Oil palm on mineral soil in Indonesia is not changing soil carbon
The amount of carbon stored in mineral soil doesn’t change whether the land has been formerly forested or not, say scientists at the World Agroforestry Centre Indonesia
About 15% of the oil palm grown in Indonesia is on peat soil. The carbon-dioxide emissions this causes are a major concern that led to the establishment of guidelines to avoid peat for new plantings. As for the remaining 85%, little is known about the changes in soil carbon brought about by oil-palm production. Some claim that the amount of carbon stored in the soil increases overall, especially if it was grassland that was converted to oil palm. Others claim the amount decreases, especially if the oil-palm is on formerly forested land.
A new study is providing some answers to these conflicting claims. Using a data set of 25 plantations stratified across all the major settings in which oil palm is found in Indonesia, the study provides a benchmark for better understanding of oil palm’s carbon storage.
‘Our conclusion is that with current oil-palm practices we can assume the belowground part of the equation to be “carbon neutral”, said Ms Ni’matul Khasanah, first author of the study and an ecological modeller with the World Agroforestry Centre Indonesia. ‘Neither positive nor negative change hypotheses were supported by the data’.
Whether derived from forest or other types of land use, whether managed by large-scale plantations or smallholders, the net change in soil carbon over the 25-year life cycle of average oil palm is zero. This does not include, however, loss of any aboveground litter layer that might have occurred during land clearance.
‘The devil is in the detail in such studies’, added Ms Khasanah, ‘as there are four management zones in a typical oil-palm plantation, some of which receive a lot of aboveground litter, are enriched with soil carbon and develop a more spongy soil structure; others are compacted and lose soil carbon, as in the harvest paths. Our study had to apply several correction factors to account for the change in effective sampling depth that is the result of the changes in soil bulk density. Earlier studies did not apply such corrections consistently and that may explain their divergent results’.
Meine van Noordwijk, the World Agroforestry Centre’s chief science advisor and a co-researcher in the study, said that, ‘The results of the study can be used to support default values for calculations of the carbon footprint of palm-oil production, at least for Indonesia, which is now the largest global producer and exporter. Our data support the move from peat to mineral soils and a focus on aboveground changes to determine whether or not palm-oil production can be called carbon neutral as a whole’.
Read the journal article
Khasanah N, van Noordwijk M, Ningsih H, Rahayu S. 2015. Carbon neutral? No change in mineral soil carbon stock under oil palm plantations derived from forest or non-forest in Indonesia. Agriculture, Ecosystems and Environment 211(15 December):195-206.
This work is linked to the CGIAR Research Program on Forests, Trees and Agroforestry