Microbial biomass C‐ and N‐dynamics in grassland soils amended with liquid manure

Turnover and fluxes of C and N through microbial biomass were investigated on a research site in the grassland region of southwestern Germany. For a period of twelve months, biomass C was determined every 2 weeks and biomass N every 4 weeks (Fumigation‐Extraction). This was done at fertilized plots as well as on plots, which had not been fertilized for eight years. Biomass C and N accounted for 1.5–7.5% of the soil C and 2–9% of the soil nitrogen. Unfertilized plots contained more biomass C and N than fertilized plots. No seasonal influence on the amount of the microbial biomass was visible. C/N ratios were not related to fertilization events. An increase of the C/N ratio with depth suggests a dominance of fungi in the subsurface horizons. Estimates of biomass C and N turnover were calculated by dividing the total measured losses of biomass by the average quantity of biomass present ( McGill et al., 1986), annual fluxes of carbon and nitrogen were calculated by dividing annual mean C(N) by the average C(N) in biomass ( Jenkinson and Ladd , 1981). Average turnover rates for biomass C varied between 1.4 and 4.5 a −1 , turnover rates for nitrogen were slower (1.2–3.3 a −1 ). Carbon Ruxes through the microbial biomass range from 5000 to 8000 kg ha −1 a −1 , while nitrogen fluxes range from 400 to 700 kg ha −1 a −1 .