Salinity, Sodicity and Flooding Tolerance of Selected Plant Species of the Northern Cheyenne Reservation

Information Highlight for the General Public

Adapted by Krista E. Pearson from a paper by Nikos J. Warrence,
Dr. James W. Bauder, and Krista E. Pearson


Table of Contents
Introduction
Scientific Basis
       a) Salinity Tolerance Ratings
       b) Sodium Tolerance Ratings
       c) Flooding Tolerance Ratings
       d) pH/Alkalinity Tolerance Ratings
Summary of Findings
Explanations and Descriptions of Plant Responses
       a) Salinity
       b) Sodicity
       c) pH/Alkalinity
       d) Bicarbonates
Appendix

Introduction

The Northern Cheyenne Reservation, located in southeastern Montana, covers 445,000 acres and is bordered on the east by the Tongue River and on the west by the Crow Reservation. One concern about coal bed methane (CBM) development in this region is the impact that CBM product water could have on native and culturally significant plants on the Northern Cheyenne Reservation.

This research was undertaken to assess the tolerance of native and culturally significant plant species to salinity, sodicity, and flooding associated with management and disposal of CBM product water. A list of thirty-one plant species was acquired from the Environmental Protection Agency and the Northern Cheyenne Tribe. Tolerances to salinity, sodicity, flooding, and pH of plants on this list have been thoroughly researched to predict how they would respond to saline-sodic water produced from CBM development.

Scientific Basis

Table 3 provides a summary of sensitivity ratings of the thirty-one plant species found within the Northern Cheyenne Reservation to soil solution salinity (ECe), exchangeable sodium percentage, flooding, and changes in soil pH. The following explanations (a through d) have been provided to help the reader understand Table 3.

a) Salinity Tolerance Ratings

     Scientific references have categorized most plants by degree of sensitivity or tolerance to salinity. Table 1 explains the general rating of plant salinity tolerances used in this report. The ECe, which measures the salinity of the soil water that is available to plants, was used to rate the salinity.

Table 1. Salinity tolerance ratings.
ECe
Salinity Tolerance Rating
Abbreviation
< 2 dS/m
Sensitive
S
2-4 dS/m
Moderately Sensitive
MS
4-6 dS/m
Moderately Tolerant
MT
> 6 dS/m
Tolerant
T

b) Sodium Tolerance Ratings

     Sodicity is expressed as SAR (sodium adsorption ratio), ESP (exchangeable sodium percentage), or as the specific sodium concentration. The rating scheme used for plant tolerances to sodium is listed in Table 2.

Table 2. Sodium tolerance ratings.
Sodium Tolerance Rating
Abbreviation
Extremely sensitive
ES
Very tolerant
VT
Data not available to justify a rating.
No data available

c) Flooding Tolerance Ratings

d) pH/Alkalinity Tolerance Ratings

     The ideal pH ranges are given. While plant species may be able to survive outside of the given ranges, they are likely to be negatively impacted, either through direct physical damage or through competition with species better adapted to the given pH.

Summary of Findings
Table 3. Summary of sensitivity ratings of thirty-one native and culturally significant plant species of the Northern Cheyenne Reservation to soil solution salinity (ECe), exchangeable sodium percentage, flooding, and changes in soil pH.
Common Name
Scientific Name
SALINITY Rating
SALINITY
Acceptable Upper Limit ECe (sat) dS/m
SODIUM Tolerance Rating
Flooding Rating Limits, Inundation
pH range
1. June Service Berry Amelanchier alnifolia S 2.0 ES; ESP 2-10, SAR 1.6-8.0 MT short term, 2 weeks no data
2. Red Osier Dogwood Cornus stolinifera S 2.0 no data available MT short term, 2 weeks 6.5-7.9
3. Common spikerush Eleocharis palustris MS 4.0 no data available T long term, 1 year -; not tolerant of permanent flooding 4.8-7.9
4. Horsetail, Field Equisetum arvense MS 4.0 no data available T long term, 1 year -; not tolerant of permanent flooding 4.8-7.2
5. Wild licorice/American Glycyrrhiza lepidota MT 6.0 VT; ESP 60, SAR 48 T long term, 1 year -; not tolerant of permanent flooding 4.8-7.2
6. Goose Berry, red shoot Ribes setosum S 2.0 ES; ESP 2-10, SAR 1.6-8.0 T long term, 1 year -; not tolerant of permanent flooding 4.8-7.9
7. Mint/Field Mentha arvensis S/MS 2.0 ES; ESP 2-10, SAR 1.6-8.0 no data available 4.8-7.9
8. Horsemint/W. Bergamot Monarda fistulosa MS 4.0 no data available no data available 5.5-7.9
9. Water Plant/Water Cress Nasturium officinale MS 4.0 no data available T long term, 1 year -; not tolerant of permanent flooding 4.8-7.2
10. Sweet Medicine Oxtropis lamnbertii MS 4.0 no data available no data available 5.5-7.9
11. Chokecherry Prunus virginiana S 2.0 ES; ESP 2-10, SAR 1.6-8.0 I very short term; < 2 weeks 4.8-7.9
12. Cottonwood, G. Plains Populus deltoides MS 4.0 no data available T long term, 1 year -; not tolerant of permanent flooding 4.8-7.9
13. Box Elder Acer negundo MT 6.0 no data available T long term, 1 year -; not tolerant of permanent flooding 4.8-7.9
14. Green ash Fraxinus pennsylvania MT 6.0 no data available T long term, 1 year -; not tolerant of permanent flooding 6.5-7.9
15. Sand bar willow Salix exigua MS 4.0 no data available T long term, 1 year -; not tolerant of permanent flooding 4.8-7.9
16. Snow Berry Symphoricarpos occidentalis MS 4.0 ES; ESP 2-10, SAR 1.6-1.8 T long term, 1 year -; not tolerant of permanent flooding 4.8-7.9
17. Cattail Typha latifolia MS 4.0 no data available T long term, 1 year +; not tolerant of permanent flooding 4.8-7.9
18. Wild Plum Prunus americana S 2.0 ES; ESP 2-10, SAR 1.6-1.8 T long term, 1 year +; not tolerant of permanent flooding no data
19. Sweet grass Hierochloe odorata MS 4.0 no data available no data available 4.8-7.2
20. Quaking aspen Populus tremuloides S 2.0 no data available T long term, 1 year +; not tolerant of permanent flooding no data
21. Saw beak sedge Carex stipata MS 4.0 no data available T long term, 1 year 5.0-7.9
22. Leafy aster Aster foliactus S 2.0 no data available T long term, 1 year +; not tolerant of permanent flooding 4.8-7.2
23. Stinging nettle Urtica dioica MS 2.0 no data available I very short term, < 2 weeks 4.8-7.2
24. Bulrush Scirpus nevadensis MT/T 6.0 no data available T long term, 1 year +; not tolerant to permanent flooding 4.8-7.9
25. Arrow leaf Sagittaria latifolia MS 4.0 no data available T long term, 1 year +; not tolerant of permanent flooding 4.8-7.9
26. Golden currant Ribes aureum MS 4.0 ES; ESP 2-10, SAR 1.6-8.0 no available data 4.8-7.9
27. Skunkbush sumae Rhus trixobata MT 6.0 no data available MT short term, 2 weeks 6.5-7.9
28. Milkweed, showy Asclepias speciosa MS 4.0 no data available I very short term, < 2 weeks 4.8-7.2
29. Western yarrow Achillea millelolium MS 4.0 no data available I very short term, < 2 weeks 4.8-7.9
30. Raspberry red Rubes idaue S 2.0 ES; ESP 2-10, SAR 1.6-8.0 no data available 4.8-7.9
31. Rose Bush Rosa arkansa MS 4.0 no data available MT short term, 2 weeks 4.8-7.9

Explanations and Descriptions of Plant Responses

a) Salinity

Generally, the most likely effect of salinity on plants is stunted growth. Increased salinity requires plants to use more energy to get water from the soil, which leaves the plant with less energy available for growth. Moderately salt-stressed plants usually appear normal, although their leaves may be darker green, thicker and more succulent than non-stressed plants. Visual symptoms (leaf burn, necrosis, and defoliation) sometimes occur, particularly in woody species. At high levels, salinity can cause physical damage and mortality. Plant sensitivity to salinity changes throughout the growing season. While most crops are relatively tolerant to salinity during germination, young developing seedlings are particularly vulnerable to salinity damage during emergence and early development. After the plants are established, they generally become increasingly tolerant of salinity in later growth stages.

One of the main effects of salinity is the delay of germination and seedling development. This delay may prove fatal if the salt-stressed seedlings encounter additional stresses, such as water stress, extreme temperature fluctuations and/or surface crusting. Also, because of evaporation at the soil surface, salt concentration in the seedbed is often higher than deeper in the soil profile. This means that roots of emerging seedlings are exposed to a greater degree of stress than indicated by usual salinity measurements which are usually averaged from soil samples taken throughout the soil profile. Plant loss during this seedling stage can reduce the plant population density to below optimal levels and significantly reduce yields.

b) Sodicity

The two main risks of high sodium levels in soil water are toxic effects and impacts on plant growth from changes in soil structure. Excess sodium present in soil water can cause soil dispersal, especially in soils with high clay contents. Soil dispersal causes loss of soil structure and surface crusting. Surface crusting leads to reduced hydraulic conductivity, reduced water infiltration, and increased water runoff. These conditions can make seedling establishment very difficult, if not impossible. Decreased drainage from sodium-induced soil dispersal can also increase the sodicity in the root zone. If water containing salts is not allowed to drain below the root zone, the salt concentration of soil water will increase as plants take up water by transpiration and as evaporation occurs. For more information on sodic soils, see "The Basics of Salinity and Sodicity Effects on Soil Physical Properties."

Sodium-induced dispersal also makes it difficult for plant roots to get the water and nutrients they need to survive. This occurs because sodic soils are likely to become and remain water logged, resulting in anaerobic conditions. If anaerobic conditions persist for more than a few days, roots fail to obtain sufficient oxygen, which reduces plant growth and can cause plant injury and eventually death.

c) pH/Alkalinity

pH is a measure of acidity or alkalinity. In general, pH less than 7 is considered acidic, pH equal to 7 is neutral, and pH greater than 7 is alkaline. The direct effect of alkalinity on plant growth is not well known. However, it is well documented that most plant species do well within a defined pH range.When abrupt changes in pH occur, plant communities shift, with more tolerant species replacing those that are less tolerant. In general, most native and culturally significant plants in arid and semi-arid environments are adapted to slightly, moderately, and strongly alkaline conditions (pH > 8).

d) Bicarbonates

Carbonate and bicarbonate salts are common in the waters and soils of eastern Montana, the presence of which increases soil alkalinity. Leaf burn, a known effect of bicarbonate salts on plants, occurs when bircarbonate rich water comes into contact with growing plant tissue. However, only a few very sensitive crops are negatively affected by bicarbonates. Levels high enough to affect plants are unlikely to occur under normal irrigation conditions with good drainage. Continuous flooding or frequent inundation can change these results.

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