Flooded soils – formation, characteristics and management

Flooded soils – Formation,
Characteristics and
Management
SAC 202 Problematic soil and their management (2+0)
1
K. Maheshwaran,Asst. Prof. (SS&AC)
Sethu Bhaskara Agricultural College &
Research Foundation

 Soils are saturated with water for a sufficiently
long time in a year to give ‘gley horizon’ resulting
from oxidation-reduction process
 Flooded soils also known as “Hydric” soils
Flooded soils
2
3 Zones in flooded soil
1. Partially oxidized high in OM
2. Mottled zone in which oxidation-reduction
3. Permanently reduced zone is bluish green

6
1
• Physical
2
• Chemical
3
• Biological
Characteristics of Flooded Soils

7
Physical changes
 Upon flooding, the pore spaces (air spaces) in
the soil become saturated with water
 As a result, the soil swells, and hard clods soften
and break into small aggregates
 Puddling completely destroys the remaining
structural aggregates and transforms the soil
into a sludge, or soupy mixture

Diffusion of molecular oxygen and
development of aerobic and anaerobic
layer
 When soil is submerged, water replace the air
in the pore spaces
 The diffusion of O2 in soil is very slow and
consumption of O2 in soil is high
 Some O2 trapped in blocked pore space is
rapidly utilized by anaerobic organisms
8

Aeration status of a submerged soil
 Immediately after submergence, the process of
gaseous exchange between soil and air is
restricted
9

Accumulation of carbondioxide
 Soil gases like CO2 & CH4 accumulate due to
submergence and also may escape as bubbles if
pressure builds up
 It has been recorded that during the first three
weeks submergence
 Some soil may generate CO2 upto 2.5 t ha-1
10

Soil compaction
 When soil is compacted all the pore space are
filled with water and no air space are present
 The soil is saturated and its bulk density is
maximum
Puddling
 Breaking down of soil aggregates into finer
aggregates
 It decease the specific volume and hydraulic
conductivity of soil creates an anaerobic layer
11

Ferrolysis
 Decomposition and transformation of clay
under periodic reduction of iron oxides to
ferrous ions
12

Electro-chemical changes
 Decrease in redox potential (Eh)
 Increase in pH of acid soil and decrease in pH
of alkaline soil
 Increase in specific conductance
 Cation exchange reaction
 Sorption and desorption of ions
13

Redox potential
 Soil is submerged the reduction of soil takes
place and reduced soil contains
 NO3
- NH4
 SO4
2- H2S
 Mn4+ Mn2+
 Fe3+ Fe2+
 CO2 CH4
14
Oxidation reduction is a
chemical reaction
In which electrons are
transferred from a
donor to acceptor

15

 Low Eh harms seed germination and seedling
emergence
 Destroy the nitrate and increase the
accumulation of ammonia
 Low Eh potential benefit for rice cultivation by
increase the availability of N, P, Si, Fe, Mn and Mo
 Decreasing the availability of S, Cu and Ze
16

Increase in pH of acid soil and decrease in
pH of alkaline soil
 When soil is submerged, its pH decrease during
the first few days reaches a minimum and then
decrease to fairly a few weeks later
 The increase in pH in acid soils due to
reduction of iron and manganese and also due
to the presence of organic matter that enhance
the process of soil reduction
17

 The decrease in pH of alkali soil and calcareous
soils may be due to the release of sufficient
amount of CO2 during decomposition of
organic matter
 CO2 produce hydrogen ions reacting with soil
water and decrease the soil pH
18

Increase in specific conductance
 The increase in conductance during the first few
weeks of submergence is due to the release of
Fe2+ and Mn2+
 The decline after the maximum increase is
mainly due to the precipitation of Fe3O4 nH20
and MnCO3
19

Biological changes
 The absence of soil air (and particularly oxygen)
in flooded, puddled soils causes a change in the
varieties of microbes, or microscopic organisms
which live in the soil
 Microbes existing in the absence of oxygen are
known as anaerobic microbes
 Consequently, the rate of decay of organic
matter tends to be slow in flooded soils
20

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Chemical changes
 The upper zone, a thin 1-10 mm, absorbs
oxygen from the water, turns brown in color,
and reacts to nitrogen like an unfolded soil
 This zone is called the oxidized zone, in
reference to its chemical condition of being
oxidized.
21

 The lower zone, which extends down as far as
the water, is extremely low in available oxygen,
turns dark blue or gray in color, and takes on
chemical properties quite different from those
of the oxidized layer above
 This lower zone is known as the reduced zone.
22

 Installation of tube-wells for irrigation and
vertical drainage
 Construction of surface drains and tile drains
 Construction of water channel
 Planting of eucalyptus trees in water logged
soils
 Providing artificial drainage system
 Fixing cropping pattern
 Optimum use of water
23
Management of flooded soils

Levelling of land It removes water by run off
Drainage It removes excess water from root
zone
Controlled irrigation Results good drainage
Flood Construction of bund and check water
flow from the rivers to the cultivable
lands
Planting tree with high
transpiration rate
Transpiration helps excess water
remove from soil
Selection of crops Select resistant crops for water-logged,
eg. Rice, jute and sesbania can tolerate
water logging condition
24
Management of flooded soils

Flooded soils – formation, characteristics and management

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Flooded soils – formation, characteristics and management