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GP76

Location: Boisdale.Australian Soil Classification: Melanic, Eutrophic, Black DERMOSOL.
Geology: Holocene floodplain deposits.General Landscape Description: Floodplain of Avon River.
Mapping Unit: Clydebank: Thomson.Site Description: Dairy grazing paddock.

Photo: Site G76 Landscape
Site GP76 Landscape


Soil Profile Morphology:

Surface Soil

A10-30 cm Very dark brown (10YR2/2); fine sandy clay loam; moderate coarse blocky, parting to strong fine polyhedral structure; strong consistence dry; pH 5.9; gradual change to:
Photo: Site G76 Profile
Site GP76 Profile
Subsoil
B2130-50 cmBlack (10YR2/1); fine sandy clay loam; weak coarse prismatic, parting to strong fine polyhedral structure; pH 6.3:

B2250-90 cmDark brown (7.5YR3/2); fine sandy clay loam; moderate coarse prismatic structure; pores evident; pH 6.8:

B2390+ cm Brown (7.5YR4/2); fine sandy clay loam; weakly structured; pH 7.1.

Key Profile Features:
  • Uniform clay content throughout soil profile.
  • Well structured upper profile (parting to fine polyhedral shaped peds).

Soil Profile Characteristics
:

Horizon
pH
Salinity Rating
Surface
(A1 horizon)
Moderately Acid
Low
Non-Sodic
-
Subsoil
(B21 horizon)
Slightly Acid
Very Low
Non-Sodic
None1
Deeper Subsoil
(at 90 cm)
Slightly Alkaline
Very Low
Non-Sodic
-
1 Slight dispersion after remoulding.


Graph: pH levels in Site G76





The surface is moderately acid. The
upper subsoil is slightly acid becoming
slightly alkaline at 90 cm.
Graph: Sodicity levels in Site G76



The profile is non-sodic throughout.
Graph: Salinity levels in Site G76



The surface salinity rating is low. The
subsoil rating is very low throughout.
Graph: Clay% in Site G76




The clay content remains constant

throughout the profile.


Horizon
Horizon Depth
(cm)
pH
(water)
pH
(CaCl2)
EC 1:5
ESP
%
Exchangeable Cations
Ca
Mg
K
Na
meq/100g
A1
0-30
5.9
5.2
0.12
10
2.9
0.94
0.22
B21
30-50
6.3
5.3
<0.05
10
2.8
0.31
0.2
B22
50-90
6.8
5.7
<0.05
10
3.2
0.17
0.21
B23
90+
7.1
6
<0.05
7.3
4.3
0.08
0.24

Horizon
Horizon Depth
(cm)
Exchangeable Aluminium
mg/kg
Exchangeable Acidity
meq/100g
Wilting Point pF2.5
Wilting Point
pF4.2
Coarse Sand
(0.2-2.0 mm)
Fine Sand
(0.02-0.2 mm)
Silt
(0.002-0.02 mm)
Clay
(<0.002 mm)
A1
0-30
14.4
4
44
24
21
B21
30-50
<10
8.6
10.3
2
51
23
20
B22
50-90
9.5
2
52
22
19
B23
90+

Management Considerations:

Whole Profile
  • Plant Available Water Capacity (PAWC) is considered to be moderate (estimated at 105 mm) for this soil profile. This is based on an estimated effective rooting depth of 50 cm (i.e. surface soil and upper subsoil). The denser and more coarsely structured deeper subsoil is likely to restrict rooting depth, although not to the same extent as some of the more sodic subsoils in the region. Much of the plant available water (i.e. 70 mm) will be in the surface (A1) horizon. PAWC has been estimated using a model developed by Littleboy (1995) which uses analytical data for clay%, silt%, fine sand%, coarse sand % and wilting point
  • Infiltration of water will be rapid throughout the upper soil profile due to the well developed structure and pore space available
Surface (A) Horizons
  • The relatively deep surface soil is well structured (parting to many fine polyhedral shaped peds) and has a weak consistence. As a result, very good seed-bed conditions are provided
  • Infiltration of water into the well structured surface soil will be quite high. This horizon will also be well drained
  • The nutrient holding capacity of the surface (A1) horizon is moderate (based on the sum of the exchangeable cations). Organic matter is important in soils such as these with high fine sand contents for enhancing soil fertility, water holding capacity and aggregation. Nitrogen levels are also high reflecting the high organic matter levels
Subsoil (B) Horizons
  • The upper subsoil soil is also well structured (parting to many fine polyhedral shaped peds) and will provide a good environment for roots and relatively rapid water movement
  • The deeper subsoil becomes more coarsely structured and will be more restrictive to root movement
Comments from Landholder:
  • Black soil dries out more than red soil and becomes cloddier
  • Floods every 20 years or so.
Profile Described By: Mark Imhof and Ian Sargeant (22/04/1998).
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