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  • Writer's picturePorpeang farm Thailand

Biochar - An ancient farming method for the modern world

Updated: Jan 29, 2020

A simple forgotten farming method that vastly improves poor soil conditions and at the same time combats harmful greenhouse gases. It sounds too good to be true, doesn't it? Its apparent potential is enormous, so let's have a close look at what all the hype is about.

Exploring the amazon
An early Amazon expedition

Terra Preta

The Portuguese Terra Preta, meaning "Black Earth," is an old-world soil building technique that was developed by the ancient Amazonian civilizations over 7000 years ago.

They used it as a permanent solution to solving the problems of reduced fertility in their tropical soil.

Large deposits of this black earth are still found even today in depths of up to 2m.

Terra Preta soil cross-section
Cross-section of Terra Preta soil to a depth of 2m

What is Biochar?

Biochar is simply charcoal that is best utilized as a soil amendment for both soil health benefits and carbon sequestration. Biochar is a robust and stable solid; it is extremely rich in carbon and can remain productive in the soil for thousands of years.

Like many other charcoals, Biochar is created from biomass through a process known as Pyrolysis.

The land or agricultural soil is fertilized using fertilizers (synthesized or natural).

Synthesized ones may be effective early in the beginning but later often have negative side-effects on crops. Natural ones or bio-fertilizers are mostly used, but they cannot sustain the fertility of the soil for prolonged periods.

This can often be solved by adding charcoal to the soil. Charcoal is amongst one of the purest forms of carbon, and it helps in sequestering the carbon captured from carbon dioxide emissions, thereby helping to retain the quality of the soil.

It helps the bound & clumped ions to dissociate and to move freely all throughout the soil. Some of the researchers found this solution in recent years. It's widely known that charcoal could be the decay of anything.

Researchers have found a 'new' method to sustain soil fertility for a long time. This is by using Biochar instead of random charcoal. Biochar is basically a form of charcoal that is produced from organic plant matter, which helps in absorbing CO2 (carbon dioxide) from the air and fertilizing crops.

Untreated Biochar
Untreated Biochar

Top soil depletion

Depletion in soil organic matter & soil nutrients, the decline in agricultural productivity, and changes in climate due to anthropogenic activities are posing significant threats to the sustainability of agricultural production in tropical regions.

Chemical fertilizers have, of course, played a vital role in increasing agricultural productivity over the past half-century.

Declining soil quality & loss in per capita land area demanded the increased use of inorganic fertilizer.

However, the use of inorganic or chemical fertilizers for improving the agricultural yield & soil fertility is not a sustainable approach.

It has been widely taken in that the excessive use of chemical fertilizers, mainly being nitrogen, has the ability to deteriorate soil environment & can also lead to the mineralization of organic matter.

The world's population has been fed for almost the last half-century owing to these modern practices of green revolution. Even so, these practices have become environmentally destructive, unsustainable and are also unable to satisfy the needs of the population.

So it is becoming essential to restore the contaminated soils by using organic fertilizers. The use of Biochar as a natural fertilizer is quite a novel approach having potential benefits to both the environment & agriculture.

Applications of Biochar to soils as a technique to improve the quality of farming land has emerged in recent years.

Carbon sequestration

Biochar has the ability to aid in coping up with the high levels of greenhouse gases (GHG) and is helpful for carbon sequestration.

Various pieces of evidence and studies showed that the utilization of Biochar could be beneficial for the improvement of:

Soil organic Carbon,

the capacity of water holding,

stimulating soil microbes,

increasing the microbial activity

decreasing in needs and leaching of fertilizers,

availability, and retention of nutrients,

soil aeration,

bettering the growth & yield of crop growth

reducing the fluxes of greenhouse gases through anthropogenic activity & increase in sequestering carbon.

What are the environmental benefits of Biochar?

Dealing with climate change

Due to the burning of fossil fuels, & the decomposition of biomass, an excessive amount of carbon dioxide is being released into our atmosphere. This increases the carbon levels in our atmosphere.

However, by applying Biochar on these soils can help decrease the emission of carbon dioxide as Biochar has the ability to store up to 50% of the carbon from the feedstock.

Biochar is highly stable, & that's what makes it restrain the emission of carbon dioxide from organic decomposition significantly, & it also plays a vital role in controlling the release of methane & nitrogen dioxide gases from the soil.

A study has revealed that by applying Biochar made up of municipal biowaste, about 90% of nitrogen dioxide (NO2) can be suppressed in dampened Typic Hapludand (volcanic ash soil) in a laboratory experiment.

Another study reported that by mixing of 20 grams of Biochar in 1kg of soil has the ability to reduce emission levels of nitrogen dioxide (NO2) by up to 80% in grass pots & almost 50% in soybean.

The reduction in the release of nitrogen dioxide (NO2) happens because of the aptitude of Biochar to adsorb & retain the ammonium in soils & then lessen the availability of nitrogen for the denitrification process.

Studies have shown that the agricultural soils contribute 12% in the total methane emissions globally (mostly from paddy rice soils.)

The emissions of methane from the soil that were treated with Biochar mainly depend on the type of soil, the properties of Biochar, & the water condition.

In the fields, the methane emissions were 34% higher from the fields which had been treated with Biochar.

However, the emissions of nitrogen dioxide (NO2) were found 40-51% less in soils than that of those soils which had not treated with Biochar.

These facts clearly show that global warming gases from soils decrease by amending soils with Biochar.

Reducing pollution of waterways

The application of Biochar on the soil helps in the reduction of off-site pollution.

It increases the retention of nutrients like phosphorus and nitrogen in the soils, aid in decreasing the leaching of nutrients of soil into the groundwater, & helps in saving the nutrients from erosion due to surface water flow.

When nutrient loss is controlled in the soil, nutrients available for the cultivation of crop increases. This reduces the amount of fertilizers required for the growth of crops.

Reduction of leaching has been verified in many greenhouse studies & can be predicted by realizing the adsorption behaviour of Biochar.

As far as the erosion is concerned, as yet, there has not been any separate study conducted for that, but it can be expected that the nutrients soluble in the soil are less likely to be eroded compared to those nutrients which are adsorbed or attached on the surface of soil sediments.

By implementing Pyrolysis of animal manures, a significant amount of reduction can be achieved in the mobility of phosphorous of animal manures.

This technique can help to reduce the weight & volume of the manures and will make the disposing of waste easier.

It has the ability to convert the soluble inorganic phosphate present in the manure into the adsorbed phosphate in Biochar.

There is a need for an extensive study to explore more such behaviours & properties of this charred manure, & it should strongly emphasize the phosphorous dynamics with Biochar.

Air pollutant 'Scrubbing' with Biochar amendments

Studies have shown that Pyrolysis seems to propose added opportunities as by the application of Biochar into the soil leads to the reduction of greenhouse gases (carbon dioxide, nitrogen oxides & sulfur oxides) from flue gas, which decreases their emission.

During the exothermic process, carbon dioxide (CO2) is precipitated on the surfaces of the Biochar.

This process could well be helpful in the reduction of carbon emissions in the atmosphere due to the burning of fossil fuels.

Simultaneously, the precipitation process results in the formation of Biochar, which highly rich in nitrogen content that could be used as a substitute for nitrogen-based fertilizers.

Such benefits require investigations furthermore.

Unused scrap timber for making biochar
Scrap timber for making biochar

Reduction of environmentally hazardous materials

Biochar is exceptionally efficient as it has the ability to absorb major environmental contaminants in the soil.

Many organic pollutants can be sequestered by using Biochar to alter their effects on the environment eventually.

Due to its resisting nature towards microorganisms & its extraordinary absorption qualities, Biochar acts as an active binding phase for different pollutants in the environment.

There are carbonized, & non-carbonized types of organic matter in Biochar, which plays a significant role in sorption. The sorption of pollutants is done by the carbonized & non-carbonized sections of Biochar which depends on their bulk and surfaces.

To exemplified, it is reported that the sorption of pesticides using the Biochar made up of incompletely burned wheat & rice residues is 400 to 2500 times highly efficient than that of typical soil.

Reports have shown that charcoals derived from red gum have the efficiency to sorb Diuron-a pesticide, from polluted soil.

Studies have revealed that charcoal works best in high temperatures (e.g. 8508°C), & their capacity enhances (helped by the higher surface area and micropores.)

A study showed that Biochar derived from Pinus radiata have higher efficiency for the sorption & desorption of a pollutant called phenanthrene from the soil.

A study showed that Biochar combined with manure derived from dairy has the sorption capacity for heavy metals like lead & other organic contaminants.

Studies have shown that the sorption capacity of the soil of hydrophobic organic compounds is higher when treated with Biochar. This depends on carbon levels in the soil, properties of Biochar, & time required by the soil & Biochar to contact with each other.

A study conducted on organic compounds revealed that the heavy metals present in the soil significantly affect the adsorption of several organic pollutants on Biochar & also interfere with their transport and fate.

Biochar is more likely to adsorb biological contamination like persistent organic pollutants (POPs) as they have a high affinity for Biochar because it is naturally occurring.

Studies have revealed that applying Biochar to the soil contaminated with polyaromatic hydrocarbons (PAHs) can help the sorption of PAHs from the soil.

collecting biochar
On our farm in Thailand we use Biochar to help regenerate depleted topsoil

What are the agricultural benefits of using Biochar?

Many studies exclaim that the application of Biochar on the soils can enhance the content of organic matter in the soils & improves the fertility of the soil.

Several studies show that by the addition of Biochar in the soils, it will result in better soil texture, more porosity, reasonable structure, and density and particle size distribution.

As Biochar has high porosity and more surface area, it will help in providing space for microorganisms that are beneficial for the soil and also help in the binding of essential anions and cations.

Many pieces of research provided evidence that by the addition of Biochar, the growth rate of the crop increased, quality of water improved, reduction in nutrient leaching, reduction in the acidity of the soil, more water retention, and decrease in fertilizer use.

In the presence of added nutrients, the nutrients uptake by plants increased, the growth rate increased significantly by the application of Biochar in soils.

Using Biochar to improve the soil for crop production

Any process related to the creation of bioenergy tends to affect the land negatively and leads to excessive accumulation and removal of biomass from the land.

These extremely exhausting procedures have the potential to degrade the soils excessively, poses detrimental effects on the productivity of soil, cause habitat destruction, and off-site pollution.

The application of Biochar can resolve these problems through Pyrolysis in combination with organic matter as it helps in recovering almost about half of the amount of original carbon.

Moreover, Biochar is also considered to be highly effective in the restoration of the fertility of soils.

Many pieces of research confirmed that the use of Biochar leads to the improvement of soil productivity.

The extraordinary properties and benefits of the use of Biochar are not only limited to only the area which was disturbed for obtaining biomass to generate bioenergy, but it can remain persistent in the soils for almost two to three years.

This shows that if the Biochar is applied to the lands which are not used for bioenergy production, it will increase the fertility of the soil. It will also help in reducing the pollution of the soil of that land from the inorganic chemicals.

Biochar improves nutrient availability in soils

By incorporating Biochar in the soils, it will result in better soil texture, more porosity, reasonable structure, and density and particle size distribution.

As Biochar has high porosity and more surface area, it will help in providing space for microorganisms that are beneficial for the soil and also help in the binding of essential anions and cations and increase cation exchange capacity (CEC).

Biochar application leads to an increase in the pH of the soil, and that leads to improved availability of phosphorous and potassium. When Biochar is applied to the soil, the oxidation process is observed on the surface of particles.

The reason for the reported high CEC is the oxidation of aromatic carbon, which leads to the formation of carboxyl groups. The increase in CEC aids in increasing the fertility of the soil, as the nutrients will remain attached to the soil opposing the leaching process because of CEC.

When highly oxidized organic matter attached to the surface, it will create a negative charge on the surface. This results in a decrease of positive charge on the sites.

However, the results from the studies showed that the effect of Biochar is more expected on the soils having macropores.

Using Biochar can increase the production of a crop

An increase in crop production happens because of the increase in soil fertility due to Biochar, the growth of seeds increased, and crop yield also increased significantly as compared to the soils not having Biochar.

A study revealed that the increase in dry radish matter happened due to the presence of Nitrogen fertilizer along with Biochar. Still, there was no increase in the yield even with the highest rate of 100 t ha-1 in the absence of nitrogen fertilizer.

Another study claimed the increase in the yield of maize grain by almost 98% with the application of Biochar at the 15 and 20 t ha-1.

A lot of similar results were observed in the soil of paddy rice in China, whereby the addition of 10 and 40 t ha-1 of Biochar the yield of rice increased by 12 to 14% in the soils with no added fertilizer, and with the addition of Nitrogen fertilizer 8.8 to 12.1% increase in the yield, respectively.

What's the difference between Biochar & charcoal?

The straightforward answer to is Biochar is used as a soil amendment, & charcoal is used as a fuel.

A complete answer is charcoal is made by heating wood by Pyrolysis (an absence or near absence of oxygen).

This process releases volatile compounds (carbon monoxide, hydrogen, aliphatic & aromatic hydrocarbons) as well as water vapour & soot (basically, the wood is releasing a volatile form of smoke).

Some of the smoke is directed to a place within the process where it combines with air. During burning it creates more heat, that drives the process (heating more wood), while some of this smoke is then fed back into the cooling or cooled blackened (carbonized) wood, & the carbonized wood absorbs and collects the smoke.

This process makes the resulting charcoal easier to light, & increases the energy content. The re-absorbed smoke gives the charcoal a characteristic greasy feeling against the skin, & the blackness that's left on the skin will likely need washing off with soap & water.)

For biochar production, the smoke is similarly used to drive the process, but none of the smoke is directed back onto the cooled char. Instead, the surplus smoke can be piped somewhere else & burned to produce heat for a separate process.

Alternatively, it can be used to fuel an internal combustion engine, or condensed into wood vinegar. Biochar, if rubbed against the skin, should not feel "greasy", & should not require soap to wash it off. Just clean water should wash most of it off.

Well made Biochar will be lighter in weight & contain less BTUs per volume than charcoal.

Three simple & cheap ways to make Biochar

Making Biochar can be as cheap & simple or expensive & complex as you want to make it.

1. Campfire Method

The simplest but least efficient way is with a campfire. Make any size fire with any type of wood & burn it until it creates a bed of embers/coals.

Then separate the coals & extinguish them. You can extinguish them with water or by collecting them in a metal can & sealing the lid. You can also smother them with dirt from your garden.

In any event, oxidation must be stopped. The remaining coals are crude, but an effective form of Biochar. This process requires no equipment & it is arguably the best way to start with Biochar (providing you like to make fires & have scrap wood or brush available.)

The Biochar will function but will not be the same grade that can be created in a temperature-controlled kiln.

A simple cone pit to make Biochar

2. Cone pit method

Cone pits also cost nothing to create & the size can be varied to suit your production needs & land available.

Wood burns twice. Firstly from wood to char, & then from char to ash.

The second part can only occur with the presence of oxygen. On flat even ground the Biochar produced during burning is difficult to protect from oxygen entering from around the sides.

In a cone pit, the Biochar is covered with more & more wood as it is produced.

A fire is lit in the bottom of a pit. Then dry wood is then gradually added as fast as the fire will allow.

You must always push the fire almost to the point of smothering it, but without actually smothering it.

It is critical always to keep a clean-burning fire, meaning no smoke.

If it becomes a little bit smoky, back off, & let the fire catch up.

If the fire is raging, add more wood to smother it out a bit. This way, you are constantly covering the newly created char with fresh layers of wood, which they become char, and so on.

When you near the top of the pit's capacity or the end of your wood supply, you finish with smaller diameter wood. The smaller bits of wood chars quickly.

Let the flames die down; then you are left with a large bed of beautiful red hot glowing coals. At this point, if you have done it right, the entire pit has turned to char.

You can then either hose it down immediately, or when time allows, cover it with soil to snuff it out, then uncover it a couple of days later to harvest. Use water for controlling high levels of dust.

3. Fire barrel method

First, take a metal oil drum, turn it over, & cut a 10″ hole in the bottom.

Build a simple fire, then upend the drum on top of it, so that the hole is positioned at the top (this will be where the smoke will exit.)

Leave a 1/4″ gap in the bottom; this allows just a little oxygen to feed the fire from below.

Now begin feeding your carbon source through the top hole.

The middle section of the drum will be making the charcoal as it burns without oxygen. This would be good for loose things like loose grass clippings, dry manure, weeds, & brush, etc.

inoculating biochar
On Porpeang farm we mainly inoculate Biochar with our goat manure

How to inoculate/charge Biochar

Biocharging or inoculating Biochar actively accelerates soil recovery and mycorrhizae growth. This, in turn, creates healthier, stronger and more nutrient-dense produce.

Compost charging

The most straightforward & efficient method to Biocharge Biochar is to mix it in with your compost piles. This creates stacking functions to benefit both the Biochar & your compost.

Even if you buy your Biochar pre-inoculated, rather than producing it yourself onsite, it will still be improved by maturing in your compost pile.

Don't be afraid, you can add as much Biochar as you wish, even up to a 50-50 mix with your compost, so don't worry too much about overdoing it.

Rapid Biochar charging with compost tea, worm casting & leachate

Another way to inoculate your Biochar is a little bit more labour-intensive, but you can complete the process in hours or days, instead of months.

First, fill a 210 litre (55 gallons) drum with fresh water & Biochar.

Note that if you are using municipally treated water, let it sit for a few days to remove any harmful chlorine.

Then add your compost tea or worm castings & leachate to the barrel with some soil from the area where you will be using the finished Biochar.

Let's say you are going to apply the Biochar to your fruit orchard, add some soil from around a healthy, robust tree in that orchard.

This helps charge your Biochar with the perfect microbiology blueprint for your specific orchard.

Once everything is mixed up, insert a long length of tube, like a length of PVC pipe into the barrel & direct air from a blower into the tube.

Alternatively, a pond aerator and air stones can be used.

The aeration process supercharges the inoculant & gives the beneficial microbes a massive head start, and helps them adhere to the Biochar. This process should be continued for 12-24 hours.

crushing Biochar in a bag
Simple method of crushing Biochar in a bag prior to applying it on the farm

How to effectively apply Biochar

Tilling Application

Spread pure inoculated Biochar about a 6mm (¼in) thick on the soil before normal tilling. It is best practice to carry this out at the same time you till in your other soil amendments.

For larger areas such alike pastures, the ideal amount of Biochar to till or disc in is one ton per acre. If you don't have that amount, spread out what you have & add more Biochar each time you amend your soil.

No-Till Application

You can spread pure inoculated Biochar around a grow area, then mulch as normal to hold the Biochar in place.

It takes about 10 pounds of Biochar to cover 100 square feet (9.3m2) properly.

For potted plants, use pure Biochar at a ratio of about 1:16 with your potting soil – about ½ cup per gallon of soil (118ml per 4 litres of soil).

This ratio is perfect for raised beds as well, one gallon (4 litres) of Biochar per 16 gallons (64 litres) of soil.

In all cases, till or no-till, if you inoculated Biochar in compost (at ratios up to 1:1, remember), just apply compost as usual – the presence of Biochar doesn't change the amount of compost used.

Potential drawbacks of applying Biochar

Soil loss by erosion is a possible issue when top dressing Biochar to soils. This occurs by wind or water transporting small, light Biochar particles. Proper incorporation of Biochar into a soil blend is necessary.

There is a possible risk of contamination of Biochar exists (dioxins, PAHs, heavy metals,) when contaminated feedstocks are used, or the process conditions used in making the Biochar are such that temperatures >500 C are used.

The removal of residues for use as a feedstock for Biochar production could result in reduced incorporation of crop residues into soils. This could potentially lead to harming soils. For example, this could be the case if farmers were using all of the straw they produced in a field to make Biochar.

Extremely high rates of biochar application could have negative effects on earthworm survival rates. However, this would be in cases where application rates are greater than 67 kilograms per square meter of land. This amount would be considered an impractical level of Biochar application.


Biochar application to the land helps to increase soil fertility, improve soil texture, improve sorption for nutrients, which then helps in reducing the use of fertilizers, which leads to the decrease in pollution through fertilizer runoff.

Biochar is highly efficient in increasing crop production and yields.

One of the significant benefits of Biochar is that it's helping in combating climate change by sequestering the carbon dioxide from the atmosphere.

It can also be used for the rehabilitation of destructed landforms.

Biochar is posing many benefits to the environment agriculture and economy in the longer run, so it is highly recommended to incorporate it in agriculture practices.

Poor soil conditions in Northeast Thailand

Most of the arable soils in Northeast Thailand are typical tropical sandy soils.

Their main primary & secondary minerals are quartz & kaolinite because parent materials have been severely weathered.

As a result of the destruction of natural vegetation to make room for cultivation, the soil organic matter is low, resulting in low cation exchange capacity (CEC) & low pH.

Amelioration of these soils requires liming, fertilization & application of organic matter and 2:1 type clay minerals.

A part of the arable soils in the region are salt-affected, salinization being intensified by deforestation.

How we are incorporating Biochar on our Thai farm

Here on Porpeang farm Thailand we have started to produce & apply Biochar on our land.

Wood is sourced from fallen timbers, wood offcuts from farm projects, surplus bamboo & leftover wooden stems from feeding our goat herd.

We make our Biochar in simple cone pits, without the need of a barrel or rocket stove.

After creating the Biochar, we then quench it with water from our onsite borehole.

The chunky Biochar is then smashed up in an old rice bag to the desired size before we begin to inoculate it.

We inoculate our Biochar in three different ways:

1. Speading it out on the floor of our chicken coop.

2. Adding it to our vermicompost tank.

3. Applying it underneath our raised goat house.

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