Microbial biomass in soils of Russia under long-term management practices

 Non-tilled and tilled plots on a spodosol (C_org 0.65–1.70%; pH 4.1–4.5) and a mollisol (C_org 3.02–3.13%, pH 4.9–5.3), located in the European region of Russia, were investigated to determine variances in soil microbial biomass and microbial community composition. Continuous, long-term management practices, including tillage and treatment with inorganic fertilizers or manure, were used on the spodosol (39 years) and mollisol (22 years). Total microbial biomass (C_mic), estimated by the substrate-induced respiration (SIR) method, and total fungal hyphae length (membrane filter technique) were determined seasonally over a 3-year period. Long-term soil management practices (primarily tillage and fertilizer application) led to decreases in total microbial biomass (80–85% lower in spodosol and 20–55% lower in mollisol), decreases in the contribution of C_mic to C_org (2.3- to 3.5-fold lower in spodosol and 1.2- to 2.3-fold lower in mollisol), and 50–87% decreases in total fungal hyphae length compared to non-tilled control plots. The contribution of fungi to total SIR in virgin mollisol and fallow spodosol plots was approximately 30%. However, the contribution of fungi to SIR was approximately two times greater in tilled spodosol plots compared to a fallow plot. In contrast, the contribution of fungi to SIR in tilled plots of mollisol was less (1.4–4.7 times) than for a virgin plot. In summary, long-term soil management practices such as tillage and treatment with organic or inorganic fertilizers are important determinants of soil microbial biomass and the contribution of fungi to total SIR. Received: 28 April 1998