Humus
Topic: Geomorphic Processes: Weathering, Mass Movement, Erosion and Soil Formation · NCERT: Class 7, Ch 1 "The Story of Indian Farming"; Class 11, Ch 5 "Geomorphic Processes"
Meaning
Humus is the fine, dark organic matter in soil. It forms when bacteria and other tiny organisms break down dead leaves, plants and animals. Humus holds water and nutrients, which makes soil fertile. How much humus builds up depends on climate. In cold climates bacteria work slowly, so humus collects. In humid tropics dead matter oxidises (combines with oxygen and breaks down) quickly, so humus stays low.
Example
The forest soils under the cold coniferous forests of the Himalayas have a thick, dark top layer. This is because dead needles and leaves rot slowly there and humus builds up.
Don't confuse with
- Peat: humus is well-rotted, fine matter mixed into the soil. Peat is half-rotted plant matter that piles up in cold, waterlogged places.
- Laterite: laterite is a soil that is low in humus because the hot, wet tropical climate breaks down organic matter fast.
Related concepts
- Soil-forming factors
- Parent material
- Residual and transported soils
- Climate as a soil-forming factor
- Eluviation
- Illuviation
- Desilication
- Peat