The response of Valencia orange trees to irrigation in Uruguay

Abstract

effects of different drip irrigation regimens on mature Valencia orange trees growing in southern Uruguay were studied over a five year period (1995-2000). These treatments were: no irrigation (T1), irrigation at 50% ETc (T2), 100% ETc (T3), 150% ETc (T4), and irrigation-stress-irrigation (T5, equal to T3 except during the period from approximately mid-December to mid-February, when no irrigation was provided). Trunk cross-sectional area and crown volume increased linearly with the amount of water applied. Flower number and fruit setting were not affected by the treatments. T3 gave the best yield, which on average was 31% higher than that obtained with T1. Fruit size was the yield component most affected by irrigation treatment. The exportable yield of the T3 trees was almost double that of the T1 trees (36.7 and 19.2 t ha-1 year-1 respectively). T2 allowed a seasonal water saving of 738 cubic m ha-1 year-1 but produced smaller trees; nonetheless, the reduction in exportable yield was only moderate (14%). T4 used more water than T3 and produced larger trees, but led to no improvement in yield. The complete restriction of irrigation during the initial phases of fruit enlargement (T5) led to a smaller water saving than that provided by the T2 regime (547 cubic m ha-1 year-1) and a greater reduction (22%) in the exportable yield.