Soybean growers who plant no-till after corn can lose roughly a quarter of their seed before emergence: plant 100 seeds into untilled ground and, on a typical Ontario farm, only about 65 survive, against 80 to 90 in a tilled seedbed. Those figures from University of Guelph assistant professor Josh Nasielski frame a three-year on-farm study that is starting to explain why no-till soybean establishment fails — and what machinery settings might fix it.

The agronomic backdrop is stark. Soybeans cover three million acres in Ontario, the province's top field crop, ahead of corn at two million acres. A decade ago, no-till adoption in soybeans fell from 80 per cent to 50 per cent, and Nasielski suspects it has slipped further since. Higher corn yields leave more residue to manage, and rising seed costs make the traditional workaround — bumping seeding rates by 30,000 or 40,000 seeds per acre to offset thin stands — increasingly expensive.

"There are a lot of soil health benefits with reducing tillage intensity and it saves costs," says Nasielski, who holds the MacSon professorship in agronomy for eastern and northern Ontario. "But there's been a dramatic movement back towards some form of tillage between corn harvest and soybean planting."

Twelve fields, 50-plus measurements

Rather than run controlled-environment trials, Nasielski's team worked in commercial fields. Over three growing seasons they monitored 12 soybean fields across Prince Edward, Stormont, Dundas and Glengarry counties, with field work led by master's student Lance Javier and supported by technicians and graduate students Ian DeSchiffart, Michael Gebre and Iraj Yagoubian, plus specialists John Sulik and Richard Heck.

Before planting, Nasielski interviewed each collaborating farmer about field history, disease and pest pressure, drill or planter setup, combine residue-management settings and tillage practice. The crew then used remotely sensed data to map surface corn residue and topography, quartering each field into high-residue, low-residue, high-topography and low-topography zones. From each zone they took two samples and recorded more than 50 soil measurements, including bulk density, shear strength and aggregate size distribution.

After planting, they scored furrow closure, seedbed roughness, clods, hairpinned residue and planter performance. A month later they counted plants per acre and measured plant-to-plant spacing, spacing variability, planter misses and multiples, and mean emergence time. For seeds that never emerged, they trenched the rows and checked for compaction, disease and moisture.

Shear strength, not compaction, is the main suspect

Because the study is observational, the team uses random effects and mixed models, standardizing variables within each field rather than imposing treatments. Two preliminary findings stand out.

First, higher seedbed bulk density coincided with lower actual seeding rates relative to the farmer's target. The direction of causality is still unresolved: a compacted seedbed may be impairing the drill's metering, or a planter fault may be both dropping seeds and compacting the furrow.

Second — and more consistent across fields — higher seedbed shear strength tracked with poorer stands. Notably, shear strength is not compaction. "Compaction is basically defined by bulk density of the seedbed and there was no relationship between bulk density and shear strength," Nasielski says. Even after accounting for clay content and soil moisture, something about how the planter or drill reconsolidates soil while forming the furrow drives shear strength. He suspects planter or drill setup plays a role, but the analysis is not yet complete.

Residue placement, not residue load

The third finding concerns corn residue in the furrow. "We saw quite a few times that residue would get mixed into the furrow, get hairpinned, and that hairpinned residue would basically act as a shield and stop that soybean seedling, its hypocotyl, from emerging," Nasielski says.

A manipulation trial at the Winchester Agricultural Research Station tested the mechanism directly. Summer students removed all residue before planting, then returned twice as much residue onto the field after planting. That treatment produced the study's highest yield: 53 bushels per acre. Residue quantity, in other words, is not the problem; residue placement at planting is.

"It's about making sure that residue is handled correctly around planting because you don't want that residue interfering with the drill," says Nasielski. Translating that into specific drill settings requires further work. "We're not 100 per cent there yet, but at least we're narrowing down what the actual problems are."

What comes next

Data collection wraps up this year, after which the team will apply more complex statistical methods to isolate causes and identify practical fixes. One early lesson already holds: the amount of corn residue on a field does not, by itself, predict soybean establishment success. "The next step is just identifying potential causes, eliminating things that do not seem to be causes and then trying to get more targeted solutions," Nasielski says.

For now, no-till soybean growers should scrutinize row-unit residue management and furrow-closing behaviour ahead of next spring, and watch for the team's follow-up analysis on drill and planter setup. The project is supported by Grain Farmers of Ontario, MITACS and The Ontario Agri-Food Innovation Alliance.