Submergence of soils in water leads to several physical, biological, and chemical changes. Oxygen levels decrease as water replaces air in pore spaces, promoting anaerobic conditions. This allows reduction reactions to occur, changing soil properties like pH, redox potential, and nutrient availability. While phosphorus, potassium, iron, and manganese availability increases, nitrogen can be lost through leaching or denitrification if not properly managed, and sulfur, zinc and copper availability decreases overall. Careful water and nutrient management is needed for optimal crop growth in submerged soils.

1. EFFECT OF SUBMERGENCE IN SOILS AND ITS
MANAGEMENT
Presented by
Preethi.K.D
2014602009
TNAU, Coimbatore

2. Submerged soils
• Soil mass is drowned in water
• Soils are saturated with water for a long time
in a year
• Result in the formation of gley horizons due to
oxidation – reduction processes.

3. • The oxygen movement through the flooding water is usually
much slower than the rate at which oxygen can be reduced in
the soil.
• This situation may result in the formation of two distinctly
different layers being formed in a waterlogged soil.
• On the top is an oxidized or aerobic surface layer where
oxygen is present, with a reduced or anaerobic layer
underneath in which no free oxygen is present.

4. Oxidized and reduced soil layer

5. Changes
• Physical changes
• Biological changes
• Chemical changes

7. Depletion of oxygen
• Under submerged
condition the water
replaces the air in the
pore spaces.
• As a result oxygen
diffusion in the water
layer above the soil is
very slow.
• Oxygen trapped in
blocked pore spaces is
rapidly utilized by
facultative anaerobic
organisms

8. • The rapid declines of O2 from the soil are accompanied by an
increase of other gases produced through the microbial
respiration.
• The major gases that accumulate in the flooded soils are
carbon dioxide (CO2), methane (CH4), nitrogen (N2), and
hydrogen (H2).

9. Soil compaction
• Compaction is the increase in soil
density caused by dynamic loading.
• As moisture increases the cohesion
among the soil particles decreases, this
leads to compaction

10. Bulk density
• In compacted soil the voids are filled with water i.e.,
no air voids are present and no soil water is expelled
from the voids, the soil is saturated and its bulk density
is maximum.
• PB = Ppγw / 1+ (Pp w /100).
Where,
PB Bulk density
Pp Particle density
w Water content
γw Unit weight of water

11. Puddling
• Puddling is very common in Asian rice-producing
countries.
• Puddling, intensive wetland cultivation, breaks the
natural aggregates to finer fractions.
• Puddling as mixing soil with water to render it
impervious.

13. • In submerged soils, aerobic microorganisms become
quiescent or die, and facultative and obligate anaerobic
bacteria proliferate.
• In the absence of oxygen, many facultative and obligate
anaerobic bacteria oxidize organic compounds with the
release of energy in a process called “anaerobic fermentation”
• In the submerged soils, organic-matter decomposition is
retarded because of lower carbon assimilation rates of
anaerobic bacteria.

14. • In a submerged soil, the facultative and obligate anaerobic
organisms utilize nitrate (NO3−), manganese (Mn4+), iron
(Fe3+), sulfate (SO4 2−), dissimilation products of organic
matter, CO2, and H+ ions as electron acceptors in their
respiration, reducing NO3− to dinitrogen (N2), Mn4+ to Mn2+,
Fe3+ to Fe2+, SO4 2− to sulfide (S2−), CO2 to CH4, and H+ to
H2 gas

16. pH
• Soil pH is an important chemical property
because of its influence on soil
microorganisms and availability of nutrients to
plants.
• Soil pH indicates acidity, alkalinity, or
neutrality of a soil.

17. Under submerged condition
• The pH of acidic soils increases and alkaline
soils decreases
• Overall, pH of most soils tends to change
toward neutral after flooding
• A majority of oxidation–reduction reactions in
flooded soils involve either consumption or
production of H+ /OH− ions

18. In acidic soils
• The increase in pH of acidic soils is mainly
determined by reduction of Fe and Mn oxides,
which consume H+ ions.
These reduction processes are shown in the
following equations:
• Fe2O3 + 6H+ + 2e− ↔ 2Fe2+ + 3H2O
• MnO2 + 4H+ + 2e− ↔ Mn2+ + 2H2O

19. In alkaline soils
• The decrease in the pH of alkaline soils is associated
with the microbial decomposition of organic matter,
which produces CO2, and the produced CO2 reacts
with H2O to form carbonic acid, which dissociates
into H+ and bicarbonate (HCO3−) ions.

20. Oxidation – reduction potential
• Oxidation–reduction or redox potential has significant
influence on chemistry of iron and other nutrients in the
submerged soils
• Oxidation–reduction potential is measured in millivolts, and
symbol used for this chemical change in flooded soil is Eh.
• Oxidized soils have redox potentials in the range of +400 to
+700 millivolts, whereas waterlogged soils’ redox potential is
generally in the range of -250 to -300 millivolts

21. • As the O2 depletes from the waterlogged
soils, reduction processes occur in sequence.
• Nitrate and manganese compounds are
reduced first, then ferric compounds are
reduced to the ferrous form, and at last
sulfate is reduced to sulfide.
• Redox potential decreased with flooding of
rice soils

22. Nutrient availability
• Availability of essential macro- and
micronutrients is significantly influenced in
the submerged soils

23. Nitrogen
• Nitrogen is a key nutrient in improving growth
and yield of crop plants in all agroecosystems.
• Its main role is in increasing the
photosynthesis process in the plants, which is
associated with improving grain yield.
• A major part of N in the flooded soils is lost
through leaching and denitrification

24. • Nitrate produced in the surface oxidized layer
of a waterlogged soil can easily move
downward by diffusion and percolate into the
underlying reduced layer, where it is rapidly
denitrified
• Accumulation of NH4+ in the waterlogged
soils would mean that the N is not lost from
the soil–plant system,

25. Phosphorus
• Phosphorus (P) plays an important role in the
growth and development of crop plants.
• Phosphorus availability is increased in the
flooded soils because of the reduction of ferric
phosphate to the more soluble ferrous form
• P uptake in flooded alkaline soils also
improves because of the liberation of P from
Ca and calcium carbonate resulting from the
decrease in pH.

26. Potassium
• The reducing conditions caused by flooding result in
a larger fraction of the K ions being displaced from
the exchange complex into the soil solution.
• This may leads to greater availability of K

27. Sulphur
• In flooded soils, SO4 2− ion is reduced to hydrogen
sulfide (H2S) by anaerobic microbial activities.
Furthermore, in flooded soils, Fe3+ reduction to Fe2+
precedes SO4 2− reduction.
• Fe2+ will always be present in the soil solution by the
time H2S is produced, so that H2S will be converted
to insoluble iron sulfide (FeS). This reaction protects
microorganisms and higher plants from the toxic
effects of H2S
• Overall, availability of S is reduced in flooded soils
due to formation of insoluble FeS.

28. Zinc and Copper
• Zinc and copper (Cu) concentrations generally
decreased after flooding soils.
• The decrease in concentration with the flooding may
be associated with increase in soil pH after flooding.

29. Conclusion
• The most significant chemical changes are increase in
the pH of acidic soils and decrease in the pH of
alkaline soils, reduction in the redox potential
• Availability of P, K, Si, Fe, Mn, and Mo increased in
flooded soils, and availability of S, Zn, and Cu
decreased. Availability of N depends on its proper
management.