Crop yield response to water - Cra

Box 2 Crop and soil measurements to schedule grapevine irrigationPlant, crop and soil indices of water status have been tested in vines grown indiverse environments. The table below presents some examples, and: Suggested RDIregimes outlines the application of some of these methods in irrigation scheduling.Measurement of leaf water potential is time consuming and requires considerableexpertise, but seems more consistent than faster measurements including trunkdiameter and stomatal conductance.Under the conditions of the study of Girona et al. (2006), midday leaf water potentialoutperformed soil water balance as a trigger for irrigation, i.e. leaf water potentialcaptured spatial variability better, and crops managed using this plant-based indexhad less variability in yield and berry composition, that could potentially improvethe homogeneity of grape juice. Thermal, visible and hyperspectral imagery areattracting increasing attention (Moller et al., 2007; Rodriguez-Perez et al., 2007).These technologies, coupled with GIS, allow for effective account of spatial variationat relevant scales from region to fields. There is a large variation in cost and expertiserequired for the implementation of these approaches, form relatively cheap, easyto-usehand-held infra-red thermometers to tractor-mounted, air-borne or satelliteimagery across wide spectral ranges. Soil water status can be assessed indirectlythrough predawn leaf water potential, and directly through measurements with arange of instruments including neutron probes, time domain reflectometry andpressure transducer tensiometers (Chapter 4). A water balance model is often apractical alternative to direct measurements of soil water status (Pellegrino et al.,2006).Suitable indices for irrigation management need to combine flexibility, and a reasonableaccuracy-to-acquisition cost ratio in terms of time, resources and skills. In addition to tradeoffsbetween accuracy and cost, there are also trade-offs between the multiple effects ofirrigation on yield, quality, reserves and diseases (Pellegrino et al., 2006). Pellegrino et al.(2006) developed an elegant method that combines a soil water model and simple, empiricalresponse function that allow for the changes in crop responsiveness to water deficit throughthe growing season (Section 5.1).grapevine 479