The document discusses different sources of irrigation water including rainfall, surface water sources like rivers and lakes, groundwater sources like shallow wells, and combinations of surface and groundwater. It describes factors to consider for different water sources like quantity needs, quality, and competing uses. Water quality parameters for irrigation include electrical conductivity, sodium absorption ratio, and concentrations of salts, sodium, calcium, magnesium, and toxic elements. The document provides classifications for water salinity levels and sodium hazards and their suitability for irrigation on different soil types.

1. 11
Presentation-2
Sources of irrigation water
Irrigation /water supply to the soil means increase moisture content
which is very much essential for plant growth.
The main sources of irrigation water:
1. Rainfall
2. Irrigation source
Factors for Sources of irrigation
Water Sources for Irrigation
 Quantity needs
Quality factors
Surface water sources
Groundwater sources
Surface and groundwater combinations
 Certified well drillers and well code
 Conflict and competition for water

2. 2
Different ways of sources of irrigation water
1. Surface water
2. Atmospheric water other than precipitation
3. Flood water
4. Ground water
5. Surface and ground water
1.Surface water
Lakes, Rivers, Streams, Drainage ditches and private ponds
Presentation-2(contd.)

3. 3
2. Atmospheric water other than precipitation
Atmospheric water is dew/fog in the cloud. The dew/cloud falls
in the soil surface wet and seepage through it. In some parts of
the world the contribution of atmospheric water in forms other
than precipitation is significant. In portions of Western Australia,
sufficient dew forms to produce good pasture. In the Negeb
desert south west of the Dead Sea, dew is largely responsible
for summer growth of grapes. The scant rainfall of 10 to28
centimeters annually is augmented with 100 to 250 nights of
dew a year.
Source of water from atmosphere should have the
following atmospheric conditions are: (1) considerable dew
formation, (2) fog and clouds and (3) high humidity.
3. Flood water: Flood water inundated the land area. Flood
water in some cases irrigates to plant. But it is not supplied by
man. As floods pass over the surface of the land, water is
absorbed by the soil and stored for subsequent use by plants. In
some region growth of crops wholly depends upon flood water.
Presentation-2(contd.)

4. 4
4. Ground Water
Ground water is the water underneath the soil surface where voids of
soil is filled up with water. Ground water by capillarity from the water
table into the root zone can be a major source of water for crops
growth. To be most effective without seriously restricting growth,
ground water should be near but below the depth from which the major
portion of the plant’s water needs are extracted. If ground water is
within the normal root zone, plant growth is definitely suppressed. If
ground water is too near the surface, the land’s ability to economically
produce most crops becomes almost nil. However, a water table within
the lower portion of the root zone may supply a considerable amount
of water and thereby reduce the cost of irrigation more than it offsets
the loss of production. The optimum depth of water table is that
depth which gives the maximum economic return.
Examples of ground water
Deep tube wells, Shallow tube wells, Shallow suction wells,
Horizontal suction wells.
Presentation-2(contd.)

5. 5
5. Surface and ground water combination :
1. Pumping small well into pond as a reservoir
2. Allows a smaller pump, pumping continuously to
store water for larger pump to pump for shorter time
3. Very inefficient
-Requires pumping water twice
-Ponds are very leaky reservoirs
Presentation-2(contd.)

6. 6
Quality of irrigation water:
Irrigation water quality and proper irrigation management both are
critical to successful crop production. Different crops require
different irrigation water qualities. Therefore, testing the irrigation
water prior to selecting the site and the crops to be grown is critical.
Irrigation water quality determination parameters are three
categories:
1. chemical
2. physical and
3. biological
Presentation-2(contd.)

7. 7
Types of impurities in water making unfit for irrigation
1. Sediment concentration in water
2. Concentration of soluble salts in water
3. Sodium ions proportion to other cat ions
4. Concentration of toxic elements present in water
5. Bicarbonate concentration(Sodium + Magnesium)
6. Bacterial contamination
Presentation-2(contd.)

8. 8
1. Sediment concentration in water
The effect of sediment present in the irrigation water depends
upon the type of irrigated land. When fine sediment from
water is deposited on sandy soils improved the fertility of
irrigated land. On the other hand, eroded sediment deposited
on irrigated land reduced its fertility.
2.Concentration of soluble salts in water
Salts of calcium, magnesium, sodium and potassium present
in the irrigation water may injurious to plants. When present
in excessive quantities, they reduce the osmotic activities of
the plants and may present adequate aeration, causing
injuries to plant growth. The injurious effects of salts on the
plant growth depend upon the concentration of salts left in
the soil.
Presentation-2(contd.)

9. 9
Computation of salinity concentration in irrigation water
The salinity concentration of the soil solution (Cs) after consumptive
water (Cu) has been extracted from the soil may be calculated from
the following equation:
C × Q
Cs = (1-1)
[{Q – (Cu - Peff )}
Where,
Q = The quantity of water applied
Cu = Consumptive use of water
Cs = Salinity concentration of soil solution
Peff = Useful rainfall
(Cu - Peff ) = Used up irrigation water
C = Concentration of salt in irrigation water
C × Q = Total salt applied to soil with Q amount of irrigation water
Presentation-2(contd.)

10. 10
The salt concentration is generally expressed as ppm (parts per
million) or mg/l (milligram per litre).
Criteria for salt concentration:
• Salt concentration (Cs ) ≤ 700 ppm = Suitable to all plants
• Cs > 700 ppm and ≤ 2000 ppm = Harmful to some plants
• Cs > 2000 ppm = Injurious to all crops
Example-1-1
Find out salinity concentration of soil solution(CS ) and water
quality where the following data are given below:
Q = The quantity of water applied = 5000 liter
Cu = Consumptive use of water for its growth = 500 liter
Peff ) = Used up irrigation water = 300 liter
C = Concentration of salt in irrigation water = 500 mg/liter
Presentation-2(contd.)

11. 11
Solution
We know from equation (1-1)salt concentration of soil solution
(CS)
C×Q
CS =
[ Q – (Cu - Peff )]
Given, Q = 5000 liter
C u = 500 liter
Peff = 300 liter
C = 500 mg/liter
Putting the respective values in the above equation
500 ×5000
CS = = 520.83 mg/l ( ppm) Ans
{5000 – (500 —300)}
Since we know when Cs ≤ 700 ppm, the water is suitable to all plants
So the above water is suitable to all plants. Ans
Presentation-2(contd.)

12. 12
Measurement of salt concentration
Salt concentration is measured by electrical conductivity of
water.
Electrical conductivity (EC)
The tool for the measurement of salt concentration is
called Electrical Conductivity and express as dsm1
Salt concentration is directly proportional to electrical
conductivity of water expressed in micro mhos per
centimeter(micro mhos/cm).
Presentation-2(contd.)

13. 13
Types of Electrical Conductivity(EC)
Four types
1.Low conductivity (C1) of water : Electrical conductivity ≤ 250
micro mhos/cm at 250 C
2. Medium conductivity (C2) of water: Electrical conductivity
ranges from 250 to 750 micro mhos/cm at 250 C
3.High conductivity (C3) of water : Electrical conductivity
ranges from 750 to 2250 micro mhos /cm at 250 C
4. Very High conductivity(C4) of Water: Electrical conductivity >
2250 micro mhos/cm at 250 C
Presentation-2(contd.)

14. 14
Lecture-2(contd.)
TDS ppm or mg/L EC (dS/m) Salinity hazard
<500 <0.8 Low
500 - 1000 0.8 - 1.6 Medium
1000 - 2000 1.6 - 3 High
> 2000 > 3 Very high
The most common parameters used for determining
the irrigation water quality, in relation with its salinity,
are EC and TDS (Total dissolved salt).

15. 15
Sl.
No.
Type of water Suitable for irrigation
1. Low salinity water (C1) .
Conductivity between 100 -250
micro mhos/cm at 250C
Suitable for irrigation to almost all
crops and all kinds of soils. Very little
salinity may develop for which slight
leaching is required.
2. Medium salinity water (C2). :
Conductivity between 250 -750
micro mhos/cm at 250C.
Normal salt tolerant plants can be
grown without much salinity control.
3. High salinity water (C3):
Conductivity between 750- 2250
micro- mhos/cm at 250C
Only high salt tolerant plants can be
grown. Special measures are needed for
salinity control.
4. Very high salinity water (C4):
Conductivity above 2250 micro
mhos/cm 250C.
Generally unsuitable for irrigation.
Reference: USDA. Handbook No. 60(1954)
The measurement of quality of irrigation of water by
electrical conductivity are shown in the following Table 1– 1
Table 1-1
Presentation-2(contd.)

16. 16
3. Proportion of Sodium ions to other cat ions
Almost all the soils contain calcium and magnesium ions and
small quantities of sodium ions. The percentage of sodium is
generally less than 5% of the total exchangeable cat ions. If
this percentage increases more than 10% soil grains breaks.
The soil becomes less permeable and of poorer tilth. It starts
crushing when dry and its pH (Hydrogen ion concentration)
increases towards that of alkaline soil.
High Sodium soils are
sticky when wet and are prone to form
Plastic clods and they crust on drying
Presentation-2(contd.)

17. 17
Measurement of soil ion concentration:
United States Salinity Laboratory (USSL) staff
introduced the concept of Sodium Absorption
Ratio(SAR) to predict sodium hazard in the soil.
The parameter used to determine the sodium hazard
is SAR. This parameter indicates the amount of sodium in
the irrigation water, in relation to calcium and magnesium.
Calcium and magnesium tend to counter the negative effect of
sodium.
Presentation-2(contd.)

18. 18
Sodium adsorption ratio is a measure of the amount of sodium
(Na) relative to calcium (Ca) and magnesium (Mg) in the water extract
from saturated soil paste. It is the ratio of the Na concentration divided
by the square root of one-half of the Ca + Mg concentration. Soils that
have SAR values of 13 or more may be characterized by an increased
dispersion of organic matter and clay particles, reduced saturated
hydraulic conductivity and aeration, and a general degradation of soil
structure.
Na +
SAR = (1-2)
√ ( Ca ++ + Mg++ ) / √ 2
Where the concentration of the ions is expressed in equivalent
per million (epm).
Presentation-2(contd.)

19. 19
Magnesium Absorption Ratio (MAR)
The proportion of magnesium ions present in the soil is generally
measured by a factor called magnesium absorption ratio (MAR) to
predict magnesium hazard in the soil.
The magnesium absorption ratio is calculated by the equation as
follows:
MAR = { Mg /(Ca + Mg)} × 100
Epm is obtained by dividing the concentration of
salt in mg / litre or ppm by its combining weight
(atomic weight) i.e.
epm = (Atomic weight)/ Valence
Presentation-2(contd.)

20. 20
Types of SAR and its standard Values
When the value of SAR lies between
1. Low Sodium water (S1) 0 – 10
2. Medium Sodium water (S2) 10 – 18
3. High Sodium water (S3) 18 – 26
4. Very high Sodium water(S4) > 26
Remedy
Application of gypsum (CaSO4 ) can reduce the SAR
value of water or soil.
Presentation-2(contd.)

21. 21
Sl.No Type of water Useable to irrigation
1. Low sodium water
(S1). : SAR value lying
between
0-10
Suitable for irrigation on almost all soils
and for all crops. Unsuitable for highly
sensitive to sodium such as stone-fruit
trees and adocados, etc.
2. Medium sodium water
(S2). SAR value lying
between
10 - 18
Can use in hazardous fine textured soil
with the application of gypsum. It also
can use on coarse –textured or organic
soils with good permeability.
3. High sodium water(S3)
: SAR value lying
between 18- 26
Harmful for almost all soils. For
irrigation requires good drainage, high
leaching, gypsum addition etc.
4. Very high sodium(S4):
SAR value above 26
Generally unsuitable for irrigation.
Table 1-2 : The safe irrigation water
Presentation-2(contd.)

22. 22
Depending upon the Electrical Conductivity EC (representing salt content)
of water, the exchangeable sodium percentage ESP (representing
percentage of sodium with respect to total exchangeable cat ions) and the
pH value of the soil – the soils are classified as three divisions(Table 1-3)
1. Saline
2. Alkaline
3. saline- alkali
Sl.
No.
Classification EC in micro-
mhos/cm
ESP pH
value
1. Saline soil or white alkali > 4000 < 15 ≤ 8.5
2. Alkaline soil or Non
saline alkali or Sodic soil
or black soil
< 4000 > 15 8.5 to
10
3. Saline- alkali soil > 4000 > 15 < 8.5
Table 1-3
Presentation-2(contd.)

23. 23
4. Concentration of potentially toxic elements
A large number of elements like boron, selenium, etc. may be
toxic to plants. Traces of boron are essential to plant growth,
but its concentration above 0.3 ppm may prove toxic to some
plants. The concentration above 0.50 ppm is dangerous to
nuts, citrus fruits cotton. Cereals and certain truck crops are
moderately tolerant to boron, while dates, beets, asparagus
etc. are quite tolerant. Even for the most tolerant crops, the
boron concentration should not exceed 4 ppm.
5. Bi-carbonate concentration as related to concentration of
calcium plus magnesium
High concentration of bi-carbonate ions may result in
precipitation of calcium and magnesium bi-carbonates from
the soil-solution. Sodium hazards create due to the increment
of relative proportion of sodium ions.
Presentation-2(contd.)

24. 24
6. Bacterial contamination
Bacterial contamination of irrigation water is not a
serious problem, unless the crops irrigated with
contaminated water are directly eaten without being
cooked. Cash crops like cotton, jute, etc. which are
processed after harvesting, can therefore, use
contaminated water without any trouble.
Example 1-2
(a) What is the classification of irrigation water having the following
characteristics:
concentration of Na, Ca and Mg are 22, 3 and 1.5 milli-equivalents
per litre respectively and the electrical conductivity (EC) is 200
micro-mhos per cm at 25 0 C ?
(b) What problems might arise in using this water on fine textured
soils
(c) What remedies do you suggest to overcome this trouble?
Presentation-2(contd.)

25. 25
Solution :
Given,
Na + = 22 milli - equivalents per litre
Ca ++ = 3 milli - equivalents per litre
Mg++ = 1.50 milli - equivalents per litre
Electrical Conductivity, (EC) = 200 micro mhos/cm at 25 0 C
(a) We know, Sodium Absorption Ratio (SAR) : expressed as
Na +
SAR =
√ { ( Ca ++ + Mg++) / √2 }
Presentation-2(contd.)

26. 26
Putting the values in equation (1-2)
22
SAR = = 14.67
√{( 3 + 1.5) / √ 2]}
We know, as per category of SAR
SAR 10 – 18 = classified as medium sodium water S2
Electrical conductivity 100- 250 micro mhos/cm at 25 0 C,
classified as = Low conductivity C1
Computed SAR is within 10-18, SAR
Hence the given water classified as S2
Presentation-2(contd.)

27. 27
(b) In the textured soils, the medium sodium (S2) water creates
following problems:
• less permeable
• it starts crusting when dry
• becomes plastic and sticky when wet
• PH increases towards alkaline soil
(c) Remedy
CaSO4 (Gypsum fertilizer) addition either to soil or water can
overcome the sodium hazards.
Presentation-2(contd.)