Designing Sustainable Wastewater Reuse Systems: Towards an Agroecology of Wastewater Irrigation - Governing the Nexus: Water, Soil and Waste Resources Considering Global Change - page 170

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Degree of Restriction on Irrigation
Potential Irrigation Problem Units None Slight to Moderate Severe
In ltration (affects in ltration rate of water into the soil; evaluate using ECW and SAR
together) 3
SAR 0-3 and EC W = >0.7 0.7-0.2 <0.2

3-6 >1.2 1,2-0.3 <03

6-12 >1.9 1.9-0.5 <0.5

12-20 >2.9 2.9-1.3 <1.3

20-40 >5.0 5.0-2.9 <29

Specific Ion Toxicity (affects sensitive crops)
Sodium (Na) 4
surface irrigation SAR <3 3-9 >9

sprinkler irrigation meq/l <3 >3

Chloride (CI) 4
surface irrigation meq/l <4 4-10 >10

sprinkler irrigation meq/l <3 >3

Boron (B) mg/L <0.7 0.7-3.0 >3.0

Miscellaneous Effects (affects susceptible crops)
Nitrate (NO 3 -N) mg/L <5 5-30 >30

Bicarbonate (HCO 3 ) meq/L <1.5 1.5-8.5 >8.5

pH Normal Range 6.5-8.4

a Adapted from FAO (1985)
b EC w means electrical conductivity, a measure of the water salinity, reported in deciSiemens per
metre at 25°C (dS/m) or in millimhos per centimetre (mmho/cm); both are equivalent
c SAR is the sodium adsorption ratio; at a given SAR, in ltration rate increases as water salinity
increases
d For surface irrigation, most tree crops and woody plants are sensitive to sodium and chloride;
most annual crops are not sensitive. With overhead sprinkler irrigation and tow humidity (<30
percent), sodium and chloride may be absorbed through the leaves of sensitive crops
Source: USEPA ( 2012 : 3-7)

USEPA recommendations on other toxic elements in irrigation water

Constituent Maximum Concentrations

for Irrigation (mg/L)

Remarks

Aluminium 5.0 Can cause nonproductiveness in acid soils, but

soils at pH 5.5 to 8.0 will precipitate the ion and
eliminate toxicity

Arsenic 0.10 Toxicity to plants varies widely, ranging from

12 mg/L for Sudan grass to less than 0.05 mg/L
for rice

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