In terms of its use in Namibia, one of the key characteristics of biochar is its capacity for increasing the amount of water held in the soil. The images below show the porous structure of charcoal which give it that capacity. This structure also provides a perfect substrate for bacterial and fungal growth essential for healthy soil.
It is very important that the charcoal is prepared properly before application. This is done by adding the dry biochar to a mixture of water and nutrients, then soaking it for a suitable period. We refer to this as ‘charging’.
The addition of charged biochar at suitable application rates, in this case we start with between 5 and 20 tonnes per hectare equivalent, rapidly increases soil fertility. Soil flora and hence fauna will thrive over time and establish a healthy productive stabilised soil.
Another advantage of adding carbon/charcoal to the soil is to reduce atmospheric carbon and reduce greenhouse gases, helping to attenuate climate change.
Soluble soil nutrients and minerals dissolved in the water are also held in the soil longer. Leaching from the soil is decreased. Also plant root hairs can penetrate the biochar structure and absorb nutrients more efficiently.
Biochar also decreases acidity. It may not produce a rich soil as found in more temperate climes but it can, in conjunction with good land management, help produce a soil that is sustainable and productive.
Any dry biomass can be pyrolyse to form charcoal. In India the SFP has used many types of locally grown unwanted agricultural waste and invasive species of thorn bush to make biochar. Chipped Prosopis wood and paddy (rice) straw amongst them. The same type of materials could be used in Africa.
Surprisingly Namibia is a major exporter of charcoal. Most of this is made from problematic invasive species that choke rivers and drive out indigenous species by aggressively seeking water.
The government is offering subsidies to farmers for which in return they clear portions of their land of these invader species. Other entrepreneurial farmers have then bought the charcoal made from this ‘waste product’, sorted, graded, bagged it and sold it to chainstores in Europe. This has become an important small industry in Namibia providing many jobs.
One of the byproducts is a charcoal dust that cannot be sold for the same profit as other grades. However this charcoal can be used for soil application and the toxicity analysis mentioned below relates to this type of charcoal. In the Sesfontein area where there is no available biomass to make biochar, this could be the answer and it is one of the things SFP is investigating.
A very important part of our work is to ensure that the char we put into the soil is not in any way toxic. One of the properties of biochar is that it will remain in the soil for a long time. Because of this there is no need to keep applying biochar unless you want to increase the overall concentration. There are many theories on what application rates and overall concentrations should be. Decisions will depend on many factors and needs to be researched thoroughly before large scale application begins. Hence the importance of field trials.
Terra Preta soil in South America was first made by human intervention about 600 years ago and that soil is still fertile and producing crops. So it is very important that we ensure the biochar we use is of a high quality. Much work is being done with respect to this qualification and we are working with scientists in Europe and the US to define best practice.
The chart above is comes from a analytical report compiled by the British Biochar Foundation in the UK. It shows results for charcoal made in Namibia that we want to use for our projects.