Abstract
and stomatal conductance (gs) are needed when regulated deficit irrigation (RDI) strategies are applied.
The aim of this experiment was to compare sap flow and canopy temperature (Tc) measurements with
more classical methods like s or gs to predict the effect of deficit irrigation on fresh fruit weight in
citrus trees. The experiment was performed during the summer of 2011 in a Clementina de Nules
orchard undergoing RDI. Sap flow was determined by means of the compensation heat pulse method in
well-watered and RDI trees. Tc was measured continuously with infrared thermometers (IRTs) mounted
over the canopies and also weekly with an infrared hand-operated thermographic camera taking frontal
images of the sunlit side of tree crowns. Concurrently, s and gs were also measured on all trees. Results
showed that the evolution of the relative transpiration obtained with the sap flow sensors was in agreement
with the plant water stress experienced. The values of Tc obtained with the fixed IRTs, normalized by
air temperature (Tc −
Ta) were in general poorly related with s and gs. However, when Tc was obtained
from thermal imaging, there was a good correlation with s in days of relatively high water stress (i.e.
when s differences among treatments were >1.0 MPa). The average fruit weight at harvest was significantly
correlated with all the stress indicators, and the best correlation was that of thermographic Tc
followed by s and gs. Overall, results showed that in citrus trees Tc measurement obtained from thermal
imaging is a good tool to predict the effect of water deficit on fresh fruit weight.
