Assessing the impact of land-use on deep drainage in Mediterranean environment of southern Australia

Johann Nogueira (A), Robert Norton (A) , Roger Armstrong (B), Jason Brand (B)

A - Joint Centre for Crop Innovation, The University of Melbourne, PO Box 260, Horsham, Victoria, 3401, Australia
B - Department of Primary Industries, PO Box 260, Horsham, Victoria, 3401, Australia

TAKE HOME MESSAGES
• A tool is being developed to allow growers to make decisions based on their climate and soil type as to which is the best vegetation system for their farm to minimise deep drainage, which is a major cause of dryland salinity.
• Current research indicates that the best bet options to minimise recharge are lucerne (Medicago sativa) as its deep root system uses all the available moisture and dewaters the soil below wilting point , Saltbush (Atriplex spp) which produces biomass during the summer months when feed is low and hence in an ally farming system, will lead to year round feed for stock, and Tagasaste (Chamaecytisus proliferus) which pumped the soil dry below wilting point, but its biomass production was low.
• Native Wallaby Grass, which was previously thought to minimise deep drainage was found to become dormant during periods of water stress and does not use up all the available water in the soil profile or utilise the episodic summer rainfall.

DRYLAND SALINITY
The clearing of natural perennial vegetation including native grasses, trees and shrubs and replacement by annual crops and pastures may reduce annual transpiration and increase water stored in the soil profile, resulting in increased risk of deep drainage. Drainage beyond the root zone of plants leads to loss of potential yield and contributes to rising water tables and the development of secondary salinity.


DEEP DRAINAGE UNDER VARIOUS VEGETATION SYSTEMS
Experiments were established in May 2004 to quantify the water balance and potential deep drainage occurring on two key ground flow systems of the Wimmera catchment of Victoria, southern Australia. The experiment evaluated five land-use systems (Lucerne, Native grass pasture (dominated by Danthonia spp.), annual grain cropping, alley farming with either Tagasaste or Saltbush, compared to a three year fallow) in terms of water use, rooting depth, biomass production and canopy light interception. Lucerne and Tagasaste extracted most water from the soil profile and had deep root systems. Native pasture extracted least water and had a shallow root system.

The implication of these findings will be used for development of profitable land-use systems that manage deep drainage in the Wimmera catchment. Native pasture systems were believed to minimise deep drainage, however this research demonstrates that the ability of native pasture to survive dry conditions, which prevailed during this experiment, was due to physiological dormancy during periods of water stress rather than a deeper rooting system enabling extraction of moisture from deeper in the profile.

DEVELOPMENT OF OPTIONS FOR FARMERS
Information derived from these experiments along with other glass house trials are being used to parameterise and validate a computer simulation model (PERFECT). This model will be used to predict the potential deep drainage under different land use systems depending on the soil and climate type of the area. By managing the soil moisture in the root zone of the paddock, we will be one step closer to controlling the inflow into the water table, hence managing secondary salinity.

Acknowledgements
Project supported by Wimmera Catchment Management Authority: National Salinity Action Plan. This project team is based at Department of Primary Industries (Horsham) in calibration with The University of Melbourne.

Contact
Johann Nogueira:j.nogueira@pgrad.unimelb.edu.au