An average soil sample is 45 per cent minerals, 25 per cent water, 25 per cent air, and 5 per cent organic matter. Different-sized mineral particles, such as sand, silt, and clay, give soil its texture.
Soil is approximately 46 per cent oxygen, 28 per cent silicone, 8 per cent aluminum, 5 per cent iron, and 4 per cent calcium. (CRC Handbook of Chemistry and Physics, 77th Edition).
The most important plant nutrients are nitrogen (N), phosphorous (P), and potassium (K).
In one gram of soil, the number of bacteria ranges from 100,000 to several billion.
Soil stores 10 per cent of the world’s carbon dioxide emissions.
A fully functioning soil reduces the risk of floods and protects underground water supplies by neutralising or filtering out potential pollutants and storing as much as 3750 tonnes of water per hectare.
Topsoil is the most productive soil layer. Natural processes can take more than 500 years to form 2 cm of topsoil.
Climate, vegetation, age of rock, relief and parent rock affect soil formation.
According to the Indian Council of Agricultural Research (ICAR) Indian soil types range from alluvial soil, black soil, red soil, laterite soil to desert soil, mountain soil, saline and alkaline soil, peaty and marshy soil.
Oldest soils in the world:
The sandy soil of the Namib Desert in Africa has existed for more than 55 million years according to the World Wildlife Federation. (Spriggs, Amy. ‘Namib Desert’. World Wildlife Fund. 2011)
According to the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Land and Water’s, the clay soils of Australia are millions of years old and among the oldest in the world.
According to a study in the University of Minnesota, the rocky soil of the Sierra Nevada Mountains is estimated to be 750,000 years old. (Geological Survey Professional Paper, Volumes 1036-1043)