South Africa Wine Technical Yearbook 2025

TABLE 1. The chemical status of the Longlands soil that was irrigated with winery wastewater over a 15-year period near Rawsonville before the study began. Depth (cm) pH (KCl) P (mg/kg) Basic extractable cations (cmol c .kg -1 ) EPP’ (%) ESP’ (%) Na + extr K + extr Ca 2+ extr Mg 2+ extr 10 4.1 270 1.5 2.2 8.4 2.5 15.3 10.4 20 4.3 209 0.5 0.9 4.9 0.7 12.9 6.7 30 4.6 208 0.4 0.7 3.9 0.6 11.9 7.1 60 4.6 255 0.1 0.5 0.9 0.2 26.9 7.0 90 4.6 264 0.1 0.5 0.9 0.2 28.6 7.9

levels were relatively high for sandy soils. 13 This suggested that the sludge probably had a high CEC. The Ca extr was the dominant cation, whereas Na extr was the lowest throughout the profile (Table 1). The extractable potassium percentage (EPP’) was relatively high in the deepest soil layers. In contrast, the extractable sodium percentage (ESP’) was highest near the soil surface. Soil potassium, sodium and pH High amounts of WWW irrigation were applied in the course of the study (Figure 2A). The application of WWW increased the K + extr levels in the 0-10 cm layer, and, to some extent in the 10-20 cm layer, at the end of the harvest periods (Figure 2B). Despite the seasonal fluctuations, K + extr steadily increased over the three years in the first two soil layers compared to the levels at the beginning of the study. After three years of WWW application, there was no significant increase in K + extr levels deeper than 20 cm depth (Figure 2B). Similar to K + extr , irrigation with WWW increased the Na + extr levels in the 0-10 cm and in the 10-20 cm layers, at the end of the harvest periods (Figure 2C). In May 2012, the Na + extr was also slightly higher in the 20-30 cm layer compared to the rest of the study period. Despite the seasonal fluctuations, Na + extr tended to increase slightly over the two-and a-half-year study period in the first two soil layers compared to the levels at the beginning of the study. At the end of the study period, there was no increase in Na + extr deeper than 20 cm depth (Figure 2C). Since there

FIGURE 2. Temporal variation in (A) rainfall and winery wastewater irrigation, (B) soil K + , (C) soil Na + , and (D) soil pH (KCl) where winery wastewater was applied to a Longlands soil near Rawsonville.

was little change in Na + extr levels with depth throughout the profile, it suggested that most of the applied Na + was leached beyond 90 cm. Irrigation with WWW increased the soil pH (KCl) slightly until May 2012 (Figure 2D). In November 2012, the soil pH (KCl) showed a decrease and tended to remain constant until November 2013. Variation in soil

pH (KCl) was not related to variation in monovalent cations. However, addition of organic acids from WWW could be associated with the decrease of soil pH due to H + dissociation from carboxyl functional groups. 14 While the soil pH increase could be associated with high concentration

of total alkalinity in wastewater that contains bicarbonate ions,

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TECHNICAL YEARBOOK 2025