Short notes on the Laterite Soils

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These soils were first of all studied by F. Buchanan in 1905. Their name has been derived from the Latin word ‘Later’ meaning brick. When wet the soils are as soft as butter but become quite hard and cloddy on drying. These are the typical soils of the tropical areas characterised by seasonal rainfall (monsoonal conditions).

The alternations of wet and dry season leads to the leaching away of the siliceous matter of the rocks and the formation of such soils takes place. According to some scholars the lateritic weathering of basic and intermediate rocks like granite by hydrolysis is responsible for the formation of such soils.

Their red colour is due to the presence of iron oxide; the colour being yellow-grey on the top and red below. The main development of these soils has taken place in the highland areas of the plateau.

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Lateritic soils cover an area about j .22 Lakh sq. km (3.7% of the country’s area). These are well developed on the summits of the Sahyadris, Eastern Ghats, Rajmahal hills, Satpuras and Vindhyas. They also occur at lower levels and in valleys. Important areas include Kerala; Chikmagalur, Shimoga, North and South Kanara, Coorg, Belgaum, Dharwar, Bidar, Bangalore, Hasan, KolarandMysore districts of Karnataka; Ratnagiri, Satara, Sindhudurg and Kolhapur districts of Maharashtra; Medak, Nellore and East Godavari districts of Andhra Pradesh; Balasore, Cuttack, Ganjam, Mayurbhanj and Sundargarh districts of Orissa; Barddhaman, Birbhum, Bankura and Medinipur districts of West Bengal; Sibsagar, Lakhimpur, North Cachar Hills and Nowgong districts of Assam; Garo Hills of Meghalaya; and Santhal Pargana district of Jharkhand.

It has been observed that there is a general relationship between altitude and the chemical com­position of laterite soils. The soils on the higher areas are generally more acidic than the low lying areas. The chemical analysis of these soils provides silica 32.62%, aluminium 25.28%, iron 18.7%, lime 0.42%,
phosphorus 0.07%. In general these soils are rich in iron, and aluminium but poor in nitrogen, potash, potassium, lime and organic matter. Although they are of poor fertility but respond favourably to manuring yielding a variety of crops like rice, ragi, sugarcane and cashewnuts.

On the basis of the size of their particles the laterites may be divided into following three sub­types.

(a) Ground Water Laterite-it is a hydrated soil mainly found in areas of excessive soil moisture. The colour is light red and the soil is not very fertile.

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(b) Deep Red Laterite-this is a basic type of laterite where the thickness of layer goes to 0.5m. The soil is generally rich in ferrous oxide and potash but contains less amount of kaoline. The fertility is not high and the soil is utilised in raising plantation (tea) crops.

(c) White Laterite-Due to presence of kao­line its colour is milky or white. The soil is not very important from agricultural point of view.

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