Modelling irrigated Eucalyptus for salinity control on shallow watertables
Zahra Paydar A D , Neil Huth B and Val Snow CA CSIRO Land and Water, GPO Box 1666, Canberra, ACT 2601, Australia.
B CSIRO Sustainable Ecosystems, PO Box 102, Toowoomba, Qld 4350, Australia.
C AgResearch, Private Bag 11008, Palmerston North, 5301, New Zealand.
D Corresponding author. email: Zahra.Paydar@csiro.au
Australian Journal of Soil Research 43(5) 587-597 https://doi.org/10.1071/SR04152
Submitted: 19 October 2004 Accepted: 26 April 2005 Published: 8 August 2005
Abstract
With increasing salinity in irrigation areas, the option of tree planting in areas with shallow groundwater is seen as an ‘environmentally friendly’ alternative for controlling salinity. This study uses simulation modelling to investigate the long-term effects of planting Eucalyptus grandis in irrigated areas with shallow and saline watertables in the Riverine Plains where concerns exist about salinity effects on irrigated agriculture. APSIM, a 1-dimensional model of the soil–water–plant system, was modified to describe the interaction between the watertable within the plantation with the, normally shallower, watertable in the surrounding irrigated pasture. The model was tested against measured data and then used to simulate a range of different environmental conditions (depth and salinity of the groundwater, soil) and management options (irrigation with different amounts and salinity). The results of a total of 702 simulation runs helped to identify conditions in which irrigated plantations may be viable and how the irrigation of these plantations may be managed to decrease the impact of salinity on tree growth. The results indicated that if irrigation is to improve productivity, it must be in large amounts (1000 mm or more) and of good quality to have a significant effect on tree production. Irrigation with low salinity water (EC <2 dS/m) can only be used to reliably increase production in conditions where there are deeper watertables (4 m or deeper) on fast-draining soils. In these cases, flexible irrigation practices (scheduled irrigation) need to be employed in order to manage the salt levels within the tree root-zones. The viability of plantations is likely to decrease with increasing irrigation water salinity as salt accumulation in the profile reduces the ability of the trees to act as natural sinks. Depending on the irrigation and groundwater salinity, trees might be effective only up to a few years (as little as 9 years). Optimum response of trees to irrigation is only predicted with fresh water and scheduled irrigation (up to 1700 mm/year). However, if ample fresh water was available, other higher value cropping options are likely to be sought by land managers. Furthermore, the large amounts of water added to the plantation will have negative effects (water and salt export from the plantation) on the surrounding land, which will need further intervention to be sustainable.
Additional keywords: salinity management, saline watertable, simulating trees, plantations, Eucalyptus grandis.
Acknowledgments
We acknowledge partial funding from the Joint Venture Agroforestry Program of the Rural Industry, and Land and Water Resources, Research and Development Corporation. The authors also wish to thank Jim Morris and Tom Baker for providing data used in the model testing and for sharing their understanding of 3 systems. Richard Silberstein and Paul Feikema are thanked for providing the experimental data in Kyabram.
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