Characteristics of denitrification in different soil layers in a greenhouse vegetable cropping system

Silicone tubes installed at 50 cm and 90 cm respectively in situ were applied to monitor concentrations of N2O in soil profile in a greenhouse tomato cropping field, and a robotized incubation system was used to measure potential production of N2O, NO and denitrification. The results show that the occurrences of the N2O peaks at the depths of 50 cm and 90 cm were just after irrigation / fertilization under the conventional N treatment (CN), and the N2O concentration at the depth of 50 cm is higher than that at the depth of 90 cm, varying from 2.15 to 50.77 l/ L at 50 cm, and from 2.74 to 14.05 l /L at 90 cm. Under the control treatment (CK), the N2O concentrations at both depths are almost not affected by irrigation, varying from 1.43 to 2.75 l/ L. Denitrification mainly occurres in the layer of 040 cm, and due to carbon limitation, denitrification in the layer of 40100 cm is relatively weak. However, after 48 hours incubation with carbon addition, denitrification in the lower soil layer shows a similar denitrification potential as the surface soil. Under anaerobic conditions, the N2O and NO emissions from the upper layer (040 cm) are much higher than those of the lower layer (40100 cm). High N2O concentrations are observed at the 50 and 90 cm in situ, might be diffused from the surface soil. Therefore, field flux measurements might underestimate the N2O emission. Since the lower layer has similar denitrification potential as the surface soil, denitrification loss should not be ignored under the conditions with leaching of both nitrate and organic carbon.