Effect of dicyandiamide and polymer coated urea applications on N2O, NO and CH4 fluxes from Andosol and Fluvisol fields

Soil type influences the effectiveness of enhanced-efficiency fertilizers in reducing nitrous oxide (N2O) and nitric oxide (NO) emissions, although the effect has not been well studied. We measured N2O, NO and methane (CH4) fluxes after the application of enhanced-efficiency fertilizers and conventional fertilizer (urea) in two contrasting soils, an Andosol and a Fluvisol, in lysimeter fields. Brassica rapa var. perviridis L.H.Bailey (komatsuna) was cultivated for 1.5months in spring and in autumn. A nitrification inhibitor, dicyandiamide (DCD), and polymer coated urea (CU) were tested in the spring and autumn experiments, respectively. In spring, DCD was effective in reducing N2O and NO emissions in the Andosol but not in the Fluvisol, compared with urea. Nitrification was likely to be a more important production process for N2O and NO in the Andosol than in the Fluvisol. This difference in N2O and NO production processes was inferred to be the main reason why DCD effectively reduced N2O and NO emissions only in the Andosol. Yield-scaled N2O emission for DCD was lower by 63% than for urea in the Andosol, but no difference was observed in the Fluvisol. In autumn in the Andosol, CU increased N2O emission compared with urea, but no difference was observed for NO emissions. In the Fluvisol, CU was not effective in reducing N2O and NO emissions. CH4 uptake from the Andosol was significantly higher than that from the Fluvisol. Fertilizer type had no effect on cumulative CH4 uptake in either soil. Our results showed that the effectiveness of DCD and CU in reducing N2O and NO emissions varied with soil because the main production processes of these gases varied with soil.