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Biochar - A Multitude of Benefits

AgMRC Renewable Energy Newsletter
December 2009

Don Hofstrand
Co-director
Agricultural Marketing Resource Center
dhof@iastate.edu

This is the first in a series of articles on biochar.  In future articles we will focus in more depth on specific aspects and applications of biochar. 

Five hundred years ago Spanish explorers, winding their way through the Amazon River Basin of South America, came upon an interesting phenomenon.  As is traditional for rainforest soils, the explorers found soils of low productivity that were leached of plant nutrients and organic matter.  However, periodically they would find small patches of black highly productive soils.  Upon further investigation they found that these patches were created by local Indian tribes using the partial burning of biomass.  Essentially, they made these soils from biochar (charcoal).

Figure 1.  Comparison of traditional rainforest soils (left) with biochar plot (right).

 
Source: International Biochar Initiative   http://www.biochar-international.org/biochar/soils

Five hundred years later scientists find that these patches of soil still exist and are as productive (or more productive) than when the Indians formed them.  This has led to a flurry of scientific investigations about the potential for biochar as a soil amendment and productivity enhancer in modern agriculture.

Major benefits of biochar

Charcoal or biochar when used in this context, is made by the pyrolysis of biomass (pyro means fire and lysis mean decomposition).  Biochar is produced from thermal decomposition of organic material under a limited supply of oxygen and at relatively low temperatures.  Pyrolysis is a form of baking biomass in the absence of air to drive off volatile gasses, leaving carbon behind.  So it produces bioenergy in the form of gas and oil, along with the biochar. This energy can be recoverable and used as a renewable fuel.  As shown in Figure 2, biomass in the form of crop residues, bioenergy crops, manure or organic wastes will produce about 50 percent biochar, which is returned to the soil, and 50 percent bioenergy in the form of synthesis gas and bio oil.

Figure 2.  Slow pyrolysis produces biochar and bioenergy.
 
Source: International Biochar Initiative   http://www.biochar-international.org/biochar/soils

The pyrolysis of biomass into biochar and energy creates four primary benefits.
1)    Improvement of the productivity of soil to achieve higher yields.
2)    Creation of a bioenergy as a substitute for fossil fuels.
3)    Sequestration of carbon in the soil that will reduce atmospheric carbon dioxide.
4)    Management of waste.

Improve soil productivity

As a soil amendment, biochar helps to improve the Earth's soil resource by increasing productivity and crop yields, reducing soil acidity, reducing the need for some chemical and fertilizer inputs and potentially providing other soil benefits. 

Field trials using biochar have been conducted in the tropics over the past several years. All showed positive results on yields when biochar was applied to field soils and nutrients were managed appropriately. USDA has begun field trials on highly fertile Iowa Mollisol soils.  Initial results are positive but several more years of trials are required to substantiate these results.

Biochar has the ability to improve soil fertility, leading to higher crop yields.  Applied to the soil in a finely ground form, biochar’s vast surface area and complex pore structure is hospitable to the bacteria and fungi that plants need to absorb nutrients from the soil. So, biochar provides a secure habitat for beneficial microbial activity that is important for crop production to flourish.

Biochar has been shown to reduce the soil emissions of nitrous oxide (as a greenhouse gas, it is 310 times more potent than carbon dioxide) and improve the uptake of methane (21 times more potent than carbon dioxide).  Soil emissions of nitrous oxide account for about half of the greenhouse gas emissions from corn production (one quarter of the emissions from corn ethanol production).  So, reducing nitrous oxide emissions by 50 percent or more would greatly improve the carbon footprint of corn production, along with corn-ethanol production. 

Biochar has also been shown to reduce soil acidity.  Soils in large parts of the world suffer from acidity (low pH).  Biochar retains nutrients in soil directly through the negative charge that develops on its surfaces, and this negative charge can buffer acidity in the soil. Currently, soil acidity is corrected by applying large amount of lime.

Because of biochar’s ability to enhance the availability of plant nutrients, soil nutrient retention is improved.  This means that less fertilizer needs to be applied which reduces the cost of producing the crop.  Moreover, char-amended soils have shown reduced runoff of phosphorus into surface waters and leaching of nitrogen into groundwater.  So, pollution caused by fertilizer run-off into streams and rivers is reduced which helps reduce the size of the “dead zone” in the Gulf of Mexico, as shown in Figure 3.

Figure 3.  Dead zone in the Gulf of Mexico


Biochar has the potential to increase the world’s agricultural productivity by improving degraded soils.  For example, in tropical areas of the world, an agricultural method called “slash and burn” has often been used where rainforest is cut down and farmed for a few years until the soil is depleted of nutrients and then abandoned, at which time the farmer moves on to a new location and cuts down more rainforest and repeats the cycle.  Biochar has the potential to change “slash and burn” to “slash and char” agriculture.  Instead of abandoning nutrient depleted tropical soils, the productivity of the soil can be improved with the use of biochar, and the need to repeat the “slash and burn” cycle is ended.     

Produce bioenergy

The process produces bioenergy such as syngas and bio-oils.  This bioenergy can be “upgraded” to transportation fuels like biodiesel and gasoline substitutes to replace fossil fuels. 

To capture the energy contained in biomass, the bonds that hold the biomass molecules together must be broken.  The chemical energy that is released is a mixture of molecules collectively called synthesis gas.  Syngas (from synthetic or synthesis gas) is composed mainly of carbon monoxide and hydrogen, and sometimes carbon dioxide and other minor molecules.  It is combustible and has half the energy density of natural gas.

Syngas can be used directly as an energy source (e.g. gas turbines) or as an intermediate in the production of synthetic natural gas, ammonia and other energy sources.  Syngas can also be used as an intermediary in producing synthetic petroleum or liquid fuel (e.g. diesel fuel).  In addition, syngas has the potential to produce many of the products and chemicals currently created from petroleum. 

The other bioenergy product is bio-oil.  Bio-oil can be used as a substitute for fuel oil or heating oil.   It also has the potential to be used in a bio-refinery where valuable chemicals and compounds are extracted and the remainder is upgraded to fuel or syngas.

Sequester carbon

Biochar has the unique ability to sequester carbon and thereby reduce atmospheric carbon. To understand this we need to examine the earth’s carbon cycle.

The earth contains huge storehouses of carbon.  Carbon is sequestered in our oceans, soils and vegetation as shown in Figure 4.  Carbon is continuously flowing back and forth between these carbon storehouses and the atmosphere.  For example, when plants grow they take in atmospheric carbon dioxide, use the carbon to build the plant structure and expel the oxygen back into the atmosphere.  When the plant dies and disintegrates (or is processed) the carbon in the plant is released into the atmosphere where it combines with oxygen and forms atmospheric carbon dioxide. 

However, a portion of the carbon that is released into the atmosphere comes from the burning of fossil fuels (crude oil, coal and natural gas) that have been stored deep inside the earth for millions of years.  These carbon emissions, in contrast to the natural carbon emissions, gradually build up atmospheric carbon over time. 

Figure 4.
 

The challenge in mitigating climate change is to stop or reduce the level of atmospheric carbon.  To accomplish this we must examine our activities to determine if they are carbon positive, carbon neutral or carbon negative.
  

  1. Carbon Positive (causes a buildup of atmospheric carbon)

•    Emitting sequestered carbon into the atmosphere.  For example, using carbon based resources such as coal, crude oil and natural gas that have been sequestered in the earth for millions of years and emitting the carbon into the atmosphere.

  1. Carbon Neutral (the level of atmospheric carbon does not change)

•    Taking plant based carbon that previously had been removed from the atmosphere and used to build the plant structure through the process of photosynthesis and emitting this carbon back into the atmosphere.  For example, the carbon emitted from a corn ethanol plant where atmospheric carbon was used to make the corn grain is emitted back into the atmosphere (the fossil fuel energy used to grow the corn and process it into ethanol is carbon positive).

•    Sequestering fossil fuel based carbon back into the ground.  For example, capturing carbon dioxide from a coal fired facility and sequestering it deep in the ground.

  1. Carbon Negative (causes a reduction in atmospheric carbon)

•    Taking plant based carbon that originated from the atmosphere through photosynthesis and sequestering it in the soil.  For example, biochar is created from the burning of biomass (formed from atmospheric carbon) and sequestering the biochar (carbon) in agricultural soils.

So biochar has the unique ability to reduce atmospheric carbon levels. 

To effectively sequester carbon, biochar appears to have several advantages. 
 

  1. Stability – As shown in the rainforest plots in the Amazon Basin, biochar appears to sequester carbon for hundreds if not thousands of years.  It is resistant to the microbial breakdown that is common with crop residues and other types of soil organic matter.  Crop residues break down in a couple of years and humus oxidizes in less than 25 years.  So, biochar is not subject to the “leakage” that is a concern for carbon sequestered with no till farming and the carbon capture and sequestration of fossil fuel carbon emissions (e.g. coal).

 
Source: International Biochar Initiative   http://www.biochar-international.org/biochar/soils

  1. Measurable – It appears as though it will be easier to measure the amount of carbon sequestered through biochar than many other forms of carbon sequestration. 
  1. Cost – Sequestering carbon with biochar is relatively low cost and requires little energy for sequestration, especially when compared to other forms of sequestration.  For example, sequestering carbon from a coal fired facility requires the smokestack capture of the carbon dioxide, pressurizing it, potentially transporting it long distances and forcing it deep into the earth. 
  1. Oxygen Sequestration – Sequestering carbon dioxide directly means that oxygen is sequestered with the carbon.  However, sequestering carbon with biochar means that only the carbon is sequestered.

Manage waste

Agricultural wastes are usable resources for pyrolysis bioenergy production.  Not only is energy obtained in the charring process, but the quantity of waste materials is significantly reduced.  Similar opportunities exist for urban and industrial wastes.

References

Tenenbaum, D. 2009. Biochar: Carbon Mitigation from the Ground Up. Environmental Health Perspectives. 117(2).  

Biochar. Wikipedia, the free encyclopedia.

Ebert, J. Syngas 101. Biomass Magazine. 

Lehmann, J. 2007. Bio-energy in the black. The Ecological Society of America

Lehmann, J., Joseph, S. (eds.) 2009. Biochar for Environmental Management. Earthscan.

The International Biochar Initiative (IBI)

Syngas. Wikipedia, the free encyclopedia.

 

 

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