Nitrogen fertilizer has nearly doubled in price since December, but most farmers need to purchase it to grow a corn crop high in yield and quality. How can they get the best return on that investment and reduce the risk of losses to the environment?
One answer could be variable rate nitrogen management: strategic application of fertilizer that favors the more productive parts of a field and reduces inputs on the less productive ones. The UVM Extension Northwest Crops and Soils Program (NWCS) team has been evaluating this method on farms since 2024, and data show that farmers can reap savings and reduce potential for nitrogen losses without compromising yield and quality.
“It’s the next phase of managing nutrients—going to a finer and finer scale,” says UVM Extension Professor Heather Darby, who’s co-leading the research. “Fields are variable, and current technology allows us to understand that variation and make better, more precise use of nutrients.”
If one area of a corn field has poor drainage, poor soil quality, and/or more compaction, it doesn’t have the capacity to produce high yield, regardless of nutrient inputs. Spreading high rates of nitrogen in such compromised areas doesn’t make economic or environmental sense.
“We’re trying to match nutrient applications to the potential for plants to uptake the nutrients,” says UVM Extension Agronomy Specialist Jeffrey Sanders, a research co-leader. “In really healthy areas of a field, we want to apply more nutrients to try to get more yield, but in areas that are poor or less healthy or have less yield potential, we want to cut back on fertilizer so it’s not at risk of running off into surface waters.”
The research team, which includes precision agriculture specialists with NWCS and the Franklin and Grand Isle Farmer’s Watershed Alliance, has been gathering data since the 2024 growing season on seven Vermont farms in Franklin County and will continue for the next few years. They’re focusing on corn because it has high nitrogen demands based on target yields, and yields can vary substantially throughout a field. Around July 4, farmers traditionally use a single rate of nitrogen to topdress (spread on the ground) corn fields, regardless of variation in yield potential. New technology provides opportunities to use nitrogen more precisely.
For each field, the research team uses historical yield maps or Normalized Difference Vegetation Index (NDVI) data obtained from satellite imagery to establish management zones based on yield target. Image 1 shows an example of a field with zones of high, medium, and low yield potential.
Participating farmers manage the research fields as they normally would until it’s time to topdress the corn with nitrogen. The team then conducts pre-sidedress nitrogen tests (PSNT) in each management zone in each field to establish baseline nitrogen needs. They adjust the rates based on realistic yield goals for each management zone, create prescription maps, and use Ag Leader software to program the Innotag 860 Euro high-precision spreader. The spreader, with an onboard computer connected to a GPS system, applies nitrogen at variable rates across the management zones in each field.
At the end of the season, the farmer and research team collect yield data for each field to assess correlations between yield and nitrogen fertilizer rates. They also compare the amount of fertilizer used to how much the farmer would traditionally have applied to identify any reductions in cost or nutrient load. These data help them understand the return on investment of variable rate nitrogen application.
Results so far vary by farm, likely due to differences in soil, moisture, and management practices. Erratic weather in 2024 and 2025 also complicated matters. Comparing the amount of nitrogen applied on fields with variable rate management to those with traditional (one-rate) management has shown mixed results. Most farms have shown a reduction in the amount of nitrogen applied to fields with variable rate management; however, some growers who historically used low rates of nitrogen in their fields saw an increase. Yields were also variable, though productivity was not drastically lower than yield goals for any of the fields.
In general, the total amount of fertilizer applied with variable rate management has been lower than fields with traditional management. A good example is the field shown in Images 2 through 4. Image 2 shows the management zones, based on historical yield data. Image 3 shows the amount of nitrogen applied on the field, which corresponds closely with the management zones. Image 4 shows how many bushels of corn were harvested from the field at the end of the season.
The data collected show that, in general, the highest productivity zone (green) produced the greatest yield, and the lowest productivity zone (red) produced the least. The total amount of fertilizer applied was 1.62 tons, which is 0.58 tons less than the farmer would have traditionally applied. Despite the decreased amount of fertilizer, yields were not drastically lower than in previous years. The grower was able to reduce the amount they paid for fertilizer while maintaining yields—increasing profits while contributing to improved water quality.
Though these results are promising, there is still work to do. A major challenge has been inconsistent yield data. Yield monitors are new technology that greatly improve our ability to track crop yield and quality. However, the monitors can be difficult to operate on farms using them for the first time, which has led to loss of yield data for several fields, preventing further analysis. To address this issue, Daniel Bliss, a precision agriculture specialist with NWCS, has begun mapping all the fields at each farm to ensure better yield data and lighten the load for hard-working farmers.
Farmers have expressed strong interest in variable rate nitrogen management, especially this year. The cost of urea, a common nitrogen fertilizer made from natural gas, cost $530 per ton in December and now costs nearly $900 per ton. By saving on fertilizer, a farmer could cover the cost of an Innotag 860 Euro high-precision spreader in a few years, says Sanders.
“For people with yield monitors and other equipment, this is a next logical step,” Sanders explains. “If there’s a better way to do something, farmers will do it.”
The research team has been providing education and outreach on variable rate nitrogen management at conferences and on-farm events and will provide detailed information at the NWCS Annual Field Day in Alburgh, VT, on Thursday, July 23.
This research has been funded by the Agricultural Clean Water Initiative Program of the Vermont Agency of Agriculture, Food and Markets’ Water Quality Division (grant # 02200-WF-CWF-2023-005).
For more information, please contact Jeff Sanders at 802-309-1315 or jeffrey.sanders@uvm.edu or Daniel Bliss at daniel.bliss@uvm.edu or 802-999-1657.