South Africa Wine Technical Yearbook 2025

Introduction More than 95% of South African wineries currently irrigate their wastewater onto land through sprinkler systems. 1 In this regard, in South Africa, the regulations for irrigating with winery wastewater (WWW) are contained in the General Authorisations for irrigation with wastewater. 2 It is well known that WWW contains high levels of potassium (K + ) and sodium (Na + ), because wineries use K + and Na + -based cleaning agents. 1 Therefore, using WWW for land disposal adds substantial amounts of these salts to the soil. Irrigation with WWW could be beneficial to overall soil fertility, although long-term application could have negative effects on soil chemical properties. 3,4,5,6 Land application of wastewater can increase the levels of soluble and exchangeable forms of K + more rapidly than with conventional inorganic fertilisers. 7 A survey carried out in South Africa to assess the soil chemical status where WWW had been disposed over prolonged periods showed that such irrigation increased soil K + to a depth of 90 cm. 8 In addition, the land disposal of WWW almost inevitably induced negative effects, irrespective of soil type. Furthermore, it was concluded that (i) in general, effluent disposal is poorly planned and managed, and disposal sites rarely seem to have been properly selected, because their soil properties are inappropriate for effluent disposal. In particular, deep sandy soils are unsuitable for disposal by ponding, mainly because of their high infiltration rates (IR), high permeability and low water storage capacity, and (ii) many disposal sites are too limited in area to permit the large volumes of effluent to be absorbed without surface runoff. This problem persists despite the presence of Kikuyu swards and sandy subsoil. In pastures irrigated with WWW for over 100 years, total organic carbon (TOC), nitrogen (N), K + , Na + , calcium (Ca 2+ ) and magnesium

FIGURE 1. The Longlands soil form near Rawsonville showing no clear stratification.

(Mg 2+ ) levels increased relative to the control. 9 Although soil K + , Na + , Ca 2+ and Mg 2+ of pastures irrigated with WWW for 15 to 20 years increased, these increases were not as substantial as where pastures had been irrigated for 100 years. Irrigation using WWW increased soil TOC. 4 In addition, soil K, as well as salinity and sodicity levels, were higher in wastewater-treated plots compared to control plots, particularly woodlot and pasture sites at certain wineries. Taking above-mentioned into consideration, the objective of the study was to investigate the effect of WWW irrigation on the chemical soil properties and potential environmental impacts at an existing grazing paddock at a winery near Rawsonville where WWW has been Details of the experimental site in an existing cultivated pasture grazing paddock where WWW had been applied for over 15 years have been given previously. 10 The trial layout, description of the application of the WWW to the experimental site, as well as water quality, have also been given previously. Characteristics and properties of the soil at the Rawsonville site The soils around Rawsonville were applied for many years. Materials and methods

formed from the alluvium of the Breede River and are relatively young. The soil at the site selected for the study showed no clear stratification (Figure 1) and contained a mottled subsoil, thus qualifying it for inclusion in the Longlands soil form 11 or a Gleyic, Albic, Arenosol. 12 The apedal soil consisted of fine sand. The B-horizon showed few fine mottles with distinct contrast and brown colour. Soil sampling and analysis Soils were collected as described previously. 10 Briefly, initial samples were collected before the start of the study in March 2011. Thereafter, samples were collected twice a year at 0-10 cm, 10-20 cm, 20-30 cm, 30-60 cm and 60-90 cm depth layers. All analyses were carried out by a commercial laboratory according to methods described previously. 10 Results Initial soil chemical status After continuous irrigation with WWW for 15 years, the soil was acidic throughout the profile, i.e. the pH (KCl) was less than 4.5 (Table 1). The soil Bray II P was high in all soil layers, i.e. more than 20 mg/kg which is considered to be the norm for sandy soils The basic cations declined with depth. By far the highest concentration of all cations occurred in the 0-10 cm layer. These

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TECHNICAL YEARBOOK 2025