Farm Progress

Apply nitrogen this fall or wait until spring? 147748

If you decide to apply N in the fall, anhydrous ammonia is the least risky form to use.

John Otte 1, Economics Editor

October 10, 2016

5 Min Read
FALL VS. SPRING: The debate on nitrogen fertilizer application timing takes on greater importance with tight crop margins and concern about increased potential for nitrate loss with fall application. Some farmers have switched to applying N in spring instead of fall.

Iowa corn growers will soon be preparing for next year’s crop and making decisions about nitrogen applications. Nitrogen management is critical for growing healthy corn, and in Iowa, growers are sensitive to their role in helping build a more sustainable world. Ultimately, they are faced with the often-daunting question of whether fertilizer applications can be both profitable and sustainable. Usually, the delicate balancing act begins with the decision of whether to apply nitrogen in the fall or hold off until spring.

Wait until soil temperature cools down before applying

If you decide to apply N in the fall, keep in mind anhydrous ammonia is the only form of commercial nitrogen fertilizer Iowa State University agronomists approve of applying in the fall. Anhydrous is in the ammonium form which is more stable and has less risk of loss than the nitrate form. The nitrate form of N is more mobile.

“Also, if you apply manure or anhydrous ammonia in the fall, we recommend waiting until soil temperature at the 4-inch depth is below 50 degrees F and the weather forecast indicates soil temperature will stay below 50 degrees,” says ISU Extension field agronomist Mark Johnson. “That’s usually in early November in Iowa. This is critical because the conversion of ammonium to nitrate is much more rapid when soil is above 50 degrees than below 50.”

You can monitor soil temperatures for each county in Iowa at

Apply the right source, right rate, right time, right placement

There is a disciplined application approach that has long proven effective. It’s using the BMPs and the 4Rs to make nitrogen management decisions.

“When we talk about sustainability in agriculture, specifically as it relates to nutrient management, it really goes back to a foundation of best management practices, or BMPs, in conjunction with the Fertilizer Institute’s 4R Program,” says Eric Scherder, field scientist with Dow AgroSciences at Huxley in central Iowa. “We can address some of the challenges we’re facing with nitrogen leaching and surface application runoff more effectively using this approach.”

The 4R program is a concept to help farmers select the right fertilizer source at the right rate, at the right time, with the right placement. While source, rate and placement are important, often the most scrutinized decision (both from an economic and sustainability standpoint) is timing of application.

Fall vs. spring N application, consider the pros and cons

Each year, growers need to consider various factors when deciding when nitrogen should be applied. Complicating the decision are those who call into question research data documenting the effectiveness of fall applications.

“There are a number of reasons why we do fall fertilizer applications,” Scherder says. “One consideration is infrastructure. If every farmer was forced to apply in the spring, we wouldn’t have the equipment or product available to meet the demand. Time and weather are also big factors since the number of days fit for fieldwork in the spring is usually limited. Another important factor from an economic perspective is that growers can often take advantage of more favorable fertilizer pricing in the fall.”

Environmental concerns resulting from nitrate leaching and denitrification, regardless of whether the N is fall-applied or spring-applied, also complicate the equation. Because all nitrogen sources are by nature mobile and susceptible to loss, there are inherent risks.

Use nitrification inhibitor with fall-applied anhydrous ammonia

“When considering fall application, there are certain nitrogen sources like liquid UAN that are probably not the right source for fall application,” Scherder says. “A fall anhydrous application is more common, although risk of loss still remains. Regardless of the form of nitrogen applied, we recommend growers use a nitrogen stabilizer with fall nitrogen applications.”

Studies from Dow AgroSciences with N-Serve and Instinct II nitrogen stabilizers show soil nitrogen retention increased by 28% and nitrogen leaching decreased by almost 16%. N-Serve and Instinct II also have been proven to provide an average 7-bushel-per-acre increase compared with untreated acres by keeping more nitrogen in the root zone for crops to use. This was the average yield return vs. non-treated acres across the 2015 Dow AgroSciences trials.

“Sustainable farming practices are an integral part of delivering food to feed a growing world,” says Susanne Wasson, U.S. crop protection commercial lead with Dow. “We recognize there’s a balancing act of helping growers achieve return on investment while doing so in a sustainable way. By providing technology such as N-Serve and Instinct II, growers are able to achieve strong yields in a way that positively impacts the environment, including reducing nitrate loss into groundwater.”

Consider both the economic and environmental concerns

As growers look ahead and try to anticipate what’s coming for the next six months, they’ll be weighing several factors that will ultimately lead them back to BMPs and the 4Rs. It’s not a perfect science, and there will always be variables. Take the last couple of years in Iowa for example when the ground wasn’t fit, there was too much rain, etc.

 “If you look at the economics alone, if nitrogen is leaching, growers are literally just washing dollars down the soil,” Scherder says. “With denitrification, nitrogen is escaping in the air. Both of these losses have an adverse economic impact, but growers are also concerned about the environment and sustainability. When growers are applying fertilizer with a nitrogen stabilizer, they are negating both economic losses and adverse environmental impact.”

Regardless of whether Mother Nature shines favorably on fall application or decides to halt things and you wait until next spring to apply your N, the fine line of maximizing profit by minimizing nitrogen loss and promoting sustainability should always be top of mind, says Scherder. For more information about protecting fall-applied nitrogen, visit

About the Author(s)

Subscribe to receive top agriculture news
Be informed daily with these free e-newsletters

You May Also Like