Nitrogen efficiency an ongoing study for Discovery Farms

Gloria Hafemeister


The UW-Discovery Farms Program has been looking at nitrogen efficiency by tracking all sources as it cycles through the growing season from the soil to the corn plants.

Megan Chawner has worked with this study, evaluating farms in five different regions of Wisconsin, including the Rock River Basin.

During a field day sponsored by Discovery Farms, Chawner said, “This study gives farmers and consultants the tools to assess their own nitrogen use. We are not changing nitrogen recommendations for corn production in Wisconsin or suggesting in-season changes.”

Participating farmers, such as Bill and Rhonda Rohloff and son Ty, hosts of the event, provide records about nitrogen applications, timing and yields as nitrogen is tracked and each field is followed to harvest.

Manure and alfalfa credits are important, and the study looks at the interaction of these and commercial fertilizer, which has a big impact on crop production and environmental risk.

Chawner pointed out that farmers can tweak a little, but there are so many variations such as temperature, rain and tillage methods, and it is important to provide the nitrogen when the plant needs it.

The availability of nitrogen from manure applications is dependent on many factors.

Livestock manure contains ammonium and organic nitrogen, depending on the animal’s diet, as well as the manure handling system, she said. Manure organic nitrogen needs to go through a decomposition process before it is available to plants.

“Organic matter decomposition begins upon application and exposure to satisfactory temperature, moisture and microbes,” Chawner said. “It is a process that happens throughout the year of application and into next year’s.”

Lab findings

Lab and field studies show 30-40 percent total nitrogen contained in cattle manure is available throughout the first application year. As long as an accurate manure application rate is assigned to an accurate book value or lab analysis based on manure nutrient content, manure nitrogen credits will hold through the summer.

She added, however, that slight variations year to year will occur, based on variations in temperature and moisture.

Cool wet springs, for instance, delay manure organic decomposition and sometimes slow early season availability.

Last year’s study indicated that many fields had substantial amount of unaccounted nitrogen. Extra nitrogen could have come from several sources, including previous manure applications, past legumes, soil organic matter or leftover commercial nitrogen. She said this does not suggest that zero nitrogen should become a normal practice, but it does show that a particular field within a particular farming system can have residual nitrogen even without new application.

Last year’s experience, Chawner said, has shown participating farmers that keeping records and calculating Nitrogen Use Efficiency is a way to help balance the economic and environmental considerations relating to nitrogen management.

As Discovery Farms continues to build its database, farmers will be able to find more answers to their concerns as they fine-tune their fertilization.

As co-director of the UW Discovery Farms Program, Eric Cooley coordinates and implements water quality research; collects and disseminates data; and develops educational materials based on Discovery Farms’ research.