Technical Yearbook 2023

TABLE 2. The chemical status of the soil in the 0 - 150 mm soil layer of the micro-sprinkler irrigated Shiraz/110 Richter vineyard irrigated full surface at Nietvoorbij research farm near Stellenbosch as determined in May 2020. Treatment no. Catch crop/cover crop combination pH (KCl) EC (mS/m) Extractable cations (cmol (+) /kg) K Ca Mg Na 1 Pearl millet/Oats 5.87 22 0.50 2.57 0.75 0.18 2 Pearl millet/N-fixing mixture 5.93 18 0.50 2.60 0.80 0.17 3 Dolichos beans/Oats 5.83 33 0.51 2.53 0.78 0.18 4 Dolichos beans/N-fixing mixture 5.77 28 0.50 2.67 0.72 0.20 5 Chicory/Oats 6.10 22 0.42 2.70 0.76 0.23 6 Chicory/N-fixing mixture 6.10 20 0.50 2.70 0.81 0.18 7 None/Oats 5.20 22 0.25 2.47 0.69 0.13 8 None/N-fixing mixture 5.10 49 0.32 3.03 0.90 0.18 LSD (p=0.05) 0.49 18 NS NS NS NS

have been reported previously. 2,3,7,8 Trends after three years for the Shiraz vineyard are given in figure 2. Irrespective of catch crops, the use of diluted winery wastewater for irrigation of the vineyard increased soil K compared to the raw water treatments compared to the pre-treatment values (figure 2). Consequently, ExPP increased (data not shown). Conclusions There were no significant differences in soil K, Ca, Mg and Na that could be related to the different summer catch crop and bare soil treatments of the open land where diluted winery wastewater was used for irrigation. Using diluted winery wastewater for irrigation of the open land increased soil pH (KCl) , K and Na over time regardless of the catch crops cultivated. The application of diluted winery wastewater rather than raw water in the vineyard, regardless of the catch crop cultivated, tended to increase soil K, particularly in the top-soil. This was expected given that winery wastewater contains high levels of K. Although irrigation with diluted winery wastewater had almost no other effects, element accumulation particularly with respect to K and Na, might be more prominent in regions with lower winter rainfall. It should be noted that in lighter textured soils, more effective leaching is likely to result in less salt accumulation. Abstract Wineries use potassium (K) and sodium (Na) based cleaning agents which results in high levels of these elements in its wastewater. Using winery wastewater for irrigation therefore adds substantial amounts of these salts to the soil. The objective of this study was to determine the effect of irrigation of open land and a vineyard with diluted winery wastewater on the soil chemical status. Diluted winery wastewater was applied to open land where the soil

of 10 different fodder producing catch crops were compared to the soil of a control where no summer catch crop was cultivated. Diluted winery wastewater was also applied to a Shiraz vineyard where combinations of three different fodder producing summer catch crops and two winter cover crop treatments were compared to a control. Catch crops were not cultivated in the control treatment during the summer, but there were still two winter cover crop treatments. The region where the field trials took place has a Mediterranean climate. There were no significant differences in soil K, Ca, Mg and Na of the open land experiment that could be related to the different summer catch crop and bare soil treatments. Trends after four years showed that using diluted winery wastewater for irrigation of the open land increased soil pH (KCl) , K and Na regardless of the catch crops cultivated when compared to pre-treatment values. The application of diluted winery wastewater rather than raw water in the vineyard, regardless of the catch crop cultivated, tended to increase soil K, particularly in the top soil. It should be noted that in lighter textured soils, more effective leaching is likely to result in less salt accumulation in the top-soil. Irrigation using diluted winery wastewater might also cause more prominent K and Na accumulation in regions with low winter rainfall. Acknowledgements • The project was funded by Winetech and the Agricultural Research Council (ARC). • ARC for infrastructure and resources. • Staff of the Soil and Water Science division at ARC Infruitec-Nietvoorbij for technical support.  References https://www.wineland.co.za/winery-wastewater-for irrigation-part-4/

For more information, contact Carolyn Howell at howellc@arc.agric.za.

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TECHNICAL YEARBOOK 2023