#443 added classes related to soil layer

[KrishnaTO]

Added classes:

• soil layer
• soil layer bottom depth
• soil layer top depth

closes #388

[cmungall]

I am not enthused about adding more investigative processes to ENVO, there is no clear dividing line between ENVO and OBI here. But we can add contingent we may need to offload these later

[marieALaporte]

We need that term has we need to record when the process happens. But maybe you can suggest a better way for handling time here.

[pbuttigieg]

I am not enthused about adding more investigative processes to ENVO, there is no clear dividing line between ENVO and OBI here.

It's not a biomedical investigation, so it's fine in ENVO. If that branch grows enough, we would spin off a new ontology for environmental assessments and investigations.

[marieALaporte]

if having the term 'soil profile characterization process' is a blocker for this PR, we can remove it for now, as we did for 'soil profile'.
This PR is creating the following terms:

• soil layer bottom
• soil layer top
• soil layer bottom depth
• soil layer top depth

We are also proposing to add the term 'soil layer' as a synonym for 'soil horizon'

[dr-shorthair]

Hold your horses here folks.

Layers and Horizons

'soil layer' is not a synonym for 'soil horizon' (in Australia and New Zealand, at least).

• Horizons are defined by what are broadly understood to be 'genetic' processes, or at least some compositional classification
• Layers are more general, and are often just an arbitrary depth interval (e.g. 0.5-2 m)

profile vs sequence-of-horizons

There has been a lot of discussion around the definition of 'profile' down under as well.

There is a soil body, which is usually composed of horizons - i.e. of layers that are defined by compositional or genetic properties.

Then there is the profile, which is the set of horizons as observed at a specific site, in a core, on a section, or in the wall of a pit.

The 'profile', with its specific measurements and observations, and interpretation, is actually a sample of the soil body, or of the sequence-of-horizons. It is at least in part an artefact of the observational and sampling strategy, rather than an intrinsic representation of nature.

[dr-shorthair]

@bsimons14 @abhritchie @meganrwong I suggested some alignment with ANZ here

[dr-shorthair]

See comment above

[marieALaporte]

Thanks for the feedback @dr-shorthair.
If I understand correctly the difference between a soil layer and a soil horizon, if that a soil layer might not match a soil horizon as it can be sampled at any depth.
Back to ENVO, there is currently a term 'soil horizon' which is under 'layer' and defined as 'A layer which is parallel to the soil surface and which has roughly homogenous physical, chemical and biological properties relative to the soil layers above or beneath it'. Based on the assumption that a soil horizon is a soil layer, but a soil layer is not an horizon, I propose to create a 'soil layer' class under 'layer', and to move 'soil horizon' below that class. Then 'soil layer bottom' and 'soil layer top' can be moved under this new 'soil layer' class as well. What do you think?

Regarding soil profile, we decided to not include it in this PR as we understood that it might not be in the scope of ENVO.

[dr-shorthair]

Thank you @marieALaporte - yes, soil-horizon as a sub-class of soil-layer is OK.

There may (later) be an opportunity to align this with geology models, but this will be fine for now.

[marieALaporte]

I added soil layer and moved soil horizon under it.
@dr-shorthair let me know if that looks good now. Thanks