-sufficient in feed (alfalfa, corn silage and grain) production, and imported only protein and mineral supplements. Most (85%) of the surveyed dairy farms fed P in excess of the recently updated National Research Council (NRC) requirements, and 40% of the farms had more manure P than what was required by their crops. On these P surplus farms, lowering dietary P to the levels recommended by the NRC would reduce the number of farms having a positive P balance by 67%, and the amount of land in positive P balance by 60%. The only feasible strategies for achieving P balance on farms having a high animal stocking rate may be manure export, the addition of cropland for manure spreading, and/or reductions in livestock (cow and/or heifer) numbers. Workshops with farmers, their nutrient management consultants and veterinarians focused on the results of this on-farm research, and to explore opportunities and constraints farmers face in reducing dietary P to recommended levels. Recent extension updates report reductions in dietary P levels on Wisconsin dairy farms. Some of the study results have been incorporated into University of Wisconsin Cooperative Extension publications. The survey instrument used to collect information on P feeding practices of dairy farms has been widely requested and has been adapted for use in Iowa, Ohio, Pennsylvania and Wisconsin.
Technical Abstract: Nutrient management regulations for livestock operations are focused on a farm¿s ability to recycle the phosphorus (P) contained in manure. Most efforts to improve dairy manure management emphasize manure handling, storage, and land application techniques. Little is known about relationships between dairy feeding practices and manure P excretion under farm conditions, or between herd size, cropland area and a farm¿s ability to recycle manure P through crops. A survey of 98 representative dairy farms in Wisconsin showed that most farms were self-sufficient in forage (alfalfa, corn silage) and grain production. Stocking rates ranged from 0.45 to 2.57 cows per hectare. Farms having stocking rates of less than 1.07 cows per hectare were self-sufficient in feed production. Approximately 50% of the farms were self-sufficient in feed production, 68% produced 90% of their feed and 80% produced 80% of their annual feed requirement. The P content (DM basis) of the dairy diet ranged from 2.3 to 8.5 with an average of 4.0 g P kg-1. Approximately 85% of the surveyed dairy farms fed P in excess of the recently updated National Research Council (NRC) requirements. There was a good relationship between dietary P and manure P. Of the annual manure P excreted by cows fed a diet supplement, approximately two-thirds was derived from homegrown feeds and one-third from imported mineral and protein supplements. Approximately 40% of the farms had a positive P balance (manure P exceeds harvested crop P). On these farms, lowering dietary P to the levels recommended by the NRC would reduce the number of farms having a positive P balance by 67% and the amount of land in positive P balance by 60%. For farms having a high animal stocking rates, manure export, the addition of cropland for manure spreading, and reductions in livestock (cow and/or heifer) numbers are the only feasible options for achieving P balance.