Crop yield response to water - Cra

out in Spain under more common growing conditions including moderate density orchards(1 100-1 600 plant/ha), and using vigour-reducing rootstocks such as clonal quince (BA-29or M-C) indicated no significant effect on fruit size at harvest in response to RDI Stage I ascompared to Control irrigated trees (Marsal et al., 2002a; and Asin et al., 2007). In one case,where trees grew in isolated large containers of 120 litre, deficit irrigation during Stage Iactually reduced final fruit size at harvest (Marsal et al., 2000). Furthermore, several attemptsin Spain during the nineties to use RDI during Stage I in commercial orchards aimed to increasefruit size above that of fully-irrigated trees, proved unsuccessful.Water stress responses during Stage IIWater stress during Stage II of fruit development decreased final fruit weight and lower fruitdiameter (Behboudian et al., 1994; Marsal et al., 2000; Naor, 2001; Marsal et al., 2002a; andO’Connel and Goodwin, 2007). Water stress at this time mainly reduces fruit cell size (Marsalet al., 2000) and, as a consequence, final fruit size at harvest.Water stress responses during postharvestThere are few studies available on this topic. One study attempted to use RDI in postharvest forSpadona European pear where the elapsed time for deficit irrigation was three months (fromAugust to the end of October) (Naor et al., 2006). The results of the experiment indicatedthat water could be saved, provided midday SWP did not surpass the threshold of -2.2 MPa.A positive effect related to moderate postharvest water stress (i.e. SWP >-2.2 MPa) was that,during the following season, return bloom and fruit yield increased significantly compared tofully irrigated and severely stressed trees (Naor et al., 2006).Similar results regarding increased return bloom have been found by Marsal in Spain for thecultivar Conference. However, in his study fruit set was lower for these trees with higher bloomand this ended up reducing yield but increasing fruit size.Water RequirementsThere are only a few reports available on ET c information for pear trees. One study useddrainage lysimeters of 105 litre capacity and conditions close to hydroponics with the soilsurface covered to avoid soil evaporation (Buwalda and Lenz, 1995). The study consideredthree different cultivars, two training systems and presence or absence of fruit. The effectof both cultivar and training system on tree water consumption was significant; althoughthe differences can be explained by differences in leaf area. However, the presence of fruitincreased tree water consumption by 36 percent as compared to de-fruited trees, independentlyof leaf area (Buwalda and Lenz, 1995). These differences were probably related to increasesin stomatal conductance and therefore leaf photosynthesis and transpiration which arefrequently observed under higher cropping conditions of pear (Marsal et al., 2008).The crop coefficients obtained in the lysimeter study (Buwalda and Lenz, 1995) were referredto the Priestley and Taylor ET o equation, and did not consider a soil evaporation component.Nevertheless, the reported values were quite low, with maximum values of 0.38 for cv.Conference with a leaf area index (LAI) of 2.0. Water use in this study must have been restrictedpear 381