Effect of lime-nitrogen application on N2O emission from an Andosol vegetable field

Lime-nitrogen (calcium cyanamide, CaCN2) is used as a nitrogenous fertilizer, pesticide, and herbicide. During the process of decomposition of lime-nitrogen in the soil, dicyandiamide (DCD), a nitrification inhibitor, is formed. Therefore, lime-nitrogen application may mitigate nitrous oxide (N2O) emission from the soil. We conducted a field experiment to investigate the effect of lime-nitrogen on nitrification and N2O emission in fertilized soils, and a soil incubation experiment for further analysis of the effect of the lime-nitrogen. In a field experiment we compared four nitrogen (N) fertilizer treatments: CF (chemical fertilizer), LN100 (application of all N fertilizer as lime-nitrogen), LN50 (application of 50% of N as lime nitrogen and the remainder as chemical fertilizer), and CFD (chemical fertilizer with DCD). In a soil incubation experiment, we also studied two nitrogen treatments: CF and lime-nitrogen. Soil nitrification activity was lower in the LN100, LN50, and CFD plots than in the CF plot. The duration of this reduction in soil nitrification activity was longer in the LN100 plot than in the other plots. We found an apparent decrease in the N2O emission rate between 7 and 14 days after fertilization in the LN100, LN50, and CFD plots compared with that in the CF plot. This period of decreased N2O emission paralleled that when DCD was detected in the topsoil layers of the former three plots. Moreover, in the soil incubation experiment, cumulative N2O emission was significantly lower in the lime-nitrogen treatment than in the CF treatment, although the difference in cumulative N2O emission among the plots was not significant in the field experiment. Correlation analysis suggested that application of lime-nitrogen affects N2O emission by controlling both the first (ammonium to nitrite) and the second (nitrite to nitrate) soil nitrification reactions, whereas DCD blocks only the first nitrification reaction.