Humus - The top layer of soil that contains not only rocky particles, such as clay and sand (generally a small proportion) and water,  but also dead and rotting leaves,  dead wood,  dead animals (eg mammals, insects, mollusks) and feces.   Bacteria, protists and fungi thrive in this zone, causing decomposition.   Humus is rich in nitrogenous nutrients, which are the by-products of decay and are used mainly by plants as a fertilizer for growth.  The humus is an essential part of Rainforest (and most other) ecologies.

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