DENITRIFICATION AND NITROGEN IMMOBILIZATION AS AFFECTED BY ORGANIC-MATTER AND DIFFERENT FORMS OF NITROGEN ADDED TO AN ANAEROBIC WATER-SEDIMENT SYSTEM

The effects of wheat straw and different forms of N on denitrification and N immobilization were studied in an anaerobic water-sediment syst em. The water-sediment system was supplemented with various combinatio ns of wheat straw and N-15-labelled and unlabelled (NH4)2SO4 or KNO3, and incubated anaerobically at 30-degrees-C for 10 days. N-15-labelled and unlabelled NO3-, NO2-, NH4+, and organic N were determined in the water-sediment system. The gases evolved (N2, CO2, N2O, and CH4) were analyzed by gas chromatography at regular intervals. Larger quantitie s of N-15(2)-N and organic N-15 were formed in wheat straw-amended sys tems than in non-amended systems. Trends in CO2 production were simila r to those of N2-N evolution. The evolution of N2O and CH4 was negligi ble. Denitrification processes accounted for about 22 and 71% of the a dded (NO3-)-N-15-N in the absence and presence of wheat straw, respect ively. The corresponding denitrification rates were 3.4 and 12.4 mug N -15g-1 dry sediment day-1. In systems amended with (NO3-)-N-15-N and ( NO3-)-N-15 +NH4+-N without wheat straw, 1.82 and 1.58%, respectively, of the added (NH3-)-N-15-N was immobilized. The corresponding figures for the same systems supplemented with wheat straw were 5.08 and 4.10% , respectively. Immobilization of (NO4+)-N-15-N was higher than that o f (NO3-)-N-15-N. The presence of (NO3-)-N did not stimulate NH4+-N imm obilization.