Crop yield response to water - Cra

water content is high enough to avoid mild water stress. Further, the evaporative demand andvine water consumption are low at this time.Achieving a specific fruit dry matter (DM) target has been identified by the industry as a keycomponent in the ongoing sustainability of kiwifruit production. Moreover, the minimum DMcontent for marketable fruit has been established in some countries (e.g. 15 percent DM isthe minimum threshold for European markets (EC, 2004). The accumulation of DM in the fruitdepends on maintaining high canopy photosynthesis, which is related to the training system, thelight distribution inside the canopy and the level of orchard management (irrigation, fertilization,protection from biotic stress). Photosynthetic rates recover within about 10 days upon re-wateringin severely (-1.0 MPa predawn LWP) stressed vines (Montanaro et al., 2007) but apparently the lossin dry matter accumulation during a stressed period is never recovered.Kiwifruit is quite sensitive to water stress throughout the whole growing season, hence soil watercontent should not decline below 70 percent of the water available in the root zone (Miller etal., 1998). Knowledge of the effective soil volume explored by roots is of great significance whendesigning and managing irrigation of both mature and young orchards (Figure 8). Because of thepeculiar kiwifruit root system, which has low dominance of root apex and a high number of lateralroots (Figure 9 and Photo 1), the kiwifruit has an overall high rooting density in the explored soilvolume (~ 0.9 cm per cm 3 ) (Miller et al., 1998) in comparison to other fruit tree species, but thelack of dominance of a tap root slows down and limits the exploration of the subsoil by kiwi roots.This pattern of root exploration may be partly responsible for the high sensitivity of kiwi to waterdeficits.photo 1 Root system of a self-rooted kiwifruit vine uprooted at the end of the fourth year afterplanting.KIWIFRUIT 495