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Integrated Pest & Crop Management


Peter C. Scharf
University of Missouri
Plant Science & Technology
(573) 882-0777

Losing and Replacing Nitrogen

Peter C. Scharf
University of Missouri
(573) 882-0777

Published: July 5, 2015

On the first of June, it looked like there would probably be a few corn fields with nitrogen problems in Missouri. Now, on the first of July, it looks like there will probably be a few corn fields that don't have nitrogen problems. All but the southeastern corner of the state has received over 12 inches of rain in May and June (https://plantsciencesweb.missouri.edu/nutrientmanagement/Nitrogen/Nitrogen_watch_2015/poorly-drained_Midwest_Jun_30.htm), which is my rule of thumb for when N issues will occur on most poorly-drained fields. The area with excess rainfall extends across nearly all of Illinois, northern Indiana, northwest Ohio, southern Iowa, eastern Kansas, and southeastern Nebraska.

That's a lot of corn.

Many are aware of the nitrogen issues. They can be hard to miss driving down the road. But the same unrelenting wetness that has prevented soybean planting from being finished has also prevented ground application of extra nitrogen fertilizer on most fields.

Fortunately an unprecedented level of aerial application has stepped in to take up the slack. I have heard of at least 18 planes applying N to corn in Missouri, with at least half a dozen more in both eastern Kansas and western Illinois. Mostly they are flying on 100 pounds of urea/acre (46 pounds N/acre), but in some cases 150-based on the level of deficiency I’ve seen in many fields, I think the higher rate is a good idea.

arial view of nitrogen loss in field

On June 30 (Tuesday), I flew from Moberly to Centralia, Mexico, Laddonia, Monroe City, and back to Moberly. In the southern parts of that trip, I would say that 90% of the fields needed more N, and in the northern parts, 50%. It was not unusual to see a field that badly needed more N next to a field that looked pretty good, as in the photo at the left. This suggests that N management, as well as soil and rainfall, can play a big role in the crop's N status and appearance.

I've heard from a number of sources that many farmers are balking at spending any more money on this crop. Extended wetness on poorly-drained soils has probably in some cases damaged the crop’s yield potential. However, I am still convinced that for most of the N-stressed fields I have seen, even the ones with 3 inches of standing water in them, an investment in additional nitrogen will double or triple the money spent. In my experiments with rescue N, the worse the corn looked, the bigger its response to rescue N.

If you are unsure about whether a rescue N application will pay, a yield loss map from NVision Ag is my recommendation for the best way to balance cost against need. Yield loss estimates are based on crop color in an aerial photo. I own this company, so I have a conflict of interest that you should be aware of. However, I've been saying for many years before having this financial conflict that aerial photos are the best way to evaluate whether more N is needed. We're using technology developed at, patented by, and licensed from the University of Missouri.

arial view of nitrogen loss in field

NVision Ag can also turn the aerial photo into a rate control file to put the N where it's needed. Nitrogen loss is patchy in many fields (right). The wet areas lose a lot of N, and the less wet areas can have enough left to produce full yield.

Over the fields analyzed by NVision Ag so far this year, average predicted yield loss due to N deficiency is just shy of 40 bushels/acre (range 17 to 85), and average N rate recommendation has been about 55 pounds of N/acre. The bulk of these fields have been in the western half of Missouri, where (outside of the river bottoms) N deficiency is less severe than what I've seen in eastern Missouri.

However, few planes can apply nitrogen variably, and few ground rigs have been able to get into fields. Even when it dries out, corn is now tall enough in most fields to interfere with the spread pattern on high-clearance spinner spreaders. In severely stressed fields, and there are a lot of them out there (photo below), running a high-clearance spinner on a narrower-than-usual swath width will be a lot better than doing nothing. High-clearance sprayers with drops will remain an excellent treatment option on many fields, and one that allows for variable-rate application.

arial view of nitrogen loses in field

Planes will remain an option physically, but in practice the pilots will bolt from N application to fungicide work if it's available. Getting a plane in to apply N as soon as possible is probably the best option for many farmers as I write this.

Although it's been the most difficult spring I've seen in my 20 years in Missouri, I have to say that I am thrilled with the response of farmers and the fertilizer industry to the N deficiencies that have developed this year. We are light-years beyond where we were in 2010, the last year when I saw a LOT of yellow corn in Missouri. The number of fields getting the nitrogen they need to express their full yield potential is way up from 2010. And I feel that yield potential is still good in many fields. Despite the stress from excess water, we have a soil profile that is full of water on July 1. In a state where corn yields are usually limited by water availability in July, this is a great situation.

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REVISED: September 30, 2015