The role of shrub-belts and lucerne for intercepting water and reducing deep drainage

Salinity in the upland regions of eastern Australian states is often due to excess water accumulating in the lower parts of the landscape where it mobilises salt. Preventing the movement of water down slope is one way to mitigate this form of salinity. Soil acidity and topography severely limit the areas suitable for deep rooted perennial pasture species such as lucerne which could use soil water before it accumulates at the bottom of the slope. Belts of shrubs planted on the contour could potentially create dry soil buffers that are capable of absorbing water flowing down slope as either surface flow or sub surface flow across the soil A/B horizon interface.

At the EverGraze Proof Site at Wagga Wagga, the shrubs component aimed to examine the impact of shrub belts planted across the slope on recharge and subsequent soil moisture conditions at the bottom of the slope. Because shrub belts may potentially compete with pasture for water and nutrients, measurements to assess the degree of competition between shrubs and annual pasture or lucerne were made once the shrubs had become large enough to compete with the neighbouring pasture for resources. The spacing of the shrub belts, and the type of shrubs planted, is comparable with the component study investigating lamb survival, but the requirement to have a uniform slope meant this study was best conducted on a smaller, more uniform site.

The key finding from the site was:

Acacia shrubs belts planted at the break of slope in the Wagga environment do not provide recharge (deep drainage) or water-logging control further down slope, but will also not effect production of surrounding pastures.  Lucerne is a more effective option for managing recharge and waterlogging where it can be planted.

Results are discussed further on the following page: The role of shrub-belts and lucerne for intercepting water and reducing deep drainage.