Technical Yearbook 2024

fractional use (augmentation) of winery wastewater with raw water for irrigation promoted the accumulation of nitrogen (N) and phosphorus (P) in the roots of the LOR2 experimental grapevines (Figure 2). Furthermore, the Na and chloride (Cl) in the grapevine roots (Figure 3) sampled from the LOR2 shallow sand experimental plot were substantially higher compared to those of the control, which had been irrigated with raw water only (Figure 3). This indicated that the grapevine stored these elements in its below-ground structure. The in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation promoted the accumulation of P and K in the roots of the experimental grapevines at the LOR1 deep sand plot measured in May 2021 (Figure 4). In contrast to the LOR2 shallow sand experimental plot, there were no detrimental effects of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation on Na and Cl accumulation in the grapevine roots at the LOR1 deep sand experimental plot (Figure 5). Permanent wood At pruning in July 2019, visual observation revealed that salts had precipitated on the grapevine trunks in the LOR2 experimental plot after two seasons of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. The Na, manganese (Mn) and iron (Fe) in permanent wood sampled from grapevines in the LOR2 shallow sand experimental plot in September 2019 was substantially higher compared to the control (Table 1). This indicated that the grapevine stored these elements in the permanent above-ground structure. Although grapevines in the experimental plot were irrigated with raw water from September 2019, the damage to the grapevine trunks was still visible at the end of November

FIGURE 2. Variation in (A) N, (B) P and (C) K in the grapevine roots sampled from the 0 - 30 cm and 30 - 60 cm soil depth layers at LOR2.

were washed carefully, dried and analysed by a commercial laboratory as described previously. 2 Permanent wood was sampled at the LOR2 shallow sand experimental plot and control in September 2019 and July 2021. Permanent wood was sampled at the LOR1 deep sand experimental plot and control in July 2021. Samples were analysed as described previously. Results Soil In September 2019, soil potassium (K) of the LOR2 experimental plot was considerably higher than the control to a depth of 90 cm (Figure

1). In contrast, soil sodium (Na) only tended to be higher to a depth of 60 cm in the root zone. This suggested that the raw water irrigation had leached the Na beyond the root depth. In this case, the Na was probably released over time as the parent material weathered after soil preparation. It should be noted that the soil Na in the 30 - 60 cm layer of the experimental plot was above the proposed norm of 0.4 cmol/kg, where negative grapevine responses can be expected (Conradie, personal communication). Roots Results indicated that the in-field

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TECHNICAL YEARBOOK 2024