Notice, calculate nitrogen use efficiency

by Lynn Grooms originally written for Agriview

Wisconsin is different from other states in many ways. Wisconsin farmers practice more crop rotations than farmers in other states. America’s Dairyland has more cows than most states … and it puts to good use ample supplies of dairy manure as nitrogen-rich fertilizer.

Nitrogen-use efficiency can be relatively simple to calculate. But Wisconsin’s diversified farms and soils create a need for Wisconsin-specific benchmarks of nitrogen-use efficiency. Enter University of Wisconsin Discovery Farms, which started a nitrogen-use efficiency project in 2015. The project involved working with farmers around the state to measure nitrogen-use efficiency. Abby Augarten, nitrogen-use efficiency project coordinator for UW Discovery Farms, recently discussed the project at the UW Discovery Farms Conference in Wisconsin Dells, Wisconsin.

Nitrogen-use efficiencies are calculated as ratios of outputs to inputs – crop removal to nutrient application. Corn growers look to maximize nitrogen uptake and produce economically viable yields. Optimal efficiencies may be achieved with reduced nitrogen rates. So it’s important to consider efficiency in the context of corn yields and net return on fertilizer applied, stated UW Discovery Farms in a publication titled “Nitrogen Use Efficiency: Statewide Nitrogen-Use Efficiency Benchmarking for Corn Grain and Silage.” UW Discovery Farms measured nitrogen-use efficiency in four main ways.

  • partial-factor productivity
  • partial-nutrient balance
  • agronomic efficiency
  • uptake efficiency

UW Discovery Farms began working with farmers in southeastern Wisconsin counties – Dane, Dodge, Jefferson and Rock, Augarten said. The project then was expanded to work with farmers in three watersheds.

  • Dry Run Watershed in St. Croix County
  • Elk Creek Watershed in Buffalo and Trempeleau counties
  • Jersey Valley Watershed in Vernon and Monroe counties

The project expanded again in 2016 – to farm fields in the northeastern Wisconsin counties of Door and Kewaunee.

UW Discovery Farms monitored nitrogen-use efficiency on about 60 farms between 2015 and 2017. Monitoring involved 128 corn fields harvested for grain and 85 corn fields harvested for silage. Those fields reflected Wisconsin’s varied soil types and farm-management systems. Farmers used various crop-production practices.

The project’s researchers have three main goals for the ongoing project.

  • to establish state and regional nitrogen-use efficiency benchmarks for Wisconsin-specific cropping systems
  • to determine if the measures can complement nutrient-management planning
  • to evaluate how farmers can use nitrogen-use efficiency as a tool when deciding to change nitrogen-management practices

To help measure how much nitrogen was being used on participating farms, UW Discovery Farms worked with farmers to plant zero-N – or zero-nitrogen – test strips. Those strips generally were 100 feet long by about 25 feet wide or the width of a fertilizer applicator. Nitrogen-test strips provide many benefits, according to the UW Discovery Farms publication.

  • They quantify how much nitrogen is supplied by the soil. That helps farmers who are trying to determine if changes in management practices – such as cover cropping, reduced tillage or manure applications – affect soil’s ability to supply nitrogen. Farmers also could use the information to make site-specific management decisions based on soil-type differences and field specificity.
  • They help farmers understand how much nitrogen is used by a corn crop as well as how much nitrogen a crop didn’t use due to leaching.
  • They measure the economic value of nitrogen applications. That value is tied to yield gains and not total yield.

UW Discovery Farms continued the project in 2018 with farmers in Dunn, Pepin and Sauk counties, and will measure results through 2020.

Many farmers in Wisconsin use manure, perennial legumes – such as alfalfa – and cover crops as nitrogen sources. Those farmers are more likely to have residual nitrogen in their soils from season to season, according to UW Discovery Farms. Pre-plant nitrate and pre-sidedress nitrate tests can help farmers determine how much nitrogen is in soil from the previous season.

Zero-nitrogen test strips indicate yield achieved with residual and mineralized nitrogen in the soil. So nitrogen-use efficiency values that use those data show the economic efficiency of nitrogen added through fertilizer and manure, according to the organization’s researchers.

By comparing a field’s nitrogen-use efficiency to that of other fields in the region, Wisconsin farmers can determine whether they should make a change in management or continue monitoring. Benchmarks on how to adjust nitrogen-management plans to improve nitrogen-use efficiency are available from UW Discovery Farms. The project received support from a grant the U.S. Department of Agriculture’s Natural Resources Conservation Service. Visit for more information.