Early-relative-maturity soybeans, planted early in the northern Corn Belt, offer great yields — and the possibility of establishing better cover crops after harvest
As an independent agronomist who straddles the intersection of traditional row-crop agronomy and the principles of soil health, I am constantly on the hunt for “system hacks” that integrate these two philosophical camps in ways that ultimately increase productivity and profitability. That’s a big ask, given that many believe the integration of soil health principles — notably reduced tillage and cover crops — comes with significant cost and a yield penalty.
But what if we can have our cake and eat it too? What if there are ways to integrate soil health practices that do not compromise yield and profitability, but instead enhance them? These are the system hacks that I relentlessly pursue, under the belief that there is indeed synergy when combining traditional agronomic principles with soil health practices.
Covering Up North
The best example of a system hack I’ve discovered is the concept of early-planted, early relative maturity (RM) beans. Early-RM beans can deliver similar yield compared to later-RM beans while offering farmers a significantly earlier harvest window, enabling them to then establish a cover crop prior to winter.
I own an agronomy consulting business in northwest Wisconsin, and most of the farms I work with are north of the 45th parallel. We are closer to the North Pole than the equator. As such, our growing season is far more condensed than most acres in the Corn Belt. Every day above the freezing point must be taken advantage of to grow profitable crops.
Many farmers in this part of the world, and many ag industry “experts,” proclaim that covers and no-till can’t work here. It’s too wet. It’s too cold. This is pure hogwash. Years of experience have shown that we can quite successfully employ cover crop and no-till practices while preserving yield potential. In fact, when Mother Nature throws us extremely dry or wet growing seasons, I have often observed the superior functionality of soil health-focused cropping systems, as the soils underneath these crops tend to buffer the extremes.
I have collected 9,064 unique, weighed soybean-yield data points across the last seven growing seasons from farms across east-central Minnesota and northern Wisconsin. From this information-rich database, three important relationships stand out.
Early-RM Beans and Yield
First, let’s explore the relationship between soybean RM and yield. Like corn, there is a positive relationship between RM and yield: longer-day varieties tend to yield more than shorter-day varieties. Figure 1 shows that there is a 0.9 bu./acre increase for every 0.1 increase in RM. To use a practical example, there is a 4.7 bu./acre yield gain when comparing a 1.0 RM soybean with a 1.5 RM soybean.
There are a number of important caveats when interpreting this aggregate data. This 0.9 bu./acre RM value cannot be applied to specific circumstances in the field. No farmer, agronomist or university researcher can claim that shifting from a 1.0 RM bean to a 1.5 RM bean will deliver a 4.7 bu./acre advantage. Soybean variety agronomic characteristics will always be the primary driver of relative performance. A 1.0 RM bean variety with superior white mold tolerance will likely stomp a 1.5 RM variety with weak white mold tolerance in fields with white mold pressure.
Agronomics matter — a lot. I ask readers to consider this data from a bird’s-eye-view perspective. These are big-picture trends and should be interpreted as such.
The Planting Date Effect
Figure 2 demonstrates the relationship between yield and planting date. University of Wisconsin soybean specialist Shawn Conley has performed a mountain of research on this topic. His data, on a much larger geographic scale, matches the observations I’ve pulled out of the same dataset referenced above: early-planted soybeans yield more. In fact, some, including Dr. Conley, have stated that soybean planting date may be the single biggest driver of soybean yield that farmers can control. I tend to agree.
The data in Figure 2 shows that there is a 0.43 bu./day loss in soybean yield for every day that soybeans do not get into the ground. Planting date matters — big time. I respectfully ask those of you committed to planting your corn before your beans to consider this data carefully. Bonus thought: beans can germinate at 46 degrees, whereas corn prefers 50.
Early RM + Early Planting: A System Hack
The data I’ve presented so far is building up to the big reveal: early RM soybeans planted early can hang with longer-RM beans. But wait — didn’t the data show a strong positive relationship between RM and yield? It did, and now it’s time to take this analysis a step further by combining planting date, RM, and yield into a single analysis that reveals a unique and unexpected anomaly.
Figure 3 shows yield by planting date, similar to the data in Figure 2. However, this time soybean RM is broken into three distinct groups: early RM (blue line), mid-group RM (red line), and late RM (green line). I would like to draw your attention to the blue line at the A4 and M1 planting weeks. These are the two most important data points; they imply that there is no meaningful yield loss when early RM beans are planted in the first two weeks of our historical planting window here in the northern Corn Belt. This breaks all the rules, doesn’t it?
I’ve ground-truthed this concept over a couple of growing seasons on the farms I consult with. Having identified a 0.4 RM bean with superior agronomic characteristics, I can cite numerous circumstances in which this bean, planted in the first week of May, yielded 60-plus bushels/acre in a county where the average is 42 bushels.
Take note of how the blue line appears to fall off a cliff when you get into the second week of May. The data implies that planting date is key to making this system hack work. Figure 2 shows the importance of planting date on yield; why is that effect magnified for the success of early RM beans? I believe it is due to sunlight and moisture availability, which offer key advantages to early beans. With a condensed life cycle, early-RM beans are going to enter the flowering and pod-fill stages earlier than later-RM beans. Doing so gives them the advantage of more sunlight and (usually) more moisture in the earlier parts of summer. There are likely other factors, but these stand out as logical considerations.
The Covered Advantage
What is the real advantage of these early-RM beans if they yield on par with later-RM beans? Time — that most precious of resources, which all of us wish we had more of.
A rule of thumb states that each 0.1 RM of soybean translates to roughly one day at harvest. Using a practical example, the RM difference between an 0.4 soybean and a 1.4 soybean is one full maturity group, or ten 0.1 increments, which is about 10 days at harvest. What could you do with 10 days after harvest? A lot, I say.
These early-RM beans allow you to get started sooner. That means you finish sooner. And if you are a soil health enthusiast with a narrow window of establishment up here in the great North, that means covers like cereal rye can be planted at the end of September versus later in October. It may not seem like much, but that 10-day window can mean the difference between 55 and sunny and 35 and rainy. It’s a big deal.
In fact, there are a couple of circumstances in which rye was planted after soybean harvest on Sept. 20. This date may seem silly to those in more southern climates, but it is quite significant north of the 45th. Early September is considered the cutoff for planting overwintering cover crop species that are not cereal rye. As you go further into September, covers like clover, hairy vetch, and various brassicas simply do not have enough time to establish well and perform their duties in the gap between growing seasons. I would love to hack the system in such a way as to establish a legume cover after soybeans going into next year’s corn rotation. We’re not there quite yet, but we’re getting closer with mid-September soybean harvest.
I’ve spoken with a number of farmers at conferences around the country who are already on the early-RM soybean bandwagon for their own various reasons. Bravo to those system hackers who have reaped the benefits of this contrarian practice. My goal in this venture is to use large-scale, reliable data to quantify the benefits of these “off the rails” strategies to assure farmers that crazy ideas like this have merit.
I am certain there are many more system hacks out there yet to be discovered, limited only by the creativity and commitment of rule-breakers willing to deploy them.
