Deep tillage of soil can be a promising tool in offsetting greenhouse gas emissions, according to Concordia researchers

Climate researchers have identified intensive agriculture as a major source of greenhouse gas emissions for decades. And larger, more urbanized populations are forcing the industry into expanding its practices that release carbon dioxide and other greenhouse gases into the atmosphere.

One way of helping to offset those emissions is to capture and sequester carbon. Key to this is soil organic carbon (SOC), the carbon components of the organic compounds found in the world’s topsoil. This is composed mostly of soil biota, such as earthworms and decomposing organic materials. Globally, SOC stores about 1,500 petagrams of carbon in the first metre of topsoil — more than all of the carbon in the atmosphere and terrestrial vegetation combined. And it can accommodate more.

This is the topic of a new study led by Concordia PhD student Qi Feng and Chunjiang An, assistant professor in the Department of Building, Civil and Environmental Engineering at the Gina Cody School of Engineering and Computer Science. In it, the researchers conduct a meta-analysis of 43 separate studies to further understand the relationship between deep tillage and SOC. Zhi Chen, Qi’s co-supervisor and professor in the same department, and PhD student Zheng Wang co-authored the paper.

They found that the relationship is positive: deep tillage can enhance SOC, and so help sequester carbon by 7.79 per cent. The technique is especially effective in arid regions, since deep tilling loosens compacted soil, allowing more humidity and nutrients to penetrate it at lower levels.

Digging for answers

“There have been many studies focusing on the ways human activity and land use has influenced the dynamics of soil carbon, but they mainly look at what happens in the upper 20 centimetres,” Feng explains.

“Deeper soil layers have attracted much less attention. Those have a much larger volume than the upper layers, and have some unique environmental factors, such as less fresh carbon input and less exposure to oxygen. Compared to the surface soil, it is less saturated with soil organic carbon.”

Deep tillage is not a new method of farming. In fact, it is already practiced worldwide. And while it has been shown to improve crop yields, the constant soil disturbance it creates, and the high costs of investing in new machines and technologies, have led to some agriculture practitioners abandoning deep tillage altogether.

Feng says the meta-analysis approach involving 430 comparisons across 43 separate papers gave the researchers the kind of breadth they needed to see big-picture issues, which are often lost in more focused papers.

“These studies addressed some of the same questions but had different or inconsistent results,” she notes. “By using meta-analysis, we were able to aggregate information to identify stronger results, find general patterns and see relationships that may not have been evident in the individual studies.”

According to An, the research can be a tool for governments looking to increase crop yields and simultaneously promote carbon sequestration.

“We hope this paper will provide governments with enough evidence for them to consider providing some guidelines to farmers around deep tillage.”

The Natural Sciences and Engineering Research Council of Canada (NSERC) provided support for this study.

Read the cited paper: “Can deep tillage enhance carbon sequestration in soils? A meta-analysis towards GHG mitigation and sustainable agricultural management.”