Recent high yields recorded by Francis Childs in Iowa and by others have usually been from fields where corn is grown continuously.

This has resulted in support for the idea that such yields may be high because corn follows corn. There is no known research data supporting this idea; our recent work in Illinois shows that in direct comparisons, corn following corn produces 7 to 10 percent less yield than corn following soybean. On the most productive fields, continuous corn can certainly produce high yields, but inputs needed to produce such yields must be investigated and rationalized.

While we have accumulated a considerable amount of data on the nitrogen response of corn following corn compared to that of corn following soybean, we do not know the effects of some of the “high yield practices” used by some producers, including those producers who are attempting to produce yields above 300 bushels per acre. Such practices typically include deep and thorough fall tillage, high N rates, and high plant populations. Most fields also have high to very high P and K levels, usually as a result of high inputs from fertilizer and/or manure over a period of years.

While this set of practices clearly results in high yields, it is possible, or even likely, that some of these practices may contribute little or nothing to yield. This study is designed as a way to isolate the effects of deep tillage, additional plant nutrient supply, and higher plant population, and interactions among these factors, on corn yield at a number of productive sites in Illinois.

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