Bring out the distribution of Laterite soils in India and their specific use for agriculture. (2014)
- Laterite is the end-product of weathering under a hot climate with a strongly seasonal rainfall, where alternating wet and dry spells leach away silica and bases and leave a residue rich in iron and aluminium oxides.
- Its distribution therefore maps not a rock type but a climatic process, and its agricultural value is governed by what that process has removed rather than by what it has left.
Distribution
The summit tracts
- Laterite is developed above all on the summits of the Western Ghats between 1,000 and 1,500 m, and on the Eastern Ghats, the Rajmahal Hills, the Vindhyas, the Satpuras and the Malwa Plateau — high, well-drained surfaces where leaching is most complete.
The lower and coastal tracts
- It also occurs at lower levels and in valleys, and is well developed in south Maharashtra, Karnataka, Telangana, Andhra Pradesh, Odisha, West Bengal, Kerala, Jharkhand, Assam and Meghalaya.
- The Konkan and Malabar coastal plateaux carry the most extensive low-level laterite in the country.
Agricultural Character and Use
The limitation
- Because of intensive leaching and a low base-exchange capacity, typical laterite soils lack fertility and are of little use for ordinary crop production — they are acidic, poor in nitrogen, phosphate, potash, lime and humus, and drain excessively.
Where they succeed
- When manured and irrigated, laterites and lateritics support the plantation crops on which the peninsular coasts depend — tea, coffee, rubber, cinchona, coconut and arecanut — because these are deep-rooted perennials tolerant of acidity.
- In low-lying tracts, paddy is grown where water can be impounded on the impermeable subsoil.
- Laterites in Kerala, Karnataka, the Chota Nagpur region of Jharkhand, Odisha and Assam respond well to nitrogen, phosphorus and potassium, which is why fertiliser response trials on these soils show among the sharpest yield gains in the country.
- Elsewhere the soils carry only grazing grounds and scrub forest.
- A non-agricultural use is decisive locally: laterite cuts easily with a spade but hardens like iron on exposure, making it the traditional building stone of the west coast.
A Reassessment the Older Accounts Miss
- The bare laterite plateaus of the Konkan, locally the sadas, were long dismissed as wasteland. Recent ecological work has shown them to be seasonal-ephemeral ecosystems of high endemism, flushing with specialised herbs after the first rains and supporting distinctive rock-dwelling fauna, alongside ancient petroglyphs.
- They are now being lost rapidly to quarrying, mango and cashew plantation and land-use conversion — so the policy question has shifted from how to make laterite productive to whether all of it should be converted at all.
- Laterite is therefore best judged as a soil of narrow but real capability: agriculturally marginal, decisive for plantation economies, and ecologically far more valuable than its poverty in nutrients suggests.