Three fertigation strategies were compared in a drip irrigated Dan-ben-Hannah/Ramsey vineyard near Paarl in the Berg River Valley region of South Africa during the 2002/03 and 2003/04 seasons. Fertilisers were applied either (i) three times per season, (ii) once a week from bud break to flowering, from fruit set to véraison and for six weeks after harvest or (iii) in five to seven pulses per day. For each of the fertigation strategies, grapevines bore normal or high crop loads, viz. 26 or 36 bunches per grapevine respectively. Daily irrigation pulses of 20 to 40 minutes each maintained soil water matric potential above-0.01 MPa in the wetted bulbs. Daily pulses accumulated to a seasonal total of ca. 490 mm irrigation compared to ca. 260 mm for weekly irrigation. Root structures of grapevines irrigated by means of daily pulses had adapted by forming extremely dense root systems in the small wetted bulbs compared to the less frequently irrigated grapevines. Monitoring diurnal grapevine water status revealed that the different fertigation strategies did not affect water constraints up to véraison. During berry ripening, daily pulse irrigated grapevines experienced less water constraints in the morning, late afternoon and during the night than less frequently irrigated ones. However, the grapevines did not experience any detrimental water constraints throughout the season, irrespective of fertigation and irrigation frequencies or crop load. It was evident that grapevine water status not only depends on the size of the root structure, but also on the soil environment in which the roots function.
The annual wastewater quality dynamics of a winery from which wastewater was sourced for a field experiment investigating the dilution of winery wastewater for vineyard irrigation were determined. Annual mean monthly pH ranged from 4.2 to 6.8 and was lower during grape harvest than in winter. Electrical conductivity (EC) increased from the start of harvest (February) and reached a maximum in May, followed by a decline to a minimum in August. The increase in EC probably originated from cleaning agents used in the winery, as well as K + in the grape lees and spillage from the grape fermentation process. With the exception of August, EC exceeded the critical value of 0.75 dS/m, which is the salinity threshold for water used for grapevine irrigation. The mean monthly chemical oxygen demand (COD) level increased from January and was highest at peak harvest (March). The K + and Na + levels in the winery wastewater increased from February to May. The sodium adsorption ratio (SAR) ranged from 2.4 to 9.0 and increased from January to June. Although COD concentration in winery wastewater is the preferred indicator of water quality for the South African wine industry, it did not provide a reliable indication of suitability for irrigation. However, EC was strongly determined by the K + concentration. This was to be expected, since K + is usually the most abundant cation in winery wastewater. Therefore, EC would be a more reliable indicator of winery wastewater quality than COD concentration, particularly with regard to the concentrations of cations such as K + and Na +
In South Africa, grapes are an important crop in the Western and Northern Cape provinces. The wine industry makes a significant contribution to the economy in these regions. Wineries generate large volumes of poor quality wastewater, particularly during harvest. Information on actual amounts of water used by wineries is limited and appears to be inconsistent. Usually, most of the raw water entering wineries ends up as wastewater. Winery wastewater has high levels of chemical oxygen demand (COD) and contains high levels of K + and Na + . There is considerable variation in wastewater quality parameters between wineries, as well as a strong seasonal variation. In most cases, the wastewater is used for the irrigation of small, permanent-pasture grazing paddocks. The use of winery wastewater for vineyard irrigation could have many potential benefits for the wine industry. Irrigation with wastewater containing high levels of K + could be beneficial to soil fertility, although long-term application could have negative effects on soil chemical properties. In terms of South African guidelines, wineries must register their intended wastewater use with the Department of Water and Sanitation. The quantity of wastewater irrigated on a weekly basis has to be monitored and the wastewater quality has to be measured monthly. Weekly water balances should be drawn up with the assistance of a soil scientist. When selecting crops for irrigation with winery wastewater, soil characteristics and climatic conditions, as well as wastewater quality and quantity, should be considered. It is important to quantify soil chemical responses to the application of winery wastewater every three months.
The effects of soil water depletion and irrigation cutoff during ripening on yield, quality and evapotranspiration (ET) of table grapes were studied to refine irrigation strategies needed during hot, dry summers. Six irrigation treatments were applied to two cultivars, viz. Sunred Seedless and Muscat Supreme, from the 1998/99 until 2000101 seasons in a field trial in the Hex River valley of South Africa. Grapevines of all treatments were irrigated with micro-sprinklers at 40% plant available water (PAW) depletion before veraison and after harvest. Two treatments were irrigated at 20% and 40% PAW depletion from veraison to harvest. Four more treatments were applied by cutting off irrigation at these two depletion levels when total soluble solids reached 12°B and 15°B, respectively. According to earlier results, best overall performance for Sunred Seedless was obtained where irrigation at 40% PAW depletion was cut off at 15°B compared to the worst, i.e. where irrigation at 20% depletion' was cut off at 15°B. For Muscat Supreme, irrigation at 20% PAW depletion, either continued until harvest, or cut off at 15°B, resulted in optimum overall performance. Although yield and quality responded differently, this study showed that the ET of the two cultivars responded in a similar way to the irrigation treatments under the given conditions. The ET of grapevines irrigated at 40% PAW increased from 1.6 mm day-1 in September to a maximum of 5.4 mm day-1 in January. Irrigation at 20% PAW depletion increased the maximum ET to 7.3 mm day-1. For both soil water depletion levels, irrigation cutoff at 12°B and 15°B resulted in, respectively, ca. 75% and 65% PAW depletion at harvest. Mean daily ET during January decreased to 4.1 mm day-1 and 5.0 mm day-1 after the irrigation had been cut off at 12°B and 15°B, respectively. The crop coefficients, which decreased accordingly, can be used to reduce irrigation to obtain optimum table grape yield and quality, particularly for Sunred Seedless.
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