After receiving the results of a water analysis, there are several components that need to be reviewed to determine suitability of the water for the planted crop. If the water does not meet the expected suitability range, it may require ammendments (e.g. gypsum or acid) or mixing with other water sources to prevent crop loss. Below are five questions that are usually asked when reviewing a water sample as well as some other information regarding a water analysis and conversions.
- Does the salt concentration (ECw) pose a potential problem (osmotic effects)?
| Crop |
Unit |
Degree of growth or yield reduction |
| None |
Increasing |
Severe |
| Almond and Walnut |
dS/m |
<1.1 |
1.1 -3.2 |
>3.2 |
| Pistachio |
dS/m |
<4.0 |
4.0 - 8.0 |
>8.0 |
- Are there specific elements (B, Cl, and Na) that could accumulate to potentially toxic levels?
| Element |
Unit |
Crop |
Degree of growth or yield reduction |
| None |
Increasing |
Severe |
| B (boron) |
mg/l (ppm) |
Almond and Walnut |
<0.5 |
0.5 - 3.0 |
>3.0 |
| Pistachio |
<4.0 |
4.0 - 10 |
>10.0 |
| Cl (chloride) |
meq/l |
Almond and Walnut |
<4.0 |
4.0 - 10 |
>10.0 |
| Pistachio |
<20.0 |
20 - 40 |
>40.0 |
| Na (sodium) |
SAR(none) |
Almond and Walnut |
<3.0 |
3.0 - 9.0 |
>9.0 |
| Pistachio |
<5.0 |
5.0 - 10 |
>10.0 |
| Na (sodium) |
meq/l |
Almond and Walnut |
<4.0 |
4.0 - 7.0 |
>7.0 |
| Pistachio |
<20.0 |
20 - 40 |
>40.0 |
- Could the water chemistry contribute to unstable surface soil structure and lower water infiltration rates?
| Lab Information |
Unit |
Potential of Water Infiltration Problems Developing |
| Unlikely |
Increasing Likelihood |
Likely |
| Ratio of SAR/ECw |
ratio |
<5.0 |
5.0 - 10.0 |
>10 |
| Ratio Ca/Mg |
ratio |
>2.0 |
2.0 - 1.0 |
<1.0 |
- Could the water chemistry be prone to plugging drip emitters, microsprinklers, or filters?
| Lab Information |
Unit |
Potential for Water Infiltration Problems Developing |
| Unlikely |
Increasing Likelihood |
Likely |
| ECw |
dS/m |
<0.8 |
0.8 to 3.0 |
>3.0 |
| HCO3+CO3 |
meq/l |
<2.0 |
2.0 - 4.0 |
>4.0 |
| Mn (manganese) |
mg/l |
<0.1 |
0.1 - 1.5 |
>1.5 |
| Fe (iron) |
mg/l |
<0.2 |
0.1 - 1.5 |
>1.5 |
5. How much nitrate-nitrogen is in these irrigation water supplies?NO3-N (mg/l, ppm) x 2.7 = lbs N per acre-foot of water NO3 (mg/l, ppm) x 0.6 = lbs N per acre-foot of water LABORATORY DETERMINATIONS AND UNITS FOR EVALUATING IRRIGATION WATER
| Test |
Symbol |
Unit |
| Electrical Conductivity |
ECw |
dS/m or mmhos/cm |
| Total Dissolved Solids |
TDS |
mg/l (ppm) |
| Calcium |
Ca |
meq/l |
| Magnesium |
Mg |
meq/l |
| Sodium |
Na |
meq/l |
| Sodium Adsorption Ratio |
SAR |
none |
| Adjusted Sodium Adsorption Ratio |
SARadj |
none |
| Chloride |
Cl |
meq/l |
| Sulfate |
SO4 |
meq/l |
| Bicarbonate |
HCO3 |
meq/l |
| Carbonate |
CO3 |
meq/l |
| Acidity/Alkalinity |
pH |
none |
| Boron |
B |
mg/l (ppm) |
| Nitrate-nitrogen |
NO3-N |
mg/l (ppm) |
| Manganese |
Mn |
mg/l (ppm) |
| Iron |
Fe |
mg/l (ppm) |
CONVERSION FACTORS FROM MILLIGRAMS PER LITER (mg/l or ppm) to MILLIEQUIVALENTS PER LITER (meq/l).
| Cation/Anion |
Symbol |
Conversion Factor |
| Bicarbonate |
HCO3 |
61 |
| Calcium |
Ca |
20 |
| Carbonate |
CO3 |
30 |
| Chloride |
Cl |
35 |
| Magnesium |
Mg |
12 |
| Sodium |
Na |
23 |
| Sulfate |
SO4 |
48 |
