Crop yield response to water - Cra

FIGURE 14Seasonal dynamics of crop coefficients for vines in (a) central Washington (46 o N, USA) and (b)São Francisco (9 o S, Brazil). Sources: (a) Evans et al. (1993) and (b) Teixeira (1999).0.8a0.60.40.2oldergenericThompson SeedlessCrop coefficient0.070 90 110 130 150 170 190 210 230 250 270 2901.21.0byoungerChenin Blanc, Cab SauvignonRiesling0.80.6Italy0.40.2140 160 180 200 220 240 260Day of yearbetween crop coefficient and leaf area index is not unique. The relationship between cropcoefficient and leaf area index may also show hysteresis, i.e. the relationship is different forincreasing or decreasing K c (Netzer et al., 2009). To deal with these problems, Williams andAyars (2005) proposed an approach to characterize crop coefficients on the basis of canopy lightinterception, and demonstrated the robustness of a practical grid-method to measure the amountof shade cast on the ground by table grapes.wATER PRODUCTION FUNCTIONSThe diversity of production systems targeting different combinations of fruit volume and qualitycontribute to the large scatter in the relationship between yield and water use. Furthermore,scarcity of data means the actual shape of the function remains speculative in particular forrelative ET c below 0.4 (Figure 15). In common with other tree crops yield is maintained untilrelative ET c approximates 0.8, and a consistent almost linear decline is observed in the rangeof relative ET c from 0.8 to 0.4. The data for Tempranillo wine grapes suggest a more sensitiveresponse to relative ET deficits in contrast with the response of table grapes (Figure 15). Thisis probably because of a limitation in the maximum ET c imposed by pruning and other culturaltechniques in the case of wine grapes, while such limitation is not normally imposed in tablegrapevine 477