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Sponsored: Nitrogen Loss: Now What?
After the corn crop has been planted, we have to think about protecting it post emergence, through pollination, and beyond. One very important piece of the puzzle is to make sure the corn crop has adequate nitrogen (N). Nitrogen availability can be greatly impacted by the weather that has occurred since the N application was made. The N may have been applied very recently with the planter, or it could have been applied five months prior as fall anhydrous ammonia. Regardless of when it was applied, the temperature, method of application, form of N, and amount of moisture since that application will determine how much will be available for the growing crop. Most of the time the greatest loss of N occurs in the months of April, May, and June. This is when pre-plant N has been applied but the corn crop has only taken up a relatively small portion of what it will need.
A corn plant’s N needs are low until it reaches the V8 growth stage. At this point, it begins to rapidly uptake N until about tassel emergence when the corn plants slow their N uptake. During this period, the corn plant takes up almost half of its total N needs. That’s why it’s important to evaluate N levels in the soil that will allow applications to be made before the rapid uptake of N occurs at V8. There are several options that can help you determine what the N needs are. First, a Pre- Sidedress Nitrate Test (PSNT) can estimate the amount of N available in the soil. It’s especially useful if the corn crop is following a manure application or alfalfa crop.
Another option is using tissue analysis. This is of limited value early on because it only tells what is going on with the plant at the time the samples were taken. The third choice is the Illinois Soil Nitrate Test (ISNT), which is designed to predict the soils potential to provide N through mineralization later in the season. If you have planned to apply an N sidedress or are concerned that you do not have enough N left from previous applications, there are options available to help determine the amount to apply or if any additional is needed at all.
In this chart, Beck's Practical Farm Research (PFR)® data demonstrates the value of splitting N applications between pre-plent incorporated and a sidedress application, instead of applying all N in one pass before planting. There are other studies in our PFR book and elsewhere that show increased return on investment when all N is applied as a sidedress application, but with the unpredictable weather that occurs in much of the Corn Belt during this sidedress time it is wise to split up the application. This offers a longer window for the sidedress application to occur without potential yield reductions.
This article was first featured in the May 2016 issue of Beck's CropTalk newsletter. Click here to read the full version.