Salinity

Speaking of the salinisation of vast areas of land
Western Australia could unenviably hold the title of salinisation 
capital of the modern world.

I say modern world as much of the middle east near the Medditerranean
where covered with forests where today stands desert.
The cause of the desertification there is a result of of the same
efforts that have caused our salinisation here, 
extensive land clearing for agriculture.

Our problem was that with our very gentle topography which was 
heavily covered in deep rooted perennial trees and shrubs that
were very good at extracting water from depth and surviving drought,
the salts in these soils were spread through a large layer of the soil
profile between the soil surface and the water table beneath.

When the deep rooted perennials were removed and replaced with
shallow rooted annuals that make up the bulk of the cropping systems
here, then the demands on the water table crashed.  
Hence when the next seasons rains came along the water table rose
and rose and rose.  Bringing those salts with it.  
In less than 5 years in some parts of the state the watertable 
had risen to the surface during the winter rains. 
The evaporation of that water over summer left a residue of salt behind.

This has since built up over the years to the extent that salt pans have 
developed with layers of salt several centimeters thick.
Nothing grows here where once these seasonally inundated areas
where covered with Melalueca, Eucalyptus and hundreds of other species.
that sucked massive amounts of water up and back out into the atmosphere.

Talking to a farmer once in Dowerin he broke into tears as he described
how the paddock he cleared in 1920 had a shallow dam (less than a meter)
in the middle with water so pure they used it for drinking.
Less than 5 years later it was salty and crops wouldn't grow in the paddock.

Even the experiences of the ancient farmers of the eastern medit are still
not 
appreciated today.

Rod
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Rod Randall
Weed Risk Assessment
Weed Science Group, Agriculture Western Australia

                 "I weed..." 
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