Land-use change in tropical peatland potentially results in a large amount of carbon dioxide (CO) emissions owing to drainage, which lowers groundwater level (GWL) and consequently enhances oxidative peat decomposition. However, field information on carbon balance is lacking for rubber plantations, which are expanding into Indonesia's peatlands. To assess soil CO emissions from an eight-year-old rubber plantation established on peat after compaction, soil CO efflux was measured monthly using a closed chamber system from December 2014 to December 2015, in which a strong El Niño event occurred, and consequently GWL lowered deeply. Total soil respiration (SR) and oxidative peat decomposition (PD) were separately quantified by trenching. In addition, peat surface elevation was measured to determine annual subsidence along with GWL. With GWL, SR showed a negative logarithmic relationship (p<0.01), whereas PD showed a strong negative linearity (p<0.001). Using the significant relationships, annual SR and PD were calculated from hourly GWL data to be 3293±1039 and 1408±214gCmyr (mean±1 standard deviation), respectively. PD accounted for 43% of SR on an annual basis. SR showed no significant difference between near and far positions from rubber trees (p>0.05). Peat surface elevation varied seasonally in almost parallel with GWL. After correcting for GWL difference, annual total subsidence was determined at 5.64±3.20 and 5.96±0.43cmyr outside and inside the trenching, respectively. Annual subsidence only through peat oxidation that was calculated from the annual PD, peat bulk density and peat carbon content was 1.50cmyr. As a result, oxidative peat decomposition accounted for 25% of total subsidence (5.96cmyr) on average on an annual basis. The contribution of peat oxidation was lower than those of previous studies probably because of compaction through land preparation.
Soil carbon dioxide (CO2) emission consists of peat decomposition, root respiration, and litter decomposition. Although there are some publications on soil respiration in oil palm plantations, information of CO2 emission from palm litter (frond) decomposition is still limited. Therefore, our objective was to estimate the CO2 emission from frond decomposition in an oil palm plantation on tropical peat. The study was conducted in a smallholder oil palm plantation with two different cultivars (M and S) on peat in Jambi, Indonesia, using meshed litter bags of 40 cm x 80 cm. The temporal pattern of carbon loss was similar to that of dry weight loss, following a negative exponential. Annual carbon inputs through pruned fronds into the plantation were 189 and 281g C m−2 year−1, respectively, for M and S cultivars. Annual CO2 emissions through oxidative frond decomposition were estimated to be 98 and 153 g C m−2 year−1 for M and S cultivars, respectively. The annual CO2 emission from oil palm litter decomposition accounted for about 13% of soil heterotrophic respiration of oil palm plantations on tropical peatland.
Seasonal fluctuations of water table depth are very important regarding the sustainable peat management on tropical peatland. Water level depth can affect the greenhouse gases emissions and as the main indicator for peat fire risk management. Therefore, direct measurement of water level dynamics in the peat burning area is absolutely necessary. The research objective was studied the water level fluctuations on burning peatland in Central Kalimantan, Indonesia. Water level measurement performed manually in the field and ditch, every week from February to December 2014. Water level from February to December 2014 were -86.6 and -51.9 cm, on the ditch and field, respectively. Peat soil water level was strongly correlated to the variations of rainfall.
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