Summer deficit irrigation in a hedgerow olive orchard cv. Arbequina: relationship between soil and tree water status, and growth and yield components

Stem water potential (psi(stem)) is a useful tool for irrigation scheduling in tree crops, provided threshold values for growth and production are determined for each physiological period. Four irrigation treatments were evaluated in a hedgerow olive orchard. Control (CON) was irrigated using soil water sensors to maintain the root zone close to field capacity. Severe water deficits were applied by irrigating at 30% CON from end of fruit drop to end of July (DI-J) or from end of July until beginning of oil synthesis (DI-A). Less severe water deficit was applied in July and August by irrigating at 50% CON (DI-JA). Continuous measures of soil moisture, Ws, and shoot length were recorded in all treatments. Fruit dry weight and oil content were measured at the end of the experimental period and at harvest. Relative extractable soil water to 0.8 m depth (REW) and psi(stem) were highly correlated and influenced by irrigation treatment. Shoot growth, fruit characteristics and oil production were correlated to psi(stem). Shoot growth was reduced by 50% relative to CON by irrigating at psi(stem) of 1.3 MPa. Fruit dry matter and oil content (g fruit-1) were linearly reduced as mean summer psi(stem) decreased. Oil production was highly related with psi(stem)in August but not in July. Water can be saved in July by irrigating at psi(stem) of -2.9 MPa but psi(stem) should be maintained higher than 2.0 MPa in August to prevent decrease of oil production.