19th World Congress of Soil Science - Brisbane, AustraliaResearch areas: Germany, Laos, Thailand, Vietnam
Excursions: Australia, China, Germany, Hungary, Morocco, Thailand (NE-part)
Excursion 1: South Coast on 1 August 2010
This tour featured some of the coastal environments of Brisbane's urban fringe. Sandwiched between Brisbane and the Gold Coast is the sugar cane area, generally referred to as 'Rocky Point' taking its name from the sugar mill. Coomera contains areas of urban development south of Pimpama. The Rocky Point Sugar Mill assignment area is the smallest cane growing region in Queensland. Closure of the mill would have a devastating effect on the cane industry in the Woongoolba area. The area is undoubtedly under pressure from urban expansion. south east Queensland is the fastest growing area of Australia, comprising approximately 30% of Australia's population growth.
Soils of the Brisbane region
The soils in Queensland are strongly determined by their parent materials. Hence, the distribution of soil types largely reflects the underlying geology. Because the geology of the Brisbane area is dominated by hills of hard metamorphic rocks and quartzose sandstones, urban extension has not had a major effect on agricultural production. Agriculture in SE Queensland is concentrated on the alluvial plains to the west, north and south of the city. Pockets of market-gardening still survive on the red earthy soils around Sunnybank and on the Ferrosols associated with the old basalt remnants in the Redlands area.
Soil Profile 1
Soil type: Mollic Gleysol (Thionic, Humic, Eutric, Clayic)
Parent material: estuarine deltaic sediments
Coordinates: S -27.74482° E153.28204°
Landform: originally a swamp depression on the coastal plain
Climate: average annual rainfall: 1270 mm, average annual evaporation: 1560 mm
Land use: irrigated sugar cane
Figure 1: Coastal plain under sugar cane production (left). Gleysol from estuarine delataic sediments (right).
The visited soil belongs the group of acid sulfate soils (ASS). ASS are naturally occurring soils and sediments that contain iron sulfides, such as pyrite (FeS2). The iron sulfides remain chemically stable while buried in oxygen-free, waterlogged environments. However, when the iron sulfides are exposed to oxygen, they undergo a series of chemical reactions and produce sulfuric acid. One tonne of iron sulfides can produce about 1.5 tonnes of sulfuric acid when oxidized, which have major environmental effects.
In their undisturbed, waterlogged state ASS may range from dark grey muds to grey sands and sometimes peats. They are usually soft, sticky and gel-like in appearance and have a pH close to neutral (6.5 - 7.5). These soils contain iron sulfides, which have not been exposed to air or oxidized. They are known as potential acid sulfate soils (PASS) because they have the potential to oxidize to sulfuric acid. When ASS are exposed to air, the iron sulfides oxidize and sulfuric acid is produced. These soils contain oxidized iron sulfides and are known as actual acid sulfate soils (AASS). AASS are very acidic (pH<4), vary in texture and often contain a yellow mottle called jarosite.
The term ASS includes both AASS and PASS. AASS and PASS are often found in the same soil profile, with AASS generally overlying the PASS.
Excursion 6: Lockyer Valley on 7 August 2010
This tour went west of Brisbane to the Lockyer Valley, the 'salad bowl' of south-east Queensland. Together with the adjacent Fassifern Valley and the eastern Darling Downs, it supplies about 40% of Queensland's major vegetable crops. Close to markets, the Lockyer Valley alluvial plains are blessed with fertile and productive soils, a mild sub-tropical climate and a significant ground water reserve that makes it a unique resource for the state. Consequently, it grows the most diverse range of fruit and vegetables of any area in Australia.
Dryland and irrigation salinity is a common problem in the Lockyer and associated valleys. The Darbalara site is typical of the dryland forms. The heavily cleared catchment is comprised of sandstones of the Koukandowie Formation in the eastern ridge, and Gatton Sandstone in the lower slopes. It has experienced increased recharge. resulting in increased soil water and groundwater flow. A high angle alluvial fan exists, a common feature in the sandstone hillslopes. These fans are typically sandy in nature, and provide a good conduit for groundwater to the lower landscape. In downslope direction, the low gradient toe of the fan merges with the heavy clay alluvial plain of Laidley Creek. There, the catchment is also slightly constricted by sandstones. Consequently, the combination of the catchment constriction, the restriction to surface flow, and the decrease in conductivity of the alluvial deposits lead to shallow groundwater. Evaporite concentration of salts has led to increased salinity over time, and the incised streams are often groundwater windows. Solonetz are the major reference soil group at the Darbalara site.
Figure 2: The Darbalara site (left), typical Solonetz at Darbalara site showing round-topped columnar surface structure (right).
Soil Profile 2
Soil type: Grumic, Mollic, Calcic Vertisol (Pellic)
Parent material: stratified alluvium
Coordinates: S -27.547271° E152.32854°
Landform: backplain on alluvial plain
Land use: vegetable production
Figure 3: Vetisol from alluvial deposits.
Soil Profile 3
Soil type: Endofluvic, Calcic Chernozem (Clayic)
Parent material: levee on alluvial plain
Coordinates: S -27.54302° E152.32755°
Landform: levee on alluvial plain
Land use: vegetable production
Figure 4: Alluvial plain under vegetable production (left). Chernozem from alluvial deposits (right).
19th World Congress of Soil Science, 2010. Excursion giude - Excursion 1 - South coast, 1 August 2010.
19th World Congress of Soil Science, 2010. Excursion giude - Excursion 6 - Lockyer Valley, 7 August 2010.
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