By Matt Rundle, NK® Agronomist

Ontario soybean researchers were hard at work in 2020 conducting trials to help fine-tune soybean management. 

Ontario Ministry of Agriculture, Food and Rural Affairs Soybean Specialist Horst Bohner and University of Guelph Associate Professor Dr. David Hooker presented their research findings at the Ontario Agricultural Conference earlier this winter. 

Here are some key management takeaways I noted from their presentations and thoughts on how their insights could contribute to greater soybean success on your farm.

Takeaway #1: Planting no deeper than 1.5 inches provides the best opportunity for optimum stand establishment and yield.

In Bohner’s 2020 plant stand trials, based on 15” rows at 175,000 seeds/ac in a no-till system, planting at 1.5” resulted in adequate establishment of above 130,000 plants per acre across all planting dates tested. Soybeans planted shallower at 1” also showed sufficient stands, however, beans planted deeper at 2” and 2.5” resulted in unacceptable plant stand loss. When Bohner compared yields across his trials, both the 1” depth (60.1 bu/ac) and 1.5” (60.4 bu/ac) also showed a significantly higher yield compared to the beans planted deeper at 2” (56.9 bu/ac) and 2.5” (55.8 bu/ac).

Based on this research, I think it’s clear that when moisture is not limiting, planting deeper than 1.5” does not pay and if growers plant shallower than 1.5” they increase dependence on spring rains for germination. In most conditions, with adequate soil moisture, the sweet spot is 1.5”. Growers should only consider going deeper if soil conditions are dry and they need to get the seed into moisture.

Takeaway #2: Don’t worry about planting too early. Soybeans can tolerate the cold and produce high yields as long as they’re planted into fit soil conditions.

Bohner tested soybeans’ ability to tolerate cold planting conditions during the chilly 2020 spring. He planted soybeans at 1.5” on April 22 when the air temperature was 3°C. It then dipped to -4°C within 12 hours after planting. The freezing conditions, however, had practically no impact on plant stand or final yield, which came in at 64.1 bu/ac. Another trial planted on April 25 in slightly better conditions (13°C at planting with a 0°C low) yielded similar at 63.4 bu/ac.
 
I think the key point here is soil conditions.  If the soil is not fit the planter may “smear in” the seed and the seed trench may not close. If that happens, it’s time to park the planter. But if the soil is fit and the weather forecast looks favourable, growers can drive on. With the genetics and treatments of today’s seed, we are seeing improvements to soybean seed tolerance to cold temperatures as compared to previous studies.

There’s lots to do during the busy planting season, so if growers can get an early start on planting soybeans they’ll likely finish early. This is important because the yield potential for soybeans is reduced in late May and drops dramatically when planted in June. Fields planted later are delayed in their development as compared to early plantings, which reach canopy closure earlier in the season. Since the longest and strongest days of solar radiation are experienced in June and July, fields that are planted in June are unable to optimize photosynthetic production during some of the best days of sunlight of the entire growing season. 

Another reason for the yield decline in late planted soybeans links to plant physiology. When soybeans are planted earlier, they have a longer vegetative stage, allowing them to gain more branches and increase nodes. They also flower earlier which creates a longer reproductive stage. It is for these reasons that earlier planting typically adds up to higher yield.
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Takeaway #3: Understanding the maturity rating of your seed is critical for variety selection. Check OSACC trial ratings and consult your seed retailers to determine variety maturities and where they fit best on your acres.

Dr. David Hooker took a close look at maturity ratings for soybeans in the Ontario Soybean and Canola Committee (OSACC) trials and noted significant maturity differences for varieties with similar maturity group ratings. According to Hooker, some varieties may have a similar maturity group rating — 1.0 for example — but there can be up to four days difference in actual days to maturity. He also cited examples of six days difference in varieties rated within 0.1 of a maturity group and up to nine days in varieties within 0.3 of a maturity group.

This is important because if growers don’t have a true understanding of a variety’s maturity, they can either lose yield when planting varieties that don’t utilize the full length of the growing season, or they may choose a soybean variety with a delayed harvest maturity, which can affect the timeliness of winter wheat planting. Hooker notes that the average yield loss across all OSACC tables for delayed soybean maturity is 0.7 bu/ac per day delay in maturity.  Therefore, growers should fine-tune variety selection from a list of adapted varieties (i.e., similar maturity group ratings or Table in OSACC trials according to days to maturity). 

We typically recommend growers plant multiple varieties across their acres to access different genetics and manage risk. Having a strong understanding of the days to maturity of each variety ensures that your genetic choices can optimize yield where and when they are planted.