Deficit irrigation strategies in vermentino for improving groundwater use in clay soils

Abstract

The effects of deficit irrigation strategies on soil water dynamics, vines physiologic and productive performance were studied in Vermentino grapevines grown on a deep clay soil, during 2009 and 2010, in South Sardinia (Italy). From fruit set until three weeks before harvest, classic deficit irrigation (DI40 and DI80) and partial root-zone drying (PRD80 and PRD40) strategies were set (supplying 80% and 40% of crop evapotranspiration, ETc) to investigate which ones effectively improve irrigation water use while preserving yield and grape quality. Soil moisture content and distribution patterns (from 10 to 100 cm depth), leaf gas exchanges and stem water potential were monitored using portable devices. Vegetative growth, canopy density and vigour were measured using non-destructive methods. Exposed leaf area, leaf area/yield ratio and Ravaz Index were calculated to evaluate growth-yield balance. Berry weight and composition were analysed at harvest. For each treatment, different moisture dynamics along the soil profile were observed all through the seasons. Except for DI40, treatments lead to high soil moisture content in deep soil layers. Vines experienced low to moderate water stress and showed slight decreases in photosynthetic rate along the season and high stomatal sensitivity to soil moisture availability. Intense shoot growth, high canopy density and vigour were observed in all treatments, but plants remained well source-sink balanced. DI40 and PRD40 were the most efficient strategies in water saving. Minor and mostly transitory effects of the highly watered treatments on °Brix, pH and titratable acidity were indicative of slight berry developmental delay. A substantial amount of water can be conserved by reducing the fraction of ETc replenishment, without relevant negative impacts on fruit yield, while maintaining balanced sugar/acids ratio in the must. PRD promoted sub-surface water accumulation, available for roots uptake; this can contribute to minimize the negative impact of hot and dry seasons, both on vine physiological and productive responses.