The application of wood ash to soil has been a commercial farming practice since 1790 with the first patent of a potassium soil supplement from burnt trees. Also known as potassium ash or potash, the potassium carbonate molecule remains very important as one of the three primary macro elements in synthetic fertilizers, recognized as NPK (Nitrogen, Phosphorus, Potassium).
Unfortunately today, cheap potassium is primarily a product of mining salt and coal, which are energy intensive and a detriment to our environment. The process also puts toxic heavy metals such as cadmium and arsenic into the environment as many learned from the Tennessee River coal ash disaster a few years ago.
Potassium from wood ash is an organic carbon based source, though it requires heat energy to produce. But when derived locally, from homes and farm wood burning kiln or fire pits, it makes use of an existing waste product, that does not pollute with heavy metals. From coal mines, extraction and combustion, is a destructive and wasteful process.
Wood ash may raise the pH of the soil due to the alkalinizing effects of potassium. It also contains important trace elements that are not present in coal derived ash. Aside from muddying up the soil, even with heavy application, wood ash is not harmful to plants. It is used in moderation on acid loving plants and may contain too many salts for seedlings.
Biochar is a newly advanced form of carbonized plant materials that is gaining attention among soil scientists and those optimizing non-soil hydroponic and aquaponic growth media. This rich carbon matter is derived from other burnt farm products such as straw, sawdust and coconut coir.
Upon adding it to soil or soil-less growth media it contributes trace elements, potassium plus other macro minerals; plus it possesses physical and electro-physical characteristics that dramatically improve plant growth and produce yield. Referred to by scientists at University of Georgia Agriculture Department in Athens Georgia, as “black gold” for agriculture, biochar sequesters CO2, it protects soil microbes, retains water and nutrients.
Unlike typical ash which burns in high oxygen environment, biochar is made from low-oxygen burning methods such as a rocket stove or specialized kiln cooked to a temperature as high as 1000 degrees Fahrenheit. A simple version may easily be made from a modified steel drum.
Image Source: BEST Energies