Fruit yield and quality of 'Valencia' orange trees under long-term partial rootzone drying

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.