Doctoral Degrees (Soil Science)

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Browsing Doctoral Degrees (Soil Science) by Author "Howell, Carolyn Louise"

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    Using diluted winery effluent for irrigation of Vitis Vinifera. Cv. Cabernet Saugvignon and the impact thereof on soil properties with special reference to selected grapevine responses.
    (Stellenbosch : Stellenbosch University, 2016-03) Howell, Carolyn Louise; Hoffman, J. E.; Myburgh, P. A.; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.
    ENGLISH ABSTRACT: Wine production is an important industry in the Western and the Northern Cape regions of South Africa. Wineries produce large volumes of poor quality wastewater, particularly during harvest. International requirements, as well as national legislation, are putting pressure on wine producers regarding the responsible management of winery wastewater, which may have a large-scale detrimental impact on the environment. Currently, the Department of Water and Sanitation is drafting new legislation aimed at wineries to allow beneficial crop irrigation as a General Authorisation. In this regard, a multidisciplinary research project to investigate the impact of diluted winery wastewater on soils, crop growth and product quality was initiated and funded by the Water Research Commission of South Africa. The project was also co-funded by Winetech and the Agricultural Research Council. The possible re-use of winery wastewater for vineyard irrigation was investigated in a Cabernet Sauvignon vineyard in a sandy soil near Rawsonville in the Breede River Valley. Wastewater obtained from a co-operative winery was diluted to levels of 100, 250, 500, 1000, 1500, 2000, 2500 and 3000 mg/L chemical oxygen demand (COD), using water obtained from the Holsloot River. The dilution was carried out individually for each concentration in 15 m3 tanks at the vineyard. Control grapevines were irrigated with river water. In addition to the field trial, a pot trial was also included to determine the effect of diluted winery wastewater on near-saturation hydraulic conductivity (K) of four different soils. In general, soil potassium and sodium increased with an increase in COD level of the diluted winery wastewater, i.e. a decrease in dilution of the wastewater. Although irrigation using diluted winery wastewater had almost no other effects, element accumulation particularly with respect to potassium and sodium, might be more prominent in soils with higher clay contents or in regions with low winter rainfall. After three years, near-saturation hydraulic conductivity of shale-derived soil, alluvial and aeolian sands decreased with a decrease in the level of wastewater dilution. This indicated that severe degradation in hydraulic properties can occur if diluted winery wastewater is used for irrigation, and might even be aggravated if undiluted winery wastewater is used. Irrigation of grapevines using diluted winery wastewater did not affect grapevine water status, vegetative growth, production or evapotranspiration, irrespective of the level of dilution. Results showed that irrigation of grapevines using diluted winery wastewater did not have detrimental effects on juice characteristics with regard to ripeness parameters and ion content. Wine sensorial characteristics were not affected by irrigation using diluted winery wastewater. The grapevines did not respond to level of COD per se. This indicated that sufficient aeration occurred between irrigations which allowed organic carbon breakdown. Although salinity and sodicity levels in the diluted winery wastewater were below the thresholds where growth and yield reductions are expected for grapevines, it should be monitored frequently. The low salinity and sodicity levels in the diluted winery wastewater could be a further explanation why the grapevines did not respond negatively to the wastewater irrigation. Based on the above-mentioned results, the following criteria should be considered for possible amendments to the General Authorisations for wineries when using diluted wastewater for vineyard irrigation: (i) COD must be diluted to 3000 mg/L or less, preferably to less than 2000 mg/L to avoid unpleasant odours in the vineyard during irrigations, (ii) electrical conductivity (ECiw) must be less than 0.75 dS/m, (iii) sodium adsorption ratio (SARiw) must be less than 5, (iv) the soil must have a low cation exchange capacity, (v) unrestricted internal drainage in the root zone, (vi) irrigation water must not percolate beyond the root depth, (vii) only micro-sprinklers should be used, (viii) irrigation must be applied in such a way that bunches are not wetted, (ix) at least 50% plant available water depletion should be allowed between irrigations to allow sufficient aeration for oxidation of organic material applied via the irrigation water and (x) irrigation frequency and volumes must be such that wine quality is not reduced.