Dryland salinity is a very serious problem in Australia and it is seriously affecting some of our best agricultural land. Western Australia is the first state to recognise and address the problem.
Western Australia has an estimated 1.8 million hectares of farmland (10% of the productive area) already salt-affected to some extent and this area could double in the next 15 – 25 years and then double again. This equates to 6 million hectares (about 15 million acres) or 30% of WA’s wheatbelt being salt affected in the next 50 years if nothing is done.
Over a third of the state’s divertible water resources is brackish or saline (undrinkable for humans or stock) and a further 16 percent is of marginal quality.
Salinity also poses a major threat to natural diversity (biological and physical), rural towns, capital infrastructure, tourism and recreation areas and the ability to support new export industries. Already farmers homes and towns have had to move because the rising water table has brought salt to the surface.
The fundamental cause of salinity is the replacement of perennial, deep-rooted native vegetation with the annual crops and pastures used in agriculture. Settlers only 40 years ago were ordered to remove every tree on their property as a condition of purchase.
Annual crops and pastures do not use as much of the incoming rainfall as did the native vegetation (even in low rainfall areas) as they have a very shallow root system. Rain falling on the land passes through the root system and this unused water either runs off or infiltrates beyond the root zone and accumulates as ground water.
As the ground waters rise, salts that have accumulated in the subsoil for thousands of years are brought closer to the surface, reducing plant vigour and eventually causing the death of plants.*
Measurements indicate that in some places there are 10,000 tonnes of salt stored beneath each hectare of land. A study of one area showed that after land clearing, water tables rose by 20 meters in less than 20 years and broke the ground surface within 11 years of clearing. To compound the problem, WA is not well serviced with rivers and creeks so the surplus water cannot get away.
To help remedy this huge dry land salinity disaster in the wheatbelt, W.A. government departments, farmers, universities and industry have combined to investigate the possibility of planting millions of deep-rooted oil ‘mallee’ trees to soak up the excess water and lower the water table.
A second objective of the study is to see if a viable eucalyptus oil distillery can be established which would provide farmers with an on-going income.
Felton Grimwade & Bosisto’s, in conjunction with a WA company, is involved in getting farmers to plant up to 20% of their land with mallee eucalypts. The trees are being planted in strips several rows wide along the contour of the land. Space is left between the strips for cropping and grazing.
These new trees prevent the surplus water reaching the water table by taking in the water that falls below the root zone. The trees are growing very well and early indications are that they are achieving their goals.
Blue Mallee trees have produced good oil yields and three or four W.A. mallee species identified by the Department of Conservation and Land Management as high eucalyptus oil producers have also done well.
Felton Grimwade & Bosisto’s is assisting with this important land care program.