Tree placement strategies for salinity control in dryland farming systems of southern Australia
Robinson, N., Harper, R.J., Smettem, K.R.J. and McGrath, J.F. (2004) Tree placement strategies for salinity control in dryland farming systems of southern Australia. In: ISCO 2004 - 13th International Soil Conservation Organisation Conference, 4 - 8 July, Brisbane, Qld, Australia
Western Australia alone up to 450 species are threatened with salinity-induced extinction. The integration of woody perennials into farming systems is often advocated as a method of reducing recharge and remediating dryland salinity. Whereas complete revegetation is feasible in higher rainfall catchments where improved water quality is an outcome, such a planting strategy is impractical in lower rainfall areas due to the need to maintain cereal cropping. It is thus necessary to consider methods of integrating trees with agriculture that allow agricultural production whilst also improving the water balance. In low rainfall areas (<400 mm yr-1) two options for incorporating trees have been proposed, alley farming between belts of trees and short phases of trees rotate with agriculture.
A survey of rooting depths of belts of farm forestry species (oil mallees (Eucalyptus spp.), Eucalyptus astringens, Acacia acuminata and Allocasuarina huegeliana) aged 4 to 11 years old found soil was dried to depths ranging from 4 to 10 m, with evidence of drying up to 15 m laterally. Phase farming with trees reduces recharge via the creation of a dry soil buffer to capture the leakage under subsequent annual crop rotations. In 2001, Eucalyptus globulus, E. occidentalis, Acacia celastrifolia, Pinus radiata and Allocasuarina huegeliana were planted at four densities 500, 1000, 2000 and 4000 stem ha-1, as well as 500 stem ha-1 plus fertiliser. Species survival and growth were predominately affected by site characteristics and slope location as well as density in the second year of growth. Soil water content under high density Eucalyptus plantings was depleted to depths of 4 m after 2 years. The implications of these results for the use of deep-rooted perennials for recharge reduction and salinity control are discussed.
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