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Tropical peatlands could be a potential source of nitrous oxide (N2O) which has a significant impact on global warming. To reduce N2O emission and develop best management practices for peatlands, the formation and emission rates of N2O as affected by land-use management (i.e., changing peatland into agricultural land) and the factors affecting the process must be understood. Therefore, one field and three laboratory incubation experiments were carried out during 1998–99 using peatland soils from 12 sites in South Kalimantan (Indonesia) and one site in Sarawak (Malaysia) to quantify the N2O emission and the factors affecting it. The results from the field experiment showed that land-use managements, changing water table and locations had a significant impact on N2O emission. Changing peatland into cultivated lands (cultivated upland and paddy field) enhanced the N2O emission. For example, cultivated upland Cassava crop resulted in the highest amounts of N2O emission (1.04 mg N m−2 h−1) compared to other treatments. The N2O emission during 1998 was higher than those during 1999 because of the changing water table and dry season in 1998. The laboratory experiments showed that the N2O emission was also strongly influenced by land-use management, soil moisture contents, addition of ammonium fertilizer or rice straw and soil depths. For example, the flooded conditions stimulated the N2O emission compared to that at 60% moisture contents. Similarly, the addition of ammonium fertilizer suppressed the N2O emission compared to control treatments because of the high ammonium contents that inhibit nitrification. Nevertheless, incorporation of rice straw to soil samples from 20 to 40 cm soil depth stimulated N2O emission.

Nitrous oxide (N 2 O) 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 N 2 O and NO emissions in Japanese Andosols. Results showed that there were no significant differences in the total amount of N 2 O 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 N 2 O and NO emissions in the earlier period shortly after fertilization. The results also indicated that soil moisture had a much more significant effect on N 2 O and NO emissions than the form of urea. From 40% to 100% wfps, there was a positive relationship between N 2 O emission and soil water content and a negative relationship for NO. The flux ratio of NO/N 2 O 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 N 2 O and NO emissions when a rich N supply exist in soil.

Three nitrogen chemical fertilizers were applied to soil – controlled-release urea (CU), a mixture of ammonium sulfate and urea with nitrification inhibitor (AM), and a mixture of ammonium sulfate and urea with no nitrification inhibitor (UA). N2O and NO fluxes from an Andosol soil in Japan were measured six times a day for three months with an automated flux monitoring system in lysimeters. The total amount of nitrogen applied was 20 g N m−2. The total N2O emissions from CU, AM and UA were 1.90, 12.7, and 16.4 mg N m−2, respectively. The total NO emissions from CU, AM and UA were 231, 152, and 238 mg N m−2, respectively. The total NO emission was 12–15 times higher than the total N2O emission. High peaks in N2O and NO emissions from UA occurred for one month after the basal fertilizer application. The N2O emissions from CU and AM during the peak period were 50% of those from UA, and the NO emissions were less than 50% of those from UA. After the peak period, the N2O and NO emissions from CU were the highest for two months. A negative correlation was found between the flux ratio of NO–N to N2O–N and the water-filled pore space. A diel pattern with increased N2O and NO fluxes during the day and with decreased fluxes during the night was observed.