Crop yield response to water - Cra

(McCarthy and Coombe, 1999), but even in that particular trial, sensory attributes changeddifferentially over time.Water requirementsCrop evapotranspiration increases with vine age from establishment until the canopy and rootsystem reach their full capacity to capture radiation and water (Figure 13). For established vines,seasonal ET c in semi-arid to arid environments, e.g. central California (United States), and Riverina(Australia) ranges from approximately 500 to 800 mm (Williams and Matthews, 1990). Figure14 shows the seasonal dynamics of K c as affected by crop age and environment (temperate vstropical). The seasonal dynamics of crop coefficients comprises two phases with increasing K c fromonset of active growth to peak canopy size, and decreasing K c during leaf senescence. Assuminglinearity, the average rate of increase of K c was 0.005 d -1 for young vines, 0.007 d -1 for older vinesin Washington, and 0.013 d -1 in the tropical São Francisco region. In the declining stage, the rateof change in K c was 0.006, 0.011, and 0.042 d -1 , respectively. In addition to differences in rate ofchange in K c , non-zero K c at the onset of the irrigation season in tropical environments reflects thelack of dormancy and continuous physiological activity during the year in tropical environments.More refined crop coefficients could be obtained on the grounds of a direct, often non-linearassociation with canopy light interception or related variables such as leaf area index. Owing tolarge variation in canopy structure with pruning and training systems, however, the relationshipFigure 13Change in crop evapotranspiration (ET c ) with vine age in Washington, USA. ET c was measuredin large drainage lysimeters. Seasonal (1 April to 31 October) reference evapotranspiration(ET o ) derived from Penman (alfalfa reference) is also shown; the dotted line is the average.Adapted from Evans et al. (1993).1400ETo (mm)1300120011001000500400ETc (mm)3002001000Vine age (years after planting)RieslingChenin BlancCabernet Sauvignon1 2 3 4 5 6 7 8476crop yield response to water