Mikrobieller Stickstoffumsatz in der Rhizosphäre

Abstract

The potential nitrogen immobilization rate of a soil bacterial community was investigated in a laboratorial experiment. The amount of nitrogen immobilized by the bacterial biomass in conditions which were not carbon limited depend on the growth rate of the bacteria and their C/N ratio. Both factors were measured under optimal growth conditions with increasing amounts of ammoniumnitrate (0, 50 and 100 mg N/1). The bacterial growth was four times higher in the 100 mg N/1 nitrogen fertilized treatment compared to the control without nitrogen and the C/N ratio varied between 6.1 and 8.6. If we take these fluctuations into account and calculate the potential nitrogen immobilization rate of the microbial community in a diluvial sand soil, we receive amounts between 45 and 128 kg N/(ha · d). This is a lot of nitrogen which could be transferred within one day if carbon is not limited and the growth conditions are optimal (28 °C and saturated oxygen). In which time course the microbial immobilized nitrogen will be remineralized or transferred into the soil organic carbon pool is not yet understood. Models describing nitrogen transfer rates in soils for fertilization recommendations could probably be improved when these microbial immobilization rates would be included.