Cattle feeders are accustomed to thinking about feed nutrients in terms of the biology of cattle nutrition and the economics of feed costs. However, as federal, state and local governments adopt increasingly stringent regulations governing the land application of manure, feeders need to think about the environmental and economic impacts of nutrients that pass through the animal.
“We know as a feedlot we produce certain quantities of manure nutrients,” says Galen Erickson, an assistant professor at the University of Nebraska in Lincoln. “But now we’ve got to show or illustrate that we are adequately distributing those nutrients when we apply manure to cropland. That hasn’t been done in the past.”
Phosphorus has traditionally been seen as a beneficial nutrient that should be added as a supplement to feed rations. But researchers are increasingly finding that phosphorus supplements are unnecessary, particularly when cattle are given a corn-based diet, and that supplementing their diet with phosphorus can lead to excessive concentrations of the nutrient in their manure, which can lead to surface-water contamination.
The EPA, for its part, has not yet put in place regulations that would specifically govern the amount of phosphorus-laden manure that producers can apply to cropland. However, Dr. Erickson points out that EPA is emphasizing P issues in their new CAFO regulations. These regulations require livestock producers to conduct regular phosphorus-based risk assessments of fields receiving manure, and based upon the outcome, producers could be required to begin distributing manure at a P-based rate or end all manure application on a field. “Some producers are very conscious of this, while others are waiting to see what happens with some of these rule changes,” he says.
In the meantime, Dr. Erickson is working with Richard K. Koelsch of the University of Nebraska and Raymond Massey, a University of Missouri economist, to develop a system to help feeders determine their cost of distributing phosphorus-laden manure. They hope to have the formula completed this summer.
“The result will be a formula to figure out the cost of phosphorus management,” Dr. Erickson says. He adds that although many feeders apply manure as a fertilizer to grow a variety of high-value grain crops, they may find it more financially advantageous to either change their feed or apply their manure on less-lucrative forage crops that consume higher levels of phosphorus.
“Until you know how much it really costs to distribute manure, you don’t know which strategy to take,” Dr. Erickson says, adding, “I think we can still have these economical feeds, but there’s no doubt we have to do a better job of distributing phosphorus in the future.”
Indeed, increasingly stringent nutrient-management regulations, which encompass everything from phosphorus to nitrogen and other nutrients, are changing the way feeders look at croplands.
“Nutrient management is going to be a very big issue going forward,” says Phil Brink, a livestock industry environmental consultant based in Lafayette, Colo. “Before, the goal was to make as much money as we could off of crops. Now, the goal is to get rid of wastewater at the lowest possible cost. This can change the way land is managed, the crops that are planted and the amount of commercial fertilizer that’s used.”
Unfortunately, the nutrient balance in feedyard manure is often not what crops need. “In feedlot manure and wastewater, we often have too much phosphorus relative to nitrogen,” Mr. Brink says. “So if we apply manure or wastewater to meet crop nitrogen needs, we end up over-applying phosphorus in some instances.”
Mr. Brink adds that some states already have Concentrated Animal Feeding Operation permit regulations that require the feedlot owner to perform nitrogen-leaching and phosphorus-transport risk assessments on each field where waste will be applied. “The results of these risk assessments indicate whether manure and wastewater can be applied to meet crop N requirements or crop P requirements,” he says.
Dr. Koelsch, for his part, adds that feeders in some areas of the country have insufficient control of feedlot runoff. Part of the problem is that holding ponds sometimes don’t work as well as they should in higher-precipitation regions.
Researchers, however, are finding that vegetative treatment systems can reduce and eliminate the need for holding ponds in some cases while providing better environment controls. “The idea is to have a permanent vegetative system that naturally filters the discharge,” Dr. Koelsch says. For runoff management, veg-etative treatment systems potentially have less impact on groundwater than containment ponds in many situations. “Ponds are falling more out of favor and there is more interest in vegetative filtration systems,” Dr. Koelsch adds. “I think an alternative that involves no or limited storage and that uses vegetative treatment areas will be an alterative we look at more and more, especially in areas that get more rainfall.”