Determining of optimum irrigation schedules for drip irrigated Shiraz vineyards in the Breede River Valley

[摘要] ENGLISH ABSTRACT: Shiraz/110R grapevines, growing in a fine sandy loam soil in the Breede River Valley,were subjected to ten different drip irrigation strategies during the 2006/07, 2007/08and 2008/09 seasons. Grapevines of the control treatment (T1) were irrigated at 30%to 40% plant available water (PAW) depletion throughout the growing season.Grapevines of three treatments were irrigated at 70% to 80% PAW depletion from budbreak until véraison (i.e. when ca. 95% of grape berries have changed colour),followed by either irrigation at 30% to 40% PAW depletion (T2) or a continuous deficitirrigation (CDI) strategy (T3) or irrigation at 70% to 80% PAW depletion (T4) duringripening. The CDI strategy was obtained by applying ca. half the volume of water thatwas applied to the control. This allowed the soil to dry out gradually betweenphysiological stages (i.e. bud break and véraison or véraison and harvest).Grapevines of three further treatments were irrigated at ca. 90% PAW depletion frombud break until véraison, followed by irrigation at 30% to 40% PAW depletion (T5) or aCDI strategy (T6) or irrigation at ca. 90% PAW depletion (T7) during ripening.Grapevines of two treatments were irrigated by means of a CDI strategy from budbreak until véraison. For both treatments, the soil water content (SWC) was allowedto dry out gradually until ca. 90% PAW depletion was reached. After véraison, theSWC of the one treatment was maintained at ca. 90% PAW depletion by applying onlyfour small irrigations of three hours each during ripening (T8). The soil of the othertreatment, received an irrigation at véraison to refill the SWC to field capacity (T9)followed by the CDI strategy during ripening. Grapevines of the tenth treatment wereirrigated at ca. 90% PAW depletion between bud break and véraison followed by apartial profile refill (PPR) strategy during ripening (T10). In order to obtain the PPRstrategy, SWC was only maintained between 40% and 60% PAW depletion.Evapotranspiration varied between 3.5 mm/day and 0.1 mm/day for driest and wettesttreatments, respectively, during the period between December and February. Thiswas substantially less than the volumes required for full surface irrigation. Forirrigations applied at 30% to 40% PAW depletion (T1), 70% to 80% PAW depletion(T4) and ca. 90% PAW depletion (T7) levels throughout the season, crop coefficientsfor the Penman-Monteith reference evapotranspiration (ETo) were 0.4, 0.2 and 0.1,respectively.Under the given conditions, the different irrigation strategies did not have any effecton root distribution and density. Shoot growth of grapevines exposed to high tosevere water deficits in the pre-véraison period stopped before mid December.Shoots of grapevines that were exposed to high or severe water deficits beforevéraison followed by more frequent irrigation during ripening showed activere-growth. These trends occurred during all the seasons.The level of PAW depletion reflected strongly in the plant water potential in thegrapevines. Leaf water potential was influenced by the prevailing atmosphericconditions, whereas stem water potential was less sensitive to atmosphericconditions, but responded more directly to soil water availability. Due to the goodrelationships between pre-dawn leaf, mid-day leaf, mid-day stem and total diurnalwater potential, it was possible to re-classify the water status in terms of previousclassifications for these water potentials based on pre-dawn measurements. Waterconstraints in T1, T2 and T5 grapevines were classed as experiencing no stress,whereas the T7 and T8 ones experienced strong to severe water constraints beforeharvest.High frequency irrigation strategies during ripening delayed sugar accumulation dueto dilution of sugar in the larger berries. Except for the wettest strategy, and wheregrapevines were subjected to the CDI strategy throughout the season, berry massincreased during ripening, i.e. from véraison to harvest. Water deficits had a negativeeffect on berry mass, bunch size and yield. Where higher soil water depletion levelswere allowed, irrigation strategies had a positive effect on the irrigation waterproductivity of grapevines compared to the frequently irrigated or CDI strategies.Higher water constraints in grapevines, particularly during ripening, improvedsensorial wine colour and enhanced some of the more prominent wine aromas, e.g.spicy and berry. Grapevines that were irrigated at a high frequency during ripeningproduced wines with diluted character flavours and aromas and inferior overallquality. Under the given conditions, sensorial wine colour and spicy character werethe dominant factors in determining overall sensorial wine quality.

[发布机构] Stellenbosch University