Indiana corn growers planted an additional 1.1 million acres of corn in 2007 compared to the previous season, for a total of 6.6 million acres (USDA-NASS, 2007). Essentially all of the additional corn acres came at the expense of a decrease in soybean acres. Consequently, the number of acres planted to second-year corn and/or continuous corn increased markedly. Farmers’ planting intentions for 2008 are yet unknown, but the amount of aggressive tillage being conducted in corn stubble fields this fall would suggest that many farmers plan to continue planting corn following corn.

From an agronomic perspective, a continuous-corn cropping system is fraught with hazards (Butzen, 2006; Lauer, et. al., 1997; Pedersen & Lauer, 2003; Vyn, 2004) and typically yields less than corn in a crop rotation system. Most growers understand this. However, some are equally concerned that soybean rust (Phakopsora pachyrhizi), soybean aphid (Aphis glycines Matsumura), or other major soybean stresses in coming years may result in unacceptably low soybean yields and/or high production costs.

Consequently, some growers are willing to accept the known risks associated with growing corn following corn in order to avoid the uncertain risks associated with soybean production. While most agronomists certainly do not encourage monoculture of any kind, they can at least offer suggestions for mitigating the downside risks of corn following corn for growers who feel pressured to do so. More detailed information can be found in the references listed at the end of this article.

Nitrogen Fertility Issues

Most agronomists agree that optimum nitrogen (N) fertilizer rates for corn following corn are higher than for corn following legumes (including soybean), with estimates ranging from 30 to 50 additional lbs. N/acre (Butzen, 2006; Vitosh, et. al., 1995; Vyn, 2004). Coupled with the oft-cited 7-10% lower yield potential of continuous versus rotation corn, the higher required optimum N rates for continuous corn “adds insult to injury.” Preliminary analyses of Purdue’s 2007 Nitrogen Trials from five locations agree with previously published data in that second-year corn required, on average, 35 lbs./acre more N than corn following soybean, even though second-year corn yields ranged from 7 to 22% less (data not yet published).

Nitrogen fertilizer prices continue their upward trend in response to high domestic natural gas prices, reduced domestic N fertilizer production, and a greater volume of imported N fertilizer (personal communication with Mike Hancock, Fertilizer Administrator, Office of Indiana State Chemist). Corn growers must remember to factor in higher N fertilizer requirements for corn following corn, and possibly high N fertilizer prices, when developing comparative budgets for alternative crop rotations.

Another consideration for growers who routinely sidedress most or all of their N fertilizer is the fact that obviously more days will be required for this operation if more corn acres are planted. However, sidedressing must be completed within a certain time period. Plant height limitations imposed by traditional ground-driven sidedress applicator tools add to the logistical headaches of covering more corn acres in a timely fashion. High-clearance applicators (e.g., Hagie, Spra-Coupe) that can either dribble liquid N between the rows or inject liquid N via coulters offer an option for lengthening the sidedress window.

P and K Fertility Issues

Corn removes more soil phosphorus (P) and less soil potassium (K) per acre than soybean (Vitosh, et. al., 1995). Per bushel of grain, corn removes 0.37 and 0.27 lbs. of P2O5 and K2O, respectively, while soybean removes 0.80 and 1.40 lbs. of P2O5 and K2O, respectively. A 180-bu. corn crop therefore removes 67 lbs. per acre of P2O5 and 49 lbs of K2O while a 60-bu. soybean crop removes a total of 48 and 84 lbs of P2O5 and K2O, respectively.

A one-time move to second-year corn will have negligible effects on P and K soil fertility levels. Over a number of years of corn following corn, however, growers should monitor soil P and K levels and adjust P and K fertilizer application rates accordingly.

Stand Establishment Issues

Higher levels of corn residue associated with continuous-corn cropping systems on poorly drained soils in Indiana can create difficult stand establishment conditions due to slowed warming and drying of the soil. High levels of surface residue (including old rootballs) often also physically interfere with the furrow opening and closing functions of the corn planter’s row units (Nielsen, 2003).

Not only can germination and emergence be delayed or uneven, but so can initial seedling development. Delayed stand establishment thus lengthens the period of potential seedling exposure to seedling blights or insect pests and increases the risk of lower-than-desired populations and/or higher numbers of weakened plants that are less able to tolerate later-occurring stresses.

Mitigate the risk of poor stand establishment by selecting hybrids with superior seedling vigor ratings. If you will be switching only part of your soybean acres to second-year corn, target better-drained fields in your farming operation. Where practical, consider burying the stalk residues with tillage to better facilitate seedbed preparation and planting. Consider adopting strip-tillage practices (Vyn, 2004). In no-till corn with heavy surface trash conditions, consider the use of row-cleaning attachments for the corn planter. Avoid planting excessively early in order to minimize the risk of sub-optimal soil temperatures during germination and early seedling establishment. Consider using starter fertilizer, especially N, in a traditional 2 x 2 placement at rates no less than 20 lbs./acre of actual N. Consider the use of either soil-applied insecticide or insecticide-treated seed if the risk for secondary insect pests (wireworm, seedcorn maggot, etc.) is high (Obermeyer, et. al., 2005a).