Resources and Development
Soils of India
Tell India's soil types apart and match them with crops.
Soil is slow to make. It takes millions of years to form a few centimetres of soil. What makes it: relief, parent rock, climate, vegetation and other life, and time. Heat and cold crack rock, running water, wind and glaciers break it, and decomposers add humus. Think of crushing a glass: the powder is still glass. In the same way, the parent rock decides much of what the soil is like.
The soil profile (Fig. 1.5). From the top down: top soil (the upper layer), subsoil (weathered rock, sand, silt and clay), substratum (broken parent rock) and finally unweathered bedrock.
Alluvial soil: the most widespread. The whole northern plains are made of it, laid down by the Indus, the Ganga and the Brahmaputra. It is also found in the deltas of the Mahanadi, Godavari, Krishna and Kaveri.
- Bangar (old alluvium) has more kankar nodules.
- Khadar (new alluvium) is finer and more fertile.
- It has potash, phosphoric acid and lime: good for sugarcane, paddy, wheat, cereals and pulses. So these areas are farmed intensively and crowded with people.
Black soil (regur): the cotton soil. Formed from lava in the Deccan trap. It covers the plateaus of Maharashtra, Malwa, Saurashtra, Madhya Pradesh and Chhattisgarh.
- Very fine and clayey, so it holds moisture well.
- Rich in calcium carbonate, magnesium, potash and lime, but poor in phosphorus.
- It cracks deeply in hot weather, which lets air into the soil.
- Sticky when wet, so it must be ploughed soon after the first shower.
Red, yellow and laterite.
- Red soil forms on crystalline igneous rocks in drier parts of the Deccan. Iron makes it red; it looks yellow when hydrated.
- Laterite comes from the Latin later, 'brick'. Heavy rain washes the nutrients out (leaching: remember 'L for laterite, L for leaching'). It is acidic and poor, but with soil conservation it grows tea and coffee in the hills of Karnataka, Kerala and Tamil Nadu, and red laterite suits cashew nut.
Arid and forest soils.
- Arid soil is red to brown, sandy and salty. The heat dries out the water and leaves salt behind, so it has little humus or moisture. A layer of kankar lower down stops water soaking in. With irrigation it can be farmed, as in western Rajasthan.
- Forest soil is found in hilly, forested areas. It is acidic and low in humus near the snow, but fertile on river terraces and alluvial fans lower in the valleys.
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