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Pecatonica Without the “P”

Changes in farming practices have been shown to greatly reduce phosphorus runoff - without hurting the growers’ bottom line

Conservation experts and farmers alike are pretty pleased with the news from Pleasant Valley.

A seven-year pilot project in this 12,000-acre sub-watershed of the Pecatonica River showed that it’s possible to significantly cut phosphorus and sediment losses from agricultural land by zeroing in on problem areas.

Changing farming practices on selected fields on just 10 of the valley’s 61 farms reduced the amount of phosphorus entering the Pecatonica from Pleasant Valley during major storms by more than a third. Steps such as reducing tillage and planting crops that leave more residue to protect the soil caused estimated average annual losses of phosphorus and sediment entering the stream to drop by 4,400 pounds and 1,300 tons, respectively.

The project partners— UW scientists, public agencies, local farmers and The Nature Conservancy—began in 2006 by collecting baseline data on water quality in the Pecatonica below Pleasant Valley and below a nearby watershed that served as a control. From 2010 through 2012, conservationists worked with farmers to implement new practices. Data from 2013 showed that those efforts paid off.

“We can say with 90 percent confidence that this project made a real reduction in the phosphorus losses,” says CALS soil scientist Laura Ward Good. “Farmers who changed their management practices reduced their estimated phosphorus and sediment losses by about half.”

A key tool in the research was SnapPlus, software developed at CALS that estimates each field’s potential for phosphorus runoff under various management scenarios.

“In many cases the higherrisk areas were fields on steep slopes, where silage had been grown in consecutive years so there wasn’t much crop residue to hold the soil, and where soil phosphorus levels were high—possibly because past manure applications had supplied more phosphorus than crops required,” Good says.

Once they’d identified high-risk fields, team members worked with landowners to assess the likely impacts of switching practices on that land—not just on runoff, but also on yields, expenses, feed supplies and other factors that govern the success of the enterprise.

Results to date indicate that farmers can make the needed changes without reducing their bottom line if the practices are tailored to the needs of the farm and growers can proceed gradually.

“No tilling is very good for the environment, for example, and you can get high production,” points out UW–Extension specialist Jim Leverich, the project’s on-farm research coordinator. “But you have to pay close attention to the details. You don’t have as much latitude. You can’t make any mistakes.”

“The trick is to give farmers the time to adapt, to search among the best management practices to see how they fit into their systems. If they have time to utilize the practice on a small scale first, they’ll start to see the advantages and maybe start to use it on more acres,” Leverich says.


Soil Forensics:

Sediment is sediment to you and me, but not to Jasmeet Lamba PhD’14, who as a graduate student worked with professors Anita Thompson and K.G. Karthikeyan along with soil and water conservation engineer John Panuska (all in the Department of Biological Systems Engineering). Lamba was able to “fingerprint” sediment suspended in the stream and figure out where it came from. Lamba analyzed soil samples from throughout the Pleasant Valley watershed for naturally occurring metals and radioisotopes. Soil from different types of land—stream banks, woodlands and farm fields—has different concentrations of these telltale markers. By comparing those samples to others collected from the river, he determined that about 70 percent of the sediment exiting the Pleasant Valley watershed in the stream originated from farm fields, while about 30 percent came from stream banks.