If you don’t know, it’s time to find out. Phosphorus levels in swine manure are becoming one of the pork industry’s hottest environmental issues. Not only are the new Concentrated Animal Feeding Operation regulations requiring you to keep phosphorus records, but so are many states.

Even though phosphorus is an essential element for normal hog growth, development and reproduction, it also can present some problems.

To get a better understanding of the impact phosphorus has on the pork industry, Alan Sutton, nutrient-management specialist at Purdue University, offers insight into reasons why knowing your “P levels” is so important.

  1 The key reason that phosphorus is a concern for the pork industry, is that a shortage of land for manure application can create a phosphorus buildup in soil that could then enter water sources, potentially from runoff or leaching.

High phosphorus levels in water accelerate the eutrophication process, and often result in excessive production of phytoplantkton such as algae and cyanobacteria. This reduces oxygen levels in bottom waters. Under certain circumstances (such as at night, under calm, warm conditions) it also can impact surface waters. The lower oxygen levels can lead to fish kills and significantly reduce diversity of aquatic organisms.

The potential phosphorus-pollution threat from the livestock industry to U.S. waters is site specific with high phosphorus levels on high-risk soils or highly erodible land and related to the concentration of animals producing the manure compared with the amount of available land to apply the manure, says Sutton.

  2 Repeatedly applying manure to the same cropland, mostly at nitrogen-based rates, is another reason why phosphorus levels are such an issue. Under that scenario, Sutton says a producer could be over-applying phosphorus by 2.5 to 3 times the amount that crops will utilize. “Phosphorus from grain in a typical swine ration is not very available for the pig to use,” he notes. “Until recently, producers added inorganic phosphorus supplements to provide enough available phosphorus for the pig, but that increases the excretion in manure. Today, they can use new technologies, such as using phytase or some other means to provide phosphorus.”

There are two reasons to minimize over-formulation of phosphorus. First, it’s a waste of money, especially since phosphorus is the second most expensive nutrient in rations. For example, assuming a feed-to-gain ratio of 2.8:1 for pigs weighing up to 50 pounds, and a feed-to-gain ratio of 3:1 for pigs greater than 50 pounds, you could save about 9 cents per hog marketed. That includes the savings in reducing phosphorus in the diet by 0.1 percent and including the cost of adding phytase. You could potentially save more money by taking other measures to reduce phosphorus even further.

Second, minimizing over-formulation is the easiest and cheapest way to reduce phosphorus excretion.

  3 A third concern involves swine genetics. Sutton points out that research is needed to determine the phosphorus requirements of new swine genetic lines. Currently, phosphorus requirements are being used from nutrition research that is 10 to 20 years old.

There are three options to lower the amount of phosphorus in swine diets:

1) Add phytase (an enzyme that breaks down phytic acid) to the diet.

2) Select feed ingredients with more available phosphorus contents.

3) Develop feed grains, such as low-phytic-acid corn or soybeans, with higher amounts of available phosphorus.

Adding phytase is probably the easiest and most common method. “The pork industry has pretty well accepted the use of phytase if they want to reduce phosphorus excretion,” says Sutton.

In corn and soybeans, phosphorus is tied up in phytic acid. In order to release phosphates from the phytic acid so that the animal can absorb them, an enzyme has to break the bond. That’s where phytase comes in.

A pig has a low amount of phytase in a normal system. Phytase helps a pig utilize nutrients, including several other minerals.

The key advantage of using phytase is that it reduces the animal’s phosphorus output allows you to reduce supplemental phosphorus in the ration, and changes the composition of its fresh manure. There are conflicting reports of whether using phytase increases or decreases water-soluble phosphorus. If it does increase water-soluble phosphorus, and you surface-apply the manure, some reports say it could run off into surface water. Once again, more research is needed to get answers to these questions, says Sutton.

    4 Another issue to look at involves manure composition. What is the phosphorus level after the manure is stored for weeks or months? Phytic acid phosphorus is broken down because of microbial activity in a pit. Recent research shows that a significant reduction takes place rapidly, within 30 days. Other dissolved phosphorus forms also decline, probably due to microbial incorporation over a 30- to 90-day period.

Still, the real issue is to formulate diets to excrete a lot less phosphorus. With a commercial-base phytase, Sutton contends pigs excrete 20 percent to 30 percent less phosphorus than a traditional diet, depending on the formulations.

Indeed, phosphorus is a big issue for the pork industry. “If we continue to try to formulate swine diets based on available phosphorus, instead of total phosphorus, pigs may not perform as well,” says Sutton. “Ultimately, the industry needs to conduct new research on the requirements of today’s pigs and the availability of phosphorus in feed sources to better understand how to reduce phosphorus manure excretion.” n

Iowa DNR Will Implement Phosphorus Rule

In Iowa, the state’s Department of Natural Resources is required to implement phosphorus-based

nutrient-management plans, thanks to legislation (S.F. 2293). Virtually all CAFOs in every state will use the NRCS 590 standard, which uses a phosphorus index or phorphorus-based application rates.

In addition to nitrogen requirements, all nutrient-management plans – for new and existing confinement operations – must be based on a phosphorus index on a phase-in schedule.

Iowa’s DNR has drafted a proposed phosphorus index, and it appears the rules will go into effect in early 2004, according to the Iowa Pork Producers Association. The DNR will consider public comments and make its recommendation to the Environmental Protection Commission, which will vote on the final rule.

The legislation establishes a phosphorus-index implementation schedule for NMP’s based on the date the original plan was submitted to the DNR.

  • If the original NMP was submitted to the DNR before April 1, 2002, a phosphorus index will be required for the operation within four years after the rules go into effect.
  • If an original plan was submitted after April 1, 2002, but before the rules were adopted, the phosphorus index will be required within two years after the effective rule date.
  • Any original plan submitted after the phosphorus index is adopted must meet that index. The proposed rule requires the use of the Iowa Phosphorus Index, developed by USDA’s Natural Resources Conservation Services’ Technical Committee. The proposed rule will require nitrogen and phosphorus management based on the index categories.

The Phosphorus Index is a tool used to assess the potential for phosphorus to move from agricultural fields to surface water. It uses an integrated approach that considers soil and landscape features, as well as soil conservation and phosphorus-management practices per field.

For more information, go to the IPPA Web site at www.iowaPork.org or to http://www.ia.nrcs.usda.gov/technical/PhosPhorus/PhosPho russtandard.html