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Yatir Winery, Tel Arad | y_yatir@zahav.net.il

Devlopment of skilled irrigation method for primium wine production in Yatir

20/07/2016 מירה איתן

Grape wine growth is expanding worldwide in general and in Israel as well, particularly during the last decade. Today, there are 5,500 hectares of planted wine vineyards in Israel. In red wine cultivars, inducing drought stress at a particular stage of growth for increasing aroma, colors and compounds in the berry skin is required to improve wine quality. However, continued stress may damage the vineyards and reduce yields in the long term. The purpose of the research was to examine new irrigation methods for grapevines by using a model based on annual climate data and canopy size measurements.

The growth season was divided into three different periods in accordance with the berry phonological stage: Stage 1- from fruit set to bunch closure (the berries in the cluster are touching each other). Stage 2 - from bunch closure to veraison (berry soften and color change from green to red); and Stage 3 - from veraison to harvest (25.2 0Brix). The research was conducted in a 7-hectare commercial vineyard located in an open space in the middle of the Yatir forest. The crops of the vineyard were transmitted to the Yatir winery of the Carmel winery group.

The study was conducted on three main red wine cultivars: Cabernet Sauvignon, Merlot and Shiraz.

During the years 2011, 2012, and 2013, two main irrigation treatments were examined: a “common irrigation practice” and a new irrigation “model.” The common irrigation practice is based on the assumption that at the beginning of the growing season the soil is highly saturated and therefore long irrigation intervals are required. Later in the growing season when the soil becomes dry, irrigation intervals become shorter. During the growing season, evaporation demand increases, therefore shorter intervals do not reduce the grapevines’ stress level. The common practice recommended by the Agriculture Ministry suggests that it is required to initiate irrigation during the bloom period of the growing season. However, due to the low precipitation average in the Yatir region, it is common to initiate irrigation during the bud break period of the growing season. The water amounts of irrigation starts with 5 mm once a week and is raised to 7 mm once every 5 days.

The changes of the intervals and the water amounts are determined by visual estimation of the canopy status and by the development of the drought stress (the decrease in soil water and increase of temperature). The model treatments are based on environmental data from a near-by meteorological station (calculated with the Penman-Monteith equation) and leaf area index (LAI) data.

The stress factors changed throughout the growing season. During Stage 1 high stress factor was applied and during Stages 2 and 3 reduced stress was applied (50ˉ>20ˉ>20% ETC). The water amounts were applied twice a week in the same day of the week. Another “long interval” model treatment was applied in the Merlot cultivars. In this treatment the calculation of water amount was similar to the model, but the irrigation interval was applied every 5 days. Physiologic parameters were examined throughout all experiments in order to study the effect of different water regimes. The parameters examined were: mid-day stem water potential, LAI, stomatal conductance and photosynthesis rate.

At the end of each growing season, each vine was harvested separately and the yield components and quality were measured. Wine was made from each treatment separately and tasted by a professional wine maker panel to estimate the wine quality. The results show that the vines that were irrigated according to the model (50ˉ>20ˉ>20% ETC) during Stage 1 (intensive cambial activity and differentiation of the next season clusters) had extensive vegetative growth and improved stem water potential compared to the common irrigation practice.

However, low irrigation during Stages 2 and 3 led to the most significant water stress (even compared to the vines irrigated in the common irrigation practice) .
Except for the Merlot cultivars in 2011, the total yield of the model treatments was significantly higher over the entire study period compared to the common irrigation practice treatments. In some of the years and in some of the cultivars, the wine quality resulting from the model treatments was lower than the common irrigation practice treatments, but even in these cases the wine was sufficient to be defined as high-quality wines (premium). In the Shiraz there was no difference between the two treatments in the wine quality.