Linking canopy temperature and trunk diameter fluctuations with other physiological water status tools for water stress management in citrus orchards.

The continuous monitoring of crop water status is key to the sustainable management of water stress situations. Two deficit irrigation (DI) treatments were studied during the maximum evapotranspirative demand period in an orange orchard (Citrus sinensis (L.) Osb. cv. Navelina): sustained deficit irrigation irrigated at 55% crop evapotranspiration (ETC), and low-frequency deficit irrigation treatment, in which the plants were irrigated according to stem water potential at midday (Ψstem). Additionally, a control treatment irrigated at 100% of ETC was established. The daily canopy temperature (TC) was measured with an infrared thermometer camera together with measurements of trunk diameter fluctuations (TDF), Ψstem and stomatal conductance (gS). The time course of all physiological parameters and their relationships were analysed, confirming that canopy air temperature differential (TC - Ta) variations and TDF are suitable approaches for determining the water stress. In addition, the maximum daily shrinkage (MDS) and TC - Ta showed high sensitivity to water stress in comparison to Ψstem and gS. Significant relationships were found among MDS and TC - Ta with Ψstem and gS, for monitoring the crop water status by means of MDS vs Ψstem and TC - Ta vs Ψstem. Thus, the combination of these techniques would be useful for making scheduling decisions on irrigation in orchards with high variability in plant water stress.