Technical Yearbook 2024

JULY

Treated municipal wastewater for irrigation (Part 5): Soil hydraulic conductivity By Carolyn Howell, Karla Hoogendijk, Philip Myburgh, Vink Lategan & Eduard Hoffman

Introduction The effect of irrigation using wastewater on soil chemical

properties is well documented, but its effect on soil physical properties, e.g. soil hydraulic conductivity and infiltration rate, is largely unknown particularly when used for vineyard irrigation. 1 This could be due to the fact that changes in soil physical properties are difficult to quantify, because they tend to occur only over the long term and are greatly variable. 2 Furthermore, most of the studies were conducted in laboratories using artificial solutions rather than in situ . Results of a laboratory study investigating the effect of sodium adsorption ratio (SAR) and potassium adsorption ratio (PAR) on soil hydraulic conductivity showed that it was considerably reduced when the SAR or the PAR exceeded 20. 3,4 In another

Abstract A long-term trial was conducted in commercial vineyards in the Coastal region of South Africa to assess the impact of irrigation with treated municipal wastewater (TMW) on Cabernet Sauvignon and Sauvignon blanc vineyards. Grapevines were irrigated using TMW for 11 years and were either rainfed (RF), irrigated with TMW via a single dripper line (SLD) or received twice the volume of wastewater via a double dripper line (DLD). The near-saturation hydraulic conductivity ( K ns ) for the DLD treatments was lowest. The K ns at the surface of the soil could also be related to the electrical conductivity of the saturated soil extract EC e in the topsoil. It should be noted that the results of this study represent specific in-field situations in three commercial vineyards under one set of climatic conditions.

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TECHNICAL YEARBOOK 2024