Two protocols for following soil methane enrichment were used, one with methane dosed as a carbon source ([Cl-soil) and one with methane plus minerals ([C + Ml-soil). Methane oxidation occurred much faster in soil receiving minerals in addition to methane than in the control soil receiving only methane. In both treatments, only a small fraction of methane (2% to 14%) was converted into microbial biomass C. Nevertheless, a strong increase in soil microbial biomass (up to 1.5 to t&fold) was achieved in the [C + M] -soil in a 3-week period. Due to methane application, the NO,- content of the soil was significantly decreased, by 83% to 90% in the [Cl-soil and by 56% to 83% in the [C + Ml-soil. Soil enzymatic activities were slightly increased in the [C + Ml-soil only. The soil-methane incubation did not alter the composition of the monitored microbial populations in the soil or in rhizosphere of plants. In the [Cl- soi 1, methane incubation resulted in reduction of the shoot dry wt. of maize by 8% to 12%. In the [C + Ml-soil under non-limiting mineral-nutrient status, a significant increase in shoot dry wt. was observed for maize (13%), a neutral effect was registered for spinach and a negative effect was observed for wheat.