Articles
COMBINATION OF SAP FLOW AND EDDY COVARIANCE TECHNIQUES TO OBTAIN LONG TERM TRANSPIRATION IN A PEAR ORCHARD
Article number
846_3
Pages
53 – 60
Language
English
Abstract
In order to obtain long term, inexpensive and reliable data on transpiration (T) or evapotranspiration (ET) of woody crops, eddy covariance (EC) and a currently available, low-cost sap flow (SF) method can be combined.
This was applied in a pear orchard.
The experimental work took place during summer 2007, at the Oeste region, central Portugal (Vale de Maceira, Alcobaça) on a 2.5 ha plot, inserted in an area of 34 ha of pear and apple orchards.
During selected periods, ET was measured by the EC method and soil plus understorey water loss (Es) was measured using a set of microlysimeters.
Closure error for the energy balance by EC method was 11%. From ET and Es measurements, T was calculated by difference (ET-Es) and compared with the results from SF measurements upscaled to the stand level.
This comparison provided experimental evidence of underestimation from SF measurements using the original calibration equation, for the conditions under study, as observed in previous experiments.
Radial profile and natural gradients (by use of a third sensor) were taken into account but did not explain the underestimation.
Night T seamed related to VPD. The relationship obtained, allowed an adjustment of the results from long term SF measurements, obtaining corrected T data for the duration of the vegetative cycle.
From the seasonal T data, coefficients used in irrigation engineering could be derived, average T/ETo being 0.32.
This was applied in a pear orchard.
The experimental work took place during summer 2007, at the Oeste region, central Portugal (Vale de Maceira, Alcobaça) on a 2.5 ha plot, inserted in an area of 34 ha of pear and apple orchards.
During selected periods, ET was measured by the EC method and soil plus understorey water loss (Es) was measured using a set of microlysimeters.
Closure error for the energy balance by EC method was 11%. From ET and Es measurements, T was calculated by difference (ET-Es) and compared with the results from SF measurements upscaled to the stand level.
This comparison provided experimental evidence of underestimation from SF measurements using the original calibration equation, for the conditions under study, as observed in previous experiments.
Radial profile and natural gradients (by use of a third sensor) were taken into account but did not explain the underestimation.
Night T seamed related to VPD. The relationship obtained, allowed an adjustment of the results from long term SF measurements, obtaining corrected T data for the duration of the vegetative cycle.
From the seasonal T data, coefficients used in irrigation engineering could be derived, average T/ETo being 0.32.
Publication
Authors
N. Conceição, M.I. Ferreira
Keywords
water use, Pyrus communis L. cv. ‘Rocha’, Granier method, transpiration, evapotranspiration, natural temperature gradients, Oeste
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