Soil fertility refers to a soil's ability to sustain plant growth through adequate nutrient supply and lack of toxins. Soil fertility comes from inherent nutrients in parent material and acquired fertility from inputs like manure and fertilizers. Factors affecting soil fertility include climate, topography, and microorganisms. Soil pH impacts nutrient availability, with acidic soils having issues like aluminum/manganese toxicity and phosphorus deficiency. Saline soils form in arid areas due to low rainfall, poor drainage, and accumulation of salts from irrigation water, fertilizers, or sea spray. Liming can remedy acidic soil problems by raising pH and supplying calcium and magnesium.

1. SOIL
FERTILITY

2. What is soil fertility?
Soil fertility may be defined as the inherent capacity of
soil to supply plant nutrients in adequate amount and
suitable proportion and free from toxic substances.
Soil productivity is the ability of the soil to produce
crop per unit area.

3. Types of soil fertility
Inherent or Natural Fertility:
The soil, as a nature of them, contains some nutrients which is known
as ‘inherent fertility’. Among the plant nutrients, nitrogen,
phosphorus and potassium is essential for the normal growth and
yield of crop. Indian soil contains 0.3 to 0.2 per cent nitrogen, 0.03 to
0.3 per cent phosphorus and 0.4 to 0.5 per cent potassium. The
inherent fertility has a limiting factor from which the fertility is not
decreased.

4. Acquired Fertility :
• The fertility developed by application of manures
and fertilizers, tillage, irrigation etc. is known as
‘acquired fertility’. The acquired fertility has also a
limiting factor. It is found by experiment that the
yield does not increase remarkably by application of
additional quantity of fertilizers.
• So it is necessary to apply fertilizer on the basis of
nutrient content of a soil and it is estimated by soil
testing.

5. Factors affecting soil fertility
Parent Materials
Climate and Vegetation
Topography
 Physical Condition of Soil
Soil Age
Micro-Organism and Soil Fertility
Availability of Plant Nutrients

6. The availability of nutrients depend mainly on
the following factors:
(a) Soil aeration.
(b) Soil pH.
(c) Activity of microorganism.

7. Soil pH??
Soil pH is a negative loagrithm of hydrogen ion
concentration.
Soil pH or soil reaction is an indication of the acidity or
alkalinity of soil and is measured in pH units.
The pH scale goes from 0 to 14 with pH 7 as the neutral
point.
pH< 6.5 referrs to acidic soils
pH in between 6.5-7 neutral soils
PH more than 7 saline soils

8. Acid soils
Acid soils occur in those areas where rainfall is
higher, i.e. precipitation > evapo-transpiration
In India Acid soil covers >100 million ha’s
Soil acidity is defined as proton (H+) yielding
capacity of soil during its transition from a given
soil pH to a reference pH (Jackson,1958).
Acid soils have been defined by the soil having pH less
than 5.5 in 1:1 soil-water suspension (USDA).

9. Properties of acid soil
1. Low pH
2. Low CEC and BS
3. Intermediate texture / coarse textured (Sandy loam to Loam) –
dominance of Kaolinite /ic/ illitic minerals and sesquioxides
4. Low organic matter content (except hilly region and forest soils)
5. Low P content but N is variable
6. High amount of Fe and Al in soil solution
7. Low in available nutrients- Ca, Mg, P, S, K and N

10. Factors responsible for soil acidity (OR sources of H ions in soils)
1. Formed mainly due to acidic parent materials - granite
2. Leaching of bases caused by heavy precipitation and also crop removal of
Ca, Mg, K, etc. (legumes exhaust Ca and Mg)
3. Continuous application of acid forming fertilizers: Ca and other bases are
displaced by NH4 ion, leading to the formation of CaSO4 which is leachable.
4. Microorganisms are responsible for the decomposition of organic residues
and nitrification produce strong acids.
5. CO2 evolved during OMD and root respiration dissolves in water form weak
H2CO3: The carbon dioxide evolved during decomposition of organic matter
and root respiration, dissolves in water to form weak carbonic acid.
6. Acid Rains: Airborne SO2 and NO2 emitted from the combustion of coal,
gasoline and other fossil fuel are converted into H2SO4 and HNO3, through
oxidation and dissolution in rain water cause acid rains. Such rain water have
pH < 2.0
7. Some H+ ions are also released by plant roots as H+ ions are exchanged
for other nutrients cations in the soil solution/soil solids.
8. Soils containing high sulphides (FeS2)

11. Harmful effects of soil acidity (or problems of acid soils):
Strongly acidic soils are not productive for most crops. On strongly acid soils, the majority
of crop plants produce yields less than their potential for one or more of the following
reasons.
1. Some plants simply do not grow well at low pH, i.e., the plants are not adopted to
low pH.
2. Elements such as Al, Mn and Fe become so soluble that they are toxic to plant
growth. Thus, toxicity of Al, Mn and Fe is noticed acid soils.
3. Phosphorus and molybdenum become insoluble and unavailable to plants. Thus
the deficiency of P and Mo is observed in acid soils.
4. Bases such as Ca, Mg and K will be leached out and deficiency of these nutrients
is noticed.
5. Nitrogen, P and K deficiency is observed because of very slow decomposition
(oxidation) of organic matter due to reduced microbial activity at low pH.
6. In addition to plant growth, the activities of the following micro-organisms are
greatly reduced in acid soils.
a. Nitrogen fixing bacteria
b. Nitrifying bacteria (bacteria that converts NH+
4 to NO3
-)
c. Various microorganisms that decompose organic matter
Only fungus can survive in acid soil. Note that H+ ion itself is not harmful but harmful
effects mentioned above are noticed at higher concentration of H+ ions in soil.

12. Crop production constraints in acid soil and their
management:
I. Physical
1. The upland acid soils are coarse textured, usually compact at soil
surface and have low OM besides distinct acidity.
2. High IR, low WHC, high permeability, high BD, and soil crusting -
basic features of these soils.
3. Seed germination is effected by crust formation.
4. Nutrient loss in these soils is considerably high except NH4
+- N and
phosphate.
Addition of organic matter or fine earth fraction, ridge and furrow tillage
conservation tillage, contour and strip cropping, inter cropping of cereals with
legumes, bench terracing, raising of field bunds for in-situ rain water
harvesting are some of the suitable methods for raising crops in upland acid
soils.

13. II. Nutritional and Microbial
1. Low availability of Ca, Mg, P, Mo, B and Si,
2. high availability of Fe, Mn, Cu and Zn. Low pH,
3. low OM content associated with deficiency of Ca, Mg, P and Mo
influence the microbial population, activity and survival.
4. The bacteria and actinomycetes perform better in intermediate pH
and higher pH range whereas fungi perform better under acidic pH
range.
III. Chemical
1. Common problems in respect of chemical properties are low pH, low
CEC (due to dominance of 1:1 type of clay ),
2. Low base saturation (16-67% ),
3. High Al, Fe and Mn saturation percentage,
4. High P fixing capacity and clay fractions consisting of rather low
surface active minerals.
These could be managed simply by amelioration by liming. Organic amendments reduce exch. Al in
soils due to precipitation of Al ions by OH- ions released from exchangeable ligand.

14. Liming of acid soils: Liming refers to addition of lime to an acid soil in order to
neutralize the soil acidity.
2H-clay + CaCO3 ↔ Ca-clay + H2O + CO2↑
Acid Lime Normal soil
Benefits of liming: Liming raises the soil pH by removing H and Al ions from the
soil and thereby eliminates most major problems of acid soils. The beneficial
effects of liming are as follows;
1. Liming supplies Ca, Mg - raises pH and level of bases and lessens the toxicity
of Al, Mn and Fe.
2. Corrects the deficiencies of P and Mo by making them soluble available to
plants.
3. Corrects the deficiencies of basic nutrient cation such Ca, Mg and K.
4. Increases the availability of N, P and S by improving the microbial activity and
thereby hastening the decomposition of organic matter.
5. Encourage the growth of microorganisms such as nitrifying bacteria, nitrogen
fixing bacteria, organic matter decomposing bacteria, etc.
6. Stabilises the soil structure by forming Ca - humate complex and improves
root distribution.

15. Liming materials: defined as the substance whose Ca and Mg
compounds are capable of neutralizing the soil acidity.
1. Quick lime (CaO) / Burnt lime / oxide of lime / simply lime.
2. Slacked lime [Ca(OH)2] or hydrated lime/ hydroxide of lime
3. Calcitic lime stone (CaCO3) / Agricultural lime or carbonate
of lime which is ground lime stone.
4. Dolomite lime stone (CaCO3. MgCO3) - high in Mg
5. Industrial wastes rich in Ca, Basic slag-Ca silicate
Lime recommendations: Soil pH is a measure of the degree of
soil acidity /basicity. pH is otherwise is an indicator of whether lime
should be applied to the soil. But it is not a measure of how much
lime is needed to obtain a desired change in pH.

17. FORMATION OF SALT SFFECTED SOILS
Arid and semi-arid climate: Due to low rainfall and
high evaporation, soils are alkali in reaction.
Low rainfall is not sufficient to leach out the soluble products
of weathering and hence the salts accumulate in the soils.
During rainy season, the salts dissolve in rain water and
move down in the lower layers. In dry weather condition,
the salts move up with the water and are brought up to the
surface where they are deposited as the water evaporates.
Primary minerals: During the process of
weathering, various constituents like Ca, Mg and
Na gradually released and made soluble

18. Poor drainage: during the period of high rainfall, the
salts are leached from the upper layer and, if the
drainage is impeded, they accumulate in the lower
layer when water evaporates, the salt is left in the areas
or in basin shaped areas.
Excessive use of basic fertilizers: Use of basic fertilizers
like sodium nitrate, basic slag etc. may develop soil
alkalinity
High water table: The ground water of arid regions
usually contain considerable quantities of soluble salts.
If the water table is high, large amounts of water move
to the surface by capillary action and evaporated
leaving soluble salts on the surface.

19. Overflow of sea water over lands: Low lying areas near
the sea which get sea water during tides, salt water
accumulates and enrich the with salts.
Salts blown by wind: In arid regions near the sea,
appreciable amount of salts are blown by wind year
after year and gets deposited on the surface
Introduction of irrigation water: The ground water of
arid regions are generally saline in nature with
judicious irrigation the percolating water may get
linked with the saline ground water.
During the dry weather the soluble salts of the ground
water may, thus get carried to the surface and increase
the salinity of the land. The irrigation water may be
itself rich in soluble salts and add to the salinity of the
soils.

20. 20
Type of soil EC (dSm-1) ESP (%) pH
Saline > 4.0 <15 <8.5
Sodic < 4.0 >15 >8.5
Saline-Sodic > 4.0 >15 >8.5
USSL Staff
Richard et al.,1954
Classification of salt affected soils
Indian system classification:
Type of
soil
EC
(dS m-1)
ESP (%) pH Na/(Cl+SO4)
Saline >4.0 <15 < 8.2 <1
Sodic <4.0 >15 > 8.2 >1
Gupta and Arbol (1990)

21. 21
Soil in which salt are accumulated or dominated by soluble
salts (Cl, SO4 of Ca, Mg, Na and K) that adversely affect the
growth of most crop plants with a electrical conductivity of
more than 4 dS/m, pH of less than < 8.5 and exchangeable
sodium percentage of <15.
Soil Salinity

22. • Saline soils contain appreciable amounts of salts, ECe > 4.0 dS/m, that
impair the growth and productivity.
• The salts are primarily composed of Cl- and SO4
2- of Ca2+, Mg2+ and Na+
• The concentrations of K+, NH4
+, HCO3
-, CO3
-2 B, and NO3
- is
• comparatively low.
• Though saline soil contains an excess of Na salt, its colloidal complex
(clay micelle) is not sodiumized hence pHs of saline soil is >7.5 but <
8.5, ESP is <15 and SAR is <13.
• Soils posses good physical condition. They are in well flocculated
condition with good aggregate structure.
• They are permeable to water and air and as such good aeration is found
in these soils.
• Saline soils are often recognized by the presence of white crust of salts
on the surface, hence the name white alkali is given to these soils.
• In Russian, the term Solonchak is used to denote saline soils.

23. Causes of Salinity in soil
1. Primary source of salts in soil is from rock weathering. During
weathering process soluble salts are formed. Solute movement
with water is the determining factor in soil salinization process.
2. Fluctuating depth of ground water or water table leads to soil
salinity.
3. In arid region less rainfall available to leach the salt and high
rate of evaporation causes concentration of salts in soil at
various layer.
4. Coastal Area: Due to inundation of sea water.
5. Irrigation water containing high concentration of soluble salts
(Na salts) leads to soil salinity.
6. Due to drainage restriction, reduces permeability of soil.

24. Crop choice
• Rice is preferred crop in alkali / sodic soil as it can grow under
submergence, can tolerate fair extent of ESP and can influence
several microbial processes in the soil.
• Agroforestry systems like silviculture, silvipasture etc. can
improve the physical and chemical properties of the soil along
with additional return on long-term basis.
• Some grasses like Brachariamutica (Para grass) and
Cynodondactylon (Bermuda grass) etc. has been reported to
produce 50 % yield at ESP level above 30.

25. Dry land salinity
Irrigated salinity

26. Soil Salinity Class
Conductivity of the
Saturation Extract
(dS/m)
Effect on Crop Plants
Non saline 0 - 2 Salinity effects negligible
Slightly saline 2 - 4 Yields of sensitive crops may be
restricted
Moderately saline 4 - 8 Yields of many crops are restricted
Strongly saline 8 - 16 Only tolerant crops yield
satisfactorily
Very strongly saline > 16 Only a few very tolerant crops
yield satisfactorily
Classes of soil Salinity

27. Management strategies
i) Bulky organic manure, green manure, crop residues and
other biological materials which produce week organic acids
help in creating temporarily in acidic condition and help in
reclamation
ii) Leaching with good quality water (low SAR) must follow the
application of the reclaiming materials
iii) A good crop rotation is an excellent insurance agt. Sodicity
problem; rice-dhaincha; Dhaincha-rice-berseem is good
iv)Frequent irrigation with small quantities of water is the
successful irrigation management practices
v) Sometimes, permeability of soil can increase by deep
ploughing

28. 28
Soil which are characterized by the presence of high
exchangeable sodium that adversely affect the growth of most
crop plants with pH of more than 8.5, Exchangeable sodium
percentage of >15 and a electrical conductivity of less than 4
(dS/m) .
Soil Sodicity

29. Presence of black patches on soil
Crop production is less than normal soils
Soils have very poor physical property due to
dispersion
Presence of coloumnar or prismatic structure in
B horizon
Waterlogging is common after heavy irrigation
29
Features of sodic soil

30. Management and reclamation of sodic soil
Amendments Organic manure Water management
Soluble calcium
containing
Acids and acid forming
CaSO4. 2H2O
CaCl2
Elemental S
FeSO4
FeS2
AlSO4
DSW
H2SO4
Drainage
Irrigation

31. 31
• Soil which are characterized by the electrical conductivity
of more than 4 (dS/m), high exchangeable sodium
percentage of > 15 that adversely affect the growth of most
crop plants with pH of less than 8.5.
• These soils form as a result of the combined processes of
salinisation and alkalization. If the excess soluble salts of
these soils are leached downward, the properties of these
soils may change markedly and become similar to those of
sodic soil.
Saline sodic soil

32. Management of saline-sodic soil
• Application of suitable amendment such as gypsum to
replace Ex.Na on the clay complex
• Subsequent removal of released sodium and other salts by
proper impounding of water and leaching
• Leaching of the soil without replacing Ex.Na results in
the formation of sodic soil which is more harmful to
plant growth than saline-sodic soil

33. Saline soil
1. White crust formation at the soil
surface
2. Good physical condition with good
aggregate structure
3. Permeability of soil for air and water
is good
4. No waterlogging with adequate
drainage and good aeration
5. Soils are friable with good tilth
6. Failure of crop is due to high salt
concentration or high osmotic
pressure which reduces availability of
water-exosmosis and plasmolyis
occur
Sodic soil
1. White crust formation with localized
black coloured spots or patches called
slick spots
2. Poor physical condition with
deteriorated soil structure. Hard pan
or clay pan in subsoils or Bhorizon
with columner or prismatic structure.
3. Low permeability
4. Waterlogging with restricted drainage
and poor aeration
5. Soils are hard and cloddy when dry
and sticky when wet with poor tilth
6. Failure of crop is mainly due to poor
physical condition of soil which
reduces availability of air (poor
aeration), water and nutrients to
plants.