A device for scheduling irrigation in fruit tree orchards from sap flow readings

Abstract

The aim of this work was to design and test a controller (CRP) able to calculate the irrigation dose automatically, suitable for high frequency irrigation in fruit tree orchards. The device consisted of three (replicates) measuring units (MU), a control unit (CU) and a pump and electrovalve controller (PEC). The MUs collected information on the transpiration (Ep) dynamics within the orchard, with the compensation heat-pulse method. Each MU made sap flow readings in one normally-irrigated (NI) tree and in one over-irrigated (OI) tree used for reference. The time course of the EpNI/EpOI ratio was used by the CU for calculating the irrigation dose (ID) daily. The system was programmed to apply a deficit irrigation in which the trees were bound to use part of the readily available water in the soil. Laboratory tests showed a high performance of the CRP for amplifying and filtering output signals from the sap flow probes. The field test showed the CRP was able to collect and handle sap flow data, to calculate ID according to the design algorithm, and to control the pump and electrovalve for supplying the desired ID to the experimental plot. Whether the use of the CRP means an improvement on irrigation scheduling, as compared to standard methods, was not evaluated in this work.