Crop yield response to water - Cra

Figure 7Effect of midday light interception of apples on their K c values - data from a weighinglysimeter study of commercial size trees within an orchard in Mollerussa (Lleida, Spain)(Girona et al., 2011).1.21y = 0.2e0.03xR² = 0.89470.8Kc0.60.40.200102030 40 5060Average midday light interception (%)Water Production FunctionsWater production functions for apple are difficult to generalize because they are affected bymany factors such as training system, crop load, pruning and thinning practices, and whetherthe target is total (as for juice production) or fresh marketable yields.Figures 8 and 9 present the response of total and marketable yield to a decrease in ET c determinedin Lleida, Spain. In both cases, it seems that relative ET c may be reduced by about 15- 20 percentwithout having a negative impact on final yield. Similar results were found in Israel where fruityield >70 mm was unaffected by increasing K c above 0.84 (Figure 10).Water management of fresh market apple production should take into account that: 1) fruit sizeis highly dependent on crop load thus it should be optimized to maximize yield of marketable sizefruit; 2) apples tend to have a biennial bearing pattern in response to high crop load, thus crop loadshould be optimized to allow stable production for each season. In one specific experiment withGolden Delicious (Figure 10), crop yield of marketable size (>70 mm) increased with both annualirrigation level and crop load, and the maximum crop yield was achieved at the highest load atmaximum apple ET c (equivalent to 84 percent of the seasonal ET o ). It should be emphasized thatpotential fruit size was high during this season and, although the threshold of maximum commercialcrop yield could be higher; optimal crop load that avoids biennial bearing lies between the twohighest crop loads (Figure 10) and may change with climatic conditions.APPLE 341