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Tropical peatland forests are changing rapidly to meet the food demands of the growing population and economic development. We report greenhouse gases emissions from secondary forest to paddy field and rice-soybean rotation field in South Kalimantan, and upland in Jambi, Indonesia. Gas samples were taken from peatland surface and analyzed for CO2, CH4 and N2O. Land-use change from forest to paddy field significantly decreased the CO2, but increased CH4 emission. Change from forest to paddy-soybean rotation field significantly reduced N2O and CO2 emissions, but had no significant influence on CH4 emission, so Global Warming Potential should be considered.
Peat soil, greenhouse gas emission, land-use change, microbial activity, GWP.
The forest area in Indonesia has reduced by 35% during the last three decades and has mostly been converted to agricultural land. Tropical peatland forests seem to change in a similar way and continue to be converted to meet the food demand of the growing population in many of Asian countries (Watson et al., 2000). Peatland has a significant amount of carbon stock and some nitrogen in the soil which could be a source of the greenhouse gases carbon oxide (CO2), methane (CH4) and nitrous oxide (N2O). We reported that the path of methane from paddy soil to the atmosphere is mainly through the rice plant (Inubushi et al., 1989) and also the greenhouse gas emitting, and CH4 producing and oxidizing, soil microbial activities in a sago palm plantation in Sarawak, Malaysia (Inubushi et al., 1998), paddy field, and upland field in South Kalimantan and Jambi, Indonesia (Inubushi et al., 2003; 2005; Furukawa et al., 2005) in order to give a direction for such land conversions. In this paper, we review the effect of land-use management on N2O, CH4 and CO2 emission and their controlling factors from peatlands in Indonesia.
Gas samples were taken from inland and coastal peatland surfaces in Amuntai and Gambut, South Kalimantan, respectively, and also from Jambi, Sumatra, Indonesia, by the closed-chamber method and analyzed for N2O, CH4 and CO2 by ECD-GC, FID-GC and TCD-GC, respectively. Peat samples were also collected from 25-60 cm soil depth and analyzed for soil physical, chemical and biological properties. Details of the sites and methods have been described previously (Inubushi et al., 1998; Hadi et al., 2000). A laboratory incubation experiment was conducted to determine the controlling factors of gas production.
Chemical and microbiological properties of tropical peat soil Land use change from secondary forest to paddy field and paddy-soybean rotation in Amuntai, inland peat area, significantly decreased organic carbon and total nitrogen contents in the soil. The amounts of soluble organic carbon were also higher in secondary forest than in paddy field and paddy-soybean rotation fields.
Greenhouse gas emissions from tropical peat soil under land-use change Land-use change from secondary peat swamp forest to paddy field in coastal peatland at Gambut tended to increase annual emissions of CO2 and CH4 to the atmosphere, while changing land use from secondary forest to upland tended to decrease these gas emissions. No clear trend was observed for N2O for which negative annual values were recorded at three sites. It was also observed in Jambi, Sumatra that land-use change from drained forest to lowland paddy field significantly decreased the CO2 and N2O fluxes, but increased the CH4 flux in the soils. Change from drained forest to cassava field significantly increased.
N2O flux, but had no significant influence on CO2 and CH4 fluxes in the soils. Average CO2 fluxes in the swamp forests of 94 mg C m–2 h–1 were estimated to be one-third of that in the drained forest. Groundwater levels of drained forest and upland crop fields had been lowered by drainage ditches while swamp forest and lowland paddy field were flooded, although groundwater levels were also affected by precipitation. Groundwater levels were negatively related to CO2 flux but positively related to CH4 flux at all investigation sites. The peak of the N2O flux was observed at -20 cm of groundwater level.
To find out controlling factors for N2O production in peat soil, a laboratory incubation experiment was conducted with four different moisture contents of 70, 80 and 100% and submerged conditions. It was observed that 100% moisture content produced highest N2O production followed by submerged conditions.
We found already that there was no significant difference in CH4 emissions from peat surface in secondary forest and sago palm plantation (1.1+/-0.61 and 1.39+/-0.82 mg CH4 m-2 hr-1, respectively) (Inubushi et al., 1998), although CH4 emissions from deeper peat layers depended on soil depth and amendments such as inorganic nitrogen or organic carbon (N fertilizer and plant residue). CH4 accumulated in the surface soil layer in sago palm plantation was significantly lower than deeper soil layers, probably because CH4 oxidizing bacteria are active near soil surface so that CH4 was oxidized before it could be emitted to the atmosphere. Recently, Melling et al. (2005a) reported that on an annual basis, both forest and sago were CH4 sources with an emission of 18.34 mg C m-2 yr-1 for the former and 180 mg C m-2 yr-1 for the latter. Only the oil palm ecosystem was a CH4 sink with an uptake rate of -15.14 mg C m-2 yr-1. Melling et al. (2005b) also showed that soil CO2 flux was highest in the forest, followed by oil palm and sago (2.1, 1.5 and 1.1 kg C m-2 yr-1, respectively). Takakai et al. (2006) reported N2O fluxes from a grassland, three croplands, a natural forest, a burned forest and a regenerated forest in Central Kalimantan, Indonesia, with mean annual N2O emissions in the range 7.1 - 23 kg N ha−1 year−1 . N2O emissions from cropland were significantly higher than in natural, regenerated and burned forests, suggesting that changing land use from forestry to agriculture will increase N2O production. The fact that the emission of the gases was affected by soil moisture revealed possible seasonal changes in the dynamics of these gases as affected by changes in the seasonal and diurnal soil moisture level. More detail measurement of the seasonal emission of these gases from tropical peatland is therefore recommended for each ecosystem to determine mitigation techniques for greenhouse gas emissions from tropical peatland. Quantitative discussion about global warming potentials (GWP)1 is also needed since there are always trade-off relations or “leakage” when mitigation is applied.
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| Global warming - Greenhouse effect 
