Spring deficit irrigation promotes significant reduction on vegetative growth, flowering, fruit growth and production in hedgerow olive orchards (cv. Arbequina)

An irrigation experiment was conducted during 5 years in two hedgerow olive orchards (C and L) cv. Arbequina in Central Spain. The control treatments (C1 and L1) were irrigated to maintain the “wetted bulb” near field capacity throughout the season. Three deficit-irrigation treatments were applied from shoot growth (April-May) until pit hardening (beginning of July) with water applications relative to control, C2, C3, C4 (50, 25, 0%) and L2, L3, L4 (40, 17, 0%), respectively. Treatments reverted to full irrigation after pit hardening. During the treatment period a series of phenological events occurs: bud break, shoot growth, flower differentiation, flowering, fruit set, fruit drop and pit hardening. Responses of vegetative growth, flowering, fruiting, fruit characteristics and production were evaluated through their relationships with midday stem water potential (Ψstem). Flowering was shown to be the most sensitive period to deficit irrigation and the major determinant of final production through reductions on fruit number and oil content. With high water during flowering (mean Ψstem before irrigation >−1.0 MPa) trees developed more nodes, leaves, fertile inflorescences and fruits per inflorescence with consequent high production (1278 kg oil ha⁻¹). Oil production was significantly reduced (64% of maximum) when Ψstem was allowed to fall below −1.5 MPa at flowering and was halved at −1.7 MPa, reducing water productivity from 0.26 to 0.21 kg oil m⁻³. In contrast, Ψstem could be reduced to −1.8 MPa after flowering until pit hardening without effects on fruit drop, fruit size or oil content. Fruit drop increased when Ψstem from flowering until pit hardening was below −2.71 MPa. Fruit oil content at harvest was strongly related with fruit dry weight at pit hardening. Vegetative growth occurred continuously during spring, although mainly during flowering, and could not be reduced by deficit irrigation without reducing production. The results are advantageous to irrigation management in this and similar climatic regions where Spring is a critical period for olive production due to variable temperature, rainfall and crop water demand. They establish the high thresholds of Ψstem required to guide irrigation management during Spring without yield loss, and the substantial resulting loss when this threshold is exceeded. They also reveal that deficit irrigation strategies cannot be used in Spring to control canopy size in hedgerow orchard without serious impact on yield.