Technical Yearbook 2024

NOVEMBER

In-field fractional use of winery wastewater with raw water (Part 4): Grapevine and wine responses By Carolyn Howell & Reckson Mulidzi

Introduction Although extensive literature is available regarding the irrigation of grapevines with saline water, 1,2,3,4,5,6,7 very little is known about the effects of irrigation using augmented winery wastewater on grapevines. Recent studies have shown that approximately 3 - 5 m 3 of winery wastewater, with high organic load and variable salinity and nutrient levels, is generally produced when a ton of grapes is crushed. On the other hand, limited irrigation water supplies could be to baseline values. However, the experimental plots of cane mass at the sandy clay loam (Breede River region) and shallow sand (Olifants River region) were lower than baseline values. This suggested that the in-field fractional use Abstract Very little is known about the effects of winery wastewater irrigation on grapevines. However, wineries produce large volumes of poor-quality wastewater, particularly during harvest. If this wastewater could be used to irrigate vineyards with no detrimental impacts on either grapevines or wine, it could become a sustainable alternative water source for vineyard irrigation. 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 for four seasons. At the end of the trial, the cane mass of the deep sand experimental plot in the Lower Olifants River region and the sandy loam plot in the Breede River region were comparable

restricted further in future allocations of irrigation water. 9,10 It was previously reported that irrigation of grapevines using winery wastewater diluted up to a maximum chemical oxygen demand (COD) level of 3 000 mg/L did not affect vegetative growth or any of the yield components compared to raw water control. 11 There was also no response in element content in the leaves and shoots. Where winery wastewater was used to irrigate two vineyards in California, there was an accumulation of potassium (K) and sodium (Na) where the (augmentation) of winery wastewater with raw water had adverse effects on the vegetative growth of these grapevines and was likely related to the accumulation of sodium (Na) in grapevine parts. The extremely low yield measured at the shallow sand (Olifants River region) experimental plot was probably due to the region’s very low rainfall due to drought and the excessive amounts of elements applied via the irrigation water, which were not leached. Although wine sensorial quality was not affected by the in-field fractional use of winery wastewater with raw water, wines did not always conform to statutory requirements with regard to their Na content. This was specifically notable in regions with lower rainfall. Results indicated that winery wastewater can be a beneficial source of alternative irrigation water, particularly in areas where grapevines are normally grown under dryland conditions and during drought. Young grapevines were established successfully with the in-field fractional use (augmentation) of winery wastewater with raw water in the Coastal region. Based on the project results, the authorities should consider possible amendments to the General Authorisation for wineries when using the in-field fractional use (augmentation) of winery wastewater with raw water for irrigation of vineyards.

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TECHNICAL YEARBOOK 2024