The Charcoal Vision: A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, while Improving Soil and Water Quality
David Laird, USDAⁱ, ARS, National Soil Tilth Laboratoryⁱ, April 12,2008
In, Agronomy Journal • Volume 100, Issue 1 • 2008

ABSTRACT
Processing biomass through a distributed network of fast pyrolyzers may be a sustainable platform for producing energy from biomass. Fast pyrolyzers thermally transform biomass into bio-oil, syngas, and charcoal. The syngas could provide the energy needs of the pyrolyzer. Bio-oil is an energy raw material (∼17 MJ kg−1) that can be burned to generate heat or shipped to a refinery for processing into transportation fuels. Charcoal could also be used to generate energy; however, application of the charcoal co-product to soils may be key to sustainability. Application of charcoal to soils is hypothesized to increase bio-available water, build soil organic matter, enhance nutrient cycling, lower bulk density, act as a liming agent, and reduce leaching of pesticides and nutrients to surface and ground water. Th e half-life of C in soil charcoal is in excess of 1000 yr. Hence, soil-applied charcoal will make both a lasting contribution to soil quality and C in the charcoal will be removed from the atmosphere and sequestered for millennia. Assuming the United States can annually produce 1.1 × 109 Mg of biomass from harvestable forest and crop lands, national implementation of Th e Charcoal Vision would generate enough bio-oil to displace 1.91 billion barrels
of fossil fuel oil per year or about 25% of the current U.S. annual oil consumption. Th e combined C credit for fossil fuel displacement and permanent sequestration, 363 Tg per year, is 10% of the average annual U.S. emissions of CO2–C.

Bioenergy Activities at Ames, IA

Research Project: Ecologically-Based Soil Management for Sustainable Agriculture and Resource Conservation (3625-12000-012-00D) (D.L. Karlen, LS)

Objective: To develop innovative, ecologically-based crop and soil nutrient management practices for enhanced productivity and negligible off-site agricultural impacts.

Hypotheses:
1. Long-term average crop yield from chisel-plowed Clarion-Nicollet-Webster soils will decrease significantly by removing crop residues for biofuels production.
2. With no-tillage, at least 2 t/ac of the surface crop residue can be harvested from Clarion-Nicollet-Webster soils for biofuels production without significantly decreasing long-term average yield.
3. With intensive crop management (i.e. increased plant population, fertilizer rates, and narrow row spacing) more than 2 t/ac of biomass can be harvested from Clarion-Nicollet-Webster soils for biofuels production without significantly decreasing long-term average no-till yield.
4. With cover crops more than 2 t/ac of biomass can be harvested from Clarion-Nicollet-Webster soils for biofuels production without significantly decreasing long-term average no-till yield.
5. Applying charcoal (biochar) will significantly increase the Soil Management Assessment Framework (SMAF) rating for Clarion-Nicollet-Webster soils where crop residues are harvested for biofuels production.

Research Project: Biogeochemical processes influencing formation and stabilization of soil organic matter and soil structure (3625-11120-011-00D) (D.L. Laird, LS, David.Laird@ars.usda.gov)

Objective: Determine the role of clay minerals and charcoal in the formation and stabilization of soil organic matter and soil structure

Hypotheses:
1. Charcoal additions to soil will have a positive impact on crop productivity in a Midwestern corn-soybean cropping system.
2. Charcoal additions to soils will stimulate formation of clay-humic complexes and the formation and stabilization of new biogenic soil organic matter.
3. Charcoal additions to soils will reduce nitrogen and pesticide leaching by increased adsorption.

The Charcoal Vision: Producing Bioenergy while Simultaneously Enhancing Soil and Water Quality and Permanently Sequestering Carbon
David Laird, Science Magazine, August 30, 2007

Interpretive Summary: The US is rapidly pursuing development of a cellulosic ethanol industry. This strategy is of concern to agricultural scientists, farmers, and conservationists because harvesting biomass crops will have an adverse impact on soil and water quality. This report describes the Charcoal Vision, which is a scenario for processing biomass by pyrolysis to generate bio-oil and charcoal. The bio-oil could be used to offset fossil fuel oil and the charcoal could be returned to the soil from which the biomass was harvested. Returning the charcoal co-product of pyrolysis to the soil is anticipated to build soil quality, increase agricultural productivity, and improve water quality. National deployment of the Charcoal Vision could generate enough bio-oil to meet 25% of the current US consumption of fossil fuel oil. The scenario would simultaneously reduce net US emissions of carbon dioxide to the atmosphere by about 10%. This report will help policy makers develop strategies that simultenously benefit energy security, global change, environmental quality, and rural economies.

Technical Abstract: Processing biomass through a distributed network of fast pyrolyzers has many advantages relative to the cellulosic ethanol platform. Fast pyrolyzers thermally transform biomass into bio-oil, syngas, and charcoal. The syngas can be used to provide the energy needs of the pyrolyzer. Bio-oil is an energy raw material (17.0 MJ/kg) that can be burned to generate heat or electricity or shipped to a refinery for processing into transportation fuels. Charcoal should be returning the charcoal to the soils from which the biomass was harvested. Application of charcoal to soils is hypothesized to do several positive things for soils, including; supply nutrients, increase bioavailable water, build soil organic matter, enhance nutrient cycling, lower the bulk density, and act as a liming agent. Application of charcoal to soils is also anticipated to reduce the leaching of pesticides and nutrients to surface and ground water. The half-life of carbon (C) in soil charcoal is in excess of 1,000 years. This means that soil-applied charcoal will make both a lasting contribution to soil quality and the C in the charcoal will be removed from the atmosphere and sequestered in the soil for millennia. Assuming the U.S. can annually produce 1.1x10^9 Mg of biomass from harvestable forest and crop lands, then, national implementation of the Charcoal Vision would generate enough bio-oil to displace 1.91 billion barrels of fossil fuel oil per year or about 25% of the current U.S. annual oil consumption and thus offset 234 Tg of fossil fuel C emissions to the atmosphere per year. Furthermore, assuming that fixed C in the char is not biologically degraded, application of char to soils would sequester 139 Tg of C per year. The combined C credit for fossil fuel displacement and permanent sequestration, 373 Tg per year, is 10% of the average annual U.S. emissions of CO2-C.

Distinguishing Black Carbon from Biogenic Humic Substances in Soil Clay Fractions
Laird, David, Chappell, Mark, Martens, Dean, Wershaw, Robert, Thompson, Michael
Geoderma, October 3, 2007
Interpretive Summary:
Soil organic matter, often called humus, contributes substantially to the quality of soils by stabilizing soil structure and both retaining and helping to cycle plant nutrients. The chemical structure of soil humus is very complex, but has been thought in the past to be a complex polymer with a backbone of aromatic carbon. We developed a method to physically separate aged charcoal from soil organic matter. The charcoal contributed about 8% of the carbon in the three soils we studied. The charcoal was old and was not very available to soil microorganisms. The true humus was the fraction of the soil organic matter left after the charcoal had been extracted. The true humus was young and readily available to soil microorganisms. The true humus had very little aromatic carbon; rather it was a mixture of fatty acids and sugar-like structures. This discovery means that many of the previously proposed models for the structure of soil humus are wrong, because most of the aromatic carbon is in the charcoal not in the true humus. This study will help scientists to understand how soil organic matter is formed and stabilized in soils. Such information is needed to design agricultural management systems that build soil organic matter. Policy makers need to understand that charcoal is a natural component of soils and that adding charcoal to soils will help build soil quality because in the future conservation practices may include adding charcoal to soils.
Technical Abstract:
Most models of soil humic substances include a substantial component of aromatic carbon (C) either as the backbone of humic heteropolymers or as a significant component of supramolecular aggregates of degraded biopolymers. Here we report that most of the aromatic C in the clay fraction of three studied soils was associated with discrete particles (0.2-2 um) of pyrogenic black carbon (BC), which were physically separated with the coarse clay subfraction. The physically separated BC particles contained approximately 60% aromatic C, with the remainder being a mixture of aliphatic, anomeric and carboxylic C. We hypothesize that as BC particles aged in soils their surfaces were oxidized to form carboxylic groups. Further, we suggest that anomeric and aliphatic C accumulated in BC particles either by adsorption of dissolved biogenic compounds from the soil solution or by direct deposition of biogenic materials from microbes living within the BC particles. The biogenic soil organic matter that was physically separated with the medium and fine clay subfractions was dominated by aliphatic, anomeric, and carboxylic groups with little aromatic C and existed as diffuse filamentous clumps and films binding clay particles together. The lack of aromatic C in the biogenic soil organic matter is inconsistent with the heteropolymer model for the formation of humic substances.