Crop yield response to water - Cra

Figure 5Hypothetical seasonal course of leaf or stem-water potential for olive trees subjected todifferent strategies of deficit irrigation. Green horizontal lines bracket the range betweenfully hydrated trees and turgor loss point, vertical orange lines limit the interval of waterdeficit. Values will vary in different climate and soil conditions. Legend: broken line, fullyirrigatedbaseline; solid line, SDI; dotted line, RDI 1 ; broken and dotted line, RDI 2 .RDI 2 RDI 1SDIcontrol-1-2ψ (MPa)-3-4-5180 200 220 240 260 280Day of yearThe RDI 2 strategy may be useful in soils with a high clay percentage to allow the root systemnot to be exposed to high humidity for long periods.Other RDI strategies that have been sought include the concentration of the water deficit inthe ‘off’ year, when the crop load is so low that vegetative growth in not affected much bythe water deficits. In the ‘on’ year, the water saved in the previous year is applied to maximizefruit production with minimum water deficits. The only published test performed with thisstrategy (Moriana et al., 2003) did not give as good results as the previous three strategiesdescribed above. Also, the management of water supply under this strategy is not easy, and itwill require commitments of water supply that exceed the current season and that, therefore,may be hard to implement by many water agencies.Because olive irrigation is a relatively new practice, often irrigation authorities cannot deliversufficient water to meet the full orchard requirements and are promoting deficit irrigationpractices. Reasons include lack of sufficient water supply, equity considerations, the limitationsimposed by the original tree spacing of the rainfed orchards, and priority for urban uses. Whensupply is limited to such levels, use of drip irrigation is a must, with as few emitters per treeas possible. Also, growers should irrigate as infrequently as feasible (once or twice a week)to minimize E losses and avoid prolonged exposure of olive roots to high soil-water levels inOlive 311