GP38

Site GP38 Landscape

Soil Profile Morphology:

Surface Soil

A1	0-17 cm	Dark greyish brown (10YR4/2); sandy loam; weak medium polyhedral, parting to weak fine polyhedral structure; firm consistence dry; pH 5.8:	Site GP38 Profile
A2	17-20 cm	Pale brown (10YR6/3) with a yellowish brown (10YR5/8) mottles in patches; sandy loam; contains many (40%) ferruginous nodules (2-10 mm in size); pH 6.4; discontinuous change to: Note: Sometimes the A2 forms a hard capping on top of the B21 horizon.
Subsoil
B21	20-60cm	Yellowish brown (10YR5/6) with strong brown diffuse (7.5YR5/8) mottles; medium heavy clay; weak coarse prismatic, parting to moderate coarse blocky and medium polyhedral structure; strong consistence dry; pH 6.5:
B22	60-90 cm	Yellowish brown (10YR5/6) with diffuse reddish yellow (7.5YR6/8) and dark red (2.5YR4/8) mottles; moderate coarse prismatic, parting to coarse blocky structure; many slickensides; pH 7.3:
B23	90+ cm	Yellowish brown (10YR5/6) with reddish yellow (7.5YR6/8) mottles; many slickensides present; pH 7.1.

• Strong texture contrast between surface (A) horizon (17% clay) and sodic subsoil (B21) horizon (79% clay).
• Accumulation of ironstone nodules in the subsurface horizon.
• Vertic properties (i.e. significant shrink-swell characteristics) in deeper subsoil.

	The surface is moderately acid. The subsoil is slightly acid becoming slightly alkaline at 60 cm.		The upper subsoil is sodic; becoming strongly sodic at depth.
	The salinity rating is low throughout the profile.		The clay content increases significantly at the A/B horizon interface.

Horizon	Horizon Depth (cm)	pH (water)	pH (CaCl2)	EC 1:5	NaCl	Exchangeable Cations
						Ca	Mg	K	Na
						meq/100g
A1	0-17	5.8	5	0.06		2.7	2	0.29	0.4
A2	17-20	6.4	5	<0.05		1.1	1.3	0.09	0.29
B21	20-60	6.5	5.1	<0.05		3	10	0.4	1.8
B22	60-90	7.3	6.3	0.24		1.6	32	0.2	12
B23	90+	7.1	6.3	0.28	0.06	1	9.9	0.15	13

Horizon	Horizon Depth (cm)	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	0-17	8	20	41	17	17
A2	17-20	5	30	39	17	3
B21	20-60	28	5	8	2	79
B22	60-90	31	3	5	1	83
B23	90+		9	14	6	67

• Plant Available Water Capacity (PAWC) is considered to be quite low as effective rooting depth is likely to be restricted to the surface horizons. The dense and coarsely structured upper subsoil is likely to restrict rooting depth.

• The surface soil has a low nutrient holding capacity. Organic matter is important for enhancing fertility of soils such as these with high sand contents.
  
  
• The surface (A1) horizon disperses moderately after remoulding, indicating that structural degradation (e.g. surface sealing, exacerbated hardsetting, increased cloddiness) may occur if the soil is cultivated or overstocked in a moist to wet condition. Also, raindrop action on bare surface soil may also promote dispersion. Surface cover should be maintained to protect against raindrop damage.

• The coarsely structured upper subsoil is sodic and has a low exchangeable calcium to magnesium ratio (i.e. a high level of exchangeable magnesium relative to calcium). This may result in nutrient imbalances (e.g. calcium deficiency). At 50 cm the subsoil becomes strongly sodic and extremely sodic at 90 cm with strong dispersion. As a result of these conditions root and water movement is likely to be restricted in the subsoil. The use of gypsum in association with deep ripping, has been advocated by some researchers as an effective way to ameliorate sodic subsoils but this may not be an economic option. Deep ripping should not be carried out when the subsoil is in a moist to wet condition.
  
  
• The subsoil displays vertic properties (i.e. slickensides) which indicates that significant shrinking and swelling occurs with wetting and drying cycles. This may disturb the roots of some plants. The shrinking and swelling also has engineering implications (e.g. disturbance to fence lines).

• Traffickable most times.