Grey Sodosol (Deep Sandy surfaces)

General Description

Within the Undulating Low Hills unit, this soil is located higher in the landscape. The water erosion hazard is high on this soil type because of the presence of non-wetting (see water repellent) sands, slope and slope length. The wind erosion hazard is also high because of the structureless sandy surface soil. Poor management of these soils will decrease productivity locally but also have off-site impacts on other soils located in other units. Particular issues of concern include water run-off leading to erosion and flooding of soil positioned lower in the landscape. For further information on erosion in the Wimmera see Land Degradation.

Surface soil:	Deep loamy sands and sands, weakly structured , slightly acid.
Subsoil:	Heavy clay, sodic, non-dispersive, low salinity, slightly acid. Abrupt change in soil texture between surface and subsoils.

Major Limitations

Soil Problem	Result
Weakly structured surface soil.	Wind erosion.
Sandy texture.	1) Low water holding capacity but responsive to light rains.
	2) Low nutrient holding capacity.
Non-wetting sand.	Poor infiltration of water on dry soil.

Management Suggestions

The low water and nutrient holding capacity and risk of wind erosion makes this soil type undesirable for cropping. The cost of inputs to grow a crop compared to the returns is high as is the risk of not achieving a satisfactory crop. Permanent perennial pastures or native vegetation which will provide wind protection to other soils is recommended.

Soil Problem	Management Suggestions
Weakly structured surface soil.	Continuous groundcover i.e. stubble & pasture retention/reduced tillage.
Water holding capacity.	Improve organic matter via above suggestion.
Nutrient holding capacity.	Improve organic matter via above suggestion.
Non-wetting.	Groundcover, addition of clay *.

* The addition of clay to non-wetting sands is a relatively new practice and although it is likely to be beneficial, the practice may not be economically viable.

Soil Characteristics

Water Infiltration and Permeability
Infiltration on these soils is generally high but can be restricted by the non-wetting sands that reduce water infiltration to dry soils. Resultant water run-off may lead to rill erosion. When wet, the sandy textured surface soils are highly permeable but permeability of water into the subsoil is restricted by hardpans and sodic subsoils. As a consequence, lateral flow of water along the top of the subsoil will reduce available water for use by plants growing on this soil and exacerbate degradation problems on soil and units lower in the landscape.

Water Holding Capacity (Soil water storage capacity)
Surface soils have a low clay content and as a result, the capacity to hold and store moisture is low compared to a clay soil. This characteristic is moderated by the depth (80 cm) of the surface soil. The light texture allows the soil to release moisture to crops and pastures following light rains. That is, the surface soil holds as much water however less water is required to instigate growth. Although the subsoil is deep, it does impede the vertical movement of water as shown by the mottled colour of the subsoil. Lateral flow of water along the top of the subsoil is likely in wet years, decreasing the volume of water able to be exploited by the plants growing on this soil type.

As with most of the other soils, subsoil clays have moderate water storage capacity. However, because of the clay texture and structure of the clay much of the water remains unavailable to plants.

Retaining vegetation cover and minimising soil disturbance will assist in improving soil structure and increasing the water holding ability of the surface soils Deep rooted perennial pastures may assist in opening up the clay subsoil over time. Deep rooted annual crops are unlikely to benefit the structure of the subsoil due to the depth to subsoil.

Soil Salinity
Soil salt levels are very low for both surface and subsoils. As with other soils located higher in the landscape, effective use of water by plants growing on this soil type is important to reduce salinity impacts lower in the landscape. Increasing water use through good crop and pasture husbandry, the use of deep rooted pastures or re-establishing native vegetation will assist in reducing the risk of salinity in lower areas.

Soil Erosion
The weakly structured or friable nature of these sands, together with their high position in the landscape, considerably increases the risk of wind and water erosion. Any soil lost through wind or water erosion removes nutrients and decreases the depth of soil from which plants can effectively access nutrients and water. The risk of erosion is increased by the absence of adequate groundcover (minimum of 30% cover year round) due to fire, cultivation, or more commonly, over-grazing. Careful management of these soils, considering the influence of landform and the impact of management practices further down the catchment, is important in these high risk areas.

Soil pH
Surface and subsoils are acid due to: 1) the absence of carbonate materials being deposited by wind during the formation of this soil and 2) the high permeability and low nutrient holding capacity of the surface soil. These soils are unlikely to respond to lime due to the slight nature of the acidity and the production potential of these soils is likely to make the treatment uneconomic. No extra management options are required to correct pH.

Fertility Status
The sandy loam layers have a poor ability to hold nutrients, as compared to a clay and leaching by water can be severe. Increasing organic matter in the soil assists the surface soil nutrient holding capacity. Low levels of phosphorus, calcium, potassium, sulphur, nitrogen and trace elements copper, zinc, molybdenum and cobalt have been recorded. Retaining vegetation cover and reducing cultivation will assist in maintaining and building up existing levels of organic matter.

Soil Performance Under Management

Response to Cultivation
Cultivation is not recommended as these soils are prone to extreme wind erosion. The friable nature of the surface soils makes them well suited to direct drilling. Although rolling may be required to provide a firm seedbed and to conserve moisture, thereby improving germination and establishment rates. These soils are easy to work and offer very low draft resistance to machinery. There are no compaction problems. The surface soil remains soft after wetting-drying cycles and are non-sticky when wet. These soils are prone to erosion and techniques that reduce the need for soil disturbances, such as direct drilling, are best suited.

Plant Establishment (Germination, Emergence)
The sandy friable condition of the surface soil assists in crop establishment. High moisture loss is possible with cultivation (including the sowing operation) and compaction may be needed to provide a firm seedbed.

Root Development (Limits to depth)
The sandy soils allow for good root development in the surface soil. The poor fertility may reduce plant size. Roots will penetrate to depth seeking moisture and nutrients. Most annual crops and pastures are unlikely to have root growth impeded by the impermeable clay layer at 80 cm. Although the surface soils are deep, it is still critical to prevent soil erosion in order to maximise production capacity.

Chemical Residues
Agricultural chemicals such as herbicides and pesticides are made inert via four main processes; a) direct binding to soil particles particularly clays and organic matter, b) direct binding to surface organic matter such as stubbles, c) chemical hydrolysis (chemical breakdown) and d) microbial breakdown. Each of these processes is affected by soil type, soil moisture and temperature, soil pH, organic matter content and microbial activity.

Higher levels of organic matter will increase binding sites for chemicals in the soil, increase the overall microbial activity and the breakdown of the chemicals in the soil.

Sulphanyl Urea herbicides will be less soluble in the acid soils. As breakdown of the chemical is by microbial activity and acid hydrolysis, the breakdown of the herbicide will be faster as compared to that on an alkaline soil.

Imidazolinones will be more soluble in the acid soil and be readily leached from the surface soil. The quantity of rainfall will greatly affect plant back periods (check the label).

Triazines may be leeched from the lighter soils, collecting on the heavier subsoils. The depth to subsoil will reduce residue problems.

Trifluralin is fixed to the surface soil and is degraded by microbial activity. Rainfall directly influences its persistence. Lontril is fixed onto and persist on stubble material.

Management

These soils are best suited to plants that provide vegetation cover throughout the whole year as wind and water erosion can be severe. Permanent perennial grasses supported by subclovers and or lucerne provide good groundcover and increase the length of grazing. The re-establishment of native vegetation for stock and crop wind protection (shelter belts) is recommended particularly on lighter soils or along ridges. Although soils are capable of being cropped with wheat, oats, barley or lupins and utilising stubble retention and minimum tillage or preferably direct drilling. Cropping is not recommended due to the high risk of crop failure and soil erosion. Currently, these soils support many low grade clover stands with annual grasses due to the high cost involved in establishment and maintaining high pasture production. The incorporation of clay into these light sandy surface soils has increased the pasture establishment options for many landowners and reduced the non-wetting nature of the surface soils.

Implications for Revegetation
Revegetation activities should be undertaken in the autumn to capitalise on the moisture available. Spring planting’s are prone to the summer dry periods and may not enable adequate establishment.

Adequate soil cover should be retained to reduce moisture loss and prevent erosion.

Current Practices
These soils are currently sown to perennial pasture such as sub-clover and lucerne, and are occasionally cropped with oats, wheat, barley and lupins.