[Denitrification Loss and N₂O Emission from Different Carbon Inputs in Orchard Drains Sediments]

The orchard is an important economic crop in Taihu Lake region. Heavy nitrogen application in orchard results in great nitrogen loss to drainage ditch, and unbalanced carbon nitrogen ratio. Therefore, carbon might be an important limiting factor for sediment nitrification and denitrification. A soil incubation experiment controlled by the acetylene inhibition method was conducted under laboratory conditions to study the denitrification loss and N₂O emissions of orchard drainage ditch soil. We designed five carbon input levels of 0, 5, 25, 50 and 100 mg·L^-1, which were noted as C₀, C₁, C₂, C₃ and C₄, respectively, meanwhile there was 5 mg·L^-1 net nitrogen input in the form of KNO₃ in each treatment. The results showed that carbon inputs could stimulate both denitrification rates (D_N) and N₂O emission rates. Carbon and nitrogen ratio had a significant effect on N₂O emission rates and denitrification loss rates (P<0.05). When the carbon and nitrogen ratio was 10:1, total cumulative denitrification losses and N₂O emissions were both highest (319.26 μg·kg^-1 and 6.20 μg·kg^-1, respectively) among the treatments, which accounted for 1.28% and 0.02% of net nitrogen input, respectively. This result indicated that the carbon and nitrogen ratio of 10:1 was most favorable for N₂O emissions and denitrification process in sediments.