Source: Ohio State University

Given the potential for greater economic returns, many grain farmers are planning to increase their corn acreage in 2011. Although much of this additional corn will be produced in fields following soybean or wheat, some will be produced in fields following corn. Continuous corn is not recommended by most agronomists. In Ohio, corn grown following soybeans typically yields about 10 percent more than continuous corn. Benefits to growing corn in rotation with soybean include less disease and insect buildup, less crop residue, and less nitrogen fertilizer use. Growers who intend to plant second year corn should consider management practices that will minimize potential yield losses. The following are some key steps for managing risks in corn following corn.

1. Plant corn on the most fertile, well drained soils to reduce stress and maximize yield potential. Avoid droughty soils as well as poorly drained soil conditions. Studies across the Corn Belt have shown that the yield differential between continuous corn and corn grown in rotation with soybeans is greatest when yield potential is low. This yield advantage to growing corn following soybean is especially pronounced when drought occurs during the growing season. In a study conducted in Minnesota, the yield advantage to an annual rotation of corn and soybean compared with monoculture was frequently greater than 25 percent in low yielding environments.

2. Plant Bt rootworm resistant corn hybrids or apply soil insecticides in areas where western corn rootworm problems have occurred. Bt corn requires either a 20 percent or 5 percent refuge, depending upon the transgenic hybrid chosen, to prevent resistance development. Corn rootworm problems on refuge acres may be managed with soil-applied insecticides, or high rate formulations of seed treatments albeit that seed treatments often do not manage the population adequately under high rootworm populations. If Optimum AcreMax RW is planted, no refuge is needed because this hybrid has 10 percent refuge in the bag, also known as RIB ("refuge in a bag").

3. Adjust nitrogen rates. Optimum nitrogen rates for corn after corn are generally higher than those for corn after soybean and the additional nitrogen required ranges from 30 to 50 lbs nitrogen/ A.

4. Select hybrids that have demonstrated high yield potential across diverse environments and stress conditions. Only hybrids with above average ratings for drought tolerance, stalk strength, and emergence under stress conditions (low temperatures and cold, wet soils) should be considered. Select corn hybrids with resistance to gray leaf spot, northern corn leaf blight, anthracnose and gibberella stalk rots, and diplodia ear rot. The severity of these disease problems is much greater in reduced tillage systems where residues are present. In the past, the use of foliar fungicides has not been considered economical for disease control in field corn regardless of the rotation followed. Strobilurin fungicides have received much attention recently and university data have shown that along with the triazoles, they are effective against the major foliar diseases. However, fungicides are usually not economically beneficial if resistant hybrids are planted. The greatest yield benefits are seen when susceptible hybrids are planted, especially in continuous-reduced or no-till corn, and conditions are favorable for disease development.

5. Develop strategies for dealing with increased crop residues. Use stalk choppers and knife rolls on combine heads, spread trash uniformly during harvest, consider strip tillage, avoid no-till where practical, avoid no-till planting on top of old rows, use row cleaners, and plant hybrids with good disease resistance, emergence and seedling vigor.

Studies in Ohio and Indiana have shown that increasing the amount of tillage from no-till to chisel to moldboard plow decreases the yield difference between continuous corn and corn rotated with soybean, especially on poor drained soils. No-till cropping systems are more likely to succeed on poorly drained soils if corn follows soybean rather than corn. The influence of crop rotation on corn response to tillage and soil type has been well documented in long-term OSU-OARDC studies. On poorly drained Hoytville silty clay soils in NW Ohio, where corn followed soybean, yield differences between no-till and tilled ground were greatly reduced. Crop rotation with soybeans had much less effect on corn response to tillage on well-drained Wooster silt loam soils in NE Ohio.

In recent years, agronomists and farmers in Illinois reported that corn following corn yielded as much, or nearly as much, as corn following soybean. However this was not the case in 2010. According to Dr. Emerson Nafziger, corn extension specialist at the University of Illinois, lower yields of corn following corn in 2010 came as a shock. In an Oct. 2010 newsletter article ("What Ailed Corn following Corn in 2010," online at here), Dr. Nafziger listed several factors that may have contributed to problems of corn following corn in 2010. One of the factors involved "allelopathy" (the inhibition of growth in one species of plants by chemicals produced by another species), a concept we don’t hear that much about when discussing continuous corn.

Dr. Nafziger noted, "Corn plants following corn in cool, wet soils tend to be affected a lot by where their roots are in relation to last year's residue, including root remnants. A lot of the residue even in tilled fields was not buried very well, and it's not hard to imagine that a lot of new-crop roots were close to a lot of old-crop residue. We think that's a negative, perhaps due in part to allelopathy, perhaps from temperature effects, and maybe from some diseases that can carry over. Allelopathy starts with the release of substances as crop residue starts to break down, and it diminishes over the course of breakdown. Residue after the fall and winter was unusually well preserved into the spring in 2010, and this could have contributed to the problem."

Another question addressed by Dr. Nafziger concerned differences between "corn following corn" and "continuous corn," with the former referring to second-year corn (following soybean two years earlier) and the latter to corn that follows at least two years of corn. Illinois researchers showed that second-year corn tends to yield a little more than continuous corn, but they have not been able to determine if that calls for differences in management. Moreover they did not think that second-year corn fared much better than continuous corn in 2010.