Water use of grazed salt bush plantations with saline watertable

Abstract

Old man saltbush ( Atriplex nummularia) has been widely planted on salt affected land in south-east Australia to provide a vegetative cover which can be used as a fodder reserve. Such plantations are also perceived as having the capacity to use saline groundwater and hence affect the extent of shallow watertables. This paper examines the water use characteristics of saltbush plantations which are regularly grazed and established above shallow watertables (1–2 m). Soil chloride, water content, soil water and sap isotope composition ( δ 2H), leaf water potential, stomatal conductance, sap flow and climatic conditions were monitored during dry summer and moist winter conditions at two plantations in southern NSW. The results indicated that the transpiration rate of old man saltbush was very low (less than 0.3 mm day −1) throughout the monitoring period. The low transpiration rates were associated with a low leaf area index (0.35), low stomatal conductances and low xylem water potentials. At most times of the year the plants used shallow water sources derived mainly from rainfall. However, up to half the transpiration at the driest time of year (March) was derived from groundwater. Although saltbush can establish and grow slowly on highly saline land its capacity to transpire saline groundwater is small relative to rechange from irrigation and rainfall. Hence, saltbush plantations are likely to have a negligible hydrological impact.