Effects of timing and intensity of deficit irrigation on vegetative and fruit growth of apricot trees

• Timing and duration of deficit irrigation affect vegetative growth and apricot yield.
• Regulated deficit irrigation reduced apricot yield only at severe water deficits.
• Continuous deficit reduced apricot yield due to vegetative and fruit growth reduction.
• Fruit size and yield decrease when deficit irrigation relief delays beyond stage III.
• Deficit irrigation increased apricot root length density close to the drip-line.

The effect of different deficit irrigation strategies were studied over a four year period in mature apricot trees (Prunus armeniaca L., cv. Búlida) to ascertain how the intensity and duration of water deficit affects the growth of the root and aerial (shoot, trunk and fruit) parts of the tree, and hence future tree productivity. The irrigation treatments consisted of: a control, irrigated at 100% of seasonal crop evapotranspiration (ETc); continuous deficit irrigation (CDI) at 50% of ETc; two regulated deficit irrigation (RDI), at 100% of ETc only during the critical periods, and reduced to various percentages of ETc during the rest of the season. Soil and plant water status, yield, vegetative and fruit growth were measured in the different treatments. Vegetative growth decreased according to the intensity and duration of the water deficit applied, and depending on the phenological period when the water deficit occurred. Deficit irrigation promoted a decrease in trunk and shoot growth by a 33% on average, although root length density increased nearly double in the 0–0.25 m drip-line band compared with the Control trees. In the RDI treatments, trunk growth and pruning were significantly reduced only under severe water deficit conditions. While CDI proved to be detrimental for maintaining fruit yield due to the significant reduction in vegetative growth, which led to a decrease in the number of fruits per tree, the RDI treatments only led to reduced yields when the water deficits during the non-critical periods were severe, tree trunk growth being significantly reduced as a consequence. Also, fruit size and total yield decreased when deficit irrigation relief was delayed until after the onset of stage III. Overall, water saving up to 22% affected negatively to the total yield and the number of fruits per tree, by reducing the tree growth.