A general algorithm for automated scheduling of drip irrigation in tree crops

Judicious irrigation necessitates development of technologies that apply the precise amount of water demanded by crops. The goal is to schedule irrigation according to the particular requirements of each orchard and to the variability encountered during the season caused by weather conditions, canopy development and other factors. For supporting a precise and low labour management of irrigation here we propose and depict an algorithm that coordinates seven automatable tasks: (1) estimation of irrigation needs, (2) adaptation to a particular irrigation setup, (3) execution of the schedule, (4) soil and/or plant monitoring, (5) interpretation of sensor data, (6) reaction to occasional events and (7) tuning the model of irrigation needs. This is illustrated with three examples from a peach orchard where a software tool implementing the algorithm was configured to manage irrigation under different strategies. They included two alternative methods for estimating the crop water needs: a typical water balance based on reference evapotranspiration (ETo) and a variation based on the measurement of solar radiation intercepted by the canopy. They also included two types of sensors for feedback: soil water probes and dendrometers, the latter for applying regulated deficit irrigation. The results show that the proposed algorithm provided a common framework that could be embraced under different irrigation strategies to support autonomous control through the season, requiring no more data than those acquired and processed by the same system and enabling some degree of tolerance to failures. Overall, some advantages were the fast response to changes in factors such as weather conditions whose effect is rather predictable. At the same time the algorithm self-adjusted through feedback to variation in orchard-specific factors related with crop development and phenology which would be hard to model. The separation between agro-meteorological and hydraulic concerns in different steps of the algorithm facilitated the adaptation to the particularities of each irrigation setup, simplifying the use of commercial equipment from different manufacturers.