Browsing by Author "Muller, Katharina"

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    Grapevine cation and anion transfer : a perspective from the soil to wine chemical and sensory properties
    (Stellenbosch : Stellenbosch University, 2017-03) Muller, Katharina; Strever, Albert; Howell, Carolyn; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Soil salinity and sodicity occurs mostly in arid and semiarid environments. Saline soils contain high concentrations of soluble salts like sodium chloride (NaCl) in the solum or regolith of the soil. Sodic soils are defined as having a high concentration of sodium ions compared to other cations on the soil particle surface. Grapevines are known to be moderately sensitive to salinity. Both soil salinity and sodicity have an adverse effect on plant growth, whether directly or indirectly. Soil salinity and sodicity have a deleterious effect on the grapevine’s physiological responses, including yield reduction, decrease in shoot growth and increase in cation and anion concentrations in the fruit and final wine, and may also affect the biochemical pathways, consequently leading to toxicities, deficiencies and mineral imbalances in the grapevine. The most important cations associated with salinity are Na+, Ca2+ and Mg2+, whereas the most important anions are Cl-, SO42- and HCO3-. These ions may occur naturally in the soil, however they are more commonly added to the soil through irrigation or may be exacerbated through persistent droughts. Cation and anion analysis in the leaves, the petioles and grape components is essential for the prevention of the negating effects these cations and anions have on grapevine physiology, the grape juice, the final wine product and the export feasibility. The OIV (Oeno 6/91) resolution in regard to sodium states that “When wine contains excess sodium (excess sodium is equal to the content of sodium ions less the content of chloride ions expressed as sodium), it is generally less than 60 mg/L, a limit which may be exceeded in exceptional cases…”. The limit in South Africa is 100 mg/L Na content. As a result of these restrictions, some wines are rejected from the export market. High concentrations NaCl also has an effect on the sensorial quality of wine, and may as a result be described as flat, dull, soap, seawater-like and saline. In this study, soil salinity and sodicity occurrences were investigated on two farms, Farm A Chenin blanc and Farm B Chenin blanc and Pinotage in the Paardeberg area. These plots were divided into ‘high’ and ‘low vigour’ according to salinity and sodicity levels. Soil analysis was conducted at three depths to confirm the presence of high cation and anion concentrations in the soil. Meso-climate loggers were installed on both farms in order to analyse the climatic effects on the grapevine. Vegetative and reproductive measurements were conducted including trunk circumference measurements, shoot measurements, destructive leaf area measurements, berry sampling and harvest measurements. Investigations were also conducted on the effects of high cation and anion concentrations in the soil, different grapevine parts (leaves, petioles and canes), grape berry parts (juice, homogenised, skin and sediment) and in the subsequent wines. In addition to this, the effects of these cation and anion concentrations on grapevine growth, wine composition and the sensorial profile of the wines were also determined The study aimed to provide insight into the positive and negative aspects of possible soil cation and anion transfer to the grapevine, grape juice and wine. Soil samples confirmed the presence of salinity/sodicity in the plots. This had an adverse effect on the growth as well as yield per vine. Shoot, petiole and leaf analysis showed high concentrations of sodium, reaching values greater than 1500 mg/kg. The juice cation and anion analysis showed high levels of sodium for some plots, however chloride levels in the leaves, petioles, grape juice and wines were found to be below harmful limits. There were differences between juice, sediment, skin and homogenised sample analysis, confirming that the sediment contained the highest cation and anion content. Descriptive sensory analysis showed no significant differences in terms of their saltiness, however some wines exhibited significant differences between aroma and taste descriptors. The high salt content in the wine may have had a positive effect on the taste of the wine. At low salt concentrations wines may appear to be sweeter, or less bitter. This study showed that high saline or sodic soils had an effect on the grapevine growth, specifically the trunk circumference, shoot growth and leaf area. The different cation and anion concentrations found in the shoots, leaves and petioles showed that some cations and anions were translocated from the soil to the grapevine parts. The grape juice obtained from the grapes also showed high levels of certain cations, however the juice sediment analysis exhibited the highest concentrations of cations compared to the skins, the homogenised and juice samples. The sensory analysis showed that at certain concentrations, wine aroma and taste could be affected positively or negatively, however this was dependent on the concentrations of the cation and anions.