|Abstract: ||The experimental work, on the water use of a pear orchard (Pyrus communis cv.
‘Rocha’), took place in the region of Oeste, Portugal (lat. 39º 28’ N, long. 9º 7’ W), during the
growth periods of 2004 and 2007.
Measurements of sensible and latent heat (evapotranspiration - ETec), obtained with
the eddy covariance technique, and other energy balance components, took place in 2004 (12
days in August) and in 2007 (43 days from June to September). In 2007, sap flux was also
measured, using the Granier method (from May to September), as well as the radial profile of
sap flux velocity, using a heat pulse method (compensation technique). The Granier sensors
have been built with innovative technical improvements, aiming at the measurement of
temperature natural gradients in real time, simultaneously with sap flow measurements.
Using transpiration results (calculated as the difference between ETec and soil
evaporation obtained with lysimeters) and sap flow measurements it was possible to calibrate
the Granier method. The following function was obtained: 1.958
154 10 5 +
= × ×
i i u K , where ui
is the sap flux density [m3.m-2.s-1] and Ki+1 is the flux index.
As a result of the calibration performed, a seasonal variation of transpiration could be
obtained, with a mean value of 1,1 mm.day-1 in 2007, corresponding to an average basal crop
coefficient of 0.32, with a minimum in May (0.25) and a maximum in August (0.37).
Considering the soil evaporation component and the understorey transpiration, a crop
coefficient of 0.6 was obtained in 2004 and 0.7 in 2007, clearly below the tabled values.
Key-words: evapotranspiration, irrigation scheduling, sap flow, Pyrus communis L. cv.
‘Rocha’, energy balance, sparse vegetation|