Beneficial biochar

Biochar is one of many organic substances that can be added to soils to make them more fertile. What is it? What does it do? Why is it worth using it in addition to organic fertilisers? Where can you get it, or how can you make it yourself? 

What is biochar?

Charcoal is, to use the official definition, a carbon-rich solid material produced by thermal decomposition of organic material in the absence, or under limited supply, of oxygen.

Charcoal is called biochar when it is added to soils for the purposes of improving soil fertility.

Biochar is very porous and it weighs little because it contains many small air-filled pockets.  It acts like a sponge. When biochar is mixed with soil its pockets will gradually fill with water from the surrounding soil. Over time that water will leach back into the soil and keep it moist. Soils that contain biochar are less likely to dry out.

This in itself is enough to lead to more microbes surviving and thriving in this soil and more successful crops. 

The effect on microbes and plants is even more pronounced if you add biochar to soil after allowing its pockets to fill with liquid organic fertilisers, such as seaweed extract or fish emulsion. 

Added to biochar these fertilisers will provide long-lasting, slow-release nutrition. Microbes will find these pockets and make them their home. In turn they will attract other micro-organisms. The accumulated effect of many micro-organisms congregating in and around biochar binds many nutrients together effectively. The result is that rain no longer leaches them out of the soil.

In one of the Food Garden Group's past workshops presenter Letetia Ware compared the pockets in biochar to a block of flats in a city.  The block of flats provides accommodation to many microbes.  If you allow biochar to soak in a mix of organic fertilisers before adding it to soil, you provide microbes with a place to live and free food!

Biochar is very stable. It does not break down in soil for many hundreds of years. That fact, and its interactions with nutrients and microbes make it unique.

How did mankind discover biochar?

When the Portuguese arrived in the Brazilian Amazon they found areas where the soil was much blacker and much more fertile than in other areas. 

They did not immediately understand why this was so, because the people who had added the biochar that was responsible for the blackness and fertility, were no longer there. 

They called this soil terra preta (black soil). They found that terra preta remained fertile, while in other soils the nutrients simply leached out because of massive rainforest rains.

The production of biochar today

Farm and forestry wastes (feedstocks) currently used to produce biochar on a commercial scale include tree bark, wood chips, saw dust, crop residues (nut shells, straw, and rice hulls), grass, and organic wastes including distillers’ grain, dry pulpy wastage from the sugarcane industry, mill waste, chicken litter, dairy manure, and even dried sewage and paper sludge.

It is made by heating dry organic material to 450 - 600 degrees Celsius while excluding oxygen. The process is called pyrolysis. 

Biochar without anything added is sometimes called non-activated biochar.

Biochar that is loaded with organic fertilisers for agricultural purposes is known as activated biochar or inoculated biochar.

Biochar and climate change

There is another reason why today, in the age of climate change, it would be great if the world began to produce and use biochar in a big way.

At present in many countries around the world enormous quantities of farm waste are burned, causing huge air pollution problems, and the addition of enormous amounts of carbon-dioxide to the atmosphere. In other places farm waste is put in landfill, where it degrades and decomposes, releasing carbon-dioxide into the atmosphere.

By converting farm waste into biochar and then adding the biochar to soils, carbon is stored long term in soil rather than allowing it to become part of the earth's atmosphere. What was once a waste product, is used to improve soils.

There are many people working towards finding methods to convert farm and forestry waste into biochar on a commercial scale. 

One non-profit organisation I came across is Warm Heart World Wide.  They are helping thousands of Thai smallholder farmers change from their standard practice of burning crop residues after harvest to producing biochar. You can find out more about them here.

A number of projects for the production of biochar are underway in Tasmania (September 2022). For example, a saw mill at Glen Huon is gearing up to soon begin the production of commercial quantities of biochar made from eucalyptus sawdust. You can find more about this project here.

Where to buy biochar?

• In northern Tasmania Terra Preta Developments (Rosevears) sells Frank's Char (see https://www.terrapretadevelopments.com.au/products/biochar/ )

• In southern Tasmania Longley Organic Farm (Hobart) sells locally-made biochar (see https://www.longleyorganicfarm.com.au/biochar )

• In southern Tasmania the people behind The New Black expect their biochar made from eucalypt sawdust to be available to retailers and online for home gardeners in late 2022. Please email Christina at christina@thenewblackbiochar.com.au if you would like to order their product.

• In southern Tasmania Horticultural and Landscape Supplies (HALS) at Brighton produces biochar using waste products from the food industry. For more information visit  https://www.horticulturalsupplies.com.au/biochar

It is recommended that you activate biochar before using it (see below).

Can I make my own biochar?

The answer is 'yes', and below are three methods for doing so.

Making your own biochar is a great alternative to buying it, but there is one thing you need to get right: make sure your end-product is charcoal with little or no ash.  Ash is very alkaline. Adding ash to soil, especially if you do it repeatedly, will take the pH to above 7. Most vegetable crops will not grow well under those conditions.

Method 1: make charcoal from your woody garden waste

This method is recommended for people who live in rural areas and who have a lot of woody garden waste.

Food Garden Group member Dirk S. provides a step-by-step guide describing how he makes biochar in his backyard. All you need is enough room to safely light a fire and enough garden prunings. You will find all the details plus photos in Backyard Biochar .

Method 2: use charcoal from your wood heater

This method can be used by anyone anywhere.

At home we mostly burn our wood heater only in the evening. The following evening, before starting the next fire, I remove any charcoal that is left over from the previous night (leave the ash, no ash!), and store it in a metal bucket where any coal that might still be warm can't do any damage. 

When the bucket is full, it is emptied in the bin in the photo below. That adds up to quite a bit of charcoal over the course of the winter months.

Method 3: make charcoal in a trench in the ground

This method is for people who live in rural areas and who have a lot of woody garden waste.

This method comes closest to pyrolysis - burning at high temperatures with minimal oxygen (discussed earlier in this blog post). It produces the purest biochar of the three methods described here. 

You need one sheet of roofing iron without any holes, a big heap of dry woody garden waste, and a spade.

1. Dig a trench in the ground (close to where your woody garden waste is) that is around 70 cms deep, slightly shorter and slightly less wide than the sheet of roofing iron you have.  Make the trench slightly-sloping in from the top of the trench to the bottom of the trench.
2. Start a fire at the bottom of the trench, and once established, throw in your woody garden waste, bit by bit (not in a large bundle), so the fire does not smoke a lot, and also does not become a big bonfire.
3. Keep adding material until the trench is full.
4. Now put the sheet of roofing iron over the trench and seal the edges with the loose dirt from digging the trench, stamping down the soil until no more smoke escapes. 
5. Add more dirt to the edges if you see smoke escape.
6. Don't touch the sheet of roofing iron: it may become quite hot.
7. Come back after 24 hours. The charcoal is ready for digging out of the trench.

Warm Heart World Wide persuaded many Thai farmers to use this method on a large scale. For more info go to https://warmheartworldwide.org/biochar-trench/ .

How do I activate biochar?

Some biochars you buy are already activated/inoculated. Please read their description or ask the supplier. If your biochar is already activated, continue reading under the next photo. 

Biochar does not need to be activated to be a useful soil additive. However, activated biochar will be much more effective than biochar that is not activated.

Here is how I activate my biochar: at the end of winter I crush my bin with charcoal by walking over it in my gumboots until all the bits are small. Then I transfer the charcoal to a large bin (see below),  add a bucket of water + seaweed fluid and a bucket of water + fish emulsion fluid, mix it all thoroughly, and leave the mix to soak for a fortnight. 

Instead of the fluids mentioned above, or in addition to them, you could use worm wee or chook poo slurry or fluid made from compost. What you are adding is food for microbes, so you can add anything that they like. Don't make your mix of potions too complicated. More is not always better. 

After having activated your biochar you don't need to wait for it to dry. You can use it straight away. However, if you want to store it in bags for later use, that is fine too.

How should I use biochar in my garden?

Add it to your compost heap or directly to a garden bed, then mix it in thoroughly.

Biochar does not break down. It is there for the long haul. It does not 'disappear'. It is best not to add a lot of biochar to your soil or compost heap all at once. Instead, add small amounts a few times a year.

Most biochars are alkaline and most Tasmanian soils are acid. Biochar might increase the pH a bit, but that will be okay. Nevertheless, it's not a bad idea to check the pH of your soil before adding biochar. Most vegetables prefer a pH of between 6.5 and 7. If the pH is above 7, bring it down to below 7 (see blog post Acid or Alkaline?) before adding biochar.

At present (September 2022) there are no clear recommendations in regard to the amount of biochar that has an optimal impact on soil fertility. This is because it depends on what feedstock the biochar was made of and the fact that research into biochar is not yet advanced enough (see below).

Research into the use of biochar in modern agriculture

The use of biochar in modern agriculture is still quite new. Scientific research has confirmed the benefits of biochar as mentioned above, but a lot more research is needed (September 2022). For instance:

• Biochar made from wood is different from biochar made from other feedstocks. It is not yet clear whether some feedstocks are preferable over others, or whether some soil types benefit most from some biochars.
• There are as yet no generally recommended application rates of biochar.
• There are as yet no decade-long or longer trials of the use of biochar on agricultural soils.
• There are as yet no quality standards for commercially available biochars.

Australia is playing a leading role in the research and uptake of biochar and food gardeners are encouraged to try this unique soil additive.

Biochar received a major endorsement in the ABC Landline episode of 2 October 2022. In that episode a researcher discussed a recent finding that for every 1% carbon you add to soil, you increase its water holding capacity by 10 to 30 tonnes per hectare. She commented that this makes biochar a no-brainer in a country like Australia.

The following comment by a biochar scientist stood out for me: for every 

The following science journal articles helped me write this blog post:

1. Preparation, modification and environmental application of biochar: A review (Elsevier 2019)
2. Biochar:A Sustainable Approach for Improving Plant Growth and Soil (InTechOpen   2018)
3. Opportunities and constraints for biochar technology in Australian agriculture: looking beyond carbon sequestration (CSIRO Publishing 2014)
4. Biochar Application to Soil: Agronomic and Environmental Benefits and Unintended Consequences – Elsevier 2011)

May your crops thrive,

Max Bee