Effects of different irrigation regimes on a super-high-density olive grove cv. "Arbequina": vegetative growth, productivity and polyphenol content of the oil

The effects of multiple irrigation regimes on the relationships among tree water status, vegetative growth and productivity within a super-high-density (SHD) "Arbequina" olive grove (1950 tree/ha) were studied for three seasons (2008-2010). Five different irrigation levels calculated as percentage of crop irrigation requirement using FAO procedures (Allen et al. in Crop evapotranspiration. Guidelines for computing crop water requirements. Irrigation and drainage paper 56. FAO, Rome, 1998) were imposed during the growing season. Periodically during the growing season, daytime stem water potential (Psi(STEM)), inflorescences per branch, fruits per inflorescence and shoot absolute growth rate were measured. Crop yield, fruit average fresh weight and oil polyphenol content were measured after harvest. The midday Psi(STEM) ranged from -7 to -1.5 MPa and correlated well enough with yield efficiency, crop density and fruit fresh weight to demonstrate its utility as a precise method for determining water status in SHD olive orchards. The relationships between midday Psi(STEM) and the horticultural parameters suggest maintaining Psi(STEM) values between -3.5 and -2.5 MPa is optimal for moderate annual yields of good quality oil. Values below -3.5 MPa reduced current season productivity, while values over -2.5 MPa were less effective in increasing productivity, reduced oil quality and produced excessive crop set that strongly affected vegetative growth and fruit production the following season. On the basis of the result given here, irrigation scheduling in the new SHD orchards should be planned on a 2-year basis and corrected annually based on crop load. Collectively, these results suggest that deficit irrigation management is a viable strategy for SHD olive orchards.