There is a flush of nitrous oxide (N₂O) emissions during cracking of clay paddy soils. The goal of the study was to control the high N₂O emissions by adding nitrification inhibitor dicyandiamide (DCD) during the development of cracks. The specific objective of this study was to investigate whether DCD could inhabit N₂O emissions during soil cracking and re-irrigation. Soil columns incubation experiments were conducted by adding 5000 ml solution containing different amounts of (NH₄)2SO4 and DCD to paddy soils. Thereafter, the soil columns were dried at 30-32℃ in a greenhouse for 10 days. After the 10th day, the columns were re-irrigated with 5000 ml distilled water and left to dry again at 30-32℃ in the greenhouse.
The dynamic changes of daily N₂O emissions flux and the concentration of dissolved N₂O and pH of leaching solution showed that the treatment with DCD addition and without nitrogen fertilizers (A treatment) had the lowest N₂O emissions, the mean emissions flux was 340.91 μg m-2 h-1. However, the treatment with high amount of DCD and nitrogen fertilizers addition (E treatment) had the highest emissions, the mean emissions flux was 9280.23 μg m-2 h-1. The results showed that after the crack development attained maxima, the re-irrigation inhibited the N₂O emissions. The dissolved N₂O was over-saturated in leaching solution. Moreover, the results indicated that DCD could inhibit the N₂O emissions when low amount of (NH₄)2SO4 was added, but DCD could not inhibit N₂O emissions efficiently when high amount of (NH₄)2SO4 was added even though the ratio of (NH₄)2SO4 and DCD was the same (10∶1). The inhibition of N₂O emissions by DCD was more efficient when the ratio of (NH₄)₂SO₄ and DCD was 10∶1 than their ratio was 10∶1.5 and 10∶2. There was no significant correlation between N₂O emissions flux and dissolved N₂O in leaching solution. Similarly, no correlation was obtained between N₂O emissions flux and pH of leaching solution either. While a positive significant (p < 0.05) linear correlation existed between dissolved N₂O and pH of leaching solution, in general, the addition of DCD could inhibit N₂O emissions under continuous and dynamic variance of water regimes during the incubation. The most efficient inhibition of the role of DCD as a N₂O emission inhibitor was the added amount of commercial nitrogen fertilizer and the content of ammonium-nitrogen (NH₄-N) in soils. Considering to reduce the N₂O emissions, re-irrigation is one of the ways that can be used to control N₂O emissions after cracks were produced in paddy soils.