Soil water depletion by Eucalyptus spp. integrated into dryland agricultural systems
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Spatial patterns of soil water depletion by Eucalyptus spp. were surveyed to assess the potential of tree belts and short rotation phase farming with trees for groundwater recharge reduction and salinity control. Soils were sampled to depths of up to 10 m in transects perpendicular to 4- to 7-year-old mallee eucalypt belts (Eucalyptus horistes, E. kochii ssp. plenissima, E. loxophleba ssp. lissophloia, E. polybractea) and in a 4 year-old block of E. astringens. Results indicate that the eucalypt species can exploit soil water to depths of at least 8–10 m within 7 years of planting. The root systems of these eucalypts were able to penetrate clayey subsoils with bulk densities of up to 2.0 g cm−3. Leaf area indexes of tree belts were 2–10 times greater than those predicted for natural vegetation, probably as a result of exploiting a greater amount of soil water stored under the agricultural system. The lateral influence of mallee belts, as indicated by soil water contents that were depleted to wilting point, ranged from 15–42 m. The resulting dry soil zone provided an effective barrier to groundwater recharge by incident rainfall thereby lessening the risk of salinisation in the agricultural landscape. The width of this barrier to recharge was predicted to range from 7 m to 54 m based on leaf area.
KeywordsSalinity Agroforestry Water use Root distribution Groundwater Mallee eucalypts
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This work was funded by the Australian Government’s Farm Forestry Program Project 983197 “Putting Trees in Their Place. We wish to thank the Bailey, Bird, Gould, Stanley and Young families, the Great Southern Piggery and the Department of Agriculture for allowing sampling to be carried out on their properties, and Andrew Stilwell, Robert Archibald, Shelley McArthur and Yvette Oliver for assistance in the field and laboratory.
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