Organic Waste Recycling

404 Organic waste reuse and recycling: technology and management

Table 8.6 Relationship of potential problems to concentration of major inorganic
constituents in irrigation waters for arid and semi-arid climates (Ayers and Westcot
1976)

Problem and related constituent No problem Increasing
problem

Severe
problem
Salinitya
EC of irrigation water, mmhos/cm

Permeability
EC of irrigation water, mhos/cm
SAR (sodium adsorption ratio)b

Specific ion toxicityc
From root absorption
Sodium (evaluated by SAR)
Chloride, meq/L
Chloride, mg/L
Boron, mg/L
From foliar absorption
(sprinklers)d
Sodium, meq/L
Sodium, mg/L
Chloride, meq/L
Chloride, mg/L
Miscellaneouse
HCO 3 - , meq/L
HCO 3 - , mg/L

<0.75

>0.5

<6.0

<3

<4

<142

<0.5

<3.0

<69

<3.0

<106

<1.5

<90

0.75-3.0

<0.5

6.0-9.0

3.0-9.0

4.0 – 10

142-355

0.5-2.0

>3.0

>69

>3.0 >106

1.5-8.5

90-250

>3.0

<0.2

>9.0

>9.0

>10 >355

2.0-10.0

>8.5

>520

pH Normal range = 6.5-8.5
Note: Interpretations are based on possible effects of constituents on crops and/or soils.
Suggested values are flexible and should be modified when warranted by local
experience or special conditions of crop, soil, and method of irrigation.
a Assuming water for crop plus water needed for leaching requirement will be applied.

Crops vary in tolerance to salinity. Electrical conductivity (EC) mmhos/cm x 640 =
approximate total dissolved solids (TDS) in mg/L or ppm.
b

[]()Ca Mg/ 20.^5

SAR Na

+

=

where Na = sodium; Ca = calcium; Mg = magnesium, in all meq/L.
c Most tree crops and woody ornamentals are sensitive to sodium and chloride (use

values shown). Most annual crops are not sensitive.
d Leaf areas wet by sprinklers (rotating heads) may show a leaf burn due to sodium or

chloride absorption under low-humidity, high-evaporation conditions. (Evaporation
increases ion concentration in water films on leaves between rotations of sprinkler
heads.)
e HCO 3 - with overhead sprinkler irrigation may cause a white carbonate deposit to form

on fruit and leaves.