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p r a c t i c a l w i n e r y & v i n e ya r d M a r c H 2 0 1 4 53 g r a p e g r o w i n g and soil in relation to the degree of vine water stress: 12 1) Severe water stress prior to flowering and fruit set is likely to have a negative impact on crop potential for both the cur- rent and subsequent growing seasons. 2) Timing of irrigations is critical, and an individual block assessment at key phe- nological growth stages is imperative. This assessment should take into con- sideration vine vigor, root distribution, target crop yield and wine style. 3) Environmental factors to consider include current and forecast temperature and evaporation rates, water quality, soil moisture status and water-holding capac- ity of the soil. Each factor needs to be assessed progressively throughout the growing season and will carry a different degree of importance at various times. Under extreme cases of water shortage, minimizing the risk of a loss in crop and/ or wine value may be more important than a loss in productivity. In this case, water should be allocated to those blocks from which the greatest monetary value will be gained. how much water should be aPPlied and when? In order to make informed decisions about how much water to apply and timing of those applications, a water budget is required, along with a measure of vine water status. Water budgeting is simply the process of balancing the output of water lost from vines through evapotranspiration and the amount of water readily available to vines via the soil. Determining the water status of vines is generally done directly using plant- based measures or indirectly using soil- based and/or climate-based measures. Plant-based measures H.R. Schultz and M. Stoll and S. Tyerman et al. discussed current and emerging tech- nologies for measuring vine physiological parameters. 22,27 A variety of instruments currently available provide information that can be used to determine irrigation requirements and include measures of: • water potential (a pressure chamber or a psychrometer), • stomatal conductance (a porometer), sap flow, • leaf temperature, • trunk diameter. While these devices are generally used for research rather than commer- cial purposes, this is likely to change as some have the potential to be devel- o p e d i n t o u s e r- f r i e n d l y i r r i g a t i o n scheduling tools. Soil-based measures Since relationships can be established between vine physiological parameters and changes in soil water measurements, it is generally easier to assess vine-water status using devices that measure either soil water suction or volumetric soil water content. The correct installation and positioning of such equipment is important if the data is to be representa- tive of the vineyard. Climate-based measures Water use by a vineyard is closely related to evaporation from an exposed water sur- face. The standard meteorological device to measure evaporation is the Class A pan evaporimeter. Crop factors are used to convert pan evaporation (Epan) to vine- yard water use. However, this is not the preferred method when the canopy cover is incomplete. beauty and brawn Stockton, CA 95205 • 209.944.0921 westernSquare.com Lean, Green and Made in America WESTERN SQUARE I N D U S T R I E S Increasing demand for supplementary irrigation will only be met if acquisition and use of water by vines is optimized.