Biochar as a soil amendment and carbon sequestering tool

Photo courtesy http://2.bp.blogspot.comBy Vuthisa

It is surprising how many people cart away their yard waste (renewable biomass) to landfill sites or dispose thereof in open burns until only ash remains.  I say: Make your own biochar instead.

What is biochar and what is the difference between biochar and charcoal?

They are identical in many respects, but the telling difference is in how they are used.  Charcoal is used as a fuel.  Crushed charcoal mixed into soil as a soil amendment is biochar.

As a soil additive, biochar offers numerous potential benefits

Unlike fertilizers, biochar has an extremely long life in soils. Charcoal is carbon-rich and gives it the ability to persist in the soil indefinitely by not being susceptible to biological decay.  Biochar also attracts microbes and beneficial fungi, holds on to nutrients that are put into the soil. i.e. biochar works better the second and third year than it does the first.  One of the major challenges in agriculture is to make the nutrients in the soil available to the plant when the plant can benefit from them.  Fertilizers can often only be applied early in the growing season, before the crop canopy closes and field operations are no longer feasible.  Unfortunately, between the time the fertilizer is applied and the crop takes it up, fertilizers can be leached out of the soil by excess rainfall, consumed by weeds, or metabolized by microbial activity in the soil.  Biochar helps conserve plant nutrients by storing them within its matrix and making the nutrients available when the crop needs them.  This happens because of a property in biochar, certain clays, and soil organic matter known as Cation Exchange Capacity (CEC).  CEC is a measure of the capacity of biochar to retain ions, such as ammonium and potassium cations, in an exchangeable form that is available to plants.  CEC not only helps conserve the fertilizers added to the crop during the growing season, but also improves the ability of the soil to capture and retain nutrients from other sources available at other times.  For example at the end of the growing season crop residues are often left in fields to decompose.  When this organic matter decomposes, biochar captures some of the nutrients released, leaving those nutrients for the next growing season.

Biochar in soil also has the ability to hold moisture and save on irrigation costs.  Biochar modifies the soil’s performance by retaining moisture and making it available during periods of low precipitation and hot, dry soil conditions.  This is possible because biochars have very large internal surface areas – typically over 100 square metres per gram.  This internal surface area adsorbs moisture when water availability within the soil is high and releases it back into the soil when water availability is depressed.  Some may think that biochar being black in color would heat up in the sun, but biochar helps the soil stay moist even in full sunlight.  Biochar also has significant impacts on soil drainage.  Clay soils which are typically poorly aggregated are too tight and do not drain effectively.  Ineffective drainage results in extended periods of inadequate soil aeration.  Other soils, especially sandy soils may drain too efficiently.  Overly efficient drainage can shorten the benefit of periodic wetting.  In both cases, the addition of biochar compensates for the native soil deficiency in the following ways:

Clayey and poorly aggregated soils become less compacted and provide better aeration

Sandy soil acquire additional bulk moisture storage capacity

Biochar also makes a significant contribution to mycorrhiza by promoting microbe populations.  Mycorrhiza is a fungi that has a symbiotic relationship with plant roots and contribute to a healthy soil-plant nutrient exchange.  Biochar increases the availability of mycorrhiza by:

Detoxifying soil water by adsorbing compounds that inhibit microbe growth

Providing a  protective habitat for microbes

Improving soil moisture management in which mycorrhiza thrives

 

Biochar can mitigate climate change

By reducing consumption of fossil fuel and

Capturing CO2 and sequestering carbon in the soil

In a world dependent on fossil energy, it is easy to see the carbon capture benefits of biochar as offsets against current and future fossil fuel emissions.  Many scientists believe there is already an unsafe excess of carbon dioxide in the atmosphere, this obligates the nations that caused the excess to abate it.  It is notable that from the year 1850 to 2000, 34% of carbon dioxide emissions have been attributed to land clearing.  Therefore, in a sense, the first goal of biochar is to restore the carbon lost from the soil due to the past 150 years of agricultural practice.  After that, the particular durability of biochar will enable the build-up of more carbon in soils, with further fertility benefits as the existence of Terra preta soils have shown us.  Terra preta soils are fertile, black biochar-rich soil found in scattered tracts throughout the Amazon basin, also, the pre-Columbian civilization responsible for creating that soil, dating back to 450 to 8,000 B.C.  Charcoal has the potential to sequester gigatonnes of atmospheric carbon per annum, making it the most potent engine of atmospheric cleansing we possess.  Approximately 8 percent of all atmospheric CO2 is absorbed by plants each year. If just a small proportion of the carbon captured by plants can be pyrolysed and transformed into charcoal, humanity’s prospects will be much brighter, for this will buy us time as we struggle to make the transition to a low emissions economy.

How do you make biochar?

The production of charcoal and biochar has a common root.  Before fossil coal emerged during the Industrial Revolution (18th Century) the word coal meant charcoal – the black fuel made from wood.  The basis for all charcoal and biochar production is pyrolysis: essentially, breaking wood down into its chemical constituents by heat, with little or no oxygen.  We do not use the same archaic methods of yesteryear, with the development of cylindrical metal vessels and high temperature refractories.  Good biochar has high porosity, extensive micro-structure, and adsorption capacity that enable beneficial interactions between microbes, nutrients, and water in the soil.  The so-called 55/30, a simple closed retort, is popular with biochar enthusiasts.  In a typical configuration, the “55/30″ consists of a 55-gallon (200 litre) outer drum containing the fire around a 30-gallon (100 litre) inner drum acting as the enclosed retort.  A 30-gallon barrel, open at one end standing with the open end down on flat surface, makes a simple and serviceable closed retort.  Click here for a collection of all types of biochar making kilns: http://www.carbon-negative.us/Burners.htm

Vuthisa opted for the Portable Metal Kiln Method for biochar production, which differs from conventional open burn methods in five ways:

The steel plate is very thick and not only lasts longer than 55 gallon drums, but allows the contents of the kiln to “cook” in the absence of charcoal by means of a tight sealing lid

The drum can be made oval to fit in two sealable 55-gallon drums, yet also allow burning material to be added to heat the drums

Small sized feedstock, typically found in yard waste, such as twigs and branches are ideal for this system as it will not turn to ash, as with larger horizontal type kilns that can take up to 3 days to cool down, reducing small diameter feedstock to ash

Large quantities of biochar can be produced as opposed to the 55/30 type closed retort that produces small quantities

The kiln can be rolled long distances to adjacent feedstock piles without any difficulty, yet can still fit on the back of pickup trucks.  More information can be found here: http://www.vuthisa.com/biochar

Resources

http://biochar-books.com/The_Biochar_Revolution The Biochar Revolution – Transforming Agriculture & Environment – Edited by Paul Taylor

http://vuthisa.com/2009/11/14/make-charcoal-in-your-own-backyard/ Make charcoal in your own backyard

http://www.scribd.com/document_downloads/16916390?extension=pdf Biochar for Environmental Management: Science and Technology Edited By Johannes Lehmann and Stephen Joseph

http://www.mycorrhizae.com/ Mycorrhiza

http://www.carbon-negative.us/Burners.htm Biochar producing kilns

http://biochar.bioenergylists.org/ Biochar discussion list website

http://bioenergylists.org/ Improved Biomass Cooking Stoves

To obtain access to more URLs relating to the above subject matter (not for public viewing) send your request through to: http://vuthisa.com/contact-us/

http://za.linkedin.com/in/vuthisa

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