The Problematic soils are major constrain for agriculture. Understanding their properties in important for providing solutions. Sodic soils are one of them mainly found in coastal areas and Arid climate conditions. Further knowledge about management of sodic soils is necessary.

1. SODIC SOILS
K. Avinash
I M.Sc. (Ag.) Soil Science
Department of Soil Science and Agricultural Chemistry
Tamil Nadu Agricultural University, Coimbatore
SAC 511 MANAGEMENT OF
PROBLEM SOILS AND WATER
(2+1)

2. Characters of Sodic soil

3. Alkaline hydrolysis - e.g. sodium carbonate
The surface is dry and hard
EC = 4 dS/m at 25 °C
pH = 8.2 to 10
ESP > 15

4. Low level of Ca & Mg
Dispersed clay particles
High level of sodium
Absent of white surface
Organic matter - Black sodic soils

5. Source: FAO 2015; Butcher et al. 2016; Zaman et al. 2018; Sahab et al. 2021
Global distribution of salt-affected land area

6. Source: Encyclopedia of the Environment
(unknown date). https://www. encyclopedie-
environnement.org/en/zoom/land-
salinization/
Global distribution of saline, sodic, and saline-sodic soils

7. Source: FAO 2015; Butcher et al. 2016; Zaman et al. 2018; Sahab et al. 2021
Distribution of salt-affected land area in India

8. Source: CSSRI database 2010

9. Tamil nadu
These are essentially
found in the central
Tamil Nadu covering
• Ramanathapuram
• Cuddalore
• Kanchipuram
• Tirunelveli
• Thanjavur
• Pudukottai
• Madurai
• Tiruchirapalli
Source: CSSRI database 2010

10. Genesis of Sodic soils

11. • Soils formed from rocks having high
proportion of bases are become
saline / sodic in nature. eg. Basalt,
Sand stone etc.
Parent material
Low rainfall

12. • One of the important reason for the
development of Sodic soil is insufficient
water to remove bases from soil horizon
and thereby accumulation of salts in
soil.
• This is more common in semi arid and
arid regions where the rainfall is usually
low.
Low rainfall
High Evaporation

13. • Water along with salts reaches the
surface from sub surface of the soil
by capillary raise due to high
evaporation in arid and semi arid
regions.
• This results in accumulation of salt at
surface of the soil while water alone
moves to atmosphere.
High Evaporation
Poor drainage

14. • Water logged salinity / sodicity is a
common seen in low-lying area of
inlands particularly in high clay soils.
• Improper drainage leads to
accumulation of salts at surface
horizon and becomes reason for
entry of sodium in clay complex.
Poor drainage
Poor quality irrigation waters

15. • Continuous use of poor quality sodic
water for cultivation accumulates
salts / sodium in the soils.
Poor quality irrigation waters
High water table

16. • High water table at alluvial plains and
other areas leads to improper
drainage, which leads to
accumulation of salts in soils.
High water table
Sea water intrusion

17. • In coastal regions seawater intrudes
into land and pollutes the soil as well
as ground water of that locality.
Sea water intrusion
Base forming fertilizers

18. • Continuous application of base
forming fertilizers for cultivation is also
causes soil salinity / sodicity. eg.
NaNO3
Base forming fertilizers

19. Plant growth in Sodic soils

20. Graph showing relation between ESP and
hydraulic conductivity
• Influence on the physical soil
properties.
• Increase in exchangeable sodium –
Dispersed soil - results - breakdown
of soil aggregates.
• Lowers the permeability of the soil
to air and water.
• Impermeable surface crusts that
hinder the emergence of seedlings.
Effect of excess exchangeable sodium

21. • Affects soil pH.
• lowering the availability of some essential
plant nutrients.
• For example, the concentration of the
elements calcium and magnesium in the soil
solution is reduced as the pH increases due to
formation of relatively insoluble calcium and
magnesium carbonates by reaction with
soluble carbonate of sodium, etc. and results
in their deficiency for plant growth.
pH Solubility of CaCO3 me/l
6.21 19.3
6.50 14.4
7.12 7.1
7.85 2.7
8.60 1.1
9.20 0.8
10.12 0.4
Source: FAO

22. N Nitrogen in Sodic soils
• Sodic soils are generally deficient in available nitrogen.
• Nitrogen losses - highest under alternate aerobic and anaerobic conditions -
sodic soils.
• Losses of N (ammonia) - volatilization - high pH.
• affect the transformations and availability of applied nitrogenous fertilizers.
• Increasing soil pH and sodicity - Increases the time for complete hydrolysis of
urea.
• Reduced hydrolysis in soils of high sodicity was attributed to the possible
effect of high pH on the activity of the enzyme urease or the direct effect of
carbonate ions on the formation of ammonium carbonate.

23. • In Potato crops - twice as much nitrogen was needed as when
under conditions of good soil structure.
• Crops grown in sodic soils generally responded to higher levels of N
application compared to crops grown in non-sodic soils but
otherwise similar soil and climatic conditions.
• Generally recommendation - sodic soils fertilized at 25% excess -
recommendation for normal soils. (CSSRI, Karnal - Annual Reports 1980).
• Application of additional nitrogen
• compensated the yield reduction - increasing levels of ESP.
• Increased uptake of calcium and magnesium;
• Decreased uptake of sodium
N

24. P Phosphorous in Sodic soils
General trend of phosphorus
availability in relation to pH and
degree of sodium saturation.
• Barren sodic soils has positive correlation between
soluble P status and the EC of the soil.
• Due to presence of sodium carbonate - resulted
formation of soluble sodium phosphates
• The soil calcium - calcium carbonate form - not
available to the plants.
• The crops grown in freshly reclaimed sodic soils did
not respond to applied P fertilizers for 4-5 years
because of their high available P status
Source: Pratt and Thorne (1947)

25. • Increasing soil sodicity resulted
in reduced uptake of potassium
by most crops.
• Lack of response to applied K in
sodic soils observed.
• It was attributed to the
presence of K-bearing minerals
in the soil which could supply
sufficient K to meet the crop
requirements.
ESP
K % in 30 day old plants
Safflow
er
Linseed Cowpea
s
Raya Sunflow
er
7.6 3.06 1.66 2.04 3.94 2.24
12.5 2.53 1.56 1.96 3.49 2.46
16.6 1.95 1.40 1.92 3.38 2.63
23.0 1.58 1.23 1.92 2.87 3.02
44.2 1.25 0.95 1.89 2.12 2.64
Source: Singh et al., 1979, 1980, 1981; Chhabra et al., 1979
K Potassium in Sodic soils

26. Ca Calcium in Sodic soils
• Increased uptake of sodium - decreased uptake of calcium by plants.
• Increase in ESP - Increase in Na concentration of plants > Decrease in
the Ca concentration.
• For this reason the plants often accumulate sodium in toxic quantities
before the calcium becomes limiting for plant growth.
• However, when the exchangeable sodium levels are very high, calcium
is often the first limiting nutrient, for example when the soils contain
appreciable quantities of free sodium carbonate and the soil pH is high
such that application of amendments is absolutely necessary.

27. M Micronutrients in Sodic soils
• High pH, low organic matter content and presence of calcium
carbonate strongly modify the availability of micronutrients to
plants grown in sodic soils.

28. • Zinc deficiency has been widely reported for crops grown in sodic
soils and is accentuated when an amendment is applied to a Zn-
deficient sodic soil.
• Several field studies have shown significant increase in crop yields
due to application of zinc.
• Field studies by showed that application of 10 kg ZnSO4/ha was
sufficient to mitigate the deficiency of Zn in rice grown in an
amended, highly sodic soil.
Zn Zinc in Sodic soils

29. Fe Iron in Sodic soils
• Iron is limited - Due to high pH & calcium carbonate.
• Addition of iron salts to correct the deficiency was generally not
useful unless it was accompanied by changes in the oxidation
status of the soil brought about by prolonged submergence and
addition of organic matter.
• There is increase in the extractable Fe and Mn status of a sodic
soil upon submergence up to 60 days; more when organic
materials (rice husk or farmyard manure) were incorporated in
the soil.

30. B Boron in Sodic soils
• Present in the toxic range.
• A positive correlation between water soluble boron and the pH
and EC of soils.
• In a laboratory study - reduction in the water soluble boron
content of a highly sodic soil upon addition of gypsum observed.
• At high pH and sodicity, boron - highly soluble sodium
metaborate - Gypsum is converts it to relatively insoluble calcium
metaborate.
• Reduced uptake of boron by grasses with decreasing ESP due to
gypsum application.

31. Mo Molybdenum in Sodic soils
• solubility of Mo increases with pH and for this reason forage
grown on sodic soils is likely to accumulate Mo in excessive
quantities, which may prove toxic to the animals feeding on them

32. F Fluoride in Sodic soils
• Water extractable fluoride increased with increasing sodicity and
pH.
• F content of plants increased with increasing ESP and decreased
with application of P fertilizer.

33. Reclamation of Sodic soils

34. Reclamation of Sodic soils
• Gypsum or calcium chloride - supply soluble calcium - replacement of
exchangeable sodium, or other substances.
• Organic matter (i.e. straw, farm and green manures), decomposition and
plant root action also help dissolve the calcium compounds found in most
soils, thus promoting reclamation but this is relatively a slow process.
• The kind and quantity of a chemical amendment to be used for
replacement of exchangeable sodium in the soils depend on the soil
characteristics including
• The extent of soil deterioration,
• Desired level of soil improvement including crops intended to be grown and
economic considerations.

35. Reclamation of sodic soils
Chemical amendments
Calcium Salts
Soluble
Gypsum
Calcium
chloride
Low soluble
Grounded limestone
Acids or acid forming substances
Sulphuric
acid
Iron
sulphate
Aluminiu
m
sulphate
Sulphur Pyrite
Organic amendments

36. • white mineral - occurs extensively in natural deposits.
• It must be ground before it is applied to the soil.
• Soluble in water.
• Direct source of soluble calcium.
• Gypsum reacts with both the Na2CO3, and the adsorbed sodium as follows:
Gypsum (CaSO4.2H2O)
Na2CO3 + CaSO4 -> CaSO3 + Na2SO4 (leachable)
𝑵𝒂
𝑵𝒂
𝐂𝐥𝐚𝐲 𝐦𝐢𝐜𝐞𝐥𝐥𝐞 + CaSO4 <-> Clay micelle + Na2SO4 (leachable)
𝐺𝑅
𝑚𝑒
100𝑔
=
𝐶𝐸𝐶(𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝐸𝑆𝑃 − 𝑓𝑖𝑛𝑎𝑙 𝐸𝑆𝑃)
100

37. • Highly soluble salt
• supplies soluble calcium directly.
• Its reactions in sodic soil are similar to those of gypsum:
Calcium chloride (CaCl2 2H2O)
Na2CO3 + CaCl2 -> CaCO3 + NaCl (leachable)
𝑵𝒂
𝑵𝒂
𝐂𝐥𝐚𝐲 𝐦𝐢𝐜𝐞𝐥𝐥𝐞 + CaCl2 <-> Clay micelle + NaCl (leachable)

38. • Oily corrosive liquid.
• Purity – 95%.
• Calcium carbonate reacts to form calcium sulphate and provides soluble
calcium indirectly.
• Chemical reactions involved are:
Sulphuric acid (H2SO4)
𝑵𝒂
𝑵𝒂
𝐂𝐥𝐚𝐲 𝐦𝐢𝐜𝐞𝐥𝐥𝐞 + CaSO4 <-> Clay micelle+ Na2SO4 (leachable)
Na2CO3 + H2SO4 -> CO2 + H2O + Na2SO4 (leachable)
CaCO3 + H2SO4 -> CaSO4 + H2O + CO2

39. • Solid granular materials.
• High degree of purity.
• soluble in water.
• Dissolve in soil water and hydrolyse to form sulphuric acid, which in turn
supplies soluble calcium through its reaction with lime present in sodic
soils.
Alum Iron sulphate FeSO4.7H2O Aluminium sulphate (Al2(SO4)3.18H2O
FeSO4 + 2H2O -> H2SO4 + Fe (OH)2 H2SO4 + CaCO3 -> CaSO4 + H2O + CO2
𝑵𝒂
𝑵𝒂
𝐂𝐥𝐚𝐲 𝐦𝐢𝐜𝐞𝐥𝐥𝐞 + CaSO4 <-> Clay micelle+ Na2SO4 (leachable)

40. • yellow powder.
• Purity from 50 percent to
more than 99 percent.
• Not soluble in water
• S - undergo oxidation to form
sulphuric acid which in turn
reacts with lime present in the
soil to form soluble calcium in
the form of calcium sulphate:
Sulphur
SO3 + H2O = H2SO4
2 S + 3 O2 -> 2 SO3 (microbiological oxidation)
𝑵𝒂
𝑵𝒂
𝐂𝐥𝐚𝐲 𝐦𝐢𝐜𝐞𝐥𝐥𝐞 + CaSO4 <-> Clay micelle+ Na2SO4 (leachable)
CaCO3 + H2SO4 -> CaSO4 + H2O + CO2

41. • Oxidation of pyrite are complex and appear to consist of chemical as well
as biological processes.
• The first step in the oxidation is nonbiological and iron II sulphate
(ferrous) is formed
• Bacterial oxidation of iron II sulphate - by Thiobacillus ferrooxidans,
Pyrite (FeS2)
4 FeSO4 + O2 +2 H2SO4 -> 2 Fe2 (SO4)3 + 2 H2O
2 FeS2 + 2 H2O + 7 O2 -> 2 FeSO4 + 2 H2SO4

42. • Subsequently iron III sulphate (ferric) is reduced and pyrite is oxidized by
Chemical reaction.
• Elemental sulphur so produced may then be oxidized by T.
thiooxidans and the acidity generated favours the continuation of the
process.
Pyrite (FeS2)
4 FeS2 + 2 H2O + 15 O2 -> 2 Fe2 (SO4)3 + 2 H2SO4
2 S + 3 O2 + 2 H2O -> 2 H2SO4
Fe2 (SO4)3 + FeS2 -> 3 FeSO4 +2 S

43. Reference
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2. Bresler, Eshel, Brian L. McNeal, and David L. Carter. Saline and sodic soils: principles-dynamics-modeling. Vol. 10. Springer Science & Business Media,
2012.
3. Mandal, A. K., R. C. Sharma, G. Singh, and Ie Dagar. "Computerized Database On Salt Affected Soil In India, Technical Bulletin No.
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4. https://www.fao.org/3/x5871e/x5871e05.htm#4.4%20Reclamation%20and%20management
5. Sumner, Malcolm E. "Sodic soils-New perspectives." Soil Research 31, no. 6 (1993): 683-750.
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Reclaimed Sodic Soil" Journal of Plant Nutrition 45, no.8.(2022): 1240-1252.
8. Gupta, Manjul, Pankaj Kumar Srivastava, Suman B Singh, Nandita Singh, and Shri Krishna Tewari, "Organic Amendments with Plant-Growth-
Promoting Fungi Support Paddy Cultivation in Sodic Soil" Communications in Soil Science and Plant Analysis 46, no.18.(2015): 2332-2341.
9. Mishra, V K, A K Nayak, C S Singh, S K Jha, Rahul Tripathi, Mohammad Shahid, R Raja, and D K Sharma, "Changes in Soil Aggregate-Associated
Organic Carbon and Nitrogen after ten Years under Different Land-Use and Soil-Management Systems in Indo-Gangetic Sodic Soil" Communications
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44. Thank You