Abstract: Ethylene, produced by spore-forming bacteria in anaerobic microsites, is a critical regulator of microbial activity in soil. It has a central role in a self-regulating microbial cycle in soil with important implications for rates of turnover of organic matter, availability of plant nutrients, and incidence of soil-borne plant disease. Recognition of the presence of numerous anaerobic microsites, especially in the rhizosphere, is the key to understanding ethylene formation in field soils. These microsites may also affect directly the availability of plant nutrients in soil, and this is discussed. Nitrate nitrogen stops ethylene production in soil by poising the redox potential. Similarly, it may interfere with uptake of plant nutrients. This calls for a reappraisal of the supposed benefits of nitrification in agriculture.