Effects of agricultural land-use change and forest fire on N2O emission from tropical peatlands, Central Kalimantan, Indonesia

Nitrous oxide (N2O) fluxes from tropical peatland soils were measured at a grassland, three croplands, a natural forest, a burned forest and a regenerated forest in Central Kalimantan, Indonesia. Only croplands received fertilization (665–1278 kg N ha−1 year−1). Mean annual N2O emissions from croplands were 21–131 kg N ha−1 year−1 in 2002–2003 and 52–259 kg N ha−1 year−1 in 2003–2004, and were significantly higher than the emissions from other comparable sites. Cropland N2O emissions were among the highest values reported from cultivated tropical, temperate and boreal organic soils. Mean annual N2O emissions were 7.1 (2002–2003) and 23 (2003–2004) kg N ha−1 year−1 from grassland, and were significantly higher than in natural, regenerated and burned forests (0.62, 0.40 and 0.97 kg N ha−1 year−1 in 2002–2003 and 4.4, 4.0 and 1.5 kg N ha−1 year−1 in 2003–2004, respectively). Annual N2O emissions did not differ significantly between forests in 2002–2003, but were significantly lower in burned forest in 2003–2004. Annual N2O emission was significantly correlated between years. Regression analysis revealed that annual N2O emissions in 2003–2004 were 1.9-fold the corresponding 2002–2003 value (annual precipitation of 2339 and 1994 mm, respectively). N2O fluxes were higher during the rainy season than during the dry season at all sites except the regenerated forest. N2O fluxes in cropland and grassland were significantly lower when the water-filled pore space (WFPS) was less than 60–70%, and increased with an increase in soil NO3–N concentration when WFPS exceeded this threshold. Thus, changes in soil moisture were important in controlling seasonal changes in N2O emission. Our results suggest that changing land use from forestry to agriculture will increase N2O production. The effect of forest fires on N2O emission from these soils was not clear.