Technical Yearbook 2024

Methods Details of the plot selection, augmentation, climatic conditions, irrigation application, water quality and nutrient load were given previously. 13 Briefly, there was a loamy sand (C1) and sandy clay loam (C2) experimental plot in the Coastal region, a sandy loam (BR1) and sandy clay loam (BR2) experimental plot in the Breede River region, as well as a deep sand (LOR1) and shallow sand (LOR2) experimental plot in the Lower Olifants River region. Experimental plots were irrigated using the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. Baseline soil samples were collected at the six plots between July and August 2017 before the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation commenced. Each of the vineyards had an experimental plot that was irrigated with winery wastewater, and this was compared to the rest of the surrounding block, which acted as the control at the end of the project in September 2021. Samples were collected at three positions along the grapevine row. Samples for each depth were pooled together to create a composite sample. They were collected over 30 cm increments to a depth of at least 60 cm in all experimental and control plots and up to 300 cm at the LOR2 deep sand plot using a modified soil auger (Figure 1). A commercial laboratory analysed the samples for chemical parameters according to methods described previously. 11 The extractable sodium percentage (ESP´) and extractable potassium percentage (EPP´) of the soils were calculated. Results Soil pH (KCl) of the C1 and C2 experimental plots was lower in September 2021 compared to the baseline values (Figure 2) and was still within the norm of 5.0 - 7.5 recommended for optimal grapevine growth. 14 In September 2021, the soil pH (KCl) of the BR1 experimental plot was lower than the baseline values for the 30 - 60 cm and 60 - 90 cm soil layers (Figure 2). The soil pH (KCl) for the BR2 experimental plot was generally lower in September 2021 compared to the baseline values. In contrast, the soil pH (KCl) of the LOR1 experimental plot tended to be higher in September 2021 compared to the baseline values (Figure 2). It was previously reported that after two seasons of being irrigated according to the in-field fractional use (augmentation) of winery wastewater with raw water, grapevines at the LOR2 experimental plot were performing poorly. Therefore, the wastewater irrigation had to be terminated at the beginning of the 2019/20 season to prevent any further damage. The soil pH (KCl) of the LOR2 experimental plot when the winery wastewater irrigation was terminated was similar to the baseline values. With the exception of the LOR2 plot, in September 2021, the soil pH (KCl) of experimental plots was higher compared to their respective controls (Figure 2) and was still within

FIGURE 1. A modified soil auger was used to collect soil samples to a 3 m depth at the LOR1 deep sand experimental plot.

The latter practice also resulted in higher Na and K in vineyard soils compared to a control vineyard which was irrigated with river water. 9 In a field study where grapevines were irrigated with simulated winery wastewater, soil Na levels in the 0 - 20 cm and 20 - 40 cm layers increased. 10 The addition of wine to the simulated winery wastewater enhanced K movement to the sub-soil. In a field study where grapevines were irrigated with diluted winery wastewater, the element concentrations in an alluvial, sandy soil did not respond to the irrigation with the exception of K and Na. 11 This was probably due to the low levels of the other elements applied via the irrigation with diluted winery wastewater in relation to the K and Na. Leaching of cations, particularly K and Na occurred from only four of six different soils in a pot experiment where the soils were irrigated with winery wastewater and winter rainfall was simulated. 12 The simulated rainfall was too low for sandy and clay soil to allow leaching. Furthermore, more cations were leached from the sandy soils compared to the two heavier soils. Taking the above-mentioned into consideration, the aim of this study was to determine the effect of in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation on the chemical status of different soils to assess the fitness for use of winery wastewater for irrigation of different soil types with varying rainfall.

57

TECHNICAL YEARBOOK 2024