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The impact of wastewater irrigation by wineries on soils, crop growth and product quality
Expanded Title:Winery wastewater should be treated to specific quality standards, where after it could be stored in irrigation dams, and used for irrigation of crops. Until now, the impact of this practice has, however, not been studied comprehensively. Thus, to know the impact of irrigating with winery wastewater on the chemical composition and physical structure of the soil, grapevine performance, and wine quality, is indispensable. It is envisaged that irrigating vineyards with irrigation water with added winery wastewater might alter the wine character and overall quality, compared to vineyards irrigated with raw irrigation water. In this regard, a research project to investigate the possible use of augmented winery wastewater for vineyard irrigation was initiated and funded by the Water Research Commission with co-funding by Winetech. The general objective of the project was to investigate the sustainable use of winery wastewater for irrigation of vineyards with respect to the effect on soils, vineyard performance and wine quality. The project was a multidisciplinary study which evaluated the impact of augmented winery wastewater on soils, vineyard performance and wine quality, if any, due to poor water quality as the main objective. The possibility of re-cycling winery wastewater for vineyard irrigation was investigated in a field trial near Rawsonville in the Breede River Valley. Wastewater obtained from a co-operative winery was augmented to levels of 100 mg/L, 250 mg/L, 500 mg/L, 1000 mg/L, 1500 mg/L, 2000 mg/L, 2500 mg/L and 3000 mg/L chemical oxygen demand (COD), respectively, using raw water obtained from the Holsloot River. The augmentation was carried out individually for each concentration in 15 m3 tanks at the vineyard. Raw water from the river was used to irrigate the control grapevines. Soil samples were collected in the work rows of selected treatments after the application of wastewater irrigations in May, and again from all treatments at bud break, i.e. following winter. Samples were taken over 30 cm increments to a depth of 1.8 m. Although there were no clear trends in soil pH(KCl), ECe or acidity, ECe was substantially higher after the seasonal wastewater irrigations compared to bud break. This was probably due to the higher salt content in the augmented wastewaters. There was a close correlation between P applied via the irrigation water and the P levels in the 0 to 30 cm soil layer in the work row. Under the prevailing conditions soil K (Bray II) increased with a decrease in the dilution of the wastewater during all four seasons. Generally, soil Na increased with a decrease in the dilution of the wastewater. There were substantial differences in the amount of Na applied via the irrigation water. Although irrigation with winery wastewater had almost no other effects under the prevailing conditions, element accumulation, particularly with respect to K and Na, might be more prominent in heavier soils or in regions with low winter rainfall. Cover crops, i.e. Avena sativa L. cv. Pallinup (oats) and Pennisetum glaucum L. cv. Babala (pearl millet) were established in the work rows during winter and summer, respectively. The dry matter production (DMP) and element content of the above-ground growth of oats and pearl millet was determined over a period of four and three years, respectively. The fertiliser added (approximately R 2 800/ha/yr) to compensate for excess N and P intercepted by pearl millet, is much less than the R 15 000 to be made by selling the harvested crop for fodder. Employing only pearl millet as an interception crop could, therefore, be a sustainable practice if the COD level of the winery wastewater is between 1500 mg/L and 2500 mg/L. Soil microbial activity by enzyme analysis using a colorimetric assay was carried out in soils collected at different soil depth layers in grapevine rows over four seasons. The shifts in soil microbial communities were inconclusive, primarily due to inconsistent results. Glomalin content also decreased with an increase in soil depth, but did not respond to level of COD in the augmented wastewater. Given that both glomalin and soil microbial enzyme activity are considered good indicators of soil health, irrigation with winery wastewater should be of little to no consequence to general soil health. Irrigation of grapevines using winery wastewater augmented up to a maximum COD level of 3000 mg/L did not affect vegetative growth or any of the yield components compared to the raw water control. Consequently, the water use and water status of the grapevines was not affected by the wastewater irrigation under the given conditions. Since organic carbon did not accumulate in the soil during the study period, it suggested that the soil was sufficiently aerated between irrigation to allow oxidation. The latter probably explains why the grapevines did not respond to level of COD per se. However, it is important to note that the salinity and sodicity levels in the augmented winery wastewater were below the thresholds for grapevines. Under the prevailing conditions, irrigation of grapevines using winery wastewater augmented up to 3000 mg/L COD did not have any detrimental effects on juice ripeness parameters and ion content. Wine sensorial quality was also not affected. Under the conditions of the study, the high irrigation volumes were generally detrimental to wine quality. Since wine quality is an important aspect, particularly if wine needs to be exported, the poor overall quality is of great concern. However, there is ample evidence that less frequent irrigation, which allows higher levels of plant available water (PAW) depletion between irrigations, will enhance wine quality. This implies that the winery wastewater will probably have to be applied over large areas to allow sufficient PAW depletion between irrigations. Based on the project results, specific criteria should be considered for possible amendments to the General Authorization for wineries when using augmented wastewater for irrigation of vineyards.
Date Published:01/09/2014
Document Type:Research Report
Document Subjects:Agricultural Water - Small holder irrigation, Wastewater Management - Agricultural
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:1881/1/14
ISBN No:978-1-4312-0591-2
Authors:Myburgh PA; Howell CL
Project No:K5/1881
Document Size:3 491 KB
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