irrigation water quality

1. Quality of irrigation
water
Presentingby gopal meena

2. Introduction
All irrigation waters are not pure and
may contain some soluble salts. In arid
and semi-arid regions successful crop
production without supplemental
irrigation is not possible. Irrigation water
is usually drawn from surface or ground
water sources, which typically contain
salts in the range of 200 to 2000 ppm (=
200 to 2000 g/m3). Irrigation water
contains 10 – 100 times more salt than
rain water.

3. Various criteria are considered in evaluating the quality of irrigation water
namely:
Salinity hazard
Sodium hazard
Salt index
Alkalinity hazard

4. Salinity hazard
• The excess of salts content is one of the major concerns with water used
for irrigation.
• A high salt concentration present in the water and soil will negatively affect
the crop yields, degrade the land and pollute groundwater.
• The suitability of water reuse for irrigation with high salt content depends
on the following factors:
• Salt tolerance of the type of crop
• Characteristics of the soil under irrigation Climate conditions.
• The quality of the irrigation water plays an essential role in arid areas
affected by high evaporation rates and cause high concentrations of salt
accumulating in the soil.
• Soil and water management practices

5. country Irrigated Land Damaged by Salt(million Ha) Total irrigated Land Damaged by Salt (percent)
India 7.0 17
China 6.7 15
Pakistan 4.2 26
USA 4.2 23
Uzbekistan 2.4 60
Iran 1.7 30
Turkmenistan 1 80
Egypt 0.9 33
Subtotal 28.1 21
World Estimate 47.7 21

6. Sodium hazard
• High sodium ions in water affects the permeability of soil and causes
infiltration problems.
• This is because sodium when present in the soil in exchangeable form
replaces calcium and magnesium adsorbed on the soil clays and causes
dispersion of soil particles
• (i.e. if calcium and magnesium are the predominant cations adsorbed on
the soil exchange complex, the soil tends to be easily cultivated and has a
permeable & granular structure).
• This dispersion results in breakdown of soil aggregates.
• The soil becomes hard and compact when dry and reduces infiltration rates
of water and air into the soil affecting its structure.

7. 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.

8. Alkalinity hazard
• The “alkaline” in alkaline water refers to its pH level. The pH level is a
number that measures how acidic or alkaline a substance is on a scale
of 0 to 14. For example, something with a pH of 1 would be very
acidic and something with a pH of 13 would be very alkaline.
• Alkaline water has a higher pH level than regular drinking water.
Because of this, some advocates of alkaline water believe it can
neutralize the acid in your body.
• Normal drinking water generally has a neutral pH of 7. Alkaline water
typically has a pH of 8 or 9. However, pH alone isn’t enough to impart
substantial alkalinity to water.

9. Thank
you