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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
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)
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
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