Northern Australia - Soils

Soils

Except in the Lake Eyre Basin and adjacent areas to the east, the soils of Northern Australia are quite remarkable in global terms for their low fertility and difficulty of working. Most of them consist chiefly of hard laterite developed during period of climate much more humid than even that of Darwin today. Since there has been no mountain building in the region since the Precambrian and no glaciation since the Carboniferous, the region's soils have generally been under continuous weathering without renewal for over 250 million years, as against less than ten thousand for most soils in Europe, Asia, North America and New Zealand which have been formed from recent mountain building or glacial scouring of the land.

This immensely long weathering time means that nutrient levels in Northern Australian soils are exceptionally low because practically all soluble minerals have long been weathered out. The major constituents of most soils in Northern Australia are iron and aluminium oxides, both of which are not only very insoluble but also serve to reduce the soil pH and remove phosphorus from the soil as insoluble iron and aluminium phosphates. The insolubility of these metal oxides also serves, under the extremely harsh conditions during the dry season in the north and generally in the south, to create massive sheets which are impossible to plough.

In the Lake Eyre Basin, deposition from volcanic regions to the east has produce cracking clay soils of quite high fertility which are still often fairly low in phosphorus but have very good levels of potassium, calcium and sulfur. These soils provide the best grassland for grazing in the region. The youthful, volcanic Wet Tropics has a number of areas of fertile alluvial soils that support intensive horticulture.