Will precisely singulating soybean seed down to 1-inch plant-to-plant spacing improve pod count and potential? Several agronomists, including me, think this could be true even though there is no data yet on this question.

Corn planting is all about seed singulation and precisely placing every seed at the right depth and right spacing between seeds. Everyone appreciates the rows of corn that look like a picket fence with all the plants equally spaced and emerging at the same time. Each plant has nearly the same stalk and ear girth. We have all seen the photos and manufacturers have excelled at engineering planters that will singulate seed across a range of soil and seed size conditions. And when you look at corresponding ear size, the better the singulation the more consistent the ear size.

But what about soybeans? Will they benefit from better singulation? Soybeans have a lot of plasticity and they are supposed to compensate. Lose one or two plants, have a plant that emerges late and is small, or two plants next to each other? The plants around will branch out and fill in any gaps in spacing. We take for granted that soybeans naturally compensate for gaps and depend on adjacent plants to fill in those gaps. By the middle of the season, with the canopy in place, it looks like the crop has recovered and compensated. But has it?

Most folks discount the idea that seed singulation in soybeans is important. Just follow the conversation thread on AgTalk back in 2016. Most of the responses were negative, advising not to waste time chasing singulation because of soybean plasticity. There was no science presented in this conversation and it boils down to the fact that we just do not know. Just like twenty years ago when we didn’t know how singulation and down pressure could greatly benefit corn yield.

We know that back in the day growers drilled soybeans at populations of 200,000 and greater. Drills were known for poor seed placement and were often referred to as a controlled spill. When Roundup Ready® soybeans came to market seed costs increased and growers no longer depended on an early canopy to control weeds. As a consequence, they moved back to planters with bean seeding mechanisms and begin reducing seeding populations down to around 140,000 to 160,000. Populations still seem to be trending downwards as seed treatments and seedling vigor (survival) improve. But singulation is probably not improving.

If soybeans are planted in 30-inch rows at 140,000 with 90% establishment, 126,000 seeds have emerged as seedlings and the spacing between plants should be 1.65 inches if perfectly singulated (1/1000 of an acre is 17’5” or 209”and 126 plants/209 inches = 1.65 inches between plants). In 15-inch rows that spacing will double to 3.3 inches. Will today’s seed metering mechanisms singulate soybean seed at 1, 2 or even 3 inches? That is the question I have and have put out to Precision Planting and John Deere for comment. Maybe there is some merit in pursing this or maybe not. If there is a potential yield increase from better singulation, engineers will engineer it.

Dr. Fred Below at the University of Illinois has been conducting research on soybean yield under “Six Secrets,” and found that increasing pod count by one increased yield by 2 bushels. However, soybeans produce many more flowers and pods than they carry through to harvest with an abortion rate of 50 to 60 percent. Today the chase for yield comes down to keeping as many pods as possible through to harvest. That requires protecting the plant and foliage from pests and diseases, keeping the plant well fed so it can nourish the filling pods and alleviating stress that induces early flower and pod abortion. Seems that we should be able to manage the plant to increasingly keep more pods.

I reached out to Dr. Emerson Nafziger at the University of Illinois on whether better seed singulation and plant-to-plant uniformity would lead to a yield increase. “The real question remains whether or not plants that show uneven distribution of seed weight (yield) across the row have a lower average yield than would the same number of plants with perfect uniformity in yield. If, as the evidence seems to show, perfect uniformity in per-plant spacing does not come close to producing perfectly uniform per-plant yield, I’m not sure how one would ever answer this question (of how perfect singulation could improve yield).”

If singulation has merit, the first step is seeing if precise placement of seed leads to more even emergence, more consistent yield across a row and potentially more nodes and pods per plant. If that were proven, engineers and agronomists would figure how to make it happen.

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About the Author: Dan Davidson

Soybean agronomist Daniel Davidson, Ph.D., posts blogs on topics related to soybean agronomy. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.