______ leads to accumulation of a dark coloured amorphous substance called ______ that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.

Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.