Humus (humic acid) is the top layer of the soil and is very fertile. It looks like compost, but is degraded further than compost. Humus (humic acid) consists of degraded plant materials. As vegetable material degrades into compost, humus substances are formed. There are three elements that are extracted from these substances:
- Humic acid;
- Fulvic acid;
- Humin.
A humic substance-like compost takes at least 6-12 months to form, but in nature the formation of a humic acid layer takes much longer. A humic acid layer can be as old as 40 million years. A rule of thumb about quality is: the older, the better, and the layer has formed a few meters below ground.
Read more about humus substances here.