Effects of methyl bromide fumigation, chloropicrin fumigation and steam sterilization on soil nitrogen dynamics and microbial properties in a pot culture experiment

The effects of steam sterilization ( SS), methyl bromide ( MeBr) fumigation and chloropicrin ( CP) fumigation on soil N dynamics and microbial properties were evaluated in a pot experiment. All disinfection treatments increased the NH4+-N level and inhibited nitrification. The additional NH4+-N in the CP treatment probably originated from the decomposition of microbial debris by surviving microbes, while that in the SS treatment was attributable to deamination processes of soil organic N occurring in a less labile fraction in addition to the decomposition of microbial debris. The MeBr fumigation increased the level of - N without changing the soil microbial biomass. Based on the determinations of soil microbial biomass, substrate utilization activity ( Biolog method) and microbial community structure ( phospholipid fatty acid method), the effects of the MeBr, CP and SS treatments on the microbial community were compared. The MeBr fumigation had relatively mild and short- term effects on microbial biomass and activity, but altered the community structure drastically by promoting the growth of gram- positive bacteria. The CP fumigation had large and long- term impacts on microbial biomass and activity; the community structure remained unaffected except for the gram- negative bacteria. Steam sterilization had severe and persistent effects on all parameters. The severity of the effects decreased in the order SS >= CP > MeBr.