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Researchers investigate ’whole farm’ approach to reduce dairy pollution

04.03.2005


A new agricultural research project is looking for ways to prevent phosphorus in manure from running off into the Bosque and Leon Watersheds. The challenge is to do so without sinking the region’s dairy industry.

Funded by $800,000 in grant monies from the U.S. Department of Agriculture and the Environmental Protection Agency, the project pools the efforts of experts from the Texas Agricultural Experiment Station, Texas Cooperative Extension and Tarleton State University.
At stake is not only preserving water quality in Central Texas, but reinforcing an industry crucial to the central Texas economy, said Dr. Barry Lambert. "The city of Waco, downstream from the dairies on the Bosque River watershed, has placed much of the blame for (Lake) Waco water quality issues on the dairy industry in orth-Central Texas," said Lambert, dairy nutritionist with a joint appointment with the Experiment Station and Tarleton State. The issue centers not on the manure itself, but primarily concerns phosphorus, a component of manure.


The average dairy cow excretes about 40 pounds of phosphorus per year as manure. Phosphorus, when in the right proportion to other compounds such as nitrogen and potassium, is an essential crop nutrient. Dairy farms typically spread the manure, either composted or as a slurry from catch lagoons, on crops as fertilizer.

The typical crop is some sort of forage, which uses 1 pound of phosphorus for every 4 pounds of nitrogen. The forage is a method of recycling manure, and if the proportions of phosphorus to nitrogen were correct, it would be an efficient, environmentally friendly system. "The majority of phosphorus leaves the dairy farm as either milk or manure," Lambert said. "Phosphorus is an essential nutrient for humans, so the milk part is good."

But dairy manure is high in phosphorus, having about 1 pound of phosphorus to every 2 pounds of nitrogen. It’s this leftover phosphorus, the part that crops don’t use, that is creating the problem, Lambert said.

Some of the extra phosphorus can be bound up

  • scientists say "sequestered"
  • in Central Texas soils. But some of the phosphorus in dairy manure is water-soluble, so what isn’t sequestered is at risk of being washed off into streams and rivers by heavy rains. Once it reaches lakes and reservoirs, phosphorus itself never reaches toxic levels. At elevated levels, however, it can result in rapid algae growth. Runaway algae growth can result in fish kills through oxygen depletion and the production of phytotoxins.

In light of these facts, the city of Waco, which gets most of its drinking water from the Bosque River, filed suit against 14 Central Texas dairies in April 2004, Lambert said.

In Central Texas, phosphorus pollution has been a controversial issue, for dairies are not the only source of phosphorus run-off, Lambert said.

Natural decay of any organic material or other agricultural activities can also contribute to phosphorus run-off. It’s an accepted fact that home lawn and garden fertilizers, which are typically over-applied, are also a significant source of phosphorus run-off, he said.

Muddying the waters further, many of the federal and state environmental regulations are based on soils, climate and forage cropping systems that have little in common with those in Central Texas, said Dr. James Pierre Muir, Experiment Station forage research physiologist. "If you add assumption on top of supposition, you wind up with legislation and litigation based on very little data," said Muir, who is also a member of the research project. And Central Texas dairies are caught in between the legislation and suits, he said. Muir, Lambert and the rest of the research project team believe the answer lies in the way small changes in dairy farm management can result in wholesale reduction of phosphorus run-off.

Over the next three years, they will examine:

  • Improving phosphorus recycling on farm through less traditional forage crops;
  • Increasing phosphorus sequestering in soils;
  • Trying different crops on the streamside buffer zones already in use by dairies;
  • Using soldier fly larvae to recycle manure (See http://agnews.tamu.edu/dailynews/stories/ENTO/Nov2904a.htm);
  • Correcting cropland that has already phosphorus sequestration limits through the use of year-around forage cropping; and
  • Adjusting dairy feed mixtures so cows excrete less phosphorus in their manure.

Many of these systems have been tried in part, Muir said, but what makes this project unique is the "whole-farm" approach. Rather than just looking at how a single change affects phosphorus buildup and runoff, researchers will investigate how the various strategies reinforce one another.

"It’s really a matter of fine-tuning a system that isn’t necessarily broken but could run better," Muir said. "We have also included the dairymen as full partners in the design, implementation and interpretation of research and subsequent outreach. It is, after all, their dairies."

Along the way, the team will collect data that can be used to write regulations that reflect the "real world," Muir said. Another factor that makes the research project different from those that came before is this real-world nature, Lambert said.

"We’re doing this work on real, operating dairies. It’s not something confined to a laboratory," Lambert said. "(We will be) tracking phosphorus from the time it enters the farm until it leaves it."

Robert Burns | EurekAlert!
Further information:
http://www.tamu.edu

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