Effects of application of lime nitrogen and dicyandiamide on nitrous oxide emissions from green tea fields

The aim of this study was to assess the mitigating effects of lime nitrogen (calcium cyanamide) and dicyandiamide (DCD) application on nitrous oxide (N2O) emissions from fields of green tea [Camellia sinensis (L.) Kuntze]. The study was conducted in experimental tea fields in which the fertilizer application rate was 544 kg nitrogen (N) ha(-1) yr(-1) for 2 years. The mean cumulative N2O flux from the soil between the canopies of tea plants for 2 years was 7.1 +/- 0.9 kg N ha(-1) yr(-1) in control plots. The cumulative N2O flux in the plots supplemented with lime nitrogen was 3.5 +/- 0.1 kgN ha(-1), approximately 51% lower than that in control plots. This reduction was due to the inhibition of nitrification by DCD, which was produced from the lime nitrogen. In addition, the increase in soil pH by lime in the lime nitrogen may also be another reason for the decreased N2O emissions from soil in LN plots. Meanwhile, the cumulative N2O flux in DCD plots was not significantly different from that in control plots. The seasonal variability in N2O emissions in DCD plots differed from that in control plots and application of DCD sometimes increased N2O emissions from tea field soil. The nitrification inhibition effect of lime nitrogen and DCD helped to delay nitrification of ammonium-nitrogen (NH4+-N), leading to high NH4+-N concentrations and a high ratio of NH4+-N/nitrate-nitrogen (NO3--N) in the soil. The inhibitors delayed the formation of NO3--N in soil. N uptake by tea plants was almost the same among all three treatments.