Evapotranspiration ofVitis viniferaL.cvsSunred Seedless and Muscat Supreme in response to soil water depletion and irrigation cutoff during berry ripening

Abstract

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.

Comparing Irrigation Systems and Strategies for Table Grapes in the Weathered Granite-gneiss Soils of the Lower Orange River Region

“…The ET of more frequently micro-sprinkler irrigated grapevines (T3) was almost invariably higher from September until April compared to those that received irrigation two times per week (T4). This trend confirmed earlier reports, which showed that ET of micro-sprinkler irrigated vineyards on horizontally orientated trellis systems increased as the irrigation frequency increases (Myburgh, 2003b;Myburgh & Howell, 2007b). High evaporation peaks occurring more frequently in the case of the T3 treatment caused higher ET compared to T4 (Myburgh, 1998).…”

“…1). Similar trends were reported for a sandy soil in the Lower Olifants River region (Conradie & Myburgh, 2000) and a coarse sandy soil in the Hex River valley in the Western Cape (Myburgh & Howell, 2007b). Previous results showed that Y m values below ca.…”

“…The annual k c trend suggested that full surface evaporation losses driven by atmospheric conditions made a bigger contribution to ET in comparison to drip irrigation. The annual k c trend was similar to values reported previously for micro-sprinkler irrigated grapevines on horizontally orientated trellis systems in sandy soils (Myburgh, 2003b;Myburgh & Howell, 2007b). The microsprinkler k c values were comparable to those determined for Thompson Seedless grapevines grown for dried grape production in a sandy soil near Upington in the same region (Myburgh, 2003b).…”

“…Mean ρ b was 1678±75 kg/m 3 and 1672±96 kg/m 3 in the topsoil (0 to 400 mm) and subsoil (400 mm to 800 mm) layers, respectively. The ρ b was comparable to 1600 kg/m 3 reported for a fine sandy soil near Upington in the Lower Orange River region (Myburgh, 2003b), but higher than 1480 kg/m 3 for a coarse sandy soil in the Hex River valley (Myburgh & Howell, 2007b). The soil water characteristic curves were similar for the different layers ( Fig.…”

“…40% fine sand content. Previous studies showed that a sandy soil in the Hex River valley retained 112 mm water between -0.003 MPa and -0.1 MPa over a 1.2 m root depth (Myburgh & Howell, 2007b), whereas a sandy soil in Lower Olifants River region retained 109 mm/m RAW between -0.005 MPa and -0.1 MPa (Myburgh, 2011). The foregoing confirmed that sandy soils could retain high levels of RAW.…”