Lecture 8: Irrigation Water Quality

The Islamic University of Gaza- Civil Engineering Department

Irrigation and Drainage- ECIV 5327

Prepared by

Husam Al-Najar

Physical Parameters used in the evaluation of agricultural water quality

NTU/JTU = Nephelometric Turbidity Unit/ Jackson Turbidity Unit

Parameters Symbol Unit

Total dissolved solids

Electrical conductivity

Temperature

Color/turbidity

Hardness

sediments

TDS

EC

T

mg/l

ds/moC

NTU/JTU

mg equivalent CaCO3/l

g/l

Chemical Parameters used in the evaluation of agricultural water quality

Parameters Symbol Unit

Acidity/basicityType and concentration of

anions and cations

Calcium

Magnesium

Sodium

Carbonate

Bicarbonate

Chloride

Sulphate

Sodium adsorption ratio

Boron

Trace metals

Heavy metals

Nitrate-nitrogen

Phosphate

Potassium

pH

Ca

Mg

Na

CO3

HCO3

Cl

SO4

SAR

B

NO3-N

PO4-P

K

mg/l

mg/l

All waters used for irrigation contain varying amount of salts

• Salinization of soil and water is inevitable in climates where ET > precipitation

• Thus, drainage, either natural or artificial is essential to manage salts

• Key to sustainable irrigated agriculture in arid/semi-arid climates

Salinity

Salinity-total salt content

– Electrical Conductivity (ECw)

– Electrical Conductivity of saturated paste extract (ECe or sat)

General Irrigation Water EC Classifications

Electrical conductivity (ds/m)TDS (mg/l)Class of Water

≤ 0.25< 1000Class 1, excellent

0.25- 0.75Class 2, good

0.76-2.001000-2000Class 3, permissible

2.01-3.00Class 4, Doubtful

≥ 3.00˃ 2000Class 5, Unsuitable

Permissible: leaching is needed if usedDoubtful and Unsuitable: good drainage needed and sensitive plants will have difficulty obtaining stand.

Plants only transpire "pure" water

Salts in irrigation water remain in soil – if

not leached

Salinity Impact

Plant

– Physiological drought

– Increased osmotic potential of soil

– Specific ion toxicity

– Leaf burn

– Nutrient uptake interferences

Saline sites: salt tolerance

genotypic differences in

reaction to increasing NaCl

supply

Phaseolus bean

sugar beet

Crop Selection

Evapotranspiration vs. Salinity

(Gates et al. 2006)

Yield vs. Evapotranspiration

Schneeklothet al, 2004

ECe

Rela

tive Y

ield

(%

)

Relative Yield vs. Salinity

(Gates et al 2006)

Salinity effects

Crops classification according to salinity

Salinity rating group Threshold salinity (dS/m)

Zero yield salinity

Sensitive (almond, apple, apricot, carrot)

1.4 8.0

Moderately sensitive (corn, grape, pepper, tomatoes)

3.0 16.0

Moderately tolerant (olive, barley)

6.0 24.0

Tolerant (cotton, date palm) 10.0 32.0

Sodicity (sodic) -high sodium content

– SAR: sodium adsorption ratio

Where: Na, Ca, and Mg concentrations must be expressed as meq/l

2

Mg+Ca

Na = SAR

++++

+

Generalized Classification of Salt-Affected Soils

pHSAREC (ds/m)Classification

˂ 8.5˂ 13˃ 4.0Saline

˃ 8.5≥ 13˂ 4.0Sodic

˂ 8.5≥ 13˃ 4.0Saline-Sodic

˃ 7.8˂ 13˂ 4.0High pH

Specific Ion Concerns and Toxicities

Sodium (Na+)

Soil – sodicity

– Crusting

– Reduced infiltration

– Lower hydraulic conductivity

– Higher pH impacting nutrient uptake

Plant

– Stunted plants

– Toxicity and leaf burn potential

EC and SAR

The hazard of irrigation water sodium

on soil infiltration mustbe determined

from the SAR/EC interaction.

As EC increases relative to SAR,

infiltration problems are reduced.

Rainfall or sprinkler irrigation with

non-saline water on soils previously

irrigated with sodic water can

increase the infiltration problem.

Ayers and Westcott, 1985

Chloride (Cl-)

Contributes to EC

Essential in low amounts

Sensitive crops affected at high concentration

Leaf burn potential under sprinkler

Burn higher with daytime irrigation

Chloride tolerance criteria

Effect on cropChloride (mg/l)

Generally safe for all plants< 70

Sensitive plants show injury70-140

Moderately tolerant plants show injury141-350

Can cause sever problems> 350

Boron (B)

Essential in low amounts (alfalfa)

Toxic to sensitive crops (>1.0 to 2.0 ppm)

Fertility Sufficient in low concentrations

Degree of restriction Potential irrigation problem unit

None Slight to

moderate

Sever

Salinity

EC

TDS

ds/m

mg/l

< 0.7

< 450

0.7-3

450-2000

> 3.0

> 2000

Permeability

SAR= 0-3 and EC =

3-6

6-12

12-20

20-40

ds/m

> 0.7

> 1.2

> 1.9

> 2.9

> 5.0

0.7-0.2

1.2-0.3

1.9-0.5

2.9-1.3

5.0-2.9

< 0.2

< 0.3

< 0.5

< 1.3

< 2.9

Specific Ion toxicity

Sodium

Surface irrigation

Sprinkler irrigation

Chloride

Surface irrigation

Sprinkler irrigation

SAR

mg/l

mg/l

mg/l

< 3

< 70

< 140

< 100

3-9

> 70

140-350

> 100

> 9

> 350

Miscellaneous effects

pH

Residual chlorine (overhead

sprinkler only)

mg/l

Normal range 6.5-8.4

< 1.0 1-5

> 5.0

The Guidelines for the use of effluent waste water quality in irrigation (Takashi,

1990)

Saline sites: management

(Jordan valley)

Management Options

Saline sites: plant adaptations- screening for salt tolerance of avocado

Field Diagnosis

N deficiency symptoms: corn

Nitrogen cycle

leaching

biological N2

fixation(N2R-NH2)

Soil

nitrification(NH4

+NO3-)

uptake

mineralization(R-NH2 NH4

+)

N2O, NOx,

N2

Atmosphere

denitrification(NO3

-N2O, NOx, N2)

organic

matter

N2

NO3-

NH4+

NO3- fertilizers

NH4+ fertilizers,

urea

organic

fertilizers

(manure...)

legumes

P deficiency sypmtoms

K deficiency symptoms

Calcareous sites: B toxicity -soybean

Saline sites: salt

tolerance genotypic

differences in reaction to

increasing NaCl supply

Phaseolus bean

sugar beet

Catego

ry

Reuse condition Exposed group Intestinal

nematodes (arithemetic

mean no. of eggs

per litre)

Fecal coliform (geometric mean no.

per 100 ml)

A Irrigation of crops likely to be

eaten uncooked, sports fields,

public parks

Workers,

consumers public

< 1 < 1000

B Irrigation of cereal crops,

industrial crops, fodder crops,

pasture and tries

Workers < 1 No standard

recommended

C Localize irrigation of crops in

category B if exposure of

workers and the public does not

occur

None Not applicable Not applicable

Recommended microbiological quality guidelines for wastewater use in

agriculture

Crop Type North Gaza Middle Khanyuns Rafah Total

Citrus 2,200 5,812 3,522 173 893 12,600

Olives 145 6,200 5,552 8,000 3,000 22,897

Date Palm Only small area remaining

Almonds 2 0 511 900 1,750 3,163

Fruits 301 2,992 2,552 3,831 657 10,333

Vegetables

(protected)

4,754 286 2,347 6,470 7,525 21,382

Vegetables 6,756 3,532 5,860 17,376 13,520 47,044

Field crops 2,494 3,423 5,135 21,680 3,830 36,562

Flowers 13 0 10 10 481 514

ornamentals 12 0 0 120 0 132

Total 16677 22245 25489 58560 31656 154,627

Crop type and areas in the Gaza Strip (dunum) Source: Ministry of agriculture, 2004

Parameter Palestinian Standards

Irrigation Recharge

BOD (mg/l) 20-60 20

TSS (mg/l) 30-90 30

TDS (mg/l) 1500 1500

EC (ms/cm) - -

T-N (mg/l) 45 100

Na (mg/l) 200 230

Cl (mg/l) 500 600

SAR 9 -

B (mg/l) 0.7 1

F. Coliform (MPN/100ml) 200-1000 200-1000

Nematodes (ovum/l) <1 <1

Palestinian Standards for irrigation and groundwater recharge