Microclimatic physiological and productive effect of the overcanopy irrigation in an apple orchard

To test the efficacy and sustainability of evaporative cooling, two blocks of a commercial 'Fuji' apple orchard in Medelana (Ferrara, Italy) were subjected to two irrigation regimes: drip irrigation alone (DRI) or, between July and August (the hottest period of the year), supplemented by overcanopy irrigation (OCI). Stem/leaf water potential, leaf gas exchange where performed the day before, soon after and the day after OCI, along the growing season. Daily fruit growth, leaf and fruit temperature and microclimatic parameters within the blocks where monitored for the entire experiment. No difference was found in leaf/stem water potentials and leaf gas exchanges the day prior and after OCI. Photosynthesis, transpiration and stomatal conductance were improved on the OCI day. Also, fruit growth increased only on the OCI day, with higher rates all day long, but no further effects in the following days. Leaf, fruit temperature and microclimatic measurements within the blocks were only affected during OCI. Yield data show no difference between the two irrigation regimes. OCI in the environment tested affects tree performance only during application and a few hours afterwards. This management practice reduces water use efficiency resulting in more water applied per ton of fruit, likely a result related to the hot and humid climate of the Ferrara province.