Biochar can be defined as a charcoal produced for some biological purpose; to enhance soil fertility, as a livestock feed additive, for soil remediation in case of contamination, or to reduce nitrate and phosphate levels in agricultural water runoff. For such uses, particularly for soil fertility, the molecular structure of the char matters.
Plants have evolved over hundreds of millions of years to obtain their nutrients from topsoil, which is made of decomposed biomass ( humic matter) and minerals. The minerals are mostly positively charged, while the humic matter is negatively charged. Hence they bind together to form fertile topsoil. This happy marriage makes these minerals available to plant roots, particularly the more shallow roots of agricultural plants.
If we want to produce a biochar that optimally enhances soil fertility, we might start with the assumption that it should be as similar to humic matter in molecular structure as possible. Why? Because soil biochemistry, and the plant life it supports, will likely respond to such a biochar in the same way as they respond to humic matter. Soil, soil microorganisms and plants have evolved symbiotically over eons. This complex, mutually supportative ecosystem will not adapt to any novel idea simply because it seems good to us. Rather we must ensure our agricultural innovations are adapted to soil ecosystems.
Scientific research supports this simple assumption. The cation exchange capacity (CEC) of biochar, its ability to retain plant nutrients, depends on its molecular structure. Biochar particles produced at low temperatures will have high CEC levels because of the negatively charged OH functional groups on its molecular surfaces.1