Note: The values listed below are for a Irrigation Water having an
Electrical Conductivity (ECiw) of about one mmho/cm, which is approximately equal
to 640 milligrams per liter (mg/l) of soluble salts.
Cations
(ions with a positive charge)
Range found
Medium
Value
Enter
YOUR
Lab
Result
Anions
(ions with a negative charge)
Range found
Medium
Value
Enter
YOUR
Lab
Result
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
Sodium
(Na+)
58 - 173
115
Chloride
(Cl-)
46 - 138
92
Calcium
(Ca2+)
40 - 120
80
Sulfate
(SO42-)
96 - 288
192
Magnesium
(Mg2+)
7 - 22
14
Bicarbonate
(HCO3-)
92 - 275
183
Potassium
(K+)
4 - 12
8
Carbonate
(CO32-)
3 - 9
6
Total Sum of Cations:
217
Total Sum of Anions:
473
Milligrams of SOLUBLE SALTS per Liter: Is the sum of the Cations
plus the Anions.
From the above example: 217 mg/l + 473 mg/l = 690 mg/l
of soluble salts
Enter Your Results: (mg/l cations) + (mg/l
anions) = (mg/l soluble salts)
Pounds of SOLUBLE SALTS applied per acre foot of irrigation water
(i.e., 325,887 gallons) used:
From the above example: 690 mg/l x
2.72 = 1,877 lb. soluble salts/acre foot
Assume that you use 3.5 acre feet of water per acre: 1,877 lb. soluble salts x
3.5 = 6,570 lb. soluble salts
Enter Your Results: (mg/l soluble salts) x 2.72 = (lb. soluble salts/acre foot)
Puropose: By dividing the actual mg/l of the above
ions by their milliequivalent weight listed below, you will get the total number of
milliequivalents of a particular ion (e.g., 92 mg of chloride per liter ¸ 35.5 = 2.6 meq of chloride per liter).
This value is used to evaluate potential toxicity levels, nutrient imbalances, etc.; each
crop has a specific tolerance and threshold to any element found in the water (consult
with your laboratory for specific values relating to your crop).
The following are the
milliequivalent weights (i.e., milligrams per milliequivalent) of the major ions found in
the irrigation water:
Cations:
Calcium (Ca2+) =
20 mg/meq
Magnesium (Mg2+) = 12 mg/meq
Potassium (K+) = 39 mg/meq
Sodium (Na+) = 23 mg/meq
Anions:
Chloride (Cl-) =
35.5 mg/meq
Sulfate (SO42-) = 48 mg/meq
Bicarbonate (HCO3-) = 61 mg/meq
Carbonate (CO32-) = 30 mg/meq
General Purpose of Water Quality Analysis
The above information is used to derive the following parameters:
1) Sodium Adsorption Ratio (SAR) and adjusted Sodium Adsorption Ratio (SARadj)
2) Pounds of nutrients provided in the irrigation water
7) Water and soil amendments to use (i.e., quantity and type)
8) Assessing soil surface sealing, crusting, drainage/aeration, and other
agronomic-related uses
Consult the Salinity Management Guide for explanation and use of the above
parameters. Also, refer to the Water Quality Evaluation Guide of Sodium and Bicarbonates
found in irrigation water; this guide provides information of calculated adjusted Sodium
Adsorption Ratios, which is used to evaluate potential infiltration and permeability
problems due to the water quality of your irrigation source.
Note: Technical Questions
may possibly be quickly answered by contacting USDA, Natural Resources Conservation
Service Soil Conservationists:
