assessment of irrigation water quality

7/27/2019 Assessment of Irrigation Water Quality

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CONTENTS

• INTRODUCTION.

• SOURCES OF IRRIGATION WATER.

• WATER QUALITY EFFECTS.

• ASSESSMENT OF IRRIGATION WATER QUALITY.

• CONCLUSIONS.

• REFERENCES.

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INTRODUCTION

• Water is an important resource for growing plants. Plants, byweight, are comprised of 85 to 90 percent water.

• Chemicals in irrigation water can impact the growth of plants.

• The source of irrigation water can affect the quality of the water.

• Irrigation water quality is determined by measuring the level of dissolved elements it contains.

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SOURCES OF IRRIGATION WATER

• Water quality can vary from source to source.

• Three main sources of irrigation water commonly used by

farmers:

• Well water (open/tube well)

• Channel water from reservoir, and

• Pond water.

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WATER QUALITY EFFECTS

• Poor quality water can be responsible for slow growth, poor aesthetic quality of

the crop and, in some cases, can result in the gradual death of the plants.

• High soluble salts can directly injure roots,

interfering with water and nutrient uptake.

• Salts can accumulate in plant leaf margins,

causing burning of the edges.

• Water with high alkalinity can adversely affect the ph of the growing medium,

interfering with nutrient uptake.

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ASSESSMENT OF IRRIGATIONWATER QUALITY

• In assessing the suitability of waters for irrigation use, water

quality characteristics that affect agricultural production,

catchment condition, and downstream water quality need to be

evaluated.

• The parameters that determine irrigation water quality are

divided into three categories:

• Chemical;

• Physical;

• Biological.

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ELECTRICAL CONDUCTIVITY

• Soluble salts in water are measured by electrical conductivity expressed

as millimhos per centimeter (mmhos/cm), which is equivalent to

millisiemens per centimeter (ms/cm).

• Electrical conductivity is also referred to as specific conductance.

• EC (electrical conductivity) measures the levels of natural salinity and

salinity caused by fertilizer residues in water and soils.

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ALKALINITY & PH

• Alkalinity and ph are two important factors in determining the

suitability of water for irrigating plants.

• pH is a measure of the concentration of hydrogen ions (H+) in water or

other liquids.

• Alkalinity is a measure of the water's ability to neutralize acidity.

• In general, water for irrigation should have a ph between 6.0 and 7.0.

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CONTD..

• An alkalinity test measures the level of bicarbonates, carbonates, and

hydroxides in water from the geologic materials of the aquifer from which

the water is drawn, such as limestone and dolomite.

• Alkalinity is generally expressed as "ppm of calcium carbonate (CaCO3)".

• The desirable range for irrigation water is 0 to 100 ppm calcium carbonate.

Levels between 30 and 60 ppm are considered optimum for most plants.

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HARDNESS – CALCIUM AND MAGNESIUM

• Hardness is an indication of the amount of calcium and magnesium inthe water.

• Calcium and magnesium are essential elements for plant growth that are

reported in parts of element per million parts water (ppm) on a weight

basis.

• Calcium in the range of 40 - 100 ppm, and magnesium in the range of

30 - 50 ppm are considered desirable for irrigation water.

• Soft water (water high in Na) makes hard ground.

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SODIUM HAZARD

• Irrigation water from rivers, streams, private wells, and private ponds may contain

excess sodium (Na).

• Na can be directly toxic to plants, may contribute to raising the soluble salts (EC)

level of the growing medium, or may inhibit water uptake by plants.

• Plant problems include injury from excess soluble salts, growth reduction, and

increased susceptibility to disease.

• Sodium levels of about 50 ppm or less are considered acceptable for overhead

irrigation.

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CONTD…

• Reductions in water infiltration can occur when irrigation water contains high

sodium relative to the calcium and magnesium contents. This condition is

termed as “sodicity,”

• Sodicity causes

• Swelling and dispersion of soil clays,

• Surface crusting and

• Pore plugging.

• Sodium adsorption ratio (SAR) - most common measure to assess sodicity in

water and soil.

• The higher the SAR, the greater the sodium hazard. 14



CONTD…

• The SAR is mathematically written below

• Sodicity causes a decrease in the downward movement of water into and

through the soil, and actively growing plant roots may not get adequate

water.

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CHLORIDE

• Chloride is a common ion in irrigation waters.

• Although chloride is essential to plants in very low amounts, it can

cause toxicity to sensitive crops at high concentrations

• High chloride concentrations cause more problems when applied with

sprinkler irrigation

• Leaf burn under sprinkler from both sodium and chloride can be

reduced by night time irrigation or application on cool, cloudy days.

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AMMONIUM AND NITRATE

• Nitrogen in irrigation water (N) is largely a fertility issue,

• These nutrients are tested to give an indication of possible contamination of

the water source. If present in significant amounts (e.g., >5 ppm nitrate),

they should be taken into account in the fertility program.

• The nitrate ion often occurs at higher concentrations than ammonium in

irrigation water.

• Waters high in n can cause quality problems in crops such as barley and

sugar beets and excessive vegetative growth in some vegetables

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MICRONUTRIENTS AND TRACE MINERALS

• The most important micronutrients are copper, zinc, manganese, iron

and boron. They can occur in excessive or deficient quantities.

• Excess iron and manganese compounds may result in unsightly residues

on foliage under overhead irrigation.

• Boron is another element that is essential in low amounts, but toxic at

higher concentrations.

• Concentrations in irrigation water should be less than 0.75 ppm.

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BIOLOGICAL PARAMETERS

• Algae

• The main problem associated with excessive algal growth in irrigation

waters is the blockage of distribution and irrigation equipment.

• Excessive algal growth in water storages and irrigation ditches commonly

occurs as a result of nutrient pollution.

• Cyanobacteria

• Problems associated with cyanobacteria arise when toxins are produced in

excessive amounts during these blooms.

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CONCLUSIONS

• Irrigation water quality is determined by salt concentration and type. As

salt concentration increases, plant-available moisture decreases, which

restricts crop growth.

• We can manage the poor irrigation water by increasing salt tolerance of

plants and improving irrigation management technologies.

• Investigate any change in water quality at the earliest possible time for

effective irrigation.

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REFERENCES

• Ayres, R.S. and Westcott, D.W. (1976). Water quality for agriculture.F.A.O. Irrigation and drainage paper no. 29 F.A.O. Rome.

• Guy Fipps. Irrigation water quality standards and salinity management

strategies.

• Brian Whipker. Irrigation water quality for container-grown plants.

Department of Horticulture,usa.

• Gordon Johnson, Hailin Zhang. Classification of irrigation water quality.

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