ECOTOXICOLOGY OF SOIL FUMIGATION .2. RESIDUAL EFFECTS OF FIELD-APPLIED METHYL BROMIDE ON MICROBIAL ACTIVITIES AND THEIR REACTION TO HERBICIDES [German]

摘要

Under field conditions, methyl bromide had been applied to a sandy loam soil. Two years later, soil from the upper layer (5 cm) was sampled and under laboratory conditions it was additionally treated with the herbicides 'Flussig Herbogil' (dinoterb) and 'Fenikan' (diflufenican + isoproturon). In a parallel subtrial, half of the soil was amended with lucerne meal. During incubation up to 12 weeks, several microbial activities were investigated. As compared to non-fumigated soil, some biomass-related activities were still reduced even 2 years after field fumigation with methyl bromide, whereas nitrogen mineralization was increased. In previously not fumigated soil, both herbicides, bur to a lesser extent 'Fenikan', inhibited biomass-related activities dose-dependently and stimulated carbon and nitrogen mineralization. As compared to these effects, only little further changes occurred in the soil which had been fumigated 2 years before. Depending, however, on the herbicide, its dosage, lucerne meal amendment or sampling time, some modifications occurred especially with nitrogen transformation. The results showed that long-lasting effects of fumigation of field soil can still be found under successive laboratory test conditions, although they had not been detected at the end of the previous field trial, except for the dehydrogenase activity. Finally, microbial ecotoxicology of methyl bromide as well as the applied methods are discussed.