Determining soil order with multiple diagnistic horizons
The following soil profile is the UBC No.4-01--- LFH (3-0 cm), Ah (0-7 cm), Ahe (7-18 cm), AB (18-24 cm), Btg (24-63 cm), BC (63-89 cm). [Qestion-1] This soil is classified as Gleysolic order. I'm guessing that Btg horizon satisfies the diagnostic horizons for both Luvisolic and Gleysolic order, but because Gleysolic is more advanced order than Luvisolic, the Order is Gleysol. Is this correct? [Question-2] This soil has more than 10cm of Chernozemic A horizon (Ah + Ahe = 18cm). But it is classified as Gleysol. Is this because Btg horizon is deeper (19cm) than the Chernozemic A horizon (18cm)? Thank you!
Within each soil order there are soils that are typical representatives of that order (i.e., soils that have typical properties of the order in question), but each soil order also has soils that have properties of another order. Monolith no.4-01 in UBC collection is an example of soil that have properties of both Luvisols and Gleysols. This soil belongs to Gleysolic order and its Luvic Gleysol great group, which has Btg as its diagnostic horizon. Other great groups of the Glesyolic order do not have accumulation of clay in their B horizons.
You need to be very careful with Ah horizons, since they are present in various soil orders. Not every Ah horizon thicker than 10 cm is the chernozemic Ah. Chernozemic Ah horizon needs to satisfy all the following requirements - thicker than 10 cm, has base saturation >80%, has Ca2+ ion as most dominant ion on exchange complex, C:N <17, organic carbon <17% (weight), and it has to be present in a natural grassland soil formed in an arid to semi-arid climate. Hence, soil that has a thick Btg horizon needs to be located in a climatic region where there is enough of precipitation to allow eluviation & illuviation of clay and that does not happen in a semi arid to arid climate.
OK, I should have looked into the diagnostic horizon for the great group. Thank you for your explanation!!