How is your corn doing these days? With the heat, growing degree days are rapidly building, but how about moisture? How is the corn plant maturing, and did it get the nitrogen that you intended to give it? You may have a $750 per acre investment or more, and you have probably done all you can do, except for a last shot of nitrogen if it is not already too late.
USDA says we have plenty of acres of corn, but the yield on those acres is being determined now. In the early planted corn, kernels are being pollinated. In the late planted corn the kernel number is being determined. This is the heart of the watermelon, as far as the potential yield of your 2011 corn crop is concerned.
Some pre-tassel corn is showing brown leaves at the base of the stalk, which Purdue corn specialist Bob Nielsen says may be related to insufficient nitrogen. If that symptom is prevalent in your fields, and the crop is still small enough to accommodate a late shot of nitrogen, what are your options?
First of all, access to a high clearance applicator is necessary, whether leased or hired, Neilsen says the 200 lb per acre application of 28% urea-ammonium nitrate occurred at the V-15 stage for the corn. Although there had been 4 inches of rain in the prior 2 weeks, no rain occurred for 11 days after the application, which he suggests may have contributed to the lack of response to the nitrogen until 4 weeks after the application. Therefore, if an application can be made ahead of rain, there is a better chance for the success.
Nielsen relates another case where a V-13 application increased yield by 64 bushels per acre, compared to a starter-only application. “The results of these studies demonstrate that corn can recover from significant N deficiency stress with applications of sidedress N fertilizer even as late as V13 to V15. In a year when weather can delay field work into unconventional periods of the growing season, options still remain to recover significant yield with late sidedress N applications.”
Similar results have been reported by Iowa State fertility specialist John Sawyer. His research recorded an 8 bushel per acre increase (177 vs. 185) when 55 lb of nitrogen was applied in the V-15 to R-1 growth stages. He says that test and a similar one indicated that the best results came when good rainfall followed the application.
With crops growing rapidly and rain coming more infrequent than in the first half of the growing season, the corn is using nitrogen quickly says University of Illinois fertility specialist Fabian Fernandez. But he says if the corn is showing nitrogen deficiency that means some of the yield potential has been lost and cannot be recovered. However, he says the sooner that late season nitrogen is applied, the sooner the response will be visible, until tasseling, “Studies have shown that even until silking, corn has a great capacity to use N and produce an increase in yield if the application is done in severely N-deficient fields.”
What are your options for late season nitrogen application? Fernandez says you have several options.
1) Between-row applications of dribbled or injected UAN solutions or urea plus a urease inhibitor such as NBPT (Agrotain).
2) Another option is broadcast urea with a urease inhibitor. The urease inhibitor is important to reduce the potential for volatilization losses when the product sits on the soil surface until it is incorporated by water.
3) I do not recommend broadcast application of UAN because of the high probability of canopy injury.
4) A slow-release product (polymer-coated urea) is not a good choice at this point because you want N to be available to the crop immediately. While the coating can protect urea from volatilization (just like a urease inhibitor does), it will take time for the coating to break down and release N, further delaying availability to the crop.
5) I would not apply a foliar product simply because the amount of N that can be applied is often very low and the cost per acre too high to make that profitable
He says regardless of what you use, any surface applied product will require water to move it to the root zone. Do what you can about the need for rain.
Corn is growing rapidly and using nitrogen rapidly as well. However, many fields did not get the additional application because of wet weather at the first part of the growing season. Fertility specialists say late season applications can still be made with good yield results, if the proper type of nitrogen is used, and if rainfall can move it into the root zone.