Phase farming with trees: a new weapon in the fight against dryland salinity?

A system to overcome dry land salinization of farming systems in medium to low (300-600 mm) rainfall areas of southern Australia is proposed. Phase farming with trees (PFT) is designed to use trees grown in very short term rotations (3-5 years) to rapidly de-water farming catchments at risk of salinity, by depleting soil water while producing utilizable products such as wood fibre and biomass. The tree phase is followed by an agricultural phase of a length defined by the persistence of the hydrological buffer created by the trees. The system thus utilizes a resource (groundwater recharge) that is contributing to environmental problems while building more sustainable agricultural systems. Potential benefits include decreased salinization, improved soil structure and acting as a disease and weed break. Production of large amounts of biomass suitable for "green" electricity will decrease Australia's emissions of Greenhouse gases. The biophysical feasibility of PFT was assessed for several sites in the 300-600 mm rainfall zone of southern Australia using the WAVES model. Several scenarios were examined, with these suggesting broad differences in likely response to the PFT system. The modelling suggests that the premise of the PFT system (viz. depletion of sub-soil moisture reserves under trees and subsequent recharge under agriculture) is realistic. Moreover, the outputs suggest different tree planting strategies according to soil and hydrological conditions