Soil
Topic: Geomorphic Processes: Weathering, Mass Movement, Erosion and Soil Formation · NCERT: Class 7, Ch 1 "The Story of Indian Farming"; Class 10, Ch 1 "Resources and Development"; Class 11, Ch 5 "Geomorphic Processes"
Meaning
Soil is a living, changing mixture of mineral particles, organic matter, water and air. Chemical, physical and biological activity goes on in it all the time. It is both a result of decay (of rocks and of dead plants and animals) and a medium for growth (for plants). Soil changes with the seasons. Biological activity slows or stops when soil is too cold or too dry, and organic matter increases when leaves fall. Soil forms very slowly. According to the FAO, forming 1 cm of soil can take up to about 1,000 years.
Example
The alluvial soils of the Indo-Gangetic plains, spread across Punjab, Uttar Pradesh, Bihar and West Bengal, are rich in minerals and organic matter. They support some of the most intensive farming in India.
Don't confuse with
- Weathering mantle (regolith): the loose layer of broken rock over solid bedrock. It is only the raw material. It becomes soil once organisms add humus, pores, air and water.