SoilWise Geopackage

Soil Organic Carbon (SOC) 0–30 cm — QGIS Model

Download the model and its companion style to reproduce the workflow exactly and ensure consistent symbology in QGIS.

Warning

Model and style must be co‑located. The model file and its corresponding style file must reside in the same folder. If either file is moved or the directory structure changes, relative references will break and the style will not be applied at >runtime/build time.

1) Objective

This document describes a QGIS model that computes Soil Organic Carbon (SOC) as a depth‑weighted value in the top 0–30 cm. The workflow integrates datastream selection, 0–30 cm layer filtering, hierarchical joins across profile tables, weighted value computation per datastream, and final aggregation per soil plot.

Tip

For further information on model creation and execution, consult the official QGIS documentation for the Model Designer.

2) Expected Inputs

The model works exclusively on the SoilWise GeoPackage and uses the following tables/layers: profileelement, soilprofile, datastream, observation, soilplot. Expected relations: profileelement.ispartof → soilprofile.guid; datastream.guid_profileelement → profileelement.guid; observation.guid_datastream → datastream.guid; soilprofile.location → soilplot.guid.

3) Parameters / Constants

  • Depth window: [0, 30] cm.
  • Datastream filter:
    • guid_observedproperty = '09b9f784-0bee-49ee-aaae-9320e0e258f6' - Carorg
    • guid_observingprocedure = '9c6f5f47-352e-463b-9c4e-6320a154040a' - OrgC_wc-cro3-walkleyblack

4) Workflow (condensed)

  1. Select datastreams by observed property & observing procedure.
  2. Filter profile elements intersecting 0–30 cm: upper < 30 and lower > 0.
  3. Join soilprofile ↔ profileelement (filtered).
  4. Join with selected datastream and retain only needed fields.
  5. Join with observation to bring result_real and time.
  6. Compute oc_0_30 (Field Calculator):
    • Per row, compute a weighted contribution:
\[w = result\cdot\frac{\max(0,\min(30,low)-\max(0,up))}{low-up}\]
  • If a guid_3 (datastream) is unique → oc_0_30 = w; if repeated → see 5.2.
    1. De‑duplicate by guid_3 (one row per datastream).
    2. Statistics by soilplot (location): use sum and rename to soc_0_30.
    3. Join result back to soilplot and apply the CO_0_30.qml style.

5) Key Expressions

5.1 Row weight (depth‑weighted contribution)

\[w = result\cdot\frac{\max(0,\min(30,low)-\max(0,up))}{low-up}\]

5.2 Rule for the final per‑datastream value (no restricted macros)

  • If count(guid_3) = 1:
\[oc_{0-30} = w\]
  • If count(guid_3) > 1:
\[oc_{0-30} = \frac{1}{n}\sum_{i=1}^{n} w_i\]

6) Output

  • Final layer: soilplot with attribute soc_0_30 (SOC 0–30 cm) and the CO_0_30.qml style applied.