Field and incubation experiments were conducted to determine the emission rate of greenhouse gases, nitrogen change, populations of AOB, NOB, and fungi as well as growth of corn in response to amendment of urea granulated with and without nitrification inhibitors and zeolite. The application of urea with neem, urea with zeolite, urea with zeolite + neem, urea with zeolite + dicyandiamide, and urea with dicyandiamide (UD) decreased the N2O emissions by 16.3%, 59.6%, 66.8%, 81.9%, 16.3%, and 86.7%, respectively. Meanwhile, patterns of CH4 fluxes were mostly determined by small emissions. Increase in corn height, weight of cobs, biomass, and chlorophyll leaf contents were not significantly different between urea alone and urea with NIs and zeolite. In the incubation experiment, the highest concentration of NH4+ and N2O production was detected during the first week and it remained high up to the second week of incubation in the combination of urea with NIs and zeolite treatments, although there was no significant difference compared with urea. During NH4+ decrease, the concentration of NO3- started to accumulate from the second to the third weeks. Production of CO2 showed no significant differences among treatments. The static production of CO2 could also explain that NIs and zeolite additions did not change AOB, NOB, and fungi activities after the fourth week of incubation.
Keywords: CO2 Production; Dicyandiamide; Emission of N2O and CH4; Neem; Nitrification inhibitor; Zeolite.