Tree plantations could be used to fight salinity

Scientists estimate that a total of about 11,000 hectares of carefully placed, well-managed spotted gum plantation may help to curb the rising water tables in the area, which currently has about 55,000 hectares under rice cultivation, and about four times as much under pasture or other crops. The most suitable land for the plantations would be sandy or loam soils with low salinity groundwater at a depth of two to three metres, such as the area’s extensive sandy relics of large ancient river beds, say the scientists.

“Rising water tables, which bring stored salt up to the soil surface, threaten the long-term viability of irrigated farming there,” said Dr Tivi Theiveyanathan, a senior research scientist with the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Forestry and Forest Products. “Projections indicate that by 2020, the proportion of the 600,000 hectare region with groundwater less than two metres from the surface will increase from below 20% today to around 50% unless effective remedial action is taken.”

The sandy soil will allow deep root penetration, said Theiveyanathan, permitting the trees to begin tapping the groundwater within two to three years. Though the plantations will initially require irrigation, once they have reached the groundwater, only occasional applications to flush salt from the soil in the root zone will be required.

“Extensive tree planting is a potential option, offering income from the timber produced as well as major environmental benefits,” said Theiveyanathan. “The best plantation uptake figure for flooded gum (Eucalyptus grandis), a species widely used for farm forestry, was around 300 mm of groundwater a year. Spotted gum (Corymbia maculata) did much better, taking up to 600 mm of groundwater per year.”