Methodology of stem water potential measurement on hedgerow olive orchards

Aim of study: To evaluate the effect of leaf covering, leaf position, leaf age, time and sample size in measurements of stem water potential (Ψstem) in olive hedgerow orchards. Area of study: The experimental orchards were located in the Centre of Spain (Toledo) Material and methods: Midday Ψstem was measured using a pressure chamber in two super-intensive olive hedgerow orchards subjected to various water statuses. Main results: Measurements were taken at solar noon on shaded leaves at mid canopy height following at least 1 hour of covering. Such measurements on 5 trees were sufficient to define the water status of individual homogeneous irrigation blocks. This combination of techniques is essential for repeatable measurements of Ψstem required to establish critical irrigation points and manage deficit irrigation strategies seeking to control vegetative growth and reduce water use with minimal effect on oil yield in olive hedgerow orchards and maximum oil quality. Part of our results weren’t previously reported: 1) Covering leaves with aluminium doesn’t completely stop transpiration and leaves must be covered and located in the shaded part of the canopy. 2) Ψstem depends on leaf height on olive hedgerow. 3) Ψstem of young leaves was less variable than in older ones. 4) Ψstem at solar noon presented larger differences with previous hours than later. Research highlights: Leaves for measurements of stem water potential must be previously covered and located in the middle height of the shaded part of the canopy.