Water Journal : Water Journal April 2011
refereed paper horticultural use water APRIL 2011 157 saturated infiltration rate the same phenomena were observed with the commercial agents. Treatment A seemed to improve the initial wettability of the sand after three days, but its effect was significantly reduced a week later. It should be noted that recording the initial infiltration rate is problematic as the soil moisture which affects soil infiltration was not measured and is likely to vary between individual barrels. These observations clearly demonstrate that the simplistic model presented in the introduction section (Kranok & Tucker 2004) regarding the mode of action of wetting agents did not apply in the current study. It appears that in this study, for most wetting agents, the surfactant molecules behaved just like the natural hydrophobic organic molecules once absorbed on the sand, resulting in enhancement of soil hydrophobicity. The interaction between the surfactants and soil particles seem to be the key to a better understanding of these observations. More so, it is likely that there is no one mechanism by which surfactant is absorbed on soil particles, making it impossible based on our current understanding to predict whether the implementation of wetting agent is going to enhance or reduce water repellency. Summary and Conclusions Overall, it was observed that the initial application of the wetting agents usually improved the wettability of the sand to some extent. This was likely to be because of the reduction in the water surface tension. However, the improved wettability was short-lived and for most cases the water infiltration rates into the sand decreased within a week from application. We postulate that surfactant molecules in the wetting agents were adsorbed on the sand particles in a similar way to the organic hydrophobic material that is coating them. These findings raise a big question mark on the efficiency of surfactant-based wetting agents to treat water repellent sandy soils. Based on the current findings, not only that many products do not enhance long term wettability, some seem to enhance soil hydrophobicity. Further investigation on the interaction and adsorption between surfactants and soil particles is needed. The Authors Dr Amit Gross (email: firstname.lastname@example.org) is a senior lecturer at the Department of Environmental Hydrology & Microbiology, Zuckerberg Institute for Water Research, Blaustein Institutes for Desert Research, Ben Gurion University of the Negev, Midreshet Ben Gurion 84990, Israel. He is currently a visiting research fellow at Murdoch Universiy in Perth, WA 6150. Radin Maya Saphira Radin Mohamed is a PhD candidate at the School of Environmental Science, Murdoch University. She was an academic staff at the Faculty of Civil & Environmental Engineering, University of Tun Hussein Onn Malaysia, 86400, Johor, Malaysia. Dr Martin Anda and Professor Goen Ho (email: g.ho@murdoch. edu.au) are with the School of Environmental Science, Murdoch University. References Blackwell P, 1996: Managing water-repellent soils. Department of Agriculture and Food, Western Australia (www.agric.wa.gov.au/PC_92440. html?s=1001). Karnok K & Tucker K. 2002: Water-repellent soils. Part I: Where Are We Now? Golf Course Management 70:59-62. Karnok KJ & Tucker KA, 2004: Wetting agents: what are they, and how do they work? Golf Course Management 72:84-86. Karnok KJ, 2006: Which wetting agent is the best? Golf Course Management 74:82-83. Lai J & Ren L, 2007: Assessing the size dependency of measured hydraulic conductivity using double-ring infiltrometers and numerical simulation. Soil Science Society of America Journal 71 (6):1667-1675. Miyamoto S, 1985: Effects of wetting agents on water infiltration into poorly wettable sand, dry sod and wettable soils. Irrigation Science 6:271-279. Ritsema C J & Dekker LW, 1994: How water moves in water repellent sandy soil. Water Resources Research 30:2519-2531. Throssell C, 2005: GCSAA-USGA wetting agent evaluation. Golf Course Management 73:52-91. Water Corporation, 2010: Being waterwise outside your home. www.watercorporation.com.au/W/waterwise_gardens.cfm#Soil%20 wetting%20agents. Water Corporation, WA. Wiel-Shafran A, Gross A, Ronen Z, Weisbrod N & Adar E, 2005: Effects of surfactants originating from reuse of greywater on capillary rise in the soil. Water Science & Technology 52:(10-11) 157-166. Wiel-Shafran A, Ronen Z, Weisbrod N, Adar E & Gross A, 2006: Potential changes in soil properties following irrigation with surfactant-rich greywater. Ecological Engineering 26:348-354. Figure 9: Average (± standard deviation) relative changes in the initial infiltration rate (as measured by the double ring infiltration method) of tap water over time after application of wetting agents (time 0). Results are based on three replicates. Figure 8: Average (± standard deviation) relative changes in saturated infiltration rates (as measured by the double ring infiltration method) of tap water over time after application of wetting agents (time 0). Results are based on three replicates.
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