Fact Sheet #11 – Feb 2004
Dr Sean Murphy – Farming Systems Hydrologist, NSW Agriculture
Deep drainage is water that leaks through the soil profile beyond the root zone of annual crops and pastures. This water is lost from the annual crop production cycle and is therefore not available for extraction by crop roots.
When deep drainage water adds to the water table, it is then known as groundwater recharge. Groundwater recharge increases pressure in aquifers, which forces the flow of saline groundwater into the river system and can increase the risk of dryland salinity where water tables are close to the soil surface.
• Deep drainage, on average under Mallee woodland and perennial pasture, is less than
0.1 mm/year, and
• under cropping systems can increase by 300 fold, to around 5 to 35 mm/year.
To utilise this water, plants with a deeper root system, such as lucerne need to be incorporated into the farming system.