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The Complete Grape Growing System

The Complete Grape Growing System

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Figure 5: Relationship between SF estimated with the Granier method (original equation) and ET measured by EC method (half-hour fluxes) for periods of negligible soil evaporation (T ~ ET). Plot 1 (vineyard, Portugal), 1996.

The reasons for underestimation of the Granier method can be related with wood anatomy, more critical for ring porous species, as grapevines. For ring porous, Cleawater et al. (1999) found a 45% underestimation of sap flow density.

For daily fluxes (Figure 6) and also for periods of negligible soil evaporation, a good relationship between SF (Granier method) and ET (eddy covariance data) was found (T=1.1*Tgr15 with r2=0.84) for cv. Trincadeira (V. Santarém, 1996, 1997) and Syrah (Setúbal, 2001, 2002). This relationship, valid for ET between 1 and 3 mm.day-1, was confirmed with data obtained in pots, for the lower range, as described in Silvestre (2003). Being so, it could be applied in other situations, allowing corrections of SF measurements to obtain T, even in separate plots where EC could not be used. An application of this process was shown for small vineyard plots in slopes (Ferreira et al., 2004), enabling an interpretation of the effect of varying atmospheric demand (wind and radiation) and varying soil water content due to erosion effects, on total T and on T per unit of leaf area index (LAI).

Using this approach, T was estimated for plots 1 and 2, during longer periods (Figures 7, 8 and 10). In plot 1 (Figure 7), maximum T reached 4 mm day-1 in both years and, at maturity, when Summer drought normally imposes a moderate water stress, it reached values around 1 mm day-1and 2 mm day-1, in 1996 and 1997, respectively.

SF Granier meth. (mm day-1)

Figure 6: Relationship between daily fluxes from SF (original Granier equation) and EC methods, for negligible soil evaporation (ETec=Tec) at V. Santarem (1996, 1997) and Setubal (2001, 2002) vineyards, Portugal.

SF Granier meth. (mm day-1)

Figure 6: Relationship between daily fluxes from SF (original Granier equation) and EC methods, for negligible soil evaporation (ETec=Tec) at V. Santarem (1996, 1997) and Setubal (2001, 2002) vineyards, Portugal.

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