Biochar is a carbon-rich product obtained from the pyrolysis of biomass. As the central element of a new and highly promising integrated soil management technique it is capable of halting slash-and-burn farming in the humid tropics by making nutrient-poor, acidic soils productive. As such it offers one of the few sustainable strategies to halt deforestation while simultaneously eliminating hunger amongst subsistence farmers at the forest margins. Biochar doubles as a stable carbon sink, making it a key tool in the climate fight. 

Current slash-and-burn techniques	The alternative: slash-and-char	Biochar and electricity

Current practises 

Some 300 to 500 million subsistence farmers in the tropics rely on a land-use technique known as "shifting cultivation", which involves "slash-and-burn" practises. A patch of pristine rainforest is cleared to make available land to grow crops. However, during the clearing, the standing biomass is burned, releasing large amounts of emissions. Tropical deforestation is responsible for an estimated 20 percent of global greenhouse gas emissions. Reducing it is therefor a priority to tackle climate change. What is more, deforestation leads to the loss of unique biodiversity and of valuable ecosystem services. 

A "cycle of unsustainability"

In principle there is nothing inherently wrong about slash-and-burn based agriculture. Forest communities across the tropics have been practising the technique for millennia, allowing the forests to regenerate. But with modern population growth and the pressures on land resources that result from it, the practise has become unsustainable. Fallow periods are shortened and soils are not allowed to replenish themselves.

The key problem related to slash-and-burn farming is the rapid loss of soil nutrients. Once a forest has been cleared, there is no canopy any longer to protect soils from heavy tropical precipitation. The small amounts of nutrients contained in these already poor soils get quickly washed away after one rainy season, while the remainder leaches over the following years. A rich diversity of decomposers empties the soil further. Cleared of vegetation, the exposed surface is also easily eroded. What is left is a nutrient poor soil in which not much grows. Adding fertilizers is largely futile, because these too get washed away. Moreover, their benefits are small compared with the high costs. Subsistence farmers in these parts of the world do not have access to fertilizers, and would not be able to buy them.

Even though the bare, poor soils are located in a humid climate, they do not retain water easily. This limited water retention capacity, felt during drier periods, further limits productive agriculture. 

Another major problem encountered in the humid tropics is the high acidity of the soils. The land that is made available through slash-and-burn mainly consists of acidic ferralsols (oxisols) and acrisols. These soils are characterized by a pH which is strongly (5.5-4.5) to extremely acid (<4.5), a low cation exchange capacity and a low base saturation. This limits the type of crops that can be grown and generally results in very low productivity. Making soils less acidic requires access to inputs like agricultural lime - which is often unavailable for subsistence farmers at the forest frontier. 

Because of these two factors - rapid nutrient loss and high soil acidicity - farmers are forced to search for new land after only a few years. Typically, crop yields decline dramatically after 2 to 3 years, making the land useless. Farmers cannot produce any surplus, and are forced to slash-and-burn further in order to survive.

Reversing the cycle

The Biochar Fund helps reverse this cycle by introducing a sustainable land use practise based on restoring soil health in such a way that land becomes permanently productive. This allows farmers to grow more food, end hunger and phase out slash-and-burn.

Biochar is a type of charcoal with specific properties obtained from pyrolysing biomass. Instead of burning standing biomass from cleared forest, the resource is charred (in practise, only the vegetation of secondary forests that have sprung up on fallow plots is charred; in a later stage, field residues from biochar based agriculture become the feedstock). Fine particles of this porous biochar are added to the nutrient poor soils to remediate their problems.

The two pillars that make biochar revolutionary are the extremely high affinity of nutrients to biochar (adsorption) and the extremely high persistence of biochar (stability).

Nutrient Affinity
All organic matter added to soil significantly improves various soil functions, not the least the retention of several nutrients that are essential to plant growth. What is special about biochar is that it is much more effective in retaining most nutrients and keeping them available to plants than other organic matter such as common leaf litter, compost or manures. Interestingly, this is also true for phosphorus which is not at all retained by 'normal' soil organic matter. 

Persistence
It is undisputed that biochar is much more persistent in soil than any other form of organic matter that is commonly applied to soil. Therefore, all associated benefits with respect to nutrient retention and soil fertility are longer lasting than with alternative management.

Extensive research and trials show that biochar amendments result in measurable improvements of all the key parameters that make soils productive:

1. Biochar increases the cation exchange capacity (CEC) in soils.

2. Biochar enhances soil microbial functions. The porous structure of char forms a safe haven for microbes that make nutrients available to crops.

3. Biochar improves the nutrient retention capacity of soils by preventing leaching and erosion; this allows farmers to use organic and inorganic fertilizers in a cost-effective manner.
   

4. Biochar improves the water retention capacity of soils; the porous structure of the material holds water and prevents the moisture from evaporating.

5. Biochar increases the pH of acidic soils; depending on the soil, the effect can be similar to that of lime additions. 

Crop trials with biochar amendments combined with organic and inorganic fertilizers in highly weathered, acidic tropical soils have shown impressive yield increases that can be sustained over years. In some cases productivity showed an 840% increase compared with non-amended soils and with soils that only received fertilizers.

By making soils fertile, biochar helps reverse an unproductive, destructive land-use cycle. This has wide-ranging social and environmental benefits: food insecure rural communties get rooted on productive soils, where they can grow more food and biomass that can be further sequestered. This firmly enhances their livelihoods and contributes to ending hunger in a structural manner. The improved productivity also reduces the need to clear biodiversity-rich forests, and limits the carbon emissions that go with this.

The improved soils not only yield more food, they also yield more residual biomass from the crops. This large biomass resource becomes the feedstock to produce more biochar, which can be continuously added to the soil. What is more, when the biomass is used in advanced pyrolysis systems, it yields electricity from the syngas. This makes it possible for rural communities to gain access to efficient, renewable and affordable energy services. Because the energy is generated from locally available field residues that are converted in clean pyrolysis facilities, communities are no longer forced to burn wood fuels. Primitive biomass use is responsible for both large amounts of greenhouse gas emissions as well as serious health problems. By coupling biochar production to modern energy production, these problems can be effectively solved.

The Biochar Fund conducts its own biochar trials in selected, difficult locations amongst extremely poor rural communities at the forest frontier. Current test sites are located in the Democratic Republic of Congo and in Southern Cameroon. Research findings constantly inform and improve the development of biochar strategies suited for implementation by rural communities. The goal is to expand optimised biochar systems to as many slash-and-burn farmers as possible.

A stable carbon sink

The long persistence of biochar in soil makes it a prime candidate for the mitigation of climate change as a potential sink for atmospheric carbon dioxide. When biochar is stored in soils, it constitutes a stable, manageable and measurable carbon sink. Research into ancient terra preta soils (Amazonian Dark Earths) has shown that charcoal remains unaltered in soils for thousands of years. Modern biochar is equally inert and oxidizes only over very long periods of time. 

Nutrient poor tropical soils can store large amounts of biochar ranging from tens to hundreds of tonnes C per hectare while improving soil health. As such they can become permanent carbon sinks that help mitigate climate change in a major way. Another key advantage of biochar systems in the tropics is that they help slow deforestation and its large associated emissions. Finally, when biochar is produced in efficient pyrolysis systems, it can offer modern, carbon-negative electricity from syngas to people currently without access to efficient energy services. This prevents communities from using biomass in a primitive, climate-destructive way, as is the norm today. Thus, biochar systems can play a key role in mitigating climate change in three potential ways:

1. biochar soils are stable carbon sinks that can be built up over time and remove CO2 from the atmosphere; soils can accumulate hundreds of tonnes of C while improving soil functions 
2. biochar systems halt slash-and-burn agriculture, and thus slow deforestation and the large emissions that go with this
3. biochar produced in efficient pyrolysis plants offers clean, renewable electricity that eliminates the emissions from burning biomass in a primitive way 

Terrestrial carbon sequestration is recognised both by the International Panel on Climate Change (IPCC) as well as by the European Union as a viable method to reduce emissions. However, this technique to offset carbon emissions has not been taken up in the Kyoto Protocol (and its Clean Development Mechanism). Scientists, NGOs and conservation groups are therefor advocating its inclusion in a post-Kyoto agreement.

The Biochar Fund's aim is to connect poor farmers in the tropics who implement the carbon sequestration technique to voluntary carbon markets, until the system is recognised in the post-Kyoto framework. 

Importantly, biochar amended soils have also shown to reduce nitrous oxide (N₂O) emissions from agriculture considerably. N₂O is a greenhouse gas 300 times more potent than CO₂ and is mainly associated with the use of nitrogen fertilizers. Since the Biochar Fund makes available nitrogen fertilizers to poor farmers, the simultaneous implementation of biochar amendments offsets much of the associated N₂O emissions from the very start.

Reducing deforestation through biochar

There are several proposals aimed at reducing or avoiding deforestation in the tropics. However, these are "top-down", bureaucratic schemes that present major economic and social risks to the communities at the forest margins. When the real costs of these proposals are taken into account, they prove to be very costly.

Biochar on the contracy offers a "bottom-up" and cost-effective approach that results in multiple, concrete benefits for the communities involved. In contrast with other proposals, biochar systems are managed by the subsistence farmers themselves, who are guaranteed the carbon credits. 

A comparison of biochar and top-down schemes can be found here .