The fall of 2010 was near perfect. Perfect weather for harvest; and perfect weather to apply nitrogen ahead of the 2011 crop. But with the wet spring, you have every right to wonder if there is any nitrogen still available in your field to nourish your corn crop. Has the excessive rainfall in parts of the Cornbelt leached it beyond the reach of corn roots? 

That is a hard question for soil scientists to answer, say Daniel Kaiser and Jeffrey Coulter at the University of Minnesota. You have fought hard to get your corn planted and are hoping it has the nutrients that it needs to produce a crop.  But do you need a sidedress application.  Kaiser and Coulter provide some guidance with a look at denitrification. Their thought is that since soil temperatures have been so cool, there was little risk of loss of the nitrate form of N, and since the soil was cool, bacterial action on the nitrogen should also have been minimal.  So it should be there for the corn to use.

However, as the soil warms up there will be some risk of losing some of your nitrogen. Kaiser and Coulter say it should be a small percentage compared to all that you applied. They don’t believe you should be worried about the potential loss until you can evaluate your corn at the V4 or V5 stages to see if there are any symptoms of nitrogen deficiency. They even supplied a worksheet to aid your decision application of supplemental nitrogen.

The specialists suggests that you begin your evaluation process in the fields that had the N applied the earliest last Fall, which may have been too warm for the nitrogen to stabilize, as well as fields where soils might have been too wet to result in less optimal incorporation.  If you find a need to apply more, Kaiser and Coulter suggest side dressing.  “Although N uptake occurs throughout the growing season, peak demand generally starts at the V5 growth stage and progresses to tasseling, at which time about 60% of the total N is consumed.”

The agronomists say there is no exact recommendation for the amount of supplemental N to apply for after crop emergence. They say the worksheet they provided suggests a range of 40 to 70 lbs per acre if the corn meets their criteria. Those include 30 to 40 lbs per acre application following soybeans or 60 to 70 lbs per acre where corn follows corn on heavy soils.

They report that any type of nitrogen can be used for side dressing, even urea that is dry.  But they are quick to warn about the loss of nitrogen if it is not incorporated, or is subject to any runoff following rain. Inhibitors may be used in such cases since nitrogen will be absorbed by water and move through the soil profile. They also suggest any sidedress applications be made earlier before the crop gets too tall and to also allow nitrogen to move into the root zone while it is still needed. If the window is tight for getting any N sideressed, they suggested going to the fields first that had the greatest risk of loss.

Your potential for losing the nitrogen you applied last fall is minimal, since soils have been cool that that inhibits loss. However, if your analysis of your corn indicates a nitrogen deficiency, a sidedress application can occur with either a liquid or granular form of nitrogen as long as additional rain does not wash away the dry forms. If there is a slim chance of getting to apply any nitrogen with a sidedress application, focus on your fields with the greatest loss potential.