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Biochar is a charcoal-like substance created by burning organic waste from agriculture and forestry (also known as biomass) in a controlled process known as pyrolysis. Despite its appearance, biochar is manufactured using a unique procedure that reduces contamination and safely stores carbon. During the pyrolysis process the organic material is turned into biochar, a stable form of carbon that cannot easily escape into the atmosphere.

Physical characteristics

  • Biochar is black
  • Highly porous
  • Lightweight
  • Fine-grained and has a large surface area

Chemical composition

  • Approximately 70 percent of its composition is carbon
  • The remaining percentage consists of nitrogen, hydrogen and oxygen among other elements
  • Biochar’s chemical composition varies depending on the feedstocks used to make it and methods used to heat it.

The concept of biochar is rooted in an ancient Amazonian practice

Although biochar is a relatively new technique for carbon sequestration, the practice of applying burned biomass to improve soil quality is not. This method is based on a 2,000-year-old technique in the Amazonian basin in which indigenous people built terra preta (meaning “dark earth”) areas of rich, fertile soils.

It is still unclear whether these soils were purposely created or are just a byproduct of farming and/or cooking operations. But one thing is certain: the fertility of terra preta is substantially higher than that of the Amazon’s generally notoriously barren soils. This explains why plants grown in terra preta soil develop faster and have higher nutrient density than plants cultivated in other soils. In fact, terra preta soils still store carbon today.

Uses of biochar

Biochar has multiple uses in soil and could help in tackling the problem of soil infertility due to climate change.

  1. Enhances soil nutrients: Biochar is a natural fertilizer that improves soil nutrients while preventing leaching.
  2. Promotes soil health: Biochar is used to improve soil health by retaining soluble nutrients.
  3. Remediation of soil: Biochar is frequently used to remediate soil contaminated with heavy metals.
  4. Increases activity of soil biota: Because of its porous nature, biochar holds water and gives nutrients to microbial organisms in the soil during inclement weather.

Applications of biochar in agriculture: enhancing soil and compost properties

Soil degradation is a major issue in agriculture around the world. To address this growing issue, experts proposed adding biochar to degraded soils to improve their quality. Biochar can assist enhance soil quality in a variety of ways, including:

  • enhancing soil structure
  • increasing water retention and aggregation
  • decreasing acidity
  • reducing nitrous oxide emissions
  • improving porosity
  • regulating nitrogen leaching
  • improving electrical conductivity
  • improving microbial properties

Benefits of biochar

Biochar provides many of the same benefits as other organic materials, but it is a more permanent alternative.

  • Biochar is a lightweight, highly porous material that acts as a soil-conditioning agent, reducing soil bulk density and improving aeration and water-holding capacity of soils. 
  • Adding biochar to soil recycles nutrients that are removed from the soil when biomass is harvested.  This is because most of the nutrients contained in the harvested biomass are partitioned into the biochar during pyrolysis. 
  • Potassium, calcium and magnesium are mineralized to carbonates (CO32-) in biochar, meaning that most biochar are liming agents and can partially replace the need for agricultural lime.
  • Biochar used as a soil amendment can improve crop yields grown in degraded soils those that are eroded, sandy, or compacted.
  • Biochar has also been shown to increase water and nutrient holding capacity of soils, reducing leaching losses of nitrate (NO3) by 10% and phosphorus (P) by 40-70% (Laird et al., 2010).  
  • Due to its adsorption ability, some biochar have the potential to immobilize heavy metals, pesticides, herbicides, and hormones; prevent nitrate leaching and fecal bacteria into waterways

Biochar is being evaluated as a tool for decreasing nutrient runoff. There are two aspects to consider. If adding biochar improves soil fertility and diminishes the need for chemical fertilizers, nutrient runoff could be reduced. And if biochar-enriched soils can increase soil productivity, fewer acres of land would need to be put into production, potentially decreasing row crop nutrient loading.

The role of biochar in sequestering carbon and mitigating climate change

The natural carbon cycle on Earth is “carbon neutral.” Plants and trees collect carbon dioxide (CO2) from the air and store it in their tissue as carbon as they grow and photosynthesize. When plants die, they oxidize, releasing carbon dioxide back into the atmosphere.

However, when fossil fuels are burned, this natural balance shifts, because previously stored carbon is released into the atmosphere.

Biochar formation is a carbon-negative process, which means it lowers CO2 levels in the environment. The unstable carbon in decaying plant material is transformed into a stable form of carbon and stored as biochar during the production process.

When biochar is added to soil, it stores carbon in a safe location for hundreds or thousands of years. Simply put, if the feedstocks used to make biochar were allowed to decay naturally, they would emit more carbon dioxide into the atmosphere. By heating the feedstocks and transforming their carbon content into a stable structure that doesn’t react to oxygen, biochar technology ultimately reduces carbon dioxide in the atmosphere.

Climate change mitigation

Biochar is a multifaceted climate change mitigation approach. The bio-oil created during pyrolysis could substitute fossil fuels, avoiding additional Green House Gas (GHG) emissions. If fossil fuels were displaced to produce heat, electricity, or transportation fuels in operations occurring outside the biochar system, the pyrolysis gas would offer additional GHG emission reduction potential.

Biochar also contributes to climate change mitigation by enriching soils and reducing the demand for chemical fertilizers, which reduces greenhouse gas emissions. Improved soil fertility also promotes plant development, which consumes carbon dioxide.

Biochar can mitigate climate change in several other ways too. First, biochar sequesters carbon dioxide from the atmosphere. Second, biochar is a sustainable way to improve soil health and fertility. This is because biochar can hold onto nutrients and moisture, making it available for plants to use. Overall, the use of biochar is beneficial for the environment and agriculture.

Biochar sequesters carbon in soil, lowering atmospheric concentrations of greenhouse gases such as carbon dioxide (CO2). And biochar can assist to prevent climate change by balancing emissions of these gases. Furthermore, biochar can improve soil health and productivity, making it a sustainable and environmentally beneficial agricultural supplement.

Biochar can help to reduce levels of nitrous oxide, a powerful greenhouse gas, in the atmosphere. This is because biochar can act as a ‘sink’ for nitrous oxide, preventing it from being released into the atmosphere. Additionally, biochar can help to improve soil health and fertility, which can, in turn, lead to higher levels of nitrogen in the soil. This means that less nitrous oxide is produced when biochar is added to the soil.

Disadvantages of biochar

Although there are many advantages of biochar application in soil, there are some disadvantages as well.

  1. Limit Activity of Worms in Soil: The application of biochar in soil inhibits worm activity, which is necessary for soil production.
  2. Affect Crop Yield: Biochar increases agricultural production, however also consumes nutrients, resulting in nutrient deficiencies in growing plants.
  3. Soil Compaction: Biochar treatment on a regular basis produces soil compaction, which reduces crop yield.
  4. Lowers Efficiency of Pesticide: Biochar also influences pesticide application, diminishing pesticide efficiency in soil.
  5. Soil Degradation: The use of biochar may cause soil degradation, making soil sensitive to harsh temperatures.

However, Biochar is a versatile tool that can help us tackle many of the world’s most important problems. It is an environmentally beneficial material that can help enhance the world around us. Today biochar may be more important than ever before. As we look for strategies to retain carbon in our soil and out of the atmosphere, biochar may not be the answer, but it may be a part of the solution.



Laird, D.A., P.D. Fleming, D.L. Karlen, B. Wang, R. Horton. 2010b. Biochar impact on nutrient leaching from a Midwestern agricultural soil. Geoderma 158:436-442.


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