Long-term response of 'Clementina de Nules' citrus trees to summer regulated deficit irrigation

Abstract

Regulated deficit irrigation (RDI) has been assessed in a wide number of fruit crops. However, few are the studies dealing with long-term RDI strategies. In this work, we assessed the response of ‘Clementina de Nules’ citrus trees to summer RDI treatments [RDI-1, irrigated at 50% of crop evapotranspiration (ETc) and RDI-2, irrigated at 35% ETc] during six consecutive seasons (2007–2012). Although water restrictions were applied according to reductions over ETc, threshold values of stem water potential (−1.3 to −1.5 MPa in the RDI-1 treatment and −1.5 to −1.7 MPa in the RDI-2) were also considered for scheduling deficit irrigation. Results showed that the water stress imposed in the RDI-2 treatment had a noticeable impact on fresh fruit weight, reducing yield and economic return over the six years and more so during the first two years in comparison to a control treatment irrigated at 100% ETc during the whole season. The RDI-1 strategy had a lower impact than the RDI-2 treatment on the fresh fruit weight and did not significantly reduce yield or the economic return over the six seasons. RDI improved fruit quality particularly in the most stressed treatment by increasing the total soluble solids and titratable acidity. RDI also reduced vegetative growth although the reduction was not proportional to the level of stress reached by trees. On average for the six years, the relative trunk growth and pruning weight in both RDI treatments were reduced around 20% in comparison with the control trees. Long-term deficit irrigation did not lead to a noticeable accumulation of salts in the root zone. Overall, these results show that the RDI-1 strategy here studied can be successfully applied during six consecutive seasons in commercial ‘Clementina de Nules’ orchards allowing water savings of 15% without any detrimental effect on tree performance.