What Is Biochar and How Is It Used?

Biochar is a charcoal-like product made from biomass waste, such as wood or agricultural waste, paper mill waste, or other biological residues.

The concept for use as a soil amendment originated in Amazonian terra preta soils.

Biochar could become an important option in mitigating climate change via carbon sequestration.

Not all biochars perform the same. It depends on the biomass source, the temperature of pyrolysis, and the size of the product.

Biochar is a charcoal-like product that contains no petroleum. It is made by heating biomass such as herbaceous or woody crop residues, non-salvageable timber and slash, or animal manure, in a contained system. There are many potential uses for biochar including water treatment, land reclamation, and carbon sequestration. Biochar may also be used as a soil amendment for two purposes – to improve plant health and to store carbon. It is predicted that at least 50% of the carbon in any piece of waste turned into biochar becomes stable, locking away that carbon for a period of several to hundreds of years, offsetting its contribution as a greenhouse gas in the form of carbon dioxide.

The characteristics of biochar vary significantly depending on feedstock type and pyrolysis temperature. In general, biochar has an alkaline pH, is porous, contains fixed and available carbon, and may contain some nutrients. The nutrient content of chars for plant growth is negligible, but their high cation exchange capacity improves the effects of fertilizer applications. The most important characteristic for the improvement of soil properties (such as adsorption capacity and water retention) is biochar porosity and surface area.

The properties of biochar determine its applications to soil, and a particular biochar may not be adapted to all types of soils. Therefore, optimizing biochar for a specific application may require the selection of certain feedstocks and pyrolysis temperature.

• Manure: greater content of nutrients and cation exchange capacity; higher electrical conductivity (may increase soil salt concentration); low carbon content
• Crop and grass residue: higher potassium content; lower porosity; higher carbon content
• Wood waste: greater fixed carbon content and thus, more stable; greater porosity and thus higher water retention; biochar from conifer wood has a lower pH and would be better for alkaline soils
• Higher pyrolysis temperatures (500°C – 650°C): greater amount of micro-pores (better for adsorption of toxic substances and soil rehabilitation); higher pH; greater mineral content; lower cation exchange capacity
• Lower pyrolysis temperatures (350°C – 500°C): greater degradable carbon as source for soil micro-organisms; higher cation exchange capacity

In agriculture, biochar has the potential to increase water-holding capacity, prevent nutrient losses from fertilizers, and provide structure for the build-up of beneficial soil microorganisms. These qualities in turn may improve plant growth or crop yield.

Because of biochar’s high pH and ability to bind to heavy metals and other organic pollutants, it is being investigated as a reclamation tool on old mining lands, contaminated water sources, dairy lagoons, and more.

• In Oregon dryland wheat cropping systems, biochar application at a rate of 10 tons per acre raised soil pH and increased crop yield by almost 30%.
• In greenhouse growing media, biochar shows potential for replacement of perlite and peat moss, where it also prevents nutrient leaching (11% reduction over traditional media).
• Cacao growers in South America are applying biochar to young trees to shorten the number of years to production by half.
• Several non-profits are creating biochar gardens throughout Third World nations to improve depleted soils.
• Botanic gardens are making their own char and using it in compost mixes.
• Foresters in Colorado, Idaho, and Utah are exploring biochar production to turn dead trees (largely beetle kill) into a value-added product and as an alternative to slash and burn.
• Dairy farms are looking at using biochar to reduce phosphorus in dairy lagoons.
• Water treatment plants are looking to replace activated charcoal with the cheaper biochar to clean up polluted water that is heavily contaminated with toxic chemicals.

If biochar is used as a soil amendment, you should work the biochar into the plant’s root zone – the part of the soil surrounding a plant’s roots – incorporating the biochar into 4 to 6 inches of soil depth if possible. This way, you will make full use of biochar’s remarkable capability to hold water, retain nutrients, and host beneficial soil biology. Working the biochar into the soil also minimizes the chance that the biochar will be disturbed, dried out, or blown away.

If biochar is used to purify storm water, filter contaminants, or reduce erosion, you do not necessarily need to work biochar into the soil. In these situations, biochar is used in locations that are optimal for the specific needs of the project and often placed within containers specialized for each use case, such as landscape socks and filtration systems. For example, you can place the biochar where water is running off land, roofs, roads, or other contaminated sites – including those that are aboveground.

Biochar – that black charcoal like substance discussed so often in recent days for its miraculous effects on soil and compost - is good for more than just your garden. One of the key materials for a sustainable future of the planet, biochar has many other uses that can be integrated into new organic systems for farming, building, clothing, electronics and a whole range of consumer products. Biochar can initiate multiple cascades to optimize and recycle current material, nutrient and energy flows.

It turns out that the stable carbon matrix that biochar is made of has all kinds of interesting properties. This carbon matrix can hold on to things – water, air, metals and organic chemicals. And it also has unique thermal and electrical properties that are still being explored. Finally, the highly porous physical structure of biochar provides habitat for microorganisms. With so many different properties, biochar is bound to have a lot of different uses, but one function that all biochar applications (other than burning it for fuel) share is carbon sequestration. By fixing easily degradable plant carbon into long-lasting charcoal, carbon dioxide is slowly but surely removed from the atmosphere.