Top Crop Manager

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Optimizing a fall fertilizer application


August 9, 2020
By Top Crop Manager

The spring months are always a welcome respite after a long, cold winter. As soon as the temperatures rise again, farmers are eager to get back into their fields to begin seeding. But soil management and field preparation are important steps, and there’s no better time to do it than the autumn season.

In fact, Robert Mullen, the directory of agronomy for Nutrien, says a fall nutrient application can be beneficial in more ways than one.

“For a winter-seeded crop, like winter wheat, the primary motivation for a fall application of nitrogen is to make sure we’re encouraging good tillering of the crop and creating an environment where there’s an adequate supply of nitrogen,” he says.

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He adds a fall fertilizer application can maximize efficiency in the spring when seeding time approaches. “Equipment and field availability are generally better in the fall, to spread out the workload and benefit the farmer.”

Considering the 4Rs

When it comes to nitrogen application methods, Mullen notes it’s difficult to come up with a hard-and-fast rule to follow, as farmers need to be mindful of the 4R nutrient stewardship principles – the right source at the right rate, time, and place.

“The challenge we often find with regard to the best management practice for nutrient inputs, specifically nitrogen, is the influence of prevailing environmental conditions, including the weather pattern and type of soil,” he says, adding that weather patterns are really what dictate loss potential. When conditions are dry, a fall band application of nitrogen, followed by a spring broadcast and incorporation can be effective. But in wetter environments, the timing of a nitrogen application is critical as the risk of loss is greater.

“We’re not too concerned about leaching [in dry climates] because we typically don’t see heavy rainfall,” he says.

Soil sampling is an important piece of this decision-making puzzle, and Mullen advises sampling soil as soon as possible after harvest. “The general rule of thumb is to make sure your soil temperatures are relatively cool – below 10 C,” he says, noting applying fertilizer to frozen ground means the product will stay on the surface of the soil for the winter. If the soil is too wet, more intensive tillage may be required the following spring.

Understanding the complexity of how fertilizers work can be helpful when it comes to choosing a source. Mullen says anhydrous ammonia has traditionally been considered the most efficient source for a few reasons.

“Anhydrous ammonia acts as its own fumigant. The bacteria that are responsible for converting that product into a form that’s more mobile – specifically into nitrate – do not survive well. In a cooler soil environment, the ammonia is retained and not converted into a form that could ultimately be lost,” he explains.

“The other reason is the depth of application. Typically, we’re targeting that four- to six-, even eight-inch depth of application. The deeper we make that application of anhydrous ammonia, the fewer the bacteria that are going to be available in a high concentration to convert that product into the nitrate form.”

Urea and enhanced efficiency fertilizers are also good options. “Urea is still not a nitrate form of nitrogen,” Mullen says, explaining products that have nitrates should be avoided in the fall. “ESN is in an encapsulated urea form, so when it’s released into the soil environment is primarily affected by soil temperature.”

The bottom line

There are lots of factors to be mindful of when considering a fall fertilizer application, but with the proper knowledge in hand and the right conditions, the benefits of a fall application are plentiful.

Perhaps most importantly, Mullen reminds farmers to keep nutrient stewardship and improved nutrient management in mind.

“We want to promote 4R nutrient stewardship and improve nutrient management, primarily for the environmental benefit,” he says.