Nitrogen use efficiency
Taking credits for nutrients in a field is important, not only to save money, but also for protecting the environment.
The University of Wisconsin-Extension Discovery Farms program has been working for the last 15 years with farmers from around the state to identify ways to control nutrient losses and capture nutrients that remain in the soil.
In 2015, the program began a three-year Nitrogen Use Efficiency study in four regions of the state. The purpose of the study is to look at nitrogen losses in various types of soil and topography. Twenty-two farms are enrolled in the program, evaluating 51 fields. Discovery Farms is looking for more farms to participate in order to look at nitrogen use on a variety of soils and landscapes.
The first year's study covered farms in St. Croix County where soil is silty and loamy. The farms are mostly corn grain farms with tillage.
Farms in Monroe and Vernon Counties are silty and mostly dairy with corn silage, manure and no-till management, while the farms in Dane County have prairie soils and are mostly dairy with corn silage and some tillage.
The farms in Dodge, Jefferson and Rock Counties are mainly grain farms and a mix of tillage and no-till systems.
Megan Chawner has been working with the program and reported on the findings from the first year of the study when she spoke with farmers and crop consultants at a recent workshop in Watertown.
As the nitrogen use efficiency project coordinator, Chawner collects on-farm agronomic and water quality data and organizes project outreach. She assists farmers in evaluating the environmental and economic efficiency of their corn production management practices.
'Now that we've finished the first year of this study, we see an affect of rotation — crediting nitrogen from the previous crop,' Chawner said. 'We can also see an interaction of commercial and manure fertilizer.'
Rotations save money
UW- Extension guidelines suggest a total of 190 pounds of nitrogen per acre for corn after corn but only a total of 140 pounds nitrogen per acre for corn after soybeans, due to the difference in the nitrogen response.
This can mean a significant savings in fertilizer costs.
'Appropriately crediting nitrogen from manure and rotated alfalfa increases the nitrogen use efficiency while reducing the potential negative environmental impacts from over applications,' she said.
While results are clear in the first year of this study she added, 'One year is not enough to make recommendations. Production efficiency should be used as a long-term indicator.'
In the first-year study, Chawner pointed out that most fields had a substantial amount of unaccounted nitrogen. This could have been from previous manure applications, past legumes, soil organic matter or leftover nitrogen.
'We also need more than a year to make accurate predictions because of the role weather plays in yields,' she said. 'This year's data did not show a big yield penalty when no nitrogen was applied because of good growing conditions and a high soil nitrogen supply.'
Another part of the study looks at the differences in plant available nitrogen throughout the growing season, something that changes according to the source of the nitrogen used.
'Fields that had over half of the nitrogen applied as manure and alfalfa had higher soil nitrogen levels at pre-plant and post harvest,' Chawner said. 'At pre-side dress, except for two manure fields, over half of the commercial nitrogen had higher plant available nitrogen levels.'
While the first year of the study revealed some important data, she said in the next two years, Discovery Farms wants to quantify the effect using the nitrogen use efficiency calculations for the different management systems in the state.