Wednesday, November 7, 2007 - 1:30 PM
262-6
When Does Corn Following Corn Become "Continuous", and Do Insects Notice?.
Many producers who adopt the cropping system in which corn (Zea mays L.) follows corn are concerned about corn performance in the first season in which corn follows corn (i.e., second-year corn), and many believe that yields in the third and subsequent years will increase and become more stable. While the belief that yields will eventually improve is useful as preparation to accept lower yields when corn first follows corn, there is no experimental evidence showing that yield levels change with increasing number of years that corn follows corn. In two of six sites in Illinois, first- and second-year corn in a corn-corn-soybean rotation produced the same yield, while at two other sites, second-year corn yielded only 5 percent less than first-year corn. Corn that had followed corn for three or more years produced lower yields than second-year corn at three of the sites. Other experiments have routinely failed to show higher or more consistent corn yields, compared to those of corn following soybean (Glycine max), as the number of years of sequential corn crops increases. There has also been no consistent trend over years with regard to the response to N rates as corn is grown sequentially. While there is evidence that the use of genes incorporated into corn from Bacillus thuringiensis for increased tolerance to Western corn rootworm (Diabrotica virgifera virgifera) helps to overcome management challenges from this insect in continuous corn, root ratings in crop rotation studies in 2007 showed very low insect pressure, regardless of how many years corn had been grown in sequence, and regardless of whether Bt or soil-applied insecticide had been used. These results indicate that variations in weather and in insect pressure over years are more important in determining yields and responses to inputs than are the number of years of sequential corn crops in the same field.
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