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

Apparent steady state denitrification and N 2 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) C 2 H 2 to the air flow through the column resulted in depth profiles of N 2 O and C 2 H 4 which showed that a zone of active denitrification was underlain by a zone of C 2 H 2 reduction. About 90% of the added NO 3 − was denitrified and about 10% of the products was N 2 O. Continuous addition of ammonium chloride (25 μg N∙mL −1 ) resulted in steady state oxidation of all the NH 4 + . The introduction of C 2 H 2 (10.1 kPa), however, inhibited nitrification and caused washout and disappearance of NO 3 − from the column effluent. On removal of C 2 H 2 , nitrification activity returned only very slowly. Nitrification of added NO 2 − was not affected by C 2 H 2 . No N 2 O was detected during steady state oxidation of NH 4 + or NO 2 − in the presence or absence of C 2 H 2 , indicating that nitrification-denitrification coupled reactions did not occur under the conditions employed.