Phosphorus in Virginia continues to be an important topic among crop, poultry and livestock production systems.
The draft TMDL proposal for the Chesapeake Bay provides aggressive reduction targets for nitrogen, phosphorus and sediment.
Virginia beef cow/calf production systems have an opportunity to limit phosphorus inputs and thus increase economic benefits while minimizing environmental impacts.
In the past, phosphorus has often been over-supplemented due to its once cheap cost and at the advice of many nutritionists and veterinarians.
However, as more emphasis is being placed on meeting, not exceeding, mineral requirements to be both economically and environmentally responsible, things are changing.
Recently, dietary Calcium (Ca): Phosphorus (P) ratios of between 1:1 to 7:1 have been shown to result in similar animal performance provided the phosphorus adequately meets requirements of the production system.
For the past several years, Virginia Tech Dairy Scientists have demonstrated that P levels in dairy rations can be decreased with no negative impact on milk production or reproduction.
The fundamental information needed to be precise in meeting a beef cow’s P requirement is her stage of production and an estimate of the P content of what she is consuming.
Early, more digestible, forage growth of spring and summer pastures are typically higher in phosphorus than the mature forage found in late summer and fall forage.
Forage analysis of Virginia grass hays has indicated as much as 10 fold difference in P content (.05-.60 percent). Forage maturity, fertilization and soil type would contribute to this variation.
According to NRC (1996), the P requirement for a 1,200 pound mature cow during pregnancy is .15% P, and during lactation when she is producing 20 lbs of milk, the requirement is .19% P. Feeding P above cattle requirements will not substantially increase retention; the excess P is excreted primarily in the manure.
In an effort to more accurately and efficiently supplement phosphorus, the Virginia Agricultural Council, Virginia NRCS and Virginia Cooperative Extension are cooperating on a project which is collecting information and samples from beef cattle farms in the Chesapeake Bay watershed counties.
Samples collected from participating farms will include soil, forage and fecal as well as a questionnaire regarding fertilization and supplementation practices.
Results returned to the cattleman will reflect P status and supplementation recommendations for their cattle. Results will also be summarized by region, area and management practices to allow broader and general recommendations for P supplementation.
More efficient P supplementation of beef cows will have both economic and environmental benefits. If you are located in the Chesapeake Bay watershed counties and want to participate in the project, you can contact the following for more information:
• Local Extension office;
• Local NRCS office;
• Virginia Tech Beef Extension.