South Africa Wine Technical Yearbook 2025

TABLE 3. Soil extractable Na + balances for selected periods in the 0-90 cm depth of a sandy Longlands soil that was irrigated with winery wastewater near Rawsonville. Period Soil Na + (kg/ha) Applied Na + (kg/ha) Na + loss (kg/ha) Leached Na + (%) * Beginning End Mar 11 - May 11 1 035 1 173 1 117 979 88 May 11 - Nov 11 1 173 1 484 1 060 749 71 Nov 11 - May 12 1 484 2 664 2 734 1 354 50 May 12 - Nov 12 2 864 1 484 2 076 3 456 167 Nov 12 - May 13 1 484 2 001 3 046 2 529 83 May 13 - Nov 13 2 001 1 553 2 658 3 106 117 * Amount lost through leaching expressed as percentage of the amount applied, a figure of >100 indicating that more was lost through leaching than what was applied during that period.

FIGURE 8. Effect of cumulative (Σ) irrigation plus rain on cumulative Na + losses beyond 90 cm depth where a Longlands soil was irrigated with winery wastewater for two and a half years near Rawsonville.

Conclusions It is important to note that the study represented the worst-case scenario, i.e. the WWW disposal was carried out in a smaller paddock. Due to the high volumes of WWW irrigation plus rainfall, the inevitable over-irrigation leached large amounts of cations, particularly K + and Na + , beyond 90 cm depth in the Longlands soils. Unfortunately, the leached elements are bound to end up in natural water resources in the long run. Irrigation with the WWW did not have a pronounced effect on soil pH (KCl) . The study confirmed that injudicious irrigation with untreated WWW poses a serious environmental hazard, particularly where crops in sandy soils are irrigated. Due to the risks involved as discussed above, disposal of WWW by means of irrigation is definitely not the ultimate solution to the problem. Land disposal can only be recommended where the WWW application does not exceed the water requirement of the grazing crop, or any other agricultural crop. Wastewater application according to the K + requirement of the crop is also very crucial. This means that the WWW needs to be distributed on an area of land that is big enough so that the daily applications do not cause over-irrigation. Therefore, sound wastewater management can only be achieved by means of irrigation scheduling based

on frequent soil water content measurements. Care should be taken that the irrigation water does not leach beyond the root zone. The soil chemical status should be determined at least annually. The basis to which wastewater should be applied for a given crop should be based on water and nutrients requirement such as K + . Depending on the type of soil and quality of wastewater, each winery will need to determine the size of land needed for irrigation with WWW high in K + . The winery will also have to consider the electricity costs if wastewater needs to be pumped from nearby farms in order to be utilised for a crop requirement. Based on the foregoing, it is essential that future research should focus on selecting halophytic crops that are capable of absorbing the applied elements, particularly K + and Na + , if land disposal of WWW is the only option. Preferably, the foliage and roots or tubers should be removed from the land when the crop is harvested. The effects of K:Na ratio in diluted or undiluted WWW on soil structure stability, K + availability and leaching of elements also need to be addressed by continued research. Since the climate, particularly rainfall, will affect the accumulation and/or leaching of the elements, it is important that the research is carried out in field studies. 

For more information, contact Reckson Mulidzi at mulidzir@arc.agric.za. Reference https://wineland.co.za/winery-wastewater-irrigation-part-3/

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TECHNICAL YEARBOOK 2025