Methane dosage to soil and its effect on plant growth.

Two protocols for following soil methane enrichment were used, one with methane dosed as a carbon source ([C]-soil) and one with methane plus minerals ([C+M]-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 2.0-fold) was achieved in the [C+M]-soil in a 3-week period. Due to methane application, the NO3 (-) content of the soil was significantly decreased, by 83% to 90% in the [C]-soil and by 56% to 83% in the [C+M]-soil. Soil enzymatic activities were slightly increased in the [C+M]-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 [C]-soil, methane incubation resulted in reduction of the shoot dry wt of maize by 8% to 12%. In the [C+M]-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.