A GAS FLOW‐THROUGH SYSTEM FOR STUDYING DENITRIFICATION IN SOI

Abstract

Summary A continuous gas ‘now‐through’ system, incorporating a soil incubation cell and a gas sampling device, was developed to measure the nitrogen and carbon losses as gaseous N 2 , N 2 O, NH 3 and CO 2 from soil during denitrification under ‘steady state’ anaerobic conditions. Nitrogen was added as KNO 3 to the soil in amounts equivalent to 0, 30,100 and 300 kg N ha ‐1 . At 25 °C and one quarter of the water‐holding capacity, N 2 and N 2 O evolution accounted for most of the nitrogen lost. In the effluent gas stream, N 2 O appeared about six hours after anaerobic conditions were established, and increased steadily. Initial N, production was small and reached a maximum between 90 and 100 h with a simultaneous decrease in N 2 O evolution. Gaseous N losses were highest with the 100 kg N ha −1 treatment and accounted for 59 per cent of the nitrate lost. A weight ratio, CO 2 ‐C/(N 2 O + N 2 )‐N of 1.0–1.3 was observed in the effluent gas once a ‘steady state’ was achieved, which conforms with that expected from nitrate respiration when N, and N 2 O are produced simultaneously. When denitrification ceased, CO 2 production decreased to a steady rate. An increase in the duration, rather than the rate, of denitrification was observed when more N was added. A time lag before the onset of a maximum rate of denitrification was also observed, which increased with the amount of added N.