Agriculture Reference
In-Depth Information
It focuses on the following viticulturally important and mostly visual diagnostic features: depth to
certain characteristic changes in waterlogging, consistency, color, structure, calcareousness in
different restrictive layers, cracking, and texture trends down proÝles (e.g., texture contrast at A/B
horizon boundary or duplex character) (Table 9.5). The key layout is bifurcating, based on the
presence or absence of the particular keying property, which is usually a diagnostic property.
The key is seen as an important tool for correlating rootstock performance and soil properties,
and as a vehicle for delivering soil-speciÝc land development and soil management packages to
grape growers.
Coastal Acid Sulfate Soils
Acid sulfate soils (ASS) are saline soils or sediments containing pyrites, which once drained
(as part of land management or development measures) become acidic, and release large amounts
of acidity and other contaminants to the environment with consequent adverse effects on plant
growth, animal life, and urban infrastructures. These coastal ASS occur in tidal Þoodplains where
sources of sulfates, iron, and other salts originate from seawater and estuarine sediments, which
are less than 5 meters above sea level (AHD < 5 m). Nationally, there is an estimated 40,000 km
2
of coastal ASS, and potentially they contain over one billion tonnes of sulfuric acid. When undis-
turbed and saturated by water, ASS remain relatively benign.
The source of acid sulfate problems is pyrite, FeS
, which when oxidized produces sulfuric
acid that brings the pH below 4, sometimes even below 3, thereby causing minerals in soils to
dissolve and liberate soluble and colloidal aluminium and iron, which may leak to drainage and
Þoodwaters, killing vegetation and aquatic life; and steel and concrete infrastructures then corrode
(White et al., 1995; Sammut et al., 1996). Drainage of acid sulfate soils also results in the substantial
production of greenhouse gases, carbon dioxide, and N
2
O (Hicks et al., 1999). Development and
primary industries around Australia are facing a $10 billion legacy of acid sulfate soils (National
Working Party on Acid Sulfate Soils, 2000). Public recognition of this serious problem has been
reÞected in government legislation in New South Wales, Queensland, and South Australia. There
is much support from councils and industries to develop statutory requirements for rehabilitation.
Although the Australian Soil ClassiÝcation (Isbell, 1996) does recognize ASS, there has been
a need to develop a user-friendly and effective classiÝcation to meet the needs of local governments
and coastal authorities in a policy and jurisdiction sense, as well as to guide potential users of these
environments to information regarding processes of rehabilitation. The classiÝcation system needs
to be used in the context of a product that enables clients to use technical information (Table 9.5).
Although a plethora of complex terminology and standards have evolved in the literature in relation
to acid sulfate soils, these have been simpliÝed (Ahern et al., 1998; Department of Natural
Resources, 2000) to support the planning process, and comprise the following:
2
¤
Acid sulfate soils:
Soil or sediment containing highly acidic soil horizons or layers affected by the
oxidation of iron sulÝdes (actual acid sulfate soils) and/or soil or sediment containing iron sulÝdes
or other sulÝdic material that has not been exposed to air and oxidized (potential acid sulfate soils).
The term acid sulfate soil generally includes both actual and potential acid sulfate soils. Actual
and potential acid sulfate soils are often found in the same soil proÝle, with actual acid sulfate
soils generally overlying potential acid sulfate soil horizons.
¤
Actual acid sulfate soils (AASS):
Soil or sediment containing highly acidic soil horizons or layers
affected by the oxidation of soil materials that are rich in iron sulÝdes, primarily pyrite. This
oxidation produces hydrogen ions in excess of the sedimentÔs capacity to neutralize the acidity,
resulting in soils of pH 4 or less. These soils can usually be identiÝed by the presence of bright
yellow or straw-colored mottles of jarosite.
¤
Potential acid sulfate soils (PASS):
Soil or sediment containing iron sulÝdes or sulÝdic material
that have not been exposed to air and oxidized. The Ýeld pH of these soils in their undisturbed
state is pH 4 or more, and may be neutral or slightly alkaline.
