water logging-salinization-alkalization

RISE IN WATE TABLE, WATER LOGGING,

SALANIZATION & ALKALIZATION AND SEA WATER

INUNDATION & ITS EFFECTS ON AGRICULTURE

Rise in ground water table

  A feature common to many irrigation commands of surface

water projects is excess recharge over discharge of groundwater, leading

to rise in water table. The irrigation command areas are recharged not

only by rainfall infiltration, but also by seepage from reservoirs, canals,

distributaries and field channels, and return circulation of irrigation

water. At Haryana Agriculture University Farm, where the groundwater

table used to be at 15.6 m below the ground level in 1967 at the time of

introduction of irrigation under Bhakra canal system had gone up to 2.0m

below the ground level (Kumar and singh, 1994). The rate of rise of

groundwater table in different irrigation commands in India is given in

Table 3.1.Overall the rise in groundwater table appears to be a common

feature once the irrigation is introduced in canal commands. The rise in

groundwater table ultimately leads to waterlogging, salinization &

alkalization in irrigation commands

 Rate of rise in groundwater table

indifferent irrigation commands

Irrigation command Rise in water table

(m/year

)

Mahi Right Bank Canal, Gujarat 0.28

Rajasthan Canal 0.29-0.88

Western Yamuna & Bhakra Canal, Haryana 0.30-1.00

Sirhand canal, Punjab 0.10-1.00

Sarada Sahayak Canal, Uttar Pradesh 0.68

Malprabha Canal, Karnataka 0.60-1.20

Nagarjuna Sagar Project, Andhra Pradesh 0.32

Sriram Sagar Project, Andhra Pradesh 0.26

 Waterlogging

  Presence  of excess water in or near the root zone or standing

water above the soil surface for any substantial   period of time known as

water logging. Water logging is said to occur when the water table rises

to within the root zone of crops. The water table which is considered

harmful would depend upon the type of crop, soil type and water quality.

The actual depth of water table, when it starts affecting the crop yield

adversely, may from zero for rice to about 1.5m for other crops. The

norms for characterization of water logging are given below in Table 3.2:

 Norms for characterization of 

                  Water logging

 

Depth of water table (m)

Nomenclature

< 2.0 Waterlogged

2.0-3.0 Potentially waterlogged

> 3.0 Safe

Ministry of agriculture estimates indicate that about 11.6 million

ha, representing 3.5% of the geographical area of India, has been

suffering from physical deterioration caused by waterlogging

(Kanwar,2000). 

The National Commission on Agriculture (1976) estimated the

area affected by waterlogging in Andhra Pradesh at 3.39 million ha.

 Salinization & Alkalization

    The most well understood problem is of salinization and alkalization

of soils, which is reported to extend to 10.1 million ha in India. The

problem is increasing at an alarming rate in the canal-irrigated areas

through increase in water table, poor water management practices and

lack of drainage. The rate of increase of the problem is fast in the black

soil regions of heavy texture, with serious drainage problem. The vast

irrigation development without drainage, adequate field channels and

water management technology has seriously reduced the effectiveness of

irrigation system and aggravated the problem of salinity, alkalinity and

waterlogging. The irrigation induced waterlogging and salinity assessed

by the Ministry of Water Resources (1993) is evident from Table 3.3

 Irrigation-induced waterlogging and salinity

Region Type of problem Affected

area

(million

ha)

North- West

India

Coastal

Peninstular

area

Estern plains

and Delhi

Waterlogging and solinity 0.7-1.0

Waerlogging and incidental salinity 0.1-0.2

Waterlogging 1.0-1.5

Coastal Gujarat Coastal salinity 0.75

Usar land

western

Gangetic plains

Semi-natural sodic soil 1.25

Gupta (1998) estimated that out of 8.56 million ha area affected by

salinity & alkalinity, 3.0 million ha or 35% is in canal command area.

Likewise, out of 4.5 million ha of water logged area nearly 2.2 million ha

or 5.% is in coastal command areas. The Ministry of Water Resources

reported that in the major and medium command areas is about 2.4

million ha was affected by water logging and 3.3 million ha by salinity.

Thus the canal irrigation is the cause and effect of salinity, alkalinity and

water logging increase, but it can also be cured if conjunctive use of

surface and groundwater irrigation, drainage and scientific water

management system are adopted. It hardly needs to be emphasized that

1/3 to half of the land is getting degraded through salinization,

alkalization and waterlogging due to the canal irrigation. It is indeed too

high a price that the nation is paying for the big irrigation projects.

Added to this, is the rapidly impossibility of repair or amelioration of the

problem at advanced age of the dam is another problem.

Saline soils, also known as solanchalk, are characterized by pH of the

saturated soil paste < 8.2, exchangeable sodium percentage (ESP) < 15

and electrical conductivity (EC) of the saturated paste > 4.0 dS/m.

Excessive amounts of soluble salts, mainly Cl and SO

4 of Na, Ca and Mg

limit optimal crop growth due to direct toxic effects of salts and

increased osmotic stress which physiologically inhibits the availability of

soil water. Parent material, brackish groundwater, seepage from canals

and form irrigation systems, injudicious on-farm water use, high

cropping intensities and replacement of low water requiring crops of high

water demand gradually result in higher water table and associated

secondary salinization of soils.

Alkali soils, also known as sodic or solonetz soils are characterized by

an ESP > 15 and PH of > 8.2. The EC of these soils is variable but is

normally less than 4 dS/m in the surface soil and a hard CaCo

3 kankar

pan in the subsoil. These soils are highly dispersed and have poor water

and air permeability affecting plant growth. The groundwater quality is

generally good but in some cases it may contain high residual sodium

carbonate (RSC).

  Several workers have opined and concluded that more

construction of dams and canal is not enough and there is on urgent need

to focus attention on improved water management, command area

development system. Our big irrigation projects are considered

engineering monumental, but seem to be ending up in increasing woes of

agriculture and low payoff from investment. The increasing concern and

debate on big dams versus small water resource development structures

should be ignored as the high cost, low pay-off and consequential soil

degradation problems following in the wake of call for change in strategy

and policy of irrigation systems development, lest the history repeats

itself and civilization meets the same fate as many old irrigation

civilizations of the past.

 Prevention, control and reclamation measures

  Salinity, alkalinity and water logging in canal command areas

can be controlled by adopting suitable measures to reduce the recharge to

and increase the discharge from the problem area. The various measures

by which this can be achieved are enumerated below (Karanth, 1986).

a) Control of surface drainage into the area – Surface runoff entering

the problem area accelerates water logging, salinity & alkalinity.

Diversion coursed may be provided to divert runoff from the problem

are.

b) Provision of an efficient surface-drainage system- An efficient

surface-drainage system should be provided by constructing open ditches

and field drains to drain away the storm flow and excess irrigation water.

Proper land grading and maintenance of surface slopes improves

drainage of farmland. Slopes of draining courses may be improved and

phreatophytes and other vegetation, if preventing the drainage channel,

may be cleaned to relieve congestion. Pools, ponds and marshes should

be connected to watercourses. Where permissible fro considerations of

quality, drain water may be utilized for irrigation. This will provide

higher gradients for subsurface drainage.

c) Improving subsurface drainage- Waterlogged agricultural

lands can be relieved of excess ground water by providing underground

drains or collecting excess ground water in surface for disposal into

water.

d) Conjunctive use- Pumping from wells serves the dual purpose of

lowering the water table and salinity and releasing additional quantities

of water for use conjunctively with surface water.

e) Planning and adoption of rational agricultural practices- 

Selection and rotation of crops, depending on their water requirements,

are important agricultural practices helpful in ameliorating water

logging, salinity & alkalinity conditions. Certain crops like rice require

more water, while certain others like wheat, millets and cotton require

much less. Likewise certain crops are tolerant and sensitive to salinity.

Proper crop/variety selection assumes significance under adverse

conditions. If crops with high water requirements are always sown and

canal water is used for irrigation continuously, the chances are high that

the area will become waterlogged and buildup salinity takes place sooner

than one realizes. When such crops are to be raised, they should not be

raised on highly permeable soils. Alfalfa and eucalyptus, because of their

high intake of water, have ameliorative characteristics.

f) Lining of canals and water courses- Seepage from canals,

distributaries and field channels should be prevented or minimized by

lining or spreading impervious layers.

g)Adopting judicious water-management practices-Planning and

controlling use of water to avoid excessive and wasteful applications is

important measure that involve no extra expenditure. Excessive

application of water is as detrimental to crop growth as inadequate

application, a maxim many farmers are unaware of any need to be

educated about.

h) Adoption of water use efficient application methods like sprinkler

and drip systems in high value crops

i) Reclamation of saline and alkaline soils-

• For saline soils with efflorescence of salts at the surface:

Scraping of the surface salts and flushing with water to wash

away the excess salts

• For saline soils with high concentration of soluble  salts into

great depth but with deep water table:  Impounding rain or

irrigation water for leaching salts to a safe limit and subsurface

drains coupled with flushing to remove salts both by surface &

subsurface drainage

• For saline soils with high concentration of soluble salts into

great depth but with high water table: Lowering of water table

either by pumping or subsurface drainage

• For alkali soils: Treating the soils with chemical amendments

like gypsum & sulphur, addition of organic material viz., FYM,

crop residues, green manuring etc, leaching the products of

reaction after amendments are added, deep ploughing to  break

the  hard pan for improving drainage.                                 

After reclamation of the salt affected soils, it is necessary to prevent their

resalinization and alkalization. Maintaining a salt balance, drainage and

controlling the depth of water table will achieve this.

Seawater inundation and Sand casting

       Natural calamities, like cyclones and floods, affect nations all over

the world. Because of the large geographical size of the country. India

often faces natural calamities like floods, cyclones and droughts,

occurring fairly frequently in different parts of the country. At times, the

same area is subjected to cyclones & floods in successive seasons or

years.

    Cyclonic storm arising from Bay of Bengal often cross the east-coast

plains of Orissa, Andhra Pradesh and Tamil nadu during OctoberJanuary

resulting in wide spread

damages

to standing crops besides other

losses.

The cyclones

cause and ingression

of sea water/ tidal waves. The

latter

cause the problem

of soil salinity

and sand casting of varying

depths

in lower

reaches.