Managing Corn Following Corn
|Emerson D. Nafziger
Extension Agronomist and
Professor of Crop Sciences
With 12.9 million acres of corn in Illinois in 2007 following 10.1 million acres of soybean in the state in 2006, about one-fourth of the corn crop in Illinois in 2007 follows corn. If the demand for corn means increased corn acreage into the future such that we have 2/3rds corn and 1/3rd soybean, then half of the corn crop will follow corn every year. We’re clearly on the road to corn following corn as a “normal” crop sequence in Illinois.
While management of continuous corn has usually been thought of as more challenging than management of corn following soybean, we are learning that with newer hybrids, the management differences between these two systems may be less than we once thought:
- The fact that corn following soybean (SC) no longer provides corn rootworm protection in Eastern Illinois means that one of the main economic incentives to keep rotating corn with soybean no longer exists. Corn rootworm needs to be managed in every field where corn follows soybean or where corn follows corn (CC).
- Even though many producers report higher or equal yields from CC compared to SC, our research comparisons at Urbana continue to show modestly higher yields for SC, as shown in Figure 1.
- Despite the common belief that manages to “solve” its problems and yield the same as SC after several years of continuous corn, we have seen no sign of this in our research. Over a three-year study at Urbana, 2nd-year corn yielded the same as continuous corn, and SC yielded a few bushels more, but the difference was not statistically significant. Second-year corn does not face more problems than 5th-year or 10th-year corn.
- While the large database we use to formulate N rate guidelines shows that SC and CC in Central Illinois respond almost identically to N, our long-term rotation x N rate study at Urbana shows that CC requires an average of 19 more lb of N per acre than does SC. This difference ranges from 19 lb less to 61 lb more N for CC, and over years this N rate is not correlated to yield level.
- Despite claims that N starts to “recycle” so that N fertilizer rates decrease after several years of continuous corn, data from Urbana show no such pattern (Fig. 2). The amount of N needed is correlated to CC yield, but yield shows no trend over time.
- While it is often suggested that CC will benefit more than SC from application of a foliar fungicide, recent studies we have done in Illinois do not show this. We found a yield increase from foliar fungicide in 7 of 10 trials, but the largest increases (11 to 13 bushels) were in SC, while those in CC were only 5-6 bushels. These studies did not have high levels of disease.
- Some advocate “higher inputs” (often synonymous with “higher management”) for CC compared to SC, a study on continuous corn in Urbana has shown little response to increasing levels of tillage, extra fertilizer (including 100 more lb N), or higher plant populations (Fig. 3).
While we are continuing many of these studies to learn how to better manage CC, we do not find responses to management to be consistently different in CC compared to those in SC. Questions that remain to be answered include whether or not we can do less tillage, including strip-till, in CC, and what effect removal of residue (for conversion to biofuel) might have on yields and soils in CC.