Breaking the 100-Bushel Barrier
By: Chase Gingerich, ProVantage Specialist and Agronomy Sales
Many will read the headline and think this article is about soybeans. It’s not. This is about corn-on-corn, particularly continuous corn. 2020’s drought gave growers across the Corn Belt major challenges, but why else did continuous corn suffer an immense yield penalty? This is the question that many farmers are looking for an answer to.
Peer-reviewed university research has shown a consistent disadvantage to continuous corn compared to rotational corn. Fred Below with the University of Illinois has published many peer-reviewed articles highlighting the effects of a continuous corn yield penalty (CCYP). He states the largest factors that affect the CCYP are weather, residue and nitrogen management. In most years (with favorable weather), adequate nitrogen and residue management can overcome the CCYP. For these reasons, most continuous corn is usually managed with some sort of tillage program to help break down residue as well as fertilized with higher nitrogen rates. However, even with adequate residue and nitrogen management, some years the weather negatively affects the continuous corn rotations, leaving us with a significant yield penalty. With that clear data, why do growers opt for the challenge of adopting a continuous corn rotation?
I often hear that corn-on-corn gets better after its first year, although this presumption doesn’t come from peer-reviewed journals or university data. It likely is coming from “farmer talk” or “farm magazine talk”. Not to downplay real-world examples where continuous corn has yielded better than rotated corn; if you search enough places you will find an example where this was true. Because of the magazine talk presumption that corn-on-corn continues to get better each year, many growers think they will suffer a huge penalty after breaking the continuous corn cycle with a year of soybeans. The agronomics behind this is sequestered in the carbon penalty and C:N ratio. When a high carbon source (cornstalks) is returned to the soil, microbes pull the nitrogen out of the soil to digest the high carbon residue. This can lead to a nitrogen availability problem, which is why many growers apply more nitrogen to a corn-on-corn crop to compensate for the nitrogen being used by the soil microbes. Once the microbes break down the cornstalks, they release the available nitrogen back to the soil over time. By sticking with continuous corn, the microbes are constantly breaking down the residue and maintaining equilibrium, keeping the C:N ratio in check. However, this equilibrium doesn’t necessarily lead to higher yields in continuous corn.
Residue and nitrogen management are important for successful corn-on-corn crops. The data from 2020 suggests that even with adequate residue and nitrogen management, uncooperative weather won the battle and continuous corn suffered an immense yield penalty under extreme weather. Many growers, who have been successfully growing continuous corn the past 10 years (under more ideal weather), suffered 80 to 100 bushel yield penalties in 2020. Wet June weather didn’t allow crops to root down deep and a hot, late-season drought scorched the plants and their ability to utilize the full water profile from the soil. We observed a county-wide chunk of continuous corn with yields from decades ago of 100 to 130 bushels per acre without a trace of obvious disease pressure, corn rootworm issues, nitrogen deficiency, or residue penalties.
ProVantage data supports the same theories that Below has suggested. Long-term continuous corn can work out in some years; however, there are other years where the disaster cannot be explained. So, can you afford the risk of a continuous corn rotation? 2012 and 2013 had some very similar weather events to 2020: lack of late-season rain led to similar yield penalty losses of 80 to 100 bushel per acre.
Continuous corn can be a gamble if you need the crop for feed or even if you are shooting for high yields with higher returns. But, by using your data to evaluate the trends, you can remove the emotion from the decision to safeguard your yields and profitability. In many customers’ data we are observing up to a five-bushel yield penalty for every year corn is grown. Although you can find a case from time-to-time where fourth-year corn-on-corn yielded more than second-year corn, the data also points to some pretty hard cases where we lose 80 or 100 bushels per acre like growers are experiencing in 2020.
So, what’s the takeaway? Figure out your cost to grow your corn or continuous corn, and then plug in your anticipated return to management on what soybeans would show. The data will remove the emotion from the decision.
Remember, you will never read in a farm magazine about a grower who implemented a 20-year continuous corn rotation and successfully grew 130 bushels of corn per acre in 2020. While you also won’t read about the 100-bushel disaster from 2020, it still happened and has a lot of documentation to back it up.