Evaluation of Sap Flow Sensors to Measure the Transpiration Rate of Plants during Canopy Wetting and Drying

Muhammad Jasim Uddin ,Rod Smith,Nicola Hancock ,Joseph Foley

doi:10.5296/jas.v2i2.6134

Muhammad Jasim Uddin , Rod Smith + Show 2 more

Open Access

https://doi.org/10.5296/jas.v2i2.6134

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Abstract

Accurate measurement of transpiration is required to estimate the various components of evaporation losses during sprinkler irrigation. Among the methods, sap flow measurements have widely used for direct measurements of transpiration rate in plant. To evaluate the applicability of this method to field experiments involving canopy wetting (by sprinkler irrigation), stem flow measurements were compared with transpiration values estimated from successive mass measurements of small potted plants using pre-calibrated mini-lysimeters in a glasshouse at the University of Southern Queensland, during the period August–October 2010. From this study it was found that when the canopy was dry, the sap flow measurements mirrored the transpiration rate of plants with reasonable accuracy, overestimating the transpiration rate by about 11%. The measurements showed no evidence of time lag between sap flow and transpiration. Following wetting of the plant canopy the sap flow declined rapidly reflecting a decline in the transpiration rate transpiration and sap flow. Location of the sap flow gage on the stem was seen to be a factor with gages at different heights giving different sap flow rates again due to the buffering capacity of the stem.

Highlights

Partitioning of evapotranspiration (ET) from sprinkler irrigated cropping into its different components is not common practice due to limitations of the traditional measurement techniques
It is the dominant component of ET between irrigations, (Lawrence et al, 2007), whereas during sprinkler irrigation, canopy evaporation is assumed to be the dominant component followed by transpiration, soil evaporation and droplet evaporation (Thomson et al, 1997)
From this study it is shown that when the canopy was dry the sap flow and transpiration rates followed a similar pattern

Summary

Introduction

Partitioning of evapotranspiration (ET) from sprinkler irrigated cropping into its different components (transpiration, canopy evaporation, droplet evaporation and soil evaporation) is not common practice due to limitations of the traditional measurement techniques. Transpiration plays a different role in evapotranspiration during irrigation and non-irrigation periods. It is the dominant component of ET between irrigations, (Lawrence et al, 2007), whereas during sprinkler irrigation, canopy evaporation is assumed to be the dominant component followed by transpiration, soil evaporation and droplet evaporation (Thomson et al, 1997). The only potential way to infer the rate of transpiration during sprinkler irrigation is by measurement of sap flow. The transpiration rate for whole plants is determined by measuring the rate at which sap ascends stems (Smith and Allen, 1996). Swanson (1994) reported that sap flow measurement has several advantages including relative ease of use, ease of automation, capacity for real time measurements over a period of time as short as necessary, and the measurement of the transpiration term separate of the components of ET (Chabot et al, 2005)

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