Inactivation of Weedy Rice Using 915 MHz Microwaves with Soil Physicochemical Property and Microbiome Retention

There is a growing demand for alternative low cost and sustainable weed management technology suitable for aerobic and organic farming. In this study, 915 MHz microwave radiation was explored as an alternative technology for weed management. The specific objective was to identify the microwave power and energy levels required to inactivate weedy rice at various soil depths and to understand the impact of the treatment on soil physicochemical properties and the microbiome. Microwave power levels of 10, 20, and 30 kW were tested on soil depths of 2.5 cm, 8.9 cm, and 15.2 cm. Untreated soil samples were used as controls. The total germinability index (TGI) decreased significantly with increased power and reduced soil depth. The TGI ranged from 0.84 (10 kW for 15.2 cm soil depth) to 0 (20 kW for 2.5 cm soil depth or 30 kW for 8.9 cm soil depth). For 8.9 cm of soil depth, 176 to 265 kJ/kg of energy was sufficient to inactivate 80-100% of weeds. For 15.2 cm of soil treated with 30 kW for 30 seconds (188 kJ/kg), approximately 80% reductions in TGI and 64% in germination were observed compared to the control. Re-garding soil physicochemical properties, minimal differences were found due to mi-crowave treatments. The microwave treatment had no impact on soil total bacteria, whereas ammonia-oxidizing archaea and ammonia-oxidizing bacteria showed signifi-cant reductions as compared to control. Therefore, 915 MHz microwave heating can be a useful alternative technology for weedy rice management in rice fields. However, the technology needs to be tested in the field to optimize the energy required to achieve complete inactivation of a broad spectrum of weeds.