SOILS OF PAKISTAN
The soils in Pakistan are affected by arid climate,therefore belong to dry group,rich in basic having a high calcium carbonate content and poor in nitrogenous matter.They vary in colour from reddish brown in north to red or gray in south.The soils at the foot of mountains are sandy but becomes finer towards plains where lime concentration is occasionally found.These are derived from two types of parent material:
1) Alluvium,loess and wind blown sand.They are of mixed mineralogy.The newly deposited alluvium near the river is called khaddar and mostly consists of sand.The old alluvium of the bar uplands,called bangar consists of loams .The soils of the Thal and Thar deserts and Baluchistan are wind blown.In southern potwar a thin layer of residual slit is found . In parts of canal irrigation lands,salt afforescences are found,generally in the areas of high water table.These saline areas are known as thur or kallar.
2) Residual material obtained from weathering of underlying rocks.Most of the rocks are calcareous.In some areas granites have produced non –calcareous soil material.very small quantities of salts are released from most of the rocks. The soils are therefore,essencially non-saline.
The soils of Pakistan has acquired distinct characteristics from the parent material and by their mode of formation.The river-laid sediments have developed into alluvial soils.The desert sand have turned into distinct soils.The hills ,mountains and the plateaus produced residual soils with patches of alluvial ,loess and other soils.The soils of Pakistan can be classified into the following six soil types:
1. Black soils The principal region of black soils is the Deccan plateau and its periphery extending from 8°45’to 26o north latitude and 68o to 83o45′ east longitude. They are formed from Deccan basalt trap rocks and occur in areas under the monsoon climate, mostly of semi-arid and sub-humid types. The overall climate of black soil region may be described as hot and dry summer, 40-100 ...
1) Alluvial Soils of the Flood Plains:
The flood conditions differ from one region to another within the flood plains of Pakistan.This is because areas close to rivers are flooded each year,areas away from rivers are inundated in years of sever floods,while coastal areas are subjected to tidal flooding.This has affected the soil texture, soil water, soil pH, and other soil characteristics and led to development of different types of soils such as:
a: Loamy and Sandy Soils:
The soils develop in active flood areas and occupy the narrow strips along Indus river and its tributaries, the Jhelum,
The Chenab , the Ravi and Satluj.These soils are characterized by presence of sand and loam ,however the loam dominates the area.
b: Loamy and Clayey Soils:
These soils are found in old flood plains that lie between the active flood plains and the Bar uplands in the northern Indus plains and between the active flood plains and the desert region in the southern Indus plains. These soils are considerably stable and homogenized with saline and alkaline patches found here and there.Loam is the predominant soil and pH ranges from 8.0 to 9.0.
c:Loamy Saline Estuarine Soils:
These soils occupy a major part of Indus delta from levees to the back slopes of the Indus and its distributaries.These soils are low in organic matter,saline in most parts and their pH ranges from 8.0 to 8.5.
2) Alluvial Soils of the Bar Uplands:
These soils are located well above the flood plains in Kiran Bar, the Sandal Bar and Nili Bar areas. These soils are rich in lime , their texture is silt loamy and clay loamy , are quite fertile ,and extensively cultured with the help of irrigation.
3) Soils of the Piedmont Plains:
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Most of Pakistan soil has developed on the extensive deposits of the Indus River and its tributaries. The soil belt covers most of the plain areas of Punjab and Sindh.Aluvial soils also develop in areas of Balochistan and Pishin Basins and Makran coastal plains.Poorly developed soils also occur in desert areas of Thar , Cholistan ,Thal and Kharan.
But a large part of the soils in northern, northeastern and western mountainous regions either overlie calcareous or argillaceous rocks. However in these areas soils also form on igneous rocks of acidic to intermediate composition.
The soils of Pakistan are derived from two types of parent materials:
1)Alluvium , loess and wind –reworked sands. They are of mixed mineralogy. The formation of soil profile is a complex process which involves weathering, leaching, precipitation and blending together of minerals and organic matter. The blending together of the minerals and other organic matter in soils by the action of micro organisms involves a long period of time .Homogenization, which is a common process of soil formation in Indus Plains, requires about 20 years for the upper one foot of the soils and about 100 years for the next lower foot.
2)Residual material accumulated due to weathering of the underlying rocks .Most of these soils overlie and derive from rocks that are characteristic of each of the Himalayan subdivisions described above .If we consider the mountainous belt of Pakistan as a whole , calcareous , argillaceous and arenaceous rocks are predominant protoloiths. In the igneous group of rocks granitoid , tonalities , dionities and their equivalents predominate .Basic and ultra basics rocks are clearly minor. Metamorphic rocks are exposed aver a small areal extent mainly in the north and are composed of pelite –psammites , marbles and calcpelites. The characteristics of the soils developed over these rocks depend to varying degrees on the protolith.Very small quantities of salts are released from most rocks and soils are therefore nonsaline.Saline playa lakes , which are small in areal extent , are exceptions . Soil formation is a complex phenomenon and therefore takes considerable time. The conversion of the bedrock into regolith is a time consuming process.
CLASSIFICATION OF SOILS
The soils of Pakistan have acquired distinct characteristics from the parent material and by their mode of formation .The river- laid sediments have developed into alluvial soils. The topographic differences within the region covered with alluvial soils have produced textural, chemical and other differences. Therefore it is possible to subdivide the alluvial soils. The desert sands have turned into distinct soils. The hills , mountains and plateaus have produced residual soils with patches of alluvial , loess and others soils , accordingly the soils of Pakistan can be classified as given in Fig and are discussed below.
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1) Alluvial Soils of the Flood Plains.
Within the flood plains of Pakistan, flood conditions differ from one region to another. Areas close to river are flooded every year .Areas at some distance from the rivers are inundated in years of severe floods, while the coastal areas are subjected to tidal flooding. This has affected the soil texture, the soil water, the soil pH and other soil characteristics. Accordingly different areas have developed the following different types of soil.
a) Loamy and Sandy Soils.
The active flood plains are covered with loamy and some sandy soils. They occupy narrow strips along the Indus River and its tributes , the Jhelum , the Chenab , the Ravi and Sutlej.They are most extensive along the Indus River ,where they are (15 to 25 m) 25 to 40 km wide. Braided channels of the streams are covered with these soils. They are flooded and are free from salinity. These are renewed with fresh deposits of alluvium; whenever the area is flooded .Loams dominates the area.
b) Loamy and Clayey Soils.
The old plains are covered with loamy and clayey soils. These flood plains lie between the active flood plains (bet) and the Bar Uplands in the northern Indus Plains and between the active flood plains and the desert region in the southern Indus Plains. The old flood plains were subjected to flood in the recent past. At present they remain free from flood in most of the years. Only in years of heavy rainfall they are locally flooded. Therefore the soils have experienced considerable stability and are appreciable homogenized. Saline and alkaline patches are observed here and there locally flooded. Therefore the soils have experienced considerable stability and are appreciably homogenized. Saline and alkaline patches are observed here and there, particularly close to the desert area. In such patches the pH values range from 8.0 to 8.4 and in exception cases upto 9.0 Loam is the predominant soil with patches of clayey soils on the back slopes and in the meander scars and the channel infill .The levees and meander bars slopes are covered with sandy loams. The color ranges from brown in humid and well-drained areas to grayish brown in dry areas.
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c) Mainly Loamy Saline Estuarine Soils.
A major part of the Indus Delta excluding the tidal plains is covered with loamy saline soils. The meander bars are covered with sandy loams and channel in fills with clayey soils .In general the soils are porous .They are low in organic content .However the back swamp deposits are richer in organic matter .Homogenization has not progressed much .In most parts , the soils are saline .The pH values range from 9.0 to 8.5.
d) Soils of the Tidal Flats.
The tidal flats occupy the coastal areas along the Indus Delta. The soils are mainly clay derived from the sediments deposited by the Indus and reworked by the tides. In low-lying areas the tides visit twice a day whereas in slightly higher areas they come twice a month.The soils are stratified. The sea water has turned the soils highly saline. Sodium chloride is the main salt. There are some tidal lakes, which occasionally get filled with sea water .The sea with fine silicates sediment .This process may leave profile with high salt contents.
2) Alluvial Soils of the Uplands.
The Bar uplands (the Kirana Bar, the Sandal Bar and the Nili Bar) are Pleistocene interflutive alluvial terraces .They are well above the flood plains and have developed mature soils. They are classed as Noncalcic brown in the sub- humid areas where the soils have been leached almost free of lime. In the arid areas they are classed as Brown Soils or Sierozems. Considerable leaching of lime has taken place from Sierozems also but not as though as that from the Noncalcic Brown. In both the soils a layer rich in lime occurs at about three feet from the surface. Whereas such horizons with lime (Kankar) are encountered the SPT values register a substantial increase. Texturally the soils are silt loams and clay loams. The soils are quite fertile and are extensively cultivated with the help of irrigation. The areas therefore are densely populated and there is a lot of building activity.
Soil is a natural body consisting of layers (soil horizons) of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. Soil is composed of particles of broken rock that have been altered by chemical and environmental processes that include weathering and erosion. Soil differs from its ...
3) Soils of the Piedmont Plains.
The Piedmont Plains cover an extensive area between the Sulaiman-Kirthar Mountains and the Indus River. The relatively smaller areas occur in the northern part of the Punjab along the Pir Panjal Mountains. The foothills of these mountains are occupied by stony fans and aprons which are formed of loose material washed down front the mountains by occasion heavy rainfall. The streams beds are filled with gravel and coarse sands. Some fine material is arrested between the gravel and stones.Thses predominantly stony soils