Field Notes: Corn on corn — Considerations and concerns to best manage potential yield drag

When soybean markets take a dive or remain consistently low, growing more corn sounds like an increasingly better idea. If you’re considering upping your corn acres by way of continuous corn, then this article is for you. I’m not advocating for or against corn on corn, but rather am providing some management tips and cost considerations.

Yield Impact

Without well-thought-out management, yield reductions can often be as high as 20 to 30 bushels per acre compared with a corn-soybean rotation. This reduction is commonly referred to as continuous corn yield penalty, or CCYP.

A six-year study conducted by the University of Illinois identified three important factors contributing to CCYP. Prior to the study, it was widely assumed that increasing nitrogen fertilizer would solve the yield drag problem.

The study showed that nitrogen availability — or lack thereof — wasn’t the only factor. Several different weather- and yield-related measurements were tested to determine relationships with CCYP.

Residue Management

In addition to N immobilization, yield drag in continuous corn is more pronounced in cooler and wetter soils. Further, there is an increased risk of disease and allelopathy. The common link to each of these factors: corn residue.

What is also interesting is research suggests the degree of yield reduction increases with successive years of continuous corn production, largely due to the accumulation of residue.

Why the fuss over residue, and how are all these factors linked? Accumulated corn residue can reduce soil temperatures and reduce N availability, increase soil moisture and promote survival of insects and diseases. So, it is no surprise that yield drag in continuous corn is more pronounced in soils that already tend to be cool and wet.

Consider selecting well-drained, highly productive soils for continuous corn. To help minimize residue challenges, try to make sure that corn residue is evenly distributed across the field.

It is advantageous to use tillage to help in the breakdown of residue from a disease and pest standpoint, but it also helps soils to warm up soils faster in the spring. Using row cleaners at planting is also important in facilitating better seed-to-soil contact to improve stand establishment.

Additional Inputs

As mentioned, the immobilization of N has long been blamed for CCYP, and rightly so. Microbes are responsible for aiding the breakdown of residue, and said microbes require N. So, an additional 30 to 50 pounds per acre of N may be necessary for continuous corn acres when compared with a corn-soybean rotation.

Applying nitrogen at multiple times throughout the growing season, including at preplant and sidedress, may help increase N use efficiency. Monitor phosphorus and potassium levels on continuous corn acres.

Plentiful P and K early in the season helps promote stand establishment and minimize problems with stalk strength and stalk rot as corn plants mature.

Insect And Disease Control

Residue again being the main culprit, farmers can expect an increase in insect and disease pressure on continuous corn acres. Adverse effects can be mitigated by incorporating proactive measures, including the use of seed treatments early followed by fungicide applications as needed later in the growing season.

Seed and seedling pathogens and soil pests such as wireworms, seed corn maggots and grubs pose the biggest threat early on, particularly when residue from the previous year’s crop is prevalent.

Seed treatments with fungicide and insecticide protection can help protect seeds in the ground during emergence and promote healthy stand establishment.

Corn rootworm, if not properly managed, is another challenge in continuous corn. Planting corn with Bt traits effective against corn rootworm larvae is a good strategy, along with use of a soil-applied insecticide in particularly high-pressure scenarios.

Scout fields as the crop matures, especially during the VT to R2 growth stages for leaf and stalk diseases including stalk rots — diplodia, fusarium, anthracnose and giberella — and leaf diseases such as northern corn leaf blight and gray leaf spot. Fungicide applications help limit potential yield losses when within economic thresholds.

Herbicide Limitations

Herbicide options are limited on continuous corn acres. Once again, the leading culprit is excess residue that can reduce the efficacy of soil-applied herbicides and shield young small weeds from contact herbicide applications.

Control of volunteer corn can be especially problematic on continuous corn acres. Lodged plants and eardrop from the previous year’s harvest increases the potential for volunteer corn. Since herbicide options are limited, the only effective management approach may be cultivation.

Hybrid Selection

Don’t underestimate the important role of selecting the right hybrids. Choosing hybrids with good plant health is critical, and make sure to not plant the same hybrid on the same acres two years in a row.

Best-case scenario: Select a hybrid with no relation to the one previously grown. Lastly, work with your seed specialist and agronomist to identify hybrids that perform well in a continuous-corn program to maximize yield and manage CCYP.

For more information about specific concerns associated with continuous corn programs, visit https://crops.extension.iastate.edu/cropnews/2019/11/considerations-continuous-corn.