Crop yield response to water - Cra

in the first years of production (third to seventh year after planting) and may average 10-14tonne/ha over a 10-year period, but there are questions about the sustainability of high yieldsin the long term, and about the adaptation of many cultivars to this production system. Thearea devoted to these super-intensive plantations is about 100 000 ha worldwide.Stages of development in relation to yield determinationYield is the result of three main developmental processes that occur between flowering andharvest: fruit set, fruit growth and oil accumulation in the fruit pulp (mesocarp). Vegetativegrowth is critical in terms of olive fruit production, because flowering and fruit set originate inthe axillary buds of past year’s growth. The reproductive cycle from flower bud induction to fruitripening takes 15-18 months depending on cultivar and growing conditions, as it starts in thesummer and ends in the autumn of the following year. Flowers are usually borne in inflorescencesat the axil of leaves of one-year old wood, whereas the terminal bud of the shoot is almost alwaysvegetative (Rapoport, 2008). Shoot growth starts with bud break in spring and resumes whentemperatures are above 12 °C, as long as it is not inhibited by temperatures above 35 °C, soilwater deficit or other environmental stresses. A second flush of shoot growth is common after thesummer. Olive trees are sensitive to waterlogging and temperatures below -10 °C.Chilling is needed for flower bud differentiation. Lack of chilling results in scarce and unevenformation of flower buds. Chilling requirements vary with the cultivar but at least 10 weeksbelow 12 °C are usually needed for abundant flowering. Main phenological stages for olivetrees, described according to the two-digit Biologische Bundesanstalt, Bundessortenamt andChemical industry (BBCH) scale, include bud break, bud development, leaf full expansion,beginning of flower cluster development, full elongation of flower clusters, full flowering, fruitset, fruit development, maturity and senescence. The time sequence of main developmentalprocesses is reported in Figure 2.Olives flower in late spring, a month or two later than to many deciduous trees; timing and durationdepend on cultivar, temperature and soil water availability. Fruit set is generally low (less than 2percent of flowers) but suboptimal conditions (temperature, rain, winds) can reduce it further.Fruit growth apparently follows the typical double-sigmoidal pattern of stone fruit, althoughthere are some questions as to whether this pattern is inherent to olive fruit development oris a consequence of the interaction with environmental constraints in midsummer such as hightemperature and low water availability. Fruit pit hardening occurs about two months after fruitset. Oil accumulation in the fruit is proportional to the intercepted solar radiation and becomessubstantial in late summer for most cultivars, right after the end of massive pit lignification.At harvest, fruit contain between 10 and 25 percent oil on a fresh weight basis, depending oncultivar, crop load and growing conditions. Oil accumulation patterns in the mesocarp follow asimple sigmoid curve, but may vary with cultivar and environmental conditions.Responses to wATER deficitsOlive trees are very resistant to drought and show a high capacity to recover from prolongeddrought periods. Trees can completely re-hydrate within three days of irrigation after a waterdeficit that reached a leaf water potential (LWP) of -4.0 MPa. Even during a severe drought that302crop yield response to water