Potential of microwave soil heating for weed management and yield improvement in rice cropping

Abstract

Herbicide-resistant weeds have prompted the development of non-chemical weed-control techniques for sustainable crop production. We examined the potential of pre-emergence microwave (MW) soil treatment to suppress weeds and enhance grain yield in rice (Oryza sativa L.) cropping in two agro-ecological zones of Australia. An experimental MW weed killer, which has four, independently controlled, 2-kW MW generators operating at 2.45 GHz, was used to treat the soil before cropping under field conditions. A once-off MW soil treatment (duration 60 s) and an untreated control were assigned in a randomised complete block design with five replicates at two study locations: Dookie (Victoria) and Jerilderie (New South Wales). Simpson’s numerical surface integral approximation estimated the applied energy density of ~500 J cm–2. This energy increased the soil’s temperature up to 70–75°C in top soil horizon (0–6 cm) as depicted by infrared thermal imaging. No statistically significant difference was detected for weed control between MW and untreated control plots at either study location. At Dookie, grain yield did not significantly increase in response to MW soil treatment, whereas at Jerilderie, grain yield was 20% higher (P < 0.05) with MW soil treatment than in control plots. At Jerilderie, the irrigation water use efficiency (t ML–1) was 21% higher in MW plots than control plots. In summary, MW exposure of 60 s appeared to be an insufficient heating duration for seedbank depletion. This suggests further treatment modification followed by rigorous testing under different soils conditions using the MW prototype.