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Dicyandiamide increased ammonia volatilisation and decreased carbon dioxide emission from calcareous soil during wheat–maize rotation on the Loess Plateau

Nitrification inhibitors (NIs) have been found to retard the nitrification process, reduce N losses and increase nitrogen use efficiency; however, their effect on carbon dioxide (CO2) emission from calcareous soil has rarely been reported. A 2-year field experiment was conducted to study whether nitrification inhibition by dicyandiamide (DCD) has any effect on CO2 release from calcareous soil. The experiment comprised five treatments: a control (0 kg N ha–1) and two levels of N fertiliser applied on wheat (160 and 220 kg N ha–1) and maize (180 and 280 kg N ha–1) crops, with and without DCD. Compared with the control, a decrease in soil pH (mean 0.21 units in N fertiliser treatments without DCD and 0.11 units with DCD) and increases in cumulative CO2 emission (mean 17% and 23% in wheat and maize respectively) and cumulative ammonia (NH3) volatilisation (mean 28% and 446% in wheat and maize respectively) was recorded under all N fertilised treatments (with and without DCD). The application of DCD with N fertiliser retarded the nitrification process, as indicated by a higher NH4+-N and lower NO3–-N content, as well as a relatively higher soil pH, compared with application of N fertiliser without DCD. In addition, DCD application significantly reduced CO2 emission in both wheat (10–20%) and maize (13–14%) crops compared with crops grown with N fertiliser without DCD. However, the losses from NH3 volatilisation increased when DCD was applied at both N fertiliser levels in both wheat (38–41%) and maize (24–36%) crops. Inhibition of nitrification by DCD was more effective during the wheat than during maize season. Controlling nitrification using DCD is an effective approach to minimise CO2 emission from calcareous soils on the Loess Plateau; however, DCD application increases in NH3 volatilisation.