Sustainable Soil Management Is More than What and How Crops Are Grown - Principles of Sustainable Soil Management in Agroecosystems - page 349

14.3.3.2 Australia
Historically, Australian farmers had pasture as an alternative “crop.” This ley pasture
farming system was common up until 1990. It enabled farmers to control weeds with
animals and thereby reduce their reliance on herbicides. However, the profitability
of this farming system was challenged with poor wool prices in the late 1980s, and
it was largely replaced with continuous cropping. Running livestock in dry regions
also created soil degradation concerns with compaction common in wet heavy soils
and wind erosion common on the sandier soils.
The most obvious and concerning soil degradation issues in dryland Australian
agriculture have been wind erosion, followed by water erosion. The emergence of
saline soil in Western Australia, about 30 years after clearing of the native veg-
etation, is a serious threat to some areas of the landscape (George et al. 1997). On
the other hand, other areas experience more subtle soil degradation such as nutrient
export, compaction, waterlogging, sodicity, water repellence, and acidity.
The degree of concern for each of these issues varies across regions and states
in accordance with soil type, soil slope, geological parent material, proximity to
the coast, and the local climate. Other temporal issues also had a strong influence,
including intensity and duration of wind and rainfall events, level of soil cover, graz-
ing pressure, the level of tillage used, and the level of knowledge of techniques capa-
ble of mitigating against degradation issues.
Australia is known as a “land of drought and flooding plains.” The last 12 years
have seen about 7 years of widespread drought and 3 years of widespread flooding
plains. Such contrasting climatic conditions present soil management challenges.
The climate across southern Australia is classical Mediterranean with winter wet
(June-August) and summer dry (December-February). Toward northern NSW, rain-
fall becomes more evenly distributed throughout the year, with summer the domi-
nant rainfall period in Queensland.
The strongest Mediterranean climate is found in the southwestern area of
Australia. This area has received 40% less winter rainfall since the early 1970s. In
contrast, the northern third of Australia, during the same time, has had more rainfall.
However, there is limited cropping activity in these northern regions—though there
is grazing of livestock, mostly cattle. Therefore, the focus of this article is on south-
ern Australia where cropping is common.
Australian soil is reported to be part of the most ancient and weathered land-
scape of anywhere in the world (McArthur 2004). Large areas have a very sandy
surface—some have almost no clay in the topsoil. When sandy soil is combined with
the often dry climate, it creates a recipe for significant land degradation potential.
The clearing of the native vegetation of mostly mallee, or Eucalypt trees for agri-
cultural purposes, has predisposed these surface soils to wind (Crabtree 1990) and
water erosion (Bligh 1989, 1991). The majority of this vegetation clearing in Western
Australia occurred during the 1950s and 1960s. Over 400,000 ha was cleared each
year during that decade.
The most profound and obvious forms of soil degradation in Australia were wind
and water erosion. Immediately after the land was cleared, soil erosion (caused
by wind and water) occurred. Sandy soils, associated with the mallee vegetation