2 nd International Salinity Forum Salinity, water and society–global issues, local action 1 Salt and water balance of a salt bush grazing system—good news and bad news Richard Silberstein 1,2 , Patricia Lambert 1,2 , Wayne Hick 1,2 , Gerald Watson 1,2 , Paul Raper 3,2 1 CSIRO Land and Water, Centre for Environment & Life Sciences, Wembley, WA 2 Future Farm Industries CRC, The University of Western Australia, Crawley, WA 3 Dept of Agriculture and Food, Bunbury, WA Introduction In Western Australia alone it is now believed that there are over 1 million ha of severely salinised land and over 3 million ha at risk of secondary salinity (McFarlane et al. 2004). There are currently few commercially available crops or forages that are productive on saline land, but one option in thelow to medium rainfall zones of southern Australia is the growth of saltbush (Atriplex spp.) for grazing by sheep (Pol, 1980; Warren and Casson, 1994; Morecombe et al. 1996). Saltbushes and other halophytic chenopods such as bluebushes (Mariana spp.) are planted on an estimated 30,000 ha of saline and waterlogged soils in south-western Australia, predominantly in the low to medium rainfall (300-450mm annual rainfall) mixed crop and livestock zone (Barson and Barrett-Lennard, 1995). However, there has been some discussion over whether systems such as saltbush planted on dischargeareas would be short-lived and have minimal success, with the likelihood that salt accumulation will limit the growth and transpiration of the plants (Slavich et al., 1999), and hence their ability to have a beneficial hydrological impact. Thorburn (1997) and Thorburn et al. (1995) suggested salt accumulation in the root zone could limit growth and groundwater uptake, but that a small amount of annual leaching may result in significant growth and some watertable control. The aim of this project was to establish whether farm profitability could be improved while also improving the environmentalsalt and water balances. The project took a multidisciplinary approach involving host producers, economists, hydrologists, animal nutritionists, agronomists and ecologists. This paper reports results from the hydrological component of the study. Site description Sites were chosen at Tammin and Yealering, affected by secondary salinisation, suitable for revegetation with saltbush and salt tolerant grasses, and on farms with sheep already part of the operation. The site at Tammin lies on a Morrell soil, with high inherent salt storage overlying a deep palaeo-river channel. The top soil is 10-50 cm of sandy clay loam, grading to 9 m of fine silty clayloams, a sharp transition to at least 40 m of coarse river sand over bedrock. The watertable was about 1 m below ground and was highly saline (1.5 times seawater) and highly acidic (pH of less than 3 in some cases). A 40 ha area, with 20 ha of mature saltbush already established, was divided into 4 plots. Half the existing saltbush (10 ha) was left as it was, and half modified by removal of every second row and replacement with an “improved” mix of salt tolerant grasses . In the other 20 ha, halfwas planted to saltbush in the second year of the project, and the final quarter left to samphire and remnant salt affected pasture including volunteer bluebush. At Yealering, the soil consists of sandy clay over clay at about 50 cm, with basement rock at around 12 m. A 50 ha paddock with a uniform covering of barley grass was divided into two halves and in the second year one of them was planted to saltbush and a mix of salt tolerant grasses. Materials and methods Across all plots, piezometers were installed into shallow (2.5 m) and deep groundwater (near bedrock), neutron moisture meter access tubes were installed, and bi-annual soil sampling was undertaken to monitor salt storage over time. Soil cores were taken to 3 m for major extractable and exchangeable cations and anions, total salt storage, and nutrients analysis, and groundwater samples from all bores analysed. At Yealering, the two plots were isolated from each other and from surrounding land by a bund wall, and surface water and salt flows were measured through flumes installed in each of the paddocks. Tammin was too flat to monitor surface flows effectively. All plots were grazed with sheep, mainly in autumn (Norman et al., 2008).