Technical Yearbook 2024

DECEMBER

In-field fractional use of winery wastewater with raw water (Part 5): Assessment of the below and above ground chemical status of grapevines in the lower Olifants River region By Carolyn Howell & Reckson Mulidzi

Abstract Wineries produce large volumes of poor-quality wastewater, particularly during harvest. As water resources are limited, wine-grape producers will have to use their natural resources judiciously to produce grapes. Therefore, it is 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. 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 for four seasons. Results showed that there was a substantial accumulation of salts at the shallow sand experimental

plot in the Olifants River region (LOR2) after only two years of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. Furthermore, the accumulation of elements, particularly sodium (Na) and chloride (Cl), in the permanent structure of the grapevines at this particular experimental plot could explain the poor response of the grapevines to the winery wastewater irrigation. Under the prevailing conditions, the wastewater irrigation had to be terminated, and this soil/ climate combination should be considered unsuitable for the long-term application of winery wastewater. On a deep sand in the same region, no detrimental effects of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation were observed.

Introduction Wineries produce large volumes of poor-quality wastewater, particularly during harvest. As water resources are limited, wine-grape producers will have to use their natural resources judiciously to produce grapes. Therefore, it is important that the sustainable use of alternative water sources for vineyard irrigation be investigated. 1,2 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. 1 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 for four seasons. After only two seasons of using the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation at the shallow sand experimental plot in the Olifants River region (LOR2), the low yield and

poor vegetative growth was a matter of great concern. 2 Although the fractional ratio was changed from 0.5 to 0.25 in the 2018/19 season, it was evident that large amounts of elements were still being applied via the irrigation. It also did not seem sustainable to apply larger volumes of irrigation to increase the yield. Furthermore, results from the soil analyses after winter 2019 confirmed that in this region of low winter rainfall, that excessive salts applied via the irrigation were not leached sufficiently in winter.

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TECHNICAL YEARBOOK 2024