Evaluation of Oxidant Biocide Formulations for Soil Sanitation

Due to the phase-out of methyl bromide, alternative methods are needed for nursery soil sanitation. This study was conducted to explore various oxidation biocide formulations for deactivating pathogens in nursery soils. Soil respiration rates and deactivation of Bacillus subtilisspores were the two response variables being evaluated in this presentation. We hypothesized that a reduction in the native microbial population in soil types, (commercial top soil and potting soil) due to biocide treatments would reduce soil respiration rates. Furthermore, we suspected B. subtilis spore counts would be reduced. This experimental model was set up using several biocides: liquid chlorine dioxide, chlorine dioxide granules as a fumigant, ozone water, autoclave, and untreated soil (control).  We evaluated the effects of repeated biocide applications of 2, 4, or 6 times and a single application of chlorine dioxide granules (fumigant) on commercial top soil or potting soil. 300 µl of B. subtilisspores were introduced in the soil by means of inoculated steel washers. A single application of chlorine dioxide granules had an equivalent soil respiration rate as the autoclave treatment for potting soil. For the top soil, the autoclave treatment had a slightly lower soil respiration rate than the chlorine dioxide granules.  After a single application of chlorine dioxide as a liquid or granules, B. subtilis had an average log10 reduction of 0.69 and .030 respectively.  In future research, we plan to leave inoculated washers in the soil for the full application treatment regimen or choose another method of inoculant introduction.