Fall anhydrous application tips

If 2019 showed us anything, it’s that a season can be even more unpredictable than we ever could have predicted. Nutrient management programs – for Nitrogen in particular – faced all sorts of challenges. As our typical anhydrous ammonia application window opens, there are a number of factors we need to consider if NH3 is our primary Nitrogen source.

First, a large portion of the ammonia in anhydrous ammonia converts to a form that is bound to clay and organic matter particles in the soil. This is important, since the amount of time it stays in the ammonium form makes a big difference when as we evaluate potential Nitrogen losses.

The amount of time it stays in this ammonium form is affected by soil temperature.  In most cases, if we wait until soil temperatures are below 50 degrees Fahrenheit (at a four-inch depth), ammonium may not convert to nitrate – which is more readily lost from the soil – for up to two or three months, if not longer. It’s important to note that the conversion to nitrate doesn’t stop below 50 degrees, but it is slowed significantly.

That doesn’t mean that there are no Nitrogen losses, however, just that they are likely not large. University of Nebraska recommendations, for example, suggest applying five percent more fertilizer when applying in the fall versus application in the spring to account for losses.

The use of a nitrification inhibitor (N-Serve is one) can help reduce losses from fall N applications, particularly under certain soil types or when soil temperatures warm back up for a period after application. Check out soil temperatures at http://mesonet.k-state.edu/agriculture/soiltemp/. Note that losses can vary greatly from field to field and even within fields if soil moisture and texture differences are present. Sandy soils are more prone to loss than medium to heavy textured soils. Drier winters keep Nitrogen loss to lower levels than wet ones. What will 2020 bring?

Understand, as well, that fall applied anhydrous will start the conversion process from ammonia to ammonium to nitrate (where it is more readily lost) as temperatures increase in the spring. This could allow for nitrification to occur well in advance of corn planting, particularly if we are delayed in 2020 like we saw in 2019. If you start to see wheat greening up late February or March, nitrification has begun and will continue, even if the corn isn’t ready to take it up.

Is a little fine-tuning of your fall Nitrogen program in order? Soil types and temperatures can be obtained with a little work and can help define the fields most appropriate for fall application. A split Nitrogen program might be something to consider as well. Many of them worked well in 2019. Are they a practice we should consider on an annual basis? In the end, our goal should be a program that makes economic and environmental sense.

Rabbit Protection

We often don’t pay much attention to them until spring, but rabbit feeding actually often begins in the winter, particularly on newly planted trees and shrubs.

Start protective measures now, with at least two-foot-tall cylinders of one-inch-mesh, chicken wire, or similar barrier. You also may want to consider plastic tree wraps and liquid rabbit repellents sprayed on the plants as a secondary barrier. Repellents will need to be reapplied after every rain.

David Hallauer51 Posts

David Hallauer is the Meadowlark Extension District agent in the areas of horticulture and crops and soils.

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