Are fruit dendrometers reliable to schedule irrigation in olive trees?

Abstract

Fruit dendrometers have been intensively used in the study of fruit crop management but rarely as a water stress indicator despite being the fruit the main target of regulated deficit irrigation (RDI) studies. Our objective is to better understand the fruit dendrometers usefulness to assess water stress and to evaluate its use to schedule RDI in olive orchards. We compared fruit dendrometers with other sensors previously used as water stress indicator (i.e. trunk dendrometers and ZIM probes) and with traditional measurements such as midday leaf water potential (Ψl,md) to assess their applicability. All the sensors were installed in the olive trees after the pit hardening period (ca. May – June 2017) in plants under full irrigation (100% irrigation needs, WW) and in plants under a 45% RDI (WS). Fruit and trunk diameter growth rate (FGR and TGR, respectively) presented significant correlation with the Ψl,md for the data from the WS treatment. At the days when irrigation was applied, FGR and TGR increased, and the maximum output pressure of the ZIM probes (Pp) decreased. The TGR and Pp were firstly affected both at the beginning and at the end of the deficit irrigation period in comparison to FGR. We conclude that fruit dendrometers have potential to be a reliable method to schedule RDI, which is advantageous because fruits are more directly related to final yield than the other stress indexes used. However, they cannot be used during the whole irrigation season (when there are no fruits, or they are too small).