Compost can turn agricultural soils into a carbon sink - but no match to biochar
Applying organic fertilizers, such as those resulting from composting, to agricultural land could increase the amount of carbon stored in these soils and contribute significantly to the reduction of greenhouse gas emissions, according to new research published in a special issue of Waste Management & Research. The findings are interesting, but the bioenergy community has meanwhile gone way beyond this idea, and is instead looking at a similar but much more promising concept, namely creating soil carbon sinks with biochar, coupled to biofuel and bioenergy production.
The addition of biochar - inert carbon obtained from the pyrolysis of biomass - to soils makes for a much more stable and permanent soil carbon sink than storing carbon via compost; it also reduces fertilizer needs because of increased cation exchange capacity and the prevention of leaching and runoff of nutrients; it reduces nitrous oxide emissions substantially, boosts soil fertility and organic matter build up, and holds a huge overall potential for soil carbon storage (in fact, the system can effectively halt and reverse climate change).
When added to soils, biochar (also known as agrichar) remains unaltered for hundreds, possibly thousands of years (see the ancient Terra Preta soils). Compost derived carbon biodegrades in a matter of years, to release greenhouse gas emissions. Moreover, biochar systems can be based on the production of carbon-negative bioenergy, because the soil amendment is obtained from pyrolysis - itself a promising bioconversion technology that yields both biofuels (bio-oil) and combustible gas.
The new data on organic fertilizers and how they can play a role in creating soil carbon sinks, is fascinating though, in that they precisely highlight biochar's far greater potential. Carbon sequestration in soil has been recognized by the Intergovernmental Panel on Climate Change (IPCC) and the European Commission as one of the possible measures through which greenhouse gas emissions can be mitigated.
One estimate of the potential value of the compost approach - which assumed that 20% of the surface of agricultural land in the EU could be used as a sink for carbon - suggested it could constitute about 8.6% of the total EU emission-reduction objective.
However, capitalizing on this potential climate-change mitigation measure is not a simple task. The issue is complicated by the fact that industrial farming techniques mean agriculture is actually depleting carbon from soil, thus reducing its capacity to act as a carbon sink:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: compost :: carbon sink :: soil organic carbon :: carbon cycle :: biochar :: agrichar ::
According to Hogg and Favoino, this loss of carbon sink capacity is not permanent. Composting can contribute in a positive way to the twin objectives of restoring soil quality and sequestering carbon in soils. Applications of organic matter (in the form of organic fertilizers) can lead either to a build-up of soil organic carbon over time, or a reduction in the rate at which organic matter is depleted from soils (graph, click to enlarge). In either case, the overall quantity of organic matter in soils will be higher than using no organic fertilizer:
Their results suggest that soils where manure was added have soil organic carbon levels 1.34% higher than un-amended soils, and 1.13% higher than soils amended with chemical fertilizers, over a 50-year period. This is clearly significant given the evaluations reported above regarding carbon being lost from soils, and the increasing amount of carbon dioxide in the atmosphere, they say.
The article about the potential role of compost in reducing greenhouse gases is published on today in a special issue of Waste Management & Research, entitled Green House Gases and Solid Waste Management. The article will be free online for two months.
References:
Enzo Favoino and Dominic Hogg. "The potential role of compost in reducing greenhouse gases", Waste Management & Research, Vol. 26, No. 1, 61-69 (2008), DOI: 10.1177/0734242X08088584
Amonette, J.; Lehmann, J.; Joseph, S., "Terrestrial Carbon Sequestration with Biochar: A Preliminary Assessment of its Global Potential", American Geophysical Union, Fall Meeting 2007, abstract, December 2007.
Article continues
The addition of biochar - inert carbon obtained from the pyrolysis of biomass - to soils makes for a much more stable and permanent soil carbon sink than storing carbon via compost; it also reduces fertilizer needs because of increased cation exchange capacity and the prevention of leaching and runoff of nutrients; it reduces nitrous oxide emissions substantially, boosts soil fertility and organic matter build up, and holds a huge overall potential for soil carbon storage (in fact, the system can effectively halt and reverse climate change).
When added to soils, biochar (also known as agrichar) remains unaltered for hundreds, possibly thousands of years (see the ancient Terra Preta soils). Compost derived carbon biodegrades in a matter of years, to release greenhouse gas emissions. Moreover, biochar systems can be based on the production of carbon-negative bioenergy, because the soil amendment is obtained from pyrolysis - itself a promising bioconversion technology that yields both biofuels (bio-oil) and combustible gas.
The new data on organic fertilizers and how they can play a role in creating soil carbon sinks, is fascinating though, in that they precisely highlight biochar's far greater potential. Carbon sequestration in soil has been recognized by the Intergovernmental Panel on Climate Change (IPCC) and the European Commission as one of the possible measures through which greenhouse gas emissions can be mitigated.
One estimate of the potential value of the compost approach - which assumed that 20% of the surface of agricultural land in the EU could be used as a sink for carbon - suggested it could constitute about 8.6% of the total EU emission-reduction objective.
An increase of just 0.15% in organic carbon in arable soils in a country like Italy would effectively imply the sequestration of the same amount of carbon within soil that is currently released into the atmosphere in a period of one year through the use of fossil fuels. - Enzo Favoino and Dominic Hogg, authorsLike biochar, increasing organic matter in soils via compost may cause other greenhouse gas-saving effects, such as improved workability of soils, better water retention, less production and use of mineral fertilizers and pesticides, and reduced release of nitrous oxide.
However, capitalizing on this potential climate-change mitigation measure is not a simple task. The issue is complicated by the fact that industrial farming techniques mean agriculture is actually depleting carbon from soil, thus reducing its capacity to act as a carbon sink:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: compost :: carbon sink :: soil organic carbon :: carbon cycle :: biochar :: agrichar ::
According to Hogg and Favoino, this loss of carbon sink capacity is not permanent. Composting can contribute in a positive way to the twin objectives of restoring soil quality and sequestering carbon in soils. Applications of organic matter (in the form of organic fertilizers) can lead either to a build-up of soil organic carbon over time, or a reduction in the rate at which organic matter is depleted from soils (graph, click to enlarge). In either case, the overall quantity of organic matter in soils will be higher than using no organic fertilizer:
What organic fertilizers can do is reverse the decline in soil organic matter that has occurred in relatively recent decades by contributing to the build-up in the stable organic fraction in soils, and having the effect, in any given year, of ensuring that more carbon is held within the soil. - Enzo Favoino and Dominic Hogg, authorsBut calculating the value of this technique to climate change policies is complicated. To refine previous calculations and to take account of the positive and negative dynamics of carbon storage in soil, Favoino and Hogg modelled the dynamics of compost application and build-up balancing this with mineralization and loss through tillage.
Their results suggest that soils where manure was added have soil organic carbon levels 1.34% higher than un-amended soils, and 1.13% higher than soils amended with chemical fertilizers, over a 50-year period. This is clearly significant given the evaluations reported above regarding carbon being lost from soils, and the increasing amount of carbon dioxide in the atmosphere, they say.
The article about the potential role of compost in reducing greenhouse gases is published on today in a special issue of Waste Management & Research, entitled Green House Gases and Solid Waste Management. The article will be free online for two months.
References:
Enzo Favoino and Dominic Hogg. "The potential role of compost in reducing greenhouse gases", Waste Management & Research, Vol. 26, No. 1, 61-69 (2008), DOI: 10.1177/0734242X08088584
Amonette, J.; Lehmann, J.; Joseph, S., "Terrestrial Carbon Sequestration with Biochar: A Preliminary Assessment of its Global Potential", American Geophysical Union, Fall Meeting 2007, abstract, December 2007.
Article continues
Monday, February 25, 2008
First corn genome draft to be announced - consequences for bioenergy, food, climate change
The implications
The draft of the corn genome provides plant scientists with a lot of data to work with. It is a lot like a collection of maps, diary entries, dried plants and animal specimens brought back by naturalists' expeditions: the raw material demands years of subsequent analysis and study and can yield surprising discoveries. One scientist said "this will enable so much exciting corn research. This will raise questions about the biology of corn and provide great tools to answer them."
Those answers could help scientists modify and improve corn plants. The genome, for example, could help scientists:
- develop crops that can withstand global climate change
- add nutritional value to grain
- sequester more atmospheric carbon in agricultural soils
- boost yields so crops can meet growing demands for food, feed, fiber and fuel
In addition, what scientists learn from the corn genome will allow them to better understand other grasses The genome of corn is very similar to the genomes of rice, wheat, sorghum, prairie grasses and turf grasses. Therefore, the draft of the corn genome can help researchers improve the other cereals and grasses.Iowa State University researchers played an important role in this $32 million project. Patrick Schnable, a Baker Professor of Agronomy and director of the Center for Plant Genomics and the Center for Carbon Capturing Crops, and Srinivas Aluru, a Stanley Chair in Interdisciplinary Engineering and a Professor of Electrical and Computer Engineering, led the work at Iowa State and provided the project with expertise in corn genomics and supercomputing.
Earlier, Iowa State researchers and their U.S. Department of Agriculture collaborators already developed the B73 inbred corn line that was sequenced by the genome project. Created decades ago, the B73 line is noted for the high grain yields it contributes to hybrids. Derivatives of B73 are still widely used to produce many commercial hybrids:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: ethanol :: corn :: genomics :: genetics :: plant breeding :: biotechnology ::
The overall corn genome project is led by Richard Wilson, the director of the Genome Sequencing Center at the Washington University School of Medicine in St. Louis. He will make a brief announcement about the sequencing project and researchers will take questions during a news conference at 12:30 p.m. Thursday, Feb. 28, in the Hoover Room of the Marriott Wardman Park Hotel in downtown Washington. Wilson will also make remarks about the draft genome during a reception from 6:30-8 p.m. Thursday at the Smithsonian Institution's National Museum of Natural History on the National Mall. And Wilson will present a scientific talk about the draft genome at 8:35 p.m. Friday, Feb. 29, back at the Marriott Wardman Park Hotel. Wilson's talk will describe the draft corn genome, explain the work needed to produce it and look ahead to the research that needs to be done to improve it.
The genome project also includes researchers at the University of Arizona in Tucson and the Cold Spring Harbor Laboratory in New York. The $32 million, three-year research project is supported by the National Science Foundation, the U.S. Department of Agriculture and the U.S. Department of Energy.
Supercomputing
Schnable and Aluru led Iowa State's work to refine assemblies of the genomic sequences generated by researchers at Washington University. In addition, they identified almost 100 genes which have nearly identical copies in the genome. Schnable said these nearly identical paralogs may have played important roles during the evolution and domestication of corn and may have contributed to the ability of breeders to mold this important crop species to meet human needs. The Schnable and Aluru teams also discovered several hundred new corn genes that are not present in other plants. Some of these genes may be responsible for unique attributes of corn.
The corn genome is an especially difficult jigsaw puzzle to put together, Schnable said. There are some 2.5 billion base pairs that make up the double helix of corn DNA. The corn genome also has long lines of repetitive code. And corn has 50,000 to 60,000 genes to identify and characterize. That's about twice the number of genes in humans. Plus, 50 percent or more of the corn genome is made up of transposons or jumping genes. Those are pieces of DNA that can move around the genome and change the function of genes.
Solving all those assembly challenges took a lot of computing power and some new software technology.
Aluru and his research team developed software called "PaCE" and "LTR_par" that runs on parallel computers -- including CyBlue, Iowa State's IBM Blue Gene/L supercomputer capable of 5.7 trillion calculations per second. PaCE can generate draft genome assemblies in hours or days instead of months. LTR_par identifies retrotransposons, another mobile genetic element that can cause genome changes such as mutations, gene duplications and chromosome rearrangements.
In addition to advancing our understanding of corn, the genome project has helped Iowa State launch several academic careers. As graduate students, Scott Emrich, Ananth Kalyanaraman and Sang-Duck Seo worked on the corn genome project. Emrich is now an assistant professor of computer science and engineering at the University of Notre Dame in Notre Dame, Ind.; Kalyanaraman is an assistant professor of electrical engineering and computer science at Washington State University in Pullman; and Seo is an assistant professor of art at the University of Nevada, Las Vegas.
And so, Schnable said, the corn genome project has already been very useful. As researchers turn the first draft into new chapters describing their discoveries, he said it will be even more important to researchers and society.
Picture: Several corn varieties are on display outside Patrick Schnable's Iowa State office. Credit: Iowa State University.
References:
Iowa State University: Iowa State researchers help piece together the corn genome's first draft - February 25, 2008.
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