Crop yield response to water - Cra

Figure 4Relationships between the percentage of photosynthetically active radiation (PAR) intercepted atsolar noon and daily crop coefficients (K c ) for individual lysimeter-grown apple and pear trees frombud-break until harvest. The relationships between the percentage of PAR intercepted and dailyK c were fitted to exponential equations. Each K c value represents the average K c calculated threedays before and after the PAR measurements (source: Girona et al., 2010).Crop coefficient (Kc)1.21.00.80.60.40.2200220032004200520062002 & 2003y = 0.1189e 0.0595xR 2 = 0.82792004y = 0.0727e 0.0662xR 2 = 0.95190.00102030 4050 60Intercepted PAR at solar noon (%)a relationship between K c and the fraction of midday crop intercepted radiation less useful inpear than in peach or apple (see both Sections). Nevertheless, the use of the midday fraction ofcrop intercepted radiation (or, if midday intercepted radiation data is unavailable, the percentground cover may be used as a surrogate; see Chapter 4) provides a first approximation foradjusting the K c values for pear trees.A water-use study of Asian pear measured the water consumption of trees planted in12 medium-large drainage lysimeters (9 100 litre) and with a soil surface covered with reflectivenet (Chalmers et al., 1992). Trees were trained to a Tatura trellis and ET was determined frompan evaporation. This and another study of Asian pears (Caspari et al., 1993; and Caspari etal., 1994), reported their K c values on a per tree canopy area basis instead of ground area,and thus cannot be compared with the standard K c values. Nevertheless, the conclusion ofthe Asian pear studies is that their water requirements are somewhat lower than the valuesrecommended in FAO I&D Paper No. 56 for this crop.An inherent risk of calculating orchard water requirements is irrigation overestimation. Inthe case of pears, over-irrigation can have a remarkable negative impact on floweringduring subsequent seasons (Marsal et al., 2002a). To avoid this negative impact, accuratedetermination of crop-water requirements is essential in pear irrigation. One useful strategycould be to apply a mild deficit irrigation programme and monitor the level of stress with soilor plant measurements.Water production functionsWater production functions have been derived from four studies: Two of them for the cvs.Blanquilla and Spadona (Spadona and Blanquilla are denominations corresponding to thepear 383