South Africa Wine Technical Yearbook 2025

FIGURE 3. Effect of irrigation with river water and winery wastewater diluted to 3 000 mg/L COD (After Irr.), followed by simulated winter rainfall (After R) on extractable soil K + for (A) Rawsonville sand, (B) Lutzville sand, (C) Stellenbosch shale, (D) Stellenbosch granite, (E) Stellenbosch sand, and (F) Robertson clay.

after the simulated rainfall, irrespective of the water used for irrigation. At this stage, there is no explanation for these unexpected results for soil Ca 2+ extr and Mg 2+ extr . Acknowledgements • This article is an output of WRC Project K5/1881, entitled “The impact of wastewater irrigation by wineries on soils, crop growth and product quality”. This solicited project was initiated, funded and managed by the WRC. The project was co-funded by Winetech and ARC. • Goudini Winery for providing wastewater for the research. • 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.

applied. This confirms the importance of using natural rainfall for leaching studies. Calcium and magnesium: Although more Ca 2+ was applied via the diluted WWW, it had no effect on the level of soil Ca 2+ extr compared to the irrigation with river water, irrespective of soil type (data not shown). This indicated that the 35 mg/L Ca 2+ in the WWW was too low to increase the soil Ca 2+ extr . Likewise, the simulated rainfall had no effect on the soil Ca 2+ extr , except for a substantial increase in the Robertson clay. Similar to Ca 2+ extr , irrigation with diluted WWW had no effect on the level of soil Mg 2+ extr compared to the irrigation with river water, irrespective of soil type (data not shown). The simulated rainfall had no effect on the Mg 2+ extr in most soils. However, the Mg 2+ extr increased in the Stellenbosch granite irrigated with WWW before the rainfall simulation. The Mg 2+ extr in the Robertson clay also increased

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TECHNICAL YEARBOOK 2025