Page 45 Part B: The role native vegetation can play in preventing and managing dryland salinity Greg Steenbeeke 1 and Wendy Miller 2  2IｿFH RI (QYLURQPHQW DQG +HULWDJH Hurstville 2. Border Rivers - Gwydir Catchment Management Authority, Inverell Introduction Dryland salinity is a land degradation issue that affects approximately 40 thousand hectares (about 8%) of the Border Rivers  Gwydir catchment area. While much of this is restricted to the western slopes, some dryland salinity occurs in the east (right up to the top of the tablelands) and in the western plains, where a layer of highly saline water is known to occur beneath many of the important cropping areas. What is dryland salinity and why does it occur? Saline areas develop when water, containing dissolved ions (also referred to as salts - substances that have either a negative or positive charge), is brought to the soil surface through capillary action or soil water logging. In irrigated regions, the application of large amounts of water to crops can cause a rise in the water table, bringing to the surface salts WKDW ZHUH LQLWLDOO\ GHHS LQ WKH VRLO SURｿOH ,Q non-irrigated areas, salinity is most commonly caused by the removal of deep-rooted perennial plants in recharge areas, causing increased ZDWHU LQｿOWUDWLRQ DQG WKH VXEVHTXHQW WUDQVSRUW of salts in the subsoil to discharge areas (see Figure 5.1). This process is known as dryland salinity and is the subject of this chapter. Note though, that both processes can occur in the same area if vegetation has been removed and irrigated farming is practiced. Vegetation cover, water movement and indicators The mechanism driving dryland salinity is the movement and balance of water within WKH DTXLIHUV DQG WKH VXEVRLO ZDWHU WDEOH along with the stores of salts found there, so it is important to understand the interactions between these processes. The native vegetation of inland northern NSW originally consisted of deeply-rooted, perennial species adapted to long periods with low rainfall and occasional wet periods. With the removal of this vegetation cover, water tends to pass through the root zone and into the soil water SURｿOH ([FHVV ZDWHU PD\ DOVR HQWHU WKH VRLO SURｿOH ZKHQ WKHUH LV LQVXIｿFLHQW JURXQGFRYHU to make use of it or when the soil is very porous DOORZLQJ LW WR SDVV WKURXJK WKH SURｿOH WRR TXLFNO\ $V WKH PDMRULW\ RI WKH ｿQH URRW PDVV LQ a site is usually made up of groundcover plants (including herbs and grasses) the health, growth activity and diversity of the groundcover layer is particularly important for slowing the PRYHPHQW RI ZDWHU WKURXJK WKH VRLO SURｿOH and therefore capturing much of the water before it has the chance to enter the system. An area where water enters the soil system and XQGHUJURXQG DTXLIHUV LV NQRZQ DV WKH recharge area, and in dryland salinity management it is essential to limit the amount of water entering this part of the system. As the recharge water moves through the soil it accumulates soluble salts which add to the strength of the solution that occurs in that zone between bedrock and the soil surface. Typically this water is below the reach of all but the most deeply rooted plants such as trees and long- lived shrubs, and it is often an important factor that allows these plants to survive through long dry spells. Where the landscape allows this soil water to accumulate, such as the lower parts of hill slopes and in areas where clay soils may impede movement, it may eventually rise enough that the capillary action of the soil starts to carry it to the surface. This area is known as the discharge zone. When the water is evaporated, salts remain on the surface. It