SOIL-NITROGEN FRACTIONS AS INFLUENCED BY SAMPLE PREPARATION AND EXTRACTION

In order to evaluate the influence of extraction procedure on extracta ble nitrogen (N) fractions, fresh as well as dried soil samples were e xtracted with CaCl2 at various temperatures (20, 40, 60, 80 degrees C) for 30-120 minutes. Data obtained were compared with those from the e lectro-ultra-filtration (EUF) method. Increasing the drying temperatur e as well as the extraction temperature led to an increase in N-org co ntent. The EUF and CaCl2-method produced comparable results for all N- fractions (NO3-, NH4+, N-org) when an extraction temperature of 80 deg rees C was applied for two hours. Data presented suggested that the N- org fraction represented mainly the microbial biomass and may thus be considered as being easily available to plants.