Features Agronomy Soybeans
Maximizing soybean yields

Research indicates the optimum time for planting soybeans in Eastern Canada (above) is before May 15, while farmers in Western Canada should have planted before May 25.    File photo.

La Coop fédérée crop specialist François Labrie visited Manitoba in November 2014 and he brought along some tips for prairie soybean growers.

Labrie says in order to maximize soybean yields, growers have to understand the physiology of soybeans in the field, emphasizing that patience is a virtue when growing the crop.

Labrie says there are eight opportunities during the growing season where a grower’s decisions will affect the crop yield and profits. The first decision is the choice of a seed variety. Labrie says price and yield statistics aren’t the only factors to be considered when buying seed. Field conditions and planting times are also factors. Labrie suggests buying a variety suited to the growing season, soil conditions and resistance to local diseases and fungus infections.

His advice to growers is to plant the variety they’ve purchased at the recommended planting date. “Keep your seeds for planting at their best date. If it’s too late for them, plant a different crop,” he notes, cautioning growers shouldn’t wait too long for the ground to dry before planting as waiting to seed will reduce yield.

“If the ground is suitable for seeding, then go. If soils are very wet during the optimum planting time, stay out of the field,” he says. That’s the time to decide on whether it’s worth planting a soybean crop in that location.

According to Labrie, soybeans respond to seasonal changes in daylight and don’t rely as heavily on heat days for reproduction as corn does. Soybeans switch from vegetative growth, or trifoliolate development, to reproductive growth on June 21, the day with the most daylight hours during the year. He notes the reproductive efficiency of soybeans is quite low compared to other crops with only half the flowers on a plant producing pods. The challenge for growers is to encourage the soybean plant to produce as many trifoliolates as possible before the summer solstice using optimum seed positioning, effective row spacings and planting at just the right time.

Labrie says research indicates the optimum time for planting soybeans in Eastern Canada is before May 15 and he suggests that farmers in Western Canada should plant before May 25. So growers should relax and get their corn, which relies on heat days for development, planted before the soybeans which develop according to the available daylight hours. In fact, he says, early planted soybean seeds simply sit in the ground. Nor does an early planting mean an equally early harvest. The gain in harvest time is only one day for each three days of early planting.

The goal is to get the seeds sprouting as quickly as possible. The first leaf, or unifoliolate, has just one job and that’s to get photosynthesis underway to foster the development of the first trifoliolate. That’s when the process of nitrogen fixing begins and the foundation for a good yield is established. Labrie says there should be a new trifoliolate every four days after the first one develops, and by June 21 each plant should have four to five trifoliolates.

Seeding rates
Getting the seeds in the ground at the optimum time is just one part of the seeding decision. The number of seeds required per acre is another. Again, Labrie suggests that input costs should be the guiding factor. His calculations from research trials on the economics of seeding rates show that a planting rate of 182,200 seeds per acre (450,000 seeds per hectare) produced income of $676.11 per acre. With soy selling at $9.24 per bushel and seed costs of $57 per 140,000 seeds, increasing the seeding rate to 222,700 seeds per acre only increased income by $8.10 per acre while cost of the extra seeds was roughly $17.

Labrie says that when projected yields don’t support higher input costs, increasing the amount of seed per acre isn’t a viable option for the grower. He says a more cost effective method of increasing yields and decreasing weeds, which compete for soil nutrients and require herbicide applications, is proper placement of the soybean seeds in the field.

Because the natural canopy created by well-spaced soybean plants deters weed growth, Labrie advocates spacing rows 15 inches apart. He says crop trials indicate 15-inch rows form an effective canopy 15 days later than seven- or eight-inch rows, but 25 days sooner than a 30-inch row. Thirty-inch rows provide less protection for soil and allow late emerging weeds to fill in. Rows spaced 15 inches apart reduce weed growth, promote soybean trifoliolate growth through better light efficiency and reduce the incidence of mould because they provide more space for air movement between the plants than seven-inch rows.

Labrie says twin row planting, two rows eight inches apart with a 22-inch row between each set of eight-inch rows, produce higher yields, enough to pay for the custom seeding costs. And, he adds, navigating the field to apply insecticides or fungicides is much easier with 22-inch rows than it is with either seven- or 15-inch rows.

Planting seeds too close together within 30-inch rows won’t improve yields either, according to Labrie. It only increases the opportunity for white mould to develop in the crop. And he has some advice about seed placement within any row: “I would say up to 15 inches for spacing at one inch deep.”

Research plays a major role in the development of soybean crops in North America. Labrie, who has been a corn and soybean specialist since 2010, developing the Elite line of soybean seeds, says his job is to provide knowledge and support to the coop network sales representative. His work includes finding ways “to increase corn and soybean yield through fertilization, seeding date, seeding rate, crop protection and the use of cover crops.”

Soybeans have their genetic origins in Asia, and through the process of natural selection have developed and adapted to North American climate zones. Developing plant genetics is a long process and soybeans take longer to develop than some other crops. Labrie says, “It takes at least eight years to develop a new soybean variety.” And yield increases within varieties take even longer. He says it took 87 years to attain an increase of .38 bushels per acre while corn yields have been increasing at 1.5 per cent annually.

“The soybean yield will increase, but it’s a long process,” he says.

June 19, 2015  By Anne Cote