Organic Carbon Storage and Management Strategies for Reducing Carbon Emission from Peatlands:

A Case Study in Oil Palm Plantations in West and Central Kalimantan, Indonesia

抄録

Research was conducted in oil palm plantations cultivated on peatlands of West and Central Kalimantan. The research objectives were as follows: (i) to describe organic carbon (C) storage based on 2000–2009 survey data obtained from the Indonesian Center for Agricultural Land Resources Research and Development (ICALRD), Ministry of Agriculture, (ii) to assess carbon storage and CO₂ emission in and from oil palm plantations on peatlands, and (iii) to recommend mitigation options for CO₂ emission. Maps of peatlands based on satellite imagery from 1986, 2002, and 2008 were considered basic information for the following: (a) field observations, (b) peat sampling for analysis of organic C content, bulk density, and ash content for determining organic C storage, and (c) determining the location of oil palm plantations on peatlands for measurement of CO₂ flux. The organic C storage in peats of West and Central Kalimantan was calculated using the parameters of bulk density, peatland area, peat thickness, and organic C content, and was roughly estimated as 3,625 and 6,352 Mt (3.6 and 6.4 Gt), respectively, which is equivalent to 10.7 and 19.0% of total organic C storage in all Indonesian peats. Average CO₂ emission from oil palm plantations on peats varied from 28–69 t ha^-1 yr^-1, depending on the groundwater table, ash content, and understory cover crops. However, peat decomposition and peat thickness had no correlation with CO₂ emission. It was interesting that the ash content of peats >2–3% Fe₂O₃ showed a significant negative correlation with CO₂ emission: Y = –17.12 ln(X) + 58.707 (R²=0.785), where Y is CO₂ emission and X is ash content. Based on the correlation, we estimated that peats containing 6% mineral materials had a relatively low CO₂ emission of about 23 t ha^-1 yr^-1. This emission rate is roughly equal to the CO₂ fixed by oil palm trees for fresh fruit bunch (FFB) production (20–24 t ha^-1 yr^-1). In addition, some emitted CO₂ could be absorbed by understory cover crops, such as Nephrolepis ferns, which often dominate the floors of oil palm plantations. Therefore, recommended management strategies for sustainable cultivation of oil palm plantations on peatlands and for mitigating CO₂ emission are as follows: (i) maintaining a water table no deeper than 40 cm from the peat surface to achieve a balance between the reduction of CO₂ emission and water supply for plant growth, (ii) applying mineral material as an ameliorant wherever the mineral material content of a peat is <6%, and (iii) management of understory cover crops.