Irrigation Water Electrical Conductivity

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Irrigation WaterElectrical Conductivity
I
R V/I ohms electrical resistance
R
EC I/V 1/R mhos electrical conductance
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Irrigation WaterElectrical Conductivity

• EC depends on how far apart the plates are
• EC depends on the concentration of solutes in the
  water

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Irrigation WaterElectrical Conductivity

• Generally for irrigation water0 lt EC lt 30
  dS/m
• 1000 micromhos/cm 1 dS/m
• 1 dS/m 640 ppm dissolved salts

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Crop Salinity Tolerance
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Examples of crop salt tolerance
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Effects of Irrigation on Water Quality

• Irrigation frequently causes surface runoff
• Increased sediment losses
• Increased loss of organic nitrogen
• Increased loss of phosphorus
• Increased loss of pesticides

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Effects of Irrigation on Water Quality

• Irrigation increases the average level of soil
  moisture in the root zone
• Increased surface runoff
• Increased deep percolation and leaching from
  natural rainfall
• Increased chemical movement to both surface and
  ground water

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Effects of Irrigation on Water Quality

• All irrigation water, regardless of source
  contains dissolved chemicals
• Increased total dissolved solids content in the
  soil water
• Increased leaching of chemicals to ground water
• Increased salt content of surface runoff water

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Effects of Irrigation on Water Quality

• Irrigation will tend to increase the amount of
  Nitrate leached to ground water and lost with
  subsurface drainage
• Irrigation will tend to increase the amount of
  pesticides leached to ground water and lost to
  subsurface drainage.

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Drying up of the Aral Sea

• The total water withdrawal increased from 64.7
  km³ in 1960 to 120 km³ in 1980, of which more
  than 90 for agricultural purposes
• Its level has dropped by 17 m, its surface area
  has fallen by a half and its volume by
  three-quarters
• 550 000 ha reservoir of biodiversity have almost
  disappeared
• More than 50 lakes, covering 60 000 ha in the
  deltas, have dried up

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Aral Sea in 1985
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Aral Sea in 1994
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Drying up of Aral Sea (cont.)

• Deterioration of surface and ground waters
• Salt content in ground waters was up to 30
  g/litre (30000 ppm) (EC 50 dS/m)
• The exposed seabed
• Vast salt tracts, whose sand and dust, polluted
  with pesticides
• Dust and sand are carried by the wind to
  neighboring areas and up to a distance of 250 km
• The eolian transfer of dust and sand
• estimated at 15-75 million t/year