What is biochar and how does it work?
Some of the most productive and resilient soils in the world contain significant amounts of “natural” biochar. Like many human discoveries, biochar has likely been invented, lost, and reinvented many times. This is the oldest fresh soil improver you’ve never heard of!
Biochar is a stable, carbon-rich solid produced from organic waste materials that improves soil fertility, horticultural yields, and simultaneously sequesters carbon. Through the basic process of burning organic material in a low-oxygen, low-emissions environment, it could be one of the most powerful tools we have to renaturalize degraded soils and reduce our dependence on fossil fuels.
Below is an excerpt Biochar Handbook By Kelpie Wilson. It has been adapted for employ on the Internet.
When biochar burst onto the soil science scene in the early 2000s, its entry was so dramatic because of the rich contrast between the affluent, dim soil in which crops could be grown and the native soil: highly leached, yellow-red oxysols that could barely hold weed after clearing the jungle vegetation covering them. In these tropical rainforests, almost all the carbon is contained in living biomass.
Once a leaf falls to the ground, it is almost immediately devoured by hungry creatures. Carbon and nutrients circulate rapidly and inexorably as things eat and are eaten. Constant rain washes soluble nutrients into the soil, where microbes and roots feed. Little is left to be stored in the soil.
In contrast, the northern boreal forest accumulates chunky layers of peat formed from partially decomposed plant matter. It is too cool and droughty for life to be very energetic, and carbon builds up in the soil.
When I visited the Amazon with International Biochar Initiative in 2010 we visited an organic fruit and vegetable farm in the city of Manaus, Brazil, 50 kilometers downstream. As I walked between the rows of tomato, pepper and papaya trees, I saw pottery shards scattered everywhere on the surface of the dim soil. These newfangled farmers draw on the legacy of perhaps thousands of years of soil building by indigenous Amazonians.
The value of the land was reflected in the value of the property: land with terra preta was sold for eight times the price of smaller agricultural land. We spent a day on the farm looking at various areas where the soil was more or less enriched with biochar, and we saw a 60-foot-tall orange tree growing in the terra preta soil.
But what makes biochar so valuable? How does it work and how can we employ it to start our own soil formation processes?
Biochar is a heterogeneous and chemically convoluted material, and its effects in soil are tough to distinguish and mechanically explain. Although there are now multi-year field studies showing the beneficial effects of biochar on various crops, it is tough to draw broad conclusions from them because they employ different types of biochar in different soil types and crops. To really understand biochar, it may be more useful to first look at some of the general functions and properties of biochar.
The role of carbon in the soil
To understand biochar, we must first appreciate the role of carbon in soil. Carbon in the soil comes in many forms. There are two main pools of carbon: organic and inorganic. Organic forms can be further divided into recalcitrant carbon and labile carbon. Recalcitrant carbon is stubborn carbon that does not like to change its form because it is already chemically stable. Labile carbon is mobile and variable. Labile carbon is bioavailable (in the form of easily degradable compounds such as oils, sugars and alcohols) and physically available to microbes (unbound to minerals). The pool of organic carbon includes both living and dead bodies, decaying bodies of bacteria, fungi, insects and worms, as well as plant remains and manure.
Inorganic carbon consists of carbonate ions, which usually occur in the form of salts such as calcium carbonate, and dolomite minerals, mainly in the form of rocks and sand. The interaction between mineral compounds and organic carbon produces what we like to call humus, because minerals form convoluted relationships with organic molecules, protecting them from the hungry jaws of microbes.
The evolution of soil shows how the process of its formation works.
Before photosynthetic bacteria transformed the Earth’s atmosphere by filling it with oxygen, soil was nothing more than a mineral mixture of oxygen-free green clays. After oxygen entered the atmosphere, minerals began to react with it, resulting in red iron oxides appearing in the soil. Good organic, affluent and productive soils developed slowly only when algae and arthropods crawled out of the sea onto droughty land and took root. Life colonized the earth and began to dump its wasted, used, discarded parts onto the earth, where it created a carbon-rich feast that allowed fresh life to feed and grow, using photosynthesis to pump more and more energy into the system.
Soil building is the product of a self-reinforcing positive feedback loop – a virtuous cycle. But soil decline is also a self-reinforcing loop (vicious circle) that can result in catastrophic soil loss. Most forms of agriculture tend to deplete soil carbon by reducing the amount of natural organic nutrients from leaf and fruit fall, as well as woody debris, that can be found in native ecosystems.
However, newfangled chemical-based agriculture depletes soil carbon much more dramatically. Nitrogen fertilizers combined with tillage accelerate microbial respiration, burning carbon in the soil faster than it is replaced. Due to the loss of reservoirs of organic carbon, many soils have become almost lifeless substrates that must be constantly fed with irrigation water, mineral nutrients and pesticides to produce crops. While this practice is productive in the low term, it is not sustainable.
Is it possible that biochar can replace some of the missing carbon in the soil?
Some of the most productive and resilient soils in the world contain significant amounts of “natural” biochar. Nature produces megatons of biochar from naturally occurring forest fires. Prairie fires can also generate a lot of biochar. High grasses burn quickly and hotly; however, near the ground where the roots begin, air is excluded, so the base of the grasses will char rather than burn to ash.
This type of natural charcoal is found in some of the most valuable agricultural soils in the world: the carbon-rich chernozems of the Russian steppe and the Mollisols of the midwestern prairie states of the United States.
Scientists recently took a closer look at Mollisols and found that they contain charcoal that is “structurally comparable to the charcoal in Terra Preta soils and much more profuse than previously thought (40-50% organic C).” But as we know, biochar does not work in the same way as organic carbon. Microbes can’t eat it. So how exactly does it facilitate the soil? To really understand this, you have to go to the nanoscale, the scale of electrons.
How can we employ biochar in the soil?
One of the basic principles of good compost production is that the greater the variety of materials used, the better the compost. Bruno Glaser and his colleagues, who studied both terra preta soils and biochar in compost, proposed newfangled material flow management that combines multiple waste streams from agriculture and food processing to produce high-quality compost with maximum carbon sequestration and nutrient balance.
Much of this “waste” today is completely wasted and no attempt is made to extract any value from it. A green approach is indispensable to meet the growing demand for replenishing carbon, nutrients and beneficial microbes in agricultural soils.
An ideal biochar-based composting system would be based on the speculative reconstruction of terra preta soils. According to this model, these areas were initially garbage dumps where food waste, ash and manure accumulated. However, as the population grew, it is possible that they began to realize that landfills were turning into very fertile and productive areas. They may have begun to deliberately manage material flows of plant biomass, mammal and fish bones, ash, biochar, and human excrement, which likely led to the formation of the terra preta soils we see today.
To protect resources as much as possible, remember another rule: Employ less degradable carbon sources, such as biochar, to protect more easily degradable but nutrient-rich sources, such as manure and food waste. By the time food waste reaches the municipal composting facility, it has already begun to rot and lose nutrients. Adding biochar during waste collection could solve many of the problems associated with composting food waste.
I believe there is a lot of exhilarating work ahead to determine the optimal formulations for organic biochar-based composts and ferments, examining the effects of different types of biochar in combination with other compost ingredients.
We recognize from previous and ongoing research that biochar has many possible mechanisms of action in soil, which may occur at different scales. However, if the results of recent biochar compost research prove consistent, we already have the beginnings of a recipe book for biochar-enriched supercompost that can start the process of returning carbon and nutrients to the soil today.
We hope that all this knowledge will facilitate you prepare to experiment with your own recipes using what is available to you.