Added information variables used to the soil model implementation docs

docs/source/virtual_ecosystem/implementation/soil_implementation.md

@@ -24,3 +24,49 @@ language_info:
 ---
 
 # The Soil Model implementation
+
+## Model overview
+
+TODO - This section needs to be properly populated
+
+## Model variables
+
+## Initialisation and update
+
+The tables below show the variables that are required to initialise the soil model and
+then update it at each time step.
+
+```{code-cell} ipython3
+---
+mystnb:
+  markdown_format: myst
+tags: [remove-input]
+---
+from IPython.display import display_markdown
+from var_generator import generate_variable_table
+
+display_markdown(
+    generate_variable_table(
+        "SoilModel", ["vars_required_for_init", "vars_required_for_update"]
+    ),
+    raw=True,
+)
+```
+
+## Generated variables
+
+The soil model does not currently generate any variables. If that changes this section
+will need to be updated.
+
+## Updated variables
+
+At each model step, the following variables are then updated.
+
+```{code-cell} ipython3
+---
+mystnb:
+  markdown_format: myst
+tags: [remove-input]
+---
+display_markdown(generate_variable_table("SoilModel", ["vars_updated"]), raw=True)
+```

virtual_ecosystem/models/soil/soil_model.py

@@ -177,6 +177,8 @@ class SoilModel(
         "arbuscular_supply_limit_n",
         "arbuscular_supply_limit_p",
     ),
+    # TODO - If anything gets added to this section the implementation docs will need to
+    # be updated
     vars_populated_by_first_update=(),
 ):
     """A class defining the soil model.