Since precision farming came along twenty years ago or more and gave people the ability to variable rate apply nutrients in a field, people have wrestled with a basic concept: Does it make sense to try to bring the low-yielding areas of the field up to the high yielding areas? Or is your money better spent to realize you're only going to get so much yield form the low productivity areas, and pour on nutrients in the better soils?
Even the best of consultants and agronomists over the years have tried one way of farming, then another. The consensus for the most part seems to be today after more than two decades of trial and error that it makes more sense to invest in pushing the most productive spots to higher levels. John McGuire once believed that, and he still does to a point. However, the data management guru believes that it may not be a one-size-fits-all solution. The answer may vary depending upon the input that you are applying. McGuire operates Simplified Technology Services, based in Montpelier, Ohio.
Say you are farming red hills, where soil erosion has occurred over time, and dark, lower- productivity soils in the same field. You may find that soil test levels are actually higher on the hills than in the black ground for phosphorus and potassium because the crops over the years have not been able to use as much of those nutrients. Yields were lower there.
However, it doesn't automatically follow that you could program in a lower nitrogen rate for those soils. At one time, McGuire thought so, but now he's not so sure.
It's all a matter of having data where trials are done and comparisons of rates are made, and then making use of the findings to make decisions. What he's discovered is that sometimes corn on those red hills will respond to 200 pounds of nitrogen vs. 150 pounds per acre. Sometimes the difference is more than enough to pay for the nitrogen. So nitrogen may need to be handled differently than other nutrients in your farming plans. Nitrogen is here today and gone by next year. The other nutrients, particularly phosphorus and potassium, tend to stay around from year to year if they're not used by the crop.