Nitrogen on Corn in 2016: A First Look | The Bulletin: Pest Management and Crop Development Information for Illinois
By Emerson Nafziger, University of Illinois Extension
The 2016 cropping season was a good one in Illinois, with planting a little ahead of normal and good May moisture and temperatures to get the crop off to a good start. June was warm and, in most parts of Illinois, drier than normal; parts of western Illinois received less than an inch of rainfall for the month. Temperatures and rainfall returned to normal in July and August, though there was the usual variability from region to region, including much-above-normal rainfall in the southern end of the State.
With good May soil conditions, mineralization got off to a fast start, and the crop in most fields was dark green by the end of May and starting to grow rapidly. Without N loss conditions in June, N from both fertilizer and mineralization stayed in the rooting zone, and N availability to the crop was outstanding. Even no- or low-N strips stayed dark green in trials into the middle of June, much later than we normally see N deficiency developing.
The retention of N in the soil and its availability to the crop carried through the season to diminish the need for fertilizer N. Figure 1 shows a response to N in an on-farm trial in DeWitt County, Illinois. Not only did about 150 lb. of N maximize yield at 230 bushels per acre, but it made almost no difference whether the N was applied in the fall or in the spring. We know from our N tracking that most of the N was in the nitrate form by the time crop uptake started in late May; we can see here that in the absence of N loss (wet) conditions, nitrate stays in the soil and is available for plant uptake just like ammonium.
Figure 1. N responses from fall- and spring-applied anhydrous ammonia in an on-farm trial in DeWitt County, Illinois in 2016. Optimum points are the N rate and yield at the point where the last addition of N provides just enough yield increase to pay for that N.
Dan Schaefer of IFCA coordinated dozens of on-farm trials similar to the one shown in Figure 1. Some had fall versus spring N timing comparisons, some had all early versus some early plus sidedress, and others just compared yields at different N rates. Figure 2 shows results from 26 trials conducted across central Illinois in 2016.