Water-use efficiency reflects management practices in Australian olive groves

This study was undertaken to obtain an increased understanding of how current water management practices affect fruit yield in olives (Olea europaea L.) in Australian groves, in order to identify opportunities for improvement. We assessed the relationships between seasonal water supply and fruit yield on a range of olive groves that were either irrigated or rain-fed. All the groves experienced inadequate water supply at the start of the season until early Summer (December). This limited the transpiration (T) component of evapotranspiration (ET) and certainly constrained fruit yield. Seasonal averages for the crop coefficient (K_c) ranged between 0.30 for the lightly irrigated groves, to 0.40 for the well-irrigated groves, but fluctuated during the season from as high as 0.7 during wet periods to as low as 0.2 during extended dry periods. Peak rates for daily T in Summer ranged from 1.0 mm (53 l d^-1 tree^-1) for the rain-fed grove, to 4.0 mm (196 l d^-1 tree^-1) for groves that were regularly irrigated. We observed indications for advective enhancement of T to levels higher than the expected theoretical maxima. Transpiration accounted for between 35-67% of seasonal ET in the rain-fed and well-irrigated groves, respectively. Water-use efficiency for fruit was between 3.2-32.1 kg ha^-1 mm^-1 of ET, and between 3.1-58.1 kg ha^-1 mm^-1 of T. These were equivalent to a range of 1.2-4.2 g of fruit produced tree^-1 l ^-1 of water transpired. We found no yield advantage with irrigation that did not raise seasonal ET well above 600 mm, and T above 300 mm. The late commencement of irrigation constrained T in Spring and early Summer, the avoidance of which should increase fruit yield.