Conventional wisdom says to break out the harrow before planting soybeans, the better to expose black earth and warm the soil, but new research is putting that assumption to the test.
Dr. Yvonne Lawley of the University of Manitoba is measuring the effect of seeding date and different tillage systems on soybeans through several regions of the province.
“We see soybeans moving into areas where we have predominantly no till,” Lawley said at the recent field day at the Westman Agricultural Diversification Organization (WADO) site near Melita, where some of her plots are located this year.
“My concern is that we’re forgoing soil management to make this new crop work.”
Once a rare sight in the province, soybeans have become one of the most popular crops in terms of acres seeded this year, driving the need for more research.
This summer is the second and final year of Lawley’s project. The experiment tests both an early and late seeding date under three systems: no till, strip till and conventional disc tillage.
In 2016, test sites in Carman showed little difference in yield between tillage systems at either early or late seeding dates, while disc tillage pulled ahead in Melita’s early-seeded plots. Yields in Melita’s conventionally tilled plots easily topped 30 bushels per acre, followed closely by strip tillage while no till trailed at just over 25 bushels per acre.
Later-seeded plots, however, performed well in southwest Manitoba when planted into standing stubble, yielding the highest of the three tillage systems.
“I think what surprises me the most is probably the difference between the tillage treatments in 2016 versus 2017 where we have very different environmental conditions,” Lawley said.
Wet conditions in 2016 have been replaced this spring and summer by dry weather. While not as dry as central Saskatchewan, most of Manitoba’s agricultural landscape has received just 60 to 85 per cent of average precipitation.
“In 2016, we saw that our conventional-till treatment had good stand establishment — like our strip-till treatment — compared to the no till, but then this year we had really dry conditions during soybean emergence. We saw the complete opposite, where we had good conditions in no till, and probably the best conditions in our strip-till treatment again — that’s at least consistent between the two years.”
Moisture for emergence
Conventional tillage, however, struggled in 2017 as the same disturbance that exposed black soil also dried out already thirsty plots.
Disc-tilled plots showed by far the lowest plant establishment of the three early-seeded tillage systems, hovering around 2,000 plants per acre, compared to well over 6,000 plants per acre in zero-tilled soils and well over 8,000 plants per acre in strip-tilled plots.
In contrast, late-planted plots hovered roughly between 4,000 and 5,000 plants per acre in all three systems, with disc tillage having the highest plant density and no till, the lowest.
“Later plantings, it didn’t really matter. It was all about soil moisture for emergence,” Scott Chalmers, crop diversification specialist with Manitoba Agriculture and WADO manager, said. “Conventional tillage was the wrong practice to do in this situation this year. It just dried everything out and that also happened to us in the corn plots this year. We just couldn’t find moisture because we tilled to get the fertilizer in.”
Lawley’s research also showed that strip-tillage soil warmth topped out both other treatments in the first 14 days after planting this year. Lawley counted accumulated degrees over 10 C at planting depth and noted daily peak temperatures in particular were warmer under strip tillage.
“When you’re using strip till, there’s a round, kind of concave surface, and that rounded surface catches more solar radiation than a flat surface, which is typically left in the conventional till,” she said. “In one experiment where we were working with corn residue and we had a really rough surface and essentially had peaks and valleys, there we saw similar trends.”
The effect may be temporary, since press wheels after seeding flatten the berm, she added.
How early is early?
Across the field from Lawley’s WADO tillage trials, soybean and pulse research agronomist Kristen MacMillan, also of the University of Manitoba, is testing four planting dates starting in late April and progressing roughly every 10 days.
“The traditional recommendation is waiting until it’s 10 C and the risk of frost has passed. Farmers have already tested that recommendation and they’ve had success in some areas, so before farmers in every region of Manitoba who are growing soybeans go out and plant the last week of April or the first week of May, we want to test it, because it can be risky,” she said.
MacMillan planted both an early- and late-maturing variety at each date and the experiment has been replicated in a number of regions, including Arborg to the north and Carman and Morden in south-central Manitoba.
“This is just the first year of the trial, so I don’t have any yield data, but we’ve looked at growth staging and flowering,” MacMillan said.
Plants at both Arborg and Carman began flowering in the same short window, regardless of seeding date, initial results showed.
“They’re short-day plants,” MacMillan said “As soon as that summer solstice hits on June 21, they’ll generally start to flower within a week or two after that, so the flowering window across the seeding windows has been only about 10-12 days, which is not necessarily surprising, but it’s just kind of interesting that we have a 35-day seeding window, but they’re all flowering within 10-12 days of one another.”
Biomass and canopy closure is also being measured at flowering, part of MacMillan’s quest to determine if growth staging at anthesis can predict final yield performance.