|
Search
Wyoming
Department of Agriculture
|
|
Evaluation and Classification
System for Irrigation Waters
Printable PDF of this page
Salinity - (Salt Hazard)
-
Class 1, Low Salinity: Good water with
little or no likelihood of salt accumulation when normal
irrigation practices are followed.
-
Class 2, Medium Salinity: Can be used if
a moderate amount of excess water is applied to provide some
leaching. Plants with moderate salt tolerance can be grown
without serious yield reduction when normal cropping practices
are followed.
-
Class 3, High Salinity: Cannot be used
on clay soils or soils with poor drainage. With adequate
drainage, considerable excess water should be applied to provide
leaching. Irrigations must be more frequent than normal and soil
should be maintained relatively wet. Crops with medium or high
salt tolerance should be grown to maintain normal yields. This
water is not recommended for use under sprinkler application
methods unless leaching is practiced.
-
Class 4, Very High Salinity: Not
suitable for irrigation under ordinary conditions. May be used
occasionally on sandy soils with excellent drainage if
considerable excess water is applied for leaching and if crops
with high salt tolerance are grown. Should not be used for
continuous irrigation and is not suitable for use with sprinkler
systems.
Alkalinity - (Sodium Hazard)
-
Class 1, Low Sodium: Good water, that
can be used safely on most soils in Wyoming.
-
Class 2, Medium Sodium: Suitable for use
on sandy and loamy soils if water moves through them readily.
Can cause alkali problems on heavy clay soils, under low
leaching conditions, unless gypsum (or equivalent soil
amendments) are present or are added to the soil.
-
Class 3, High Sodium: May produce
harmful levels of exchangeable sodium in all soils and will
require special management -- good drainage, high leaching and
additions of organic matter. Soils containing natural gypsum or
other chemical amendments may make the water usable, but it is
not feasible if the water is also high in salinity (Class 3 or
4). This water will cause surface soil particles to puddle, thus
limiting water penetration.
-
Class 4, Very High Sodium: Generally
unsatisfactory for irrigation. Special conditions of low
salinity water, favorable gypsum con-tent of soils, high
leaching and special management may permit use of this water. A
complete soil analysis is recommended prior to any use of this
water.
Boron
Limits expressed in milligrams/liter (ppm)
| Class |
Sensitive Crops |
Semi-Tolerant Crops |
Tolerant Crops |
Description |
| 1 |
<0.33 |
<0.67 |
<1.00 |
Very low, no effect on crops |
| 2 |
0.33 to 0.67 |
0.67 to 1.33 |
1.00 to 2.00 |
Low, very slight effect on crops. |
| 3 |
0.67 to 1.00 |
1.33 to 2.00 |
2.00 to 3.00 |
Moderate, significant yield
depression |
| 4 |
1.00 to 1.25 |
2.00 to 2.50 |
3.00 to 3.75 |
High, large yield depression
anticipated. |
| 5 |
>1.25 |
>2.5 |
>3.75 |
Very high, non-usable |
Boron is not generally a problem in Wyoming,
but where it is present in irrigation water in large enough amounts,
it is extremely toxic to plants and may severely effect yields.
Classification numbers given in the report refer to the values for
semi-tolerant crops.
Selenium
| Class |
Limits expressed in
milligrams/liter (ppm) |
Description |
| 1 |
0.00 to 0.10 |
Low, no plant toxicity anticipated. |
| 2 |
0.11 to 0.20 |
Medium, usable - possible
long-term accumulation under particular conditions and
should be monitored. |
| 3 |
0.21 to 0.50 |
High, probably toxic
accumulation in plants if this is the only source of
water. |
| 4 |
> 0.50 |
Very high, non-usable under any
conditions. |
Selenium is a naturally occurring element in
many Wyoming soils and is only rarely found in Wyoming waters above
the concentration of 0.01 milligrams/liter. Many plant species have
the ability to take up and to concentrate selenium, thus creating a
potentially hazardous situation for livestock and humans. High
selenium levels in the soil will be more hazardous under irrigation
than dry conditions even though the irrigation water is good.
Caution should be exercised when using
irrigation drainage, impounded drainages or water from shallow
aquifers near or within irrigated areas containing seleniferous
soils. Extremely good drainage from these soils is very important.
For more information on selenium refer to
REPORT TO THE GOVERNOR, Selenium In Wyoming, Issues and
Recommendations, Governors Task Force on Selenium, June 1989.
Residual Sodium Carbonate
| Class |
Limits expressed in millequvalents/liter
(meq/L) |
Description |
| 1 |
less than 1.25 |
Safe, no augmented alkali problems
over those listed under alkali rating. |
| 2 |
1.25 to 2.50 |
Marginal, possibility of some
increase in alkali over those listed under alkali rating. |
| 3 |
greater than 2.50 |
Not suitable, for irrigation under most
circumstances. |
The presence of carbonates and bicarbonates
in excess of the calcium and magnesium may develop alkali problems
over and above those considered in the ALKALI rating. Excessive
amounts of sodium carbonate will cause severe puddling of soils,
limit water penetration if any fine particles are present in the
soil, and in severe cases, will decompose organic matter in the soil
creating black alkali conditions. The long term effects of residual
sodium carbonate must be considered since they are cumulative.
Information Sources
(1) Agriculture Extension Service, College
of Agriculture, University of Wyoming
(2) Diagnosis and Improvement of Saline and
Alkali Soils, USDA Handbook No. 60, 1954
Back
to Informational Documents
|
