Technical Yearbook 2023

NOVEMBER

Winery wastewater for irrigation (Part 4): Soil responses By Carolyn Howell, Reckson Mulidzi, Lester Sassman & Karen Freitag

Wineries use potassium (K) and sodium (Na) based cleaning agents which results in high levels of these elements in its wastewater. 1 Therefore, using winery wastewater for irrigation adds substantial amounts of these salts to the soil. Introduction In a previous study where diluted winery wastewater was used for irrigation of a Cabernet Sauvignon vineyard growing on sandy soil, soil K and Na increased with a decrease in the dilution of the winery wastewater. 2 The use of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation in different environments also increased soil K and extractable potassium percentage (ExPP). 3 Wastewater containing high levels of K could be beneficial to overall soil fertility, except where accumulation of K in soils causes excessive uptake by grapevines. This could have negative effects on wine pH which is important for red wine

colour stability. However, excessive Na application and accumulation thereof with no concomitant increase in Ca and/or Mg could have negative effects on soil chemical and physical properties. This could reduce grapevine growth, yield and quality, particularly if the elements accumulate to toxic levels. Furthermore, if deep leaching of accumulated K and Na occur during winter, it could pollute natural water resources in the long run. The objective of this study was therefore to determine the effect of irrigation of open land and a vineyard with diluted winery wastewater on the soil chemical status in loamy sand to sandy clay loam soil. Methods Diluted winery wastewater was applied to open land on the Nietvoorbij research farm where 10 different fodder producing catch crops (table 1) were compared to a control treatment where no catch crop was cultivated in summer. Diluted winery wastewater was also applied to a Shiraz vineyard on the Nietvoorbij research farm 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

TABLE 1. The chemical status of the soil in the 0 - 150 mm soil layer of the open land irrigated full surface at Nietvoorbij research farm near Stellenbosch as determined in May 2020. Treatment no. Species pH (KCl) EC (mS/m) Extractable cations (cmol (+) /kg) K Ca Mg Na 1 Pearl millet 6.20 21 0.65 2.30 0.69 0.20 2 Barsweet sorghum 6.27 25 0.69 3.17 0.83 0.25 3 Fodder radish 6.07 27 0.60 2.73 0.85 0.26 4 Eragrostis teff 6.33 29 0.68 2.93 0.86 0.26 5 Cow peas 6.37 36 0.74 3.00 0.93 0.30 6 Chicory 6.60 21 0.78 3.10 0.92 0.24 7 Dolichos beans 6.47 24 0.76 2.40 0.79 0.23 8 Vetiver grass 6.30 43 0.73 3.43 1.03 0.27 9 Bottle brush grass 6.17 23 0.45 2.60 0.83 0.21 10 Weeping lovegrass 6.10 26 0.62 2.27 0.81 0.28 11 Bare soil 6.33 23 0.71 2.13 0.77 0.24 LSD (p=0.05) NS 12 NS NS NS NS

54

TECHNICAL YEARBOOK 2023