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More Corn In the Illinois Crop Mix?

Emerson Nafziger
Department of Crop Sciences
(217) 333-4424; ednaf@illinois.edu
Emerson Nafziger
Figure 1

Figure 1. Yields of corn following corn and corn following soybean at Monmouth, Illinois.

Lower land and labor costs in other countries may well mean lower world prices for soybean in the future. Corn does not face as much external threat to production in the near future, and we think that this may eventually shift the crop mix toward more corn in Illinois. To shift acreage successfully from soybean to corn, we must learn how to better produce corn when it follows corn in the cropping system.

We know that corn following corn has almost never yielded more than corn following soybean in Illinois; in an ongoing study at Monmouth, corn following soybean has outyielded corn following corn every year for 19 years (Figure 1). Work in Minnesota and Wisconsin has shown that second-year corn, after five years of soybean and following a corn crop, yielded only slightly more than continuous corn, indicating that the beneficial effect of soybean on the following corn crop is short-term (Table 1). We expect that some producers may shift some of their more productive fields to continuous corn, while others will use three-year rotations of soybean-corn-corn on part of their acreage. We have initiated a study of this rotation at six locations in Illinois in 2002. In the study cited above, soybean yielded more following five years of corn than when it was grown in a corn-soybean rotation (Table 1).

Table 1. Yield of corn and soybean in a rotation study in Minnesota and Wisconsin
Years of Continuous Cropping
Following Five Years of the Other Crop
Corn Yield Soybean Yield
1 143 49
2 128 45
3 126 42
4 126 42
5 126 42
Continuous throughout 124 41
Rotated soy-corn 141 45

One of the key differences we have documented between corn following corn (continuously) and corn in a two-year rotation with soybean is in the response of the crop to nitrogen. The same Monmouth study cited above has shown that corn following corn almost always needs more N than does corn following soybean (Figure 2). Over many years and locations, we think that corn should receive about 40 lb more N when it follows corn than when it follows soybean. Reasons for this are complex, but the main reason seems to be the decreased availability of soil N caused by the large amount of corn residue.

Figure 2

Figure 2. Optimum N rates for corn following corn and corn following soybean at Monmouth, Illinois.

Tillage can affect how corn performs in different rotations. Researchers in Indiana showed that the average yield of corn following corn was about seven percent lower than that of corn rotated with soybean when primary tillage was used, but this reduction was about 15 percent in no-till. They also showed that the effect of tillage in overcoming the “monoculture yield decline” was greater in high-organic-matter soil than in soil with low organic matter. Similar results were found in Ohio, but continuous corn in Kentucky usually yielded as well in no-till as when tillage was used.

Other attempts to overcome the lower yield in continuous corn have shown that removal of previous-crop corn residue might be useful, if not usually practical. There may be differences among corn hybrids in their response to continuous corn, though this has not been investigated extensively. Corn grown continuously, especially without tillage, needs resistance to foliar diseases such as gray leaf spot. It is not known whether other plant characteristics, such as rooting pattern or root system size, might contribute to the ability of corn hybrids to successfully follow corn in a field.

Francis Childs, a producer in east-central Iowa who holds the current unirrigated corn yield record of more than 400 bushels per acre, produces only continuous corn for his contest entries, using modified tillage and extra fertilizer. This suggests some potential to increase yield of continuous (or, presumably, second-year) corn, though it is not known whether or not rotation with soybean might raise such yields even higher.

We would like to learn how to bring yields of corn following corn to the level of corn following soybean. It won’t be easy.

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