Continuous Direct-Injection of Aqueous Ozone in Drip Irrigation Systems: Technical Feasibility and Preliminary Validation for Nematode Control in Greenhouse Tomato Cultivation

Abstract

Climate change, together with the projected growth of the global population by 2050, represents a serious threat to food security and highlights the need for sustainable alternatives to maintain agricultural productivity. Among the main factors limiting crop yields are plant-parasitic nematodes (PPNs), which are responsible for nearly 10% of global crop losses and approximately 30% of yield losses in tomato production. The traditional use of chemical soil disinfection, including methyl bromide, has been increasingly restricted due to environmental and toxicological concerns, driving the search for safer alternatives. Aqueous ozone (O₃) has a high oxidative potential (2.07 V), and has demonstrated effectiveness in pathogen inactivation without leaving harmful residues. In this study, different ozonation strategies were evaluated for greenhouse tomato cultivation using drip irrigation in central Chile. A key technical limitation, namely O₃ instability within irrigation systems, was addressed by transitioning from a batch recirculation configuration, which showed concentration losses of up to 87%, to a much more efficient continuous direct-injection system. This approach enabled the maintenance of stable dissolved O₃ concentrations of up to 2.0 mg/L at the terminal emitters along 50 m drip irrigation lines, supplying a final irrigated area of 1,250 m2 with losses limited to approximately 15% between the irrigation head and the last emitter. A single pre-plant application resulted in marked reductions in nematode populations, including reductions of 87.6% for Meloidogyne spp., 75.6% for Pratylenchus neglectus, as well as the absence of detectable mobile stages of Pratylenchus spp. under the evaluated conditions. Overall, these results demonstrate the technical feasibility of delivering biocidal O₃ concentrations through large-scale drip irrigation systems. The observed reductions in nematode populations provide preliminary biological validation of the relevance of the delivered concentration for nematode suppresion.