Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat Does the high potassium content in recycled winery wastewater used for irrigation pose risks to soil structural stability? Xueying Liang a , Pichu Rengasamy a , Ronald Smernik a , Luke M. Mosley b, * a School of Agriculture, Food and Wine, University of Adelaide, SA 5064, Australia b School of Biological Sciences, University of Adelaide, SA 5005, Australia ARTICLE INFO Keywords: Soil dispersion sodicity Winery wastewater irrigation Recycled water Gypsum ABSTRACT Sodicity, where a high proportion of cation exchange sites are occupied by monovalent Na + ions relative to divalent cations Ca 2+ and Mg 2+ , is a widespread and serious problem globally as this can result in soil dis- persion, low hydraulic conductivity and poor aeration. It has been increasingly recognized that the presence of potassium (K + ) can also be a contributor to soil structural stability problems. The aim of this research was to investigate the long term (> 15 years) effects of irrigating treated winery wastewater on soil structural stability, for which K + comprises a high proportion of total cation concentrations, at a vineyard trial site in the Barossa Valley, Australia. Analysis of the long-term soil dataset was undertaken along with laboratory experiments to determine the current or future impacts of high exchangeable K + on soil hydraulic conductivity and dispersion. Field results showed build-up of K + in subsoils and a corresponding decline in Mg 2+ . This appears due to the higher selectivity and exchange of K + relative to Na + , and higher K/Na ratio in the wastewater. The potential dispersibility of the subsoils was demonstrated via a high turbidity of soil suspensions and high values of the Emerson Dispersion Index. Declining relative hydraulic conductivity occurred for subsoils leached with winery wastewater followed by low ionic strength water. Flocculation measurements were performed in which aliquots of CaCl 2 were added to determine the amount of Ca 2+ needed to overcome dispersion. We conclude that the long-term use of winery wastewater irrigation has potential to negatively impact soil structural stability via increasing exchangeable K + . Further field research is required but Ca or Mg based amendments could be used to reduce dispersion risks. 1. Introduction The volume of wastewater that is recycled and used for irrigation is increasing world-wide (Raschid-Sally and Jayakody, 2009). Water re- cycling is an important means to relieve water shortages and conserve water resources, particularly as climate change is increasing water scarcity (Dai et al., 2018). Re-utilization of wastewater for irrigation is now a common practice in agricultural lands. Wastewater sources can be from both municipal water treatment and industry, including wineries (Laurenson et al., 2012). Using wastewaters for irrigation is environmentally and economically valuable, because it can lessen the extent of serious water shortages while preventing surface waters being polluted from the discharge of wastewater (Bond, 1998; Arienzo et al., 2012). Wastewaters generally have a greater concentration of dissolved salt compared with most traditional water supplies, and hence cause addi- tional salt loading during land application. Usually, much of this salt is NaCl (Rengasamy, 2018). However, winery wastewater also has a high concentration of K + , which emanates from cleaning products (KOH), leaves of grapes and the wastes produced by the procedure of grape fermentation (Laurenson et al., 2012). Since winery wastewater re- cycling is capable of reducing off-site environmental effects and dis- posal costs, most wineries are keen to use their winery wastewater within sustainable vineyard operations (Hirzel et al., 2017). There have been several studies showing that when winery waste- water is used for irrigation, the Na + present can be harmful to soil structural stability (Levy and Torrento, 1995; García-Orenes et al., 2005; Odeh and Onus, 2008). Although K + has similar atomic prop- erties to Na + (i.e. they are monovalent cations with similar ionic ra- dius), less is reported of its potential deleterious effects on soil structure (Laurenson et al., 2012). Some researchers have suggested there is potential for long-term re-utilization of winery wastewater to cause structural stability problems to soils during land irrigation (Hirzel et al., 2017; Rengasamy, 2018). Due to the presence of elevated Na + and K + https://doi.org/10.1016/j.agwat.2020.106422 Received 14 May 2020; Received in revised form 10 July 2020; Accepted 28 July 2020 ⁎ Corresponding author. E-mail address: luke.mosley@adelaide.edu.au (L.M. Mosley). Agricultural Water Management 243 (2021) 106422 0378-3774/ © 2020 Elsevier B.V. All rights reserved. T