Biochar Scientific Literature Review

Biochar Scientific Literature Review

Interest in biochar has grown as a means of enhancing long-term soil fertility and sequestering carbon. Pyrolysis converts living or once-living organic matter into chemically stable, condensed carbon structures. This thermodynamic stability explains why charcoal (including what is now termed biochar) persists in soils for centuries to millennia and underlies its characterization as a form of carbon sequestration.

This review was motivated by knowledge gaps in the scientific literature regarding biochar and a lack of detailed, proven best practices for growers. This paper is a companion to a four-year research trial examining the effects of biochar and compost on the growth of a newly planted chestnut orchard at Arthur’s Point Farm in New York’s Hudson River Valley (SARE, 2026). The literature review and the field research were both funded by the National Institute of Food and Agriculture, U.S. Department of Agriculture, through the Northeast Sustainable Agriculture Research and Education program under subaward number LNE22-452R.

This review evaluates the current scientific evidence of biochar’s efficacy as an agricultural amendment and a potential mechanism for climate mitigation. We sought to distinguish findings that are consistently reproduced across studies from those that are context-dependent, contradictory, or insufficiently resolved to support practical application, particularly for temperate agricultural systems in which our project was situated.

Download the Scientific Literature Review here

FAQs

What is biochar?
Biochar is a carbon-rich material produced when organic matter such as wood, crop residues, or manure is heated in a low-oxygen environment through a process called pyrolysis. It resembles charcoal and is used as a soil amendment to influence soil properties such as pH, nutrient retention, and water-holding capacity.
Does biochar increase crop yields?
Biochar sometimes increases crop yields, particularly in degraded or nutrient-poor soils. However, research shows that yield responses are highly variable, and many temperate agricultural soils show little or no improvement after biochar application.
Do different types of biochar behave differently in soil?
Yes. Biochar properties vary widely depending on feedstock and production temperature. These differences influence pH, nutrient levels, ash content, and surface structure.
What types of soil benefit most from biochar?
Soils most likely to respond positively include acidic soils, sandy or coarse-textured soils, soils with low organic carbon, or degraded or nutrient-poor soils. These soils often benefit from improvements in pH, nutrient retention, or water availability.
Can biochar replace fertilizer?
In most cases, no. Biochar typically contains limited plant-available nutrients. Farmers generally use it alongside fertilizers or compost rather than as a replacement.
Is biochar better than compost?
Biochar and compost serve different roles in soil. Compost provides nutrients, organic matter, and microbial activity. Biochar provides stable carbon, structural porosity, water-holding capacity, and potential pH effects. In many systems, compost produces stronger short-term plant responses.
Should biochar be mixed with compost before application?
Yes, we recommend that. Farmers often blend biochar with compost before applying it to soil (see below for recommended application rates and timing). Compost can coat biochar particles with nutrients and organic matter, which may improve nutrient retention and reduce leaching in some systems.
What is the recommended biochar application rate?
Research studies commonly apply biochar at rates between 2–12 tons (~4-24 cubic yards) per acre, which is often cost-prohibitive. Typical compost rates typically range from 2-10 tons (~4-20 cubic yards) per acre. If you have identified soil constraints that, based on the science, you believe biochar will help with, then we recommend that farmers add biochar to existing compost rates at between 10-20% of the volume of the finished compost. To help weather and saturate the biochar, we recommend that you incorporate the biochar at the start of the composting process, so you will need to calculate volume based on the finished compost volume, not based on the initial volume of the compost feedstock.
Is biochar safe to use in soil?
Most properly produced biochar is considered safe for agricultural use. However, poorly produced biochar may contain contaminants such as polycyclic aromatic hydrocarbons (PAHs) or volatile organic compounds (VOCs). Biochar certifications from, including the World Biochar Certificate (WBC), provide testing protocols and quality benchmarks for biochar products. Before applying biochar, it is advisable to obtain independent laboratory analysis, rather than relying on general descriptions from manufacturers. Relevant information includes: feedstock source, pyrolysis temperature, ash content, pH and electrical conductivity, nutrient concentrations (C, Ca, Mg, K, P, B, S), and potential contaminants such as polycyclic aromatic hydrocarbons (PAHs).
How long does biochar last in soil?
Biochar can persist in soil for decades or even centuries. Its carbon structure is more resistant to microbial decomposition than most forms of organic matter.
Can farmers produce biochar on the farm?
Some farmers produce biochar using retort kilns, flame-cap kilns, or other small-scale systems. Production efficiency and emissions depend heavily on kiln design and operating conditions. In our experience, the time and resources needed to produce and process high quality charcoal for biochar while also tending to the main tasks of the farm are cost and time prohibitive.
Can biochar improve water retention in soil?
Biochar may increase water-holding capacity in sandy or coarse soils. The effect depends on soil texture, particle size, and application rate.
Does biochar improve soil microbial activity?
Biochar surfaces can host microorganisms, but research suggests that increases in microbial activity often result from compost or nutrient additions rather than biochar itself.
Can biochar reduce greenhouse gas emissions from agriculture?
Some studies suggest biochar may reduce nitrous oxide emissions or nitrate leaching in certain systems. However, results vary by soil type, crop system, and application method.
Is biochar worth using on farms?
Biochar may be useful when soils have clear constraints such as low organic carbon, poor nutrient retention, or high acidity. Because results vary widely, many researchers recommend small field trials before applying biochar at large scale. Also, evaluate whether other existing practices, such as applying compost, cover cropping, low tillage, and the planting of perennial crops may be a better and more cost-effective approach for your farm.
BIOCHAR FAQS FOR FARMERS

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