The Challenge
The use of reclaimed water (RCW) has been directly linked with colloidal dispersion, whereby the soil particles become separated, leading to a collapse of the structure and reduction in permeability. As a result, water cannot be transmitted through the soil layers subsequent to irrigation. This occurs as a result of high levels of sodium found in RCW that displace calcium in soil clays thereby increasing salinity. This effect has historically been reversed through the topical application of a calcium sulphate based mineral, also known as gypsum, to the soil at 5-10 tonnes per hectare.
Although this annual application can repair the damage caused by RCW, the calcium in gypsum can only reach the top 100 mm of soil. As a result, this leads to a loss of soil structure during seasonal rainfall. However, the ease with which water can move through the soil’s pore spaces can be improved dramatically in the soil profile through the use of waterborne gypsum.
This study was designed in order to manage the quality of soil watered with recycled water through the development and trialling of an automatic waterborne calcium doser system.
The Project
The project involved the design, construction and trial of the prototype calcium doser at the Warringa Oval in Werribee, Victoria. The gypsum dissolved in RCW was dosed at a concentration that reverses the adverse effects of sodium in the RCW used to irrigate the sportsfield. The study was conducted over the 2011/2012 summer irrigation season.
The second phase of the project involved the development and implementation of a detailed communication plan, which was aimed at conveying the project’s outcomes to key stakeholders and RCW users.
The Outcome
The project successfully identified measures to treat highly saline recycled water for use in areas with heavy clay soils, allowing for better water penetration and plant growth. The project demonstrated that waterborne gypsum is highly effective in preserving or improving the permeability/infiltration rate of sodic soils, and is equally applicable in amenity and agricultural use of RCW.
The field solubility of gypsum achieved was as high as any reported in the scientific literature, and it substantially reduced the hazardously high levels of sodium normally found in RCW used for irrigation. In turn, this demonstrably improved the permeability of the treated receiving soils, and increased soil infiltration rates four fold. Waterborne gypsum has not been used in Australia to date, and this trial shows clearly that this practice is achievable, and is easy to manage on site, improves sustainability, and is cost effective.
