Effects of urea form and soil moisture on N2O and NO emissions from Japanese Andosols

Nitrous oxide (N₂O) and nitric oxide (NO) emissions from soil are affected by many factors. Soil nitrogen source, especially N fertilizer input, and soil moisture might be the most important factors to control these two gases emission rate. In this study, laboratory incubation experiments were conducted to determine the effect of the urea form and the soil moisture on N₂O and NO emissions in Japanese Andosols. Results showed that there were no significant differences in the total amount of N₂O and NO emissions over 77 d between non-coated and coated urea (CU) treatments, except for NO emission at 40% wfps (water filled pore space) where it was reduced by 23% when CU was applied. As compared to easily decomposable urea (U), however, CU did reduce N₂O and NO emissions in the earlier period shortly after fertilization. The results also indicated that soil moisture had a much more significant effect on N₂O and NO emissions than the form of urea. From 40% to 100% wfps, there was a positive relationship between N₂O emission and soil water content and a negative relationship for NO. The flux ratio of NO/N₂O was governed by soil moisture with a greatest value at the lowest wfps treatments for each fertilizer treatment. Soil moisture could be the most important factor controlling N₂O and NO emissions when a rich N supply exist in soil.