Nitrogen: Why it’s important and what to consider before applying fertilizer

Nitrogen is a key building block of life and the most abundant element in our atmosphere — 78%, in fact. It’s vital for plant growth and a major component of chlorophyll and protein-building amino acids. Yet so little of it is naturally available in forms that plants can use. 

For millennia, plants’ ability to feed themselves relied heavily on tiny, nitrogen-fixing microbes living in the soil and the roots of some plants. These microbes turn nitrogen in the air into forms of nitrogen that plants can use. 

Although nitrogen is vital for modern growers, it is also a major cost, and excess nitrogen that escapes into groundwater, surface water, and the atmosphere can be incredibly harmful to the environment.

Growers must weigh a variety of factors to decide when, how much, and what kind of nitrogen to apply to their fields to achieve the best results, highest yield, lowest cost, and least impact to the environment. Sound Agriculture’s chief agronomist Jeff Divan, himself a grower in Iowa, shares some items growers should consider. 

Timing

The earliest a grower can apply nitrogen is the fall before the growing season.

“The biggest reason for a fall application is logistics,” says Jeff.

Growers usually have more time in the fall than in the spring, which offers time savings during the critical planting window. However, since fall is a long way from when spring crops will use the nutrient, there’s ample opportunity for environmental loss.

When nitrogen is applied in the fall, soil temperature is an important consideration, says Jeff.

“Anything below 50°F and the nitrogen is typically unreactive in the soil,” he says. ​“It’s going to stay put until spring — until we warm things back up. But if we’re above 50° at the time of application, then we are more likely to lose nitrogen.”

Nitrogen fertilizers eventually end up in either the nitrate or ammonium form. Ammonium and soil are oppositely charged, binding them together and reducing leaching. However, ammonia gas can be lost from the soil and enter the atmosphere through a process called ammonia volatilization. Applying during cooler temperatures and proper mixing can reduce this loss and mitigate ammonia’s risk to air quality and human health.

The nitrate form of nitrogen, on the other hand, has the same charge as soil. Because it’s not bound to anything, it’s prone to denitrification and leaching, both of which occur with water.

Denitrification happens when nitrates sit in saturated conditions, and it reduces the amount of nitrates available to plants by turning some into nitrogen and nitrous oxide gases, which escape into the atmosphere. Nitrous oxide depletes the ozone layer and is a potent greenhouse gas.

Unlike ammonium, nitrates move easily in water and can leach into surface or groundwater, which can have serious negative impacts on the environment, contributing to algae blooms, depriving surface waters of oxygen, and even killing fish and other aquatic life.

Stabilizers

“Regardless of when nitrogen is applied, as growers, we start to worry about excessive rains in the spring,” says Jeff.

Even if the temperature and moisture levels in the fall are just right, he says, excessive rain in the spring can wash away nitrates in the soil.

A common way to try and hold on to nitrogen until the planting season is by using a stabilizer. Stabilizers use inhibitors to do one of two things: delay the enzymes that facilitate ammonia volatilization long enough to fully incorporate the nitrogen into the soil, or stop the bacteria that turn ammonia into the more soluble and less stable nitrate.

“That’s one reason people will use a stabilizer on ammonia in the fall — it’s not so much about what’s going to happen that fall, but when spring comes, you don’t want any more in the nitrate form than there needs to be,” he explains.

Stabilizers are another cost, though, which is a big consideration. To reduce losses, maximize efficiency, and minimize cost, the ideal time to apply nitrogen is in-season when the plants are growing. ​“In-season application is the ultimate option for efficiency because you’re applying it right when it’s being taken in by the crop,” Jeff says.

Cation Exchange Capacity

Depending on a grower’s soil, however, a single in-season nitrogen application may not be ideal. A soil’s cation exchange capacity (CEC) is an important underlying factor for when a grower applies nitrogen as it is a measure of a soil’s ability to hold nutrients.

With lower CEC, it’s possible to add a lot of nitrogen at one time, but it would be prone to environmental loss. Two or three smaller applications can reduce the risk of losing nitrogen.

In an attempt to make sure enough nitrogen is in the soil, growers are often generous with the amount they apply since it’s hard to know what has been lost.

“The unfortunate part, from an environmental perspective, is that those buffer pounds are also the least stable,” Jeff explains. ​“Soil can’t hold an infinite amount of nutrients, and those extra amounts are the ones most prone to leaching and being lost.”

And that’s quite literally dollars down the drain, not to mention a risk to the environment.

Testing

Besides relying on experience, there are strategies available for growers to better understand how much nitrogen has been lost between application and planting.

Soil nitrate and tissue tests can offer some insight, says Jeff, and he’d like to see more growers using tests to see what they need. ​“They’re not perfectly accurate and it’s not necessarily a silver bullet, but it’s good information,” he says.

Some organizations like the National Resources Conservation Service (NRCS) have programs to encourage soil testing, but many growers rely on their own experience or intuition. Learning to use that information to better inform future decisions is the key to maximizing impact.

Organic Matter

There is one last, late-season opportunity to increase nitrogen. ​“Organic matter can mineralize and contribute natural nitrogen within the soil,” says Jeff, ​“but that requires warm temperatures, so it doesn’t happen until the middle of the summer. It also requires good moisture.”

Not all growers have enough organic matter in their soil to get this late-season boost, and it’s late enough in the season that growers often don’t want to rely on it. Incorporating compost or cover crops are two ways growers can improve organic matter and benefit from a late-season nitrogen boost.

Innovation

When it comes to nitrogen application, growers must consider a variety of factors, and their own experience and knowledge of their fields, to decide what will produce the highest yield at the lowest cost with the least amount of negative impact to the environment, and Jeff knows this first hand.

Sound Agriculture’s SOURCE™ for corn or soybeans is another tool for growers looking to maximize nitrogen efficiency and reduce cost. SOURCE isn’t a fertilizer; it’s a microbiome activator. Using chemistry, SOURCE stimulates microbes in the soil to increase the amount of nitrogen available to plants by activating nitrogen-fixing microbes.

“It’s a consistent and reliable in-season source of the ammonia-form of nitrogen,” explains Jeff. ​“This alternative source opens the door to use a little bit less nitrogen in those fall or pre-season applications — the ones that are so prone to loss — but still bring that same amount of total nitrogen into the equation in season, when the plants actually need it.”

Jeff says SOURCE can be used to reduce the amount of ​“insurance pounds of nitrogen” that growers use when they’re not sure how much nitrogen has been lost. Those buffer pounds are often unprofitable, he says, and more prone to entering the environment.

“SOURCE improves nitrogen use efficiency, it decreases many of those environmental losses, and ultimately it’s providing a yield lift as well,” says Jeff.

Within any field there are varying conditions, he explains. Some areas of the field may be prone to flooding, others may be drier, and some areas may have different soil qualities. As a source of consistent nitrogen, SOURCE can help even out yield potential, making lower-productivity areas more reflective of overall field quality.

“If we’re giving a shot of nitrogen to all those acres late into the season with SOURCE, when it’s actually being used, it’s different than if we apply a unit in the fall and it’s lost at different rates across those different environments,” Jeff says.

While there’s no one size-fits-all formula growers can use for determining how much nitrogen to apply and when, SOURCE gives growers another tool to help them lower costs, improve yields, and reduce environmental impacts.