Increased Use of Recycled Water for Irrigation


	Technology and Treatment

Water scarcity is an ongoing concern for many producers of horticultural crops in Australia. Recycled water offers an opportunity to improve security of supply. However, recycled water is variable in its quality and, when used for irrigation, can result in an unwanted accumulation of salt. Soil salinity can affect the productivity of various perennial horticultural crops, including grapes and almonds. To retain the advantages of supplementary irrigation sources such as recycled water, this project will investigate how to improve the flushing action of rainfall and also identify salt sensitive growth stages for crops. The outcomes resulted in improved use of recycled water and drainage systems to irrigate vineyards and almond plantations in South Australia.

The project involved crops being watered under very precise irrigation systems. The trials at a McLaren Vale vineyard tested whether using raised soil mounds built between the vines to redirect rainfall to soil directly under vines irrigated with recycled water reduced the build-up of salt. Trials on the almond orchards on the Northern Adelaide Plains used mixtures of recycled water and freshwater to identify the most salt sensitive growth stages of almonds.

The project also assessed how changing concentrations of salt in the various soils being assessed affect plant response in terms of vigour, yield and crop quality. Based on the success of the trials, the horticulture industry could expand its use of recycled water schemes for precision crop irrigation in other dry regions and improve management of soil salinity.

WORK UNDERTAKEN AND OUTCOMES

At the McLaren Vale vineyard, redirecting rainfall from the mid-row to the drip-line reduced average soil salinity by 27% and concentrations of sodium and chloride in juice by 28%. In addition, shallow ripping of compacted wheel lines further reduced under-vine soil salinity by 11 % and the concentrations of sodium and chloride in juice by 17%. At the Northern Adelaide Plains, application of non-saline water at pre-harvest was 31% more effective at reducing sodium and chlorine levels in almond trees than flushing the plants with nonsaline water, post-harvest. Late season leaf samples revealed that the trees were most sensitive to reduced salt load between pit-hardening and harvest.

SARDI staff measuring photosynthesis and leaf water potential at almond irrigation trial Photo courtesy of South Australian Research and Development Institute (SARDI)

ADOPTION AND IMPACT

An impermeable layer buried in mid-row soils to redirect rainfall and shallow ripping of compacted soils have potential as salinity management options without using additional irrigation water – an important development particularly when water is scarce. Rainfall redirection treatments also show promise for assessment with other locations and cropping systems. Sodium and chloride uptake in almonds was lowest when non-saline irrigation was applied during periods of leaf emergence and shoot growth.

Identification of the best time of the season to supplement recycled water with non-saline water improves the health of the trees and allows the use of a climate resilient water source. While the two season investigation period was too short to elicit a yield response to different timings of reduced salt load. Research into the response of almonds to the timing of salt stress will continue with support from the SA River Murray Sustainability program through to the 2017 season.

PROJECT PARTNERS
Lead organisation:	South Australian Research and Development Institute (SARDI)
Partner organisations:	Goyder Institute for Water Research
	University of Adelaide
	Treasury Wine Estates

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