Soil disinfection with ozone (O3) as an alternative to methyl bromide - a sustainable practice in agriculture

Abstract: Methyl bromide (MeBr) is an effective pre-plant soil fumigant, highly efficient herbicide, nematicide, insecticide, and fungicide, and it is used for many high-input, high-value crops to control soil pests. Being identified as a substance that depletes the ozone layer, MeBr was scheduled under the Montreal Protocol to be completely phased-out by 2005 in developed countries and 2015 in developing countries. Ozone is often used to disinfect drinking water and wastewater due to its oxidizing properties (Van Leeuwen 1996; Van Leeuwen et al. 2003). In this paper, ozone was experimented on three soil pests: Fusarium oxysporum, Phytophthora sojae and nematodes, to test its potential as an alternative to methyl bromide in soil disinfection. Samples of conidial suspensions of F. oxysporum treated with ozone, resulted in total killing of the pathogen with a dose as low as 0.84 mgO 3 /L at high ozone gas concentrations, while 31.8 mgO 3 /L killed 41% of spores in suspension at a lower gas concentration. These findings reveal the importance of gas-phase concentration (GPC), which means that at higher GPC (using oxygen as ozone carrier) the ozonation is much more efficient in killing the pathogen. The bioassay on Phytophthora resulted in 100% inhibition of the disease at a dose of 0.47 mgO 3 /kg soil. The ozonation of nematode-infected soil showed that ozone LD50 on nematodes is less than 0.5 mgO 3 /kg soil. The findings of this research imply that ozone might be an efficient and sustainable alternative to MeBr, especially that it degenerates quickly into oxygen, an environmentally-safe, non-toxic residue.