South Africa Wine Technical Yearbook 2025

depths in response to the application of WWW throughout the sampling period (Figure 2D). It increased from 4.6 to 5.0 in the topsoil and from 5.0 to 5.3 in the subsoil. Winter rainfall (Figure 2A) had an impact on soil pH. The pH values fluctuated during winter periods throughout the study period with the exception of the 60-90 cm depth wherein it remained constant from November 2011 until November 2013 (Figure 2D). After the winter rainfall seasons, soil pH decreased. This trend was observed throughout the study period with the exception of the 60-90 cm soil depth. The fact that pH was higher in the topsoil and in the subsoil implied that organic materials supplied by the WWW could be the source of the pH increase in the topsoil, while the leaching of salts to deeper soil layers increased soil pH there. It was previously reported that soil pH increased when organic anions were mineralised and H + ions were consumed after WWW application. 16 Although application of WWW increased soil pH by more than 0.2 units, the soil pH of the irrigated area remained acidic. Long-term application of WWW could lead to pH increase over time. It was expected that the G horizon would have had greater buffering capacity to pH increase than the sandy A and E horizons, but this was not the case. Soil EPP’ and ESP’ The EPP ’ showed an increasing trend throughout the sampling period (Figure 3A). The highest increase was in the 60-90 cm soil layer. The EPP’ showed similar trends to that of K extr (Figure 2B). Although no measurements were done beyond 90cm depth, it is possible that the EPP ’ could be higher at lower depth. These results indicate that the duplex Kroonstad soil did not retain the K + ions supplied via the winery wastewater. The soil ESP’ (Figure 3B) showed similar trends to Na extr (Figure 2C).

FIGURE 3. Temporal variation in soil (A) EPP’ and (B) ESP’ where winery wastewater was applied to a Kroonstad soil near Stellenbosch.

FIGURE 4. Temporal variation in soil (A) Ca 2+ and (B) Mg 2+ where winery wastewater was applied to a Kroonstad soil near Stellenbosch.

The reduction of ESP’ after May 2011 could be associated with low Na + in the WWW, as well as low soil Na + during a similar period (Figure 2C). Soil calcium and magnesium Application of WWW did not increase soil Ca extr during the study period although it fluctuated between sampling periods (Figure 4A). The WWW contained too low amounts

of Ca to make any significant impact in the soil to which it was applied. In addition, it should be noted that the application of WWW is unlikely to have any benefits of Ca 2+ supply to agricultural crops, because it is available in too small quantities from the wastewater. Results showed there was a slight increase of Mg extr only at 0-10 cm soil depth during November 2011,

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TECHNICAL YEARBOOK 2025