BALI, Indonesia (1 March, 2012)_Bacteria introduced to palm oil seedlings could help reduce the harmful greenhouse gasses emitted by the plant and improve its carbon sequestration properties, says an environmental expert.
“Microbes in the soil play a critical role in the breakdown of nitrogen from the fertilisers used to grow the plant. The problem is that after clearing the forest there is a large decline in soil microbial activity so the nitrogen accumulates and is released into the atmosphere as nitrous oxide – a GHG that is 300 times more powerful in heating the atmosphere than carbon dioxide,” said Neil Fuller, an environmental consultant with Agrinos in Indonesia, at the International Conference on Oil Palm and Environment (ICOPE) in Bali last week.
Nitrogen plays a central role in plant development but crop demand for nitrogen far exceeds that which exists in the soil naturally, so farmers often supplement soil with nitrogen fertilisers.
“While this has seen significant increases in palm oil performance, 80 percent of the plant’s carbon footprint actually comes from the nitrogen fertiliser that was used to grow it,” Fuller said.
The accumulation of organic plant matter in forest landscapes leads to a high demand within plants for nitrogen. This nitrogen demand must be met either by soil nitrogen supply or fertiliser nitrogen supplements. A large component of soil nitrogen supply comes from microbes that are able to “fix” the nitrogen into nitrate-N — a valuable food source for most plants.
Recent work by Kristell Hergoulc’h from the Center for International Forestry Research has also shown that nitrogen fertiliser can exacerbate the production of soil nitrous oxide greenhouse gases when applied to oil palms grown on deep peat.
By measuring the level of an enzyme which is used by most microbes involved in organic matter decomposition, Agrinos scientists were able to calculate the presence, and degree of prior activity of bacteria in the soil. They found that when vegetation had been removed, a sudden decline in microbial activity occurred.
Because of decreased microbial populations and the absence of plant roots, nitrate-N rapidly diffuses through the soil and can accumulate in pools where it is converted to the worrisome greenhouse gas, nitrous oxide. Nitrogen fertiliser exacerbates this problem.
Indonesia and Malaysia are the largest oil palm producing countries, supplying 85 percent of the world’s demand for palm oil. In both countries there are huge economic benefits from oil palm, with seven million hectares under plantation in Indonesia producing 16 million tons of palm oil per annum. Oil palm companies are said to employ 6 million people globally.
However, rampant deforestation and the conversion of carbon rich peat forests into oil palm plantations which accounts for 80 percent of all carbon emissions in Indonesia has raised alarm over efforts to reduce greenhouse gas emissions. A recent CIFOR study quantified the atmospheric effects on changes in land use from biofuel production and found that for palm oil grown on peatlands, the carbon emissions generated from land conversion would take hundreds of years to reverse.
The emission of carbon dioxide from forest soils caused by normal organic matter decomposition and microbial activity ranges from 4 to 10 tonnes of carbon per hectare per annum, dependent on temperature, water and light intensity. As vegetation is removed to make way for plantation forestry, carbon emissions can increase dramatically – reaching up to 65 tonnes of carbon per hectare per annum. What is of major concern, however, is the associated emission of nitrous oxide, seeing as 1 kg of it has a carbon footprint equivalent of 296 kg of carbon dioxide. Normally, nitrous oxide emissions range from 0.1 to 4.4 kg nitrogen per hectare per annum, but this can peak at over 700 kg of nitrogen per hectare per annum in the immediate aftermath of forest clearing.
However, the introduction of beneficial microbes to soils, particularly while oil palms are still young, can deliver a number of major agronomic and environmental gains, said Fuller.
“When you look at the physiological aspects of the oil palm plant after introducing microbes in the nursery, they are healthier; they have greater root mass, water use efficiency, higher growth rates and better tolerance to environmental stress.”
“Also the re-introduction of beneficial microbes to soils following the clearance of indigenous forest or the re-planting of plantation forestry can mitigate against losses of both carbon and nitrogen during the transitional stage of plantation establishment.”
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