Balancing Phosphorus Use on Your Farm

Dave Beede
Dept. of Animal Science, Michigan State University

The U.S. Environmental Protection Agency (EPA) Administrator Christie Whitman has announced that the agency is working with the agricultural community to control water pollution from the nation’s largest livestock operations while keeping American agriculture viable. Whitman, joined by Agriculture Secretary Ann Veneman, announced a final rule that will require all large Concentrated Animal Feeding Operations (CAFOs) to obtain permits that will ensure protection of America’s waters from wastewater and manure. Adherence to the rule will control runoff from agricultural feeding operations.

Balancing phosphorus (P) means that imported P equals exported P on a whole-farm basis (zero P balance). The announcement of the Environmental Protection Agency’s final rule for CAFOs emphasizes the need for meticulous on-farm P balancing and management. This management starts with accurate input of P to your cows, largely in feed supplements. Typically, imported feed P makes up the majority of imported P to dairy farms; the other input is P-containing fertilizer. Both inputs should and must be managed effectively to achieve whole-farm P balance.

Phosphorus Balancing - On many dairy farms:
1) P inputs often are greater than outputs
2) When inputs are greater than outputs, P builds-up in soil over time
3) The potential for P runoff increases when soil P builds up to excessive levels
4) P in runoff causes oxygen debt killing aquatic life and excessive algae growth reducing water quality of steams and lakes.

Being sure that total P inputs (imports) are less than or equal to total P outputs (exports) will become an important management consideration. Even if your operation does not fall under CAFO definitions, having excess P in manure and in soil will limit greatly your management options. Additionally, your profits will be reduced considerably when more P is purchased than your cows and farm need.

Optimizing Ration Phosphorus
How can you, your nutritionist, and your feed supplier optimize ration P?
1) Use the new National Research Council’s 2001 feeding recommendations. Note that the highest concentration required for high producing cows is only 0.38%, dry basis!
2) Analyze your feeds. Talk with your nutritionist and use a qualified laboratory to determine P contents of feed ingredients and adjust your inputs and rations as necessary. “Book values” for P content of feeds will not give you the management accuracy needed. Many feed ingredients, especially byproduct feeds resulting from wet- or dry-processing or fermentation (e.g., distiller’s grain), have variable P contents or values different from the book. Also, to have reliable information for your P balancing, laboratory analysis must be done by the wet chemistry method, instead of NIRS (near infrared reflectance spectroscopy). NIRS gives inaccurate estimates of actual P concentrations of most feeds.

Purchasing Phosphorus Supplements
You may be purchasing (importing) supplements, mainly for their protein, that contain varying amounts of P. Table 2 gives you ‘ballpark’ P and crude protein levels of some common protein sources and byproduct feeds. Most of these contain high concentrations of P. Review your rations carefully. You might be able to reduce costs by eliminating unneeded supplements!
Using protein sources with higher crude protein-to-phosphorus ratios will provide more of the needed protein with less P (e.g., blood meal, corn gluten meal, and soybean meal; Table 2). Actually, using protein sources or byproduct feeds that supply more P than needed in the ration (those with lower crude protein-to-phosphorus ratios; Table 2) may cost you even more money in the long run.

Adapted from: Understanding soil phosphorus: An overview of phosphorus, water quality and agricultural management practices, 2002, Nutrient and Pest Management Program, University of Wisconsin-Extension and USDA-ARS Dairy Forage Research Center.

Lower Ration P, Lowers Manure P, and Acres
Lowering dietary P to recommended levels automatically will lower manure P (Table 3). Consequently fewer acres will be needed to spread manure.

Without accurate management control of ration P levels, more acreage will be required. For example, in a 100-cow dairy farm, if ration P was lowered from 0.55% to 0.38%, the amount of land needed to spread manure would be reduced by 110 acres annually (Table 3). If ration P levels are not lowered to NRC recommendations and your operation is subject to the new CAFO final rule, you will need more acres on which to spread manure.

Summary
Managing P inputs and outputs to achieve zero whole-farm P balance must be a primary goal of dairy operations to control costs, achieve excellent environmental stewardship, and to be in compliance under the new CAFO rule. Balancing for P is achievable when dairy producers effectively manage P inputs through accurate feeding and if sufficient land base is available to spread manure P. Ration P levels in excess of those needed to meet cows’ needs result in excess manure P. Using imported feeds (supplements) with lower P levels will help reduce P in manure. The buck stops with the dairy owner or manager for effective P management. But, P balancing is achievable if feed P inputs are controlled and managed carefully and effectively.

Posted Jan 23th

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