Quality and Standards

1. Irrigation Water
Quality and Standards
Presented By :
Dr. R.K. Thakur
Assistant Professor (Soil Science)
College of Agriculture, Balaghat
Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

2.  All irrigation water contains some salt, but quantities
and kinds vary greatly.
 Since the salt and sodic status of a soil can be greatly
affected by salts in irrigation water.
 Agricultural crops receive moisture for their growth and
development mostly from two sources : (i) rain water
and (ii) irrigation water.
 Various criteria for the evaluation of irrigation water
with permissible limits for crop growth are being
discussed here :
Introduction :-

3. Salinity hazard or total soluble salt concentration
or Electrical Conductivity (dSm-1) :-
Water class Salt
concentrati
on (g L-1)
EC (dSm-1) Remarks
Low salinity (C1) < 0.16 0.0 – 0.25 Can be used safely
Medium salinity
(C2)
0.16 – 0.50 0.25 – 0.75 Can be used with
moderately leaching
High salinity (C3) 0.50 – 1.50 0.75 – 2.25 Can be used for
irrigation purposes with
some management
practices
Very high salinity
(C4)
1.50 – 3.00 2.25 – 5.00 Cannot be used for
irrigation purposes

4. Sodium hazard (Sodium Adsorption Ratio-SAR) :-
Water class SAR Value Remarks
S1 – Low Na+ < 10 Any type of crops grown and
water used
S2 – Medium Na+ 10 – 18 Drainage water used for sandy
soil
S3 – High Na+ 18 – 26 Sensitive crops are not take
S4 – Very high Na+ > 26 This water is not used for
crops.
 It is the ratio of the concentration of Na+ to the concentration of
Ca + Mg and all these concentrations are expressed in me/litre.

5. Bicarbonate hazard (Residual Sodium Carbonate-
RSC) :-
Water class RSC Value Remarks
Low RSC < 1.25 Can be used safely
Medium RSC 1.25 – 2.50 Can be used with certain
management
High RSC > 2.50 Unsuitable for irrigation
purposes

6. Salt Index :-
 The salt index is used to determine the sustainability of
irrigation water containing salts in excess of sodium
chloride.
 It is also used for predicting sodium hazards. It is the
relationship between Na+, Ca2+ and CaCO3 present in
irrigation water. All salt concentrations are expressed in
ppm.
Salt Index = (Total Na – 24.5) – [(Total Ca – Ca in CaCO3) x 4.85]
 The value of salt index is negatively for good quality
waters and positive value for water unsuitable for
irrigation.

7. Boron Concentration :-

8. Chloride Concentration :-

9. Soluble Sodium Percentage (SSP) :-
 Excess of sodium ions characterizes the water as saline or alkaline
depending upon its occurrence in association with chloride/
sulphate or carbonate/ bicarbonate ions.
 For some time in the past, the quality of irrigation water used to be
evaluated with respect to sodium based on soluble sodium
percentage (SSP) calculated as below :
 It has been useful in characterizing water, since a high value
indicates soft water and low value hard water.
 When water with excess of sodium (SSP=66) is used for irrigation,
part of it is adsorbed on the soil. Both, soils and plants are adversely
affected by high sodium irrigation water.

10. Magnesium Hazard :-
 It is believed that one of the important qualitative
criteria in judging the irrigation water is its Mg
content in relation to total divalent cations, since high
Mg adsorption by soils affects their physical
properties.
 A harmful effect on soils appears when Ca : Mg ratio
decline below 50.
 Magnesium hazard in irrigation water is expected
having Mg : Ca ratio more than one.

11. Nitrate Concentration :-
Water class Nitrate Value
(me L-1)
Remarks
Low Nitrate 5.0 Good water No problem
Medium Nitrate 5.0 – 30.0 Moderately good water
High Nitrate > 30.0 Unsuitable for irrigation
purposes

12. Lithium :-
 Lithium is a trace element may be found in most of saline
ground water and irrigated soils.
 It has been found that small concentrations (0.05-0.1
ppm) of lithium in irrigation water produce toxic effects
on growth of citrus.
 It has also been reported that saline soils of varying
degrees found in India contain lithium upto 2.5 ppm.
 Fortunately, the germination of majority of crops i.e. rice,
wheat, barley etc. are not affected with this level of
lithium content in soils.

13. Fluoride :-
 Fluorides are only sparingly soluble and are in only
small amounts.
 The concentration of fluoride ranges from traces to more
than 10 mg L-1 in natural water, and surface water do not
exceed 0.3 mg L-1 unless they are polluted.
 Irrigation with fluoride saline water (upto 25 mg L-1) has
not been found to affect yield of wheat.
 Therefore, it is doubtful if fluoride requires any
monitoring in India.
 At present, the average concentration of fluoride has not
been observed to be very high (10 mg L-1).

14. Thanks