Regulated deficit irrigation benefits the production of container-grown citrus nursery trees

Abstract

Withholding irrigation at − 15 to − 25 kPa water potential significantly saved water with minimal changes in plant growth, water relations, and percentage of shippable citrus trees on drought-tolerant and -sensitive rootstocks. We evaluated the impacts of regulated deficit irrigation (RDI) on plant growth, water relations, and biochemical variables of Valencia sweet orange nursery trees grafted on drought-tolerant Rangpur lime (RL) and drought-sensitive Swingle citrumelo (SC) rootstocks in pots. Irrigation was withheld to potting mix water potential of − 15 (mild RDI) and − 25 kPa (moderate RDI), with daily irrigation as control, in three graft growth periods (20–60, 61–120, and 20–120 days after grafting, DAG). Plant growth was reduced by moderate RDI, albeit RL induced more vigor than SC. SC induced higher CO2 assimilation rates and water use efficiency (WUE), regardless of the irrigation regime, and only trees grafted on RL decreased WUE under moderate RDI. Most leaf nutrient concentrations were increased with RDI intensity, while K levels were decreased by moderate RDI. Starch reserves were drastically decreased, while reducing sugars were increased by RDI in all plant organs, most notably in the leaves; roots represented the main source of carbohydrates for both rootstocks under water deficit. Starch concentration promptly recovered in all organs after restoring irrigation. Leaf proline concentration was 20 times higher at RDI, but decreased by 50% just 1 day after rehydration. Mild-to-moderate RDI resulted in water savings of 54–80%, but a 0–40% reduction in the percentage of shippable trees at 120 DAG; the biological responses were mainly related to the RDI duration. The production of container-grown citrus nursery trees in greenhouses could greatly benefit from the use of RDI, without major negative effects on tree quality.