South Africa Wine Technical Yearbook 2025

TABLE 4. Seasonal balances for soil Na + in the 90 cm depth increment of a sandy Kroonstad soil that was irrigated with winery wastewater near Stellenbosch. Period Soil Na + (kg/ha)

Conclusions Due to the high volumes of WWW irrigation plus rainfall, the inevitable over-irrigation leached large amounts of cations, particularly K + and Na + , beyond the 90 cm depth. Unfortunately, the leached elements are bound to end up in natural water resources in the long run. Irrigation with 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. WWW by means of irrigation is definitely not the ultimate solution to the problem. Land disposal can only be recommended where the wastewater application does not exceed the water requirement of the grazing crop, or any other agricultural crop. 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. Soil samples must be collected as deep as practically possible to make sure that elements applied via the WWW do not accumulate below the root zone. Soil responses at a winery near Rawsonville will be presented in the next article.  Due to the risks involved as discussed above, disposal of

Applied Na + (kg/ ha)

Na + loss (kg/ha)

Leached Na + (%)

Beginning

End

Mar 11 - May 11 May 11 - Nov 11 Nov 11 - May 12 May 12 - Nov 12 Nov 12 - May 13 May 13 - Nov 13

366 514 411 283 221 155

514 411 283 221 155 221

1 645 1 497 1 331 1 459 1 262 1 324 1 139 1 205 1 713 1 647 333 436

91 * 131 110 105 106

96 * 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 6. Effect of cumulative (Σ) irrigation plus rain on cumulative Na + losses beyond 90 cm depth where a Kroonstad soil was irrigated with winery wastewater for two and a half years near Stellenbosch.

cumulative leached Na + was linearly related to the cumulative irrigation plus rainfall (Figure 6). Similar to K + , the low clay content of the soil could not retain large amounts of Na + . Therefore, leaching of Na + beyond 90 cm was also not inhibited. Although, leaching of Na + from sandy or coarse-textured soils during winter rainfall also reduces the risk of accumulation and dispersion, it poses the same environmental risks as the large amounts of K + that were leached from the soil. Acknowledgements • This article is an output of WRC

by wineries on soils, crop growth and product quality”. This solicited project was initiated, funded and managed by the WRC. The project was co-funded by Winetech and ARC. • Goudini and Koelenhof wineries for their permission to work at their land and utilisation of their wastewater for research. • ARC for infrastructure and resources. • Staff of the Soil and Water Science division at ARC Infruitec-Nietvoorbij for their assistance, and in particular Mr. F. Baron for his dedicated technical support.

Project K5/1881, entitled “The impact of wastewater irrigation

For more information, contact Reckson Mulidzi at mulidzir@arc.agric.za. Reference https://www.wineland.co.za/winery-wastewater-irrigation-part-2/

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TECHNICAL YEARBOOK 2025