Timing, Placement and Soil Testing Key to Preventing Phosphorus Losses

Edge-of-field monitoring on 17 farms in Wisconsin and Minnesota highlights the need for no-tillers to apply ‘P’ under the soil surface and sample soils at varying depths.

No-Tillers concerned they’re losing too much phosphorus (P) from their fields may want to review lessons learned from 15 years of on-farm, edge-of-field water quality monitoring conducted by the University of Wisconsin Discovery Farms program and Discovery Farms Minnesota.

Discovery Farms has monitored surface water quality on 17 farms, comprising 21 fields, in Wisconsin and Minnesota for a total of 85 site-years. Phosphorus and soil losses were measured from farms of various acreage and a mix of grain and dairy operations. 

Farmers in the two states expressed the need for information on nutrient runoff that comes from privately owned farms rather than research stations or data modeling, says Discovery Farms co-director Amber Radatz. The data proved valuable in providing some conclusions and creating recommendations about farming systems’ impacts on water quality, she says. 

Keep Your Soil

The first step in reducing P loss is controlling soil loss, which includes paying special attention to farmed and non-farmed areas and where those areas intersect, Radatz says. Conservation tillage or no-tilling alone may not be enough to eliminate erosion, and pairing them with waterways or other conservation measures is more effective, she says.

According to Radatz, Discovery Farms data show the amount of soil lost through tillage and no-till was sometimes similar, but it largely depended on the terrain. Annual soil loss, measured in pounds per acre, showed tilled fields lost an average of 1,000 pounds of soil annually, but as much as 6,200 pounds on some farms. No-tilled fields lost no more…

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John dobberstein2

John Dobberstein

John Dobberstein is senior editor of No-Till Farmer magazine and the e-newsletter Dryland No-TillerHe previously covered agriculture for the Tulsa World and worked for daily newspapers in Chicago, Milwaukee and St. Joseph, Mich. He graduated with a B.A. in journalism and political science from Central Michigan University.

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