This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

The SA Water Bolivar wastewater treatment plant treated about 46,000 ML of wastewater annually to produce reclaimed water for irrigation purposes in the Northern Adelaide Plains. Water was available through the Virginia Pipeline Scheme which was the first and largest recycled water scheme in Australia serving around 250 horticultural growers.

In previous years, a combination of dry conditions and expansion of horticultural industries increased demand of reclaimed water for crop production. Growers were concerned by water quality parameters and the potential risk of soil salinity caused by using saline irrigation water. Reclaimed water sometimes contained high levels of salts which contributed to an already rising saline water table. Salts sometimes reduced water availability, were toxic to the plant, reduced nutrient availability and had negative impact on soil structure. There was concern of the cumulative effect that reclaimed water could have on soil, water, crop quality and yield.

This project was established to investigate the use of reclaimed irrigation water for perennial and vegetable crops and the effect on soil health and crop sustainability. It was initiated in consultation with growers in the Northern Adelaide Plains, South Australia who observed high level of salt toxicity on almond trees irrigated with reclaimed water. This project was requested by the Virginia Irrigation Association (VIA) to scientifically substantiate changes in soil health under crops irrigated by reclaimed water.

Soil sampling was conducted at three almond sites to compare the use of reclaimed and bore irrigation water. One vegetable site was included in the study. The study found that long term use of poor quality reclaimed water and saline bore water was not viable for almond crop production. Reclaimed water and saline bore water increased the risk of salt accumulation in the rootzone and growers were limited by the availability of good quality irrigation water in the Northern Adelaide Plains to manage soil salinity. Accumulation of salts and high concentration of chloride and sodium caused salt toxicity which ultimately impaired almond productivity. In comparison, many vegetables were able to tolerate a higher level of salinity than almond crops. Salinity of irrigation water was within the acceptable range for vegetable production.

With increasing pressure on water availability and predicted low rainfall conditions in Australia, an increase in reclaimed water salinity continued. If reclaimed water was non-saline and within the range of crop tolerance, appropriate volumes of reclaimed water as a leaching source assisted management of rootzone salinity. As it stood, bore water and reclaimed water available to the Northern Adelaide Plains was unsuitable for long term irrigation of almonds and tailored soil management strategies were essential to minimise the high risk of soil salinity, sodicity and associated soil structural decline.