“There is a complementary relationship between the adoption of herbicide-tolerant (HT) canola and conservation tillage, resulting in corresponding changes in GHG emissions,” says a paper published in the journal Sustainability in October. “Saskatchewan farmers have confirmed just how crucial the use of glyphosate is with the complementary technology of HT crops… (to) maintain sustainable land management practices.”
The paper was part of the masters’ thesis for Chelsea Sutherland, a U of S student. She collaborated with Stuart Smyth, U of S agricultural economist, and Savannah Gleim, a research officer at the university.
As part of the research, Sutherland surveyed Saskatchewan farmers to understand their land management practices in 1991-94, prior to the commercialization of GM canola, and in 2016-19.
About 130 Saskatchewan farmers completed the online survey.
One section of the survey asked producers about their tillage practices, including their use of summerfallow and how that’s changed in the last three decades.
“Survey results show that between 1991–94 and 2016–19, the percentage of hectares in the survey sample that included summerfallow… decreased from 44 percent to one percent,” the paper says. “Hectares that included CT (conventional tillage) management decreased from 51 to 3 percent.”
Many producers in the survey said glyphosate, or Roundup, was the main reason for the change in practices.
“Participants reported that glyphosate facilitated the reduction of tillage and summerfallow practices to the greatest extent; however, as a complementary technology, HT crops contributed to these management changes,” the paper said.
To estimate the climate-related benefits of reduced summerfallow and tillage, the U of S researchers used a model that correlated the change in farm practices to increased soil organic carbon (SOC).
They found that in 1991-94, the benefits were minimal because summerfallow and tillage were still common.
“(But) by 2016–19, 0.42 megagrams/ha (tonnes per hectare) of SOC was being stored each year from the virtual elimination of summerfallow…. (And) the annual net change in SOC from conservation tillage had increased to 0.12 (tonnes per ha).”
After estimating the changes in soil organic carbon, the authors estimated the change in carbon sequestration from minimal tillage and less summerfallow.
They pegged increased carbon sequestration at “0.14 Mg/ha (tonnes per hectare) from reductions in tillage practices and 0.39 Mg/ha from reductions in summerfallow practices.”
Many of these benefits occurred because of GM canola and glyphosate, the authors said.
Other scientists are less convinced about the benefits of zero-tillage when it comes to improving soil organic carbon.
University of Guelph researchers have found that soil organic carbon in the soil profile is the same in no-till and conventionally tilled systems, even in soil that has been zero tillage for decades.
“If you move towards a reduced till, no-till system it doesn’t impact total soil organic carbon in a (soil) profile. There’s lots a data to support that,” said Bill Deen, a U of G plant scientist.
However, the results depend on the depth of soil.
The top layer of soil in a no-till system has more carbon and superior soil properties to tilled land. But tilled land has more soil organic carbon at depth, Deen said in 2020.
“Total carbon isn’t changing in the two systems. In no-till there’s more at the surface. But… in conventional till, you’ve got more at depth.”
Deen doesn’t know why there’s more soil organic carbon at depth in tilled soils. It’s possible that tilling mixes organic matter into the soil, or plant roots can penetrate further into tilled soil.