Enhancing Precision Agriculture Tools for Optimised Nitrogen Management in Open-Field Borettana Onion (Allium cepa L.) Cultivation

Onion (Allium cepa L.) typically exhibits low nitrogen (N) use efficiency due to its shallow and sparse root system architecture, increasing the risk of nitrate leaching, atmospheric losses and compromising yields and quality, especially in sandy soils. This study, conducted from 2021 to 2024 in Northeastern Italy, aims to enhance site-specific top-dressing N prescription management strategies in loose soils prone to N leaching. Unmanned Aerial Vehicle (UAV) based images were acquired during the growing seasons and the relationships with ground surveys were used to develop and test crop-specific algorithms based on in-season critical N concentration and crop growing predictions, to be applied according to precision agriculture approaches. The main results showed that the average bulb yield under the Variable Rate Application (VRA) treatment was 8,798 kg ha⁻¹ dry matter, with a nitrogen use efficiency (NUE) even beyond 0.80. Treatments with less than 180 kg N ha⁻¹ resulted in only slight differencslightared to VRA, while both the 181- 200 kg N ha⁻¹ and >200 kg N ha⁻¹ treatments resulted in significantly lower NUE than the VRA strategy. This four-year trial demonstrated the feasibility of newly implemented VRA strategies in Borettana cultivation by minimising the effect of within-field variability.