Soil Disinfestation with Steam
Heat treatment can be used for soil sterilization or pasteurization (USDA, 1995). Heat distribution in the soil occurs mainly through conduction, with the isothermal fronts parallel with the soil surface (Minuto et al., 2003). Studies have shown that most plant pathogens, insects, and weeds will die when moist soils are heated to temperatures of 150°F (65°C) for 30 min. (Baker and Roistacher, 1957). The time and amount of steam needed to raise the soil temperature to 150°F depends on various soil factors including texture, type, and moisture content. Minuto et al. (2003) found that shorter steam application times corresponded to soil moisture content between 8.5 and 12% in sandy-loam soil and between 6 and 7% in a sandy soil. Steam applied to field soil that raised the temperature to 140°F for 20 min. resulted in weed control comparable to MB (Vidoto et al. 2009). One advantage of steaming in addition to pest control is that it lacks the negative environmental and worker health issues associated with chemical fumigants. Some have reported that steaming has little to no lasting negative impact on soil quality or soil microbial communities (Jäderlund et al.,1998; Norberg et al., 2001; Zackrisson et al., 1997) as opposed to the potential impact of MB fumigation (Ibekwe et al., 2001; Ros et al., 2008; Yamamoto et al., 2008). Some studies have reported a more significant change in soil microbial activity due to steam sterilization (Tanaka et al., 2003; Yamamoto et al., 2008). Differences may be related to duration of steam application and soil temperatures attained during steam treatments as well as the soil organic matter content. Another advantage pertains to increased crop growth and yields (Moyls et al., 1994; Luvisi et al., 2006). Previous work has found that strawberry fruit yields from steam treated soils were similar to MBPic (Samtani et al. 2012).