[Effects of slow/controlled release urea on annual CH₄ and N₂O emissions in paddy field]

Present study examined the influence of different types of slow/controlled release urea on rice yield and annual greenhouse gas emissions in a paddy field, and assessed the greenhouse gas intensity (GHGI, equivalent to global warming potential GWP/rice yield). The results indicated that the optimized fertilization (OPT) treatment recorded the similar yield with reduced nitrogen fertilizer (21.4%) supply compared with the farmers' fertilizer practice (FFP) treatment, and decreased the annual emissions of CH₄ (12.6%) and N₂O (12.5%) during the rice season, and N₂O emission (33.3%) during the fallow period. Application of controlled release urea (CRU) reduced CH₄ emission by 28.9% during the rice-growing season with respect to OPT treatment, and showed negligible CH₄ emission during the fallow season. However, nitrification inhibitor (DMPP) treatment was found to reduce the CH₄ emissions by 41.6% and 76.9%, and N₂O emissions by 85.7% and 6.5%, during the rice growing season and fallow season, respectively, compared with OPT treatment. In the fallow season, the N₂O emissions accounted for 76.8%-94.9% of annual N₂O emissions, which was clearly a key point for evaluation of greenhouse gas emissions in paddy. The average values of GHGI in OPT, CRU and DMPP treatments were 0.50, 0.41 and 0.33 kg·kg^-1, respectively. Considering the benefits of higher rice yield and lower annual greenhouse gas emissions, combined application of urea and nitrification inhibitor could be the best combination in paddy fields.