All fields are not equal when it comes to how much phosphorus they contribute to streams.
That's not big news. But it is something to consider for both farmers and government agencies who want to be cost-effective in reducing the amount of phosphorus reaching water bodies.
In the Pecatonica River Watershed Project in southwest Wisconsin, it's been the concept driving an approach to phosphorus management that local partners hope will be adopted by USDA and others across the country.
"I've seen a lot of projects in my 30 years of conservation work in Dane County," says county conservationist Pat Sutter. "But this one is different. Here, we went out to find out which fields of which farms are most at risk to deliver phosphorus to the stream. We inventoried 62 farms, and narrowed them down to 10 farms that had a phosphorus index greater than 6. That's the level a field has too high a potential for phosphorus losses for manure P applications to continue, and where we wanted to concentrate our work."
The phosphorus index estimates annual phosphorus delivery, in pounds, from a field to surface waters. Wisconsin is one of only a few states with phosphorus numeric standards for every stream in the state, Sutter says. Project partners wanted to concentrate on phosphorus because of its impact on algae blooms in lakes and streams.
15% of fields deliver 50% of phosphorus
"A significant finding in our modeling was that only one out of seven fields had phosphorus delivery levels with a phosphorus index higher than six, but those 15% of the fields were delivering 50% of the phosphorus to the stream," says Steve Richter of The Nature Conservancy, one of the major funding partners in the project.
Phosphorus delivery levels were identified field-by-field beginning in 2006 in the Pleasant Valley Watershed, a sub-watershed of the Pecatonica River, by a University of Wisconsin graduate student who sampled soils in fields and interviewed farmers. Baseline data was gathered through 2009; then, with project assistance, farmers began implementing practices including no till, cover crops after silage, crop rotations, and nutrient management, on the 10 farms in 2010.
In pastureland, producers fenced streams off, put in cattle crossings, improved their pasture management, and reseeded pastures. Practices will continue to be applied through 2015.
"Our models predict a 30% annual reduction in phosphorus delivery from the fields with phosphorus loads that were greater than 6 index in the beginning," says Sutter.
In just three years, farmers have changed practices in the subwatershed to reduce phosphorus runoff on 75% of the targeted fields with phosphorus levels greater than 6. No-till and nutrient management practices have been well received by farmers -- 2,100 acres, 48% of the cropland in the watershed -- is now no-till.
Nutrient management is being used on 3,000 acres, or 68% of the cropland.
Last year, phase 3 of the project was applied. This includes high cost practices including nine barnyard runoff catch systems and more than five miles of stream habitat restoration.
"One of the extra benefits from this targeted approach is that the farmers who make changes on the targeted fields end up making those and other changes on all the land they farm, so thousands of other acres are also improved," Richter says.
Side-by-side watershed test
Phosphorus loading from the Pleasant Valley watershed is being compared with phosphorus loading from the Smith-Conley watershed, a control watershed that isn't getting the same kind of accelerated assistance. Both are trout streams and have very similar features, with rolling hills of cropland and dairy and beef operations.
The project has been monitoring the two streams since the fall of 2006 for sediment, total phosphorus, dissolved phosphorus and flow, plus some nitrate monitoring. The U.S. Geologic Survey has stream gauges to measure phosphorus levels at the bottom of each watershed.
"Dry weather in the past few years hasn't given us reliable reduction figures at the water gauges," Sutter says. "But we should be able to detect that 30% reduction of phosphorus in water flows in a normal year at the USGS gauge at the mouth of Pleasant Valley compared to Smith-Conley. We're confident because of the practices that are applied, but we want to see it at USGS gauges over time."
The DNR is also tracking fish and invertebrate response in the streams, and rehabilitating small streams by narrowing them and shaping and seeding stream banks. "We've done projects like this where fish populations have rebounded by 200% to 300% after one year," says Jim Amrhein, biologist with the Wisconsin DNR.
"People are thankful for the restoration projects, and I tell them to thank the farmers in the watershed. That's because if we do the restoration work, but the land draining to the stream isn't cared for, our investment is going to be very short lived."
-Betts writes from Johnston, Iowa