Slash and burn technique is typically a misconduct in agriculture based on the belief that removal of existing vegetation will re- mineralize the soil and benefit to the next succession of plants, having as well the capacity to remove weed and unwanted vegetation and bugs.
Recent studies show that ;
- the edible nutrients provided by burning the vegetation is coming mainly from the destruction of the living ecosystem of the top soil (bacteria, fungus, …) which release minerals and nitrogen then available for plants. In tropical climate most of these nutrients will be washed away or inside the subsoil and only a small percentage will benefit the newly planted vegetation, resulting in a impoverishment of the soil. Only high plants (trees with deep tap roots) will be able to recover these minerals.
- the production of charcoal coming from the burning of the vegetation will not be activated (to be transformed in Biochar) with nutrients since gravity will push these nutrients down or away.
- The belief that ashes are a concentrated material of potassium needs to be put in perspective since most of potassium will be either evaporated with heavy smokes or washed away by rain. Only charcoal represent a stable and persistent material but needs activation.
These believes come mainly from the mimic of the process used by native Indian in the amazon. The difference is that in the latter case the slash and burn process is part of the rotation of a forest succession with a long period of recovery. Intensive agriculture does not benefits from the slash and burn technique, it only accelerates the death of soil ecosystem then lost of fertility and soil compaction. It is a short term technique creating desertification.
Other drives in this popular belief are that fire can renew life, that slash and burn of an existing forest indeed create an important reserve of nutrients and that fire can remove bugs, undesirable for the newly planted vegetation.
A Floresta Nova - A Tropical Food Forest - Brazil - Bahia - Permaculture Training 