The Healthy Soils Symposium Proceedings - Land and Water Australia

Methodology
Site selection
South-eastern Australia has a long history of mixed cereal and pasture systems, diversity in soil
types and the promotion of conservation tillage and improved pasture systems. Two broadly
defined agro-ecological zones exist representing both warm temperate wet and warm
temperate dry agriculture as classified by the IPCC, similar to those found in Mediterranean
regions of the world. The case study examines management options within the six distinct
agro-ecological regions found in these two broader climatic zones.
The moist south-east zone, which includes the High Rainfall and Slopes regions, occurs south
of the summer cropping zone and is considered the most reliable area of south-eastern
Australian for crop production. Some summer rain does occur, sufficient to be an important
source of stored water for winter crops but insufficient to regularly sustain summer crops.
This zone offers great diversity of soils, ranging from podozolic and solodic soils on the eastern
margins to grey clays and black earths. Cropping in much of the zone occurs on red earths and
red-brown earths. Soil surface layers are usually sufficiently moist for a sufficient length of time
for organic matter turnover to be fairly rapid. Crop and pasture rotations are relatively well
developed within the region and farmers have traditionally relied on legume-based pastures to
maintain soil carbon and improve nitrogen availability. As this is a livestock fattening region
(both sheep and cattle, but predominantly sheep), special demands on pasture occur.
The dry marginal south-east zone is normally considered the higher risk or marginal agricultural
lands of south-eastern Australia, apart from the Wimmera and its red clay soils which are on
the fringe of wetter warm temperate wet zone (as classified by IPCC). The Mallee lands of
Victoria, South Australia and south-west New South Wales form a large part of this zone with
annual average rainfall are in the 300-350 mm range. Individual areas planted to crops are
large, but not as a proportion of the duned landscape. Cultivated soils in the region are
generally low in organic carbon (0.3-0.6%), with soils under virgin stands slightly greater than
1.0%. Problems occur due to the inability to generate sufficient organic matter to maintain soil
structure, especially when long fallow phases are used. Residue loss through grazing plays a
significant role in this environment, with wind erosion removing surface soil and problems of
sand blasting of young crops.
Maintenance of soil fertility for production of high value wheat is a problem, especially in the
more marginal areas of the Mallee, Mid-North and Central West regions where economic
responses to nitrogen are limited. Changes in the organic carbon content of these sandy-loams
are not usually as significant as the increases in plant carbon in response to nitrogen
application. However with supplemental irrigation to boost production, changes in surface soil
organic carbon are evident, even within the first growing season. This is usually negated by the
decreased capacity of these coarse textured soils, which dominates the rainfed croplands in
the semi-arid regions of southern Australia, to retain organic matter in the same proportion as
heavy textured soils (Amato & Ladd, 1992).
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healthy soils symposium