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Orders: Brunisolic - Great Groups

The four great groups of the Brunisolic order are based on two factors. The first, pH, distinguishes between moderately to highly acidic, primarily igneous rock-derived parent materials and slightly acidic or basic, sedimentary rock parent materials. The second, presence of an Ah (or equivalent Ap) horizon, distinguishes between regions where earthworms and other soil fauna mix forest leaf litter into the upper mineral horizon and those regions where such mixing does not occur. Brunisols with an Ah horizon would primarily be found in the Mixedwood Plains ecozone of southern Ontario and Québec. Where these soils are cultivated, mixing by cultivation creates an Ap horizon, and the Ap must be at least 10 cm thick and have a colour value <4 to meet the A horizon criteria.

The four great groups are the four combinations possible for the two factors:

	Melanic	Eutric	Sombric	Dystric
A horizon	Ah or Ap  ≥ 10 cm	Ah or Ap < 10 cm or absent	Ah or Ap ≥ 10 cm	Ah or Ap < 10 cm or absent
pH	≥ 5.5	≥ 5.5	< 5.5	< 5.5

 

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