Three studies look at soil's carbon storage capacity
As atmospheric CO2 levels rise, methods to mitigate these increases are becoming very important. Three studies published in the July-August 2008 issue of Soil Science Society of America Journal explore the potential roles of soils as a C sink in different regions in the Western Hemisphere. The studies all demonstrate that C storage capacity of soils in different regions of the Western Hemisphere respond similarly to a diverse range of management practices to increase soil C input.
The studies did not yet analyse the sequestration potential of C via biochar - a recalcitrant form of carbon that can be stored in soils unaltered for centuries, perhaps even millenia. Instead they analysed the effect of more traditional soil management practises, such as the elimination of fallow or the establishment of grass. In any case, scientists are suspecting the global potential for soils to absorb and lock up carbon can be very large (previous post).
Scientists from Alberta Agriculture and Rural Development (Canada), the National Institute of Agricultural Technology, the University of Buenos Aires (Argentina), and University of California, Davis (USA) have investigated soil C balance in distinct agroecosystems under different management practices including soil tillage, N fertilization, elimination of fallow, and establishment of grass. In each case, C sequestration occurred in response to higher C input to soil; however, increase in SOC was confined to labile fractions such as the light fraction and larger soil aggregates.
Investigation: Canada
In southeastern Alberta, a long-term study showed previously that eliminating summer fallow or establishing grass significantly increased soil organic C after 6 yr. In the 12th year of the study, total organic C and light fraction C were determined in three rotations with summer fallow, two continuously cropped rotations and grass. All rotations had subtreatments with different levels of fertilization. The light fraction of soil C was obtained using density separation and consisted mostly of non-decomposed root and straw fragments.
Although soil organic C was increased by elimination of summer fallow, fertilization, and establishment of grass, gains in soil organic C between Years 6 and 12 were negligible in all treatments except the fertilized grass treatment. Most of the gains in total soil organic C were due to increased light fraction C. The results indicate that much of the gain in soil organic C in response to improved practices on semiarid prairie soils likely occurs within one decade.
Investigation: Argentina
In the semiarid portion of the Pampas, scientist compared no-till management to a conventional tillage system (disk-tillage). Emissions of CO2-C from the soil and crop C inputs were determined, estimating soil C balance under both tillage systems.
As a part of this study, a field experiment was performed during 6 yr on an Entic Haplustoll where no-till and disk-tillage was applied to a soil cropped under a common rotation in the region (oat + hairy vetch, corn, wheat, oat). From Year 3 to 6 in situ CO2-C fluxes were measured and C inputs from above and below ground plant residues were estimated.
Results showed that in the semiarid environment of the study C sequestration occurred under no-till. The sequestration process was attributed to the effect of tillage systems on crop productivity rather than on the mineralization intensity of soil organic pools:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: soils :: carbon sequestration :: no-till :: grass :: no-fallow :: biochar ::
Investigation: United States
In Kentucky (USA) a study was conducted in a corn agroecosystem experiment to test the soil C saturation concept which postulates that there is an upper limit to the equilibrium soil C level of mineral soils even when soil C input is increased. In this experiment, a gradient of soil C input was produced with four N fertilizer application rates under two tillage systems, no-till and moldboard plowing. To investigate if physical protection of organic C leads to soil C saturation, C stabilization in soil fractions that differ in C stabilization potential was determined, and the relationship between soil C input and soil organic C was analyzed.
Total soil organic C was positively related to C input, and this was primarily due to C stabilization in larger soil aggregates. In both tillage systems, however, C in the two smallest soil size fractions did not increase with greater C input. Moreover, in three soil fractions further separated from larger soil aggregates, C associated with particulate organic matter and microaggregates increased with C input, but there was no increase in C associated with silt-plus-clay, which was the smallest soil size fraction.
Haegeun Chung at University of California, Davis, the first author of the study conducted in Kentucky (USA), stated “Our results indicate that soil fractions with low C stabilization potential show C saturation. Therefore, we need to consider soil C saturation levels to better predict the change in C sink capacity and fertility of soils when soil C input increases under higher plant production or organic amendment.”
References:
E. Bremera, H. H. Janzenb, B. H. Ellertb and R. H. McKenzie, "Soil Organic Carbon after Twelve Years of Various Crop Rotations in an Aridic Boroll", Soil Sci Soc Am J 72:970-974 (2008), DOI: 10.2136/sssaj2007.0327
Alfredo Bonoa, R. Alvarezb, D. E. Buschiazzoc and R. J. C. Cantet, "Tillage Effects on Soil Carbon Balance in a Semiarid Agroecosystem", Soil Sci Soc Am J 72:1140-1149 (2008), DOI: 10.2136/sssaj2007.0250
Haegeun Chunga, John H. Groveb and Johan Sixa, "Indications for Soil Carbon Saturation in a Temperate Agroecosystem", Soil Sci Soc Am J 72:1132-1139 (2008), DOI: 10.2136/sssaj2007.0265
Biopact: FAO introduces new global soil database: allows analysis of carbon sequestration and biochar potential - July 21, 2008
Article continues
The studies did not yet analyse the sequestration potential of C via biochar - a recalcitrant form of carbon that can be stored in soils unaltered for centuries, perhaps even millenia. Instead they analysed the effect of more traditional soil management practises, such as the elimination of fallow or the establishment of grass. In any case, scientists are suspecting the global potential for soils to absorb and lock up carbon can be very large (previous post).
Scientists from Alberta Agriculture and Rural Development (Canada), the National Institute of Agricultural Technology, the University of Buenos Aires (Argentina), and University of California, Davis (USA) have investigated soil C balance in distinct agroecosystems under different management practices including soil tillage, N fertilization, elimination of fallow, and establishment of grass. In each case, C sequestration occurred in response to higher C input to soil; however, increase in SOC was confined to labile fractions such as the light fraction and larger soil aggregates.
Investigation: Canada
In southeastern Alberta, a long-term study showed previously that eliminating summer fallow or establishing grass significantly increased soil organic C after 6 yr. In the 12th year of the study, total organic C and light fraction C were determined in three rotations with summer fallow, two continuously cropped rotations and grass. All rotations had subtreatments with different levels of fertilization. The light fraction of soil C was obtained using density separation and consisted mostly of non-decomposed root and straw fragments.
Although soil organic C was increased by elimination of summer fallow, fertilization, and establishment of grass, gains in soil organic C between Years 6 and 12 were negligible in all treatments except the fertilized grass treatment. Most of the gains in total soil organic C were due to increased light fraction C. The results indicate that much of the gain in soil organic C in response to improved practices on semiarid prairie soils likely occurs within one decade.
Investigation: Argentina
In the semiarid portion of the Pampas, scientist compared no-till management to a conventional tillage system (disk-tillage). Emissions of CO2-C from the soil and crop C inputs were determined, estimating soil C balance under both tillage systems.
As a part of this study, a field experiment was performed during 6 yr on an Entic Haplustoll where no-till and disk-tillage was applied to a soil cropped under a common rotation in the region (oat + hairy vetch, corn, wheat, oat). From Year 3 to 6 in situ CO2-C fluxes were measured and C inputs from above and below ground plant residues were estimated.
Results showed that in the semiarid environment of the study C sequestration occurred under no-till. The sequestration process was attributed to the effect of tillage systems on crop productivity rather than on the mineralization intensity of soil organic pools:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: soils :: carbon sequestration :: no-till :: grass :: no-fallow :: biochar ::
Investigation: United States
In Kentucky (USA) a study was conducted in a corn agroecosystem experiment to test the soil C saturation concept which postulates that there is an upper limit to the equilibrium soil C level of mineral soils even when soil C input is increased. In this experiment, a gradient of soil C input was produced with four N fertilizer application rates under two tillage systems, no-till and moldboard plowing. To investigate if physical protection of organic C leads to soil C saturation, C stabilization in soil fractions that differ in C stabilization potential was determined, and the relationship between soil C input and soil organic C was analyzed.
Total soil organic C was positively related to C input, and this was primarily due to C stabilization in larger soil aggregates. In both tillage systems, however, C in the two smallest soil size fractions did not increase with greater C input. Moreover, in three soil fractions further separated from larger soil aggregates, C associated with particulate organic matter and microaggregates increased with C input, but there was no increase in C associated with silt-plus-clay, which was the smallest soil size fraction.
Haegeun Chung at University of California, Davis, the first author of the study conducted in Kentucky (USA), stated “Our results indicate that soil fractions with low C stabilization potential show C saturation. Therefore, we need to consider soil C saturation levels to better predict the change in C sink capacity and fertility of soils when soil C input increases under higher plant production or organic amendment.”
References:
E. Bremera, H. H. Janzenb, B. H. Ellertb and R. H. McKenzie, "Soil Organic Carbon after Twelve Years of Various Crop Rotations in an Aridic Boroll", Soil Sci Soc Am J 72:970-974 (2008), DOI: 10.2136/sssaj2007.0327
Alfredo Bonoa, R. Alvarezb, D. E. Buschiazzoc and R. J. C. Cantet, "Tillage Effects on Soil Carbon Balance in a Semiarid Agroecosystem", Soil Sci Soc Am J 72:1140-1149 (2008), DOI: 10.2136/sssaj2007.0250
Haegeun Chunga, John H. Groveb and Johan Sixa, "Indications for Soil Carbon Saturation in a Temperate Agroecosystem", Soil Sci Soc Am J 72:1132-1139 (2008), DOI: 10.2136/sssaj2007.0265
Biopact: FAO introduces new global soil database: allows analysis of carbon sequestration and biochar potential - July 21, 2008
Article continues
Tuesday, July 29, 2008
RAB: biomass now the key renewable energy source, as backlash against wind and solar grows
In recent months, the UK has changed its position on renewables, says Williams, with a backlash against many more established alternative energy sources like wind and solar power and liquid biofuels. In the transport sector, first-generation biofuels have been attacked for their potential effect on food prices and actual carbon reductions. Wind and solar are being heavily criticised for their inability to produce a consistent stream of electricity and for their cost. Wind power can be two to three times more expensive than biomass; solar PV up to twenty times, and solar CSP up to five times. There are no efficient energy storage options for these renewables, making them incapable of providing baseloads.
That is why many industry experts are now suggesting that biomass has to play the primary role in helping the EU to meet its challenging target of generating 20% of its energy from renewable sources by 2020, says the RAB's biomass chairman.
Getting serious about renewables
As we are gaining experience with renewables, it becomes apparent that only biomass is a really effective method of producing both heat and power, says Williams.
A single power station can produce around three times more energy as a windfarm for the same amount of generation capacity. It is also much more reliable and can be scaled up or down to meet consumer demand.
Whereas heat for domestic-scale commercial installations could come from intermittent solar technologies or even heat pumps, it is widely acknowledged that the primary market can only be supplied by biomass. After all, most heat comes from combustion of a fuel, and biomass is the only renewable and combustible fuel. Heat from wind or solar electricity is no serious option.
Of course, every technology has its drawbacks and for biomass the main one is sourcing a supply of fuel. The requirements to power a single station can be extensive, particularly if it is using wood as its primary fuel source.
Some plants within the UK propose to import timber from as far away as Canada and Indonesia; this has an impact on the carbon footprint of the feedstock and the energy that it produces, even though analyses show these impacts are rather small (biomass transported in large ships does not lose much of its strong energy or carbon balance).
Besides importing biomass, some developers are now looking to generate energy by burning straw, which the UK has an abundant supply of and which, as a by-product of agricultural crops, does not have an impact on the food verses fuel debate. Supermarket giant Tesco has recently been given a green light to build Britain's first ever straw-powered Combined Heat and Power (CHP) plant to meet the electricity and heating needs of one of its distribution centres.
Utilising straw for biomass represents one of the most efficient methods for its disposal and pre-empts the need for it to be ploughed back into the land.
Surging investments
As a final, but vital, benefit, the UK can meet all of its requirements from domestic sources, cutting out the need to import supplies and allaying growing concerns over energy security. Many other EU member states - particularly in Scandinavia and Eastern Europe - have very large biomass supplies as well. Trading the fuel internationally shows enormous potential as well.
So what next for the industry? More than £3.5billion (€4.4/US$7bn) was invested last year and this figure looks set to grow substantially, as green investment funds try to hedge against the credit crunch by diversifying their portfolio of renewables schemes. As costs for both wind and solar projects surge, biomass is set to retain its position as the largest renewable energy source in the EU. Over the coming years, it is expected to become the fastest growing sector:
energy :: sustainability :: biomass :: bioenergy :: energy crops :: renewables :: solar :: wind :: combined heat and power :: baseload :: emissions :: electricity :: EU ::
In the UK, a stream of projects are either coming online or expecting to do so shortly, including the world's largest plant near Port Talbot, South Wales.
Signs from the British government are also encouraging. Changes to its proposed Renewables Obligation Certificate (which offers incentives to suppliers to generate energy from renewable sources) will increase the value of energy generated by biomass in comparison with other sustainable technologies and make it more rewarding for investors to back.
In June, the Department for Business, Enterprise and Regulatory Reform (BERR) published its Renewable Energy Strategy that also made clear the important role that the industry could play, noting that there is a need to "develop a sustainable biomass market".
While this in itself is encouraging, there remains some concern over the detail.
The proposals mooted in the strategy have been primarily designed to make individual action more palatable, specifically a feed-in tariff to encourage microgeneration technologies in homes and a financial incentive mechanism to facilitate a general increase in use of renewable heat.
What they have not done, however, is to provide significant encouragement for commercial developers. There is a definite feeling by many in the industry that the current system is over-complicated and that applications are too frequently caught up in red tape.
By laying down a clear pathway that developers can follow, the government will be able to stimulate growth and at the same time provide the financial community with the confidence necessary for it to make the long-term substantial investments.
The result will be a step-change in the UK renewable sector as a whole, and the first step towards meeting the EU's 2020 targets.
Going carbon-negative
One major advantage of biomass is its potential to generate 'negative emissions' energy, that is, energy capable of withdrawing CO2 from the atmosphere.
When biomass is used in advanced power plants, its CO2 can be captured during or after combustion, and then sequestered in empty oil and gas fields.
The result is 'carbon-negative' power and heat. The more you were to use of it, the more CO2 you would be scrubbing out of the atmosphere.
The difference with other renewables is quite staggering. Whereas wind and solar both add CO2 emissions to the atmosphere over their lifecycle (wind around 30 tons CO2eq/GWh, solar PV around 100 tons of CO2eq/GW), carbon-negative bioenergy can take up to 1000 tons of CO2 per GWh out of the atmosphere.
In the UK, there are large sites in which CO2 can be stored. As the country's oil and gas sector has reached its peak, and many fields are already empty, it becomes possible to use these geological features to sequester biogenic CO2.
Biomass is the only kind of renewable energy capable of generating 'negative emissions'.
References:
UK Government: Renewables Advisory Board.
BBC: Burning ambitions - Why it is time to get serious about large-scale biomass - July 29, 2008.
Article continues
posted by Biopact team at 8:42 PM 2 comments links to this post