Special recipe creates topsoil in just five years

Faster Topsoil


Imperial had a number of old well sites that needed to be returned to their natural state once in situ extraction of bitumen was over. But a shortage of quality topsoil posed a problem. Companies are regulated to reclaim the land and recreate a natural habitat. But if you don’t have topsoil, what do you do?

Topsoil is the vital top layer of nutrient rich organic material 10 to 15 centimetres deep where plant roots, insects, and other lifeforms flourish. Today, companies salvage topsoil when it is removed for operations, but some of Imperial’s sites were from a time when this practice was not yet common place. Natural regeneration was not an option because topsoil takes thousands of years to form from the subsoil below. 

Topsoil graphic

Soil scientist Asfaw Bekele, an environmental research advisor at Imperial, and his colleagues wanted to find a solution. The research team knew some companies had tried adding compost type amendments to reclaim mined sites, but the results had not always been successful or consistent.

 “We asked ourselves if we could mimic nature in a shorter period of time?” Bekele says. “Could we understand the science better and come up with the ideal recipe of ingredients— the right things added in the right amount—that would allow topsoil to regenerate faster in the presence of growing plants?”

The team first researched the scientific literature to find out what others had done. “We found out that not all organic materials are created equally, they decompose at different rates. Adding organic materials that have different decomposition rates can help move the topsoil formation process along,” Bekele said.

The trick seemed to be to combine specific ingredients, some of which decomposed within months and others over years, as well as materials that provided an ideal soil structure. Alfalfa hay, for example, decomposes quickly releasing nutrients for plant life; wheat straw and sawdust take much longer. Charcoal seemed to be a key ingredient because it mimics the part of natural soil that supports essential microbes.

However, charcoal would make the recipe too expensive for it to be applied widely, so the team sourced a cheaper alternative, a soft coal substitute called oxidized lignite that was readily available and has similar characteristics as charcoal. “Those became the main recipe ingredients,” Bekele says.

The next step was to test their innovative ideas in a lab to get a better understanding of the soil chemistry involved in decomposition. Once they saw success, they moved the testing to greenhouses, and then to small plots of land to test the recipe in the field. “It’s always learning and improving by trial and error,” Bekele explains. “That’s why research takes so long.”

When they were confident they had a potential winner, they conducted a pilot on two Imperial sites and finally proved their special recipe could create quality topsoil in just five years!

“The bottom line for every company is whether you are successful at reclamation or not,” Bekele says. “This recipe gives them a new tool in their toolkit. It can be applied to any site anywhere in the world using locally sourced organic amendments.”

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