There is little debate that applying nitrogen in the fall can be effective and convenient. But it may not always be the most efficient or environmentally sound practice.
Farmers, environmentalists and politicians are expressing increased concern about the amount and causes of nutrient runoff, especially nitrates. And fall fertilizer application is one part of the conversation.
“The majority of nitrogen loss through tile lines occurs in April, May and June. The majority does come off in the spring. However, that leftover 40-50% lost in winter is really what you’re reducing,” said Austin Omer, associate director of natural resource policy with Illinois Farm Bureau.
“There are a whole lot of different factors there. There is not a single thing causing that nitrogen to be lost. You lose some in winter and lose the majority in spring.”
The practice of fall-applied fertilizer varies in Illinois according to geography. It is more common in the rich farmland in the central and northern parts of the state. Don Guinnip, who farms near Marshall, puts all his on in the spring.
“I’ve been in a farming atmosphere most of my life where we’ve never done it,” Guinnip said. “I live south of the glacial moraine in Clark County, where we have clay soils. Most of these soils are not tiled. Traditionally the thought has been from folks who have done research that you don’t put fall anhydrous south of the glacial moraine, south of Route 16.”
That doesn’t mean Guinnip doesn’t pay close attention to the issue. As a retired University of Illinois Extension educator and current secretary of the Illinois Corn Growers Association, he is intimately involved in the conversation about nutrient loss.
Timing of application isn’t really the bogeyman. Other factors are at play. But many believe that practices such as split spring applications may result in excessive loss of nitrogen into rivers and streams.
“I think there is a trend toward that (split applications in the spring),” said Guinnip, who is also on the state’s Nutrient Research and Education Council. “We had pretty extensive discussions about this last fall. People from Growmark, Brandt, Nutrien and other private ag companies all said they see a trend away from putting it all on in the fall. They noted a trend from anhydrous to other forms of nitrogen and a trend to using stabilizers.”
The 2019 annual report by NREC concluded that the vast majority of growers are not over-applying nitrogen. But it did show studies indicating nitrogen losses following soybeans were much more likely than application following corn.
Split applications in the spring, such as an early treatment and a side-dress following plant emergence, is becoming more popular. And while statistics show that nitrate losses are on average higher in the spring, eliminating fall nitrogen applications may help by lowering total losses.
“What a lot of research is showing is that if you consider total annual load loss in your tile lines, typically fall application will have more nitrogen lost than your split fall-spring,” Omer said. “Putting all of it on in the spring will have the least amount of nitrogen lost. But if you start applying later in season, if that plant doesn’t take up the majority of that nitrogen, then it can be lost in the following winter. It’s a pretty complex situation.”
Many farmers prefer fall application because they often have more time than in the spring, when they are busy with planting. Weather also plays a role, with most areas getting more rainfall in the spring than in the fall.
Guinnip pointed out that fertilization timing is key to efficacy as well as environmental stewardship.
“The closer you apply any kind of a product to the plant when the plant can use it, the better it is,” he said. “If you’re putting anhydrous on in November and the plant doesn’t need it until next June, you have a lot of product lying out there in the environment that is at risk.”