Australia: The Land Where Time Began

A biography of the Australian continent 

These plains cover an area of 12,500 km² in western Victoria. What little remains of the native vegetation is restricted to small blocks in various places such as public and private land and road reserves. To discover the pre-settlement vegetation of the area it is necessary to consult historical records. Based on these records it appears the vegetation at the time of settlement was grassy woodland on the rises and flats and on the shallow depressions and claypans it was grassland.

The topography of the area is mainly plains and depressions between low linear hills. The mean annual rainfall varies between 350 and 500 mm, but the mean annual potential evaporation rate is 1450 mm. During the Tertiary, shallow marine incursions covered the area as the Murray Basin subsided, depositing marine sediments that underlie large parts of the present surface. As the seas retreated from the north-northwest to the south-southwest, they left strandlines of sandy beach ridges, features of the present landscape. The Pleistocene ice age brought dry, windy conditions to the area, indicated by the west-east aligned aeolian sand dunes.

In the western parts, the soils are mainly grey, cracking-clays that are self-mulching. Gilgais are common in these grey soils that develop cracks. In the central parts the most common soils are of a red duplex type. The surface layers of the clay soils are neutral to saline,  alkaline at greater depth. These soils are friable when moist becoming sticky when wet, and when dry set hard. In spite of their high water-holding capacity, but water availability to plants roots can be restricted by a number of factors such as soil structure. The brown self-mulching clays that are similar are less common and gilgais are less common in them. The red duplex soils differ in texture between the surface layers and the sub-soil at 10-30 cm. Drying after wetting results in the soil setting hard. They are alkaline and sodic, and have low content of phosphorus and nitrogen. Their fertility is low to moderate.

The effects of normal European style farming on an Australian soil can be seen in this area, where there can be a stark contrast between fields farmed in the traditional way and neighbouring fields where conservation farming, with limited-till or no-till farming is practiced.

Soils that were productive have become less productive, and in some areas gilgais have been eliminated by levelling under cropping. The soil has become compacted and much of the rain runs off and floods occur, instead of penetrating into the soil as used to happen. Fields where conservation farming methods are used have some localised patches of waterlogging, but on adjacent farms where traditional methods are used the fields can be flooded for months at a time and when the machinery can be taken onto the field to plant a crop the results are patchy, contrasting with the uniform crop growth on the fields where conservation methods are used.

White reports an elderly farmer telling how he remembered 'hearing the water running in the crabholes' on his grandfather's farm when 'some crabholes were that big, you could've hidden a truck in them.'

Sources & Further reading

Mary E White, Running Down, Water in a Changing Land, Kangaroo Press, 2000