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