Effects of Microwave Oven Treatment on Microorganisms in Soil

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Abstract
Procedures were developed for routine microwave (MW) radiation treatment of soil to eliminate or reduce populations of soil-borne plant pathogens. Shredded, naturally-infested soil in plastic bags was exposed to full power in an MW oven. Assays on selective media indicated that the effects of MW treatment on populations of soil microorganisms increased with increasing treatment time, decreased with increasing treatment time, decreased with increasing amounts of soil, and decreased with increasing soil water content between 16 and 37% (weight water/dry weight soil). No pronounced effect of soil type was noted for 5 mineral soils. Treatment of 1 kg soil at 7-37% water content for 150 s eliminated populations of Pythium, Fusarium and all nematodes except Heterodera glycines in all soils tested. Marginal survival of Rhizoctonia, cysts of H. glycines, and vesicular-arbuscular mycorrhizal fungi was observed in some soils at this treatment rate. Treatment of 4 kg of soil for 425 s gave comparable results. Compared with autoclaving (1 h on each of 2 days in succession) or methyl bromide-chloropicrin (98-2) fumigation (0.454 kg/45 kg soil), MW treatment released less nutrient into the soil solution, had less effect on soil prokaryotes, and resulted in less recolonization of soil by Fusarium and other fungi. MW treatment was a convenient and rapid method of eliminating soil-borne pathogens from soil without excessive detrimental effects.