Phosphorus reduction in watersheds goal of workshops for farmers, ag professionals

Minnesota’s dairy belt stretches through the central and southeastern part of the state, loosely paralleling the rolling lands of the upper Mississippi River. Farmers in this region have increasingly looked to livestock manure—from dairy cows, as well as beef, poultry and swine—as a valuable local resource and an economically smart alternative to commercial fertilizers.

But like many fertilizers, manure contains phosphorus that can leave a field with surface runoff water. Excess phosphorus entering a water system causes intense algae blooms. The bacteria involved in algal decomposition can starve a water system of dissolved oxygen, killing off native fish and aquatic organisms and speeding up a lake’s eutrophication.

University of Minnesota Extension educator Randy Pepin, a former livestock industry consultant, hopes to make grid soil sampling a common practice among farmers who choose to use livestock manure. Grid soil sampling can be a cost effective way for farmers to target their nutrient application while reducing the amount of phosphorus entering the watershed.

Pepin’s statewide “Will Grid Soil Sampling Work for my Livestock Farm?" workshops use case studies developed by the Water Resource Center and University of Minnesota Extension to demonstrate the economic and environmental benefits of grid soil sampling in manure applications.

In grid sampling, fields are divided into to two and one-half acre grids, then tested for nutrients such as phosphorus and potassium. The data is used to create custom maps for farmers to guide their manure applications.

The customized maps are key: a farm’s nutrient level can vary widely based on topography, soil type, crop cover and history of manure application. Concentrating nutrient application where it’s needed increases the fertilizer substitution value of the manure and reduces the risk of phosphorus runoff into lakes, streams and the surrounding watershed. Grid soil mapping also complements other conservation practices like minimum tillage, contour tillage, strip tillage, crop rotation and buffer strips.

The McKnight Foundation-funded workshops have attracted a range of participants including regional dairy, beef, poultry and swine farmers and crop consultants, and staff of Soil and Water Conservation Districts and Natural Resources Conservation Service. “We can multiply our efforts by educating the educators,” says Pepin.

As expected, workshop participants range in their motivations. “Sometime participants just want a better understanding of phosphorus in relationship to the environment, while others are looking for a thorough understanding of the grid sampling and how to use it,” says Pepin.

Regardless of intent, all workshop participants walk away knowing how grid-sampled maps illustrate their field’s phosphorus and potassium content and how the grid soil sampling technique helps them target nutrients to where they’re needed the most.

But while Pepin’s focus is on agricultural production, dozens of human activities contribute to the problem of excess phosphorus entering our water systems.

“Industrial waste, municipal waste, impaired sewer systems, residential lawn runoff, and erosion from agriculture land and feedlots all contribute to excess phosphorus,” says Pepin. “Realistically, attaining significant reduction of eutrophication of our waters requires action from all sectors.”

Randy PepinExtension educator Randy
Pepin hopes that the
workshops will educate the
educators, widening the reach
of the grid soil sampling
technique.