Increased concentrations of chloride beneath stands of saltbushes (Atriplex species) suggest substantial use of groundwater

Abstract

Summary. This paper examines the accumulation of soil chloride and the increase in electrical conductivity of the groundwater beneath stands of saltbushes (Atriplex species) in a plant spacing trial conducted near Kellerberrin in Western Australia. The trial had a randomised block design with 5 plant spacings (1 by 1 m, 1 by 2 m, 2 by 2 m, 2 by 3 m, and 3 by 3 m), 5 saltbush species (Atriplex undulata D. Dietr., A. amnicola Paul G. Wilson, A. vesicaria Heward ex Benth., A. paludosa R. Br. and A. bunburyana F. Muell.) and 3 replicate plots (each consisting of 25 plants in 5 by 5 array). The saline groundwater at the site was between 0.5 and 1.2 m below the surface for the duration of the experiment. Over a 2-year period there was a substantial increase in soil chloride concentration beneath the saltbushes. These increases were proportional to saltbush ‘leaf density’ (weight per unit soil surface area) and inversely proportional to the initial concentration of chloride in the soil. There was a substantial increase in the electrical conductivity of the groundwater which was also proportional to ‘leaf density’. It is argued that the increases in soil salinity and groundwater electrical conductivity were primarily due to the use of groundwater by the saltbush stands. Salt accumulation data suggest that about 60–100 mm of groundwater was used (transpiration and evaporation) over the 2 years. These results are discussed in terms of the ability of saltbushes to lower local watertables, thereby making saline soils better suited to the growth of superior annual pasture species.