Optimizing soybean planting decisions

By Dusty Sonnenberg, CCA, Ohio Field Leader: a project of the Ohio Soybean Council and soybean checkoff

Adjusting management practices and optimizing soybean yields based on the planting date was the topic of a presentation by Manni Singh, Assistant Professor of Cropping Systems from Michigan State University at the Conservation Tillage Conference.

“We set the yield potential of soybeans when we plant them, and then we work the rest of the season to protect that yield potential,” Singh said. “We manage the planting date, we manage insects, and we manage diseases.”

Manni Singh, Agronomic Cropping Systems Specialist, Michigan State University

According to data collected by the Great Lakes Integrated Sciences and Assessments Center (GLISA), over the last 100 years, total rainfall has gone up by 11%. Of that rainfall, 37% occurs in heavy storm precipitation events.

“These extreme weather events in the spring cause poor field conditions and a variable planting window that farmers need to manage,” Singh said.

GLISA data also showed the average temperature is 2 degrees Fahrenheit warmer, and the frost-free season is 9 days longer.

“That 9 days is a positive since length of growing season impacts yield,” Singh said. “Farmers need to decide how to take advantage of the longer growing season, and manage the narrow planting windows.”

When managing planting date, farmers need to balance several conditions.

“Early in the season, farmers face cool wet soils, yet they have an extended growing season. By waiting until mid- season to plant, there is typically adequate soil temperature and moisture to germinate and grow the crop. By late season, the soil may lack moisture, and the growing season is shortened,” Singh said. “Planting date impacts the yield. There is about a half a bushel decline in yield for each day planting after May 1.”

With a longer season in mind, management can change to maximize the yield potential.

“Farmers need to gather important information to answer a fundamental management question,” Singh said. “How can a farmer improve yield potential or minimize input cost to increase profit?”

Variety selection is the first management decision to address.

“What maturity group should a farmer be using to maximize the growing season to the full extent? Soybeans are a daylight sensitive crop, so the question becomes if a farmer is able to plant early, should they use a longer maturity group than typical, and conversely, if planting is delayed, should they be switching to a shorter maturity group soybean?” Singh asked. “In Ohio farmers need to ask, when planting early, can a maturity be pushed from a 3.0 to a 3.5 maturity group, or from a 3.5 to a 4.0 maturity group bean.”

Michigan State University (MSU) conducted a two-year study, at two locations, looking at four planting dates, with six maturity groups. The trends in the study showed when a longer maturity group was planted early to take advantage of the longer growing season, a yield increase occurred.

“They gained 6 to 11 bushels per acre by increasing the maturity of the bean with the longer growing season. There was data collected to make sure they would mature in time. A key component was determining when each maturity group reached R7, which is defined as when there is at least one mature pod on at least 50% of the plants in the field. That is the stage when 95% of the yield potential is already determined. In the study all the beans reached maturity prior to the killing frost except for the longest maturity bean at the latest planting date. Those planted earliest with a longer maturity experienced a yield bump. They reached maturity 20 days before the first killing frost,” Singh said. “A similar response was experienced in both years.”

The study also looked at how long each maturity was spending in the respective growth stages. The greatest yield benefit was from the longer maturity beans that spent the most time in the R5-R7 growth stages.

“All the maturities took the same number of days to germinate and emerge, but the longer maturity beans spend more time in each growth stage, and the longest time in the final growth stages,” Singh said. “Those plants that had more time in each growth stage put on more nodes and set more pods, and produced more seeds per pod.”

The study also looked seeding rates, and if they should be changing to maintain the high yield potential and yet lower the upfront input cost. The study found lower the seeding rates had more branches, and also more pods were produced on each plant.

“More seeds in the ground does not increase the final yield with statistical significance,” Singh said. “There was a point however, at 50,000 plants per acre, that was statistically significantly lower, but at 90,000 plants per acre, there was not a statistical difference compared with the higher seeding rates.”

The study did find that the higher the plant population, the higher the lowest pod was set on the plant. The lower population, the lower the lowest pod was set closer to the ground. This can impact harvestability and cutter bar height.

The study did find that weed pressure increased at the lowest seeding rates. There was also higher weed pressure in the earlier plantings overall. Gaps between plants allowed for more weed pressure. The later planting dates had less pressure regardless of seeding rate because there was a more uniform emergence and final plant stand with improved growing conditions at the later planting dates.

Seed treatment was a third management consideration.

“An assumption was that early planting dates would benefit more from a seed treatment. The question was if final yields would benefit from a seed treatment based on the environment farmers are planting into at the time,” Singh said. “There was about a 5% improvement in final plant stand with the seed treatment, but it did not translate to a yield increase and profitability benefit.”

Singh acknowledged that the environment may have been a factor, since there was not enough of a pathogen or insect pressure at either of the locations in each of the years of the trial.

At an early planting date (April), longer maturity group beans showed an improved yield. There was not a benefit from increasing seeding rates above what would normally be planted, and the benefit from seed treatment was limited to improved plant stand, but not final yield.

“This may be an opportunity for farmers to save a little money by not increasing seeding rates, and possibly reducing one of the components of the seed treatment, however it is dependent on the environmental conditions,” Singh said.

When planting mid-season, (May to mid-June), the study found no impact from changing maturity groups.

“In this planting window, a farmer could switch to a shorter maturity soybean and have a larger window after harvest to plant wheat or a cover crop,” Singh said.

There was also no benefit from increasing seeding rates.

“If planting in May, a farmer could save money by slightly reducing their seeding rate (10-15%). The soil is typically warmer and there is adequate moisture to get a better emergence and a uniform stand,” Singh said. “Any benefit from seed treatment is limited to stand improvement, but it did not increase profit. Some components of the seed treatment could be eliminated based on what environmental pressure is faced.”

At a late planting date, (mid-June or July), there was a slight yield benefit by switching to a short maturity soybean.

“This was primarily due to the shorter growing season. The delayed planting conditions, showed the typical maturity beans had a 22% or higher moisture at harvest. The shorter maturity soybean had a lower moisture and higher test weight,” Singh said.

Increasing the seeding rate did show a yield benefit. Both the economic benefit and yield benefit occurred only when increasing the seeding rate (170,000 to 200,000) at the later planting date. There was not an economic benefit to using a seed treatment in the later planting date.

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