permaculture

[Lawrence London <lfljvenaura@gmail.com>]

The Biochar Journal
tBJ:How biochar works in soil
https://www.biochar-journal.org/en/ct/32-How-biochar-works-in-soil
How biochar works in soil by Kelpie Wilson

Hypotheses of biochar’s role in the development of fertile soils have
become strong arguments in favor of its intentional soil application.
However, field research trials demonstrate a range of results that contrast
overwhelming yield improvements in some places with neutral or even
negative results in other places.  The mixture of hype and science has
clouded the search for a mechanistic understanding of soil biochar
additions. Appreciating the fact that biochar materials produce widely
different results depending on soil, climate and type of biochar, the
question remains: How does biochar work in soil?

Biochar first came into broad public awareness through the example of the
Amazon, where the hypothesis is that Amazonian inhabitants added biochar
along with other organic and household wastes over centuries to modify the
surface soil horizon into a highly productive and fertile soil called Terra
Preta, which is in direct contrast to the typical weathered Oxisol soils in
close proximity. Biochar is exciting to many people because of its role in
such soil-building processes. Those who have used biochar for several years
may obtain tangible positive results, but they may not have solid concepts
and theories about how it works. Biochar is a heterogeneous and chemically
complex material and its actions in soil are difficult to tease apart and
explain mechanistically.

In this article, I will describe some of the most robust theories of how
biochar works in soils, explaining these mechanisms in common language. I
begin by examining the role of soil carbon in general and then drill down
to a "nano-scale view" looking at the chemical, electrical, physical and
biological processes that biochar seems to stimulate. While there are now
multi-year field studies that show the impact of biochar on different
crops, it is difficult to draw broad conclusions from these studies since
they use different kinds of biochar in different types of soil with
different crops. To really understand biochar, it is perhaps more useful to
look first at some general functions and properties of biochar. I look then
at its behavior in compost, which is like an experimental incubator where
many soil processes are accelerated. I review a few recent studies of
biochar in compost in order to tentatively explain what biochar actually
does when it comes into contact with organic matter and minerals – the
basic constituents of soils.
The Role of Carbon in Soil

To understand biochar, we must first appreciate the role of soil carbon.
Soil carbon comes in many forms. There are two main pools of carbon:
organic and inorganic. Organic forms can be further divided into
"recalcitrant carbon" or resistant to decay, like humus, and "labile
carbon," where the carbon is both bioavailable (in the form of easily
degraded compounds such as oils, sugars and alcohols) and physically
accessible to microbes (not bound up with minerals). The organic carbon
pool includes both the living bodies and the dead, decomposing bodies of
bacteria, fungi, insects and worms, along with plant debris and manure.
Inorganic carbon consists of carbonate ions, which are typically found as
salts like calcium carbonate, and dolomite minerals, mostly in the form of
rocks and sand. However, the main distinction of the inorganic carbon pool
is that it does not fundamentally provide microbes with energy for feeding
the soil building reactions.

The evolution of soil shows how the soil building process works. Before
photosynthetic bacteria transformed Earth's atmosphere by filling it with
oxygen, soil was nothing more than a mineral mixture of anoxic green clay.
After oxygen entered the atmosphere, minerals started reacting with the
oxygen, and red iron oxides appeared in the soil. Good organic, rich,
productive soils developed slowly only after algae and arthropods crawled
from the sea to dry land and plants took root (Fortey, 1999). Life
colonized land and began shedding its wasted, used up and discarded parts
onto the earth where they formed a carbon-rich banquet that allowed new
life to feed and grow, using photosynthesis to pump ever more energy into
the system.

Soil building is the product of a self-reinforcing, positive feedback loop.
But soil decline is also a self-reinforcing loop that can result in
catastrophic soil loss. Most forms of agriculture tend to deplete soil
carbon by reducing the amount of natural organic inputs from leaf and fruit
fall as well as from woody debris as it is found in native ecosystems.
However, modern, chemically-based agriculture depletes soil carbon much
more drastically. Nitrogen fertilizers combined with tillage accelerate
microbial respiration, burning up soil carbon faster than it is replaced.
Due to the loss of organic carbon reservoirs, many soils have become nearly
lifeless substrates that must be continually fed with irrigation water,
mineral nutrients and pesticides to produce a crop. Although productive in
the short term, this practice is not sustainable. Soil scientist Rattan Lal
(2010) estimated that "Most agricultural soils have lost 25% to 75% of
their original soil organic carbon (SOC) pool."

Is it possible that biochar can substitute for some of this missing soil
carbon? Some of the most productive and resilient soils in the world
contain significant quantities of "natural" biochar. Nature makes megatons
of biochar in the process of naturally occurring wildfires in forests
(Goldberg, 1985). Prairie fires can also generate a lot of biochar (Old,
1965). Tall grasses burn quick and hot, however, close to the ground where
the roots start, air is excluded so the base of the grasses will pyrolyze
and not burn. This kind of natural charcoal is present in some of the most
valuable agricultural soils in the world: the carbon-rich Chernozems of the
Russian steppe and the Mollisols of the US Midwestern prairie states
(Skjemstad et al, 2002; Glaser & Amelung, 2003). Recently, scientists (Mao
et al, 2012) have looked more closely at the Mollisols, and found that they
contain charcoal that is "structurally comparable to char in the Terra
Preta soils and much more abundant than previously thought (40–50% of
organic C)."
Biochar - the Electric Carbon Sponge

Carbon comes in many forms, and the terminology used to describe it can be
confusing. Organic carbon refers to the carbon in compounds that are found
in living or once-living things. Those compounds include hydrogen and
oxygen in the form of hydrocarbons and carbohydrates. Inorganic carbon
includes the carbonates such as limestone, and even though some life forms
use carbonates to make their shells or skeletons, these compounds are still
termed "inorganic". Mineral carbon refers to carbon solids like diamond and
graphite as well as the gases of carbon (CO2, CO and many others). Also,
there are numerous ways a carbon atom can be arranged in a solid which
leads to different physical structures, which are called allotropes.
Allotropes of mineral carbon, include diamond, graphite, graphene,
buckyballs and carbon nanotubes (Figure 1).

[image: 640px-eight_allotropes_of_carbon.png]

Figure 1. Eight allotropes of carbon: a) Diamond, b) Graphite, c)
Lonsdaleite, d) C60 (Buckminsterfullerene or buckyball), e) C540, f) C70,
g) Amorphous carbon, and h) single-walled carbon nanotube or buckytube.
Design created by Michael Ströck From: en.wikipedia.org—Allotropes_of_carbon

So what is biochar then? Organic or mineral carbon? Actually biochar is a
mixture of both, depending on the conditions of formation. But let’s first
look at how biochar is produced. Biochar is made by heating biomass under
the exclusion of air. This process is called pyrolysis, which includes the
drying of the biomass and the subsequent release of flammable vapors.
Technically this can be done by many different methods. Some methods use a
retort, which is a closed vessel that is externally heated. Heat is
transferred through the metal vessel and vapors pass out of a vent where
they can be burned and help heat the retort. Gasification is another method
that supplies enough air to burn the vapors, but prevents the complete
combustion of the biomass material by excluding air from the charcoal zone,
thus preserving the biochar. Many other methods of charcoal making exist
that range from simple pit kilns to multi-million dollar machines producing
energy in gas or liquid form from the vapors.

The resulting charcoal resembles a blackened, shrunken version of the
original biomass. But it now has very little hydrogen and oxygen.
Microscopically, it inherits much of the structure of the original biomass.
The only difference is the material now has been converted from lignin,
cellulose and hemicellulose to many of the allotropes of carbon shown above
(Figure 1); however, you will not find any diamonds in biochar! What you
will find is a collection of disjointed graphite crystals based on
hexagonally-shaped carbon rings, with some leftover hydrogen and oxygen
attached, along with minerals (ash) that were in the original feedstock.
These hexagonal carbon compounds are fused carbon rings.  Fused carbon
rings are also called "aromatic" carbon, (another confusing chemistry term
- it does not mean that the compound has a strong aroma, although some of
them, like benzene, do). They are very stable and it takes microbes a long
time to degrade them. The more you heat the biomass, the more of these
fused carbon rings are created (Keiluweit et al, 2010). The rings hook up
with each other to form layers and layers of discontinuous, rumpled sheets
- the graphite crystals. A single layer sheet is called graphene. Biochar's
jumble of carbon crystallites is an important source of its porosity –
imagine all the tiny spaces in the wrinkles between sheets.

Biochar starts out as organic and becomes more mineral-like with heating.
This mineral transformation creates the skeletal structure that looks like
a carbon sponge (Figure 2). While the mineral, fused–carbon ring structure
is hardly biodegradable, the recondensed vapors that can be found in the
biochar pores and on its surfaces are less aromatic and more biodegradable
and can thus be considered organic phases of the biochar.

[image: 8-kon-tiki-char2.jpg]

Figure 2. The skeletal structure of biochar looks like a carbon sponge.

The fused carbon rings are also responsible for the electrical activation
of the biochar carbon sponge. Fused carbon rings form a special bond with
each other that allows electrons to move around the molecule (Figure 3)
producing electrical properties like those that are found in engineered
carbon materials such as graphene sheets and carbon nanotubes. Depending on
the pyrolysis temperature and resulting arrangement of atoms, biochar can
be an insulator, a semi-conductor or a conductor of electricity.
Electrically active fused carbon rings also support “redox” or oxidation
and reduction reactions that are important to soil biochemistry, by acting
as both a source and sink of electrons.  In soils, microorganisms use
aromatic carbon both as an electron donor and as an electron acceptor
during metabolic chemical reactions (Lovley et al, 1996). Biochar seems to
not only serve as an electron buffer for redox reactions (Klupfel et al,
2014), but it also helps bacteria swap electrons among themselves,
improving their metabolic efficiency as a microbial community (Kappler et
al, 2014; Chen et al, 2014).

[image: 8_aromatic-pi-bonds_2.jpg]

Figure 3. The special bond of fused carbon rings, as exemplified by a
benzene molecule. Electrons in the 6 p-orbitals become delocalized around
the hexagonal carbon ring. Creative Commons CC-BY-SA:
http://en.wikipedia.org/wiki/Conjugated_system

With its pores and its electrical charges, biochar is capable of both
absorption and adsorption. Absorption (AB-sorption) is a function of pore
volume. The larger pores absorb water, air and soluble nutrients like a
normal sponge. Adsorption (AD-sorption) depends on surface area and charge.
The surfaces of biochar, both internal and external, adsorb materials by
electro-chemical bonds, working like an electric sponge.

Porosity comes in many scales, from the relatively large vascular and
cellular structures preserved from the original biomass, to the nano-pores
formed by tiny molecular dislocations. The amount of porosity depends
mostly on the feedstock material, particle size, and the highest treatment
temperature (HTT) (Brewer et al, 2014).  Temperature determines how much of
the volatiles (hydrogen and oxygen containing compounds) will be driven off
and how much pure carbon graphite is formed. Generally, porosity increases
the more volatiles are driven off, clearing the pores, although they can
re-clog when vapors are incompletely driven off and condense on the forming
biochar surfaces.  Also, at temperatures approaching 1000 degrees C, pores
begin to collapse or melt. For this reason, HTT is a key variable to know
when specifying a biochar for a particular purpose. Porosity will also
depend on the feedstock, with high ash feedstocks like grass reacting quite
differently to heating than low ash feedstocks like wood or bamboo. For
wood feedstocks, porosity typically peaks at an HTT of about 750 degrees C
(Downie et al, 2009).

When several aromatic carbon rings cling together with some hydrogen on
their outer sides they are called polycyclic aromatic hydrocarbons (PAH).
These compounds are composed of only carbon and hydrogen (Figure 4).  In
most cases, the longer they are, the more stable they are. However, 16
(identified by the US EPA) of the PAH molecules are confirmed or suspected
to be hazardous to the environment and human health. These PAHs are mostly
found in soot and tar and are produced in all sorts of fires or thermal
decomposition of biomass and fossil fuels. They are also produced when
biochar is made; however, most of them are driven off with the vapors as
their boiling point is lower than the usual pyrolysis temperature. If the
pyrolysis conditions and the separation of the solid biochar and the vapors
are not optimized (like in some gasifiers) the produced chemicals can
become a problematic contamination of the biochar and potentially hazardous
to the environment and user (Hilber et al, 2012; Hale et al, 2012).  For
that reason the International Biochar Initiative (IBI, 2012) and the
European Biochar Certificate (EBC, 2012) developed analytical protocols for
quality biochars, making sure that no hazardous substances enter ecosystems
in critical amounts.

[image: 8_pah-2.jpg]

Figure 4. Ball and stick representation of PAH examples. Clockwise from top
left: benz(e)acephenanthrylene, pyrene, and dibenz(ah)anthracene. Designed
by: Denis Bogdan,  Creative Commons CC-BY-SA:
https://en.wikipedia.org/wiki/Polycyclic_aromatic_hydrocarbon

Interestingly, biochar is also effective as a PAH adsorbent and could be
used to clean up PAH and other substances from soil (Chen & Chen, 2009).
IBI and EBC certified biochars, with low measurable concentration of PAH,
can potentially reduce the amount of leachable PAHs already existing in
soils through adsorption to the biochar. Irrespective of this fact, PAH
contents of biochar have to be controlled, as otherwise a good idea can
easily turn into its opposite. Problematic in this regard is that PAH
analyses are expensive and in most countries not yet available. To test
biochar in the absence of sophisticated analysis, you can simply smell it
and touch it. If it smells like anything don’t use it. Rub a bit on your
skin. If it feels greasy and requires soap or detergent to remove, don’t
use it without further testing. This easy field test works rather well
because PAHs only stick on a biochar in considerable amounts if condensates
from the vapor phase have been adsorbed during the production process - in
that case many other compounds leaving an odor or taste would also stick to
biochar surfaces.
A Well-Aged Cheese

Biochar is not soil. The electric carbon sponge is only an ingredient in
the mineral and organic stew that makes up soil.  The dish is usually
potluck, composed of whatever the local geology and biology provide.
However the Terra Preta soils are different. The fertility of these black,
humus-rich soils is many times greater than the surrounding, highly leached
red soils. They may have been deliberately created over centuries by people
living on densely settled high bluffs along the Amazon River.  It is
thought that the ingredients included charcoal, ash, food scraps and human
excrements, but how they actually combined to form Terra Preta is unknown.
Explaining the formation of the Terra Preta is like determining the recipe
for a fine Camembert cheese. You can analyze all the ingredients and still
have not the faintest idea how to make one if you don’t learn it from the
artisans.

One thing that is becoming obvious after a decade of biochar scientific
research and the first results from multi-year field trials is that, just
like a good cheese, the time dimension is critical. From the moment that
biochar is pulled from the kiln, its surfaces begin to oxidize and form new
compounds. These changes result in different molecules attached to the
surface, called “functional groups,” composed primarily of oxygen, hydrogen
and carbon.  These functional groups are able to bond with nutrients and
minerals, while the fused carbon rings support redox reactions and shuttle
electrons around the microbial community attached to biochar surfaces,
potentially enhancing microbial metabolism and the cycling of nutrients.
The end result of this ferment could be any one of many “terroir”-distinct
Terra Preta flavors, depending on what kind of soil, organic matter,
minerals, water and life forms come into contact with the biochar, and how
long it has to ripen. But, if you sample the cheese before it is mature,
it’s just sour milk.

Raw biochar placed in soils before it has a chance to collect a charge of
nutrients can actually reduce crop yields because 1) it reduces the
availability of plant nutrients by binding and immobilizing them and/or 2)
it may add volatile organic compounds (labile carbon) that feed a bloom of
microbes that use up nitrogen in the soil, depriving plants. These problems
are easily corrected by adding fertilizer to the charcoal application to
compensate for this effect. Once the labile carbon fraction is used up,
biochar enters a new phase - a deep time dimension where its carbon matrix
is stable for hundreds to thousands of years and may become the core of
humic substances that crystalize around the fine biochar particles
(Kluepfel et al, 2014); at least this is what the existence of ancient
fertile black earth soils suggests.

In fact, biochar, whether naturally created or man-made, may be the base of
many humic materials found in soils (Hayes, 2013). Very little humus
naturally forms in tropical soils, where high temperatures and moisture
accelerate microbial decomposition, yet Terra Preta soils have a high
content of humus. To understand why, Liang et al (2010) added new organic
matter to both a Terra Preta soil and an adjacent, poor natural soil. They
found that more of the organic matter was retained as stable humus in the
Terra Preta soil. A combination of factors may lead to this result. Biochar
surfaces adsorb carbon and retain it in compounds with minerals, supporting
at the same time a large microbial community that potentially makes more
efficient use of organic debris containing carbon and other nutrients. The
existence of this mechanism raises the possibility that Terra Preta soils
are thus able to accumulate additional carbon more efficiently than
adjacent soils .

If tropical soils need biochar to make humus, what about compost? Well
balanced compost, with the optimum C:N ratio, will contain lots of humus.
However, if there is not enough stable carbon (from wood, straw or other
lignin sources), then the easily degradable sugars, fats and proteins will
be completely consumed by microbes leaving very little substrate behind.
This is what happens in tropical soils where heat, moisture and high
microbial activity will decompose a fallen leaf nearly as soon as it hits
the ground, allowing very little soil to form.

A number of studies have demonstrated that biochar has value as an
ingredient in compost that can help capture nutrients and form humus. In
the next section, we review some of these results and explain why biochar
is valuable in compost. The answers will also tell us a lot about how
biochar behaves in soil, because compost accelerates many of the processes
that occur in healthy soil.
Kickstarting Compost with Biochar

If you look at a list of things biochar is supposed to do in soil, you'll
find it is very similar to lists you see for compost. Both biochar and
compost are said to provide these benefits, taken from various claims made
by biochar and compost manufacturers:

   - Improves tilth and reduces soil bulk density
   - Increases soil water holding capacity
   - Becomes more stable by combining with clay minerals
   - Increases cation exchange capacity (CEC - the ability to hold onto and
   transfer nutrient cations: ammonium, calcium, magnesium, and potassium)
   - Improves fertilizer utilization, by reducing leaching from the root
   zone
   - Retains minerals in plant available form
   - Supports soil microbial life and biodiversity
   - Helps plants resist diseases and pathogens
   - Helps plants grow better in high salt situations
   - Adds humus carbon to the soil carbon pool, reducing the atmospheric
   carbon pool

If compost really can do all these things, why do we need biochar? The
answer is twofold:
First, unlike biochar, compost is quickly broken down by microbial action
in soil over months to at most, decades, depending primarily on climate.
Biochar lasts at least ten times longer in most soils. Recently, I called a
California agriculture extension agent with a question about adding compost
to fields to improve water holding capacity. I was told that because of the
hot climate, at least two applications a year are needed to maintain enough
soil organic matter to make a difference in water holding capacity. Aside
from the expense of applying that much compost, there is simply not enough
compost available to support such large application rates.
Second, biochar has important synergistic effects when added to compost.
Researchers find that biochar makes faster, more nutrient rich, more
biologically diverse and more humified, stable compost. Below, I examine
several of the most important biochar effects and summarize some recent
research results.
1. Biochar keeps compost moist and aerated, promoting increased biological
activity.

The composting process is governed by various physical parameters that are
subject to alteration by the addition of biochar materials as bulking
agents. Some of the parameters that most affect compost are: aeration,
moisture content, temperature, bulk density, pH, electron buffering and the
sorptive capacity of bulking agents. Water and air are both held in biochar
pore spaces and voids, and the spaces between particles. Moisture is also
the vehicle for bringing dissolved organic carbon, nitrogen and other plant
nutritive compounds into contact with biochar surfaces where they can be
captured. Biochar’s stable carbon matrix accepts electrons from decomposing
organic compounds, buffering electric charges that might otherwise impair
microbial activity and be responsible for the production of greenhouse
gases like methane and hydrogen sulfides.

All these properties of biochar promote microbial activity in compost. For
instance, Steiner et al (2011) tested 5% and 20% additions of pine chip
biochar to poultry litter compost, and found that the addition of 20%
biochar caused microbial respiration (measured as CO2 emissions) to peak
earlier and at a higher level than either the 5% or 0% biochar treatments.
2. Biochar increases nitrogen retention

When nitrogen-containing biomass materials decay, they can release large
amounts of ammonia. Ammonium (NH4+) is the aqueous ion of ammonia. Ammonium
is generated by microbial processes and nutrient cascades that convert
nitrogen from organic forms found mainly in proteins and nucleic acids into
mineral forms (ammonium, nitrate and nitrite) that can intermittently be
converted by nitrifying and denitrifying microbes to gaseous emissions that
include volatile ammonia gas (NH3), nitrogen gas (N2), nitrous oxide (N2O)
and other reactive nitrogen gases (amines and indoles).  At neutral pH, the
aqueous ammonium (NH4+) and the gaseous ammonia (NH3) are in equilibrium.
Higher pH forces more of the aqueous ammonium into the gas phase that can
escape to the atmosphere.

Numerous studies have shown that biochar is effective at retaining nitrogen
in soils (Steiner et al, 2008; Clough et al, 2013). Several studies have
also shown that biochar enhances nitrogen retention in compost, reducing
emissions of ammonia and increasing total nitrogen retention by as much as
65% (Steiner et al, 2010; Chen et al, 2010; Huang et al, 2014).  The
ammonia retention ability of biochar can actually improve during the
composting process. Adding 9% bamboo charcoal to sewage sludge compost, Hua
et al (2009) tested sorption of ammonia on biochar during composting and
found that while ammonia retention was correlated with saturation of
binding sites in fresh bamboo biochar, this did not hold for composted
bamboo biochar. During composting the biochar is subjected to an
accelerated aging process. That means that biochar surfaces get oxidized
and enriched by carboxylic (acid) functional groups. The latter more than
doubled at the end of the composting period, improving the capacity to
exchange cations like ammonia.
3. Biochar improves compost maturity and humic content

Several studies have looked at effects of biochar on the timing and results
of compost maturation and found that adding biochar to compost reduced the
amount of dissolved organic carbon (labile carbon) in mature compost while
increasing the fraction of stable humic materials (stable carbon).
Following the addition of 2% biochar to compost, Jindo et al (2012)
recorded a 10% increase in carbon captured by humic substance extraction
and a 30% decrease of water-soluble, easily degradable carbon. They also
found an increase of fungal species diversity in the mature biochar compost
as compared to the control and proposed that these fungi were responsible
for the increased humification. Another study by Zhang et al (2013) found
that sewage sludge composted with wood biochar had up to 30% more humic
substances than the control.
4. Biochar compost improves plant growth

Biochar seems to improve the composting process, but how do plants like
those biochar-composts? Several researchers have experimented with various
combinations of compost and biochar added as separate amendments (Fisher &
Glaser, 2012; Liu et al, 2012). These studies found improved plant growth
response when biochar was added to soil along with compost. A 2013 study in
Germany looked instead at biochar composted together with other materials.
Schulz, et al (2013) tested six different amounts of biochar in compost,
from 0 to 50% by weight, and also three different application rates of each
compost type. Using oats in greenhouse pots on two different substrates
(sandy soil and loamy soil), they found that plant growth increased with
increasing application rates of each type of biochar compost, which is not
surprising since the amount of deliverable nutrients was increased, at
least by the compost fraction. However they also discovered that plant
growth was increased as the amount of biochar in the compost increased. The
biochar may either have improved nutrient retention during the composting
process with subsequent enhancement of nutrient delivery to plants, or it
promoted plant growth through some other mechanism.  However, the
researchers confirmed that synergistic effects can be achieved by adding
biochar to composts.

How could we put biochar to work in soils?

One of the basic principles of good compost production is that the wider
the variety of materials you use, the better the compost. Bruno Glaser and
his colleagues, who have studied both the Terra Preta soils and biochar in
compost, have proposed the modern material flow management scheme diagramed
below (Figure 5) for producing high quality compost with maximum carbon
sequestration and nutrient balance to help meet the growing need for
replenishing carbon, nutrients and beneficial microbes in agricultural
soils (Fischer & Glaser, 2012).

This ideal biochar compost system is based on a speculative reconstruction
of the Terra Preta soils. According to this model, these areas began as
garbage dumps where accumulation of food wastes, ashes and manure were
deposited.  However, as populations grew, it is possible that they began to
realize that the waste sites were developing into very fertile and
productive areas.  They may have begun to deliberately manage the material
flows of plant biomass, mammal and fish bones, ash, biochar, and human
excreta that likely resulted in the Terra Preta soils we see today.

[image: 8_terra-preta-nova-concept.jpg]

Figure 5.  Sustainable management of natural resources by combining biochar
with organic and inorganic wastes in compost processing (reproduced from
Fischer & Glaser, 2012). OM stands for “organic matter,” CEC stands for
“cation exchange capacity” and WHC stands for “water holding capacity.”

For maximum conservation of resources, it is important to remember another
principle: use the less degradable carbon sources like biochar to help
preserve the more easily degradable but nutrient-laden sources like manure
and food waste. I believe there is much exciting work ahead to determine
optimum recipes for biochar-based organic composts and ferments, exploring
the effects of different kinds of biochar in combination with other compost
ingredients.

>From past and on-going research, we realize that biochar has numerous
possible mechanisms for its action in soils that can occur on a variety of
different scales.  But if the results from recent biochar compost research
prove to be consistent, we now have the beginnings of a recipe book for
biochar-enhanced super compost that can kickstart the process of returning
carbon to soils today. Our industrial legacy has left us with a rapidly
deteriorating climate, and soils that are dying and eroding. Biochar, as a
form of recalcitrant carbon, may be just the medicine that degraded and
unproductive soils need.

 Please download the list of references here

https://www.biochar-journal.org/itjo/media/doc/1414798880420.pdf
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The Making of Terra Preta at the Ithaka Institute

https://youtu.be/PIMPgn1xa_E
*Published on Apr 19, 2014*

We call it Swiss Terra Preta but as you can see it's just a technique of
making biochar-compost with an adapted feedstock blending and a highly
oxygenized process. We use 10 to 80% biochar in the blend depending on the
end-use of the substrate. Rock powder and clay is essential. Biochar should
never dust. Turning the small windrows every day during the first two weeks
and then every three days the next four weeks and you will get highly
fertile black soil after four weeks.
Thanks to staring Paul Taylor on the tractor!

Further information on how to produce Terra Preta like substrates can be
found in the Ithaka Journal: Ways of Making Terra Preta
<http://www.ithaka-journal.net/wege-zu-terra-preta-aktivierung-von-biokohle?lang=en>

Ways of Making Terra Preta: Biochar Activation

by Hans-Peter Schmidt

http://www.ithaka-journal.net/wege-zu-terra-preta-aktivierung-von-biokohle?lang=en

Ways of Making Terra Preta: Biochar Activation
<http://www.ithaka-journal.net/wege-zu-terra-preta-aktivierung-von-biokohle?lang=en>
by
Hans-Peter Schmidt

*Biochar is not a fertilizer, but rather a nutrient carrier and a habitat
for microorganisms. First of all, biochar needs to be charged to become
biologically active in order to efficiently utilize its soil-enhancing
properties. There are numerous methods of activating and producing
substrates similar to terra preta aside from mixing biochar with compost. *

Biochar is extremely porous and has a huge surface area of 300 m2 per gram.
Due to its high porosity, biochar can incorporate up to five times its own
weight in water and dissolved nutrients. This property is called adsorption
capacity (AC) and depends on the pyrolyzed biomass and the pyrolysis
temperature. The highest adsorption capacity of biochar is achieved within
the temperature range of 450 ° C to 700 ° C.
<http://www.ithaka-journal.net/wpForschung1/uploads//2011/03/porose-biokohle.jpg>

Porosity of a coal ash clearly visible to the naked eye. (Photo: Andreas
Thomsen)

Another important feature regarding the particular nutrient dynamics of
biochar is its high cation exchange capacity (CEC). The CEC is a measure of
the ability to bind positively charged ions (cations) on biochar’s surface
and make them available later, under appropriate conditions, to plants and
microorganisms. While CEC depends on the surface of biochar, it is also a
chemical value, which increases through oxygen and contact with the soil
and reaches its maximum value only after some time. A high CEC prevents the
leaching of mineral nutrients, such as organic nutrients, and assures high
nutrient availability. Further, a high CEC also binds toxic molecules,
thereby protecting the soil.

The combination of biochar’s high AC and CEC make it a perfect nutrient
carrier. Microorganisms find ideal habitats in and around the biochar
through these absorbed nutrients, which, in turn, benefits the entire soil
microbial life and promotes the potential for symbiotic microorganisms and
plant roots.


Principles of biochar charging

If biochar is incorporated pure and without activation into the soil, its
high adsorption capacity and increasing CEC will result in the absorption
and fixing of available nutrients and water in the soil. This may lead to
inhibition of plant growth, at least in the beginning (several months to a
year), depending on the soil’s nutrient content. To prevent this, it is
recommended that prior to biochar’s application, biochar should be:

   1. Loaded with nutrients and water
   2. Colonized with microorganisms to ensure the fixed nutrients are more
   easily available to plants
   3. Aged by oxidation to bring CEC close to its maximum.

<http://www.ithaka-journal.net/wpForschung1/uploads//2011/03/thomsen-exp2.jpg>

The experiment by Andreas Thomsen clearly shows the importance of charging
biochar. In the picture, the upper portion shows a series of experiments
wherein pure biochar particles were added in increasing dosage. In the
lower series of the picture, the biochar was composted first for 4 months
and then cleaned of compost to make sure that only the charged biochar in
the experiment was used. While pure biochar resulted in growth inhibition
of mustard plants, charged biochar showed a significant increase in growth
(thanks to Andreas Thomsen).

There are many different viable processes in charging biochar and, thus,
producing terra preta soil-like substrates. These variables are adjusted
and modified depending on location, culture, climate, and existing
techniques. Many of these procedures have evolved over time or in
accordance with good agricultural practice. While there is no universal
formula (although patents have already been registered), the following
basic principles hold:

   1. Enough moisture present so that nutrients can dissolve and the pores
   of the coal can charge
   2. A high diversity of organic nutrients in order to prevent shortage of
   certain nutrients
   3. The most important nutrients for microbial colonization are organic
   carbon and nitrogen, which are particularly limiting in fresh coal
   4. The C / N ratio of the biochar-substrate should be 25 to 35
   5. The duration of the charge should be at least 14 days
   6. Inoculation with soil-borne microbes through the addition of
   humus-rich soil, compost tea, compost, or by selected microorganisms

The following four systems and procedures are examples of the practical
implementation of biochar activation for agriculturally related quantities.
These procedures can also be adapted for a small garden or even a balcony:
<http://www.ithaka-journal.net/wpForschung1/uploads//2011/02/bc-kompost-wurmloch.jpg>

Soil from a vegetable patch with biochar compost (about 25 cm deep). An
earthworm has lined its path with biochar-containing solution. By the way,
many laboratory tests have shown earthworms to be a great lover of biochar
substrates. Diameter about 4 mm. (Photo: Andreas Thomsen)


A. Biochar with compost

The charging of biochar by addition and mixing of compost probably
represents the best way to produce terra preta and similar substrates.
Microbial stimulation is highest in compost: nutrients are built into
complex organic compounds and the final substrate is very close to the
soil’s humus. However, most available composts are of poor quality. Poor
compost is tediously “digested” in the ground and this leads to nutrient
blockage and microbial imbalance. If you are not sure about the quality of
your compost, it is better resort to one of the other options for charging
the biochar. Good compost must have a crumbly structure, similar to that of
humus soil, and is not supposed to smell bad.

Ideally, biochar is added to the compost at about 10% of biomass when
arranging the pile, to boost the compost’s nutrient efficiency (see Fig.__
below). Frequent “turning” is important for oxygenation and homogenous
distribution of nutrients, which, consequently, promotes microorganismal
activity.
<http://www.ithaka-journal.net/wpForschung1/uploads//2011/03/nitrat-diagramm-kompost.jpg>

A preliminary experiment at the Delinat Institute has shown that the
addition of biochar significantly improved the reaction of the nitrogen
compound by stabilizing and significantly increasing plant-availability of
nitrate (NO3). Nitrogen loss is slowed down and, with it, the emission of
greenhouse gases. In a second, larger experiment, this effect will be
verified and investigated in detail. A separate article on the topic of
composting with biochar will be published in Ithaka.

The biochar produced with compost can be used again after rotting for
charging other fresh biochars. Mature composts that have not been composted
with biochar can also be used to activate biochar.

To activate, stack the biochar in approximately a 1:1 volume ratio with the
mature compost and moisten both well. If possible, mix biochar and compost
with a compost turner. This process can be repeated several times until the
ratio reaches 1:1. The mixture should be prepared at least 2 weeks prior to
its application into the soil and during that time should always be kept
moist and turned at least twice.


B. Biochar with manure from livestock

A mixture of different manure types is preferable to one type of manure.
Attention should be given to a high straw content. Since the following
method is not about composting, the manure should be stored at least 1 year
prior to use. It is better, however, if the biochar is already used as
bedding for the manure in the barn. Alternatively, it is also possible to
regularly spread the biochar in the septic tank.

The ratio of biochar to manure should be about 4 to 1. Depending on the
cultural and nutritional needs of the area, this ratio can be reduced. To
prepare the biochar:

   1. Moisten the biochar with plenty of water.
   2. Spread out the biochar into strips/bands of about 120 cm width and a
   height of about 5 cm on a humus-rich soil, when possible.
   3. Spread over it a 3 cm thick layer of manure.
   4. Put 1% rock flour into it (not necessary, but it improves the quality
   of the substrate).
   5. If the manure to be mixed is not high in straw content, put layers of
   about 10% grass, corn silage or greenwaste into it.
   6. Spread over it another layer of biochar.
   7. Moisten the whole with as much water as possible (if possible, put
   compost tea or EM-A [Effective Microorganisms]).
   8. If the ground in which the mixture will be used is too firm and less
   productive, a layer of fresh, fertile, soil should be added for microbial
   colonization of the substrate to take place.
   9. Roll over the band with a rotovator at least twice to thoroughly mix
   the substrate.
   10. Keep the mixture well moisturized for 14 days and stir it every 3
   days with the rotovator. It is recommended to cover it with fleece.

<http://www.ithaka-journal.net/wpForschung1/uploads//2011/03/biochar-pagocasagran.jpg>

Activating biochar through Method 2 in the winery Pago Casa Gran, southern
Spain.


C. Biochar with liquid fertilizers

   1. Calculate the amount of fertilizer you need for a given area. Mixing
   with biochar reduces leaching and outgassing of nutrients, so that
   fertilizer efficiency increases significantly and a total of only half of
   the conventionally calculated amount is required.
   2. Make sure that the fertilizer contains not only the main elements (N,
   P, K, and Mg) but also has a very high mineral diversity. In case of doubt,
   add some rock flour.
   3. Dissolve the calculated amount of mineral fertilizer in sufficient
   water.
   4. Give as much biochar in a period of 2 days to allow complete
   absorption of the added liquid.

Organic liquid fertilizer is preferable for charging instead of NPK
fertilizer. Liquid animal manure is an excellent example to use for
charging biochar.

Variant C is not about microbial colonization. In this example,
colonization will take place in the soil. In organic farming, mineral
fertilizer trade is prohibited.


D. Biochar – Bokashi (lactic acid fermentation of biomass)

   1. Mix straw-rich manure with 10% grass clippings, 10% biochar, and 1%
   rock flour.
   2. Spray the biomass with a solution of 3% EM-A and 3% cane molasses.
   (Alternatively, instead of EM-A, Sauerkraut [pickled cabbage] juice,
   Brottrunk [a particular juice manufactured from bread], or juices
   containing enzymes with similar high amount of lactic acid bacteria can be
   used. This can prolong the fermentation process depending on the mixture.).
   3. Compress the pile by driving on it with a tractor repeatedly as shown
   above (see picture).
   4. Cover the pile with an airtight suction foil. Cover the whole thing
   with a black foil and load it with gravel bags. (On a smaller scale, this
   can be carried out in closed containers such as buckets, barrels, or
   plastic bags.).
   5. Remove the foil after 14 – 21 days, depending on ambient temperature.
   The product will smell slightly like lactic acid!
   6. To activate a larger amount of biochar, the Bokashi can be filled up
   to 50% (vol) of biochar. For terra preta similar substrates, this
   additional amount of coal is not necessary.
   7. Water and mix the pile with a compost turner or rotovator and let it
   aerate for several days. To inoculate it with soil-borne micro-organisms,
   add some fresh soil.

<http://www.ithaka-journal.net/wpForschung1/uploads//2011/03/verdichtung-bokashi.jpg>

Compressing a biochar-manure mixture before covering it with an air-tight
foil. Bokashi fermentation is an anaerobic process. (Photo: Rolf Zimmermann)


Incubation in the soil

The activated biochar and terra preta similar substrates should be
incorporated superficially in the soil. If the appropriate technology is
not available, the substrate may simply be spread on the ground. The
anxious mixing by worms in the soil takes a little longer.

Tags: Aktivierung von Pflanzenkohle
<http://www.ithaka-journal.net/schlagwort/aktivierung-von-pflanzenkohle?lang=en>,
Bokashi <http://www.ithaka-journal.net/schlagwort/bokashi?lang=en>, Kompost
<http://www.ithaka-journal.net/schlagwort/kompost?lang=en>, Pflanzenkohle
<http://www.ithaka-journal.net/schlagwort/pflanzenkohle?lang=en>, Terra
Preta <http://www.ithaka-journal.net/schlagwort/terra-preta?lang=en>

<>

A comment from:

https://www.biochar-journal.org/en/ct/32-How-biochar-works-in-soil
Erich J. Knight, United States
06.11.2014 22:52
Fe + Biochar = Carbon Nanotubes, H2O (-As), and High SOC

Just to add some corroborating fuel to the electro-Pyrolitic fire; Fe +
Char = Carbon Nanotubes More Iron Carbon Cookery; Cooking up carbon:
sawdust and iron in the melting pot
http://www.birmingham.ac.uk/news/latest/2014/10/22-Oct-14-Cooking-up-carbon-sawdust-and-iron-in-the-melting-pot.aspx
Fe + Char = H2O (- As),... UF/IFAS researcher finds inexpensive, easy way
to filter arsenic from water
http://news.ufl.edu/archive/2014/11/ufifas-researcher-finds-inexpensive-easy-way-to-filter-arsenic-from-water.html
Fe + Char = Higher SOC,,, "ferromagnetic minerals (magnetite) lowers C
mineralization rates through reduced microbial and extra-cellular enzymatic
activity in the generated magnetic domains, thus leading to higher SOC
accumulation." Magnetite: Another link between Terra Preta de Indio soils
and biochar presented by L.Yang, E.Bicalho, K.Spokas, J.Marques Jr,
N.LaScala Jr, M.C.C.Campos, J.Novak Conclusions; Biochars vary in magnetic
susceptibility Magnetic properties of biochars affect microbial activity C
mineralization lowered due to a decrease in microbial activity Retention of
SOC in the presence of biochar is analogous to the presence of magnetite
This data supports this concept of microbial activity being influenced by
magnetic fields.