Effects of coated slow-release fertilizers on nitrous oxide emission from winter wheat field in a cool-temperate region in Japan

ABSTRACT To elucidate the effects of slow-release fertilizers on nitrous oxide (N2O) emission from fields with winter wheat cultivation in cool-temperate regions, we conducted a two-year field experiment in Hokkaido. Four types of fertilizer treatment, i.e., urea (U), coated urea (CU), coated calcium nitrate (CC), and no nitrogen fertilizer (NN) were investigated. In the U treatment, urea was applied at 40 and 90 + 60 kg N ha−1 in autumn and in spring, respectively. In the CU and CC treatments, all the nitrogen (190 kg N ha−1) was applied using coated fertilizers in autumn for the first cultivation, whereas nitrogen was applied at 130 kg N ha−1 using the coated fertilizers in autumn and the remaining 60 kg N ha−1 was applied using urea in spring for the second cultivation. The magnitudes and seasonal courses of N2O flux did not largely differ among the treatments (i.e., types of fertilizer), including the NN treatment in most of the experimental periods except that the N2O fluxes were higher in the U and CU treatments than in the CC and NN treatments at the beginning of the second wheat cultivation. In all the treatments, the N2O flux showed the highest peak immediately after basal fertilization, followed by other small peaks in autumn. After the next spring, the N2O flux consistently remained low until the wheat harvest including immediately after the end of snowmelt and after supplemental fertilizations. Cumulative N2O emissions tended to be lower in the CC treatment than in the U and CU treatments, although these differences in the emissions were not statistically significant. Although the wheat grain yields were lower in the CU and CC treatments than in the U treatments, the differences were small for the second wheat cultivation. These results indicate that reduction in N2O emission with no decrease in the wheat yield can be achieved by the basal application of slow-release nitrate fertilizer combined with the supplemental application of conventional fertilizer in winter wheat cultivation in Hokkaido, although further studies are still necessary to determine the optimum allocation levels of the basal and supplemental nitrogen applications.