Soybeans show resilience under varied conditions

Brent VanKoughnet was worried about his soybeans last spring.


Cool weather had hindered plant emergence, and when he scouted his test plots in southern Manitoba, VanKoughnet consistently found thin plant stands regardless of row spacing and other variables.


“I was kind of sick about this…. I thought this field isn’t going anywhere good,” said VanKoughnet, who runs AgriSkills, an agricultural consultancy in Carman, Man.


“I’ve lost one trial in 15 years … and I didn’t want this to be the second one.”


Three months later, the same soybean plots produced yields of 35 to 38 bushels per acre.


“It reminded me, don’t rip up a field,” VanKoughnet told the CropConnect conference in Winnipeg last month. 


VanKoughnet’s soybean trials have studied variables such as seeding rate, row spacing and seeding date.


Regardless of agronomic practices, there was minimal yield variation in most of his results. 


Beans seeded in early to late May yielded 42 bu. per acre, while crops seeded with a planter at 30 inch spacing or seeded with an air drill at eight inch spacing yielded 40 bu. per acre.


VanKoughnet said he was surprised by the resiliency of soybeans.


“We looked at seeding dates, row spacing and population and also at rolling. In each of those cases, under a wide range of conditions, they (soybeans) bounce back pretty well.”


It’s good news for soybean growers, but he said they shouldn’t rely on that resiliency.


“I’m not sure you can always count on that. There’s an advantage to try and get it right and use the ideal plan.”


For example, soybeans seeded in early May can take 19 days or longer to emerge from cooler soil, while beans planted in the third week of May, when soil temperatures are approaching 15 C, will emerge in eight to nine days. 


“In the years where we haven’t had a yield penalty, I consider that as more luck than good management…. The potential for disease problems and reduced vigour and all those kinds of things, sometimes you get away with it and sometimes you won’t,” VanKoughnet said. 


“Slightly different growing conditions and that might not have turned out as positive as it did…. You can get away with early, sometimes, but that’s not a risk worth taking.”


VanKoughnet said growers might be able to cut back on seeding rates. 


“I think we found that some of the earlier discussion of seeding rates up in the 200,000 plants, that appears to have been excessive.”


Ron Tone, a Manitoba agricultural consultant, prepared a report for the Manitoba Pulse Growers Association last year on the effects of lowering rates by 30,000 seeds per acre.


After evaluating seven field-scale strip trials in Manitoba, Tone found that higher seeding rates increased yield by only 0.3 bu. per acre. 


Assuming a seed cost of $54 per 140,000 seeds, Tone said cutting rates by 30,000 seeds saves $11 per acre.


Tone will continue his seeding rate strip trials this year to help determine the optimal seeding rates for soybeans.


Dennis Lange, Manitoba Agriculture’s crop production adviser in Altona, said VanKoughnet’s data suggest spacing doesn’t have a significant influence on yield.


“Between eight, 15 and 30 inch row or even a 22 inch row, if all conditions are good you don’t see a huge difference in yield,” he said. 


“You’ll see differences in how quickly the beans come out of the ground, but at the end of the day it’s yield that matters.”


Lange said growers who own both an air drill and a planter could take advantage of that information by using both to seed beans.


“If you want to get those beans in, because you’ve got to get them (seeded) in May, there’s no problem going in with both units. You can get the beans in a lot quicker,” he said.


“There’s no point having a piece of equipment sit there when it could be put to good use.”