Technical Yearbook 2024

activities come to an end and maximum usage of hydroxide occurs. Beyond the harvest, wastewater production is at its lowest. The major origin of winery wastewater is water used for cleaning processes and makes up approximately 78% of the wastewater generated. This water is from alkaline washing, neutralisation and rinsing water used for tanks, floors, transfer lines, bottles and barrels. These actions will increase the Na, K and H 2 PO 4 - levels in the wastewater, consequently there will be a variation in pH and an increase in electrical conductivity (EC), chemical oxygen demand (COD) and SAR. Regarding the legal requirements for irrigation water quality in South Africa, 12,13 COD, pH, EC and SAR are considered to be important. Results from a survey carried out to evaluate winery wastewater generated by South African wineries showed that the water quality parameters vary substantially between wineries. 14 Furthermore, there was a strong seasonal variation in the winery wastewater quality. A similar seasonal trend was reported for winery wastewater in Australia. 15 These trends were confirmed where wastewaters of two wineries were monitored frequently. 16 In this specific article the irrigation application, water quality and nutrient load will be presented. In brief, the primary objective of the project was to assess the fitness for use of winery wastewater for irrigation of different soil types with varying rainfall quantities and leaching levels on vineyard performance in terms of yield and quality under field conditions, as well as measuring the change in mainly Na and K status of soils. Methods At most of the experimental plots, grapevines were irrigated with the in-field fractional use (augmentation) of winery wastewater with raw water from mid-February when suitable wastewater became available from vintage processes. According to this approach, grapevines were irrigated as follows. 5 For each irrigation, 50% of the irrigation requirement was applied as undiluted winery wastewater. Raw water was applied for the other 50% of the irrigation requirement. The application of irrigations was stopped either in mid-April or the beginning of May each year when the winter rainfalls began. Irrigation was applied by means of micro-sprinklers in order to apply larger volumes of water. It should be noted that experimental grapevines were irrigated so that optimum wine quality would be obtained. Therefore, stem water potential ( Ψ S ) thresholds for optimum wine quality for the specific cultivars were used to set up the irrigation refill lines. Water meters were used to monitor the irrigation volumes of winery wastewater and raw water applied to each experimental plot. The soil water content (SWC) was measured by means of the neutron scattering technique. Three access tubes were installed on the grapevine row at each of the six experimental plots at the beginning of the project. The mean SWC of each experimental plot was calculated as the average of SWC measured at the three individual access tubes. Measurements were taken in 30 cm increments up to

a depth of 90 cm in all experimental plots and up to 180 cm in plots where deeper measurements were possible. Measurements were taken every two to three weeks, as well as before and after every irrigation application. Approximately one hour after the in-field fractional use (augmentation) of winery wastewater with raw water commenced, a 2 L sample of the undiluted winery wastewater was collected. A sample was also collected when the raw water was applied. Samples were analysed for COD at ARC. They were also analysed by commercial laboratories (Bemlab, Strand and Labserve, Stellenbosch) according to previously reported methods. 17 The potassium adsorption ratio (PAR) and SAR of the water samples was calculated. For each irrigation, the amount of raw and winery wastewater applied, as well as the element concentrations in the undiluted winery wastewater and raw water were used to calculate the amounts of elements added to the soil per irrigation per hectare. The amount of elements applied per irrigation, i.e. the undiluted winery wastewater irrigation plus the raw water irrigation, were summed to obtain the seasonal applications. Results Irrigation application In the 2017/18 season, two irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the loamy sand (C1) and sandy clay loam (C2) experimental plots in the Coastal region. Two irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the sandy loam (BR1) and sandy clay loam (BR2) experimental plots in the Breede River region. Five and six irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the deep sand (LOR1) and shallow sand (LOR2) experimental plots in the Lower Olifants River region, respectively. In the 2018/19 season, two raw water irrigations and three irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the C1 experimental plot (Figure 1). Three irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the C2 experimental plot. Three and two irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the BR1 and BR2 experimental plots, respectively. The in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation commenced at the LOR1 and LOR2 experimental plots at the beginning of the season. In total, four irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the LOR1 experimental plot. Visual observations in the LOR2 vineyard (Figure 2) in November 2018 revealed that the grapevines were growing poorly. After consideration of the EC of the undiluted winery wastewater,

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TECHNICAL YEARBOOK 2024