Nitrogen deficiency was the last thing on many farmers minds, even though we had considerable rain this summer. That's because many people applied the nitrogen by sidedress application after planting. Yet N deficiency is apparently coming back to play a role in yield impact on some fields, even some fields where N was applied sidedress at a recommended time in the season.
Too much rain, coupled with other factors, such as shallow roots that didn't allow good uptake of N, come into play. But in the final analysis, where N was short, yields will be affected, notes Bob Nielsen, a Purdue University Extension corn specialist.
The difference is in size of kernels that develop on each ear, especially if the nitrogen deficiency developed relatively late in the season, he predicts. He has purposely taken an ear form a spot with adequate nitrogen and which had the same number of rows of kernels and kernels per row as one taken from a sport where N was deficient, broke the two in half, and compared them.
What you see is a big difference if you do it near physiological maturity, or the black layer stage, he notes. The kernels on the ear that is deficient in N will be shallow compared t kernels that had enough N to develop.
If you run a yield estimate on those fields, using the standard yield formula, you'll need to be careful not to overestimate yield from the nitrogen-deficient plot. The same reasoning can apply if corn has been sufficiently drought stressed as well.
Nielsen is suggesting farmers adjust that yield estimate formula by changing the fudge factor used for division from 90 to a more appropriate number. For modern hybrids in a good year, it may be 85 or even lower. That will produce a higher yield estimate. He feels it's appropriate because modern hybrids tend to have bigger kernels.
In this case, however, you may need to increase the fudge number, say to 95, since kernels are small. And what you get is only an estimate. Especially when there are mitigating factors, such as N shortage, you may be lucky to get within 30 bushels per acre of the final actual yield, he notes.
So use it for planning purposes. But certainly don't make big financial decisions based upon what a field guide tells you, especially this year.