SW4

Location: Nirranda South

Australian Soil Classification: Fragic,Humosesquic, Semiaquic PODOSOL
Great Soils Group: Podzol
Northcote Factual Key: Uc 3.33
General Landscape Description: Gently undulating sand rises.
Geology: Quaternary sand deposits overlying Tertiary Port Campbell Limestone.

Site SW4 Landscape

Soil Profile Morphology:

Surface Soil

A1	0-10 cm	Black (10YR2/1) loamy sand; weak coarse blocky structure; pH 5.3; clear change to:	Site SW4 Profile
A21	10-25 cm	Dark grey (10YR4/1) sand; pH 5.9; clear and wavy change to:
A22	25-45 cm	Dark greyish brown (10YR4/2) sporadically bleached sand; pH 5.8; clear change to:
Subsoil
Bhs	45-65 cm	Dark brown (7.5YR3/2) sandy loam; weak consistence moist; discontinuous 'coffee rock' common (20%); strong consistence moist; pH 5.8; clear change to:
2A	65-70 cm	Brown (10YR4/3) sporadically bleached loamy sand; weak consistence moist; sharp change to:
2B1	70-80 cm	Brown (10YR4/3) with yellowish brown (10YR5/8) mottles; sandy clay loam; weak very coarse prismatic structure; very strong consistence moist; pH 6.1; gradual change to:
2B21	80-110 cm	Brown (10YR5/3) (becoming dark greyish brown (10YR4/2) with depth) with yellowish brown (10YR5/6) mottles; light medium clay (sandy); weak very coarse prismatic, parting to weak medium prismatic structure; strong consistence moist; pH 6.2:
2B22	110 cm+	Light yellowish brown (10YR6/4) with brownish yellow (10YR6/8) mottles; sandy clay; strong consistence moist.

Soil Profile Characteristics:


The surface horizon is strongly acid. The subsurface (A2) horizons are moderately acid. The subsoil (from 70 cm depth) is slightly acid.	The level of soluble salts is very low throughout the soil profile.	The surface soil is non-sodic becoming sodic at 60 cm depth.	The clay percentage increases sharply in the deeper profile.

Chemical and Physical Analysis:

Management Considerations:

Whole Profile

Plant available water capacity (PAWC) is considered to be very low (estimated at 40 mm) for this profile. This is based on available laboratory data and assumes an effective rooting depth of 45 cm. Rooting depth will be restricted by the 'coffee rock' layer.

Surface (A) Horizons

Lime may be needed to raise the pH of the strongly acid surface soil. However, other factors need to be considered before lime is recommended e.g. pasture species grown, method of application, local trial responses, likely cost-benefit.

The sandy surface horizons are very well drained but have a low water storage capacity. The low wilting point value indicates that plants will be able to utilise light rains falling on dry soil. However, due to the low storage capacity, plants will soon suffer moisture stress until further rain falls occur. Organic matter is important in these sandy soils to enhance water holding capacity.

The sandy surface soil is prone to wind erosion if plant cover is removed, and blow-outs can occur.

The surface soil has a low inherent fertility (based on the sum of the basic exchangeable cations). Such strongly leached soils are also likely to be naturally deficient in nitrogen, phosphorus, sulphur and potassium. Regular fertiliser inputs are required for intensive cropping. Nitrate and sulphate are readily soluble and easily removed by leaching. More regular but smaller applications of fertiliser will assist in reducing loss of nutrients through leaching. Nutrients lost through leaching may influence catchment water quality.

The sub-surface (A2) horizons also have a very low inherent fertility, so plant nutrition in the surface (A1) horizon is critical.

Lime application will result in increased pH levels and make certain nutrients such as phosphorus more available to plants. Many vegetables prefer a pH closer to 6.5. Burnt lime is preferred when planting Brassica species or when a rapid pH change is required (pers. comm. Geoff Morrow, State Chemistry Laboratory).

Deficiencies of the trace element molybdenum are likely to occur in acid sandy soils. Soil adsorption of molybdenum increases as pH decreases, leading to reduced availability to plants. U.S.A research has found that the following vegetables can be susceptible to molybdenum deficiency: brassica species e.g. cauliflower, broccoli and cabbage, lettuce and tomato (Clark 1984). Any deficiencies can be confirmed by plant tissue analysis. Deficiencies can be remedied with molybdenum enriched fertiliser and foliar application. Lime application on acid soils will also make molybdenum more available to plants.

Nutrients such as calcium and magnesium are usually low in strongly acid soils. Magnesium deficiency has been found to affect vegetables such as tomatoes, potatoes and cauliflowers (NSW Dept. Agric. 1987). Magnesium deficiency can be assessed by plant tissue analysis and can be treated by applying dolomite to the soil or by using a foliar spray. Calcium deficiency can affect vegetable crops such as tomatoes, lettuce, celery, brussels sprouts and potatoes (NSW Dept. Agric. 1987). Foliar spray application, adjusting soil pH with lime application or using calcium based fertilisers can be utilised to treat deficiencies.

The trace element boron (B) leaches rapidly through acid sandy soils and deficiencies are likely to occur. Susceptible crops include cauliflower, cabbage and celery (NSW Dept. Agric. 1986). Over-liming in sandy soils can make trace elements such as boron, zinc and manganese less available. Organic matter can complex with metal ions enabling trace elements (iron, zinc, copper) to become more available to plants.

Organic matter is an important source of nutrient holding capacity in sandy soils. Levels of organic matter are often low in continually cropped vegetable growing soils and inputs such as poultry manure are often recommended.

Subsoil (B) Horizons

The 'coffee rock' layer will restrict root and water movement at 45cm depth. Water movement will also be significantly restricted by the sodic and strongly dispersive deeper subsoil (from 70 cm depth).

Profile Described By: Mark Imhof, Austin Brown and Ruth Lourey, 16th April 1996.

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