Post on 21-Jun-2020
Lecture 6: Management of Treated Effluent Reuse
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 Management
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
Re
lati
ve Y
ield
(%
)
Relative Yield vs. Salinity
(Gates et al 2006)
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
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: plant adaptations- screening for salt tolerance of avocado
Field Diagnosis
Boron (B) Toxicity in treated effluent
Essential in low amounts (alfalfa)
Toxic to sensitive crops (>1.0 to 2.0 ppm)
Fertility Sufficient in low concentrations
Country/Organization Drinking Water (mg/l)
WHO 2.4
EU 1
Canada 5
Australia 0.3
Oman 0.5
Drinking water quality concerning Boron concentration according to many
countries
Tolerance CropsVery sensitive (<0.5 mg/l) Lemon , Blackberry
Sensitive (0.5-0.75 mg/l)
Avocado, Grapefruit , Orange, Apricot, Peach, Cherry,
Plum, Persimmon, Fig, kadota, Grape, Walnut, Pecan,
Cowpea, Onion
Sensitive (0.75-1.0 mg/l)
Garlic, Sweet potato, Wheat, Barley, Sunflower,
Bean, mung, Sesame, Lupine, Strawberry, Artichoke-
Jerusalem, Bean- kidney, Bean-lima, Groundnut-
Peanut
Moderate sensitive (1.0-2.0 mg/l)Pepper- red, Pea, Carrot, Radish, Potato,
Cucumber
Moderate tolerant (2.0-4.0 mg/l)
Lettuce, Cabbage, Celery, Turnip, Bluegrass-
Kentucky, Oats, Maize, Artichoke, Tobacco, Mustard,
Clover-sweet, Squash, Muskmelon
Tolerant (4.0-6.0 mg/l)Sorghum, Tomato, Alfalfa, Vetch-purple,
Parsley, Beet-red, Sugarbeet
Very tolerant (6.0-15.0 mg/l) Cotton, Asparagus
Effects of boron in plants:
Boron injury in citrus leaves
B toxicity - soybean
Boron concentration in irrigation water from Sheikh Ejleen and Al Mawasi
Master thesis: Abu Daba’an, 2017
Boron concentration in the leaves of Lemon irrigated by fresh and treated effluent at Sheikh Ejleen and Al Mawasi location
Master thesis: Abu Daba’an, 2017
Factors affecting amount of B adsorbed in the soil are:
There are many several factors influence the amount of- B adsorbed by soils. These
include pH, texture, wetting and drying, temperature. Ionic composition of the soil
solution, management practices such as liming and so on.
Soil pH:
Soil pH is one of the most important of these factors. It has been reported by several
investigators that increasing pH enhances B adsorption by soils, showing a maximum in
the alkaline pH range.
clay content :
The type of clay minerals and exchangeable ions in the soil. Generally, soils with low clay
content will adsorb less B than those with higher clay content. The greater the ability of
the soil to adsorb B, the lower the B content in the soil solution.
0
50
100
150
200
250
300
Clay Sand
mg
Bo
ron
/ kg
DM
So
ilBoron Accumulation in the Soil in Sheikh Ejleen (Clay) and El-
Mawasi (Sand)
Master thesis: Abu Daba’an, 2017
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
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