Cycle of savings

Understanding how nitrogen behaves can help you manage this valuable input better.

“It’s like a simple math equation,” says Brad Carlson, Extension educator at the University of Minnesota. 

The amount of nitrogen your corn crop actually needs is the total you seek to calculate. 

Soil has its own capacity to supply nitrogen to a crop through mineralization of organic matter. Fertilizer applications build up the total amount of nitrogen in the soil.

Both are additives that balance the natural loss of nitrogen.

Soil often loses nitrogen when saturated. Erosion, nutrient runoff, and crop removal are common contributors to nitrogen loss. Much of this is because of both denitrification, which occurs when bacteria convert nitrate to nitrogen gas and release it to the atmosphere, and leaching, which happens when nitrate moves with excess water below the root zone.

Interpreting Recommended Rates

Nitrogen guidelines or recommended rates are generally based on ideal conditions, but when you factor in soil type and weather conditions, you may need to apply more.

“If a farmer understands the nitrogen cycle, then they can more confidently adjust rates,” Carlson says.

Research has shown that because nitrogen is mobile in the environment, applying too much leaves it pound for pound behind in the field, a loss of costly inputs. As a result, the nitrogen could end up in the atmosphere as N2 gas, but in the worst-case scenario, it ends up polluting the groundwater.

Research shows yield and nitrogen application rates are not linear. “Many farmers think that corn is so much higher yielding than it used to be, thus it has to have higher nitrogen rates. In reality, the data does not support this,” Carlson explains.

Prioritizing knowledge and awareness are key, but so is a shift in mind-set.

The best yields tend to come from the healthiest soils on the farm because mineralized nitrogen is readily available for the crops. 

Carlson says increasing the nitrogen rate in a high-yielding environment doesn’t secure an even higher yield. Instead, it’s better to apply the same rate of nitrogen across the fields and work on improving the soil organic matter in the underperforming acres.

Identifying the Need For Nitrogen

Sam Peterson, a corn and soybean farmer in Northfield, Minnesota, has a goal: Find the fine line of applying just enough nitrogen without being too light. “In the past, we applied heavily and we found out through the trial that wasn’t the best approach,” he says.

Peterson and Carlson worked together on a three-year on-farm trial to evaluate crop models and the effectiveness of different nitrogen rate applications.

Peterson has split-applied nitrogen for the past 10 years and has utilized variable-rate programs for nearly eight of those.

“There wasn’t a lot of data available to back up the claims that certain programs could reduce nitrogen inputs and at least keep yields the same,” Peterson explains. “I wanted to test those out and see what program is actually the most cost-effective for the farmer.”

Through the Minnesota Corn Growers Association Innovation Grant Program, Peterson and Carlson compared a flat-rate program with programs from Encirca, from WinField United’s R7 Tool, and Peterson’s local co-op.

In each of the three years, they selected different fields to test, but chose areas with adequate drain tile, where they raised corn on corn, and did not have a manure history. At the end of the year, they compared yield results to pounds of nitrogen applied and factored in the programs’ cost, which was about $10 per acre each.

The weather and growing conditions during the first year of the trial were ideal, but a windstorm during the second year left stalk lodging and skewed their results. According to Peterson, the third-year results were the most interesting. 

“We had so much rain throughout the season that our nitrogen should have washed away if it wasn’t applied properly,” Peterson points out. “Encirca applied enough nitrogen to the corn and resulted in $100 [per acre] savings over the other two programs. We also achieved yields that were 50 bushels [per acre] better.”

  • In the Petersons’ trial, the flat-rate application (control) was set at 154 pounds of urea (46% nitrogen) per acre.
  • Nitrate Now applied an average of 130 pounds of urea per acre with a range of 295 pounds per acre to 0 pounds per acre. 
  • Encirca applied an average of 185.4 pounds of urea per acre and had a range of 213.6 pounds per acre to 115.4 pounds per acre.
  • WinField’s R7 Tool applied an average of 226.5 pounds of urea per acre with a range of 239 pounds per acre to 195 pounds per acre. 

“We had one plot 12 rows wide and 1,800 feet long in this trial that got to 278 bushels an acre on 152 pounds of nitrogen corn on corn,” Carlson explains. “The point is that your best sites produce your best yields; it’s not necessarily a matter of shoveling nitrogen onto it to get a yield like that.”

This year, Peterson spread out the risk and dedicated a significant number of acres to all three programs on the farm, knowing that just one program won’t outyield the others every year. 

On the areas with more variable soils, he uses variable-rate technology to apply only on the spots that need it, lessening the risk of nitrate leaching.

Understanding the nitrogen cycle and doing the math will help you reach a better balance on both sides of the equation.

Nutritional Management

Dan Poston, director of agronomy at Pivot Bio, is passionate about putting pieces of the agronomic puzzle together. Poston began his career as a weed scientist, transitioned into crop protection and production, and now focuses on the soil microbiome. 

From a nutritional management perspective, Poston says if you target nitrogen, you must first know it is a yield-limiting factor. He recommends an integrated approach that includes soil and tissue testing, applying nitrogen only when the crop needs it, utilizing nitrogen stabilizers and “smarter” (time-release) fertilizers, and introducing microbial products that fix enough nitrogen for themselves and
the crop.

The Nitrogen Cycle

Most nitrogen resides in the atmosphere (nearly 80%) as nitrogen gas, which is inaccessible to plants. The Haber-Bosch process, developed in the early 1900s, uses high pressure to fix nitrogen from the air with hydrogen from natural gas to produce ammonia. While the process is still used today, Dan Poston says it isn’t without problems. “We’ve leveraged the Haber-Bosch process to grow crops effectively and feed the world, but between 1.5% and 2% of all energy on earth goes into making nitrogen fertilizer. What I think is really the next phase of nitrogen management is instead asking more of microbes in the soil.”

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