Water relations, growth and yield of grapevines in Portugal’s Douro wine region

The hot and dry climate of the Demarcated Region of Douro (DRD), Portugal, particularly during the summer, induces soil water deficits that influence the growth and development of grapevines. Therefore, controlling the water supply to the soil, and concurrently the crop water status, through irrigation, it is an updated and sometimes controversial issue, which can bring significant changes in physiological processes within the plant and thus in vegetative growth, yield and quality. Water relations in grapevines have been extensively investigated over the past decades. However, more easily automated techniques have been recently used such as trunk diameter variations. On the other hand, the data reported in the literature relates to a wide range of climatic regions, varieties, phenological stages and soil moisture regimes, and consequently comparisons are frequently difficult to make. As a result the present study is undertaken to enhance understanding of the responses of cv. ‘Moscatel Galego’ grapevines to irrigation during a growing season (2009) in the DRD. The experimental design includes rain-fed plots and a trickle irrigated regime. The main objectives are to

(i) determine water availability by soil moisture readings along the vegetative cycle;

(ii) evaluate water stress indicators for irrigation scheduling, such as variations in trunk diameter, and

(iii) assess the responses of crop growth, yield and quality to different water regimes.

The work analyses several variables such as maximum daily trunk shrinkage, vegetative growth and development (e.g. leaf area, pruning weight), yield (fresh weight and number of clusters per vine) and quality (e.g. pH, total acidity, sugar content). As expected, irrigation improved vine water status and increased canopy expansion and leaf duration. Irrigation raised mean yields of fresh fruits, but had no effect on quality. The present work is part of a larger study, which includes namely the quantification of evapotranspiration and its components by eddy covariance and sap flow measurements.