Feasibility of using trunk diameter fluctuation and stem water potential reference lines for irrigation scheduling of early nectarine trees

A three-year experiment on early nectarine (Prunus persica L. Batsch cv. Flanoba) trees was carried out with the aim of studying the impact of environmental variables on the trunk diameter fluctuation parameters and the usefulness of the reference-lines derived from the relationship between different meteorological variables and plant water status indicators for sustainable irrigation scheduling. Plants were drip-irrigated and submitted to non-limiting soil water conditions. Measurements of stem water potential at midday (Ψstem), trunk daily growth rate (TGR) and maximum daily trunk shrinkage (MDS) were related with meteorological variables. MDS presented the best fitting line-regressions with both the average air temperature and vapour pressure deficit during the period 11.00–15.00h solar time, since the most important fraction of trunk shrinkage occurred during that period of time, reaching 74% of MDS (on average over the three years studied), and sometimes 90%. The cause of the poor correlation of MDS with ET0 is discussed. Despite the continuous trunk growth of the trees during the experimental period and slight difference in crop load, inter-annual differences were not observed for the three reference lines obtained in any given year (fruit growth, early and late postharvest period).