South Africa Wine Technical Yearbook 2025

FIGURE 3. The effect of municipal water and winery wastewater (WWW) on the β-glucosidase activity (μg p-nitrophenol g -1 2h -1 ) in four soils in the (A) 0-10 cm soil layer and (B) 10-20 cm soil layer in the third simulated season, as well as in the (C) 0-10 cm soil layer and (B) 10-20 cm soil layer in the fourth simulated season. Values in the same data set, that are followed by the same letter, do not differ at p = 0.05.

activities did not differ significantly between soils, but the activities of both phosphatase and β-glucosidase were appreciably greater in the Stellenbosch shale and Stellenbosch granite soils than in the Rawsonville sand and Lutzville sand. That the Stellenbosch soils were initially more acidic and contained less exchangeable Ca than the Rawsonville sand and Lutzville sand may have contributed to the greater activities of β-glucosidase and phosphatase in the Stellenbosch soils following irrigation with municipal water is possible, but a pH effect seems improbable in view of the slightly alkaline pH (pH 7.4) of the municipal water. The effect of water quality on enzyme activity was inconsistent, and the average urease (Figure 1) and β-glucosidase (Figure 3) activities were higher in the WWW than the MW treatments, whereas the converse was true for phosphatase (Figure 2). This supports the foregoing contention that enzymes differ in environmental requirements

content and higher pH than the other experimental soils contributed to the low enzyme activities in Lutzville sand was unclear. That urease correlated moderately well with glycosidase, and β-glucosidase correlated, though weakly, with phosphatase, whereas urease did not correlate with phosphatase (Table 1), implies that urease and phosphatase have different soil environmental requirements. Factors that correlate positively with urease activity include soil OM and total nitrogen contents. 16 However, because all of the soils received WWW, and the WWW differed little in composition, the urease activities in the soils irrigated with WWW should have been similar, provided that the differences between soils were small. The fact that the urease activities in the WWW treatments differed between soils suggests that the effects of the soils on enzyme activity were large in comparison with those of the WWW. In the treatments irrigated with municipal water, urease

Although the all-treatment average activities of the enzymes differed significantly between soils, the averages did not follow a consistent pattern (Figures 1, 2 and 3). Urease and β-glucosidase activities peaked in the Stellenbosch shale soil, whereas phosphatase activity peaked in the coarser-textured Stellenbosch granite soil. Nevertheless, the lowest activities of the three enzymes were all observed in the Lutzville sand which, like the Rawsonville sand, was dominated by the fine sand fraction. Despite similarities in texture between the Rawsonville sand and Lutzville sand, their enzyme activities (Figures 1, 2 and 3) differed considerably. Texture does not have an overriding effect on enzyme activity, according to previous research that showed that in a population of 20 arid region soils, urease activity correlated with neither sand, silt, nor clay percentage. 16 Whether the fact that the Lutzville sand was characterised by a lower initial organic carbon

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TECHNICAL YEARBOOK 2025