Crop yield response to water - Cra

Table 1Crop coefficients relative to grass reference crop (ET o ) for mature pear trees (Conference onquince) grown in a central leader training system and measured using a lysimeter locatedin an experimental orchard at Lleida, EEL (Spain) by Girona et al. (unpublished).DateCropcoefficient(K c )Ground cover(%)Apr. 1-15 0.30 23Apr. 16-30 0.48 30May 1-15 0.70 36May 16-31 0.80 39June 1-15 0.85 40June 16-30 0.90 40July 1-15 0.90 40July 16-31 0.90 40Aug. 1-15 0.90 40Aug. 16-31 0.70 40Sept. 1-15 0.60 40Sept. 16-30 0.50 40Oct. 1-15 0.40 40Oct. 16-31 0.35 36Nov. 1-15 0.35 25by the size of the containers because a field study found a midsummer K c of 0.9 for a pearorchard of the cv. Blanquilla with trees trained to a palmete system (Marsal et al., 2002a). ThisK c value is slightly lower than the 0.95-1.0 value that has been traditionally recommended(Allen et al., 1998). A weighing lysimeter study within a pear orchard, measured the ET cof three pear trees, cv. Conference, trained to a central leader (Girona et al., 2010). Valuesfor crop coefficients (ET o calculated according to FAO I&D Paper No. 56 Penman-Monteithequation) in midsummer were around 0.9 with a LAI of 1.4. The seasonal changes in K c valuesfor Conference trees are presented in Table 1.It must be emphasized that K c values in Table 1 are only indicative, and that they may requireadjustment to each specific training system and growing conditions. In fact, in the lysimeterstudy (Girona et al., 2010), K c showed ample variation over the years (see Figure 4), and therewere variations even within the same season after full canopy development. It appears that,at least for the cv. Conference in a semi-arid climate, pear K c increases under high air vapourpressure deficits (Girona et al., 2010), suggesting that transpiration (Tr) in pears is enhancedrelatively more than grass Tr, which is the reference crop for ET o . This effect makes the use of382crop yield response to water