Dicyandiamide Reduces Nitrous Oxide Emission in Paddy Soils

The effects of various Dicyandiamide (DCD) concentrations and variations of watering on the mechanism of nitrogen transformations and Nitrous Oxide (N2O) emission in paddy soils were investigated. The application of low concentration of DCD (0.5% of urea) delayed the N2O emission peak for 3 days while high DCD level (2% of urea) almost completely inhibited the N2O emission. Under 95% and 110% WSPF conditions, soil nitrite concentration increased and reached the peak on the 7th day with 0.5% DCD application same as in the control, while it was very low all the time in the 2% DCD treatment. Under 60% WSPF, nitrite in the soil pool decreased for all DCD treatments. Strong inhibitory effects of DCD were noted on nitrosobacterial populations without any obvious influence on soil nitrobacteria and denitrifying bacteria. At higher DCD applied level under fully moist conditions (110% Water Filled Pore Spaces (WSPF)), nitrite and nitrate concentrations kept very low throughout indicating that initial step of nitrification was completely inhibited. It was concluded that 2% DCD may be applied under fully moist conditions to increase in rice yield and to avoid release of N2O.