South Africa Wine Technical Yearbook 2025

FIGURE 1. The effect of municipal water and winery wastewater (WWW) on the urease activity (μg NH 4 + g/h) 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.

soils, namely a Rawsonville sand, Lutzville sand, Stellenbosch shale and Stellenbosch granite, were included in the pot experiment. The control treatment soils were irrigated with municipal water. For the wastewater treatments, WWW was diluted to a chemical oxygen demand (COD) level of 3 000 mg/L. Soil sampling and analyses After SS3 and SS4, the soil material representing the 0-10 cm and 10-20 cm depth intervals from each pot was analysed in the ARC Infruitec-Nietvoorbij soil microbiology laboratory to determine the activities of β-glucosidase, acid phosphatase and urease. These two seasons were selected because it was assumed that a degree of equilibration between water and soil had taken place during the course of the preceding two simulated seasons. Enzyme activities were determined by the Soil Microbiological Laboratory at ARC Infruitec-Nietvoorbij according

they are likely to persist in soils for periods that exceed the lifespans of the microorganisms that produced them. 4 The rates at which organic compounds break down are therefore likely to be more closely related to the abundance and activity of enzymes than to the numbers of microorganisms present. 5 Urease is a soil enzyme that facilitates the hydrolysis of urea into NH 3 + and CO 2 , increasing soil pH in the process. 6 β-glucosidase, another soil enzyme, biodegrades carbon (C) compounds to form glucose, which is an energy source for the soil microbial population. 7 β-glucosidase activity varies with soil OM content and type, 8 and relates positively to water-soluble carbon, total organic carbon and pH. 9 Phosphatases, on the other hand, facilitate the cycling of phosphorus (P). 10 The activities of most soil enzymes are affected by factors such as soil OM content, cropping history, soil amendment applications and temperature. 7 Enzyme activities reflect both short and long-term

changes in their respective pools of substrates and products, and are considered to be useful indicators of soil health and fertility. 11,12,13,14 To what extent enzyme activities change in response to the practice of irrigating with winery wastewater (WWW) under vineyard conditions in the Western Cape is nevertheless unknown, but it is likely that Western Cape soils will differ in their effects on enzyme activity. Taking above mentioned into consideration, the objective of this study was to determine the effects of irrigation with diluted WWW on the activities of urease, beta-glucosidase and phosphatase of four soils varying in parent material and clay content. Materials and methods Experimental layout Details of the pot experiment were given previously. 15 In brief, a pot experiment was carried out under a 20 m x 40 m translucent fibreglass rain shelter at ARC Infruitec-Nietvoorbij. Four different

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TECHNICAL YEARBOOK 2025