Abstract
Climate, soil and tree water status, fruit yields and quality of ‘Valencia’ orange trees were monitored over five consecutive seasons (2007–2012) to study the effects of irrigation placement or volume. Three irrigation treatments were imposed: conventional irrigation (CI, 100% of crop evapotranspiration on both sides of the rootzone), partial rootzone drying (PRD, 50% of CI water only on one alternated side of the rootzone) and continuous deficit irrigation (DI, 50% of CI water on both sides of the rootzone). Yield parameters were generally not affected by PRD, and only yield per tree was lower in DI than CI trees. Fruit size and juice content were also reduced by DI, and not by PRD. Both PRD and DI increased juice soluble solids and acidity, vitamin C and carotenoid concentrations, as well as fruit, juice and sugar productivity per unit of irrigation water. Overall, the straight reduction of irrigation volumes by ~55% (DI) induced an average of 4.4% leaf dehydration, which caused significant fruit size reductions and a 3.4% reduction in juice yield, corresponding to a loss of about 2.6 tons of juice and 261 kg of sugars per hectare and year. On the other hand, water savings of about 2 mega liters per hectare and year with PRD caused a mild 2.3% leaf dehydration and mainly fruit quality improvements, indicating that PRD is a sustainable irrigation strategy for ‘Valencia’ orange.
Highlights
Cultivation of fruit trees in semi-arid regions of the Mediterranean is often characterized by high evapotranspirative demand by the atmosphere and limited water availability in the soil
A five-year average of 360, 160, and 163 mm was applied with conventional irrigation (CI), partial rootzone drying (PRD) and DI, respectively, yielding water savings of about 55–56% with the deficit irrigation treatments
Our observations show that final yields of ‘Valencia’ orange trees under the Mediterranean climate of Northern Sicily were only affected by continuous water deficit and not by PRD irrigation
Summary
Cultivation of fruit trees in semi-arid regions of the Mediterranean is often characterized by high evapotranspirative demand by the atmosphere and limited water availability in the soil. For these reasons, exploiting novel irrigation strategies that can maximize crop water use efficiency is crucial for citrus fruit production. In fruit trees, regulated deficit irrigation (RDI) has proved to be a powerful tool to reduce shoot growth, improve fruit quality, and save irrigation water by imposing moderate levels of plant water stress during specific stages of crop development [1,2]. RDI studies have often documented significant fruit drop or reduced final fruit size and yields, depending on the severity or period of deficit imposition [21,22,23]. RDI remains a complex management practice for most farmers as it tightly depends on climate variables and relies on precise and expensive tree water status measurements
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