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Understanding South Australia’s Diverse Sandy Soils: Origin, Age, and Management Impact
How the soil formed is one of the main reasons.
For example, in the Upper-Western Eyre Peninsula, the sandy soils have a high pH as they contain fine shell fragments because they were derived from the ocean floor when the sea level retreated to the edge of the continental shelf between 30,000 and 10,000 years ago. On the Eastern Eyre Peninsula, the surface sands are still about 20,000 years old and can be very deep, but they were derived from sands deposited in an ancient river channel in the upper Eyre Peninsula, known as the Corribinnie Depression, so they don’t have the shell load and are more prone to developing acidity.
If we go into the Victorian and South Australian Mallee, there are old beach dunes that formed from 7 to 5 million years ago as the ocean retreated out of the Murray Darling Basin. These curve around from the north-east to the south-west and aren’t all still visible, as they have been eroded and re-worked over the last the 700,000 years into the more obvious east-west trending parallel dune systems. These soils vary in texture and depth to clay, and while they have historically been alkaline, the surface soils are becoming increasingly acidic with continuous cropping, increased nitrogen fertiliser use and the inclusion of legumes in the rotation. Many of these soils have suffered severe erosion and redeposition since land clearing, particularly through the drought years from the 1940s to the 1980s, so not all soils behave as you might expect!
Through the Limestone Coast, there is another set of younger beach dunes that have formed over the last one million years as the ocean retreated from Naracoorte in the east to its current position.
There are also large tracts of young sand that blew in across the region when the ocean retreated off the current shoreline. They are usually grey to white in colour and are seen as hummocky (lumpy), parabolic (U-shaped) dunes, that are prevalent through Little Desert, Big Desert and the Murray Sunset National Parks. These soils are naturally deficient in desirable plant nutrients and have very low clay and water holding content. They are also very prone to being water repellent.
These are just some examples of the many different types of sandy soils across southern Australia. The various combinations of parent materials, age, topography, rainfall, and land management mean there is a huge array of sandy soil profiles with different properties such as depth to clay, pH, nutrient content, presence of carbonates and toxicities from salt and boron.
