Stem EC Probe: An Innovation Irrigation Controller for Agronomic Crops

During the last 50 years, the world is drifting continuously into a water crisis. Drought areas have been doubled, irrigated areas have been doubled, and water withdrawals from aquifers have tripled. The water crisis has affected all continents. Based on mathematical models, drought periods are predicted to double in the next century. Irrigation water availability will continue to decrease. Growers will be forced to increase their water use efficiency, by using precise irrigation. Currently available water stress sensors can be divided into soil sensors and plant sensors. The former are heavily dependent on soil heterogeneity (e.g., 40 soil-probes are needed in order to measure soil water status of one tree). The accurate soil sensors (TDR and Neutron probe) are complicated and expensive, while the inexpensive sensors (as Tensiometers and Gypsum block) are inaccurate and their interpretation is questionable. Additionally, their measurements do not necessarily reflect tree water status. Plant water sensors, which give a direct measurement of plant water stress, including the pressure chambers (the most accurate technique that cannot be automated), as well as dendrometers and LVDTs (less expensive sensors) are  sensitive to air temperature and cannot distinguish between swell-shrink trends caused by daily plant-water relations and continuous stem growth. Our new stem electrical conductivity (EC) probe is based on direct frequent and accurate measurements of stem electrical conductivity which is directly and closely correlated to the most accurate technique, namely, the pressure chamber. Its measurements are also in a good correlation with the accurate stem water content values obtained by the TDR technology (accuracy of 1‰). Its operation is based on a simple, common and an inexpensive technology (a small fraction of the operating costs of the TDR technology). Interpretation of stem EC measurement results, are independent of stem identity or properties and there is no need for calibrations. It gives a direct, physiological indication (therefore reliable) of the tree’s real water need. Measurements are automatic (at pre-chosen intervals; e.g. 5 minutes), and the results, insensitive to variations in salinity and temperature, are analyzed by an algorithm. Currently, it has a proven saving of 35% in water and fertilization and it is further tested in three commercial orchards.