Trangie, lower Macquarie valley.

Introduction
The Macquarie River is a tributary of the Darling, which drains the northern part of the Murray-Darling Basin.  The study area is located in the lower Macquarie valley southeast of the township of Trangie. 

Climate
The climate is typical of a semi-arid environment with a mean annual rainfall of 492 mm and potential evaporation of over 1,800 mm annually.  The rainfall is slightly summer dominated with a mean maximum in January (54.1 mm) and a minimum in September (15.3 mm).  Temperature varies from a mean maximum in January (33.2 oC) to minima in July (15.3 oC).  Potential evaporation is greatest in January and lowest in July. 

Agriculture
The area includes both irrigated and dryland farms.  The latter is mostly wheat (Triticum aestivum L.) production and native pastures.  Irrigation is mostly for cotton (Gossypium hirsutum L.) production.

Soil
McKenzie (1992) identified Pedoderms in the Macquarie valley. 

The Trangie Cowal Pedoderm is predominant and is characterized by (i) duplex red-brown profiles (Wilga red-brown) developed from silty parent material, which have a distinct clay maxima between 0.30 and 0.80 m (i.e.,19-35%), and (ii) heavily textured red-brown coloured profiles (Byron) with distinct clay maximum between 0.30 and 0.80 m (i.e.,28-41%). 

The Old Alluvium Meander Plain Pedoderm is characterized by the Mitchell profile class, which has high coarse sand content that distinguishes it from the other red soil of the alluvial plains. 

The Old Alluvium Back Plain is more diverse and includes: Mullah - dark grey to black cracking clays (i.e.51% clay), Snake - sodic grey cracking clays (i.e.50%) closely related to Mullah, and Buddah profiles characterized by the high clay content (i.e.48%) of which smectite and kaolinite clay minerals are co-dominant with illite.

The Gin Gin profile class defines the Pedoderm of the same name.  The profiles are strongly weathered and have a uniform to gradational texture profile (e.g.31-40% clay). 

The Macquarie class, which defines the Macquarie Pedoderm, has minimal profile development and is characterized by considerable fine sand and silt fractions (i.e.median value of 40% at 0.10 m).

Land management issues
The introduction of irrigated agricultural systems in the early 1980’s proved successful, however, within 10 years isolated instances of point-source salinisation across the Trangie district became evident.  The issue was problematic in very wet years. 

However, the introduction of various land management solutions has for the most part minimised the impact of soil salinisation in terms of its threat to the environment and crop yields.  In terms of water use, most of the supply channels are no longer used to store water during the winter and many of the “leaky” water storage reservoirs have been de-commissioned.

 



Acknowledgments
As part of a larger Cotton Research and Development Corporation Project entitled “Understanding the salinity threat in the irrigated cotton growing areas of Australia: Phase 3 – Implementation and Management,” research was started in the area south-east of Trangie in 1999 in collaboration with the Macquarie Valley Landcare Group.  The project was funded as part of the Natural Heritage Trust (CW0396.99) and was entitled “Understand and manage causes of salinity in irrigated farming systems.”

EM survey
An EM34/38 survey was undertaken across the Trangie study area.  An approximate 500-m grid spacing was used.  The first 300 EM34 measurements were obtained in November 1998 and the remaining 455 were recorded in July 2000. 

At each site EM34 signal readings were made in the horizontal dipole mode at 10, 20, and 40-m coil configurations (i.e.EM34-10, EM34-20 and EM34-40, respectively). Coordinates were recorded in the Australian Map Grid (AMG84) using a Magellan NavPro5000 GPS. 

In December of 2001 complimentary EM38 survey was carried out with all 755 sites revisited and measured with the instrument in the vertical (EM38-v) and horizontal (EM38-h) mode of operation.

References
McKenzie NJ 1992. Soils of the lower Macquarie valley, New South Wales. CSIRO Division of Soils, Divisional Report No 117, Canberra, Australia.

Further Reading
Triantafilis J and Lesch SM 2005. Estimating clay content at the district-scale using electromagnetic (EM) induction survey data and geo-statistical modeling techniques.  Computers and Electronics in Agriculture 46, 203-239.

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