Better recognition of limnic materials at the great group and subgroup levels of the Organic Order of the Canadian System of Soil Classification

Abstract

In the Canadian System of Soil Classification (CSSC), soils of the Organic order are classified at the great group level primarily based on the dominant organic material in the middle tier. The system recognizes four types of organic horizons: fibric (Of), mesic (Om), humic (Oh) and coprogenous earth (Oco), of which only the latter is not recognized at the great group level of the Organic order. Furthermore, at the subgroup level, Limnic subgroups cannot have terric or hydric layers. This is problematic in soils where the middle tier is dominated by limnic materials, and those which have dominantly limnic materials and have a terric layer. We describe 29 soil profiles in Ontario and Quebec which are either poorly captured in the CSSC, or that cannot be classified into the Organic order based on their diagnostic criteria. Based on an analysis of soil survey information in five provinces across Canada, we estimate 32,057 ha of organic soils which potentially contain limnic deposits. In key vegetable-producing areas of Quebec, large organic deposits in agricultural production are subject to peat subsidence and erosion, resulting in shallower depths to underlying coprogenous earth, which is not a suitable medium for crop production. This can potentially have negative effects on crops when mixed with humic materials in the plow layer. Due to these taxonomic and agronomic considerations, we propose the addition of a new great group, Limnisol, and suggest further integration of limnic materials at the subgroup level for the Humisol, Mesisol, and Fibrisol great groups.

Mitigating CO2 emissions from cultivated peatlands: Efficiency of straws and wood chips applications in maintaining carbon stock in two contrasting soils

“…The presence of roots can also both accelerate the loss of C-CO 2 from the soil through the priming effect and add C to the soil through the production of root biomass and exudate (93,94). Moreover, erosion (6,9) and leaching processes (95) in the field can increase soil C loss. Addressing these factors in future studies would provide a more comprehensive understanding of the complex dynamics of C lost from cultivated peat soil and the potential of this biomass-based conservation strategy in preserving the soil C stock.…”

“…Drainage, however, triggers degradation processes in peat soils that lead to a continual thinning of the peat layer (subsidence) and to the release of nutrient and carbon dioxide (CO 2 ). Subsidence of arable peat soils typically ranges from 1 to 5 cm yr -1 and is mainly caused by the combined effect of [1] peat decomposition, [2] compaction and settlement, and [3] erosion (6)(7)(8)(9). Ultimately, the organic layer of these fertile lands can disappear entirely, leaving behind the underlying material, which may have less or no farming potential (10-12).…”

Advances in soil survey and classification in Canada

“…The soil classification themed manuscripts herein cover topics ranging from changes to the hierarchical structure of the CSSC to new ideas on pedogenesis, and to refinement in some underlying concepts that are critical to soil classification in the field. Proposed updates to the taxonomic system span all five levels, including proposals of new soil Orders for human-modified soils (Anthroposols; Naeth et al 2023) and shallow soils (Leptosols; , a new Great Group in the Organic Order to better recognize limnic materials (Saurette and Deragon 2023), a new subgroup in the Organic Cryosols to capture the occurrence of folic materials (Sanborn et al 2022), and modifications to the soil Family criteria . These proposals, albeit generally straightforward, have a cascading effect on the keys to soil classification since any new taxon will need to be integrated into the existing taxonomic system.…”