Does healthier soil produce significant nitrogen?
Written by Jonathan Eisenthal
Farmers who engage in soil health practices like no-till and cover crops—especially those who have engaged in these practices for ten years or more—often describe a reduced requirement for nitrogen fertilizers.
But this phenomenon has not been tested and quantified, according to soil scientist Anna Cates, who is close to completing the first year of a three-year project that closely examines the relationship of those practices to measures of biological activity in the soil, and then attempts to draw the connection with changes in the Economic Optimum Nitrogen Rate for fields where soil health practices are used. Cates is a professor at the University of Minnesota, and the director of the Minnesota Office of Soil Health (MOSH).
Cates’ project, funded by the Minnesota Corn Checkoff, uses ‘triplets’ as the basis for comparison.
“Triplets are three fields, in close proximity, each with different management. That way we can control for soil and weather during the growing season’s effects on corn yield. Precipitation (in Minnesota) can be especially localized, so it’s nice to have things close.”
Cates’ team will compare sets of three fields in Renville and Mower counties—each set includes a field where the operator has utilized soil health management techniques for one-to-three years, and a second field where these techniques have been in use for ten or more years, as well as a conventionally cultivated field without recent manure application, cover crops or small grain production. The first corn harvest of the project will occur this fall, and then N requirements and economics of these different practices should come into clearer focus.
This project puts a spotlight on The Haney Test, a soil test popular among operators trying to gauge nitrogen fertilizer requirements in settings where soil health methods are in place. The test, which looks at “pools of organic nitrogen and carbon” has not been shown definitively to predict how much nitrogen will be available for corn plants uptake . Soil that has not been disturbed typically has higher microbial activity, and organic nitrogen. But plants require the mineralized form of nitrogen.
Higher biological activity in the soil includes predators like nematodes consuming microbes, and in the process of digesting the organic nitrogen in the cells of their prey, they excrete mineralized nitrogen, which plants can use. Cates will use bait set on the soil surface to capture surface predators and estimate their numbers in the soil, then see if a correlation exists between these numbers and the presence of mineralized N in the soil.
The questions are: how much useable N is there where the operator follows a no-till and cover crop regimen? Is it higher than in conventionally cultivated fields? Is it a dependable source? Cates notes that in the process of the growing season, the growing corn crop takes nitrogen out of the soil, drawing down the bank of this nutrient. She believes her project may show that biologically active soil may offer a more consistent supply of nitrogen over the course of the entire growing season.
Fertilizer is the second highest cost to farmers, after land rent, according to the database at the Center for Farm Financial Management, called FINBIN.
“If you can increase biological activity through improvement of the soil health, you may be able to reduce N use and save money in your budget,” Cates said.
