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CropTalk: No Fall Nitrogen? No Problem.

April 2019

Published on Monday, April 01, 2019

In the February issue of CropTalk, we discussed different methods to apply anhydrous in front of planting to minimize seedling injury. Having said that, there is no guarantee that this spring will be a smooth planting season. So, what should you do if you have a tight planting window this spring?

First, I would emphasize that planting is more important than applying nitrogen (N) prior to planting. There are multiple ways to get N to a crop, so planting should take priority over N application. If you are locked into an anhydrous purchase, you can still sidedress your corn.

If you are going to apply anhydrous sidedress and have not done it before, one common question is whether or not to stabilize. Let’s examine this question. Once the corn plant hits that V7 or V8 growth stage, it begins to take up N at a high rate, estimated to be 7 to 10 lb. of N per day. With that in mind, the corn will have large N requirements within four or five leaf stages of application (assuming a V3 to V4 sidedress timing).

Anhydrous is in the ammonium form (NH4+) once it takes up a hydrogen ion from water in the soil and binds to negatively charged soil particles. The ammonium ion must go through a process called nitrification in order to be converted to the nitrate form. Nitrate (NO3- ) has a negative charge, so it is more mobile in the soil. Nitrate is the main form of N taken up by the plant simply because it is mobile in the soil through soil water. The process of converting the NH4+ to NO3- can take weeks. Depending on your soil health, drainage, temperature, soil structure, and rainfall post application (among other factors), it can take longer than that to convert. You want to have adequate NO3- N available when the corn plant hits the rapid N uptake phase. Keep that in mind when trying to decide if you should stabilize or not.

The sidedress stabilization decision is impacted by other factors as well. Are you able to apply some N through the planter? Did you use any N in a weedand- feed program? Those systems would make NO3- N available early in the season.

Most anhydrous stabilizers on the market extend the length of time your N remains in the NH4+ form and reduce the potential for loss via denitrification or leaching. They do what they say they will do. But keep in mind that you want both NO3- and NH4+ forms in the soil during the rapid uptake phase to supply the current crop needs as well as the future crop needs.

Bottom line: there is no right answer as to whether or not to stabilize. That question can really only be answered post mortem, but here are some things to consider. The odds of stabilizers paying off are much higher if you have poorly drained soil, heavy clay content, and/ or if you plant fuller season hybrids. Of course, those odds are swayed by rainfall during the season. If you are able to apply NO3- N in other forms through the planter or with other methods and have poorly drained soils, then stabilizing your anhydrous may make sense.

Ultimately, many factors outside of your control impact your decision. If you do decide to stabilize your sidedressed anhydrous, make sure you are supplying the plant with adequate NO3- nutrition early as well. Remember, the ammonium form is held tightly by your soil and will not move readily through soil water; it is somewhat unavailable until it encounters roots. Roots only intercept one to two percent of your soil by volume, so root interception is a limited method of N uptake to the corn plant.

There are multiple new methods to apply N to a growing corn crop in-season. Focus on planting the crop first, then utilize one of the many avenues available to apply N post planting. Make sure you supply the crop with ample N throughout the growing season to maximize yields.

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Author: Jim Schwartz

Categories: CropTalk, 2019

Tags: CropTalk, Nitrogen Uptake

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