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Data collected indicate rainfall chloride values may be higher than values currently being used in chloride balance studies in the QMDB, for example, Tolmie et al.
Rainfall salt content and annual average mass deposition of both chloride and total salts in the QMDB were proven to follow trends similar to those found elsewhere in Australia, although some values were higher than those determined by some previous authors.
All sites are in the eastern QMDB due to an emphasis on cropping areas, the location of long-term trial sites and catchment studies, and thus the availability of historical data.
To give some perspective, a Cl concentration in rain of 1.5 mg/L is the equivalent of an annual Cl input of 6 kg/ha for 400 mm of rainfall, 9 t/ha for 600 mm of rainfall, and 11.3t/ha for 750mm rainfall, or about one-twentieth of the rate of reduction in soil Cl observed in the QMDB cropped sites.
Many soils in the eastern half of the QMDB typically have 10-30 t/ha of Cl in the upper 1.5 m.
This large mass of salt stored in Vertosols and Sodosols, which occurs in 90% of cropped land in the QMDB, indicates the large salinity hazard inherent to the region.
Some soils in the QMDB and surrounding areas have naturally low levels of Cl under native vegetation (e.g.
(i) Large changes in soil Cl occurred since clearing of agricultural land in the eastern QMDB. On average, these sites lost 48% (0.2 t/ha.
On the other hand, the data show that primary (or inherent) soil salinity has decreased and potential root depth may have increased in cultivated soils in the QMDB, as found by Dang et al.
For the increases in drainage typically found for cultivated soils in the QMDB, this new equilibrium will be established over a time scale of 30 to >200 years (depending on drainage rate), with a new soil concentration only a fraction of the original (Fig.
The study confirmed several conclusions from soil water balance modelling for cropping in the QMDB (Yee Yet and Silburn 2003; Silburn et al.
We have begun using a combination of coting and geophysical imaging to characterise the unsaturated zone in the QMDB (Foley et al.
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