7-Waterlogging and salinity

WATERLOGGING AND SALINITYSUBMITTED BY; SAMRAMARRIUM13131506-012BOTANY 6TH

GPGC CHAKWAL.

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

WATERLOGGING

Causes of waterloggingEffects on plants growthReclamation of waterlogging

CAUSES OF WATERLOGGING1. 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.

CAUSES OF WATERLOGGING2. 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

CAUSES OF WATERLOGGING3. 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.

CAUSES OF WATERLOGGING4. 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.

CAUSES OF WATER LOGGING6. Poor water management Sometimes farmers use their land

unscientifically . Following activities are major causes of

waterlogging; Excessive irrigation Lack of inadequate drainage system.

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.

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.

EFFECT OF WATERLOGGING ON PLANTS GROWTH.v. In waterlogged soil major form of nitrogen

is ammonia which is toxic to cropsvi. 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.

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

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.

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.

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.

TYPES OF SALT EFFECTED SOILa) 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.

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.

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.

PROCESS OF FORMATION OF SALT EFFECTED SOIL.d) Desodication. The process of removal of exchangeable

sodium from the soil is known as desodication.

CAUSES OF SALINITY IN PAKISTAN.1. Poor leaching of salts.2. Irrigation water.3. Ground water.4. Other factors .

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.

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.

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.

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.

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.

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.

SALINE SOIL.f) The saline soil can be reclaimed by adequate

drainage and leaching with water.

2.SODIC SOILa) 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.

3.SALINE SODIC SOILa) 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.

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.

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)

RECLAMATION OF SALT EFFECTED SOIL1. 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 .

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.

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.

MANAGEMENT OF SALT EFFECTED SOIL. Special tillage practices. Seedbed preparation ,deep ploughing, are

necessary for saline soil.