Browsing by Author "Mulidzi, Azwimbavhi Reckson"

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    The effect of winery wastewater irrigation on the properties of selected soils from the South African wine region
    (Stellenbosch : Stellenbosch University, 2016-12) Mulidzi, Azwimbavhi Reckson; Clarke, Catherine E.; Myburgh, P. A.; Roychoudhury, A. V.; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: Due to an increase in wine production as well as an intensification of environmental legislation in South Africa, the need for guidelines for sustainable management of winery wastewater has increased. To address this, the first part of the study focused on the seasonal dynamics of the volumes and quality of undiluted winery wastewater. The soil chemical dynamics were monitored in two different soils that were irrigated with undiluted winery wastewater for three years. Over-irrigation with undiluted winery wastewater in combination with winter rainfall caused large amounts of cations, particularly K+ and Na+, to leach beyond 90 cm soil depth. Consequently, the leached elements are bound to end up in natural water resources over time. Irrigation with undiluted winery wastewater did not have a pronounced effect on soil pH(KCl). This was probably due to the decomposition of organic matter and the fact that the applied salts as well as dissolved organic or mineral acids leached beyond 90 cm depth. The practical application of irrigation with diluted winery wastewater was assessed in a pot experiment. Irrigations were applied under a rain shelter over four simulated irrigation seasons. Four soils varying in texture were irrigated with winery wastewater that was diluted to 3000 mg/L chemical oxygen demand (COD). The four soils were irrigated with municipal water as a control. The rate of K+ increase in the soil containing 20% clay was higher than in soils containing 13% clay, or less. This suggested that heavy soils will aggravate the risk of high K+ levels. The risk of Na+ accumulation increased linearly with the clay content in the soil. Low Ca2+ and Mg2+ concentrations in the diluted wastewater had no effect on the soil, irrespective of clay content. Irrigation with diluted winery wastewater increased soil pH(KCl) substantially in all soils over four simulated seasons. The soil pH increase was attributed to the addition of organic and mineral salts via the diluted winery wastewater to the soil. The effect of simulated rainfall on soils irrigated with winery wastewater was also assessed in a pot experiment. Six soils with different clay content were irrigated with winery wastewater diluted to 3000 mg/L over one simulated irrigation season. Thereafter, good quality river water simulating winter rainfall was added to the pots. The rainfall was simulated according to the long term averages of the regions were the soils originated. Leaching of cations, particularly K+ and Na+ occurred only from four of the six soils when winter rainfall was simulated. In one of the sandy soils, the simulated rainfall was too low to allow leaching. In the case of other soil where there was no leaching, high clay content of 35% in combination with low rainfall prevented leaching. Where three soils received the same amount of rainfall, more cations leached from the sandy soils compared to the two heavier soils. These trends indicated that leaching of cations was a function of soil texture and rainfall.