Technical Yearbook 2024

OCTOBER

In-field fractional use of winery wastewater with raw water (Part 3): Soil responses By Carolyn Howell & Reckson Mulidzi

Introduction Although there is extensive literature available regarding the effect of irrigation with wastewaters of various origins on soil chemical properties, 1 very little is known about the effects of irrigation using augmented winery wastewater on soil chemical status. In Australia, it is estimated that 3 - 5 m 3 of winery wastewater, with high organic load, as well as variable salinity and nutrient levels, is produced when a ton of grapes is crushed. 2 The effects of high concentrations of potassium (K) application to soils have not been extensively researched and are still unclear. 2,3 On the other hand, limited irrigation water supplies could be restricted further in future allocations of irrigation water. 4,5 If winery wastewater could be used to irrigate vineyards with no detrimental impacts on soil chemical status, it could be a possible viable alternative to using either raw river or recycled municipal water. Land application of wastewater can increase levels of soluble and exchangeable forms of K more rapidly than with conventional inorganic fertilisers, 6 and most of the K in wastewater is available immediately. Irrigation with K-rich wastewater could be beneficial to overall soil fertility, although long-term application could affect soil chemical and physical properties. 2,7 A further advantage of using winery wastewater as a source of K over the use of conventional fertiliser is that it could be an efficient recycling practice where the soil has low K. In addition to sodium (Na) and K ions, winery wastewater can also contain calcium (Ca) and magnesium (Mg) ions. 2 Neither of these ions is harmful to soil structure and can ameliorate the impacts of Na via their role in reducing the sodium adsorption ratio (SAR). Both soil K and SAR increased throughout the soil profile, where winery wastewater was used for irrigation. 8

Abstract Wineries produce large volumes of poor-quality wastewater, particularly during harvest. Since water resources are limited, wine-grape producers will have to use them judiciously to produce grapes. It is also important that the sustainable use of alternative water sources for vineyard irrigation be investigated. In this regard, experimental plots were selected in three selected production areas in the Western Cape Province, namely the Coastal, Breede River and Olifants River regions. The specific locations were selected due to their vast differences in mean annual rainfall. Within each region, two plots were selected which differed in soil texture. Grapevines were irrigated with the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. Under the prevailing conditions, soil pH (KCl) increased consistently in response to winery wastewater irrigation. Soil potassium (K) was substantially higher for the experimental plots compared to their respective controls regardless of mean annual rainfall. Consequently, soil extractable potassium percentage (EPP´) was higher. Results indicated that the increase in soil K and EPP´ was related to soil texture, amounts of K applied via the irrigation water and annual rainfall. In contrast, soil Na of all the experimental plots was similar or even lower compared to their respective controls. This indicated that there was sufficient leaching of sodium (Na) at all the experimental plots, regardless of soil texture. However, where more Na is applied via the irrigation water, Na could accumulate to levels where it could negatively impact soil physical conditions or grapevine growth and yield.

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TECHNICAL YEARBOOK 2024