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Advisor(s)
Abstract(s)
In order to validate a model of vine transpiration based on
radiative surface temperature a field trial was conducted in a
vineyard in the Do region, centre of Portugal, with the cultivar
"Touriga Nacional". The model is based on the partition of net
radiation between the components of the canopy (vines, soil, and
grass cover), considering that the vines and the undercover (sou
plus grass cover) act separately and in parallel. Thus, the latent
heat flux from the vines to the amosphere (XT) is determined
from vine net radiation (Rn) and sensible heat flux (H). The
partition of net radiation (Rn) between the undercover (Rn) and
the vines (Rn) is made considering the exponential form for
radiation extinction, with the coefficient of extinction being
corrected with a factor dependent on the zenital solar angle (p)
while leaf area index (LAI) is corrected with a clumping factor,
Q(p). Sensible heat flux from the vines (H) is calculated from
radiative temperature (Te) considering that the fluxes from the
different origins are independent and that there are two resistances
in series between the canopy and the atmosphere: the leaf
boundary layer resistance (raHc) and the aerodynamic resistance of
the crop (raH). Besides the estimation of the daily values of
transpiration, the model allows to study the evolution of the
different components of the radiation balance throughout the day.
The daily evolution of the evaporation fraction from the vines
(FE) can be approximated by a concave curve. Values of FE > 1
show that, under certain circumstances and periods of the day,
energy used for transpiration (XT) is greater than crop net
radiation, which indicates that there are exchanges of energy
between the several components of the surface, namely when
evaporative demand from the atmosphere is high and there are no
soil water restrictions. The model also shows that, regardless ofthe
soil water status, transpiration is a big part ofRn when these values
are low (in the beginning ofthe morning and late afternoon).
Description
Keywords
vineyard Região do Dão radiation
Pedagogical Context
Citation
Rodrigues P, Pedroso V, Gouveia JP, Martins S, Lopes CM and Alves I (2011). Daily evolution of the balance of radiation components in a vineyard canopy at the Dão wine region, Portugal. Proc. 17th Int. Symposium GiESCO, pp. 29-31 August- 1 September, Asti, Italy