3. WATERLOGGING
The soil whose surface layers are saturated with
water is called as waterlogged soil.
The phenomenon of rising of water table is known
as waterlogging
5. CAUSES OF WATERLOGGING
1. Seepage of water from canal system
The main cause of waterlogging in pakistan is
seepage of water from network of canal
system.40-50% water is lost from main canals
,seeps through soil and rised the ground water.
In some cases the water table has risen upto root
zones or even surface of soil.
6. CAUSES OF WATERLOGGING
2. Poor surface runoff and slow drainage.
The soil surface of pakistan is flat so surface
runoff is poor and hence slow drainage, result in
accumulation of water on soil surface and move
to the water table under the influence of gravity.
The water table has risen causes water logging
7. CAUSES OF WATERLOGGING
3. Interruption of surface runoff.
Construction of irrigation networks and housing
colonies in the path of natural drains interrupted
surface runoff ,resulting in accumulation of water
in rainy season contributes to waterlogging
through seepage.
8. CAUSES OF WATERLOGGING
4. Rainfall.
After heavy rainfall rain water percolates down
the pores between soil particles under the action
of gravity.
5. Floods.
Flood water spreads on the surface of soil in
plains. Due to inappropriate drainage system, this
water percolates in soil and raise water table
cause waterlogging.
9. CAUSES OF WATER LOGGING
6. Poor water management
Sometimes farmers use their land unscientifically
.
Following activities are major causes of
waterlogging;
Excessive irrigation
Lack of inadequate drainage system.
10. CAUSES OF WATERLOGGING
7. By breaking hardpan at a canal bed.
During cleaning season ,the digging of canals
breaks the hardpan of the soil at canal bed. It
enhances the seepage of water.
8. Railway lines /Roads.
The construction of railway lines and roads in
food plains interrupted the passage of runoff
water ,water collected in rainy season in the form
of ponds ,percolates to soil, Result in
waterlogging.
11. EFFECTS OF WATERLOGGING ON PLANT
GROWTH
Some important effects of waterlogging on plant
growth are given below;
i. The air in the soil pore is replaced by water
,leading to oxygen deficiency and hence reduce
the plant growth
ii. In waterlogged soil transport of gases is reduced
disturbing normal growth.
iii. Limited exchange of gases increase amount of
co2 which affect transpiration and water
absorption.
iv. In absence of oxygen, microbes produce toxis
substances such as methane and effects growth
of plants.
12.
13. EFFECT OF WATERLOGGING ON PLANTS
GROWTH.
v. In waterlogged soil major form of nitrogen is
ammonia which is toxic to crops
vi. Under waterlogged condition the concentration of
phosphorus, iron, manganese, silicon increases
and that of zn decreases. The increase in ferrous
ion concentration is toxic to many crops.
14. RECLAMATION OF WATERLOGGED SOIL
Various control measures are suggested for
reclamation of warelogged soil , the most important
are given below;
i. Seepage interceptor drains.
Seepage interceptor drains may be constructed
parallel to collect seepage water.
E.g. upper Chenab canal
15. RECLAMATION OF WATERLOGGING
ii. Surface drains.
Surface drains also constructed to collect
seepage water ,and proved more effective as
compared to seepage interceptor drain.
E.g. balloki sulemanki link.
iii. Lining of canals.
The canals bed are lined with two layers of tiles
placed above one another and joined together
by cement-sand plaster
E.g. balloki sulemanki link.
iv. Pumping of ground water.
Pumping out ground water by tube wells is
effective to lower the the water table.
16. SOIL SALINITY
Soil salinity refers to presence of salt in root zone of
soil. It adversely affects the growth of plants.
General symptoms of salinity;
Retarded growth.
Smaller plants with few leaves.
Dark green than normal leaves.
17. SALT EFFECTED OR THUR SOILS
The soils in which concentration of salt is very high
are called salt effected soil or thur soil. Salt effected
is a collective term which includes saline, sodic
and saline sodic soil.
It occur commonly in arid and semiarid regions ,
as well as humid and sub humid regions.
Salt effected soil has
sodium,calcium,potassium,carbonates and
bicarbonates.
18. TYPES OF SALT EFFECTED SOIL
a) Primary salt effected soil.
b) Secondary salt effected soil.
a)Primary salt effected soil.
The soil that develops as a result of natural
causes (imperfect drainage of surface and ground
water).are called primary salt effected soil.
19. TYPES.
b) Secondary salt effected soil.
The soil that develops due to accumulation of salt
as a result of rise in ground water table are under
faulty system of irrigation are called secondary salt
effected soil.
20. PROCESSES OF FORMATION OF SALT
EFFECTED SOIL.
a) Salination.
Salination is the process of accumulation of
soluble salts by which saline soil are formed.
b) Desalination.
The process of leaching of soluble salts out of
root zone is called desalination.
c) Sodication.
Sodication is the process of accumulation
exchangeable sodium in the soil which results in
the formation of sodic soil.
21. PROCESS OF FORMATION OF SALT EFFECTED
SOIL.
d) Desodication.
The process of removal of exchangeable sodium
from the soil is known as desodication.
22. CAUSES OF SALINITY IN PAKISTAN.
1. Poor leaching of salts.
2. Irrigation water.
3. Ground water.
4. Other factors .
23. 1. POOR LEACHING OF SALTS.
The original source of salt is exposed rocks and
minerals. During weathering of rocks and minerals
,large quantity of salts are brought in solution. In
arid and semi arid regions evapotranspiration
exceeds rainfall ,and rainfall is not enough to leach
out the salts from crop root zone , therefore this salt
concentration in the soil and ground water cause
salinity.
24. 2.IRRIGATION WATER.
Irrigation water is important source of salts .
However in river water of Pakistan ,concentration of
salt is low , but it still make significant contribution
to the amount of salts in irrigated soil especially
when drainage is poor.
Insufficient and unequal application of irrigation
water results in salinity.
25. 3.GROUND WATER.
Ground water is also significant source of salts in
the development of secondary salt effected soils.
4. Other factors.
Other factors are given below;
Flood water
Inland saline flats
Marine deposits
Salt loving vegetation
Sewage water
Sea water intrusions.
26. CLASSIFICATION OF SALINE SOILS.
Saline soils can be classified on the basis of
following factors;
The appearance of soluble salts on soil
On the % of soluble salts
Determining electrical conductivity of saturation
extracts(measure of quality of soluble salts)
ESP(exchangeable sodium percentage), or
SAP(sodium absorption ratio.
27. CLASSIFICATION OF SALINE SOIL
On the basis of above four factors saline soil is
divided to following three classes;
1. Saline soil.
2. Sodic soil.
3. Saline sodic soil.
28. 1. SALINE SOIL.
a) The soil containing sufficient amount of soluble salts
that hinder the germination and growth of most crop
plants are called saline or thur soils.
b) A white salt incrustation is present on soil surface ,
called white alkali soil.
c) Electrical conductivity of saturation extracts of 4 or
greater , ESP of less than 15, pH is less than 8.5.
d) Chloride and sulphate are the principal anions.
e) The saline soil is highly hygroscopic because of
presence of calcium chloride and magnesium chloride
,absorb atmospheric moisture and surface soil is moist.
29. SALINE SOIL.
f) The saline soil can be reclaimed by adequate drainage
and leaching with water.
30. 2.SODIC SOIL
a) The soil that contain sufficient exchangeable
sodium ions which effect their properties and
plants growth are called as sodic soil.
b) The ESP of sodic soil is 15 or more, electrical
conductivity is less than 4, pH ranges between
8.5-10.
c) The organic matter is dispersed over soil hence it
appears darker and called black alkali.
d) The soil can be reclaimed by applications of
chemicals.
31. 3.SALINE SODIC SOIL
a) The soil that contain both soluble salts and
exchangeable sodium in sufficient amount are
called saline sodic soil / thur bara.such soils are
result of both the processes of salination and
sodication.
b) They have ESP 15 or more , electrical
conductance of 4dsm-1 .the pH is either less
than 8.5 or more.
c) The saline acidic soil is reclaimed by application
of chemicals like gypsum.
32.
33.
34. EFFECTS OF SALT EFFECTED SOIL IN PLANT
GROWTH.
1.Osmotic effect.
Increase in salinity reduce amount of water
available to crops, it result increase in osmotic
pressure so plants required additional energy to
absorb water from saline soil. Only halophytes are
adapted to such soil.
35. EFFECTS ON PLANTS GROWTH.
2. Specific ion effect .
salinity cause specific ion effect(uptake of specific
ion at the expense of other ions). This result in
accumulation of toxic amount of sodium, chloride
and boron ions in plants.
3.Salt tolerance of crops.
Salinity effects salt tolerance of crops (ability of
crop to survive and produce economic yield on
saline soil)
36. RECLAMATION OF SALT EFFECTED SOIL
1. Leaching.
Leaching is application of excess water to soil so
that salts are remove out of root zone.
2.Growing suitable crops during reclamation.
Crops selected for saline soil must be adapted to
wet conditions and tolerant to salt .
37. RECLAMATION OF SALT EFFECTED SOIL.
3.Addition of organic matter.
Addition of organic matter help to increase soil
permeability through promotion of soil aggregation
and release of carbon dioxide during respiration
that dissolve lime.
4.Application of chemicals.
Chemical such as gypsum ,sulphur, sulphuric acid,
hydrochloric acid may be added to salt effected soil
. These chemical lower the soil pH ,reacts with
soluble carbonates and replace exchangeable
sodium.
38. MANAGEMENT OF SALT EFFECTED SOILS.
Crop selection.
Crop species and varieties may be selected by
considering salt tolerance.
Irrigation practices.
Saline soil should be irrigated heavily than non
saline soil, the soil may be irrigated before planting
to leach the salts out of soil.
39. MANAGEMENT OF SALT EFFECTED SOIL.
Special tillage practices.
Seedbed preparation ,deep ploughing, are
necessary for saline soil.
