Comparison between different methods for measuring transpiration in potted apple trees

Five different methods for measuring transpiration, which include gravimetric analysis (control), heat pulse velocity (HPV), time domain reflectometry (TDR), single leaf and whole plant infrared gas-exchange measurements, have been tested on two cultivars (Redcort and Empire) of young apple trees (Malus communis L.). The objective was to compare these methods and establish the most affordable one to be used in greenhouse conditions in order to determine and/or estimate the amount of water for an efficient irrigation management. Results obtained with TDR were particularly accurate and not statistically different with respect to the control (-4.2 %) and this was supported by the correlation coefficient (r = 0.94) found. The HPV method was sufficiently accurate and reliable for small stems, however, in our conditions this method generally underestimated the transpiration (-32.4 %). Single leaf and particularly whole plant infrared gas-exchange measurements suffered an overestimation of the transpiration with respect to the control.