Crop yield response to water - Cra

or peach. However, because fruit is harvested quite early, limited post harvest irrigation iscommon, which affects the reported K c values, sometimes much lower than the values thatmay be observed in orchards where the water supply is not limiting transpiration after harvest.Table 1 provides adjusted K c values for mature drip-irrigated apricot orchards based on anexperiment in southeastern Spain (37°52’ N; 1°25’ W) (Abrisqueta et al., 2001).Table 1Crop coefficients for mature apricot trees (soil was not tilled, trees were drip irrigated).Mar. Apr. May June July Aug. Sept. Oct.0.4 0.7 0.8 1.0 1.0 0.85 0.7 0.5WATER PRODUCTION FUNCTIONBased on results from published experiments relating yield to different irrigation regimes forapricots (Torrecillas et al., 2000 and Perez-Pastor et al., 2009) and from our own experience, anSDI programme has been outlined in Table 2 and an RDI strategy in Figure 5. This programmereduces the seasonal applied water by 20 percent relative to a fully irrigated orchard, willdecrease irrigation water use without impacting negatively on yield.Table 2Recommended crop coefficients for a SDI strategy. Data obtained in Southern Italy(40 N; 16°38’ E; C. Xiloyannis, unpublished).Mar. Apr. May June July Aug. Sept. Oct.0.4 0.5 0.6 0.7 0.85 0.5 0.5 0.5Suggested RDI RegimesAs described above, apricot trees have some positive characteristics that help them face waterrestrictions and these can be used in RDI strategies. Moreover, shoot and fruit growth areseparated (Figure 4) in late cultivars. As for peach, this is highly relevant when adopting deficitirrigation strategies devoted to the control of vegetation without affecting fruit growth.However, the opportunity to reduce water application in Stage II is limited for apricots, inparticular in early cultivars where the duration of Stage II is quite limited.A regulated deficit irrigation strategy should avoid water deficits during the critical period ofhigh sensitivity to water stress (i.e. the whole fruit growth and the early postharvest period,around 30 days after harvest). After this period, based on the amount of water available in thesoil volume explored by roots, irrigation could start being reduced just after harvest. In thisway, the trees deplete water from the deep soil layers and gradually adjust their water statuswithout affecting bud induction and differentiation processes. It is recommended that in theearly 30-day period after harvest, the predawn Y leaf should not be below -0.7 MPa. After thisperiod, a reduction of about 50 percent of the ET c is a practicable deficit irrigation strategy(Figure 5). To avoid excessive tree water stress it is desirable to monitor tree water status(minimum predawn Y leaf should not be below a threshold of -1.30 MPa, which corresponds436crop yield response to water