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NORWOOD YOUNG AMERICA, Minn. − Proper management of manure and cover crops is essential to increasing nitrogen availability in the soil and boosting overall grain yields.
“Corn or any plant, really, when it needs nitrogen and it can’t get it from the soil, the plant will start pulling it from its lower leaves, pulling it to the top to make chlorophyll,” Melissa Wilson said. “If you start seeing a lot of yellowing it could be a sign that you are applying manure too early in the season which causes nitrogen loss.”
Wilson is an assistant professor and extension specialist of manure management at the University of Minnesota. She presented, “Best management practices for manure, are they worth it?’ Feb. 21 at the Carver County Dairy Expo in Norwood Young America.
Her research and extension programs focus on best management practices for land application of manure for crop production. Wilson shared some of the best manure management practices − testing manure, applying manure after soil temperatures have cooled, hindering the use of a nitrification inhibitor and adding manure to the planting of a cover crop.
According to a survey done by the United States Department of Agriculture’s National Agriculture Statistics Service, only 27% of farmers in Minnesota knew the nitrogen content of the manure being applied, Wilson said.
“This tells us we could be doing a better job, especially in today’s fertilizer market where we need to know how much nitrogen and phosphorus we are paying for,” she said. “Knowing what’s in our manure is going to be important to think about how we’re balancing out our nutrient management plans.”
One important step in solving this problem is manure testing.
“Say you have liquid dairy manure and you think you have 15 pounds of nitrogen per 1,000 gallons, but you actually have 25 or 26 pounds. You are going to over apply that nitrogen,” Wilson said. “So, it’s really important to test your manure, especially if you are changing feeding practices or have a water leak. All of those things can really change your nutrient content.”
On average, manure travels 1.4 miles from the farm, and 65% of manure is applied in the fall, Wilson said.  
“When spreading in the fall, there is a longer period of time for the nutrients to be released and potentially lost before crops can pick them up,” she said. “With changing weather patterns soil microbes become happier in warm soils and could cause more potential loss, because these microbes are the ones that transfer nutrients into forms plants can pick up.”
Wilson encouraged farmers to apply manure after soil temperatures have cooled to 50 degrees. Based on a recent analysis, a date when temperatures would be near 50 degrees is late October.
“Higher temperatures are optimal for nitrification,” she said. “Nitrification is the process by which ammonium turns into nitrate. Nitrate is also plant available, but nitrate can be lost completely, can leach and can turn into a gas also under wet conditions.”
One thing Wilson wanted dairy farmers to note is that swine and poultry manure are more nutrient dense than dairy manure.
“You have to haul less liquid to get the same nutrient content. The dairy manure tends to be more dilute and have more bedding involved,” she said. “Wherever you see a liquid, the ammonium is closer to 50%, which means you have 50% of nitrogen plant available compared to when we have solids. The solids ammonia content is very low, and it takes a lot longer for the organic portion to breakdown and become plant available.”
Due to dairy manure being more readily plant available, some farmers add a nitrification inhibitor to slow the conversion process. However, Wilson and her team found there were no significant differences in using a nitrification inhibitor or not.
Another management practice Wilson and her team looked into was spreading manure onto cover crops.
“Can we get cover crops planted early and apply manure onto them?” Wilson said.
Wilson’s trial was conducted using a cover crop of winter rye mix which was planted on three different fields −  a sweet corn-corn, soybean-corn and a silage-corn rotation. The trial used a sweep manure injection and two different species of manure − swine and dairy; swine on the sweetcorn-corn and soybean-corn rotations and dairy manure on the silage-corn rotation. A fourth field had no cover crops and fertilizer applied; it was compared to those with the cover crops and manure application.
There were no significant differences found when adding a cover crop, but Wilson and her team discovered that when the swine or dairy manure was applied, corn and soybean yields were 3 tons more per acre.  
“This goes to show that manure has a lot of those extra nutrients, especially in the system that’s continuous corn which are pretty hard to kill,” Wilson said. “Manure can provide a lot of those micro and secondary nutrients that our fertilizers just don’t have.”
Wilson encouraged farmers to test manure regularly, apply manure when soil temperatures are cool, hinder the use of a nitrification inhibitor and if cover crops are planted, plant early so manure can be applied.

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