South African Journal of Enology and Viticulture

Changes in Physicochemical Properties and Enzyme Activities of Four Soils Following the Application of Alkaline Winery Wastewater over Three Simulated Irrigation Seasons

2025-03-10T08:06:24+00:00

The in-field fractional use (augmentation) of undiluted alkaline winery wastewater (WW) with raw water for the irrigation of grapevines can reduce the abstraction of water from natural resources and mitigate global water shortages. However, undiluted WW could pose a threat to soil function and enzyme activities, which are early soil quality indicators. Hence, this study used a pot experiment to compare changes in physicochemical properties and enzyme activities of four different soils irrigated with undiluted WW and municipal water (MW) over three simulated irrigation seasons. The soils were collected from the top 0 cm to 30 cm soil layer to which no WW had previously been applied – in the Stellenbosch (sandy loam and sand), Robertson (clay loam) and Lutzville (sand) regions. The water sources were MW, which served as the control, and undiluted WW, and they were both analysed before each irrigation event. Irrigation with undiluted WW resulted in larger increases in soil pH, electrical conductivity (EC) and exchangeable K and Na for all soils and simulated irrigation seasons. The activities of acid phosphatase, β-glucosidase and urease were negatively affected by the addition of undiluted WW. Changes in acid phosphatase activity were negatively correlated with changes in soil pH and EC, while changes in β-glucosidase activity were negatively correlated with changes in soil pH, EC and exchangeable K, Na and Mg. The pH had a dominant effect because of its influence on enzyme activities, precipitation reactions and the development of salinesodic soils. Root exudates, acidification from nitrogen fertiliser and the uptake of K by crops can mitigate the potential risk of using undiluted alkaline wastewater.

Investigating the Phenolic Composition of Merlot and Shiraz Grape Extracts and Wines Produced from Grapes With Different Seed-to-skin Ratios

2025-03-10T08:06:25+00:00

This study explored how Shiraz and Merlot grape extracts and wines made with different skin-to-seed ratios using various extraction methods differ in terms of phenolic composition. These methods included the Iland, Glories and machine-crushed techniques. Each method varied in extraction solvent, pH, extraction time and grape-processing techniques. The Iland method showed no significant differences between Shiraz and Merlot grapes in terms of anthocyanin concentration and colour density for all treatments. However, tannin concentrations and the total phenolic index varied significantly, with higher tannin levels generally observed in treatments with more seeds. Machine-crushed and microwave extraction did not significantly affect anthocyanin levels in the extracts, but showed differences in tannin concentrations, especially in Merlot grapes. The Glories method showed higher potential anthocyanin levels in the seedless treatments for both cultivars compared to those with seeds. However, the method’s evaluation of seed tannin contribution requires reassessment due to interesting findings in the seedless treatments. In winemaking, treatments with more seeds exhibited the highest anthocyanin and tannin levels, affecting the colour density and total phenolic index over time, especially with extended maceration time. Analysing tannin composition via phloroglucinolysis revealed that seed presence affected tannin molecular weight and composition, with notable differences observed between seedless and seeded treatments in the grape extracts and corresponding wines. Overall, the study underscores the intricate relationship between grape seed ratios, extraction methods and phenolic composition. The findings contribute to understanding how these factors affect wine phenolic composition and could contribute to future research on optimising phenolic extraction in winemaking.

Irrigation of Table Grapes With Refill Lines Set According to Midday Stem Water Potential - Soil Water Content and Seasonal Evapotranspiration

2025-03-10T08:06:25+00:00

Irrigation water is a limited resource in most table grape regions. Furthermore, agriculture competes with urban and industrial needs for water. If climate change reduces rainfall, it could put water resources under even more pressure. Therefore, table grape growers must use their available water efficiently by implementing sound irrigation scheduling practices. In this regard, it is fairly simple to measure midday stem water potential (Ψ_S) and calibrate instruments used for irrigation scheduling against Ψ_S. The objective of the study was therefore to develop guidelines to use this approach for table grape irrigation. The study was carried out in five red and five white commercial table grape vineyards in the Berg River Valley region. For each cultivar there were two plots adjacent to each other. The soil in the experiment plot was allowed to dry out until Ψ_S reached -0.8 MPa. The other plot was irrigated with the rest of the block according to the growers’ schedules. Soil water status and midday Ψ_S were measured concurrently to determine the relationship between grapevine and soil water status for each cultivar. Once irrigation refill points were established, grapevines in the experiment plots were irrigated accordingly for three seasons. The results showed that midday Ψ_S in most of the selected table grape cultivars was well correlated with the soil water content in the root zone. By using this approach to table grape vineyard irrigation scheduling, substantially less irrigation water was applied where grapevines were irrigated according to midday Ψ_S compared to the grower’s irrigation schedules.