Quality of Irrigation Water

• Just as every water is not suitable for human beings, in the same way, every water is not suitable for plant life.
•  water contains impurities , which are injurious to plant growth is not satisfactory for irrigation
• Various types of impurities are

1. Sediment concentration
2. Total concentration of soluble salts
3. Sodium ion concentration
4. Concentration of toxic elements

i.    Sediment Concentration in water

• When fine sediment from water is deposited on sandy soils, the fertility is improved.
  जब पानी से बारीक तलछट को रेतीली मिट्टी पर जमा किया जाता है, तो उपजाऊ क्षमता में सुधार होता है।
• If the sediment has been derived from eroded areas , it may reduce the fertility.

ii.    Total Concentration of soluble salt-

• Salts of calcium, magnesium, sodium and potassium present in water is injurious to plants.
• The effect of salts on plant growth depends largely upon the total amount of salts present in the soil solution.
• Salt concentration is measured by electrical conductivity of water in micro mhos/cm
• Concentration is expressed in ppm ( parts per million) or mg/l.
• Salt concentration in excess of 1700 ppm is harmful to few plants but concentration greater than 2000 ppm is harmful to all the plants.

iii.   Sodium ion concentration

• If percentage of sodium ion concentration increases 10% or more, soil becomes less impermeable.
• This is expressed in terms of Sodium- Absorption Ratio (SAR) and represent sodium hazards of water.

• All the concentration of ions is expressed in equivalent per million (epm).
• The SAR value can be reduced by adding Gypsum (CaSO4) to the water or to the soil.

  iv.   Concentration of Toxic Elements

• Boron Concentration should not exceed 4 ppm.
• Selenium, even in low concentration is toxic and must be avoided.

Important Questions

Q.01 Pinpoint the correct statement

A) Irrigation helps in adopting mixed cropping

B) 'Mixed cropping' means sowing of a different crop after a particular crop has been grown

C) Over - irrigation may lead to saving in fertilizers

D) Irrigation helps in avoiding mixed cropping

Q.02 The method of growing crops on ridges , running on the sides of water ditches is known as

A) Basin flooding

B) Check flooding

C) Furrow Irrigation

D) Wild flooding

Q.03 In flood irrigation the preferred method of applying irrigation water to the comparatively steeper rolling land is -

A) Check flooding

B) Border flooding

C) wild flooding

D) basin flooding

Q.04 In a mildly water scarce area suitable method of irrigation is-

A) Basin flooding

B) Sprinkler method

C) Drip irrigation

D) furrow irrigation

Q.05 Sprinkler irrigation system is suitable when ?

A) The land gradient is steep and soil is easily erodible

B) Soil is having low permeability

C) water table is low

D) the crops to be grown have deep roots

Q.06 Salinity in irrigation water is measured by ?

A) SAR value

B) Electrical conductivity value

C) pH value

D) none

Q.07 An identified source of irrigation water has ion concentration of Na+, Ca++ and Mg++ as 20, 10 and 80 mill equivalent per liter respectively. The SAR of this water is approximately?

A) 1.06

B) 2.67

C) 6.67

D) 9.67

Q.08An identified source of irrigation water has ion concentration of Na+, Ca++ and Mg++ as 20, 10 and 80 mill equivalent per liter respectively. The SAR of this water is approximately

A) Low sodium water

B) Medium sodium water

C) high sodium water

D) very high sodium water

Q.09 Addition of gypsum to the irrigation water is recommended to overcome difficulties  posed by

A) High supplies containing heavy sediment

B) High concentration of Boron

C) Highly saline irrigation supplies

D) All of the above

Q.11 Electrical conductivity of water is in between 250 to 750 micro mhos/cm, then it is classified as

A) Low salinity

B) medium salinity

C) high salinity

D) very high salinity

Q.12 Boron concentration in irrigation water considered toxic to plants if it is more than

A) 1 ppm

B)  2 ppm

C) 3 ppm

D) 4 ppm