Crop yield response to water - Cra

FIGURE 10 Crop coefficient (K c ) curve determined for a mature, drip-irrigated, apple orchard with a weighinglysimeter in 2006, at Lleida, Spain. Note that the decline in K c after harvest occurs close to theonset of leaf senescence in apple trees.K c1.21.0Apple2006Harvest0.80.60.40.20.00 50 100 150 200 250 300Day of yearmature trees that have reached their maximum size. In intensive production systems, thisis equivalent to attaining a percent ground cover (horizontal projection) of no more than70-80 percent; maximum ground cover values are generally dictated by harvesting and otherorchard mechanized operations. Mature traditional orchards and vineyards generally havelower ground cover values, although such values can be over 80 percent in a few species, suchas walnuts or table grapes.To schedule irrigation for developing plantations or in sparsely planted orchards, as is thecase in traditional plantations under limited water supply, it is necessary to relate the ET of ayoung orchard to that of a mature orchard, for which the K c values were developed. If the K capproach is used, a new coefficient is needed to compute ET as:(9) ET c = ET o K c K r,tWhere, K r,t is an empirical coefficient relating the ET of an orchard of incomplete cover to thatof a mature orchard. Here, the K r,t is related to the horizontal projection of the tree shade(ground cover).Figure 11 shows the relation between percent ground cover and percent ET of a matureorchard, based on an original one obtained experimentally for almond trees (Fereres et al.,1982) and adjusted with data from experiments on several tree species. Box 6 shows twoexamples on how to calculate the ET of immature tree canopies of different sizes. The treecanopy parameter used in the equation in Figure 11, is the horizontal projection of the canopy,without correcting for differences in leaf area density that could leave gaps within the treeshade. Note that this relationship has been developed for tree canopies of various shapes butall of them formed as isolated trees, with some sort of spherical or conical shape.Yield Response to WateR of fRuit tRees and Vines 265