Engineering topsoil to meet Imperial Oil’s oil and gas lease reclamation needs

Topsoil is often unavailable for reclaiming older well sites and remote locations. In the absence of topsoil, subsoil or mine substrates amended with organic materials have been used as topsoil substitutes. This project aimed to engineer synthetic topsoil in situ that is sustainable and of equivalent quality as native topsoil in a relatively short time. The engineered topsoil was created by amending native subsoil with theory-based amounts of a mixture of charcoal (as humin surrogate) and plant residues varying in resistance to microbial decomposition (alfalfa hay, straw, and saw dust), followed by repeated cultivation. The objectives were to demonstrate the effectiveness under field conditions and to identify which soil management system (fallow, agronomic pasture, cereal crop (barley), green manure (field pea), and native pasture) produces the highest quality of engineered topsoil within a short period of time.

Using greenhouse and field experiments, we have shown that amendment of subsoil substrates with recalcitrant carbon (biochar or humalite) together with a mix of sawdust, wheat straw, alfalfa hay, and supplemental nutrients result in a productive growing medium comparable to that of native topsoil control. it is imperative that reclamation managers ensure deep ripping of the subsoil to the desired depth so proper mixing of subsoil and organic amendments is achieved. Humalite (oxidized lignite) is an abundantly available and cheaper alternative to charcoal with the main difference being a lower pH. Humalite amendment to coarse textured soils has the potential to decrease the availability of soil nutrients such as phosphorus through adsorption. This information must be taken into account when formulating fertilizer to add after the organic amendment. Adequate nitrogen fertilization soon after organic amendment that contains humalite or charcoal is key to avoiding soil nitrogen immobilization.