Crop yield response to water - Cra

soil water. In young orchards, postharvest water restrictions did not affect yield in the shortterm (Intrigliolo and Castel, 2005). However, after four seasons of deficit irrigation, therewas a 10 percent reduction in yield compared with fully irrigated trees because the stressedtrees were smaller. Thus, long-term deficit irrigation of young trees causes a reduction inproductivity by reducing tree size. Post harvest water stress, despite its moderate detrimentaleffect in the long term, should be considered for commercial orchards not only in the case ofwater scarcity, but also as a tool for controlling vegetative growth in areas where vigorousgrowth may be a problem.Plant water stress is known to potentially affect flower bud development for the next season,but there are only a few reports on a decrease in next season crop level because of buddamage (Johnson et al., 1994). Water stress during postharvest, as measured by the SWP, wasalso correlated with the following season’s crop yields.In some cases, there was even an increase in return bloom leading to larger yield in prune treeswhere a high crop level was the target (Lampinen et al., 1995). In plum trees, water stress did notappear to be associated with the appearance of fruit disorders such as double fruit formation orfruit deep suture, as occurs in other stone fruit‐trees such as peach (Johnson and Handley, 2000).Plant water stress indicatorsMidday SWP is the most useful indicator of plant water stress in plum trees, since prior to harvestit was highly correlated with tree performance (Naor, 2004; Intrigliolo and Castel, 2005; andIntrigliolo and Castel, 2006a). Figure 2 presents the results of two studies on different varietiesof Japanese plums: Black-Gold plums (Intrigliolo and Castel, 2006a) and Black Amber plums(Naor, 2004) in the semi-arid climates of Valencia, Spain and Upper Galilee, Israel, respectively.In each location and season, tree-to tree variations of SWP were well correlated with theaverage fruit weight at harvest. However, there was no unique relationship relating SWP tofruit weight valid for all data across experiments (Figure 2). The differences in the interceptof the lines reported between seasons and locations indicate that fruit weight is not only afunction of plant-water status. In addition, the different slopes of the linear relationshipsbetween locations suggest that the effect of plant water stress on fruit growth might changeaccording to different environmental or cultural conditions. Overall these results highlight theimportance of conducting local experiments when attempting to predict the effect of plantwater stress on fruit weight at harvest.Studies using other water status indicators for plum trees have also shown that daily trunkcontraction, continuously measured with stem dendrometers (Intrigliolo and Castel, 2006b), ishighly correlated to SWP, but other factors such as tree age and tree crop load also influencethe relationship between trunk contraction and SWP (Intrigliolo and Castel, 2006b; andIntrigliolo and Castel, 2007).Water RequirementsOnly a few early studies quantified the consumptive water use of plum orchards. Therecommended crop coefficient values for plum trees are included in the stone fruit tree sectiontogether with peach trees in the FAO I&D No. 56 publication (Allen et al., 1998). A specific studyPLUM 351