Soils of Andhra Pradesh

 

The State is endowed with a wide variety of soils having less fertile coastal sands to highly fertile and productive deltaic alluviums of major river basins developed from different parent materials. The major soil groups are red and laterite, black, alluvial and coastal soils occupying 66, 25, 5 and 3 per cent of the total area, respectively.

Red soils

The red soils include red sandy soils (Dubbas and coarse chalkas), red earth with loamy subsoil (medium and fine chalkas) red loamy soils (shallow to moderately deep), red loamy soils deep to very deep and red soils with clayey sub soils. These soils are in general, rapidly to moderately permeable with good drainage conditions. Soils are neutral in reaction (pH 6.5 to 7.5) and non saline. The clay minerals consist of a mixture of kaolinite and illite with low to medium Cation Exchange Capacity (CEC). They are prone to erosion.

Red sandy soils

These coarse soils have an effective depth ranging from 20 to 60 cm indicating that they are shallow to moderately deep. The pH of the soils varies from 6.5 to 7.5 and these are non saline. The soils are rapidly permeable with intensive leaching exhibited under heavy irrigation or high intensity rain fall conditions. The clay content is usually < 15 per cent . These soils have low base exchange capacity and are poor in fertility.

Red earths

These soils show a loamy or clay sub soils. The soils with the former usually exhibit pH ranging from 6.5 to 7.5 and occur on the elevated regions nearer to hills , hill ranges and on sloping terrains. These are non saline and have low CEC. The surface drainage is good to excessive. The soils vary in depth ranging from as low as 8 to 75 cm (shallow to moderately deep). The red earths with clayey subsoil show rapid permeability at surface while the subsoil is moderately permeable. pH of these soils is ranging from 6.5 to 8.0 and these soils show more CEC than the ones with loamy sub soil. The effective depth of these soils ranges from 30 to 75 cm.

Red loamy soils

Based on depth, these soils are shallow to moderately deep red loamy soils and deep to very deep red loamy soils. The former usually have depth ranging from 20-39 cm and occur where the area was subjected to severe erosion. The surface coarse texture favor easy drainage while the subsoil is denser tending to show more clay with depth. The latter category exhibits variation in drainage viz., well drainage with light textured sub soil and moderately well to well drainage with clayey subsoil.

Laterite soils

Laterite soils are deep (0.9 to 1.8 m) to very deep (> 1.8 m), medium to fine textured with clay subsoil and rapidly permeable and well drained. These soils are formed under conditions of high rainfall with alternate wetting and drying period. The leaching of the bases leads to development of soil acidity with soil reaction (pH ) values as low as 4.0 to 5.0, in a general pH range of 4.0 to 6.0. Soils are non saline. The soils have very low CEC and ,hence, are poor in fertility.

Black Soils

These soils have a local name as regur. Deep black soils (Vertisols) have high clay content (30- 60 per cent or more) and , hence, are slowly permeable and ill drained. They exhibit an effective depth of over 180 cm. The pH ranges between 8.0 to 9.0. These soils are usually non saline at surface but salt content increases with depth. The soils exhibit high base exchange capacity due to high clay content. Moderately deep soils are loamy to clay loamy with clay sub soil, moderately drained, neutral to moderately alkaline in reaction (pH 7.0 to 8.5), non saline but have higher salt content than red soils. These soils are also having similar fertility characteristics as above.

Deltaic alluvium

These soils occurring in major river deltas have finer fraction ranging from 60 to 70 per cent. They are very deep (> 1.8 m) and lack of profile development. Drainage is a main constraint in these soils. Water table occurs within 5 cm depth coming up to ground level in basins. These soils are neutral to alkaline (pH 7.0 to 9.0) and marginal to highly saline. Clay mineral composition shows wide variations. The CEC of soils is usually high and, hence, they are productive. Taxonomically, these are Entisols and Vertisols.

Coastal soils

These are very deep (1.8 to 5.0 m and above), coarse textured with sandy sub soil, belonging to the order Entisols. The soils are rapidly permeable, neutral in reaction (pH 6.5 to 7.5) with sub soil salinity due to shallow water table and low CEC due to very low clay contents.

Salt affected soils

It is estimated that about 1 per cent of the total area of the state is under the problem soils like saline, saline-alkali and non saline alkali soils mainly occurring along the sea coast, streams and are usually interspersed in black, red and alluvial soils.

Saline soils

These soils occupy considerable area in coastal districts of the state with salts contents exceeding even 0.2 per cent reaching a high concentration of even more than 4.0 per cent. The soils have low Exchangeable Sodium Percentage (ESP) of less than 15. The pH is around 7.0 and seldom goes beyond 8.5.The high water table can cause moist conditions at the surface.

Saline – alkali soils

These soils are also occurring in the coastal districts and in some hinterland areas along the stream sides. The pH ranges from 8.0 to 10.0 while the salt content was found ranging from 0.3 to 1.5 per cent or even above. The water table is usually shallow showing not only high salt contents but also the presence of alkali carbonates.

Non saline alkali soils  

Though the pH values are similar to the above category, the salt content generally is low. The ESP values exceed 15.These soils have poor physical conditions and exhibit even water logging due to dispersion of clay clogging the pores. Though depending upon the salt content, the saline soils can be of some fertility value, the other two categories exhibit poor fertility and physical conditions affecting the crop production seriously. Management of these soils requires implementation of technologies generated so far specific to the given type of problem soil to improve its productivity .

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