Suitability of trunk diameter reference lines for irrigation scheduling with saline water in late mandarin trees with different crop load

A two year experiment on Fortune mandarin trees (Clementina × mandarina Dancy (Citrus clementina Hort. Ex. Tanaka × Citrus reticulata Blanco)) grafted onto Cleopatra mandarin (Citrus reshni Hort. ex. Tanaka) rootstock was carried out with the aim of studying the suitability of midday stem water potential (ψstem) and trunk diameter reference baselines for irrigation scheduling. Plants were drip-irrigated with saline water during the second year (EC25°C ≈ 4 dS m−1). Measurements of ψstem, trunk daily growth rate (TGR) and maximum daily trunk shrinkage (MDS) were related with meteorological variables. Among them, MDS presented the best behavior. The mean temperature during the period 10.00–15.00 h solar time (Tmd) was the environmental variable that best correlated with MDS, although there were no differences with other T-related variables (daily mean and daily maximum values). MDS data from stage III did not correlate with meteorological variables and fit-linear regressions became better with data from stages I and II (March–October), this being the period which covers 80% of total crop water requirements. Despite the different conditions that the trees were submitted to during the experimental period, i.e. irrigation water with different salinity and crop load, inter-annual differences were not observed in the reference baselines obtained.

► We study the suitability of maximum daily trunk shrinkage (MDS) for irrigation scheduling in citrus.
► Best-fit linear regressions were MDS vs vapour pressure deficit and temperature.
► Reference lines were not different between years despite of changes in salinity and crop load.
► MDS vs ψstem regression showed a low r2, which increased when phenological stages were considered.