Introduction

In any discussion of soil erosion in Australia it is necessary to place soil erosion and its effects in context. Despite the size of the Australian continent, because of constraints of climate, terrain and soil, the area potentially suited for agriculture is limited to 77 million hectares (Nix, 1976). There are many different forms of degradation affecting this land resource including: soil erosion, salinity (including both irrigation and dryland salinity), declining soil pH, a decline in soil structure, and the invasion of grazing lands by inedible shrub species.

Most of this degradation can be linked to inappropriate land uses. There is considerable interaction between the various forms of degradation; for example, erosion and soil structural decline are frequently associated with the same factors. The costs of each form of degradation are hard to quantify but one estimate is a reduction in annual production of more than A$200 million for the Murray–Darling Basin in southeastern Australia (Table 6.1). The Basin accounts for about half of the nation's rural production which is worth about A$15 000 million annually (1985–86) (Hawtrey, 1987). This review concentrates on soil erosion and soil structural decline and their combined effects on production.

Rates of erosion

On the basis of a nationwide survey conducted in 1975, some 2.7 million square kilometres or 51% of the area of the country used for agricultural and pastoral purposes (5.2 million square kilometres) requires treatment for at least one form of degradation (Department of Environment, Housing and Community Development, 1978).