| Code | Name | Size range (mm) |
|---|---|---|
| 1 | Microfine | < 1 |
| 2 | Extremely fine | 1 - 2 |
| 3 | Very fine | 2 - 6 |
| 4 | Fine | 6 - 10 |
| 5 | Medium | 10 - 20 |
| 6 | Coarse | 20 - 60 |
| 7 | Very Coarse | 60 - 100 |
| 8 | Extremely coarse | 100 - 200 |
| 9 | Gross | > 200 |
22 Horizon properties
22.1 Size classes
22.1.1 Size classes for solid soil components
The following size classification may be applied to size data gathered for peds and other solid soil components.
22.1.2 Size classes for rock fragments
The following classification may be applied to directly measured size data for rock fragments, or used when assessing rock fragment composition in detail (Section 14.2.1).
| Code | Name | Size range (mm) |
|---|---|---|
| 1 | Fine gravel | 2 - 6 |
| 2 | Medium gravel | 6 - 20 |
| 3 | Coarse gravel | 20 - 60 |
| 4 | Cobbles | 60 - 200 |
| 5 | Stones | 200 - 600 |
| 6 | Boulders | 600 - 2000 |
| 7 | Large boulders | >2000 |
22.1.3 Estimating size classes
The following images can help accurately estimate the size of soil features.
images go here
22.2 Abundance classes
22.2.1 Abundance classes for roots
| Code | Name | Description |
|---|---|---|
| 0 | None | 0% |
| 1 | Few | > 0 - 5% |
| 2 | Common | > 5 - 25% |
| 3 | Many | > 25 - 50% |
| 4 | Abundant | > 50% |
22.2.2 Abundance classes for other soil components
| Code | Name | Description |
|---|---|---|
| 0 | None | 0% |
| 1 | Very Few | > 0 - 2% |
| 2 | Few | > 2 - 10 |
| 3 | Common | > 10 - 35% |
| 4 | Many | > 35 - 50% |
| 5 | Abundant | > 50 - 75% |
| 6 | Dominant | > 75% |
22.2.3 Estimating abundance classes
The following images can help accurately estimate percentage abundance of soil features by area.
images go here
22.3 Horizon drainage
Soil drainage is an assessment of how fast water leaves a soil profile relative to supply. This characteristic can be controlled by morphological characteristics that occur in a range of combinations.
Drainage should first be assessed on a per-horizon basis. These interpretations are later summarised at a profile level (see Section 24.2.4). Table 22.5 below highlights the common characteristics associated with each horizon drainage class.
| Code | Name | Horizon Names | Typical Moisture | Main colours | Redox concentrations |
|---|---|---|---|---|---|
| VP | Very poor | O*, *r | Saturated or wet | Low-chroma | Few to none |
| PO | Poor | *r, *g | Wet | Low-chroma | Few to none, mottles more often on ped surfaces than internals |
| IP | Imperfect | *(g) | Wet to Moist | Low-chroma patterns on brighter matrix | Fe and/or Mn-rich segregations, nodules and pans |
| MW | Moderately Well | *(f) | Wet to Dry | Colour patterns but no low chroma colours | Mottles more often in ped interiors |
| WE | Well | No redox suffixes | Moist to Dry | No low chroma colours | Few to none |
22.3.1 Classifying topsoil drainage
Morphological features associated with drainage status can be hard to spot in A horizons, mostly due to their darker colour. When otherwise in doubt, a well developed A horizon should be assigned a drainage class one better than the horizon below it (usually a B, E, or C horizon). A poorly developed A horizon should receive the same class assignment as the horizon below. Use the ‘distinct topsoil’ NZSC diagnostic criteria to identify well developed A horizons.
The reasoning behind this rule of thumb is that the lack of topsoil development may be partially explained by lack of contrast in the drainage regime between the topsoil and the layer below.
Note 22.1: Wet vs wet-and-anoxic soils
Soils that are persistently wet may also become anoxic. This is more common in low-permeability soils, where slow percolation allows enough time for oxygen to be consumed entirely.