Agriculture Reference
In-Depth Information
Box 1.3
(continued)
as shown in the exposed subsoil of a duplex soil in the Sunbury region, Victoria,
Australia (figure B1.3.2). Note how the clay of the subsoil has been smeared by the
action of the digging machine. The extent of gleying and mottling enables a visual
appraisal to be made of the quality of drainage in a soil profile.
Figure B1.3.2
This orange-mottled soil occurred in the subsoil of a duplex soil in the
Sunbury region, Victoria, Australia. Note smearing of the moist clay by the excavator.
See color insert.
On the other hand, soils formed on more basic rocks are finer textured
(higher clay content), of neutral to alkaline pH, and generally well structured
due to their aggregates being stabilized by Fe and Al oxides (Fe
2
O
3
and Al
2
O
3
).
Figure 1.10 shows a gradational red soil formed on volcanic parent material of
the Cambrian period in the Goulburn Valley region, Victoria, Australia, under
an annual rainfall of 554 mm. This parent material also outcrops under a similar
rainfall in the Heathcote region, some 100 km to the southwest, which has a
reputation for producing intensely flavored Shiraz wines. Under a cooler, wet-
ter climate, basic rocks of basalt and dolerite have weathered to form deep red
loams, as in the Willamette Valley, Oregon, parts of the Yarra and King Valley
regions in Victoria, Australia, and in northeast Tasmania (figure 1.11). The
Willamette Valley region is noted for its Pinot Noir wines. Although the combi-
nation of high rainfall, natural soil fertility, and deep rooting often predisposes
