A History of Agriculture in India v1.c8.s2.t2: Black Cotton Soils
A History of Agriculture in India v1.c8.s2.t2
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Black Cotton Soils
v1.c8.s2.t2.1
The typical soil of the Deccan Trap is the *regur* or black cotton soil. It is common in Maharashtra, in the western parts of Madhya Pradesh, Karnataka, and some parts of Tamil Nadu, including the districts of Ramnad and Tinnevelly in the extreme south. It is comparable with the chernozems of Russia and with the prairie soil of the cotton-growing tracts of the United States of America, especially the black adobe of California. It is derived from two types of rocks: the Deccan and Rajmahal Trap, and the ferruginous gneisses and schists occurring in Tamil Nadu under semi-arid conditions. The former attains sometimes considerable depths, whereas the latter are generally shallow.
v1.c8.s2.t2.2
The black soil areas have, generally, a high degree of fertility, though some, mainly in the uplands, are of low productivity. The soils on the slopes and the uplands are somewhat sandy, but those in the broken country between the hills and the plains are darker, deeper and richer, and are constantly enriched by deposits washed down from the hills.
v1.c8.s2.t2.3
Black soils are highly argillaceous, fine-grained, and dark with a high proportion of calcium and magnesium carbonates. They are very tenacious of moisture, and are exceedingly sticky when wet. Owing to considerable contraction on drying, large and deep cracks are formed. They contain much iron and fairly high quantities of lime, magnesia, alumina, and potash. However, they are poor in phosphorus, nitrogen and organic matter. In all regur soils, in general, and in those derived from ferromanganesian schists, in particular, there is a layer rich in kankar nodules formed by the segregation of calcium carbonate at some depth below the surface and above the weathered rocks. The soils are generally rich in montmorillonitic and beidellitic groups of minerals.
v1.c8.s2.t2.4
In Maharashtra, the soils derived from the Deccan Trap occupy quite a large area (Fig. 6). On the uplands and on the slopes, the soils are light-coloured, thin and poor. On the lowlands and in the valleys, relatively clayey black soils are found. Along the Ghats, the soils are very coarse and gravelly. The soil is often some 6 metres deep in the valleys of the Tapti, the Narmada, the Godavari and the Krishna rivers. The subsoil contains a good deal of lime. Outside the Deccan Trap area, the black cotton soil predominates in the Surat and Broach districts of Gujarat.
v1.c8.s2.t2.5
In Madhya Pradesh, two distinct kinds of black soils are found: (i) deep heavy black soil covering the Narmada valley, and (ii) shallow black soil. The cotton-growing areas generally have deep and heavy black soils, though soils of lighter texture are also found.
v1.c8.s2.t2.6
The black soils of Karnataka are fairly heavy, with a high salt concentration. They are generally rich in lime and magnesia.