Anaerobic conditions can arise as a result of compaction or waterlogging. Production of large amounts of methane would indicate the strongly reducing conditions associated with anoxia. Effects of Toxic Substances on Microorganisms Generally speaking, organic compounds are readily degraded in warm climates, and less so in cold. Toxic metals, on the other hand, can remain in soils and cause long-term damage to soil microbial communities regardless of temperature. Sims discusses the effects of pesticides and organic and inorganic pollutants.
Pesticides can influence soil microbial activity, at times paradoxically.
Application of paraquat led to buildup of fungi and bacteria, but reductions in CO 2 production, cellulose degradation, and nitrogenase activity. Sometimes selective destruction of predators and the resultant buildup of their microbial prey can occur. Inoculation with untreated soil led to suppression of the pathogen in the treated soil, suggesting the possible role of microbial antagonists. Nitrification and symbiotic nitrogen fixation are especially sensitive to disruption by pesticides, probably in part due to the small numbers of species involved in these processes. At normal application rates, Amitrole, 2,4-DB, and diallate can inhibit nitrification for at least 8 weeks, whereas atrazine, bromacil, picloram, and simazine can do so for shorter periods.