Biochar and environmental management

Biochar and environmental management make great sense at a time when farmers need all the help available to keep soils healthy. It is one of those stories that can have a happy ending if the stars align.

First some details on the mysterious black material called biochar. It is a product, made from the burning of almost any kind of organic material —leaves, manure, grass clippings, crop residues and even sewage sludge — in low levels of oxygen.

What you get from this burn is gas and a dark, honeycombed material that is almost all carbon.

In reality it is charcoal, the light and easily transported fuel that has been used for thousands of years for cooking and metal smelting in cultures across the world.

Biochar is what we call charcoal when its use is as a soil amendment.

Why would you put a useful fuel in the soil when most of the time we seem to be digging or drilling to take fuels out of the ground?

There are two big reasons:

Biochar and environmental management #1

Adding near pure carbon as stable particles that have a honeycomb micro-structure improves soil by enhancing properties that aid plant growth.

Water retention, nutrient exchange, soil structure and biological activity all tend to increase when biochar is added to soil. And agricultural production can be up to 20% greater.

Biochar and environmental management #2

Adding pure carbon that is stable over millennia is a form of carbon sequestration that uses soil as a carbon sink.

Given the huge challenge to maintain and enhance agricultural productivity to provide enough food, fibre and now biofuels, for 7 billion souls, any assistance with productivity cannot be ignored.

And to do this without further erosion of all the other values (cultural, social, and biodiversity) and all while the climate is changing makes soil amendments a powerful option for climate adaptation.

These two reasons are at the heart of modern environmental management.

Biochar production

At the moment biochar is available in many countries for domestic use as a soil amendment to improve garden soil. This requires only small amounts in any one garden and, therefore, only small-scale commercial production of char.

If we want biochar production to be available and used widely in agriculture, where typically we might add 10 t per hectare (4 t per acre), then we face a production challenge.

The conversion rate from organic matter to char depends on the material burnt (feedstock) but a useful rule of thumb is 60% conversion.

So we need to burn 1.4 t of organic waste for every tonne of char produced.

The difficulty for bio char production is to produce at scale. If a large central facility is used then it can be challenging to 

• source sufficient feedstock
• transport the feedstock to the facility
• sort the feedstock
• maintain consistent combustion within the plant

The alternative is to go modular and have smaller, mobile combustion units that can be transported to the feedstock source. This is a great way to utilise farm waste.

Now the problem is making enough char to apply at a rate of up to 10 t per ha.

Biochar carbon sequestration

The big advantage that biochar has over many other organic soil amendments is that the carbon is stable. Combustion fixes the structural integrity of the carbon so that it is no longer a source for the normal processes of decomposition in soil.

Instead it provides the surface onto which water, nutrients can be exchanged with plant roots.

Compost on the other hand is moist, aerated and heaven for bacteria, fungi and soil animals that chomp away at it to release nutrients and CO2 - the process of decomposition.

Most of the carbon in compost rarely lasts more than a few seasons in the soil.

The stability of char means that adding char to soil is biochar carbon sequestration that makes soil a net carbon sink and a potential offset for greenhouse gas emissions.

And the numbers are significant.

For example, add 10 t ha to just 10% of the arable land in Australia (442 million tonnes of char) would translate to 1,620 million tCO2e or more than three times 546 million tCO2e, Australia's emissions from fossil fuel use in the year to December 2011.

This stable carbon also meets the strict international carbon accounting rules. It is permanent and almost impossible to reverse once applied. The activity is not common and can be more costly than traditional fertilizer use and so passes a test of additionality (better than business as usual from a carbon perspective) and it doesn't leak.

This means that it could be a very useful offset opportunity as part of a policy for emission reduction.

The biochar solution

A product that occurs naturally, that can be manufactured from waste and used to both increase food production and sequester carbon sounds too good to be true.

Well it is true for biochar and environmental management too, and has been called the biochar solution.

Before we get too carried away there is no magic bullet to the problem of climate change nor is their one for food security and that makes one bullet for both crazy talk.

And as we stand there is a major barrier to implementing the biochar solution — it costs too much.

For the moment it is hard to make money from biochar, although that could change. The economics of char production hinge on the availability feedstock, the reliability of the kilns and, most importantly, the price of oil.

Biochar and environmental management just needs these stars to align.It is likely that one day charcoal will again be used as a fertilizer and not just to boil the rice.