Enhancing water use efficiency in irrigated agriculture through variable rate drip irrigation: the case of a pear orchard in Northern Italy

Very few studies applying variable rate irrigation (VRI) by means of drip systems are described in the literature, even if localized irrigation is an effective irrigation strategy for orchards. In the agricultural season 2018, the effectiveness of variable rate drip irrigation was demonstrated in a pear orchard of about one hectare located in Lodi (NUTRIPRECISO project; RDP-EU, measure 1.2.01, Lombardy Region). Through the use of an electro-magnetic induction sensor (EMI) pulled by a quad-bike, soil electrical conductivity field maps were obtained, and two homogeneous zones were identified by applying statistical techniques. A soil profile was opened in each homogeneous zone, soil core samples were collected from each horizon, and soil water content at the field capacity and wilting point were laboratory-measured. Two irrigation management zones (MZ) were defined, corresponding to the homogeneous zones; for each MZ, the total available water (TAW) in the rooting zone was computed from the lab measurements and used to obtain the irrigation prescription map (IPM). Based on the IPM, a drip irrigation system characterized by three sectors was designed and realized: two sectors supply water to the two MZs, while the third one illustrates the 'reference irrigation management'. In the first two sectors, drip lines were optimized in terms of spacing between drippers and dripper flow rates according to the soil types. In the third sector, the most common drip lines used in orchards were installed. A wireless sensor network including two soil water content probes for each sector was used to fine-tune the frequency and duration of irrigation events in the first two sectors; in the third sector, irrigation was supplied following the farmer's habit. Drip VRI allowed to reduce the pear orchard water consumption of about 50% compared to the 'reference irrigation management', without losses in yield and product quality.