Technical Yearbook 2023

AUGUST

Winery wastewater for irrigation (Part 1): Irrigation application

and water quality By Carolyn Howell, Karen Freitag & Lester Sassman

Globally, medium to large wineries generate more than 1.5 million litres of wastewater annually, whereas small wineries generate less than 1.5 million litres annually. 1 This wastewater can be used to irrigate crops to reduce energy use and treatment costs. However, irrigation with winery wastewater needs to be optimised to minimise leaching, whilst maximising nutrient removal by means of a catch crop is a necessity. Introduction In a previous study investigating the use of diluted winery wastewater for vineyard irrigation, Avena strigosa cv Saia (oats) and Pennisetum glaucum cv Babala (Pearl millet) removed significant amounts of K from a sandy soil, whilst generating additional income. 2 These species, however, consumed substantial amounts of N whereas the concentrations of Na removed were negligible. Additional N-fixing crops and grain crops adapted to soils with more than 4% clay that reach their peak growing period during the time that wineries produce the highest volumes of wastewater need to be identified. Therefore, the objective of the project was to identify fodder producing crops that would intercept sufficient K (and Na) applied via irrigation with diluted winery wastewater on loamy sand to sandy clay loam soils in both open land and a vineyard. The selected fodder producing crops should minimise/prevent leaching and accumulation of especially K in these soils and should not have a negative impact on grapevine performance and wine quality. In this specific article, the irrigation application and water quality will be presented. The characteristics of the catch crops to be evaluated in the study were described previously. 3 Annual grasses included in the evaluation were Pearl millet, Barsweet sorghum and Eragostris teff. Perennial grasses included in the study were Weeping lovegrass, Vetiver grass and Bottlebrush grass. Annual broadleaf crops include Fodder

radish. Perennial broadleaf species include Chicory. In the study, the annual legumes included were Cow peas and Dolischos beans. Methods Diluted winery wastewater was applied to open land on the Nietvoorbij research farm where 10 different fodder producing catch crops were compared to a control where no catch crop was cultivated in the summer (table 1). In the vineyard experiment, combinations of three different fodder producing summer catch crops and two winter cover crop treatments were compared to a control (table 2). In this instance, catch crops were not cultivated in the control treatment during the summer, but there were still two winter cover crop treatments. Pictures of the catch crops are shown in figure 1. Application of diluted winery wastewater The irrigation systems only became operational at the end of February 2017, therefore the catch crops could not be sown pre-harvest in the vineyard. The catch crops on the open land were sown in March 2017. Irrigations of 7.7 mm were applied to the open land at approximately weekly intervals. The average COD of the irrigation water applied was 2 994 mg/L and the EC was 106 mS/m. The volume of diluted winery wastewater applied to the open land in 2018 was increased to approximately 15 mm per week. The same amount of diluted winery wastewater was applied to the vineyard. Irrigations were applied to the open land and vineyard at approximately weekly intervals. The average COD and EC of the irrigation water applied were 3 138 mg/L and 150 mS/m, respectively. The average Na, K, Ca and Mg content of the irrigation water applied was 94 mg/L, 155 mg/L, 109 mg/L and 17 mg/L, respectively. As expected, the winery wastewater had high concentrations of K, Ca and Na. This is similar to previous findings. 4, 5, 6 No winery wastewater was available until 25 February 2019. Given that 16 mm of rain fell on 10 and 11 March, the irrigation of the open land and vineyard only commenced in late and mid-March, respectively. The open land was irrigated on 27/03/2019, 03/04/2019 and 28/05/2019. The vineyard was irrigated with diluted winery wastewater on 19/03/2019, 28/03/2019 and

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TECHNICAL YEARBOOK 2023