The intricacies of fall-applied nitrogen

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For growers who applied their nitrogen (N) in the fall, the pressing question come growing season is how much N remains on the field – especially with higher than usual moisture rates. The answer depends on a variety of factors: weather conditions since application, where the N is in the nitrogen cycle – how much nitrification has occurred – and what type of N was applied in the fall. Depending on the answers to these questions, growers may have to apply an N top-up, or, ideally, they already have enough on the field for their crops.

Applying N in the fall after harvest is appealing to many growers because it’s a big time-saver come spring seeding time. Successfully applying N in the fall to protect against losses, such as leaching, comes down to the matter of timing. The University of Minnesota Extension recommends that growers aim to apply N when the soil temperature is below 50°F (10°C) but not yet frozen.

If the soil is frozen, the N won’t incorporate into the soil and will be vulnerable on the surface. If the soil is warmer than 50°F, the conversion of ammonium to nitrate occurs more quickly leaving more nitrate-N in the soil vulnerable to winter and early spring losses.

Even with proper application timing, spring rainfall is more likely to cause leaching of N than rainfall late in the fall, because during fall application, the soil is generally drier and can take in more moisture. If N converts to the nitrate form in the fall before freezing, there is greater potential for leaching the following spring.

Growers concerned about losing fall-applied N to the environment and having to top-up come spring, but wish to reap the benefits of fall fertilizer application, should consider using a controlled-release N fertilizer in their blend. ESN SMART NITROGEN® is currently the only controlled-release N fertilizer available in broad-acre agriculture.

ESN allows growers to plan ahead for spring and have greater confidence in how much N will remain on the field. For growers of crops requiring high amounts of N who still want to apply in the fall and in the spring, ESN gives the grower more flexibility by providing a wider application window.

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