South Africa Wine Technical Yearbook 2025

FIGURE 2. Effect of K + applied via irrigation with diluted winery wastewater over four seasons on the extractable potassium percentage (EPP') in the 0-10 cm and 10-20 cm layers of (A) Rawsonville sand, (B) Lutzville sand, (C) Stellenbosch shale, and (D) Stellenbosch granite soils. The dashed line indicates the critical EPP' threshold for grapevines. Values designated by the same letter do not differ significantly (p ≤ 0.05).

FIGURE 3. Effect of Na + applied via irrigation with diluted winery wastewater over four seasons on the extractable Na + in the 0-10 cm and 10-20 cm layers of (A) Rawsonville sand, (B) Lutzville sand, (C) Stellenbosch shale, and (D) Stellenbosch granite soils. The encircled data point was regarded as an outlier due to experimental error and was not included in the equation. Values designated by the same letter do not differ significantly (p ≤ 0.05).

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TECHNICAL YEARBOOK 2025