Continuity of water supply is an ongoing concern for many South Australian irrigation districts. For those in close proximity to urban centres, the use of recycled municipal wastewater offers improved security of supply with the added environmental benefits of reduced marine discharge and the easing of demand upon more traditional irrigation water sources. There is also an economic benefit from the lower cost of water and the reduced need of fertiliser. South Australia already recycles more than 30% of its treated wastewater and seeks to increase reuse via irrigated horticulture and amenity plantings in support of the State’s strategic priority of ‘Clean green food as our competitive edge’. However, recycled wastewater can be slightly more saline than traditional water sources. Its incorrect use in irrigated crop production can increase soil salinity, raise the concentrations of sodium and chloride ions in leaves and fruit and reduce crop performance more than other irrigation water sources.
This collaborative project, funded by The Australian Water Recycling Centre of Excellence (AWRCOE) and the Goyder Institute for Water Research, was initiated to investigate two strategies aimed at supporting the sustainable use of recycled wastewater in irrigated crop production by addressing the constraint of salinity. The project focussed on Australia’s two most valuable horticultural export products, almonds and wine, both sourced from cropping systems recognised as being moderately sensitive to soil salinity and both industries with significant plantings located within recycled wastewater irrigation districts.
The project established two field trials north and south of Adelaide, where some cropping systems, with a relatively short history of irrigating with recycled wastewater, had already reported salinity related impediments to production. Investigations focussed on a vineyard in McLaren Vale and an almond orchard on the Northern Adelaide Plains (NAP).
At the McLaren Vale vineyard, treatments consisted of installing various configurations of rainfall re-direction devices, drawing from a body of work on approaches used to enhance run-off during water harvesting, to increase leaching under supplementary irrigation conditions. In the NAP almond orchard, irrigation was historically supplied by shandying dual water sources of different qualities, recycled wastewater and groundwater. Treatments sought to temporally separate irrigation with the two water sources in order to identify in which annual growth stage trees were most sensitive to the slightly saline recycled wastewater. Treatment effects at both sites were assessed by measurement of soil salinity and moisture, salt concentrations in leaves and fruit, yield and vegetative growth.
The primary aim of this project was to improve the management of salinity in permanent horticultural plantings which receive supplementary precision irrigation with recycled water. Specific objectives were:
The methodology and guidelines developed in this project have supported both the long-term use of recycled water for a range of irrigated crops as well as supported amenity plantings by councils. The outcomes of this research have benefitted both traditional irrigators as well as informed the state's recycling guidelines (for both urban and rural communities) and have contributed to recycled water irrigation practices across tAustralia.