Explain the following :(i) Leaching(ii) Humification and mineralisation(b) What is humus?

Answer: Steps of decomposition: leaching washes soluble nutrients down; humification forms humus; mineralisation releases inorganic nutrients from humus.

(a)(i) Leaching: the process in which water-soluble inorganic nutrients released from detritus percolate down into the soil horizon and get precipitated as unavailable salts.

(a)(ii) Humification: the formation of a dark, amorphous substance called humus from partially decomposed detritus. Mineralisation: the slow degradation of humus by certain microbes, releasing inorganic nutrients (minerals) into the soil.

(b) Humus: dark-coloured, amorphous, colloidal organic matter formed during decomposition. It is highly resistant to microbial action and decomposes very slowly. It acts as a reservoir of nutrients and improves the water-holding capacity and aeration of soil.