Integrated Catchment Management

Soils

Soils

The complexity of landforms, climate, and rock types in the Motueka Catchment results in a wide variety of soils, which can be grouped into six broad classes:

  1. Soils of the floodplains and low terraces are formed from recent river alluvium and are mainly Recent and Gley soils, with Saline Gley Recent soils near the coast.
  2. Soils of the intermediate and high terraces are formed from older alluvium and are mainly well drained Brown soils with low fertility.
  3. Soils of the coastal sands are formed in a small area of beach sands and gravels near the coast.
  4. Soils of the fans are formed from older alluvium or till and have a restricted extent. They are well drained Brown soils with low fertility.
  5. Soils of the rolling and hilly lands. Hilly soils comprise a wide variety of soils distinguished according to climate and parent material. Most are classified as Brown soils with some Podzols, Ultic and Melanic soils. Fertility is generally low on the Moutere gravels and granite, and higher on sedimentary and basic igneous rocks. Soils of this group are well drained. The soils formed on Moutere gravel are prone to sheet and gully erosion when cleared, and the soils formed on weathered granite are prone to erosion when disturbed, and can release large quantities of sand into streams.
  6. Soils of the steeplands. Steepland soils also comprise a wide variety of soils distinguished according to climate, parent material and elevation. Most are classified as Brown soils, with significant areas of Podzols and Melanic soils. Fertility is generally low on greywacke, schist, argillite, quartzite, and acidic igneous rocks (granite, diorite, granodiorite) and higher on calcareous sedimentary rocks and basic igneous rocks. These soils are dominantly well drained. The soils from ultramafic rocks contain some trace elements toxic to plant health so rock exposures and screes are common.

Soil permeability
Soil permeability is important for a number of reasons.

Low permability means more runoff and greater potential for erosion and flooding.

High permeability means more water enters the soil and groundwater systems, and is likely to mean that more moisture will be retained in the soil slowing down runoff response and reducing erosive potential.

Potential rooting depth
Potential rooting depth is the depths (in metres) to a layer that may impede root extension. Such a layer may be defined by penetration resistance, poor aeration or very low available water capacity.

 

Class Min (m) >= Max (m) <= Description
1 1.2 1.5 Very deep
2 0.9 1.2 Deep
3 0.6 0.9 Moderately deep
4 0.45 0.6 Slightly deep
5 0.25 0.45 Shallow
6 0.15 0.25 Very Shallow

Profile available water 
Profile total available water (PAW) is the minimum and maximum values of profile total available water for the soil profile to a depth of 0.9 m, or to the potential rooting depth (whichever is the lesser) and, expressed as mm of water. 

Profile total available water classes and their corresponding values and descriptions are as follows:

 

Class Min (mm) >= Max (mm) <= Description
1 250 350 Very high 
2 150 250 High
3 90 150 Moderately high
4 60 90 Moderate
5 30 60 Low
6 0 30 Very low

Depth to slowly permeable layer
Depth to a slowly permeable horizon is the minimum and maximum depths (in metres) to a slowly permeable horizon. 

This is defined as an horizon in which the permeability is less than 4mm/hr. 

Classes for depth to a slowly permeable horizon and their corresponding values are described as follows:

 

Class Min (m) >= Max (m) <= Description
1 0 0.45 Shallow
2 0.45 0.6 Slightly deep
3 0.6 0.9 Moderately deep
4 0.9 1.2 Deep
5 1.2 1.5 Very deep
6 N/A N/A No impeding layer identified
go to top

Altas