A soybean plant’s yield potential is closely linked to the number of nodes — the part where a leaf is attached to the stem — it develops prior to flowering and forming pods.
Two million nodes per acre is a recommended target, explains Jason Voogt, independent agronomist and owner of Field 2 Field Agronomy in southern Manitoba, in this episode of RealAgriculture’s Soybean School.
That nodes-per-acre number can be used to both estimate yield in the growing season and work back all the way to decisions around planting populations.
“For example, if a grower is trying to achieve 150,000 plants per acre, that requires about 13 nodes per plant, if you want it to achieve two million nodes per acre,” he explains. To make that happen growers need to get soybeans growing earlier, which may require putting soys in the ground before canola to get them up and established quickly.
Related episode: The benefits of planting early (before canola)
Breaking down that math further, if plants only develop 10 nodes, there needs to be 200,000 plants to hit that two million threshold, while 15-node plants only require 130,000 plants per acre.
In addition to planting early to maximize vegetative growth in the longest days of summer, mortality — depending on planting method — and planting depth are critical factors in maximizing node-per-acre potential. “We want to be in and around that 140, 150,000 plants [per acre] in the final stand. We know that we’re going to have higher mortality with a drill, so that’s where we’re still targeting in that 190 to possibly up to 200,000 [seeds per acre]. And with a planter, depending on the row spacing, we’re probably dropping 160 to 170 [thousand seeds].”
Early weed control to provide that critical weed-free period to the plants is another factor.
Voogt notes that research conducted by University of Guelph weed scientist Clarence Swanton showed that soybean seed and plants can actually detect competition above ground. “That brings big light to the fact that pre-emerge [herbicides] are very important in keeping it weed-free right through that critical weed-free period,” he adds.
Check out this quick Soybean School episode with Jason Voogt on maximizing the number of nodes per acre: