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The main objective of this study was to analyse, in Mediterranean climate areas, the effects of different drip-irrigation strategies on field-grown grapevine ecophysiology, vegetative growth and yield, as well as on canopy and cluster microclimate, to improve quality without compromising productivity or vine life-time.

Therefore, three irrigation trials were established: a) the first trial, during 2008-2009 vintages, in a „Cannonau‟ vineyard of the Nurra wine region (Alghero, North-Western Sardinia), where drip- irrigation was applied with a sub-surface irrigation line; b) the second trial was conducted in 2009- 2010 vintages, in a „Vermentino‟ vineyard of the Parteolla wine region (Serdiana, South Sardinia), using the same drip-irrigation system; c) the third trial was established in 2011 in a „Vermentino‟ vineyard of the Nurra wine region, using surface drip-irrigation lines.

For the three experimental sites, Full (FI), classic deficit (DI) and partial root-zone drying (PRD) irrigation strategies were set after fruit-set until harvest. Furthermore, two different irrigation scheduling methods were evaluated. The first method was based on maximum evapotranspiration estimation (ETm) and replenishment of ETm fractions, using DI or PRD

strategies. In the „Cannonau‟ trial, four treatments were set: FI 100, DI 50, DI 25 (supplying 100%, 50% and 25% of ETm, respectively) and PRD (supplying 50% of ETm to one side of the root

system, allowing the other side to dry, alternating the watered side every 15 days); in the „Vermentino‟ Parteolla trial, the treatments were: DI 80, DI 40, PRD 80 and PRD 40. In the second scheduling method, used in the Vermentino‟ Nurra trial, irrigation time was set according to a plant water relations index, the midday stem water potential (Ψstem). A threshold of -0.8 MPa was defined for deficit irrigated plants to be re-watered. In this last experiment, four irrigation treatments were tested: early deficit (ED), late deficit (LD), irrigated control (IC) and non irrigated control (NC).

In order to evaluate vegetative growth during the four year trials, empirical mathematical models were developed and validated for „Cannonau‟ and „Vermentino‟, following a methodology for non-destructive estimation of primary leaf area per shoot. The validation of the models showed very good fitting both for primary and lateral leaf area estimation. This type of models can give

Ana Fernandes de Oliveira - Deficit Irrigation Strategies in Grapevine (Vitis vinifera L). Ecophysiologic Responses,

Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 186 of 234 accurate information on vegetative growth independently of the terroir, variety, year, phenological stage and training system, allowing for frequent vine leaf area evaluation at low costs.

The analysis of weather conditions in Sardinia, from October 2008 until September 2011 showed some differences in the four studied years. The 2008 vintage was not particularly hot, as compared to recent years and there was a general scarcity of precipitation. Yet, the May-September 2008 period was rainier than the mean of 1961-1990. The permanence of elevated temperatures in the hot period was higher than the historical mean. In 2009 the highest winter precipitation of the last four decades was registered and this lead to long periods of soil water saturation. From May until the end of August precipitation ceased and the thermal regime evidenced an abnormal frequency of high temperatures during the summer, 1-2°C above the climatologic mean, and also a great number of days with tropical nights, with temperatures above 20°C, which resulted in a phenologic advance and a 5 to 10 days anticipation of technologic maturity. During July and August ET0 was high but within the mean series values, and the precipitations of April and September favoured soil water availability. During the 2009/2010 winter, precipitation was slightly inferior to the climatologic mean but the following June was a rainy month, surpassing in three or four folders the historical mean values, while July, August and September were dryer than the mean. Overall, 2010 was a cold year, except for July and the second half of August. The year 2010 had less summer days than the historical mean and minimum temperatures were 1°C below the mean. In September the maximum temperatures were higher during the first half of the month, dropping drastically during the last 10 days of the month. This thermal pattern lead to a slight phenologic delay until June, a recover in July and good ripening conditions in September, with high ranges of day and night temperature. In June 2011 abundant precipitations lead to a limited water deficit and, also in July, consistent precipitations occurred. Temperature remained below the climatologic mean both in June and July, but August was particularly hot, with thermal summations above the mean of the 30 years series.

To characterise soil water regime during the irrigation experiments, water content was monitored in part of the soil explored by the roots. The fluctuations of water content in the soil profile indicated the 40 to 60 cm depth as being the preferential root absorption zone, and an important capillary ascension in the 20-40 cm of depth, with consistent higher amounts under FI 100, followed by DI 80 and PRD 80 treatments, as expected. As compared to the corresponding

Ana Fernandes de Oliveira - Deficit Irrigation Strategies in Grapevine (Vitis vinifera L). Ecophysiologic Responses,

Growth-Yield Balance, Canopy and Cluster Microclimate for Improving Quality under Mediterranean Climate Page 187 of 234 DI, under PRD treatments, moisture was higher in the watering level and presented different extraction pattern along the soil profile, probably due to the concentration of supplied water to a single side of the root-zone in each irrigation cycle.

In the 2009 „Cannonau‟ trial, the differences between treatments in terms of soil moisture were more pronounced than in 2008, accordingly with the lower contribution of precipitation to soil water resources refilling during spring 2009. DI 25 exhibited the lowest soil water content in every layer, remaining below the average measured wilting point in the last year.

Despite the significant differences in the amount of water supplied with irrigation, in the „Vermentino‟ trial of Parteolla small differences were registered in soil water content between treatments. These results were mainly determined by the presence of a water table available in deep soil layers, which continuously supplied plants, affecting the pattern of root development in the soil as well as plant water status during the whole irrigation season. The presence of a sub-surface saturated level, influenced plants response to irrigation treatments, and seems to have contributed significantly to root‟s extraction during the entire summer, affecting vegetative growth, vigour and yield, both in 2009 and 2010.

Regarding plants water status during the irrigation seasons, stem water potential of the „Cannonau‟ plants in the first trial showed a nearly constant pattern during 2008, and the most significant differences were observed after veraison. Ψstem remained above -1.0 MPa, even in the less irrigated treatment (DI 25). In 2009, a decreasing trend was observed both in PRD and DI 25, and in September Ψstem reached -1.2 MPa, while in DI 50 it remained between -0.6 and -0.8 MPa during the whole season. Plants water status recovered completely after September precipitations in all treatments of the three experimental sites, except for 2008 when scarce precipitation was recorded during that month.

In the „Vermentino‟ experiment of Parteolla region, stem water potential oscillated with the frequency of irrigation interventions (from -0.5 to -1.0 MPa) but showed a nearly constant pattern during the two irrigation seasons, even in the less irrigated treatments (DI 40 and PRD 40), indicating that plants were not exposed to water stress conditions during long periods of time.

When irrigation was scheduled using -0.8 MPa threshold, a decreasing trend in Ψstem, with

increasing evaporative demand, was observed in all treatments until veraison. This decrease was similar in ED and NC plants, which experienced severe water stress at veraison, while LD and IC