What soybean maturity group should you plant? And when and where should you plant it? Following a lengthy study and analysis period, a team of Mid-South researchers have some answers.
“This is the accumulation of four years of research — three years of in-field research on a large regional project and another year spent analyzing the data,” said Larry Purcell, University of Arkansas professor, at the recent Tri-State Soybean Meeting in Stoneville, Miss.
First, the mechanics of the project. The study was from 2012 to 2014 at 10 locations across the Mid-South. All of it was done under irrigated conditions.
There were four planting dates. “The first date was targeted to the earliest we could get into any of these fields. The last planting date was targeted towards what we thought would work for a double-crop. The other two split the difference.”
Four maturity groups were used — 3 through 6 — with four different cultivars within each group. All told, looking at all locations, there were over 6,000 plots.
“That’s a huge data set.
“Our most northernmost location was in Columbia, Mo., and the southernmost was College Station, Texas. … At all the locations the measurements we made, of course, included yield.
“We also spent lots of effort looking at seed quality. When you think about what happens when you harvest Group 3s in August in the Mid-South, seed quality is a huge issue.
“We also looked at accelerated aging, germination, grade, and oil and protein concentration. We took notes throughout the season on development stages and how we could use that information from a management standpoint. We made the typical agronomic measurements: stand counts, plant height, node numbers. Notes were also taken on lodging, shattering, green stem and any disease and insect problems that occurred over the course of the season.”
As for yield results, Purcell said he presented “only the tip of the iceberg. This is looking at the average yield response over all locations for the three years.
“The circles at the top represent the early planting dates and the triangles the late planting dates. The filled-in symbols represent the statistically highest yields for the respective planting dates. So maturity groups 4 and 5 had the highest yields. The stars indicate they were significantly higher than the later planting dates. So, the key message is: plant early.”
Somewhat surprising is that for the later planting dates the highest yields went to Group 4s and late 3s. “That goes against what I’d been taught about Mid-South agriculture where recommendations have been late-maturing cultivars for late planting. This large dataset doesn’t bear that out.”
Once again, Purcell cautioned, “these were irrigated soybeans and this may not hold up in dryland. Also, another caveat is we used narrow row spacings. Our widest row spacing was 30 inches. At most locations we were using either twin-row or 20-inch row spacing. That’s important to consider.”
The researchers also did a lot of analysis looking at yield responses by location. One example is the study at Rohwer, Ark.
“The four panels represent groups 3, 4, 5 and 6. The soybean yield is presented from zero to 100 percent. That allows us to compare all years, maturity groups and planting dates.
“What this shows is that early planting dates for Group 3s tended to produce the highest yields. That decreased over time. In Rohwer, the same was true for Group 4s. The Group 5s had a straight-line decrease. Maturity Group 6 had no significant response to planting date but note the lower yields throughout the growing season.
“We can do some interesting statistics looking at what the best response is over time. This provides the absolute highest yield for any given planting date. In Rohwer, maturity Group 4 had the highest yields over all planting dates. Maturity Group 3 came in at 98 percent with 5s at 97 percent. The highest for Group 6s was 79 to 80 percent.
“For Group 3s, April 11 was at 98 percent for the highest value. April 9 was the best for Group 4s, March 20 for 5s. Again, it made no difference for Group 6.”
Using the project findings, a soybean management guide has been put together for Arkansas. Other state guides will soon be available. The guides for Arkansas are available at the websites of the Mid-South Soybean Board and Arkansas Soybean Board.
Crop modeling and a decision support tool
Purcell and colleagues have used the results from the field experiments to come up with a crop model “that takes into account everything over this large region. The power of that is we can go back and look at historical weather data over a long time and predict what the yield was over planting dates, maturity groups and different locations. Once you have the large database with 30 years of weather data you can find some really interesting things.”
The results from the crop modeling using 30 years of weather data from multiple locations in the MidSouth was used to develop a decision support tool called Soybean Maturity, Analysis, and Planning or SoyMAP for short. “SoyMAPcan be used on your farms to determine the best-choice maturity group for your location when you plant on a specific date.
“SoyMAP bases profits or revenue using the harvested yield and the seasonal change in seed price. We’re harvesting on different dates and the market is in flux. We look at oil and meal premiums or discounts. The expenses include differential irrigation requirements when we have different planting dates or maturity groups. We hold constant our seed, fuel, fertilizer equipment and chemical costs.”
Using this information, the SoyMAP compares the probability that one maturity group will be more profitable than another for a specific location and planting date. SoyMAP is available for download.
The extensive study has also provided some interesting economic information. Purcell is “working closely with Michael Popp, an ag economist at the University of Arkansas. We’re developing something that’s kind of a portfolio approach. If you play the stock market, you don’t put everything in one stock. Instead, you spread the stocks out over different levels of risk and returns. We can do the same with soybean production, reducing risk for the producer.”
The researchers looked at 16 maturity group and planting date combinations to consider “maximum return you’d get using different combinations for a given level of risk. If you accept a given level of risk, you’ll decrease your profits by a small portion but will greatly reduce your risk.”
As an example, Purcell illustrated the analysis for Rohwer, Ark. By going with the portfolio approach over putting everything in one maturity group and planting date “we decrease our returns a rather modest 16 percent. But we also reduce our risk by 41 percent. That means a producer can look at whatever level of return is acceptable and look at the ratio for his farm that would provide that return with the least amount of risk.
“This is an entirely new way to spread those eggs out and get them out of just one basket.”
The project is a joint effort between the United Soybean Board and the Mid-South Soybean Board. “We couldn’t have done it without their generous support.
“The project was sometimes difficult to coordinate spread out over 10 locations across a large region. I’m very appreciative of our cooperators and the assistance of Lanny Ashlock (of the Mid-South Soybean Board) and Larry Heatherly (of the Mississippi Soybean Promotion Board).”