Technical Yearbook 2024

Acknowledgements • This report is an output of WRC Project K5/2561, en titled “Use of winery wastewater as a resource for ir rigation of vineyards in different environments”. This solicited project was initiated, funded and managed by the WRC. The project was co-funded by Winetech and ARC. • ARC for infrastructure and resources. • Staff of the Soil and Water Science division at ARC Infruitec-Nietvoorbij for their assistance, and in particular Mr. F. Baron for his dedicated technical support. • Backsberg, Madeba, Lutzville Winery and Spruitdrift Winery for permitting the project team to work at their wineries and in their vineyards. Colleagues at the wineries for their assistance and support. • Mr W. Smit from Netafim for advice and designing the irrigation systems. plots was higher in the 2020/21 season compared to the 2019/20 season (Figure 2D). Furthermore, results indicated that the grapevines at the LOR2 experimental plot had recovered to a certain extent after receiving only raw water for the last two years of the study. This indicated that grapevines could recover from the detrimental effects that they had incurred from the in-field fractional use (augmentation) of winery wastewater with raw water for the first two seasons of the study. Wine characteristics Sensory analyses of the experimental wines over the four vintages showed no consistent negative attributes that could be linked to potential off-odours or off-tastes that could have been carried over from the winery wastewater (data not shown). The wine Na element contents for the duration of the study ranged from 17 mg/L to 105 mg/L (data not shown). In a study carried out in Robertson, wine Na contents that ranged from 40 mg/L to 190 mg/L were reported. 25 Much higher values were reported for Australian Shiraz wine Na that ranged from 78 mg/L to 533 mg/L. 26 However, the legal limit for wine Na in South Africa is 100 mg/L. 27 Wine Na for the LOR2 shallow sand experimental plot was 105 mg/L in the first season, thus higher than this norm, and the BR2 experimental plot had wine Na contents of 102 mg/L in the second season. However, due to the termination of the wastewater irrigation after two seasons, the wine Na level at the LOR2 shallow sand experimental plot declined to 43 mg/L in the 2020/21 season. Therefore, under the prevailing conditions, wines produced where grapevines were irrigated using in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation did not always conform to statutory requirements with regard to Na content. This was specifically notable in regions with lower rainfall.

lower at harvest in the 2018/19 season compared to the 2017/18 season. In the 2019/20 season, berry mass ranged from 0.94 - 1.52 g per berry. Except for the LOR2 shallow sand experimental plot, the berry mass was lower at harvest in the 2018/19 and 2019/20 seasons compared to the 2017/18 season. Berry mass ranged from 1.33 - 1.97 g per berry in the 2020/21 season (Figure 2B). Although some differences in berry weight were observed at harvest, where different artificial winery wastewaters were used for vineyard irrigation, 20 these differences were very small, and no conclusions could be made. Similarly, using undiluted winery wastewater for vineyard irrigation at Oxford Landing had no detrimental effect on berry size. 18 In contrast, in a similar study at Angaston by the same researchers, the use of undiluted winery wastewater for vineyard irrigation consistently reduced berry weight substantially. It could be that the quality of the winery wastewater differed between the two sites in that specific study. Mean berry mass at harvest of 1.2 g per berry and 1.5 g per berry is comparable to drip-irrigated Cabernet Sauvignon values in the Breede River valley. 21 Where Cabernet is subjected to severe water constraints, i.e. Ψ L below 1.6 MPa, berry mass is expected to be about 1 g per berry. 22,23 In the case of Shiraz, the mean berry mass at harvest of 1.2 - 1.4 g per berry is comparable to values for drip-irrigated Shiraz in the Breede River valley. 24 In the 2017/18 season, lower berry mass reported in Figure 2B reflected in substantially smaller bunches and lower yield for the LOR2 shallow sand plot compared to the other experimental plots. The lower berry mass in the 2018/19 season (Figure 2B) was also reflected in substantially smaller bunches (Figure 2C) for all the experimental plots. Bunches at the BR1 and BR2 experimental plots were smaller in the 2019/20 season compared to the 2017/18 and 2018/19 seasons (Figure 2C), but bunches at the Lutzville deep sand experimental plot were bigger in the 2019/20 season compared to the 2018/19 season. The biggest bunches were obtained in the 2020/21 season (Figure 2C). In the 2017/18 season, the low yield measured at the LOR2 shallow sand experimental plot (Figure 2D) was most likely due to the prevailing drought in the region. It has been speculated that the Spruitdrift Winery lost almost 50% of its grapes in this particular season. In the 2018/19 season, the yield at all the experimental plots was substantially lower compared to the 2017/18 one (Figure 2D). The yield was so low at the LOR2 experimental plot that not enough grapes could be harvested to make experimental wine, and was most likely due to the prevailing drought in the region, as well as the excessive amounts of elements applied via the irrigation. Given the region’s low rainfall levels, excessive salts applied were also not leached from the soil during the winter period. In the 2019/20 season, yield at the LOR1 and LOR2 experimental plots was higher compared to the 2018/19 season (Figure 2D). It was evident in this season that the yield at the BR1 and BR2 experimental plots was becoming progressively lower. Yield at all of the experimental

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TECHNICAL YEARBOOK 2024