Water use of a super high-density olive orchard submitted to regulated deficit irrigation in Mediterranean environment over three contrasted years

The measurement of transpiration at the field level is a challenging topic in crop water use research, particularly for orchards. The super high-density olive orchard system is in great expansion all over the world, so these investigations are necessary to assess the trees water use under different irrigation techniques. Here, transpiration at plant and stand scales was measured using the sap flow thermal dissipation method, in an olive orchard (cv. "Arbosana") subjected to standard (SI) and regulated deficit irrigation (RDI) with a withholding irrigation period under Mediterranean climate (southern Italy). The measurement method was used after specific calibration and correction for wound effect, azimuthal and gradient errors. Water use efficiency (WUE) and water productivity were determined over three complete growth seasons (2019-2022). The seasons were submitted to highly contrasted weathers. Measurements of stem water potential and stomatal conductance showed that the RDI trees were under mild-moderate water stress only during the withholding irrigation period, otherwise the two treatments were under the same good water conditions. Following these small water differences between treatments, results showed that seasonal transpiration (Ep) was not significantly different in the two treatments in all seasons (249 and 267 mm, 249 and 262 mm, 231 and 202 mm for SI and RDI in the three seasons, respectively) and that WUE was greater in RDI treatment without any impact on yield. The main conclusion is that, when the available water in the soil is limited, olive trees decrease transpiration under any atmospheric conditions, but when the water in the soil is amply available, high atmospheric demand conditions lead to a decrease in tree transpiration.