GP55

GP55 Landscape

Soil Profile Morphology:

Surface Soil

A11	0-15 cm	Very dark greyish brown (10YR3/2); very fine sandy clay loam; massive structure; firm consistence dry; pH 5.1; clear change to	GP55 Profile
A12	15-35 cm	Dark brown (10YR3/3) with few (8%) brownish yellow (10YR6/8) mottles; very fine sandy clay loam; weak to moderate coarse polyhedral structure; very firm consistence dry; pH 5.1; gradual change to
Subsoil
B1	35-50 cm	Dark greyish brown (10YR4/2) with dark yellowish brown (10YR4/6) mottles; conspicuously bleached in patches fine sandy clay loam; moderate coarse prismatic, parting to moderate coarse blocky structure; very firm consistence dry; pH 5.2; clear and wavy change to
B21	50-70 cm	Dark greyish brown (10YR4/2) with common (15%) brownish yellow (10YR6/8) mottles; light medium clay; strong coarse prismatic, parting to moderate blocky structure; pH 5.4; gradual and wavy change to
B22	70-100 cm	Greyish brown (10YR5/2) with many (25%) brownish yellow (10YR6/8) mottles; light medium clay; strong coarse prismatic, parting to moderate blocky structure; very firm consistence dry; pH 5.4
C	100+ cm	Cretaceous mudstone

Key Profile Features:

• Lack of strong texture contrast between surface (A) horizons of subsoil (B21) horizons.

	pH	Salinity Rating	Sodicity	Dispersion
Surface (A1 horizon)	Strongly Acid	Very Low	Non-Sodic	-
Subsoil (B21 horizon)	Strongly Acid	Very Low	Sodic	None1
Deeper Subsoil (at 1 m)	Strongly Acid	Very Low	Sodic	None2

The whole profile is strongly acid throughout. The exchangeable aluminium levels in the surface horizon are very high and become extremely high from 15 cm depth to 1 metre. The surface soil is non-sodic. The subsoil is sodic. The clay content increases gradually with depth.

Horizon	Horizon Depth	pH (water)	pH CaCl2	EC 1:5	NaCl	Exchangeable Cations
						Ca	Mg	K	Na
						Meq/100g
A11	0-15	5.1	4.2	0.08		3.9	2.7	0.56	0.55
A12	15-35	5.1	4	0.07		2.3	2.5	0.32	0.59
B1	35-50	5.2	4	0.07		1.3	4	0.31	0.94
B21	50-70	5.4	4	0.07		1.3	6.2	0.47	1.6
B22	70-100	5.4	4.1	0.11		2.6	13	0.63	3.6

Management Considerations:

Whole Profile

• Much of the soil profile is strongly acid. As a result, deficiencies in molybdenum, potassium and phosphorus may occur. Manganese toxicity may also occur in strongly acid soils, particularly when poorly drained (as waterlogging may bring manganese into solution). Levels of exchangeable aluminium measured are very high throughout the profile (i.e. ranging from 150 to 320 mg/kg within the surface (A) horizons). This is likely to restrict the growth of aluminium sensitive species. A pH/aluminium test sampled across the paddock would be most appropriate to determine how much lime is needed to raise soil pH. However, other factors need to be considered before lime is recommended (e.g. pasture species grown, method of application, local trial responses, soil surface structure and likely cost/benefit).

• The inherent fertility of the surface (A1) horizon (based on the sum of the exchangeable calcium, magnesium and potassium cations) is low. The high levels of organic matter at this site are important for improving soil fertility, water holding capacity and enhancing surface soil structure.

• The dense and coarsely structured upper subsoil (B21) horizon is sodic and has a low exchangeable calcium to magnesium ratio (0.2). However, strong dispersion only occurs after remoulding. The high levels of exchangeable aluminium (280 mg/kg) in the subsoil may be the cause of the restricted dispersion. The subsoil is dense and coarsely structured which will restrict root movement down the profile.