Although the terms compost and humus are often used interchangeably, they are not the same. Compost is created through aerobic decomposition while humus is created through anaerobic fermentation.
Aerobic Decomposition Equals Compost
Aerobic decomposition occurs when organic material decomposes in the presence of oxygen. As the nitrogen and carbon react in the presence of oxygen, energy is released in the form of heat. The final result is compost.
Anaerobic fermentation occurs when organic material decomposes in an oxygen-deprived environment. As fermentation occurs the rotting matter releases methane gas. The final product is humus.
Examples of Aerobic Composting
Aerobic decomposition occurs in nature when leaves fall to the ground and combine with other organic matter. Aerobic decomposition can also be a man-made process where people combine organic matter in a compost bin.
Examples of Anaerobic Decomposition
Anaerobic decomposition occurs in nature as well, often in swamps and bogs. When organic matter drops into a bog it settles to the bottom where there is no oxygen and begins to rot.
The process of anaerobic fermentation can be very smelly, but humus can be created by enclosing organic materials in a enclosed plastic container and adding a generous amount of water. Humus is complete when it is dark brown and earthy smelling.