Research Articles (Soil Science)

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Browsing Research Articles (Soil Science) by Author "Clarke, C. E."

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    Annual dynamics of winery wastewater volumes and quality and the impact of disposal on poorly drained duplex soils
    (South African Society for Enology and Viticulture, 2018) Mulidzi, A. R.; Clarke, C. E.; Myburgh, P. A.
    The composition and volume of winery wastewater change throughout the year. Quality is usually at its worst when vintage operations are dominated by the production of red wines. The objective of this study was to investigate the annual dynamics of winery wastewater volumes and quality, as well as the effect of winery wastewater irrigation on the chemical soil properties of a poorly drained duplex soil. The study was conducted over two and half years. The wastewater contained a high concentration of potassium (K+) and low levels of sodium (Na+). The results of the study confirmed that winery wastewater did not comply with South African national legislation for wastewater irrigation with regard to chemical oxygen demand (COD) and pH throughout the study period, while some prominent spikes were observed in sodium adsorption ratio (SAR) and electrical conductivity (EC). Land application of winery wastewater resulted in the accumulation of high levels of K+ in the soil. It is important to note that this study represents the worst-case scenario, i.e. large amounts of wastewater were disposed of on a small surface, particularly during harvest and in winter. Due to the high volumes of wastewater irrigation plus rainfall, the inevitable over-irrigation leached large amounts of K+ beyond 90 cm soil depth. Unfortunately, the leached elements are bound to end up in natural water resources, resulting in the pollution of the environment.
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    Design of a pot experiment to study the effect of irrigation with diluted winery wastewater on four differently textured soils
    (South African Water Research Commission, 2016-01) Mulidzi, A. R.; Clarke, C. E.; Myburgh, P. A.
    Due to the intensification of environmental legislation, the wine industry is expected to find solutions for the treatment or re-use of winery wastewater. The objective of the study was to design and evaluate a pot experiment for determining the effects of irrigation with diluted winery wastewater on different soils. Four pedogenetically different soils were included in the experiment, i.e., (i) alluvial sand containing 3.3% clay from Rawsonville, (ii) aeolic sand containing 0.4% clay from Lutzville, (iii) shale-derived soil containing 20% clay from Stellenbosch, and (iv) granite-derived soil containing 13% clay from Stellenbosch. The pot experiment was carried out under a rain shelter at ARC Infruitec-Nietvoorbij. Soils were packed in 3.54 dm3 PVC pots to a bulk density of 1 400 kg/m3. The four soils were irrigated using winery wastewater that was diluted to 3 000 mg/L COD. Municipal water was used to irrigate the control treatment of each soil. The relatively simple mixing and irrigation infrastructure enabled irrigation of more than one soil with diluted winery wastewater in one experiment. It was possible to irrigate the soils accurately when approx. 85% of the water had evaporated as no visual drainage occurred. Since the pot experiment could be continued under the rain shelter during winter, results were obtained quicker compared to an open field study. However, weighing the pots every second day was time consuming. Therefore, it is recommended that load cells are to be used to record daily mass losses automatically in future pot experiments.
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    Effect of irrigation with diluted winery wastewater on phosphorus in four differently textured soils
    (South African Society for Enology and Viticulture, 2016-04) Mulidzi, A. R.; Clarke, C. E.; Myburgh, P. A.
    The wine industry needs solutions for wastewater treatment, as environmental legislation for its disposal is increasingly being enforced due to non-compliance. The feasibility of re-using diluted winery wastewater was assessed in a pot experiment under a rain shelter over four simulated irrigation seasons. Four soils varying in parent material and clay content, viz. aeolic sand from Lutzville containing 0.4% clay, alluvial sand from Rawsonville containing 3.3% clay, granite-derived soil from Stellenbosch containing 13% clay, and shale-derived soil from Stellenbosch containing 20% clay, were irrigated with wastewater diluted to 3 000 mg/L COD (chemical oxygen demand), whereas the control received municipal water. Irrigation with diluted winery wastewater increased the pH(KCl) in the shale- and granite-derived soils into the optimum range for P availability. Although pH(KCl) in the aeolic sand was initially above the optimum range, relatively high Na+ levels also caused available P to increase as the pH(KCl) increased. The pH(KCl) in the alluvial sand increased beyond the optimum range, thereby causing a reduction in the available P. This indicates that irrigation with diluted winery wastewater may only enhance P absorption if the pH(KCl) shift is towards the optimum. It must be noted that the results represent a worst-case scenario, i.e. in the absence of rainfall or crops.
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    MicroCT-based bulk density measurement method for soils
    (South African Institution of Civil Engineering, 2019) Le Roux, S. G.; Du Plessis, A.; Clarke, C. E.
    High-resolution micro-computed tomography (microCT) is a method growing rapidly in popularity and has been applied to various soil studies with great success, especially for 3D characterisation of pore spaces or mineral distributions. However, microCT is not typically used for soil bulk density measurements, probably due to relatively simple and fast alternatives. Besides the complex process of image analysis from microCT scans, the method is also limited in resolution, which can result in incorrect total porosity estimation. This is especially true for granular materials, such as soils with small pore spaces between particles. In this work we demonstrate a different, yet very simple methodology for microCT adapted to overcome these limitations by using only volumetric measurements of the samples, and not segmentation of pore spaces or density calibrations. This method allows accurate bulk density determination for soil clods and cores. The method is faster than tradition methods, and it allows for additional analyses, such as surface area, macro-porosity, connected pore network and macro-particle shape analysis. The method is tested and directly compared for the same samples to the traditional waxing Archimedes method, with good correlation. The microCT scans of waxed samples also indicate sources of possible error in the waxing Archimedes method by visualising trapped air and wax penetration into open pore spaces. The method is then applied to cores and local bulk density measurements, and their variability down the cores is demonstrated, which can be very useful in complex soil profiles. The method is robust in varying resolution and image blur as it makes use only of volumetric measurements of the entire sample, not image grey-value calibration or segmentation of pore spaces.
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    Response of soil chemical properties to irrigation with winery wastewater on a well-drained sandy soil
    (South African Society for Enology and Viticulture, 2019) Mulidzi, A. R.; Clarke, C. E.; Myburgh, P. A.
    Most wineries in South Africa dispose of their wastewater through land application. This is carried out by irrigating small areas of cultivated pasture with the wastewater or ponding, with the former being the more general practice. Land application of winery wastewater results in the accumulation of potassium (K+) and sodium (Na+) in the soil and leaching of calcium (Ca2+) and magnesium (Mg2+).This could lead to long term instability of soil structure. The objective of this study was to investigate the effect of irrigation with winery wastewater on chemical soil properties and potential environmental impacts. Therefore, an existing grazing paddock at a winery near Rawsonville was selected where wastewater had been applied for many years. Due to the high volumes of wastewater irrigation plus rainfall, the inevitable over-irrigation leached large amounts of cations, particular K+ and Na+, beyond 90 cm soil depth at the selected study site. These leached elements are likely to end up in natural water resources in the long run. Irrigation with 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 were leached beyond 90 cm depth. The study confirmed that disposal of winery wastewater through land application can only be recommended where wastewater application will not exceed the water requirement of the crop as well as the water holding capacity of the soil which is being irrigated.