Soil Structural Changes following Irrigation with a Potassium Rich Winery Wastewater

Research on the soil structural effects of potassium (K) in irrigation wastewaters has received limited attention due to the typically low abundance of K in most waters. Winery processing wastewater however tends to have elevated concentrations of both K and sodium (Na). This study investigated the contrasting cation dynamics under municipal and winery wastewater following irrigation to a heavy clay soil. Under laboratory conditions, accelerated annual irrigation, drying and rainfall cycles enabled temporal changes to be investigated. Despite the higher Na concentration in winery wastewater, irrigation caused a significant increase in the exchangeable potassium percentage of the soil indicating preferential retention of K over Na. Although clay dispersion was evident in soils irrigated with both wastewaters, importantly, this was greater under municipal wastewater due to the higher dispersive potential of Na over K. Soils receiving municipal wastewater also required a greater electrolyte concentration to maintain flocculation. It is thought precipitation and solubilisation of inorganic carbon during irrigation, drying and rainfall cycles, plays an important role in buffering a dramatic decrease in drainage electrolyte concentration otherwise expected during rainfall cycles. Furthermore changes in soil pH(1:5) and effective cation exchange capacity (CECe) associated with high bicarbonate loading appear to favour retention of monovalent cations, thereby influencing clay dispersion. Introduction In Australia, wastewater from many sources, including winery wastewater, are reclaimed for irrigation. In South Australia for instance, both winery and municipal wastewaters are distributed and sold to growers for irrigating grape vines. Both waters are rich in Na and, in the case of winery wastewater, K concentration is also high due to waste from grape lees, spent juice and potassium hydroxide (KOH) cleaners (Kumar & Christen, 2009). A high concentration of monovalent Na in soils has often shown to disrupt soil structure, leading to changes in many key soil physical properties such as hydraulic conductivity, infiltration rate, bulk density and soil aeration (e.g. Rengasamy and Olsson 1991; Halliwell et al. 2001; Menneer et al. 2001; Stevens et al. 2003). Based on the large hydrated ion size and its affinity to clay minerals, high levels of exchangeable K in soil also has the potential to cause clay swelling and dispersion (Levy and Feigenbaum 1996). Research on the soil structural effects of K in irrigation wastewaters has however received less attention due to the typically low abundance of K in most wastewaters (Arienzo et al. 2008).