Crop yield response to water - Cra

Data in Figure 5 suggest that there are cultivar differences in the response to ET c deficits, cv.Conference being more sensitive than Blanquilla (or Spadona). A 30 percent reduction in ET ccaused only a 12 percent yield reduction in Blanquilla-Spadona but a 22 percent decrease inConference. However, cultivar yield sensitivity to ET c deficits was similar once they showed aresponse to decreasing relative ET c ; their sensitivity remained similar with a slope for the yieldresponse to ET c of 1.2 and 1.0 for Blanquilla and Conference, respectively (Figure 5).An explanation of the differences between cultivars in the yield-response thresholdto reduction in ET c may be related to a complex interaction between three factors: i) thepositive effect of moderate water stress on increasing return bloom in the next season, ii)the limited use of fruit thinning as a commercial practice for pear, and iii) the possible fruitsetresponse to previous season water stress. In other words, changes in return bloom as aconsequence of incipient ET c reductions in the previous season, may produce higher croppingnext season, provided fruit set is unaffected. Under these circumstances, increases in cropload leads to the production of smaller fruit, but the smaller fruit size at harvest is often morethan compensated by the positive impact of higher fruit number on yield. It is interesting toFigure 6Relative revenue function developed for RDI strategies that imposed stress during StagesI and II. Data points obtained from studies of at least two year duration. Three studiesfrom Spain and one from Israel were used for the relationship (Source: Marsal et al., 2002ain Blanquilla; Marsal et al., 2008 in Conference; Marsal et al., unpublished in Conference;and Naor et al., 2000 in Spadona). Linear boundary lines consider no differences in cultivarresponse and fitting is performed through linear regression from the observations definingan upper boundary. Note the greater sensitivity to ET deficits in terms of revenue than inyield terms. FI, RDI-SI, RDI-SII, RDI-PH and SSDI stands for full irrigation, RDI during Stage I offruit growth, RDI during SII of fruit growth, RDI during postharvest and seasonal sustaineddeficit irrigation, respectively.Relative gross revenue1.00.80.60.4'Blanquilla'- Spain Overirrgation'Blanquilla'- Spain FI'Blanquilla'- Spain RDI-SI'Blanquilla'- Spain RDI-SII'Conference'- Spain FI'Conference'- Spain RDI-SII'Conference'- Spain RDI-PH'Spadona'- Israel SSDISlope = 1.30.20.00.00.20.40.6 0.81.0Relative ET Cpear 385