WATERLOGGED (SUBMERGED) SOILS

Topics covered: Meaning and def inition of waterlogging, norms

o f waterlo gging, c auses fo r waterlo gging, ad verse
effec ts/problems of waterlogged soils, management of
waterlogged soils. changes occurring in submerged soils –
depletion of O2, accumulation of CO2, electro-chemical changes
like pH, redox potential and specif ic conductance, nutrient
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 INTRODUCTION- WATERLOGGED SOILS
• Unscientif ic management of soil, water and crops in irrigation
project areas and obstruction of natural drain systems by various
developmental activities are the main causes to disrupt the
balance of inf lo w and outf lo w of water causing waterlogging
and salinization.
Meaning and Definition of waterlogging :
Meaning : In general the term “Waterlogging is understood as
stagnation of water on the land surface”.
Definition : According to Central Board of Irrigation and Power,
“When the water table rises to an extent that soil pores in the root
zone of a crop becomes saturated, resulting in restriction of the
normal circulation of air, decline in the level of oxygen and increase
in the level of carbon dioxide at least in some part of the area”.

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 Kind of submerged soil
A. Alternate submerged:
Up to 2.5 cm depth, more important for rice
cultivation. Because alternate submerged provide
better physical condition (soil aeration) for plant
growth and development.
B. Continuous submerged :
At 2.5 – 7.5 cm depth, provides the potential
to produce optimum rice yields.

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 Norms of waterlogging
1. Waterlogged area- Water table within 2 meters of land surface.
2. Potential area for Waterlogging - Water table between 2-3
meters below land surface.
3. Safe area - Water table below 3 meters of land surface.
The problem of waterlogging on account of surface inundation
or surface ponding, however is mostly due to topographical related
causes which occur in the subtropical mansoon.
The gravity or extent of the problem depends on :
1. Type o f c ro p 2. S t a ge o f c ro p 3. I n h e re n t ph ysio lo gic a l
characteristics 4. Duration of storms and 5. Soil characteristics.

• The productivity of sensitive crop eg. Pigeonpea, Maize etc.

reduces by about 30-50% of potential when these crops are under
waterlogged/saturated soil conditions for 24 to 40 hours.

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 Causes for waterlogging
• Deforestation and poor upkeep of watershed.
• Developmental activities such as construction of roads, bridges,
railway lines, buildings etc. resulting in choking of natural drainage.
• Poor natural drainage as a result of topography or unfavourable
subsoil geology like existence of hard pan at shallow depths.
• Spilling/overf lo w of rivers resulting in submergence of agricultural
lands.
• Heavy rainfall coupled with poor natural drainage.
• I n t ro du c t io n o f irriga t io n w it h o u t t a k in g in to a c c o u n t t h e
characteristics of soil and sub-soils for their irrigability.
• Heavy losses of water due to seepage from canals, distributaries and
water courses.
• Excess application of water to crops.
• Inadequate drainage and poor maintenance of existing drainage
system and outlets.
• Poor inf iltration of water due to surface crusting and formation of
hardpan in subsoils due to sodicity problem.
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 Adverse effects/problems of waterlogged soils
• There is depletion of oxygen in the root zone and increase of CO due to 2

waterlogging. The anaerobic condition affects adversely the useful

m i cr oor ga ni sm s e spe ci a l l y N- f ix i ng ba ct e r i a ( viz ., Rhi zobi um ,
Azotobacter), nitrifying bacteria etc.
• while harmful organisms proliferate and create several problems for
plant growth. Particularly root growth is adversely affected by poor
aeration. Inhibition of adventitious roots.
• Chemical and biological activities in soil are also disturbed on account of
low temperature which is the result of waterlogging conditions.
• Create the problem of increase in pests and diseases.
• Field operations become either impossible or difficult in such soils.
• Accumulation of toxic substances like methane (CH ) or mercaptans,4

sulf id es (FeS /H S), Fe 2 + and Mn 2 + etc. which affect the plant growth
2 2

adversely.
• Volatilization losses of ammonia and leaching losses of nutrient.
• Secondary salinization caused on account of salts being carried up from
lower horizons.
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Cont…
• Germination of seeds is severely inhibited by poor aeration in

waterlogged soils.

• The absorption of nutrients and water gets reduced in poorly

aerated waterlogged soils, especially uptake of N, P, K, S, Zn

and Si etc. is drastically affected.

• Premature abscission of reproductive structures occurs.

• Losses of geotropism.

• Visc osity of c ell sap inc reases and transpiration and

translocation of photosynthesis are reduced.

• Reduced activity of auxines.

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 Management of waterlogged soils
1. Provide Drainage :
• Providing adequate drainage especially in the irrigation
c o mmand /pro j e c t are a: whe n irrigatio n pro j e c ts are
formulated by the Government – provision for drainage
network should be made along with irrigation structures.
• An aerobic soil environment can be maintained by providing
surface or subsurface drainage and removing excess of
water from soil poros especially macropores.
• The soil poros get f il led with water due to continuous
seepage from canals, presence of perched or high water
table, and after rains or irrigation. The drainage of such fields
is essential for the supply of sufficient oxygen. 8
2. Improving Soil Structure : An increase in the volume of air f illed
pores can be attained by improving soil structure. Maintenance of
stable soil aggregates by use of organic manures such as animal
manures, green manures, plant residues and growing legume crops
can encourage better soil aeration.
3. Cultivation : A light cultivation or intercultural operation helps in
the exchange of gases especially in heavy textured poorly drained
soils. Light tillage operations can break the crust formed in f ine
textured soils after rains and improve soil aeration.
4. Plant Adaptations and By Following suitable crops and cropping
systems : Selection of crop species is important for growing crops
in waterlogged or poorly drained (an aerobic) soils. For example
rice thrives well in submerged soil conditions.

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5. By proper management of saline, sodic and other
degraded soils especially in irrigated area.

6. Lining of canals to check seepage from canals.

7. By judicious use of water for irrigation.

8. Following suitable soil and water management practices

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11
 PHYSICO- CHEMICAL PROPERTIES OF WATERLOGGED/ SUBMERGED
SOILS

PHYSICAL PROPERTIES
1. Oxygen Depletion ELECTRO-CHEMICAL CHANGES

2. CO2 Accumulation 1. Soil pH

3. Compaction 2. Increase Specific Conductance
4. Increasing BD 3. Decrease Redox potential
5. Massive structure
6. Lowering diffusion coefficient
of gases
Water logged
soils

BIOLOGICAL CHANGES
1. Reduced aerobic Microbial
activity CHEMICAL CHANGES
2. Mineralization
1. Soil Reduction
3. Immobilization
2. Micronutrient toxicity
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 Chemistry (Fertility and properties) of waterlogged soils /
submerged soils/ paddy soils

Changes occurring in waterlogged soils :

• As a result of submergence, the physico-chemical and
biological properties of soils change markedly and are
quite different from uplands.
The major changes occurring in a submerged soils are.
1. Depletion of oxygen.
2. Accumulation of CO2.
3. Electrochemical changes
a) pH b) Redox potential (Eh) c) Specific conductance

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1. DEPLETION OF OXYGEN DUE TO SUBMERGENCE:
• Diffusion of molecular oxygen occurs when a soil submerged,
water replaces the air in the pore spaces.
• The Oxygen-diffusion in the water layer is very slow and the rate
of O consumption is reduced.
2

• Some O is rapidly utilized by the facultative anaerobic organisms.

2

• Because of high demand of O in f lo oded Soil and slow O supply

2 2

through water, the layer soil is practically devoid/lack of oxygen

As a result of submergence, the surface soil gets differentiated into
two distinct layers.
A. An oxidized or aerobic layer near the soil surface at the interface
where O is available through diffusion in water.
2

B. The reduced or anaerobic layer below the oxidized layer where

free O is not available.
2

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2. Accumulation of CO2 :
• Immediately after submergence, the normal process of

gaseous exchange between soil and air is restricted.

• Soil gases such as CO 2, methane, H2S accumulates due to

submergence. They escape in the form of bubbles if

pressure builds up.

• It has been recorded that during f ir st three weeks of

submergence can generate upto 2.5 tonnes of CO2/ha.

• Presence of such large amounts of CO 2 which form H2CO 3

affects the chemical equilibria of Ca, Mg, Fe, Mn and pH.

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3. Electrochemical changes :
A. pH: Increase in pH of an acid soil and decreased pH of in alkaline soil
In acid/laterite soil : On f looding an increase in pH is usually noticed. The
reasons for rise in pH of acid/laterite soils on flooding are
I. Reduction of ferric and manganic compounds and release of OH ions.
Fe (OH) → Fe (OH) + OH
3 2

II. Due to production of NH and its accumulation

3

• Under acidic, anaerobic condition, nitrifying bacteria are not active and
hence accumulation of NH /NH + ions takes place.
3 4

In calcareous/alkaline soil :
• Flooding results in reverse effect namely a decrease in pH. But the pH
of the submerged soil tends to be buffered around neutrality by
substances produced as a result of submergence such as Ferrous
carbonate (FeCO ), Ferrous hydroxide Fe (OH)
3 2.

• Generally in calcareous/alkaline soils, initially pH decreases on

f lo oding and then gradually increases. The decrease in pH is more
pronounced in the soil with higher organic matter content.
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B. Redox potential : (Eh)
Def inition of Eh- “It is the tendency of chemical species either to reduce
by accepting the electron or oxidised by donating the electron is called
as redox potential”
• Eh measures the intensity of oxidation or reduction. Higher and positive Eh
values indicate oxidized conditions, while low positive or negative values
indicate reduced conditions.
• The aerobic soils are characterized by high positive potentials, ranging from
+ 500 to + 700 mV. After f looding there is a sharp drop in the potential and
within few weeks negative potentials are developed. The f looded soils may
exhibit potentials as low as – 300 to – 400 mV.
• When a soil is submerged in water, Eh decreases and become stable slowly
at a range of +200 mV to -300 mV depending on the type of soil, organic
matter present, temperature, duration of submergence and presence of
reducible substances like nitrate (NO ), sulphate (SO ) and iron (Fe )
3
-
4
-2 +3

• Due to depletion of oxygen, the reduction of oxidized compounds takes

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place in a sequential form, thereby anaerobic organisms derive their energy.
• Ponnamperuma (1965) has listed critical potentials for oxidized
compounds which determine the sequence.

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Critical Eh values of important components
in submerged soils

Reduction Eh (mV)
O2 to H2O + 380 to + 320
NO3 to N2

4+ 2+ + 280 to + 220
Mn to Mn
3+
Fe to Fe 2+
+ 180 to + 150
SO42- to S2- - 120 to - 180
CO2 to CH4 - 200 to - 280 20
Note: The prolonged submergence leads to highly reduced
toxic state. It leads to Fe2+ toxicity which may be deposited in
tissues. Sulphids (S2-/ H2S) causes injury to roots. But, it can be
controlled by draining out standing water or by keeping soil at
just saturation condition.

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c. Specific conductance :
• Specific conductance of a solution is a measure of its ionic
content. On f looding or waterlogging the soils, the specif ic
conductance of solution increases as
a) Ca and Mg are mobilized by CO and organic acids.
2+ 2+
2

b) Fe and Mn also go into soil solution following the

2 + 2 +

reduction of their insoluble oxidized counterparts and

c) A c c u m u l a t i o n o f N H +
4 ions i.e., as these ionic
concentration increases, specific conductance increases.
Note: Specif ic conductance is related to organic matter
content of soil. i.e., Higher the organic matter content higher
is the specific conductivity.

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 Nutrient transformation in flooded soils
1) Nitrogen transformation : Nitrogen is the most limiting element
under waterlogged condition.
A. Mineralization of N: In waterlogged, anaerobic soil conditions, the
mineralization of nitrogen is limited to ammonif ic ation stage due to
depletion of O2
• As such accumulation of NH4+ form of N is more under submerged
condition.

B. Loss of N : In waterlogged soils N is lost through several processes

viz., denitrif ication, NH3+ volatilization, NH4+ f ixation, leaching and run
off losses of NO3-.

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• DENITRIFICATION: Major cause of N loss in f lo oded soil on
waterlogging when the concentration of O 2 in the soil or soil
so lutio n f alls be lo w 0.1 ppm, f ac ultative anae ro bic mic ro -
organisms use oxidized form of N for their respiration and reduce
them to N2, NO, and N2O.

(NO3 - → NO-2 at Eh of value of + 0.43 Volts)

• N H 3 -VOL ATI L I ZATI ON : I n so ils w ith lo w CE C a nd high pH

(alkaline/calcareous soils), where a high ammonia concentration
o c c u rs, N H 3 ma y be lo st th ro u gh v o la tiliz a tio n w ith h igh
temperature.

• LEACHING LOSSES : Under prolonged submergence NO3 leaches

out of the root zone or denitrify before the plant utilize the N.

Intensity of leaching depends upon rate of percolation 24of

2. Phosphorus transformation: increase in availability of P under
waterlogged or submerged conditions.
• Land submergence is known to inf luence the transformation and
availability of both native and applied P.
The increase in solubility of water soluble P on flooding of soil is
attributed to a number of reactions
1. Release of P from organic residues due to mineralization.
2. Reduction of less soluble phosphate Fe(PO 4 ).2H 2 O to more
soluble Fe3 (PO4)2. 8H2O
3. Release of occluded P by the reduction of hydrated ferric oxide
coating (P is hidden in the Fe oxides instead of tetrahedral P).
4. Displacement of P from ferric and Al phosphates by organic
anions (eg: citrate).
5. Increase in the solubility of Ca-phosphate because of reduction
in pH and accumulation of CO2 in the calcareous soil.

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3. Sulphur transformation:

Reduction of SO takes place at Eh value of -0.49 volts.

4

A. Conversion of SO and other oxidized forms of

4

sulphur to hydrogen sulphide (H S).

2

B. Under anaerobic condition decomposition of

organic substances containing sulphur will result

in accumulation of mercaptan and hydrogen

sulphide. H S accumulation at the expense of

2

oxidized compounds takes place.

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 Chemical property Alterations following soil submergence / water logging

pH Towards neutral pH
Organic matter Favours accumulation of organic C and N
Reduction products More sul phi de a nd orga ni c a ci ds, e spe ci a l l y
products in degraded soils may cause toxicity or
injurious effects to growing plants
Macronutrients
Ammonium-N Release and accumulation of NH4+ favoured
P P availability improves, especially in soils high in Fe
and Al oxides
K K availability improves through exchange of K+
Secondary and micronutrients
Ca, Mg, Na Favours release of Ca, Mg and Na in solution
S Sulphate reduction may reduce sulphur availability
Fe Iron availability improves in alkali and calcareous
soils, but Fe toxicity may occur in acidic soils high in
reducible Fe
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Cu, Zn and Mo Improves availability of Cu and Mo but not of Zn