DENITRIFICATION, NITROGEN FIXATION AND NITRIFICATION IN CONTINUOUS FLOW LABORATORY SOIL COLUMNS

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Abstract
Apparent steady state denitrification and N2 fixation were simultaneously detected in soil columns supplied with a solution containing glucose (250 μg C∙mL−1) and potassium nitrate (10 μg N∙mL−1. The addition of 10.1 kPa (0.1 atm) C2H2 to the air flow through the column resulted in depth profiles of N2O and C2H4 which showed that a zone of active denitrification was underlain by a zone of C2H2 reduction. About 90% of the added NO3− was denitrified and about 10% of the products was N2O. Continuous addition of ammonium chloride (25 μg N∙mL−1) resulted in steady state oxidation of all the NH4+. The introduction of C2H2 (10.1 kPa), however, inhibited nitrification and caused washout and disappearance of NO3− from the column effluent. On removal of C2H2, nitrification activity returned only very slowly. Nitrification of added NO2− was not affected by C2H2. No N2O was detected during steady state oxidation of NH4+ or NO2− in the presence or absence of C2H2, indicating that nitrification-denitrification coupled reactions did not occur under the conditions employed.