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Serving: IA
Closeup of planter in field
MATURITY RATINGS: In recent growing seasons, farmers have found that earlier-maturing soybean varieties have yielded equally well, if not better, than varieties with recommended maturity ratings.

Maximize soybean performance

Soybean Source: Some last-minute tips to gain more return per acre.

A long winter of planning and prep work will, hopefully, pave the way for a good spring. No matter how well we plan, conditions change, or a few more things need to get done at planting time to get the most out of our fields.

I’m betting for the most part we are on the same page with big-picture issues like getting beans planted early to maximize yields, attempting to keep fertility in the optimum range, using residual herbicides and managing SCN-infested fields. We talked about big-picture topics all winter, so here I’ll hit on a few things that didn’t get discussed as much. They can make a difference and can still be addressed this spring.

Applying inoculants
We covered seed treatments in recent articles but didn’t spend much time on inoculants. With many inoculant decisions made close to planting time, consider these points.

Since the cost of inoculation is usually fairly low, and with no agronomic downside that I can think of, there are situations where we can easily give them the green light. In fields that haven’t had beans for several years, or where significant parts of a field were flooded or had ponds for more than a few days, the risk of yield loss is high enough to make treatment a good bet.

While there is limited research on the impact of drought on soil rhizobia, for the areas hit hard with drought last year, fields going to beans this year would also be good candidates for inoculants.

Outside of those situations, most of our fields have plenty of rhizobia, so addition of inoculant for that purpose typically isn’t justified. As with most agronomic questions though, “it depends.”

A complicating factor is many of today’s commercial inoculants are promoted as having new strains of rhizobium that can increase yields even under normal circumstances. Other inoculants are co-packaged with growth promoters, micronutrients, bio-fungicides or other ingredients, and are along for the ride. Take it field by field, product by product, and lean on your experiences and insight from your seed dealer to help fine-tune your approach to inoculants in these fields.

Choosing right maturity
OK, I better make this clear right away: We’re not talking about changing soybean maturities across the board right ahead of planting. With most of our seed already in local warehouses, I don’t want to give my seed dealer friends any coronary events; we are just talking about experimenting a bit!

While the “core” varieties we’ll plant are mostly on-hand and ready to go, there is always a little in-season shifting with the soybean varieties we end up planting. These acres might be a good spot for some on-farm research.

ISU Extension agronomist Mark Licht wrote a good article for the ICM news site last fall on soybean variety selection. The section on maturity selection generated a fair amount of discussion, at least in parts of Iowa where I spend a lot of time (southwest, west central and south central). Mark pointed out that you can minimize the effects of adverse weather and expand the harvest window by planting varieties with different maturities. He also mentioned that generally, later-maturing soybeans have higher yields. The fun begins in discussions where we try to figure out what range of maturity groups (MGs) to plant for a given region.

Mark recommended varieties with a range of 0.5 to 1.0 MG, a rock-solid tactic. I tend to tailor MG recommendations based on client agronomics and preference, with me leaning closer to a 1.0 MG spread, sometimes a little more on paper. I mention “on paper” because comparing maturities isn’t an exact science. As Mark noted in his article, “Actual maturities may vary and are highly influenced by environmental factors.”

With all this in mind, growers often tell me that beans on either the very high or low end of the MGs they use are yielding the best. The discussion then turns to how much further should we push —early and late — with our soybean maturities? Since our core set of soybean varieties many of us plant is likely to fall into the 0.5 to 1.0 MG spread that Mark recommends, maybe some of the in-season variety shifts are a good place to experiment.

Shorter-season beans
For example, several farm operations that I do a lot of plot work with usually plant beans with MGs from about a 2.2 through 3.2. Over the last decade or so, the various genetics have all performed fairly well in general. But a more recent trend is that their mid-to-lower MG 2s are leading the way, even as varieties are updated. In these more southern regions of Iowa, an early MG 2 is a pretty short-season bean, so there isn’t a lot of room for experimenting lower in the 2s.

On these farms, it’s the other end of the scale I see more opportunity. With an early MG 3 typically being the longest season bean planted on these farms — in a region where we could run perhaps up to 0.5 MG higher — trying some acres of mid-to-later MG 3s might be worth a shot. Sure, we may find out that the MG 2s are still better, but on the other hand, we might be able to better use our longer growing season with beans that are a little outside of our MG comfort zone.

Across Iowa there are a lot of agronomic factors to consider with variety selection, so as Mark mentions in his article, prioritize and pick your genetics accordingly. But if you have the inclination and opportunity to do so, consider pushing a few acres to the edge of your comfort level of MGs.

McGrath is the on-farm research and Extension coordinator for the Iowa Soybean Research Center at ISU.


What’s the right seeding rate?

I’m not sure what generates more “discussion” among my clients — soybean row spacing or plant populations. But it’s safe to say that both opinions and results may vary. Lucky for me, most of us aren’t in the mood to consider changing row spacing this close to planting time, so I can dodge that topic for now. As for populations, well, get ready…. It depends!

Recent industry surveys indicate in our region, most growers’ seeding rates fall in the range of 140,000 to 170,000 seeds per acre. If we extrapolate those into what harvest stands might look like, let’s go with a ballpark of 115,000 to 140,000.

How does that compare with what ISU says? This topic is worthy of an entire article, but ISU’s short version is “soybean stands beyond 100,000 to 125,000 plants per acre at harvest typically do not result in yield increases great enough to be economically important when the added seed cost is considered.”

So, for the most part, growers are at or a little above this recommendation.

Other factors affecting decisions
Going a step beyond this broad recommendation, there are other factors that will influence the right population for your situation. Row spacing, planting dates, disease and soil factors, tillage system, and seed treatments used are a few to consider as you chase the final harvest stand that is most profitable for you.

With all that said, if you are on the high (or even low) side of the population equation, consider running some trials at different populations. Or if you have the capacity, try some variable-rate population trials.

Depending on your equipment, population trials aren’t terribly time-consuming and can be interesting. We are chasing a moving target. As varieties, seed costs, soybean prices and other variables shift from year to year, you might find yourself thinking about doing population trials again next year, too.

Aside from the degree of difficulty, a lot of the same things could be said of on-farm trials for inoculants, maturity groups or countless other factors. The results of your own trials might lead to wanting even more information and more trials. Of course, once you start doing them, you might not be able to stop, but that is nothing to worry about. Have a safe and successful spring!

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