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) an d 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 biom ass and microbial community composition. Continuous, long-term management p ractices, including tillage and treatment with inorganic fertilizers or man ure, were used on the spodosol (39 years) and mollisol (22 years). Total mi crobial biomass (C-mic), estimated by the substrate-induced respiration (SI R) method, and total fungal hyphae length (membrane filter technique) were determined seasonally over a 3-year period. Long-term soil management pract ices (primarily tillage and fertilizer application) led to decreases in tot al 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 i n total fungal hyphae length compared to non-tilled control plots. The cont ribution of fungi to total SIR in virgin mollisol and fallow spodosol plots was approximately 30%. However, the contribution of fungi to SIR was appro ximately two times greater in tilled spodosol plots compared to a fallow pl ot. In contrast, the contribution of fungi to SIR in tilled plots of mollis ol was less (1.4-4.7 times) than for a virgin plot. In summary, long-term s oil management practices such as tillage and treatment with organic or inor ganic fertilizers are important determinants of soil microbial biomass and the contribution of fungi to total SIR.