In 2004, Southern Rural Water (SRW) began delivering recycled water, produced by Melbourne Water at the Western Treatment Plant, to irrigation customers in the Werribee Irrigation District (WID). Although the water was vital for enabling farmers to continue planting crops, the high salinity presented serious challenges to pre-existing methods of irrigation and soil management.
This project sought to demonstrate to irrigators the differences between using recycled water and river water on their land and the practices they could adopt to assist in managing the salinity and sodicity issues that arose. This was accomplished by enlisting the help of six farmers who allowed extensive monitoring and trials to be run on their properties over the course of two years.
The project team consisted of resources from Southern Rural Water, Department of Primary Industries and Ag-Challenge Consulting. Several growers in the WID were approached seeking permission to use a small parcel of land for intensive monitoring and trials of management practices aimed at improving the results of intensive recycled water use for irrigation. There were six sites selected for investigation into:
- Subsoil permeability
- Gypsum evaluation
- Deep ripping
- Reduced phosphorus fertiliser usage
- Fowl manure
- Distribution Uniformity (DU)
- Crop / Water usage relationship
- Leachate movement
Over the course of two years the project team monitored the soils and water usage at these sites in conjunction with field trials to assess the impact of intensive recycled water use, in relation to each of the project investigations. There were also in depth discussions with each of the six farm operators about their observations of recycled water use, the management practices they had already adopted to mitigate the higher salinity and the learning’s that they acquired through their participation in the project.
The project managed to influence many of the negative perceptions about the high salinity of recycled water as customers learned to adapt their on-farm practices to get the most out of it. Some ideas that were previously rejected by irrigators in Werribee South, such as deep-ripping, have become widespread practice. In other areas, such as low phosphorus fertiliser usage, there is still scepticism; despite the project outcomes.
It has not been possible to observe the medium to long-term impact of the project on changes to farm management practise as 2010 / 2011 have returned higher than average rainfall, filling the storages and enabling growers to return to using river water as the primary source of irrigation water. The aquifer levels have recovered sufficiently for SRW to also remove the prohibition on groundwater extraction. These events have had a notable impact on recycled water demand and usage. However, long term demand still exists and the findings of this project will remain relevant in the event that recycled water once again represents a significant portion of irrigation supply.