Water Journal : Water Journal April 2011
horticultural use refereed paper technical features 156 APRIL 2011 water three barrels were used as controls with untreated tap water. The experiment was set in randomised block design. The wetting agent solutions were prepared according to the manufacturer's instructions on the product. The barrels were left to drain for three more days and the infiltration rate was measured again using tap water in all treatments. The barrels were left to drain again for seven days and the infiltration rate was re-measured. Results and Discussion The conceptual approach of this research was to simulate an irrigation regime in a garden (i.e. pot irrigation), while studying the effect of common wetting agents. Capillary rise Initially, the capillary rise test was used as an indication of changes in the sand hydrophobicity. As expected, the capillary rise of the burnt sand was significantly higher than in the native sand, demonstrating the contribution of organic matter to the sand hydrophobicity (Figure 6). When wetting agent D was coated on the sand, the capillary rise was significantly reduced, as previously described by Weil-Shafran et al. (2006), who demonstrated that the capillary rise in clean sand that was pre- coated with non-ionic and anionic surfactants at a rate of as low as 10 mg/kg was significantly less than in the uncoated sand. Double-ring infiltrometer tests The saturated infiltration rates of water and five wetting agents through the sand were similar or slightly faster when the wetting agents were introduced to the soil as compared to the water control (Figure 7). Wetting agent C demonstrated significantly better results than the others; however, when the infiltration rate was re-measured three days later, using tap water as the irrigation medium, two observations were made: a) the average infiltration rate of the water control where no wetting agents were used was 14% lower than when initially measured, and; b) the infiltration rates of all treatments were either similar to or lower than the water control (Figure 8). These phenomena were repeated when the infiltration rate was re-measured after 10 days from the application of the wetting agents. The initial infiltration rate in all treatments was also measured (Figure 9), as it may more resemble irrigation of a pot. Similarly to the Table 2: Chemical ingredients of five commercial wetting agents. Chemical ingredients Wetting agents Chemical entity Proportion Product A Ethylene glycol-propylene glycol block polymer 80% (granular) Seaweed (Durvillea potatorum) 20% Product B Non-ionic surfactant 100% (liquid) Product C Clinoptilolite (zeolite) 69% (granular) Propylene oxide-ethylene oxide block polymer 15% Lignin 10% Cellulose 6% Product D Surfactant 10 to <30% (liquid) Product E Poloxypropylene polyoxythelene ether <15% (liquid) Poloxypropylene polyoxythelene ether < 25% Figure 6: Illustration of the effect of anionic surfactant (Linear Alkyl Benzene Sulfonate) and a commercial wetting agent on capillary rise in pre-coated sand as compared to the capillary rise in native sand with and without the organic matter (OM). Figure 7: Average (± standard deviation) saturated infiltration rate as measured by the double ring infiltration method of five wetting agent solutions and tap water into partly water-repellent sand. Results are based on three replicates.
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