Marginal organic soils, abundant in the boreal region, are being increasingly used for bioenergy crop cultivation. Northern wetlands, in their natural state, are sinks for atmospheric CO2 and sources of methane. Drainage of natural wetlands for forestry or agriculture is a common practice in Europe, Canada, Russia and Southeast Asia. After drainage of wetlands, the thickness of aerobic soil layers increases leading to an increase in the rate of organic matter decomposition. As a result, wetlands which were once a sink for carbon are turned into atmospheric carbon sources. Greenhouse gas balance studies of agricultural crops (e.g., wheat, barley, potato or forage grasses) on drained organic soils have reported large emissions of CO2 into the atmosphere. High CO2 emissions have also been reported from afforested organic soils. Drainage and clear cutting of tropical peatlands for palm oil plantations have resulted in a substantial loss of soil carbon to the atmosphere. Therefore, organic soils in general, have been included among the areas with a high risk for significant soil carbon losses and hence have been recommended by the OECD in 2007 to be kept out of biomass production for bioenergy. However, there are contradicting studies from the boreal region suggesting that organic soils can be used for bioenergy biomass production.
As an answer to the urgent need to enhance our understanding of what impact the bioenergy production on organic soils will have on the greenhouse gas balance of such soil types, a team of researchers from the University of Eastern Finland used long term field experimental data on greenhouse gas balance from a perennial bioenergy crop [reed canary grass, Phalaris arundinaceae L.] cultivated on a drained organic soil as an example and managed to show for the first time that, with a proper cultivation and land-use practice, environmentally sound bioenergy production is possible on these problematic soil types.
In a study published in GCB Bioenergy, the researchers performed a life cycle assessment for reed canary grass on this organic soil. They discovered that, on an average, this system produces 40% less CO2-equivalents per MWh of energy in comparison with a conventional energy source such as coal. Climatic conditions regulating the reed canary grass carbon exchange processes have a high impact on the benefits from this bioenergy production system. Under appropriate hydrological conditions, this system can even be carbon negative. A life cycle assessment sensitivity analysis revealed that net ecosystem CO2 exchange and crop yield are the major life cycle assessment components, while non-CO2 greenhouse gas emissions and costs associated with crop production are the minor ones. Net bioenergy greenhouse gas emissions resulting from restricted net CO2 uptake and low crop yields, due to climatic and moisture stress during dry years, were comparable with coal emissions. However, net bioenergy emissions during wet years with high net uptake and crop yield were only a third of the coal emissions.
For a careful economic, environmental and social impact of bioenergy development, more long-term studies on different soil types and climatic conditions are needed. Using long-term field data from this experiment as an example, the results highlight that the cultivation of a perennial bioenergy crop such as reed canary grass on marginal organic soils as an after-use option is beneficial.
For further information, please contact Narasinha Shurpali, PhD, tel. +358 40 355 3321, fax +358 17163750, email: firstname.lastname@example.org
Narasinha J. Shurpali, Harri Strandman, Antti Kilpeläinen, Jari Huttunen, Niina Hyvönen, Christina Biasi, Seppo Kellomäki and Pertti J. Martikainen. Atmospheric impact of bioenergy based on perennial crop (reed canary grass, Phalaris arundinaceae, L.) cultivation on a drained boreal organic soil. GCB Bioenergy (2010) 2, 130–138, doi: 10.1111/j.1757-1707.2010.01048.x.
Artikkelin kirjoitusvuosi: 2011Takaisin tämän vuoden artikkeleihin