Figure 10: Seasonal evolution of transpiration in plot 2 (vineyard at Setubal, Portugal), during 2001 and 2002.
Transpiration in plot 2 was similar in both years (Figure 10). T ranged from 1.8 to 1 mm day-1, from flowering to harvest. Maximum values of T were roughly one half of the values occurred in plot 1. There were differences in soil and cultivar, but the main reason for this difference was related with LAI. The decrease in transpiration rate during veraison to maturity was smoother than the one verified in 1996 (plot 1). This can be explained by deficit irrigation in plot 2, leading to less water stress.
In conclusion, this low cost approach provided reliable values of T for long periods. Considering the two experiments described and for average summer values for T ranging from about 3 mm/day to 1.7 mm/day, T/ETo were about 0.6 and 0.3 for plot 1 and plot 2, respectively. An intermediate result (0.5) was obtained for the vineyard in slopes, not irrigated, described in Ferreira et al. (2004).
Between middle June and late September the maximum recorded value for ET/ETo was 0.8. ET/ETo and T/ETo always decreased due to water stress, mainly the former, in spite of an increase on ETo in July and August. By the end of Summer ET/ETo was around 0.4 or below.
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