Microbial Biomass, Respiratory Activity and Nitrogen Fixation in Soddy-Podzolic Soils of the Pre-Urals Area under Various Agricultural Uses

Abstract

Indicators of the microbiological activity of virgin (mixed forest and forb–grassy meadow) and arable (permanent black fallow, permanent barley crop, field crop rotation, perennial legume crops) soddy-podzolic soils (Eutric Albic Retisols (Abruptic, Loamic, Cutanic)) of Perm oblast were studied. Depending on the type of land use, the content of organic carbon (bichromate oxidation method) in the soil varied from 0.78 to 1.57%; the carbon of microbial biomass (substrate-induced respiration method), from 366 to 1236 μg/g; basal respiration rate, from 1.62 to 3.13 µg C–CO2/(g h); and nitrogen-fixing capacity (acetylene method), from 11.53 to 77.18 µg C2H4/(kg h). The maximum values of the studied parameters were noted in the soil under the mixed forest, and the minimum values were in the soil of the permanent (42 yr) fallow. In the soil under forest, a low specific respiration of microbial biomass—2.5 µg C–CO2/(mg Cmic h)—was determined, which indicates the stability and maturity of this ecosystem. The most stable functioning of the microbial community among the arable soils under consideration was observed in the soil of the plot with the long-term (30 yr) cultivation of perennial legume crop (eastern galega, Galega orientalis). The contents of the soil organic matter and the microbial biomass carbon and the specific microbial respiration under galega were close to those of the soil of the forest ecosystem. The content of microbial biomass carbon and basal respiration displayed strong and moderate correlation dependences with the total content of soil organic carbon and its labile fraction.