Technical Yearbook 2024

K could lead to an increase in K uptake by grapevines. This could have negative consequences on grapevine responses, such as musts with high pH, malate concentrations and poor colour. 22,23,24 However, the effect of soil K on K concentrations in must is often negligible unless excessive amounts are applied. 22 Soil EPP´ at the C1 experimental plot in September 2021 was higher than baseline levels for all the soil layers (Figure 4). It should be noted that in the Western Cape fruit industry, the recommended ratio of exchangeable K is 3 - 4% of the cation exchange capacity. 25 Soil EPP´ at the C2 experimental plot in September 2021 was higher than the baseline levels up to a depth of 90 cm (Figure 4). The greater accumulation of K in the soils of the Coastal region was a result of higher amounts of K applied via the irrigation water in the 2020/21 season. 13 Soil EPP´ in all the soil layers of the BR1 and BR2 experimental plots was higher than the baseline values (Figure 4). This trend suggested an accumulation of salts during the grapevine growing season due to irrigation with winery wastewater, which contains salts. 3 In heavier soils, less effective leaching is more likely to result in salt accumulation. Soil EPP´ of the LOR1 experimental plot in September 2021 was substantially higher up to a depth of 150 cm compared to baseline values (Figure 4). The soil EPP´ of the LOR2 experimental plot when the winery wastewater irrigation was terminated was substantially higher compared to the baseline values (Figure 4). At the end of the trial in September 2021, soil EPP´ was substantially higher for all of the experimental plots compared to their controls (Figure 4). This was expected given that the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation consistently increased soil K of the experimental plots compared to their respective controls (Figure 3). In September 2021, soil Ca and Mg were higher for the C2 and BR2 experimental plots compared to their respective controls (data not shown). In contrast, soil Na of all the experimental plots was similar or lower compared to their respective controls (data not shown), indicating sufficient leaching of Na at all the experimental plots, regardless of soil texture. Consequently, the ESP´ of the soils from the experimental plots and their respective controls were similar (data not shown). Acknowledgements • This report is an output of WRC Project K5/2561, entitled “Use of winery wastewater as a resource for irrigation of vineyards in different environments”. This

Conclusion Under the prevailing conditions, soil pH (KCl) increased consistently in response to the in field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. As expected, soil K was substantially higher for the experimental plots compared to their respective controls regardless of mean annual rainfall. Consequently, soil EPP´ was higher where the in-field fractional use (augmentation) of winery wastewater with raw water was used for vineyard irrigation. Results indicated that the soil K accumulation and consequent increase in soil EPP´ was related to soil texture, amounts of K applied via the irrigation water and the mean annual rainfall. The K increases could have a negative impact on wine colour stability should K be taken up by the grapevine in sufficient quantities. In contrast, soil Na of all the experimental plots was similar or even lower compared to their respective controls. This indicated sufficient Na leaching at all the experimental plots, regardless of soil texture. However, where more Na is applied via the irrigation water, Na could accumulate to levels where it could negatively impact soil physical conditions or grapevine growth and yield. Grapevine and wine responses will be presented in the next article.  solicited project was initiated, funded and managed by the WRC. The project was co-funded by Winetech and ARC. • 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. • Backsberg, Madeba, Lutzville Winery and Spruitdrift Winery for permitting the project team to work at their wineries and in their vineyards. Colleagues at the wineries for their assistance and support. • Mr W. Smit from Netafim for advice and designing the irrigation systems.

References https://www.wineland.co.za/in-field-fractional-use-of-winery-wastewater-with-raw-water-part-3/

For more information, contact Carolyn Howell at howellc@arc.agric.za.

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TECHNICAL YEARBOOK 2024