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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SODIUM CHLORIDE TOLERANCE OF SELECTED HERBACEOUS PERENNIALS A N D THE EFFECTS OF SODIUM CHLORIDE O N OSM OTIC ADJUSTMENT A N D IO NIC UPTAKE IN THREE SPECIES OF HERBACEOUS PERENNIALS

DISSERTATION

Presented in Partial Fulfillment of the Requirements of the Degree Doctor of

Philosophy in the Graduate School of The Ohio State University

Laura M. Deeter, B.S.

The Ohio State University

2002

Dissertation Committee: Approved by

D r. Steven M. Still, Advisor Dr. Daniel Struve Dr. T. Davis Sydnor Advisor Dr. Pablo Jourdan Horticulture and Crop Science Graduate Program

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number 3039464

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Copyright by

Laura Deeter 2001

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. “From the experiments that I have tried using salt as a garden manure, I am fully prepared to bear testimony to its usefulness...the application of salt and its utility as a manure was yet imperfectly understood. It is a matter of uncertainty whether it acts directly as a manure or as a kind of spice or seasoning, thereby rendering the soil a more palatable food for plants."

(Mr. Thomas Hogg, quoted by Cuthbert Johnson, Esq. “Observations of the Employment of Salt” in Ladies Home Journal Pp. 39 circa 1900.)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT

An increasing number of perennial species are being utilized in public areas. The

freeway system is including a greater number of perennials in beds as a part of highway

beautification projects. These plants are often subject to extreme stresses: pollution,

lack of maintenance, lack of irrigation, and highway deicing chemicals, specifically

sodium chloride. In order to ensure these plantings are in place fo r several seasons, a

greater understanding of stress, stress tolerances and plant responses to stress is

required.

Sodium chloride is still the most-used deicing chemical in northern parts of

North America. Consumer demand for safe, snow and ice-free roads has led to large

quantities of sodium chloride spread over the freeway system for many years. There

are many advantages to using sodium chloride. It is safe to handle, inexpensive, easy to

store, and highly effective over a wide range o f conditions. It does however, have

several disadvantages. It is corrosive and ineffective below -9° C. It causes millions of

dollars in damage ever/ year to roads, cars, and bridges. The dollar amount for

environmental damage is more elusive to measure, but in terms o f damage to

groundwater, soil systems and roadway plantings sodium chloride is highly detrimental.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thirty-eight species of plants were screened for tolerance to sodium chloride

solutions applied to the growing medium. Five were able to grow under the highest

salt level applied: Armeria maritima ‘Splendens’, Calamagrostis xacutiflora ‘Karl Foerster’,

Leymus arenarius (formerly Etymus glauca), Pennisetum alopecuroides, and Dianthus

xallwoodii ‘Helen’.

From the list developed in screening trials, three species of varying tolerance

were selected and planted into a field plot at the OSU Waterman farm in Columbus,

O H . Armeria maritima ‘Splendens’, Leucanthemum xsuperbum ‘Becky’, and Monarda

didyma ‘Blue Stocking’ were chosen in order to determine if results from experiments

done in the greenhouse accurately predicted dormant survivability. During the 1999 -

2000 w inter season NaCI in the form of rock salt was applied with a rotary spreader.

Plant height, visual conditions, and shoot dry weight w ere recorded in the spring.

Results from the field study indicate that fo r these three species, results from a

greenhouse study could be used to predict salt tolerance levels.

These same three species were then grown in IL containers in a growth

chamber. Salt solution (0.25N NaCI) was applied to half the plants over the course of

four weeks. During this time, height, width, number o f leaves, and visual symptoms

were recorded. Armeria was highly salt tolerant. There were no symptoms, and

neither height nor width changed. Leucanthemum showed a wide range of visual

symptoms, including marginal necrosis, complete leaf death, death o f the apical

meristem, wilting o f foliage, change in foliage color and death. The leaves ofMonarda

developed marginal necrosis, which rapidly progressed until the entire leaf abscised.

iii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rapid plant death occurred in all Monarda replications. In addition to the visual

symptoms, osmotic potential and Na*. Cl', K*, and Ca2+ concentrations were

measured. Armeria was able to lower its osmotic potential during the course of the

experiment. This species also took up large quantities of Na+, which was found in the

leaf tissue. Finally, Armeria was able to continue uptake of K+ in the presence of Na*.

as there was little change in the amount of K* found in leaf tissue. Sodium was not

found to any great degree in eitherLeucanthemum o r in Monarda. Neither of the latter

tw o species was able to continue K* uptake under salt stress. Calcium levels remained

unaffected in all three species. N either Leucanthemum nor Monarda was able to lower

osmotic potential. Based upon the results of this study, it is likely these tw o species

were killed due to osmotic problems and not through specific ionic effects.

Soil samples were also collected from the field plot and analyzed for changes in

texture, bulk density, electrical conductivity, and concentrations of Na+, K* and Ca2+.

There w ere no statistical changes in either bulk density or soil texture. The general

trend for bulk density however, was for it to increase as salt concentration increased.

Soil samples taken in the high salt plots showed higher levels o f Na*. and decreased

levels o f both K* and Ca2*. Electrical conductivity was also greater in the salt-affected

areas than in control plots.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dedicated James, Caitlyn and Sean Deeter

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS

I would like to thank my dissertation committee for all the help they have

provided during the course of this degree. I would especially like to thank Dr. Steven

Still for serving as my advisor and for providing me with opportunities I would not

have had otherwise. Dr. Still, The Anderson’s and the P.LA.N.T. Seminar also need

special thanks fo r making this all possible w ith funding. T o D r. Jim Metzger and D r.

Don Eckert for providing lab equipment. To Dr. McMahon for offering her knowledge

on experimental design. To D r. Steve St. Martin fo r helping me apply statistics to this

research. To Liz Hunt, Jim Vent, and Mark Schmittgen for helping with the greenhouse

and field studies in many ways.

There were several nurseries that provided plants. George Pealer, owner of

Millcreek Nurseries, and his employees w ere able to provide many species of plants.

Harlan Hamernik of Bluebird Nurseries donated plants ail winter long for use in the

growth chamber. Springbrook Nurseries also donated plants for use in the

greenhouse experiments.

Of all my friends here in graduate school there are several who provided

special assistance in some manner. Thanks to D r. Denise Adams fo r her patience,

advice and assistance. Nicole Cavender fo r help rating, her invaluable advice, and fo r

v i

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. listening to me when I needed it most. To Wendy Gagliano, who provided much

needed assistance in many classes and with the soil analysis. To Laura Burchfield who

has become my dear friend.

To my family, James, Caitlyn and Sean who have had to put up with me during

the trying times when I wanted to quit and for encouraging me not to. To my Mom

and Dad, who related horror stories so I knew I wasn’t alone in this.

There are many other groups who should also be thanked for making this

journey with me: the students I enjoyed teaching, the other graduate students who

have helped along the way, the staff here in the department and finally the volunteers

and staff of the Chadwick Arboretum.

Thanks to all who made this possible. I couldn’t have done it without you.

v ii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. VITA

January 5, 1968 Born — Urbana, Illinois

1995 B.S., The Ohio State University Columbus, Ohio

1995 — 2000 Graduate Research Assistant Department of Horticulture and Crop Science The Ohio State University Columbus, Ohio

2000 — 2002 Assistant Professor Horticulture Technology The Ohio State University ATI Wooster, Ohio

FIELDS OF STUDY

Major Field: Landscape Horticulture

v iii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS

Abstract ...... ii

Dedication ...... v

Acknowledgments...... vi

Vita...... viii

List of Tables...... x

Ust of Figures...... xii

List o f Symbols...... xvii

CHAPTERS

Introduction ...... I

Review of Literature...... 3

What is Salt...... 3 Properties of Salt...... 4 Production of Salt ...... 7 Deicing Salt ...... 8 Impacts o f Sodium Chloride — Man Made Structures ...... I I Impacts o f Sodium Chloride — Groundwater...... 16 Impacts o f Sodium Chloride — Animal Life...... 19 Plants - General...... 20 Halophytes...... 26 General Tolerances...... 35 Nutrient Interactions...... 44 Photosynthesis...... 47 Na7H+ Antiport...... 50 Mannitol...... 52 Genetics ...... 55

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Salt and Soils...... 57 Reclamation o f Salt Affected Soils ...... 63

1. Treatment effects of various NaCI levels on 38 species of herbaceous perennials...... 70

Introduction ...... 70 Materials and Methods...... 75 Results...... 86 Discussion ...... 100

2. G row th and survival o f herbaceous perennials (Armeria maritima Splendens’, Leucanthemum xsuperbum ‘Becky’, Monarda didyma ‘Blaustrumpf) to winter application of NaCI and its effects on soil physical properties in a Crosy day-loam...... 122

Introduction ...... 122 Materials and Methods...... 126 Results...... 135 Discussion ...... 150

3. Osmotic relations and N A \ CL', 1C A N D CA2+ uptake in three species of salt stressed perennials (Armeria maritima (M ill) ‘Splendens’, Leucanthemum xsuperbum (Ingram) ‘Becky’ and Monarda didyma (L) ‘Blaustrumpf...... 156

Introduction ...... 156 Materials and Methods...... 159 Results...... 163 Discussion ...... 172

Appendix A Soil Physical Properties ...... 177

Appendix B Equations ...... 235

Appendix C Relative salt tolerance of woody plants...... 236

Appendix D Relative salt tolerance of herbaceous plants...... 244

Appendix E Common units of salt measurement and th eir conversions 249

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Appendix F Listing of proper plant nomenclature with authority ...... 250

General discussion...... 276

Bibliography...... 285

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES

Table Page

1. Listing of physical properties o f sodium ch lorid e ...... 6

2. USDA standards fo r salinity hazard ratings fo r drinking w ater 16

3. Lethal concentrations of sodium chloride and time of exposure fo r several species of freshwater fishes...... 20

4. Mean foliage sodium content of Pinus strobus at varying distances, during January and April, 1991 after deicing chemical application ...... 22

5. Classification of salt affected soils ...... 27

6. Perennial taxa used in the greenhouse-screening experiments 78

7. Amounts of NaCI added to tap water to create the stock solutions used in salt tolerance screening experiments ...... 81

8. Rating system given to all evaluators to visually rate the roots and shoots o f all plants treated with various concentrations of NaCI solution.. 86

9. Shoot average visual ratings o f 38 species of herbaceous actively growing herbaceous perennials treated with 250ml three times a week for eight week with one of five different levels of sodium chloride applied to the soil...... 88

10. Root average visual ratings o f 38 species of herbaceous actively growing herbaceous perennials treated with 250ml three times a week fo r eight week with one o f five different levels o f sodium chloride applied to the soil...... 90

11. Tolerance of perennials to soil applied sodium chloride...... 95

x ii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table Page

12. Average dry weights ( 12 replications) of actively growing herbaceous perennials treated three times a week for eight weeks with 250ml of one of 5 levels of NaCI solution from 0.00N (control) to 0.25 N ...... 96

13. Tolerance of herbaceous ornamental perennials to soil applied sodium chloride, listed by rating...... 117

14. Properties o f Normal Soils compared to Acid, Saline, Sodic and Saline-sodic soils...... 153

15. Representative bulk densities of soils as affected by texture, compaction ...... 203

16. Bulk density for several soil profiles Mgfm3...... 204

17. Consistence terms for soils at the three moisture levels...... 208

18. Approximate equivalents of the different methods of expressing soil energy levels...... 219

19. Ability of certain crop plants to withstand restricted aeration 223

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES

Figure Page

1. Arrangement o f Na* and C l' ions in the sodium chloride crystal 5

2. Institute o f Safety Analysis (TISA) estimates of actual costs of rock salt application ...... 12

3. Environmental Protection Agency estimates o f actual costs of using rock salt ...... 13

4. N ew York State Energy Research and Development Authority (NYSERDA) estimates for actual cost of rock salt application 14

5. Mean content of sodium chloride in the foliage of Pinus strobus 23

6. Classic witch’s brooming on a deciduous plant from road salt injury...... 24

7. The influence o f salinity of the growth of 5 species of halophytic plants...... 29

8. Salt glands along the stem o f Mesembryanthemum crystallinum...... 32

9. Yield reductions for various crops under increasing salinity regimes.... 39

10. The pathway for mannitol biosysthesis...... 53

11. A desert soil with a salt crust...... 57

12. The relationship between soil pH and the availability of select plant nutrients...... 65

xiv

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure Page

13. Applications o f gypsum cause leaching o f Na+ ions from the clay particles ...... 67

14. Diagram o f the experimental design fo r the third experiment showing the location of each of the blocks of plants ...... 82

15. Physical layout of the greenhouse experiments...... 83

16. A plastic bag was placed around the base o f the plants receiving foliar salt spray to minimize NaCI solution dripping into the media...... 84

17. Dry weights of the five most salt tolerant perennials...... 98

18. Dry weights of the six least salt tolerant perennials...... 99

19. Re-growth of Heuchera sanguinea ‘Chatterbox’ after salt treatments had been removed fo r 5 w ee ks...... 101

20. Limonium latifolium showing salt excretion from the leaves 106

21. Symptoms o f salt damage to Sedum ‘Herbsfruede’ after 8 weeks o f soil applied N aC...... I 109

22. Visual ratings o f roots and shoots o f five o f the most salt tolerant herbaceous perennials treated with 5 levels of NaCI... 112

23. Visual ratings of shoots and roots o f six o f the least salt tolerant herbaceous perennials treated with 5 levels of NaCI. 113

24. Achillea millefolium growing on the ocean-facing primary dune... 119

25. Sampling locations for soil samples taking along various roadways in Central O hio...... 127

26. Apparatus for determining particle size distribution by the hydrometer method...... 129

27. Experimental layout of the field plots for testing dormant applications o f sodium chloride on three species o f herbaceous perennials differing in salt tolerance...... 131

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure______Page

28. Photograph of field trials one week after planting...... 132

29. Results of pH and EC analysis done on samples taken from three locations in the Columbus area...... 135

30. Measurements of sodium content from soil samples taken in three different sites in the Columbus area during the 1996 w inter...... 136

3 1. Bulk density of a Crosby soil after one season of winter rock salt application applied with a rotary spreader...... 137

32. Soil texture averaged over all samples taken from a field plot after one season o f winter application of rock salt with a rotary spreader...... 139

33. Average electrical conductivity of a Crosby soil after one season of winter NaCI application...... 141

34. Average sodium content of a Crosby soil after one season of NaCI application...... 142

35. Average pH of a Crosby soil after one season o f winter NaCI applications...... 143

36. Field photos of control Leucanthemum xsuperbum ‘Becky’ 144

37. Field photos of control Armeria maritima ‘Splendens’...... 144

38. Field photos of control Monarda didyma ‘Blue Stocking’ ...... 144

39. Field photos of high salt level Monarda didyma ‘Blue Stocking’ ... 145

40. Field photos of high salt Armeria maritima ‘Splendens’...... 145

4 1. Field photos of high salt level Leucanthemum xsuperbum ‘Becky’.... 145

42. Field photos of mid salt Armeria maritima ‘Splendens’...... 146

43. Field photos of mid salt Leucanthemum xsuperbum ‘Becky’ 146

44. Field photos of mid salt Monarda didyma ‘Blaustrumpf...... 146

xvi

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure______Page

45. Height measurements for three species o f perennials after 10 weeks of NaCI application...... 148

46. Average dry weights of three species o f perennials after 10 weeks of dormant season NaCI application...... 149

47. Photograph o f field trials...... 155

48. Armeria maritima ‘Splendens’ showing location o f one newly forming rosette...... 162

49. Effects of no salt and 0.25 N NaCI treatments on plant height of three species of herbaceous perennials over a four-week application period...... 168

50. Number o f fully expanded leaves of Monarda didyma ‘Purple Mildew Resistant’ in no salt and 0.25N NaCI salt stressed plants over the course of four weeksof treatment 169

5 1. Number of fully expanded leaves o f Leucanthemum xsuperbum ‘Becky* in no salt and 0.25 N NaCI salt stressed plants over the course of four weeks of treatment...... 170

52. Osmotic potentials for three species of herbaceous perennials differing in salt tolerance after four weeks of treatment with either no salt (control) or with a 0.25N NaCI solution...... 171

53. Effect of four weeks of either water or 0.25 N NaCI solutions on the content Na*. Cl', 1C and Ca2+ ions in the leaves of three species of herbaceous perennials with varying salt tolerance...... 172

55. The soil system, showing the three phases...... 180

56. Soil texture classification scheme illustrating the percentages o f sand, silt and clay in a given soil type...... 182

57. ‘Typical’ soil profile, illustrating the major horizons that are present in a well-drained soil in a temperate region...... 184

58. A soil profile from a forested region in Minnesota...... 186

x v ii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure______Page

59. A grassland soil from Minnesota...... 186

60. Coarse particle size distribution...... 189

6 1. Diagram of the relative sizes of soil particles, from coarse sand down to clay...... 191

62. Two soils with different aggregation...... 198

63. Various structural types found in soils, and their ‘typical’shape 199

64. Representation of the relationships between the three phases of the soil system...... 209

65. Downward water movement in a soil with obvious layering 215

66. The relationship between soil pH and the availability of selected plant nutrients...... 229

x v iii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF SYMBOLS

Symbol Meaning

P,...... Particle Density

M, ...... Mass o f Solids

Vs ...... Volume o f Solids

Vt ...... Total Volume

Va ...... Volume of Air

Vw ...... Volume of water

Vf ...... Volume of water and air

f ...... Soil Porosity

W eight of Sample

W dry...... W eight o f D ry Sample

Vfc,, Velocity o f fall (cm/s2)

g...... Acceleration of gravity (cm/s2)

r ...... Equivalent radius (cm)

D , ...... Density of particle (g/cm3)

D 2...... Density of Solution (g/cm3)

xix

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Symbol Meaning

n ...... Viscosity of Solution (dyne-s/cm2)

e...... Void Ratio

Mw...... Mass of W ater

...... Volume of Wetness

g...... Gravitational Potential

o ...... Osmotic Potential

m...... Matric Potential

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION AND RATIONALE

Plants in an urban landscape are subject to many environmental

stresses. Extremes of temperature, drought, pollution and soil compaction are

ail typical stresses on an urban plant. These are in addition to more ‘natural’

stresses such as disease and pest problems as well as competition from other

plants. In many northern areas road salts are simply another stress on urban

plants.

In northern states, roads must be cleared of snow and ice, often several

times a day during a harsh winter. The public demands safe driving conditions

and has unofficially adopted a ‘zero-tolerance’ rule for ice and snow on

roadways. Since the 1940’s the use of deicing chemicals has increased

steadily due to this ‘zero-tolerance’ demand (US Geologic Survey, 1997).

There are several chemicals available for deicing, including sodium chloride,

calcium chloride, sand/clay mixes and Calcium Magnesium Acetate (CMA); but

sodium chloride is the most commonly used. It is inexpensive and easy to use.

It has a long storage life and is relatively safe to handle (Kaufmann, 1960).

Ohio is one of the largest producers of sodium chloride (Kaufmann, 1960) and

this contributes to its widespread usage as a deicing chemical within the state,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. despite its known deleterious effects on the environment as well as man made

structures.

Sodium chloride can build up in soils in high amounts and there is

growing evidence that it takes longer to leach from soils than previously

thought, in some cases, more than three years are required for sodium chloride

from one season to leach through the soil (US Geologic Survey, 1997). Since it

is applied every winter, this doesn’t allow enough time for thorough leaching.

Sodium chloride has an observable effect on many woody plants and several

researchers including Dirr (1978), Lumis (1979) and Hofstra (1977) have

studied this. However the effects of sodium chloride on herbaceous

ornamentals is an area that has not been previously studied. Based upon the

extensive list of symptoms that occurs in woody plants it is erroneous to

assume that herbaceous plants will suffer no damage because they are

dormant. This research looked at the effects of sodium chloride on several

species of commonly available herbaceous plants (perennials) in order to asses

the tolerances of these plants in an effort to develop a listing of plants that

might thrive in areas of high salt applications. In addition, it looked at possible

mechanisms of tolerance/intolerance within three species of herbaceous plants.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. REVIEW OF LITERATURE

In perusing the literature on salt damage, plant salt tolerances and plant growth

in saline soils, it became apparent that the history of salt and its economic importance

was, until recently, lacking. There is some interesting and important history that is

needed to fully understand the relationship between humans, plants, and salt. A recent

book. Salt A World History, (Kurlansky, 2002) provides a full history of this chemical, and

its importance to human survival, economics and agriculture. As a prelude to

information on salt damage and salt tolerance, I present this brief history of salt in an

effort to provide a more complete story.

W HAT IS SALT?

The English word salt is derived from the Latin sal. This, in turn, is derived from

the G reek hals, meaning sea (Kaufmann, I960). In chemical terms, a salt is an acid

where the hydrogen is replaced with a metal. In lay terms salt generally refers to table

salt, rock salt o r road salt, each simply meaning sodium chloride. In this paper, the term

salt shall be used synonymously with sodium chloride unless otherwise stated.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PROPERTIES OF SALT

Salt is almost never naturally pure, although concentrations of 99.9% NaCI are

not unknown, they are unusual. The average analysis is often over 98%. In salt of marine

origin, traces of many other impurities are usually found. The most common insoluble

impurities are anhydrite, dolomite, calcite, pyrite, quartz and iron oxides. The most

common soluble impurities are Ca2+, Mg2*, K \ C 0 3, and S 0 4'.

Salt crystallizes readily with the maximum amount of symmetry. This includes

three axial planes parallel to the cube faces, six diagonal planes, a center of symmetry,

and 13 axes of symmetry. The class is hex-octahedron. It is generally seen in cubic

formation, but this varies greatly depending upon impurities. The individual crystals may

also arrange themselves into several different shapes, including the octagon,

dodecahedron or hopper-shaped, and this depends upon environmental properties of

the brine. The arrangements of the individual ions are shown in Figure. I.

Salt is relatively soft, rating a 2.5 on the Mohs’ Scale (a hardness scale o f I - 10

for minerals), and is scratched by calcite, although it is harder than gypsum. It is also

quite brittle, and will break into smaller crystals with both compression and expansion

pressure. This fragility results in crystals o f varying sizes in commercially produced salt.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. YfT i~ JT £ ~ ?

Figure. I Arrangement of Na+ and Cl* ions in the sodium chloride crystal (adapted from Kaufmann, 1960) (Small and Grey -> N a+, Large and Black Cl*)

Natural salt is either transparent or translucent. Pure salt is colorless, and the

range of colors seen in ‘natural’ salt is due to impurities. Iron oxides cause yellowing or

browning. Blues are thought to be the result of diffraction of light on colloids. Solid

white is due to the dispersal of light in finely grained salt (Kaufmann, I960). Table I

contains a listing o f basic physical properties of sodium chloride.

The vast majority of the Earth’s salt is contained within the oceans. Rubey

(1951) estimated there are 4.5 million cubic miles of salt contained within the oceans.

Terrestrial salt supplies pale in comparison and are actually oceanic salt that has been

deposited on land over geologic history (White, 1942). Today salt is mined from many

sources, including ocean, lake and groundwater. Terrestrial sources include playa (salt

deposits on a desert basin resulting from evaporation of a saline lake), bedded (salt

embedded in sedimentary rock) and flowage salts (squeezing of beddage salts from

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. pressure caused by the Earth’s crusts, resulting in plastic flowing and Anally rupturing

through the surface. It is a unique response of sodium chloride to extreme pressure.)

(Landes, I960).

Atomic Number 28 Boiling Point 1465 C (@ 1 atm) Composition (CI-) 60.66 % Composition (Na+) 39.34 % Density 2.16 g/cmJ Hardness 2.5 Mohs Linkage Type Ionic Melting Point 800.8 C Molecular Weight 58.448 SpeciAc Heat 0.2077 Cal/deg g H eat o f Solution -1.8 Kcal/gmol SpeciAc Gravity 2.14

Table I. Listing of Physical Properties of Sodium Chloride. (Adapted from Handbook for Chemistry and Physics, 1992)

Our oceans average 3.5% salt content, although it can vary from I -5% depending

upon depth and local environmental conditions. However, the composition is always

similar and remarkably constant from site to site. Chlorine dominates (55%) followed

by sodium (31%), sulfate (8%), magnesium (4%) and Anally calcium and potassium at

approximately I % each (Landes, 1960).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The most abundant solute in ground water is sodium chloride, which varies from

almost non-existent (pure water) to almost completely saturated. There is evidence

that deicing salts will move into soil and groundwater (US Geologic Survey, 1997, and

Reznicek, 1980) and eventually make both saline. Further discussion o f the effects of

sodium chloride on soil and groundwater is included later in this review.

PRODUCTION OF SALT

Salt occurs naturally in 28 states. Only 14 states, however, have deposits large

enough to mine effectively. Salt is generally exploited in one of four major ways: I)

Mining of rock salt deposits, 2) Brines created by water being pumped from the surface

3) By exploiting natural brines and 4) Evaporation o f seawater (Landes, 1960). Seawater

evaporation has been utilized for centuries and was practiced by the ancient Greeks,

Romans and Egyptians (Shepstone, 1939). The practice often produced bitter tasting

salt because of the impurities found in ocean salt. Only 65% o f the final product was

sodium chloride; other elements included: 28% magnesium salts, 4% gypsum, and trace

amounts of anything else in the seawater (See, I960). It is not a widely practiced

method utilized today, except by some primitive peoples; but throughout history it was

an economical way for a community to produce salt.

Salt mining is almost identical to coal mining and many of the same equipment

and practices are used. It is generally safer to mine salt vs. coal since the dust problems

are absent, however, water leaching must be more tightly controlled in a salt mine. The

same procedures including rooms, shaft sinking, and prospecting can be utilized for salt

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mining (vonPerbandt, 1960). Brine wells are similar to oil wells in that large shafts are

sunk into the brine field and the brine is pumped out for purification. It can also be

transported via pipeline (Deutsch, 1960).

Michigan is the number one producer of sodium chloride in the United States

and produces approximately 25% of the total annual output. Other states with high

production include Ohio, Texas, N ew York and Louisiana (Landes, I960).

DEICING SALT

Rock salt, the most commonly used deicer is 97% NaCI and is 39.3% Na* and

60.7% CL. On a per ton basis this translates into 786 pounds of Na+ and 1214 pounds

of Cl'. In water, these chemicals ionize as shown below:

NaCI + water -> ioniDnon -» Na+ + Cl'

The ionization of NaCI is the reason the freezing point of water is lowered. The

freezing point of a solution of salt water is -21° C. The ionization of NaCI to its

respective ions in solution means there are many Na* and Cl' in water, which interact

with the hydrogen bonds between water molecules. These changes in the bonding of

water molecules whereby the hydrogen bonds are broken and replaced with Na* bonds

lowers the freezing point of water. As listed in Table I, the heat of solution of sodium

chloride is - 1.8Kcal/gmol, which means that it requires heat to break the hydrogen

bonds of water. This heat can come from the atmosphere, the highway surface, from

latent heat or from the pressure and friction of moving vehicles (Kirschensteiner, 1974).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Due to the slow rate of solution of sodium chloride, the particles will eventually

work their way to the road surface where they weaken the bonds between the surface

and the ice. Not only does this contribute to melting the ice, but also it allows traffic

and plows to break up the ice, getting it more quickly to the side of the road

The first recorded use o f salt as a deicer was in the 1930’s, although it was

mixed with sand at that time (Landes, 1960). Due to the fact that sand clogged sewers

and pipelines, sodium chloride was added to reduce the amount of sand used and to

prevent the sand from freezing. It wasn’t until the 1960’s that salt became widely used

as the deicer of choice. The public demand for safe, ice and snow free roads has greatly

contributed to this increase. It is inexpensive (averaging $25/ton), and relatively effective

over a wide range o f temperatures. It is easy to store, has a long storage life, and safe

for workers to handle. It is estimated that northern states apply 10 million tons of salt

per year to US roads. Use can vary greatly from state to state. Ohio averages 900,000

tons per year and Michigan averages 700,000 tons per year (D ’ltri, 1992).

Rock salt is generally produced in four sizes: N o. 2, N o. I , CC and FC, which are

screened through different mesh sizes (No. 2 is the largest and FC the smallest). CC is

the preferred size for road salt, although if the ice is very thick No. I may occasionally

be used (Kaufmann, 1960). Various substances, such as calcium chloride or magnesium

chloride, are added to rock salt to prevent caking, and to inhibit corrosion.

Salt is inexpensive and relatively effective. Its ineffectiveness below -9° C and its

corrosiveness have historically been considered its major disadvantages. W hen

environmental costs are calculated however, sodium chloride is NOT the cheapest way

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to prevent ice formation on roads. The state of New York funded a study which

showed “that fo r every $ I spent on road salt, $57 in damage” (N ew York State Energy

Research and Development Authority, 1987) to bridges roads, cars, utility lines and

drinking water occurred. This extrapolates out to $62 billion per year in the United

States (D’ltri, 1992). And this fails to take into account the damage to soil, vegetation,

water and wildlife.

There are other alternatives to sodium chloride available. CMA (calcium

magnesium acetate) is one such product. Since its cost at this time is $600 - $700 per

ton, it is not widely utilized. However, it doesn’t cause corrosion, is effective over a

wider range of temperatures than sodium chloride, is readily biodegradable by

microorganisms, and is not toxic to plants and wildlife. Although its use is currently

limited, several states have legislation pending that seeks to reduce the amount of salt

applied on roads by increasing the use o f CM A as a deicer.

Others feel the high cost of CMA will limit its use by municipalities and are

working to develop other products. These products include urea, methanol, and a new

product marketed under the name Ice Shear ™, (Na-acetate and Na-formate), as well as

other combinations of Na-acetate and Na-formate (combining them with other sodium

carboxylates). There are advantages and disadvantages to all o f these products. Urea is

highly effective and relatively inexpensive, but the nitrates will readily leach into ground

water and are environmentally unsafe. Methanol is unsafe to w o rk with and could prove

a liability for states and cities, which limits its use, although it is highly effective, with

limited environmental effects.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The carboxylate compounds are a promising group o f chemicals that need

further research. They can be applied in either liquid o r solid form, exhibit a good

ability to lower the freezing point of water, penetrate ice, and break the bonds between

ice and pavement. In laboratory tests, they have proven more effective than CM A . Test

animals showed there is little toxicity at low amounts. Highway runoff should have little

effect on vegetation and groundwater, again, in low quantities. Unfortunately, the

products have not been widely studied, and the studies that have been done have only

looked at acute exposure. Chronic, low-dose, studies have yet to be done; therefore,

the potential for long-term environmental damage is present, and as yet, an unknown

factor. However, the preliminary test results warrant a closer look at this group of

chemicals (Bank, 1996).

IMPACTS OF SODIUM CHLORIDE - MAN MADE STRUCTURES

The initial cost of sodium chloride as a deicer is small. However, its long-term

costs are exorbitant. From the mid 1970’s to the late 1980’s several studies w ere done

to determine the long-term cost of rock salt as a deicer. The results of three such

studies are shown in Figures. 2, 3, and 4.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Underground Utilities Application Corrosion Costs 1% 20%

Highway Corrosion Vehicle 16% Corrosion Environmental 63% 1%

Figure. 2 Institute o f Safety Analysis (TISA) Estimates o f Actual Costs of Rock Salt Application

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Underground Utilities Corrosion Application Costs 1% Highway 7% Corrosion 17%

Environmental 7% Vehicle Corrosion 69%

Figure. 3 Environmental Protection Agency Estimates o f Actual Costs o f Using Rock Salt

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Underground Utilities Corrosion 10% Application Costs Vehicle 2% Corrosion v 36%

Highway Corrosion Environmental 45% 7%

Figure. 4. N ew York State Energy Research and Development Authority (NYSERDA) Estimates for Actual Cost of Rock Salt Application.

Sodium chloride causes pitting in steel, and concrete, with a corresponding loss

of strength. It causes cars to rust and is a major factor in pothole formation. It causes

many more freeze/thaw actions over the course of a winter than would occur without

salt. The freeze/thaw actions cause small cracks to develop in the concrete, which

become larger over time. This degrades the highway system, forcing costly repairs. In

laboratory tests McCrum (1988) determined the corresponding loss of tensile strength

in concrete to be approximately 30 percent. Certain specimens showed losses of 50

and 70 percent after 6 months of exposure to sodium chloride, clearly indicating the

damage possible from rock salt. Steel structures also showed decreases in strength and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. large quantities of pitting under laboratory conditions (McCrum, 1988). This increases

the damage to highways as the concrete cracks and the rebar becomes exposed. Any

exposed metal surface is susceptible to corrosion. Corrosion is an electrochemical

process, whereby the metal undergoes oxidation. The basic corrosion reactions are

illustrated below.

M Mn+ + ne' (the dissolution of a metal) 2hT + 2e' -> H2 (the cathode reaction that corresponds to the above reaction) 4H+ + 4e' + 0 2 -> 2H 20 0 2 + 2H20 + 4e' 40H' (the depolarization reactions) (Manning, 1976)

As a protective film of hydrogen builds on the metal polarization occurs and

corrosion ceases. The last tw o equations are secondary reactions and control the rate

of corrosion. Events that promote these two equations will increase the rate of

corrosion.

One of the major players in corrosion is electrolyte conductivity. The chloride

ion is the most important ion, as sodium has little to no effect on the rate of electrical

conductivity, but chloride in solution dramatically increases electrical conductivity. Even

at very low concentrations, chloride increases corrosion due to its mobility and its

ability to diffuse through most protective films. The ability to lower the freezing point

of a solution also increases the amount of corrosion that occurs due to the continuation

of the processes at lower temperatures (D’ltri, 1992). Thus, although initial costs for

sodium chloride usage is relatively low, long-term costs are very high.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IMPACTS OF SODIUM CHLORIDE - GROUNDWATER

According to the Ontario Ministry of Transportation, road salt is the major

chemical pollutant of the environment (D ’ltri, 1992). There are guidelines for levels of

Na+ in water that the USDA has established (Table 2).

Low 70 to 175 mg/L Medium 176 to 525 mg/L High 526 to 1575 mg/L Very high > 1575 mg/L

Table 2. USDA standards for salinity hazard ratings for drinking water. The amounts tolerated by people are variable and persons with depressed immune systems, the elderly, and infants may find that the lower amounts correlate to higher levels o f danger (www.saltinstitute.org)

In addition, the EPA states that sodium chloride should be classified as an

environmental contaminant, and subject to some of the same regulations as other

hazardous chemicals. The Environmental Protection A ct states, a “contaminant means

any solid, liquid or gas...” the use of “which may:

1. Impair the quality of the natural environment for any use that can be made of it. 2. Cause injury or damage to property or to plant of animal life. 3. Cause harm or material discomfort to any person. 4. Adversely affects the health or impair the safety of any person. 5. Render any property or plant or animal life unfit for use by man.” (Adamache, 1980).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. It is well documented that sodium chloride causes injury to plants, animals and

humans. Much of the environmental damage comes from salt applied to freeways. Salt

eventually percolates through the soil and enters groundwater supplies. It is unclear just

how much of this runoff gets into the groundwater. Estimates range from 20% to 50%

(Frost, 1988, and McConnell, 1972). In 1997 the US Geologic Survey published the

results of a 5-year study of the effects of sodium chloride on groundwater.

Massachusetts, Illinois, and Wisconsin all showed chloride concentrations greater than

250mg/l as a direct result of road salt applications. In Toronto, some groundwater

contained concentrations exceeded 400mg/l. Along the freeway the levels in the soil

solution were I3,000mg/I. The properties of any given site will dictate how much

sodium or chloride moves into the soil profile and eventually into the groundwater.

With a course-textured soil, water percolates much quicker than with a fine textured

soil. It is clear there are measurable amounts of deicing chemicals getting into the

environment.

In Wisconsin several studies were conducted that showed the amounts and

effects o f rock salt on two w ater systems. The first, Trout Lake had a large amount of

groundwater inflow. The second, Sparkling Lake had neither inflow, nor outflow. The

spring snow melts go directly into groundwater by seepage. Normal Cl' concentrations

in these two lakes range from 0.3 to 0.5 mg/l; concentrations above this indicate

contamination from road salts. Following the 1991 winter. Cl' concentration in

Sparkling Lake was 3.7 mg/l, which was up from 2.6 mg/l in 1982 (the last tim e it was

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. measured) and indicated a 0.15 mg/l increase per /ear. This extrapolates to 2.3 tons of

salt per year accumulating in the groundwater system. (Seawell, 1999)

Chloride concentrations in groundwater are generally less than I0mg/l (US

Geologic Survey, 1997). Chloride salts are highly soluble, do not enter into redox

reactions, are not adsorbed onto mineral surfaces, and play few biochemical roles. They

are highly mobile, although this movement can be restricted in fine textured soils due to

their large size. This mobility is the main reason that groundwater is often highly

affected by chloride runoff from deicing chemicals (Hem, 1989). Sodium concentrations

can range from 6 to 130 mg/l in the groundwater in areas with non-saline soils. Sodium

can be picked up by water percolating though the soil, but it is generally held tightly to

the cation exchange complex and its movement into groundwater is hard to predict (US

Geologic Survey, 1997), which is why the Cl* ion is used as an indicator for deicing

chemical runoff. There have been several studies showing that although runoff of

deicing chemicals can affect groundwater, rivers and large streams are not adversely

affected due to dilution of salt by the time it reaches the rivers (Hanes, I960).

However, smaller streams may be greatly affected and the area immediately adjacent to

the road is highly affected.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IMPACTS OF SODIUM CHLORIDE - ANIMAL LIFE

Salts that enter streams, rivers, and ponds act as a weak electrolyte. This can

change the electrical conductivity (EC) of the water. In a freshwater system the addition

o f \% NaCI puts many species of single celled organisms in danger (Adams, 1973).

Studies on freshwater fish also showed high levels o f toxicity due to deicing chemical

runoff (Table 3).

The concern for mammals is not as great due to the fact that both sodium and

chloride are essential elements for all animals, man included. Many animals are attracted

to salt licks. Domesticated animals are often fed salt as a supplement to their diet. The

mammalian kidney system is quite capable o f handling excess salts in large quantities, if

the animal is healthy otherwise. It is when the immune system is depressed for any

reason that excess salts become a problem. Infants, the elderly and infirm often have to

be very careful with their salt intake, especially sodium. There are also many studies

illustrating the fact that high sodium intake in even healthy humans can decrease athletic

performance greatly (Phillips, 1998). Therefore, salt that gets into groundwater can

have adverse effects on animals, including man, especially if there are other factors

involved (Hanes, R. et al, 1976).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of NaCI - PPM Goldfish 10,000 1 240 Plains killifish 16,000 1.6 96 Green sunfish 10,713 1.7 96 Gambusia 10,670 1.06 96 Red shiners 9,513 0.095 96 Fathead minnow 8,718 0.087 96 Black bullhead 7,994 0.079 96 Trout 400 0.004 N /A Bluegill 8100 0.081 N /A

Table 3. Lethal concentrations of sodium chloride and time of exposure for several species o f freshwater fishes. Adapted from Jones, 1964, and Schraufnagel, 1967.

PLA N TS - GENERAL

Injury to plants comes from several sources. The most damaging is salt that

enters the soil solution and becomes part of the cation exchange. O ther injury comes

from salt solution that is volatilized and spread by passing cars, as well as salt in snow

piles that melts later in the season. The symptoms seen in plants vary with the type of

salt the plant receives, as well as with the species o f plant. Plants with a thick cuticle are

generally more tolerant to air-borne salts (Hofstra, 1979). Bud size, the anatomy of the

bud scales, twig and bark thickness are also important determinants of air-borne salt

tolerance (Hofstra and Lumis, 1975).

In needle-leaf evergreens the symptoms of aerial salt are usually seen as

browning of needles beginning at the tip, reduction of new growth, and premature

needle drop. This damage is highest on the side hieing the road, and decreases to zero

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. toward the backside of the tree. This browning may not be evident until May or June

and can even increase as the summer progresses (Lumis, 1975). Damage is also more

apparent on plants that are closer to the roadside. Table 4 shows sodium content of

Pinus strobus trees planted at various distances from the road at two different times of

the year. Figure 5 displays the same information graphically, which makes it easy to see

that the levels o f sodium chloride in the leaves o fP. strobus are actually greater in April

than in January. This also partly explains why most plants will not start to show

symptoms o f salt injury until much later in the season, when those symptoms are often

attributed to other causes. Note that although sodium content decreases with time,

there is still a significant amount of Na* in the tissue in April, and plants quite far from

the road still received damaging levels of salt (Lumis, 1975).

Symptoms specific to deciduous trees included failure of buds facing the road to

open, or a delay in opening, new growth arising from the basal sections of branches

facing the road, failure to flower on the side facing the road, although flowering was

normal on the backside of the plant. The vast majority of symptoms will face the road,

and this is a key indicator for salt damage vs. damage from other agents.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Distance Sodium Content Date (m ) (ug/g)

January 67 4950 ± 900 a April 67 3380 ± 270 b January 103 1980 ± 240 cd April 103 2 4 7 0 + 100 e January 154 2030 ±.330 cdef April 154 2450 ± 240 ce January 215 1430 ± 290 fg April 215 1950 ±_I80 d |anuary 277 780 ± 190 hi April 277 1110 ± 180 gh January 378 420 ± 80 j April 378 820 ± 170 hk January 610 370 ± 100 j April 610 600 ± 170 ijk January 1018 420 ± 180 ijk April 1018 600 ± 230 ijk

Table 4. Mean foliage sodium content of Pinus strobus at varying distances, during January and April 1991 after deicing chemical application. Distance is from the pavement edge. Means with the same letter are not significantly different at P = 0.05. (Adapted from D’ltri, 1992)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6000

5000

Amount of NaCI present in soil 3000

(ug/g) 2000

1000

67 103154 215 277 378 610 1018

Distance from road (m)

O January EH April

Figure 5. Mean foliage content of Pinus strobus at varying distances, during January and April 1991 after deicing chemical application. Distance is from the pavement edge. Means are significant at P = 0.05.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure. 6. Classic witch’s brooming on a deciduous plant from road salt injury. (From UDSA Salinity Research Labs, www.usda.org/salinity)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Some general symptoms and patterns are:

• The injury is more severe on the side facing the road, and plants may take on a one sided appearance due to dieback. • The damage is more pronounced on the up-wind side of the plant. • Plants further from the road show fewer symptoms, the greatest injury occurs approximately between 0 and 60 feet from the road. There are reports of highly sensitive trees showing damage as for away as 1200 feet (Hootman, 1992). • Injury to evergreens generally appears in late winter, while the injury to deciduous plants may not be apparent until spring or even summer. • Branches that are above the spray zone are either not injured or are injured to a lesser degree. • Damage increases with the volume and speed of traffic as well as with the amount of salt applied to the road. • Branches covered by snow are generally not injured. • If plants are damaged over the course of several years they will lose vigor and may die. • Plants that are marginally hardy are more severely affected. • Plants at intersections, at the foot of a hill, or on poorly drained soils are injured more severely. • Plants injured over several years become m ore susceptible to secondary diseases and insect problems. • Salt spray can only penetrate a short distance into dense plants. • Plants that are protected from salt spray will not show symptoms. • Flower buds are m ore sensitive than leaf buds to salt spray. • Witch’s broom is a common symptom on plants affected overseveral years, especially on the side facing the road (Figure. 6). • Marginal leaf burn, abnormal leaf color, reduction in leaf, flower and fruit, premature foil coloration and premature defoliation, and stunting are all possible symptoms of salt damage. (Adapted from Hofstra, 1975, and Johnson, G. 1999).

Plants are also more or less tolerant o f salt depending upon the growth stage

they are in and the other types of stresses they receive. Seed germination is the stage

most sensitive to salt, and even many halophytes cannot germinate in a highly saline

soil (Ungar, 1991). Seedlings are also highly sensitive to salinity, and adult plants are

least sensitive. In 1993, Bolarin et al. showed that with Lycopersicon esculentum, a salt-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sensitive plant, tolerance increased as the plants matured, if the treatment began prior

to emergence. If the salt treatment began post emergence, 45-day-old plants were the

most tolerant. If the plants were fully mature when treatment began, tolerance was

independent of growth stage (flowering, fruiting and vegetative). In all cases, growth

and yield w ere significandy reduced. This showed that even a salt sensitive plant could

adapt to low levels of salt in the soil if given the time to develop a mechanism that

allows for regulation of internal concentrations of Na* and Cl'.

HALOPHYTES

It is logical that plants have developed an ability to tolerate salt. Organisms

that arose from single celled creatures living in oceans evolved in a highly saline habitat.

Thus it is only natural for plants adapted to shoreline areas, or those areas that are

infiltrated with seawater on a regular basis, to have developed the ability to deal with

excess salts in their systems. Haiophytes are plants that are tolerant o f saline, sodic,

or saline/sodic conditions (see Table 5). There are several accepted definitions of a

halophytic plant. One of the more commonly used is a plant that is tolerant of 0.5%

NaCI in the soil. This is equivalent to 5000mg/g NaCI or I960mg/g Na* in the soil.

For many inland, northern states, that is approximately 50 times the amount of Na*

found naturally in the soil (Catling, 1980).

For terrestrial plants, however, the situation is very different. Their

distribution throughout the world shows they are tolerant of a wide range of

conditions. In North America alone, there are many native, terrestrial haiophytes

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. including: Pucdnellia nutalliana, Distichlis stricta, Hordeum jubatum, Suaeda depressa,

Salicomia rubra, and Atriplex triangularis, to name just a few. One interesting point to

make is haiophytes are generally not found where there are low levels of salt in the

soil. Although they are highly adapted fo r dealing with salt stress, they apparently

cannot compete with glycophytes under less stressful conditions (Ungar, 199 1).

Normal <4 <15 Saline >4 <15 Sodic <4 >15 Saline-Sodic >4 >15

Table 5. Classification of salt affected soils based upon saline, sodic and saline/sodic situations. EC is electrical conductivity o f the soil and ESP is exchangeable sodium percentage. (Adapted from www.saltinstitute.org.)

High levels of salt in the soil can even affect haiophytes' growth. For

haiophytes, such as Salicomia, Salsola, Suaeda, and Halocnemum, growth is promoted by

moderate amounts of salt, and only at high levels is growth impaired. Facultative

haiophytes, (Glaux maritima. Aster tripolium) grow on moderately saline soils, and when

salt levels rise growth is greatly impaired. Far more species are indifferent, that is they

are normally found on non-saline soils. However, if soil salinity rises a small amount,

the plants show no effects (Phragmites communis, Atriplex hastata and some species of

Pucdnellia). A t higher levels o f salt, these plants show significant effects. The vast

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. majority o f plants however, are halophobic, o r glycophytes, and do not tolerate even

low levels o f salt in the soil. Figure. 7 shows growth for five haiophytes on various

levels of saline media.

The methods of salt tolerance among haiophytes are almost as varied as the

number o f species o f halophytic plants. However, “All plants can be killed by salt

solutions if the concentration is high enough. The ability to survive at a particular

salinity is important ecologically in influencing the natural distribution of plant species

in salt affected soils.” (Flowers, 1989).

In general, the methods of salt tolerance can be divided into four broad categories:

1. Limit the rate of transpiration. This limits the number of ‘bad’ ions in the plant, especially in the shoot. However, this strategy also limits photosynthesis and growth. 2. Regulate the concentration of ions in the transpiration stream. This requires a mechanism fo r discrimination between ‘good’ and ‘bad’ ions as well as a method(s) for regulating them. N ote that exclusion isn’t the same thing as regulation. 3. Regulate the shoot ion concentration through growth. If there is an increase in the ions inside the plant cell, the cell can reduce the concentration by either growing larger (succulence) or by dividing into many cells (branching). These ‘bad’ ions can then be utilized fo r osmotic adjustment, but this often means higher growth rates, and m ore uptake o f ‘bad’ ions. 4. The plant can remove the ions from the shoots in a variety of ways: leaf abscission, export of ‘bad’ ions back to the phloem, or via salt glands.

It is important to remember that these methods are not mutually exclusive and

many plants use a combination of methods to handle excess salt. In the study of true

haiophytes (euhalophytes or obligate haiophytes), some grow best where the water is

brackish; soil levels o f salt are very high on the seacoast or along the shores of salty

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. water, such as the Great Salt Lake (26% by weight). Some examples areUmonium

and Salicomia. Atriplex sp. will grow readily in slighdy less salty soils.

600

500

Q 300

3 200

100

0 0.1 0.2 0.3 0.4 0.5 NaCI Concentration (M)

Salicomia europaea • Aster tripolium * Suaeda maritima Spartina foiiasa Puccinellia peisonis

Figure. 7. The influence o f salinity on the growth o f five species of halophytic plants. The amount of dry matter production of five species of haiophytes in relation to the amount of NaCI in the growing medium. Adapted from Ungar, 1991.

There are no angiosperms that are obligate haiophytes. Normally, plants that

are considered haiophytes are not found in non-saline soils, as they generally cannot

compete as well as the glycophytes that also live there.

In haiophytes, the osmotic potential o f leaf cell sap is highly negative. Atriplex

will not freeze until the temp drops below -I4C, and its osmotic potentials are

approximately - 17.0 MPa. A “normal” plant has an osmotic potential of approximately

-I to -3 MPa. Mangroves have almost pure water in their xylem and lower the water

potential via tension (Scholander, 1965). 29

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Some haiophytes are accumulators (Atriplex), and the osmotic potential is

continually lowered throughout the growing season. Some haiophytes are salt

regulators (wheat), and limit the amounts of Cl* and Na+ that are allowed to enter the

plant at the ro o t zone. Mangroves are capable o f excluding 100% of the salt in the soil.

Some plants develop succulence in response to salt. The leaves swell by absorbing

water so that concentrations of salt do not increase. Ice plant ( Mesembryanthemum) is

a good example. Rapid growth will also dilute salt concentrations in tissues. O ther

organic compounds build up in the tissues and this also helps to regulate osmotic

balance (proline is common, as is mannitol and occasionally other sugar alcohols).

Excess salt can be exuded on the surface of the leaves, which maintains a constant

concentration within the tissues. Some haiophytes have observable salt glands on their

leaves. It is likely that Na* is transported out o f the cells via an antiport with FT. The

ion is moved out of the cytoplasm into extra cellular spaces and into vacuoles.

Secretion is one method utilized by many species o f haiophytes. Salt glands are

often visible parts o f plant anatomy (Levitt, 1972). Salt glands are generally located on

both the upper and lower surfaces o f leaves, although their exact location varies by

species (Figure 8). Excess salts are moved into these glands by an as yet unknown

mechanism. Both temperature and oxygen levels influence this mechanism, suggesting

it requires energy. Once the levels build up in the glands, it is excreted onto the

surface o f the leaves, where it can be washed o ff with morning dew o r rainfall. This

has the effect on increasing the salinity of the soil directly around the plant, which

helps to prevent competition with other species (Bradley, 1999).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Spartina angilca had the highest levels o f salt secretion o f four species studied,

followed by Umonium vulgare, Gaux maritima and Armeria maritima. It would appear the

levels of secretion correspond to the salinity levels of the native habitats of these

species. The study also showed that the levels o f N a* in the tissues o fSpartina were

very low compared to the other species, which means that Spartina has the ability to

keep its internal Na* concentration very low. Armeria maritima, one of the species

studied, had the lowest levels of Na* secretion, and relatively high N a+ tissue content.

This would imply that it is far more tolerant of Na* in its tissue than Spartina, which

has developed mechanisms for excreting excess Na* (Rozema et al, 1981). Ungar,

(1991) reported that Armeria maritima also had reduced photosynthesis in the presence

o f large quantities of salt. Although Armeria is highly salt tolerant and is native to

coastal outcroppings o f the British Isles, there are observable effects of salinity on the

plant. The mechanism(s) by which it is salt tolerant are not fully understood at this

point however.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure. 8. Sale glands along the stem o f Mesembryanthemum crystallinum. Salt concentration in these glands can exceed IM NaCI. (Bohnert, 1999)

Plants growing on saline soils also have problems assimilating potassium.

Sodium competes with the uptake of K* via a low affinity mechanism, and also K* is

generally much less abundant on saline soils. However, the presence of Ca2+ can

modify this to a great deal. If sufficient Ca2* is present, a high affinity uptake system

operates and K* is taken up at the ‘expense’ o f Na*. The use o f C A 2+ on saline soils

might increase their agricultural productivity. Lowering the pH also makes the Na*

easier to leach from the soil. It is proposed that Ca2+ applied to the soil before Na*

levels become a problem within the plant This retains the structural integrity of

membranes, and minimizes the leakage of cytosolic K*.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The function o f the stomata in haiophytes is one area th at has not been studied

in great detail. Given that Na* and Cl' travel in the transpiration stream, this is an area

that needs further attention. Robinson et al (1997) reported two major adaptations of

guard cells in haiophytes. The first was the ability to utilize Na* instead of 1C to

regulate opening and closing o f the stomata. In species that assimilate large quantities

of Na* such that it becomes a dominant ion in the cytosol, they have the ability to

utilize Na* to regulate opening and closing of the stomata. The second mechanism is

the ability to limit Na* entrance to the guard cells. It is this mechanism that suggests a

top down regulation that may be readily bred into salt-intolerant crops. This is an area

that needs further research. The haiophytes Leptochloa fusca and Pucdnellia nutalliana

both utilize water more efficiently under conditions of high salt, whereas the

glycophytes Hordeum sp. and Triticum sp. do not seem to have mechanisms for

increasing water use efficiency (Gorham, 1987, Guy and Reed, 1986, Rawson, 1986,).

Haiophytes have methods for seed germination, which is the growth stage

usually most sensitive to salinity. Some species remain dorm ant until the area is no

longer flooded; some have a very low ionic content so that imbibition can take place

(Ungar, 1991).

Many species o f haiophytes have reduced photosynthesis under saline

conditions, yet others maintain the same photosynthetic rate. Tamarix ramosissima

had no changes in photosynthetic rate, although its growth was reduced by up to 60%

under saline conditions (Kleinkopf, 1974). This indicates that Tamarix ramosissima had

decreased biomass due to increased levels o f ion pumping. Several researchers had

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. determined that many haiophytes actually have increased photosynthetic rates, but

the amount of chlorophyll is dramatically reduced (Ungar, 1991). Some haiophytes

have Na7hT antiporters at the tonoplast level, enabling them to sequester Na* in the

vacuole. Still others have these antiporters in the epidermal layer of the roots,

limiting uptake of Na* at the root level (Ungar, 1991). Books have been written

about the physiology of haiophytes, and it is not this writer’s purpose to go into great

detail here, suffice it to say that the methods and physiology underlying salt tolerance

is highly varied from family to family, and even from species to species.

There are several papers published in the last 20 years that would indicate that

haiophytes are slowly, but steadily moving into areas that traditionally they have not

occupied. The most prominent of these are roadside habitats. In 1978, Reznicek

(1980) discovered several species of haiophytes growing along the freeways in

Michigan. He showed that the areas newly dominated by haiophytes were always low

depressions, and areas closest to the median. Soil tests showed that exchangeable

sodium ranged from 567 — 2815 mg/kg. Although not all roadside areas are dominated

by haiophytes, as soils become increasingly saline from applications of deicing

chemicals, there is sure to be a shift in the populations of plants normally found in

these habitats. Reznicek discovered that roughly 22% of the flora along a 4 km stretch

of road was halophytic. Braidek et al (1984) showed similar trends for Ontario, where

up to 25% o f the roadside species where halophytic. These plants w ere also found in

highly irrigated agricultural fields. Since haiophytes generally cannot compete with

glycophytes under non-saline conditions, the presence of haiophytes in agriculture

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. indicates a rising level o f salinity. Allison Cusick did a study in 1984 on the halophyte

Carex praegradlis. This plant is a native species commonly found in moist, poorly

drained sites in western North America. It is now found as far east as Ohio, and the

movement o f this particular species was highly correlated with the use o f deicing salts

along the freeways. Although not a dominant presence along freeways it is almost

always found in areas with the highest salinity. C.praegradlis is now found in 25 Ohio

counties and is one of the dominant species along 1-75, which runs in a north/south

direction in the western part of the state. It is an ornamental plant that could readily

be utilized for erosion control, or in areas where road salts preclude the planting of

other species.

GENERAL TOLERANCES

Many studies have been carried out over the years to determine the

range of salt tolerance within large groups of plants. Hanes et al., ( 1966) studied 18

species o f woody plants to determine the amount o f damage that might be expected

after one year of application o f deicing salts. Gleditsia triacanthos var. inermis was highly

tolerant to both sodium and calcium chloride. Fagus sylvatica, Acer saccharum, Betula

papyrifera, and Cerds canadensis w ere all moderately tolerant to both types o f salt, but

if the rates of application w ere high, they were killed after one year. Fraxinus

Pennsylvania and Liriodendron tulipifera w ere both killed at even the lowest levels of

salt. Lonicera maackii and Ligustrum vulgare were highly tolerant to both types o f salt,

while Weigela florida, Forsythia xintermedia, Spiraea japonica, and Rosa sp. w ere

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. intolerant, resulting in plant death after one season of application. Some o f the

tolerant evergreens studied included Juniperus chinensis ‘Pfitzeriana’, Juniperus

horizontalis, and Yucca filamentosa. Intolerant evergreens included Pinus strobus, Picea

abies, and Tsuga canadensis, each being killed after one season’s application. The type

o f injury seen and the salt that caused the most damage varied with species. For

example, calcium chloride was more damaging to Pinus strobus, Tsuga canadensis was

most sensitive to sodium chloride. Townsend (1980) studied six woody species; Camus

florida, Platanus occidentalis, Quercus palustris, Gleditsia triacanthos, Pinus strobus and

Styphnolobium japonicum (syn. Sophora japonica). Morphological effects ranged from

chlorosis, marginal necrosis, leaves turning purple, and needle death. Sophora japonica

showed the least amount of injury, and Comus florida and Platanus occidentalis showed

the greatest amount of injury. It was shown that chloride accumulated in great

amounts in the leaves and sodium accumulated in the stems, although at much lower

concentrations.

Several other researchers have studied the effects of sodium chloride on

several species o f woody ornamentals and the results are summarized in Appendix C.

One interesting note is there are several contradictions in classification of salt tolerant

plants. One researcher may determine a plant is intolerant, while another may

determine the same species is moderately tolerant. This may stem from several

factors including soil type, the actual salt used, the growing conditions, environmental

factors, and age o f the plant.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Salt tolerance is highly dependent upon the stage of growth the plant is in when

application is made. Gleditsia triacanthos var. inermis is highly salt tolerant when mature,

however, seedlings showed high levels of damage when Cl' salts w ere applied (D irr,

1973). Once again, chloride levels in the shoot and leaf tissue correlated to damage

seen in the plant. There can also be high levels o f variation within species. In 1994,

Allen et a.l determined that Taxodium, which has populations that occur in brackish

areas in the southern United States as well as populations that grow in non-saline

waters, showed high levels o f variability in salt tolerance. In general, those plants from

brackish areas exhibited greater amounts of tolerance than those from non-brackish

waters. Although all plants showed reductions in growth at the highest salinity levels,

this indicated that breeding fo r salt tolerance should be possible by utilizing ecotypes

from brackish waters.

Macadamia seedlings were determined to be moderately tolerant to soil applied

salts (Hue and McCall, 1989). Seedlings accumulated high concentrations of N a* and

showed corresponding decreases in Ca2+ and IO. The K7Na* ratio corresponded to

damage and a ratio o f 1.5 equaled a 50% reduction in growth.

Melons (Cucumis melo.) were determined to be salt sensitive, although two

cultivars Revigal and Evan Key were determined to be salt tolerant and showed growth

and melon development that was approximately 82% of the control plants (Mendlinger

and Pasternak, 1992, and Franco et al, 1993). Franco et al. also established a

relationship between leaf area and tolerance, suggesting this might be used as a

screening technique for this species.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Triticum is salt sensitive. Reggiani (1994) showed that three wheat cultivars

accumulated Na+ and Cl'. Na* was confined to the roots, while Cl* was found in large

quantities in both the roots and shoots. Tissue growth was inhibited as salinity levels

increased, and one highly sensitive cultivar showed a growth decrease of 90%. This

study also showed that K+ content was greatly affected by the presence of NaCI.

However, the cultivars that were most tolerant showed an ability to prevent Cl'

translocation to the shoot as well as an increased ability for osmoregulation. Other

grass species, including Cynodon sp. and Poa pratensis, showed high levels of salt

tolerance under testing conditions (Francois, 1988, and Kenkel et al 1991).

Although there are crop plants tolerant o f soil salinity, many are notoriously

intolerant. Some of the more tolerant crops include Rangpur lime, Cleopatra

mandarins, several cultivars of grapes, onions and garlic and artichoke. Some of the

more intolerant crops include raspberries, blackberries, boysenberries, oranges,

lemons, avocados, tomatoes and tobacco (Bernstein, 1965). Figure 9 shows a listing of

some common crop plants and the effects that increasing salinity has on yield

reduction.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Yield Reductions vs. Soil Salinity for Field Crops

Eiectncal Conductivity in mmhos. cm at 25°C 0 2 4 6 8 10 12 14 16 18 20 Barley ■ Sugarbeets g§gn h i Sorghum I ■■ Soybean S ■■ Rice ■ H Maize ■ ■ ■

C °wPeas ■ m q - 10% 10- 25% 25-50% > 50% Beans I Hi ■■■■ ■■■■ Yield Decrease

Figure 9. Yield reduction for various crops under increasing salinity regimes, in the order of greatest salt tolerance to least salt tolerant. (Taken from www.saltinstitute.org)

As previously mentioned, many countries, including the United States are

finding crop fields are increasing in salinity levels with high levels of applied irrigation

water. In addition, groundwater in many countries is also becoming contaminated.

W ith fresh w ater supplies potentially endangered, researchers are looking at the

possibilities o f watering plants with saline water. It makes sense to look at ornamental

plants for this purpose, as growers do not need to worry about affecting taste or fruit

development.

Several species o f annual bedding plants have been analyzed (Zurayk,. e t al.

1993) for salinity tolerance. It was determined that Solenostemon (syn. Coleus), 39

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Pelargonium, and Chlorophytum were moderately tolerant, and could have low levels of

saline water used for irrigation without detrimental effects. Mesembryanthemum was

highly tolerant and Begonia was intolerant. This study also showed that the ability to

exclude Na* from the shoot tissue correlated strongly to salt tolerance. This

contrasts what other researchers determined for woody plants.

Sonneveld (1983) also looked at bedding plants for tolerance to salt.

Carnations (Dianthus caryophyllus) and chrysanthemums (Dendranthemum xmorifolium,

syn. Chrysanthemum moriflorum) showed moderate tolerance, while gerbera daisy

(Gerbera jamesonii), anthurium (Anthurium andreanum), and hippeastrum (Hippeastrum

vhtatum) w ere all intolerant to soil applied salt. Ishida (1979) looked at Dianthus

caryophyllus ‘Coral’ grown in sand and soil cultures. A t low levels of saline w ater (to

100 ppm) there was no damage to the plants. However, at higher levels (from 250 -

3000 ppm sea water) damage was visible. Plants had decreased height and fresh

weight. Flowering was delayed above 500 ppm. Generally, the appearance o f damage

was earlier in the soil grown plants than in the sand grown plants. This is expected as

Na* are generally held tighdy to the cation exchange and will displace other cations. A

clay soil has more ability to bind particles than does a sandy soil.

O th er herbaceous plants have also been studied. In 1979, Pitelka looked at

Solidago juncea and Agropyron trachycaulum (syn. Bymus trachycaulos) growing along the

roadside. Roadside populations w ere compared to tw o old-field populations.

Although both populations were quite salt tolerant, the roadside populations were far

more salt tolerant, and were able to produce significantly more biomass, although at

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the highest levels of salt, the Solidago juncea were killed. In germination studies with

these two species, neither plant showed an ability to germinate in the presence of high

concentrations o f salt, but germination was not affected at the lower salinity levels.

A few other herbaceous ornamentals have been studied in the last few years.

Opuntia ficus-indica showed reduced growth to 60% o f the control plants and had

increased osmotic pressure associated with tissue dehydration. The plants adapted by

adjusting their osmotic pressure to maintain the gradient between the dadodes and

the external solution. This was also associated with a decrease in water content.

Potassium content also decreased, but this could have been due to the reduction in

growth (Nerd, 1991). Opuntia humifiisa (syn. O. compressa) responds differently to

salinity (Silverman, 1988). It accumulated large amounts of Na* in the dadodes, and is

quite salt tolerant, unlike its relativeOpuntia ficus-indica.

Phragmites communis, the common reed grass, is highly salt tolerant and will

grow in brackish waters. Matoh, ( 1988) studied populations of Phragmites growing in

brackish waters in Japan. The population studied was growing next to the halophyte

Salicomia europaea. Salicomia accumulates NaCI in the leaf cells (Munns, 1983), and

plants in the grass family generally exclude NaCI from their cells at the root level, as

well as having a large preference for IO (Albert, 1973). Matoh looked at Phragmites

communis and determined that although optimal growth occurred in fresh water,

growth was generally unaffected at NaCI concentrations up to 300mM. The

concentrations o f solutes inside the plants changed as the NaCI concentration

increased, but the overall growth was unaffected. This implied that Phragmites is able

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. co adjust its osmotic potential to maintain a more negative potential than the

surrounding medium. Salt tolerance in Phragmites was linked to three things: an

efficient mechanism fo r Na* exclusion, a high affinity fo r K \ and a tolerance for tissue

dehydration. Germination of Phragmites was also studied. Seed collected from plants

growing in fresh w ater had lower germination than seeds collected from plants

growing under saline conditions, suggesting two ecotypes o f Phragmites (Matoh, 1988).

In 1972 Waisel reported similar findings for Phragmites communis.

A few species of tu rf grasses have also been studied. For all grasses studied,

there was reduction in growth and yield along with a differential sensitivity to sodium

chloride. Kentucky bluegrass is the most sensitive, followed by bromegrass, red fescue

and Kentucky fescue. All plants took up sodium preferentially over potassium and

showed signs of potassium deficiency. W hen high levels of potassium were added in

addition to the deicing chemicals, this effect was alleviated. Kentucky fescue was able

to uptake both sodium and chloride at high concentrations before damage was

noticed, indicating this plant is tolerant o f these ions in its tissue. The conclusion for

these grasses was that liberal, but balanced fertilizer programs can minimize the

harmful effects o f deicing chemicals (Ungar, 1991). In 1985 Greub looked at forty

species o f roadside grasses and rated them for salt tolerance based upon visual ratings

and dry weights. The results are summarized, along with the sensitivities of many

other herbaceous plants in Appendix D.

As illustrated in Appendix D, a number of herbaceous plants have been studied

for salt tolerance; however, several of these were based upon observation of a plant in

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a site where it received large quantities of salt naturally, such as near/in brackish

waters. In addition, the number of plants in this list with ornamental value is limited.

Many are crop plants or haiophytes, as there is very little information about the

performance o f ornamental plants under salt stress. However, many of the genera

listed here have ornamental species.

Horticulturalists have often assumed there would be no damage from deicing

chemicals to herbaceous ornamentals simply because the plants were dormant during

the time of application. Most of the studies with herbaceous plants (whether

ornamental or not) have been conducted utilizing actively growing plants. These

studies often look a t the effects of salinity on crop yield, o r germination rates as

measurements of salt tolerance. While these measurements make sense for crop

plants, they are not the most accurate indicators for ornamental plants. Ornamental

plants are obviously not needed for food, nor is seed production generally considered

an important function of ornamentals.

As mentioned above, there are enumerable woody ornamentals that show

injury from deicing chemicals. These plants are dormant when road salts are applied;

yet, they show a wide range of symptoms up to and including include plant death.

Much of the damage comes from salt that gets into the soil solution and subsequently

into the plant. It would be erroneous, then, to assume that herbaceous plants are not

going to suffer any damage from deicing chemicals simply because they are dormant

and generally have no above-ground structures in winter.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. NUTRIENT INTERACTIONS

Dirr, (1974, 1975, 1976 and 1990) has drawn several conclusions about the

behavior of woody plants in response to sodium chloride. In general plants will show

physical signs o f injury when tissue NaCI levels reach 2.7 percent. Therefore, even

plants that receive low levels of sodium chloride can, over time, become severely

damaged. It is also possible that a plant’s ability to preclude C l' from the leaves

correlates with increased salt tolerance. Increased levels of Cl' in the leaf tissue

directly correlated with increased amounts of damage visible on the plant. W ork with

tw o pine species, P. thunbergii (tolerant) and P strobus (highly sensitive) showed that P.

strobus accumulated Cl' in the needles at twice the rate o f P. thunbergii (Rose, 1988). In

addition, with some species, the method of application conferred differential survival

rates. Thuja occidentalis withstood soil applied salts, but not aerial applied salts;

however, the exact opposite was true for Juglans nigra (Lumis, 1974).

Some earlier work by Bernstein et al. (1971) agrees with Dirr’s data that Cl' is

accumulated at higher rates in the leaves than Na*. However, the range of plant

response to high levels of Cl' is very wide. Some plants Feijoa( , Rosa, Ilex, Hibiscus and

Viburnum) showed high levels o f marginal necrosis while others (Trachelospermum,

Pittosporum, some species o f bamboo, Lantana and Pyracantha) shed th eir leaves before

large amounts of necrosis were noticed. In some species, ( Ligustrum and some citrus

fruits) bronzing o f the leaf tips and margins were indicative o f salt damage. In some

species all three responses occurred ( Ilex and Feijoa). The amount of Cl' accumulated

in the leaves was approximately I % when damage was first noticed visually. Even the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. salt tolerant species showed visible damage at Cl* levels above 2 percent. This w ork

also showed that in most cases Cl' was the ion responsible for the majority of the

damage, as the damage was much less when non-chloride salts w ere tested.

Salt can also greatly influence the pH o f the soil, which can change the nutrient

status of the soil. This has a direct impact on the health and growth of plants;

however, salt can also directly influence the behavior o f several ions including

potassium, magnesium and calcium. Also, the addition of certain nutrients prior to salt

stress can alleviate some of the symptoms and allow plants to grow where they might

not otherwise (Ungar, 1991). Zekri ( 1993) determined that the addition of NaCI to

the medium affected the nutrient status o f citrus seedlings. Specifically, it increased the

levels o f Na*. Cl', N , P, and K* in the tissues, but reduced Ca2* and Mg2*. The addition

o f C a C 0 4 to the saline media enhanced germination and survival. Arachis hypogaea,

groundnut, is a moderately salt tolerant plant and only shows significant decreases in

germination and yield at ESP over 15. As ESP increased, Na* increased significantly.

K*, Ca2*, and N decreased with increasing ESP as well. The other micronutrients,

including P, S, Mg2*, Fe2*, Mn2*, Zn2* and Cu2* showed no differences as ESP increased

(Singh, 1985). Saur, et al in 1995, studied Pinus pinaster, maritime pine. Their results

show P. pinaster to be a moderately salt tolerant non-halophyte. Overall growth was

significantly reduced at the higher concentrations o f salt. Besides the increases in Na*

and Cl*, the plants showed marked increases in N and K* accumulation in the root

tissue, and significant decreases in P, Ca2* and Mg2* in root tissue, although the

concentrations did not appear to become deficient. The Na/K ratio is considered one

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the more important factors for plant salt tolerance (Flowers, 1983). With a high

ratio the plants are more salt tolerant, which is consistent with the results of this

study.

Age is also a factor in ion relations, just as for salt tolerance. In Medicago sativa,

which has both salt tolerant and intolerant lines, the older leaves generally will

accumulate more sodium and chloride than the younger leaves. However, the younger

leaves will accumulate potassium, which is then lost from the older leaves. Calcium

distribution was also age dependent, with the younger leaves having higher

concentrations of calcium than older leaves. The reverse was true for magnesium

(Ashraf, 1994). These results do not agree with the results of Jaschke and Pate (1991),

who found that in Ridnus communis, the older leaves accumulated calcium and the

younger leaves accumulated magnesium.

Sodium and potassium are indistinguishable fo r many plants (Gorham, 1994),

thus for plants in saline soils, they may take up Na* instead o f K* and experience K*

deficiency. This deficiency results in the disturbance o f several metabolic processes,

especially those that involve water relations. Salt tolerant plants are often able to

distinguish between the tw o ions. Gorman (1994) studied several species of perennial

wheatgrass. He showed that plants with the D-gene, which enables the plant to

differentiate between Na* and K* were more salt tolerant than plants without this

gene. Plants lacking this gene were unable to differentiate and took up Na*

preferentially over K*. The reverse was true for plants with the gene. They were able

to discriminate between the two ions and uptake K* preferentially over Na*. thus

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. excluding Na* from the shoot tissue and making these plants more tolerant. A

moderately salt tolerant cultivar of Lycopersicon esculentum ‘Ekdawi’ showed a similar

ability to differentiate between Na* and K*. thus maintaining high levels of K* in the

tissue (Taleisnik, 1994). Similar results have been found for Beta vulgaris (Magat, 1988)

and Brassica napus (Porcelli, 1995) and Spartina altemifblia (Bradley, 1991), all of which

are salt tolerant to one degree or another. Each of these plants has the ability to

exclude Na+ from entering the plant; in addition, each plant has the ability to

preferentially uptake K+ from the medium so that Na+/K+ ratios do not get out of

balance. Sorghum halepense, johnsongrass, is a highly salt tolerant, noxious weed. Its

close cousin, S. bicolor, the grain crop, is much less tolerant (Longenecker, 1974). S.

halepense had a much lower N a/K ratio than does S. bicolor, showing a preferential

mechanism at work. S. halepense appears to have a sodium exclusion mechanism at

the root level, and is better able to adjust osmotically than S.bicolor (Yang, 1990).

PHOTOSYNTHESIS

Plants increase in biomass by the production o f carbon products as a result of

photosynthesis. Photosynthetic rate is dependent upon several factors including leaf

surface area, and the rate of photosynthesis per leaf (Terry, 1984). Salinity can reduce

the dry weight of plants through a number of direct and indirect methods, and thus

can have a direct affect on photosynthesis. Terry, (1984) determined that sugar beets

had reduced dry weight at very low salinity levels, only 25mM NaCI. Reductions

increased as salinity levels increased in a linear fashion. In addition, if nitrogen and/or

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. potassium was limiting, the effects o f salinity w ere more pronounced. For sugar beets,

moderate, incremental, increases in salinity (up to l50mM NaCI) had no noticeable

effect on photosynthetic rate. A t higher salinity levels, there were distinct changes.

There were marked increases in chlorophyll content along with increases in other

chemicals, including cytochrome f, thylakoid membrane lipids and proteins and rubisco.

A t these high salinity levels, photosynthesis is affected via lowered stomatal

conductance, and lowered amounts of chlorophyll. The reduction in stomatal

conductance also reduced the rate of transpiration (Terry, 1984). Longstreth et al

(1984) looked at the rate of C02 uptake over a range of salinity levels for

Akemanthera philoxeroides, alligator weed. Although there was no reduction in

intercellular C 02 (thus no reduction in C 02 availability) overall C 02 uptake was

reduced by 51% at 400 millimolar NaCI. Akemanthera, a plant capable of osmotic

adjustment, is moderately tolerant over changing salinity levels, which is apparently

more stressful on plants than constant salinity (Dainty, 1978). O th er physiological

responses w ere an increase in leaf thickness and a reduction in dry weight with

increasing salinity levels.

Celery, Apium graveolens, is a highly salt tolerant crop plant. Studies show that

gas exchange is unaffected even under very high (200mM NaCI) levels of salt.

Although growth was slowed at the highest levels, it did continue, showing that

photosynthesis was able to continue. Celery shifted its photosynthetic carbon

partitioning from sucrose to mannitol (Everard, 1994). Spartina aftemiflora, a

halophyte, showed lower photosynthetic rates, and higher above ground respiration

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. rates under high salt stress compared with plants not under salt stress. Leaf weight

also increased, although the levels o f sodium chloride in the leaves did not. This

reduction in photosynthesis, coupled with the increase in respiration, lowered carbon

gain significantly (Hwang, 1994). This study showed that even haiophytes could be

detrimentally affected at high salt levels. However, the researchers also showed that if

plants w ere given time to acclimate to increasing salinity, photosynthetic rates

eventually returned to normal. A similar response was noticed with the halophyte

Salicomia fruticosa, whereby plants grown in medium salinities had no reduction in

photosynthesis, but plants grown at extremely high salinity levels had significantly

reduced rates of photosynthesis, although plants w ere not killed. Again, if the plants

were given time to acclimate, photosynthetic levels w ere not as significantly affected

(Abdulrahman, 1981). One plant, Galenia pubescens, a non-facultative halophyte, had

such a high rate of photosynthesis under non-saline conditions that reductions in

photosynthesis under saline conditions did not significantly impact growth rates or

biomass production. This plant is now being studied as a possible forage crop on

saline soils (Wallace, 1982).

Aster tripolium is a halophyte that uses osmoregulation to adapt to high levels of

salinity as the plant has no glands or other structures for salt secretion (Shennan,

1987). This plant showed a reduction in stomatal opening with increasing salinity

levels, although photosynthesis remains unaffected. This means thatAster tripolium

reduces transpiration, which increases water use efficiency, but allows photosynthesis,

and hence growth, to continue. It is the buildup of sodium ions in the epidermis that

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. causes this change in stomatal opening; however, this reduction isn’t sufficient enough

to prevent photosynthesis from occurring, thus allowing growth to continue, which

helps to maintain the salt carrying capacity o f the shoot tissue (Perera, 1994).

According to Ungar, (1991), Armeria maritima is another halophyte that shows

an ability to accumulate sodium in large quantities. It also has a measurable reduction

in photosynthesis in response to high levels o f salinity. However, this reduction in

photosynthesis does not appear to significantly impact the plant’s ability to thrive in a

highly saline environment. No studies have been done to date to explain the

mechanism(s) of salt tolerance o f Armeria maritima. Perhaps it is similar to Aster

tripolium in that it accumulates large quantities of sodium, has reduced photosynthesis,

but not reduced growth.

H7Na* ANTIPORT

Salt tolerant plants often have an ability to isolate Na* away from areas of

metabolic activity. Plant cells, with the presence of a large, membrane bound vacuole,

are potentially well suited for this ability. Many plants have been shown to have an

H7Na+ antiport at the tonoplast for this purpose. This provides an efficient

mechanism for avoiding the deleterious effects of Na* on metabolism. In addition, with

large quantities o f ions in the vacuole, it provides a method for maintaining the osmotic

balance of the plant cell, by maintaining the gradient. Hordeum vulgare grown in sodium

chloride solution develops an H7Na* antiport in the tonoplast of roots (Garbarino,

1988). Several other researchers have discovered this H7Na* antiport in the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. tonoplast of several species of plants (Niemitz, 1985, Blumwald, 1985, and Guem,

1989). It has been found that a similar antiport exists in the plasmalemma in tobacco,

(W atad, 1986) barley roots (Ratner 1976 and Jacoby, 1988), red beet (Jacoby, 1988)

and the halophyte Atriplex nummularia (Braun, 1988). Wilson, (1995) determined that

in Lycopersicon esculentum and L cheesmanii, there was evidence of this type of antiport

in root tissues, especially in the halophytic species L cheesmanii. However, Wilson

found no evidence of this type of antiport at the tonoplast level in either plant,

although other researchers have found evidence supporting a tonoplast Na7H+

antiport in Lycopersicon (Mennen, 1990). Since Na* interferes with K* uptake it is

reasonable to assume that salt tolerant plants will show higher activity for pumping

N a+ out o f the cell and for pumping K* into cells. This turns out to be the case for

many halophytes (Tikhaya, 1981) vs. glycophytes, which do not posses this ability to

the same degree.

The halophyte Salicomia bigelovii (Ayala, 1996) has the ability to uptake and

compartmentalize Na* as a result of antiport activity. Atriplex nummularia, as previously

mentioned, also utilizes a similar method for compartmentalization of sodium ions.

Niu (1993) compared the response of Atriplex to that of Nicotiana tabacum, a

glycophyte, and found the glycophyte was incapable of the same level of H*ATPase

activity. However, the glycophyte did show increased H+ATPase activity, just not

enough to counteract the detrimental effects of Na+ on metabolism. The halophyte

showed a far greater capacity to induce a plasma membrane H*ATPase response. This

also illustrates that halophytes have adapted many techniques for tolerance to various

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. levels o f salinity in the growing medium. These same modifications, while they may be

present in some glycophytes, are generally not present in the amounts or are effective

enough to confer salt tolerance to non-halophytic plants.

The Arabidopsis thaliana genome-sequencing project identified a gene similar to

one in yeast, which when over expressed, conferred limited salt tolerance to

Arabidopsis, which is otherwise highly salt sensitive. Plants over expressing this gene

showed sustained growth up to a 200-millimolar sodium chloride solution. Further

studies showed a correlation with salt tolerance and higher than normal levels of

t-TATPase activity at the tonoplast level (Apse, 1999). The researchers feel this shows

a definite possibility for engineering plants with increased salt tolerance.

MANNITOL

A relatively new area of study in salt tolerance is the relationship of mannitol

and other sugar alcohols, salt tolerance and the role these chemicals play in

osmoregulation. Although it has long been known that plants use sugars to regulate

water relations within the plant, the role of sugar alcohols in salt tolerance is

something relatively new. Mesembryanthemum crystallinum, common ice plant, is

becoming the model plant for w ork in salt stress. In the past it has been the model for

physiological w ork due to its being a facultative CAM plant. Under stress, it switches

from C3-photosyntheisis to CAM. It has a genome twice the size ofArabidopsis, so it is

relatively small and easy to w ork with; it has a fast growth rate, and has five

developmentally distinct morphological phases, each of which respond differently to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. stress (Bohnert, 1998). Mesembryanthemum uses several mechanisms for salt

tolerance: exclusion o f salt during water uptake, storage o f Na* out o f harm’s way,

and the ability to accumulate large quantities of sugar alcohols for osmoregulation. A

gene for the synthesis of mannitol I -phosphate dehydrogenase has been cloned and

put into Nicatiana, Arabidopsis and Lycopersicon, which are all salt sensitive. A fter

transformation, all plants were moderately salt tolerant (Bohnert, 1994). In addition,

Mesembryanthemum mutants lacking in this gene, were sensitive to sodium chloride and

behaved in a fashion similar to other salt sensitive plants (Bohnert, 2000). The

corellation between these factors suggests that osmoreguation by accumulation of

mannitol (or other sugar alcohols) may be an important mechanism of salt tolerant

plants. Mannitol

3 PGA MannitoM-P

Sucroao

CHLOROPLAST CYTOSOL

0 Mannot o4-P Haductaaa 0 NoniovowM oTHoaa P Oahydroganaao 0 Sucroao 6 P Symhaaa

Figure. 10. The pathway for mannitol biosynthesis (Pharr e t al. 1999).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Celery, Apium graveolens, is a highly salt tolerant crop plant, and mannitol is one

of the major products of photosynthesis (Loescher, 1992). This has allowed for the

discovery of the pathway for mannitol synthesis, Figure. 10. Mannitol confers salt

tolerance to the plants, and is generally found in the chloroplasts, but as can be seen

from Figure 10, that is not the site o f biosynthesis, suggesting translocation into the

chloroplast. For the chemical to confer salt tolerance it must be present in amounts

greater than lOOmM. However mannitol can also provide protection to non

photosynthetic cells as well. Ceils of celery were grown in suspension on either

sucrose or mannitol as the sole carbon source and stressed with NaCI. The mannitol

cells were twice as salt tolerant as cells grown on sucrose. Both cells w ere able to

increase their osmolality to the same degree, however when 300mM of NaCI was

added the cells grown on sucrose did not survive whereas the cells grown on mannitol

did. Both cells were non-photosynthetic, thus the protection is not at the level of the

chloroplast. Both cells grew equally well in the absence o f NaCI. This points to a role

for mannitol that exceeds simple osmoregulation. This mechanism is not fully

understood at this point (Pharr, et al. 1999).

It has been suggested that mannitol-accumulating plants are more salt tolerant

due to the ability o f mannitol to scavenge free radicals. Leaf disks of transformed

tobacco were resistant to the herbicide paraquat, which is lethal due to the generation

o f free radicals in membranes o f tissues. The mechanism(s) by which mannitol

scavenges oxygen radicals is not yet known (Pharr et al, 1999).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. It would seem that simply inserting the gene for mannitol synthesis into

glycophytes would solve many problems. However, it is not that simple. Plants that

do not normally make mannitol do not have a pathway for its catabolism. Therefore,

they have a tendency to grow slower (Karakas et al, 1997). In addition, if the species

in question makes other types of hexols, the introduction of mannitol might disrupt

metabolism by producing dead-end oxidation products (Moore, 1997). It is also costly

to break down, as the Km is quite high (Stoop, 1995). Mannitol dehydrogenase is

found in high levels in plants that make mannitol, such as celery, and there is evidence

that celery uses mannitol as a source fo r energy fo r phloem loading and unloading

(N olte, 1993). There are several other species in which the pathway fo r mannitol

production has been found including Antirrhinum, Petroselinum Hill, and Ugustrum L

(Pharr, 1999). The promising genetic work done to date shows more work needs to

be done. While this information may not be directly relevant to this study on salt

tolerance of herbaceous ornamentals, it is placed here in an attempt to provide a more

complete picture of the work done to date and the limited understanding of how

plants cope with salt. It shows there are enumerable methods of salt tolerance and

what has developed in one species, does not necessarily hold true for all species.

GENETICS

Classical plant breeding for salt tolerance has not produced reliable results.

The major problem with this approach is the lack of information relating to the genetic

basis for salt tolerance (Al-Khatib, 1994). The ecotype differences discovered in many

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. traditionally salt tolerance species compounds this issue even further. Although in

theory it would seem possible to develop a salt tolerant line o f plants from a salt

tolerant ecotype, in reality, this has proven a difficult and often elusive task to

accomplish. W o rk with soybean suggests salt tolerance is linked to one gene (Abel,

1969) but w ork with barley, sorghum and Lucerne suggests it is a complex o f genes

(Norlyn, 1990). Noble (1984) was able to increase the salt tolerance of Lucerne

through breeding. Allen furthered this w ork and showed that with several cycles of

breeding it was possible to improve the germination percentage of Lucerne grown in

saline media dramatically (Allen, 1985).

With the advent of modern genetic technology it may become possible to

introduce genes that will confer salt tolerance to non-salt tolerant plants. Researchers

at Auburn University (Wu et al, 1996) using Arabidopsis were able to identify four salt

overly sensitive mutants, which they termed sos I - 1, sos I -2, sos I -3 and sos I -4. W ork

with these plants illustrated they are >20 times more sensitive to NaCI than wild

types. They are also incapable of growing in media with less than I mM potassium.

This suggests these plants lack a mechanism for high affinity potassium uptake and are

taking up sodium preferentially over potassium, which corroborates w ork showing

that a mechanism fo r potassium uptake in the presence of salt is highly important in

salt tolerance (Wu, 1996).

Some exciting work from the University of Toronto has isolated a single gene

for the Na7hT antiport (Blumwald, 1999). Using Arabidopsis, the gene encoding the

Na7hT antiport was introduced whereby the plant overproduced the antiport. All the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. modified plants showed sustained growth through a range of salinities, where the wild

type was killed. One of the unique features of this genetic research is that all plants

have this gene already. Thus the modifications did not involve inserting a foreign gene,

but rather causing the over expression of a gene that is already present, a far easier

process (Blumwald, 1999).

Figure. I I . A desert soil with a salt crust. (From www.saltinstitute.org)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SALT AND SOILS

A common problem in agriculture is the accumulation of salts from

irrigation water. Evaporative water loss causes increases in the concentration of

solutes in the soil, making the soil saline. In extreme cases, the soil can become

unusable. A white crust that forms on the surface characterizes a saline soil, (Figure

II).

There are three classifications o f salt affected soils: saline, sodic, and saline-

sodic. They are separated based upon the electrical conductivity (EC) of the soil, and

the exchangeable sodium percentage (ESP). A saline soil has an EC greater than 4

mmhos/cm and an ESP less than 15%. A sodic soil is exactly the opposite, the EC is

less than 4 mmhos/cm and the ESP is greater than 15%. A saline-sodic soil has both an

EC greater than 4 mmhos/cm and an ESP greater than 15% (see Figure. 9). Although

these soil types do not necessarily refer specifically to sodium chloride, sodic and

saline-sodic soils have high quantities of exchangeable Na*. Once the percentage of

Na* gets high, it replaces other cations on the exchange complex, especially calcium,

magnesium, ammonium, and potassium. A large quantity o f sodium makes the soil

surface crusty, making water penetration difficult, if not impossible. The pH is

generally quite high, causing problems with nutrient uptake. Aggregation is minimal,

and the soil often becomes puddled (Brady, 1993). Saline and sodic soils generally

occur where the water table is shallow and close to the surface. As the water is

evaporated, the salts accumulate in the soil. Irrigation only exacerbates this situation,

and these soils are not recommended for irrigation. Although this will be discussed in

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. more detail later in this review, the application o f large quantities of gypsum can

greatly improve a sodic soil, allowing calcium to become the dominant cation and

forcing the leaching o f sodium. This also improves soil aggregation and structure.

Under other situations, large quantities o f w ater can leach sodium (and especially

chloride) though the soil profile. The soil needs to become saturated well below the

root zone for this to be effective and beneficial to plants.

The topography of the land also influences how rock salt will behave. Salt can

move vertically through the profile as well as horizontally across the soil surface. In

areas where the w ater simply runs off the surface, due to steep slope, o r an

impenetrable crust, both sodium and chloride will tend to build up in the soil.

Topography dictates whether or not irrigation can be utilized, as well as the types of

irrigation used, the types of drainage systems and other water management tools that

can be used in any given situation. This explains the differences in sodium chloride

found in seemingly similar roadside sites (Scherer et al, 1996).

Soil physical properties greatly influence how deicing chemicals will behave.

The properties of texture, structure, depth, permeability as well as chemistry all play

an important role in determining how sodium chloride will behave in the soil as well as

the effects it may have on the environment and plants in particular. [See Appendix A

for a review o f soil physical properties.]

Sodium ions build up in soils after applications from deicing chemicals. As

sodium levels increase from successive years’ applications, the soil structure breaks

down allowing more sodium to enter the system, causing even greater increases in

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sodium levels, and eventually resulting in deflocculation o f the soil. The levels are

highest closet to the road. In some cases high levels of Na* have been found more

than 30 ft. from the roadside (Hutchinson, 1966). As salt is applied over a number of

years the amount of sodium in the soil builds. If precipitation is low, there is little

leaching and sodium will remain in the soil over a prolonged period of tim e.

Hutchinson (1966) noted that after three years the sodium concentration at 15cm

depth was up to 8 times higher than before salt application. Increases are noticed up

to 30 - 40 feet from the roadside, although concentrations decrease as distance

increases. Additional research indicated that between 54 to 92% of the sodium

chloride applied from one season was still present in the soil the following June

(Hutchinson, 1967). Chloride levels in soil are generally low er than sodium levels due

to leaching, although the general pattern seen with sodium is also found fo r chloride,

it is interesting to note that chloride levels increased greater when applied as sodium

chloride vs. calcium chloride. This is probably due to the favorable effects of calcium

on soil structure, whereas sodium is highly detrimental to soil structure (Hanes et al.

1976). Two conclusions can be drawn from this. First, the highest levels are closest

to the roadside, and decrease with increasing distance. Second, the more seasons a

road is salted, the higher the concentration in the soil and the greater the area

contaminated (Hutchinson, 1966 and 1967, and Hanes, 1976).

Salt concentrations are also highest at the surface and decrease with increasing

soil depth. Generally the top I -2 cm of soil will contain the highest concentration of

sodium and chloride. There are fluctuations to this general rule made possible by

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. irregular salt application rates, differences in adsorption properties of the soil, and the

amount of compaction in the soil (Berthouex, 1968). In heavily salted areas the levels

o f sodium chloride in the soil remained high until a 127cm depth. It is possible to leach

salt from the soil with rainfall, but it can take several months fo r levels to return to

normal. Hutchinson found that in June, up to 92% o f the chloride and 57% o f the

sodium still remained in the soil. It wasn’t until late summer that all the chloride had

leached through to the groundwater. The depth of the water table can also affect the

amount o f leaching (Toler, 1974).

Many researchers have confirmed the detrimental effects of sodium on soil

structure. Sodium replaces Ca2* on the cation exchange complex, and this is the

source of most of the damage. When the cation exchange becomes saturated with

Na* the soil becomes highly alkaline, and the pH can go as high as 10. Soil colloids

become dispersed and move down the soil profile. This leaves the soil with poor

structure, poor water permeability, and poor aeration (Brandt, 1973). There are many

variations on the behavior of sodium in the soil profile due to other external and

environmental factors. Positively charged ions are attracted to the negatively charged

soil particles. However, sodium ions have only one charge, are relatively large, and are

usually well hydrated; therefore, they are only weakly attracted to the cation exchange.

Most o f the sodium will remain in solution and readily leach from the soil system.

Calcium is comparatively small and has two positive charges; this means it is attracted

quite strongly to the cation exchange, but excess amounts will leach away. In many

soils in highly humid regions, aluminum ions are strongly attached to the cation

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. exchange, thus inhibiting sodium, almost completely. In soils that are already high in

calcium and magnesium, sodium is also vulnerable to leaching due to the firm contact

of these ions to the cation exchange (Hanes, 1976).

Deicing salts high in chlorides have other indirect effects on soils. The

chlorides encourage the leaching of other cations (such as potassium, calcium and

magnesium) that are essential for plant growth and, in the presence o f sodium, may

cause clay particles to defiocculate. Sodium can cause soils to become more dense

and compacted; the smaller pore spaces then inhibit aeration, water infiltration, and

leaching of salts, making the soil a poor environment for plant growth.

In cases o f extremely high salt concentrations, the surface of the soil may

become covered with a crust of salt, rendering the soil impermeable. Any future

applications of salt remain on the soil surface and are never leached (Figure. 12).

Under most situations in temperate zones, this is unlikely to occur as spring rains and

snowmelt are generally enough to leach most salt through the soil, preventing

situations from reaching the stage of impermeability. However, in irrigated land, in

certain soil types, and under desert conditions, this occurs regularly and renders a

large portion of the arable land unsuitable for agricultural use.

A high water table changes the behavior of salt in the soil. If the water table is

near the surface, evaporation is increased. As water moves up through the soil profile,

salts are also transported. As the water evaporates, these salts are left behind,

increasing the salt concentration at the surface of soil. This is most likely to occur in

the summer months when precipitation is lowest. (Prior, 1967)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Salt in the soil also raises the osmotic pressure and the pH. The pH o f the soil

gready influences plant health. W ith changes in pH, there are changes in nutrient

availability (see Figure 13). One study determined that salt concentrations o f 1080

mg/kg Na* and 2577 mg/kg Cl' had an osmotic pressure of 1.5 atm. Leaching reduced

this to 0.5 atm by the end of June (Hanes, 1976). As mentioned previously, pH also

tends to increase due to high salinity levels. Hanes ( 1976) reported increases from 5.4

to 8.4 from added sodium chloride in one type of soil. However, not all soils will

respond in this manner. Grosedose, (1976) determined that applications of NaCI

reduced the pH in the soil. W hen the salt was leached the pH increased, suggesting

that buffering agents were also leached o u t with rainfall.

RECLAMATION OF SALT AFFECTED SOILS

Reclamation of a salt affected soil is simply the removal of the soluble salts

from the soil profile, especially the root zone. In some cases the salt can be removed

via leaching. In other cases, additional amendments, such as gypsum o r sulfur may be

required. Added salts may take up to three years or longer of leaching, in order to

reach plant safe levels (US Geologic Survey, 1998 and Amundson, 1985). A fte r 5 years

o f leaching, the levels of Na* in the soil w ere reduced over 50%, compared with non

saline affected soils (Amundson, 1985). O nly after 15 years o r longer, w ere the levels

of Na* reduced to a point where only the most sensitive plants could not grow . Large

quantities o f water can leach ions, especially negatively charged ions such as Cl'

through the soil in a relatively short time period. One study showed that by July, the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. levels o f C l' had dropped significantly from ambient rainfall alone (US Geologic Survey,

1998). Other studies show that Na+ takes far longer to leach, and if the levels of Na*

have built up to the point of changing the physical properties o f the soil, leaching is

probably no longer an option, and other, chemical means become necessary. In

addition, there have been no studies to show what happens to the leachate once it

leaves the rhizosphere. How much enters the groundwater is another issue that

needs to be studied. The long term effects of sodium chloride leaching into

groundwater have not been studied, from either an environmental standpoint, or a

human health standpoint, much less from a plant health standpoint. It is only the short

term effects that have been studied extensively.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 12. The relationship between soil pH and the availability o f selected plant nutrients. Wide bands indicate greatest availability or activity, and narrow bands indicate limited availability/activity. Fungi are active throughout the entire range, bacteria are active through most of the range and are only greatly affected at pH lower than 5. Plants are gready affected and th eir health depends upon the pH of the soil. The greatest availability of most plant nutrients for most plants is at pH approximately 5.5 — 6.0. (Adapted from Brady, 1990).

The application of gypsum (CaSO4'2 H 20) is the main remedy fo r sodic soils. If a

soil is leached using water alone, calcium is often removed, and sodium becomes the

dominant cation. However, the use of gypsum causes Ca2+ to become the dominant

ion on the cation exchange, thereby removing Na* down through the soil profile

(Figure 13). Applications of high levels of potassium will also remove sodium from the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. soil (D ’ltri, 1992). Phosphates, sulfates, and nitrates are effective in removing chloride

and also in reducing the amounts o f chloride taken up by plants, but they have no

effect on the behavior of sodium, either in the soil or in the plant. Large quantities of

nitrogen fertilizers are often used to counteract the effect of chloride in plants,

although the mechanism is poorly understood. One study showed that applications of

high levels of calcium prior to application o f sodium, reduced plant damage significantly

(Ungar, 1991). Kumar (1990) undertook a 6-year study to look at the effects of

gypsum application on a highly sodic soil and compared it to the effects o f growing rice

and barley to ameliorate sodicity on the yield o f wheat. The amount of gypsum

required was 12—15 tons per hectare to begin to ameliorate the effects of sodicity.

After 5 years of rotating rice and barley, wheat yields were good. The best results

w ere to combine the two: large quantities o f gypsum and a crop rotation o f rice and

barley for 5 years, followed by wheat planting. In this case the yield o f wheat was

relatively high.

Nawar and Petch (1987) performed a laboratory study using PVA (polyvinyl

alcohol) to reclaim salt affected soils. It was highly effective in reducing o r preventing

clay dispersion under a wide range of NaCI concentrations. The largest effects were

seen with a fully hydrolyzed polymer under conditions where it could remain soluble.

If the NaCI levels in the soil were exceedingly high, the effectiveness was reduced due

to precipitation of the PVA. PVA did maintain soil hydraulic conductivity under

laboratory conditions. This illustrates that this may be one possible solution to

reclaiming a salt affected soil under certain conditions.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Na+ M + +CaS04 ^ v Ca + Na?^ gypsum

= Clay particle

Figure. 13. Applications of gypsum causes leaching o f N a+ ions from the clay particles. From www.saltinstitue.org.

Kelsey et al performed an experiment in 1996 using container planters along a

roadside for studying the effectiveness of mitigation strategies undertaken to reduce

the amount o f plant damage from deicing chemicals. The planters were higher than

ground level by 2.5 feet. There were three miles o f such planters along a street in

Chicago. Their results showed that calcium chloride did not affect the survivability of

plants and it positively impacted the levels of sodium in the planters. However, they

also determined that the levels o f calcium chloride needed to significandy reduce

sodium levels would be cost prohibitive and there might be plant damage at those

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. levels. They also discovered chat the use o f high-density snow fencing significantly

reduced the levels of sodium chloride reaching the planters. Once again though, the

maintenance of such fencing is very expensive and it was in disrepair often enough to

significantly impact its effectiveness. They did state that using more pliable, easier to

maintain fencing should be studied. The other results of this study were as follows:

1. Irrigation of the planters in the spring effectively removed salts. During the winter of 1994, such irrigation was not made available, and the plant loss was dramatically increased. 2. Soil testing can be utilized to determine the proper amount of water needed to leach salts from the soil. 3. The use of ornamental trees in high-speed medians should be avoided due to continual, high damage resulting from deicing chemicals. 4. Dorm ant oils do not affect plant survival. Its use should be discontinued. 5. Spraying the foliage of the plants was effective in some cases and should be studied further. 6. Utilizing gypsum as an amendment to mitigate the loss of soil structure from sodium should be implemented. It is the only effective means o f restoring soil structure barring complete soil replacement (Kelsey, 1996).

The problem with all of these solutions is they are only practical on a small-

scale basis, o r with crop plants where yield can be significantly increased by these

methods, making their cost worthwhile. In a roadside planting, the best way to

prevent damage from deicing chemicals is to simply not apply them at all. However,

this is generally impractical as well. Alternative deicers need to be investigated more,

and perhaps, in the long run, this will be ou r only option. As environmental costs are

realized, NaCI will no longer remain the least expensive option for snow and ice

removal. Planting salt tolerant species along the roadside is the best option at the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. moment. Current deciding practices can continue until other methods become less

expensive and plant loss will be greatly reduced. One of the best methods for

reducing environmental damage would be for drivers to learn to cope with a certain

amount of snow and ice on the roadways. This would decrease the levels of deicing

chemicals required, decrease damage to cars, bridges, roadways as well as plants. A t

the present time however, this seems impractical due to current attitudes regarding

snow and ice on the roads. None o f these methods are mutually exclusive, and the

best solution would be to utilize a combination of several methods to reduce

environmental damage from deicing chemicals.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER I

TREATMENT EFFECTS OF VARIOUS NACL CONCENTRATIONS ON 38 SPECIES OF HERBACEOUS PERENNIALS

INTRODUCTION

Herbaceous perennials are becoming increasingly popular in public areas.

Street plantings, corporate parkways, and even parking lots contain ever-increasing

numbers of perennials. Perennials add diversity, color and texture, but do not need

annual replanting or frequent mowing, and can eventually reduce maintenance costs

over annuals and turf. However, plants grown in public areas often face

environmental conditions not seen in private gardens: temperature extremes,

pollution, lack of irrigation, compacted soils, and in temperate climates, the

additional stress of large quantities of deicing salts. During extreme winters large

quantities of deicing chemicals are applied. Even during a relatively mild winter,

deicing chemicals are applied, although in considerably lower amounts (Andrea

Stevenson, personal interview, April 22, 1999).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sodium chloride is still the most commonly used deicer. It is inexpensive,

available in large quantities and effective over a wide range of conditions (US

Geologic Survey, 1998). Vehicle traffic and snow removal operations volatilize the

salt solution; the solution is dispersed with wind currents and lands on foliage and

branches o f roadside plantings. Salt dissolved in melted snow moves into the soil

solution. Because o f the possibilities of damage, it is im portant to know the

tolerance of herbaceous perennials to sodium chloride.

Information on salt tolerance of ornamental herbaceous perennials is

limited. The American Horticulture Society Flower Finder (Andre Viette ed., 1992) and

550 Perennial Garden Ideas (Fell and Heath, 1994) are two references with such

information. The first lists plants that grew well at an author’s seaside residence,

based upon observations. The second does not provide the origin of the

information. Anecdotal accounts of plant salt tolerance based upon observed

growing conditions and survival rates provide the basis fo r most o f the lists of salt

tolerant plants. There are several web sites available with listings o f salt tolerant

ornamentals. The USDA Salinity Research Laboratory at Riverside, CA provides

comprehensive, research backed, information for woody perennials. Although

some herbaceous material is also listed, information specific to ornamental species

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is lacking. Colorado State University, The University of Nebraska, and North

Carolina State University also have W eb pages listings salt sensitivities of woody

ornamental plants. However, herbaceous ornamental information is also lacking

from these sites, which otherwise treat the topic thoroughly, if from a layperson’s

point of view.

It is not that information on the performance of herbaceous plants is lacking

in the literature. Indeed, much work has been done with crop plants and

halophytes. However, information on horticulturally important herbaceous

ornamental species is sketchy and incomplete at best. There are many genera of

ornamental plants with salt tolerant species including: Agropyron, Artemisia, Aster,

Carex, Leymus, Festuca, Galium, Gunnera, Helianthus, Juncus, Lathyrus, Limonium,

Panicum, Pucdnellia, Sdrpus, Solidago, Silene, and Spartina (Ungar, 1991). Within the

research on salt tolerance however, the species studied tend to be known

halophytes, such as Festuca rubra, rather than the ornamental Festuca glauca and its

cultivars. Many of the plants on the above list are commercially available, however,

the species studied were generally not considered ornamentally important.

Over the years, several researchers have worked with a limited number of

herbaceous ornamental plants to research at their salt tolerances and adaptations.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dianthus caryophyllus ‘Coral* grown in sand had limited tolerance to diluted

seawater, and was killed at levels of 3000-ppm seawater, although some plants

showed limited amounts of tolerance at 250-ppm seawater (Ishida, 1979). This

Dianthus species is the cut flower carnation, and is generally not seen in northern

landscapes, as it is not hardy north o f USDA Zone 7 (Still, 1994). Thus, the

information, while important, would be restricted in its usefulness in determining

roadside salt tolerance, except perhaps in slightly warmer climates.

Two roadside weeds, Solidago juncea and Agropyron trachycaulum (syn. Etymus

trachycaulos) showed “considerable amounts of tolerance" (Pitelka, 1979) to sodium

chloride. In addition, it was discovered that roadside plantings exhibited higher

levels of tolerance than container grown plants (Pitelka, 1979). Armeria maritima

and Festuca rubra both showed decreased growth and photosynthesis when treated

with “high" levels of salt water. However, these decreases did not prevent them

from thriving in highly saline areas (Cooper 1982). Aster tripolium showed an

increase in dry mass under 2% salinity; however, continual water logging with saline

w ater killed the plants (C ooper 1982, and Baumeister, 1962). Imperata cytindrica

actively secretes chloride during salt stress (Amarasinghe, 1989). The above

mentioned research indicates that w ork is being done with herbaceous plants and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. shows there are measurable effects of salt on herbaceous plants, including

halophytes. The various levels of saline water utilized as well as the different units

of measurement point to a general lack of uniformity within the realm of salt

research. This might not be unexpected for a topic still in its infancy. However, it

makes comparisons and general statements difficult at best.

Another troublesome issue is that within any given population of plants,

there can be a wide range of salinity tolerances. Dune plants, such as Solidago

sempervirens, have populations that are sensitive to salt spray. Several ecotypes of

this species exist within any given population. Those plants closest to the ocean,

along the primary dunes are the most salt tolerant and are capable of survival even

under conditions of continual salt spray. Individuals within the same general

population, but located further back on the dune are less salt tolerant. Under

laboratory conditions the plants facing the ocean on the primary dunes w ere able

to reproduce under highly saline conditions, whereas plants from the leeward side

were not capable of reproduction under the same saline conditions (Cartica and

Quinn, 1980).

Information on commercially available perennials remains sketchy and

incomplete. Since herbaceous plantings are increasingly utilized along freeways,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. parking lots and commercial sites, more information is now needed on how these

plants react to high levels of sodium chloride. The main objective of this research

was to assess the responses of several commonly available herbaceous perennial

species to soil applied salinity in order to begin to develop a listing of species that

might survive in areas receiving sodium chloride as a deicing chemical.

MATERIALS AND METHODS

A greenhouse experiment was designed to complete the above-mentioned

objectives. The thirty-eight species of herbaceous ornamentals were selected based

upon popularity and availability in the trade. During initial selection of species,

several herbaceous experts were asked to think of plants that might display salt

tolerance based upon exterior physiology, pubescent o r succulent foliage for

example, or based upon the reputation of the plant as tough durable landscape

plants. The most popular plants from this list provided the starting point for

ordering plants from the nursery. This experiment was repeated a total o f three

times. For the first experiment, plants were obtained from Springbrook Gardens in

Mentor, Ohio; plants for the next two experiments came from Millcreek Gardens

in Ostrander Ohio. The final, complete listing of herbaceous ornamentals utilized is

shown in Table 6.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. One-liter container grown plants were purchased from one of the above-

mentioned perennial nurseries in late winter, transplanted into #1 containers (~ 4L)

containing Scott’s Metro Mix 360 growing media. This is a peat-based media

containing vermiculite, processed bark ash, a small nutrient charge and a wetting

agent. Approximate pH after wetting is 5.3 — 6.5. Once transplanted, the plants

were given 2 weeks to acclimate in the greenhouse prior to the start of salt

treatments. The three experiments took place during different seasons due to

availability of plants and greenhouse space. Twice the experiments ran during late

spring and into early summer. Once, the season was early to mid summer. The

cooling system for the greenhouse was set at 18° C for the duration of acclimation

and the experiments; however, outside temperatures often prevented the

greenhouse from being cooler than 24° C. On occasion, the temperatures were as

high as 30 - 35° C. N o supplemental lights w ere provided. Plants w ere watered as

needed with tap water, generally once per day, although this could vary with some

species, depending upon its water usage. Some species required less water than

others, while several species needed water two or three times a day during the

hottest days of the spring and summer. Watering needs were determined by visual

analysis o f the media in addition to manual discerning of moisture content by touch,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and lifting the pots to determine how heavy they were. None of the plants wilted

or appeared to suffer from water deficiency due to lack of water (as opposed to

salt stress, which can mimic drought symptoms) at any point during the

experiments.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Achillea ‘Moonshine’ Geranium sanguineum Achillea millefolium ‘Apfelblute’ Hemerocallis ‘Cherry Cheeks’ (Apple Blossom) Hemerocallis 'Stella de O ro ’ Armeria maritima ‘Splendens’ Heuchera micrantha ‘Palace Purple’ Artemisia ‘Powis Castle’ Heuchera sanguinea ‘Chatterbox’ Artemisia schmidtiana ‘Nana’ Hosta ‘Undulata Mediovariegata’ (syn. Aster novi-angliae ‘Purple Dome’ H . undulata ‘Mediovariegata’) Astilbe ‘Peach Blossom’ Iris sibirica ‘Caesar’s Brother’ Athyrium felix-femina Lavandula angustifolia ‘Hidcote’ Calamagrostis xacutiflora ‘Karl Leucanthemum xsuperbum ‘Becky’ Foerster’ Limonium latifolium Centaurea montana Liriope muscari Cerastium tomentosum Lythrum virgatum ‘Morden Gleam’ Coreopsis grandiflora ‘Early Sunrise’ Monarda didyma ‘Blaustrumpf (Blue Coreopsis verticillata ‘Moonbeam’ Stocking) Dianthus dettoides ‘Flashing Lights’ Pennisetum alopecuroides Dianthus xallwoodii ‘Helen’ Perovskia atriplicifolia Echinacea purpurea ‘Magnus’ Rudbeckia fulgida var. sullivantii Leymus arenarius (syn. Elymus glauca) ‘Goldsturm’ Festuca glauca (syn. F. cinerea) ‘Elijah Hylotelephium ‘Herbsfruede’ (Autumn Blue’ Joy) Gaillardia xgrandiflora ‘Goblin’ Solidago ‘Crown of Rays’ Geranium xoxonianum ‘Claridge Druce’

Table 6. Perennial taxa used in the three greenhouse screening experiments.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The plants were fertilized with 200-ppm nitrogen in the form of Peter’s 20-

10-20 complete fertilizer three times during the experiments. The first time was

the day prior to the start of salt treatments. The media had a small amount of

fertilizer, which it was felt would suffice during the two-week acclimatization of the

plants. Plants were then fertilized approximately every three weeks thereafter,

roughly during the third and sixth weeks after treatment initiation. Each plant was

given approximately 0.09m2 of growing space during the course of the eight-week

experiment. Each species was pruned to a height of between 5-8cm (depending

upon the species) tw o days prior to initiation of the treatments to ensure all plants

within a species started at similar heights.

The plants were arranged in a randomized complete block design for each

repetition of the experiment. There were 38 species x 4 replicates x 5 treatment

levels for a total o f 760 plants. A typical setup is shown in Figures 14 and 15.

Although the locations of the various blocks varied, the general setup remained

similar for all repetitions. Thus each treatment block had one of each of the 38

species. W ithin each block the plants were also randomized.

There w ere five treatment levels for each experiment: control (no added

sodium chloride), 0.05N , 0.1 ON, 0.20N, and 0.25N NaCI solution. Each plant

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. received a soil drench of the proper solution three times per week for the entire

eight-week period. The various solutions were contained in I70L (44gal) white

plastic stock cans placed on rollers. The cans held 150L of solution each and were

kept covered to prevent evaporation and to discourage algal growth. Table 7

shows the amount of NaCI added to tap water to create the various solutions.

Food grade NaCI was utilized for two reasons: it is almost the same quality as

reagent grade, being 99% pure (vs. 99.9% for reagent grade) and second it is far less

expensive than reagent grade (www.USDA.gov.foodsafety). On treatment days,

250mL of solution was carefully poured into the media to prevent splashing of the

salt solution onto the foliage. In some cases the solution would leach from the

bottom o f the pot and in other cases it did not. N o attem pt was made to collect

leachate.

As plants formed flowers, they were removed. This would maintain the

plants in a vegetative growth stage in an attempt to prevent complications from a

phase change, which can dramatically impact salt tolerance in some species (D irr,

1973). Otherwise, plants were not pruned after the initial pruning at the start of

the experiment.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. NaCI added Solution (g) (N) 0 0 0.05 435 0.1 862 0.2 1723 0.25 2154

Table 7. Amounts of NaCI added to l50mL tap water to create the stock solutions used in salt tolerance screening experiments.

This experiment was repeated three times. During the first two

experiments a second, complete series of plants received a foliar application rather

than a soil drench o f one of five levels o f sodium chloride solution: 0 (control),

0.05N, 0.1 ON, 0.20N and 0.25N . This doubled the number of plants in the

greenhouse. Plastic bags were placed around the base o f the plants receiving foliar

solution to prevent the salt solution from dripping into the media (Figure 16).

Plants were removed from the bench for spraying to ensure no salt solution landed

on other plants. Each plant was sprayed with a hand sprayer to the point where

the solution was dripping from the foliage, which amounted to approximately 10 —

15ml per plant (approximately 0.21 g NaCI per application at the 0.25N NaCI level).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. After the salt solution stopped dripping from the foliage, the plant was placed back

on the bench. No attempt was made to collect any excess solution.

0.25 0.20 0.20

0.10 0.10 0.05

0.25 con con

con 0.20 N 0.05

.005 0.10 0.25

0.10 0.05

con 0.20 0.25

Figure 14. Randomized complete block design for the third experiment showing the location of each of the blocks. Each repetition of the experiment was constructed in a similar manner, although block location varied, con = control, 0.05 = 0.05N NaCI, 0.I0 = 0.I0N NaCI, 0.20 = 0.20N NaCI, 0.25 = 0.25N NaCI. N = north side of the greenhouse. The small blocks at either ends of the diagram represent the cooling system.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 15. Physical layout o f the greenhouse experiments. The large white containers to the left held the various NaCI solutions.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 16. A plastic bag was placed around the base of the plants receiving foliar salt spray to minimize NaCI solution dripping into the media.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ac the end of 8 weeks three evaluators visually rated the shoots and roots

of each plant on a scale o f 1-5 (Table 8). Each plant was gently removed from its

pot, the pot turned upside down and the plant placed back on top of the pot. This

meant that evaluators could look at the roots and shoots of the plants at the same

time with minimal disruption o f the root systems. A shoot rating of 3.75-5

represented a salable plant in the industry. A ro o t rating of 4-5 indicated healthy

white roots with minimal to no damage visibly apparent. Lower numbers

represented increasing amounts o f damage for both roots and shoots. Plants rating

a 3.75 or above in a given salt level were considered tolerant to that level. A root

rating of 3.0 or above in addition to the shoot rating of 3.75 or above was needed

to label a given species fully salt tolerant to that level.

Shoot dry weight was also taken on all surviving plants. Plants were cut off

at the soil level and weighed. Shoot tissue was then dried for 48 hours at 200

degrees Fahrenheit. This temperature and time was enough fo r most plants, which

were then removed and weighed again. However,Hylotelephium ‘Herbsfruede’ is a

very thick, succulent plant, and all specimens of this species required tw o additional

days of drying to remove all the moisture from the tissue.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Analysis was completed using Analysis of Variance, and descriptive statistics,

including means, standard deviation and standard error, 0.05 confidence interval, on

Jandel Scientifics’ Sigma Stat and Sigma Plot. D ry weights means w ere separated

utilizing two-tailed z-test for comparisons and sum of squares for contrasts.

Plant unaffected, no 5 apparent damage 4 Minimal damage 3 50% damage More than 50% 2 damaged/dead tissue, but some green tissue remaining Plant is dead, showing no 1 green tissue

Table 8. Rating system given to all evaluators to visually rate the roots and shoots of all plants treated with various concentrations of NaCI solution. Raters were allowed to utilize half increments if they felt a plant did not fit neady into a given category.

RESULTS

One-way ANOVA showed significant differences and interactions between

salt level and species. This is not unexpected, as others have reported species

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. differences. Different species o f plants should naturally have varying levels o f salt

tolerance. At the lowest levels of salt application, most plants had high visual

ratings, indicating little damage, which declined gradually with higher treatment

levels. Tables 8 and 9 show the average shoot and ro o t visual ratings fo r all species.

Armeria maritima was the only plant to show salt tolerance at the 0.25 N soil

drench for both the shoots and the roots. Calamagrostis xacutifora ‘Karl Foerster’,

Leymus arenarius (syn. Efymus glaucus), Dianthus xallwoodii ‘Helen’ showed either

shoot tolerance or root tolerance, but they all lacked the tolerance in both levels.

Root tolerances for these four plants would indicate the plants are relatively salt

tolerant (Tables 9 and 10) and would recover quickly at the end of salt application.

However, Amneria was the only species to show high tolerance fo r both roots and

shoots.

None of the plants met the requirements for tolerance in both the roots

and shoots. However, two species showed very good root tolerance, although

their shoots showed obvious damage. Festuca glauca ‘Elijah Blue’, and Pennisetum

alopecuroides showed good root tolerance at the 0.20N NaCI level, but their shoot

ratings were not high enough for them to be considered tolerant, and they are then

placed into the moderately tolerant category.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Achillea millefolium 'Apple 4.33a 3.71b 3.46c l.79d I.l3e Blossom' Achillea 'Moonshine' 4.50a 3.38b 2.96c 1.83d 1.21 e Armeria maritima 4.71a 4.33b 4.13b 3.88c 3.96c ‘Splendens’ Artemisia 'Powis Castle' 4.29a 3.79b 3.33c 2.l7d 2.3 3e Artemisia schmidtiana 'Nana' 4.04a 3.63b 2.88c l.67d 2.2 le Aster novi-angliae 'Purple 3.96a 3.04b 2.96b 1.79c 1.21 d Dome' Astilbe 'Peach Blossom' 3.54a 2.17b 1.63c I.OOd I.OOd Athyrium felix-femina 3.88a 2.96b 1.25c l.08d I.OOd Calamagrostis xacutiflora 4.25a 4.50a 4.00b 3.00c 3.29c 'Karl Foerster' Centaurea montana 3.71a 2.63b 1.13c 1.08c 1.00c Cerastium tomentosum 3.17a 2.54b 1.17c 1.00c 1.00c Coreopsis grandiflora 'Early 4.33a 2.25b 1.00c 1.00c 1.00c Sunrise' Coreopsis verticillata 4.54a 3.08b 1.88c 1.13cd l.08d 'Moonbeam' Dianthus deltoides 'Flashing 4.29a 2.38b 1.00c 1.00c 1.00c Lights' Dianthus xallwoodii 'Helen' 4.88a 4.21b 3.67c 4.00b 3.75c Echinacea purpurea 'Magnus' 4.25a 2.17b 1.13c 1.00c 1.17c Leymus arenarius 4.38a 4.13b 3.92b 3.17c 3.04c Continued on pg. 89

Table 9. Shoot average visual ratings of 38 species of actively growing herbaceous perennials treated with 250ml three times a week for eight week with one o f five different levels of sodium chloride applied to the soil (0.00N NaCI - control, 0.05N NaCI, 0.1 ON NaCI. 0.20N NaCI and 0.25N NaCI) Based upon a visual scale of 1-5 (I = dead, 5 = no damage). Different letters indicates a significant difference at the 0.05 level. This comparison is between individual species at different levels. No attempt is made to separate means between different species.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 9 (continued)

Hemerocallis 'Cherry Cheeks' 4.33a 3.88b 3.25c 2.54d l.88e Hemerocallis 'Stella de Oro' 4.79a 4.08b 3.71c 2.96d 2.46e Heuchera micrantha 'Palace Purple' 4.92a 2.33b 1.33c 3.08d l.08e Heuchera sanguinea 'Chatterbox' 4.96a 3.13b 2.71c l.88d l.46e Hosta 'Undulata Mediovariegata' 4.83a 4.58b 3.92c 2.67d l.88e Iris sibirica 'Caesar's Brother' 4.29a 4.08b 3.50c 2.l7d l.88e Lavandula angustifolia 'Hidcote' 4.46a 2.33b 1.08c 1.00c 1.00c Leucanthemum xsuperbum 'Becky' 3.92a 4.17b 3.75c 2 .l7d l.54e Limonium latifolium 4.13a 4.33b 3.04c 2.50d 2.92c Liriope muscari 4.38a 4.63b 3.71c 2.67d 2.33e Lythrum virgatum 'Morden Gleam' 3.96a 3.25b 2.08c l.75d l.25e Monarda didyma ‘Blaustrumpf 4.21a 1.71 b l.2 lc I.OOd 1.17c Pennisetum alopecuroides 4.21a 4.79b 3.71c 3.33d 3.00e Perovskia atriplicifolia 4.17a 3.46b 2.71c 1.83d l.29e Rudbeckia fulgida var. sullivantii 4.50a 2.13b 1.00c 1.00c I.l7 d 'Goldsturm' Hylotelephium ‘Herbsfruede’ 4.79a 4.63a 3.67b 3.63b 2.04c Solidago 'Crown of Rays’ 4.67a 4.21b 2.38c l.46d l.04e Festuca glauca 'Elijah Blue' 4.83a 4.38b 3.38c 3.25c 2.79d Gaillardia xgrandifora 'Goblin' 4.46a 3.58b 2.33c l.25d 1.21 d Geranium sanguineum 4.33a 3.46b 1.46c I.l7 d I.OOd Geranium xoxonianum 'Claridge Druce' 4.54a 3.17b 1.38c 1.32c I.OOd

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Achillea millefolium 'Apple 4.63a 3.88b 3.38c 1.75c 1.13d Blossom' Achillea 'Moonshine' 4.92a 3.42b 2.92c l.79d 1.21 e Armeria maritima 5.00a 4.38b 4.21b 3.46c 3.46c ‘Splendens’ Artemisia 'Powis Castle' 4.83a 4.00b 3.33c 2.29d 2.33d Artemisia schmidtiana 'Nana' 4.79a 3.75b 2.83c 1.63d I.OOe Aster novi-angliae 'Purple 4.83a 3.50b 3.17c 2.04d l.25e Dome' Astilbe 'Peach Blossom' 4.04a 2.17b 1.63c I.OOd I.OOd Athyrium felix-femina 4.17a 2.83b 1.29c l.08d I.OOd Calamagrostis xacutiflora 4.79a 4.63a 4.13b 3.33c 3.54c 'Karl Foerster' Centaurea montana 4.67a 2.75b l.2lc I.l7cd I.OOcd Cerastium tomentosum 4.04a 3.04b 1.25c 1.13cd I.OOcd Coreopsis grandiflora 'Early 4.79a 2.54b 1.00c 1.00c 1.00c Sunrise' Coreopsis verticillata 4.79a 3.17b 1.88c 1.13d I.l7 d 'Moonbeam' Dianthus deltoides 'Flashing 4.92a 2.63b 1.13cd l.08cd 1.25c Lights' Continued on Pg. 9 1

Table 10. Root average visual ratings o f 38 species of actively growing herbaceous perennials treated with 250ml three times a week for eight week with one of five different levels o f sodium chloride applied to the soil (0.00N NaCI - control, 0.05N NaCI, 0.1 ON NaCI, 0.20N NaCI and 0.25N NaCI) Based upon a visual scale o f 1-5 (I = dead, 5 = no damage). Different letters indicates a significant difference at the 0.05 level. This comparison is between individual species at different levels. N o attempt is made to separate means between different species.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 10 (continued) mmK X K 9 BEH Hemerocallis 'Stella de O ro1 5.00a 4.2 lb 3.75c 3.00d 2 .l3 e Heuchera micrantha 'Palace Purple' 5.00a 2.46b 1.33c l.08d l.04d Heuchera sanguinea 'Chatterbox' 5.00a 2.96b 2.54b 1.79c 1.63c Hosta ‘Undulata Mediovariegata' 5.00a 4.71a 4.00b 2.92c 2.50d Iris sibirica 'Caesar's Brother' 4.92a 4.38b 3.75c 2.58d 2.42d Lavandula angustifolia 'Hidcote' 4.46a 2.38b 1.04c 1.00c 1.08c Leucanthemum xsuperbum 'Becky' 4.79a 4.29b 3.67c 2.38d 2.29d Limonium latifolium 4.71a 4.50a 3.08b 2.67c 2.92b Liriope muscari 4.67a 4.75a 3.83b 2.92c 2.56c Lythrum virgatum 'Morden Gleam' 4.75a 3.42b 2.13c l.75d l.46e Monarda didyma ‘Blaustrumpf 4.50a 1.88b l.2 lc 1.00c 1.63b Pennisetum a/opecuroides 4.88a 4.92a 3.83b 3.42c 2.96d Perovskia atriplidfolia 4.58a 3.50b 2.67c l.75d I.l7 e Rudbeckia fulgida var. sullivantii 'Goldsturm' 4.54a 2.0be 1.00c 1.00c 1.00c Hylotelephium 'Herbsfruede’ 5.00a 4.58b 3.38c 3.33c l.79d Solidago 'Crown of Rays' 4.96a 4.33b 2.54c 1.71 d l.l 3e Dianthus xallwoodii 'Helen' 5.00a 4.17b 3.42c 3.13d 2.50e Echinacea purpurea 'Magnus' 4.71a 2.38b 1.25c I.OOd 1.29c Leymus arenarius 5.00a 4.33b 4.08b 3.38c 3.29c Festuca glauca 'Elijah Blue' 4.92a 4.17b 3.13c 2.96d 1.7 le Gaillardia xgrandiflora 'Goblin' 4.54a 3.71b 2.42c l.38d I.OOe Geranium sanguineum 4.71a 3.63b 1.46c l.2 lc I.OOd Geranium xoxonianum 'Claridge Druce' 4.83a 3.25b 1.38c 1.29c 1.38c Hemerocallis 'Cherry Cheeks' 5.00a 4.00b 3.25c 2.50d 2.46d

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Many other species can also be considered moderately tolerant to deicing

salt, as they met the requirements of having a shoot rating of >3.75 at the 0.20N

NaCI concentration along with a >3.0 root rating. Hemerocallis ‘Stella de O ro \

Leucanthemum xsuperbum ‘Becky’, Hosta ‘Undulata Mediovariegata’, Uriope muscari,

and Hylotelephium ‘Herbsfruede’ all met the requirements to be considered

moderately tolerant.

Many species had good ro o t tolerance and recovered rapidly once the salt

applications ceased. However, they did not fit our rigid requirements for moderate

tolerance. Those species include: Artemisia schmidtiana ‘Nana’, Aster novi-angliae

‘Purple Dome’, Iris sibirica ‘Caesar’s Brother’, and Limonium latifolium. These species

were consequently labeled moderately sensitive. The 0.1 ON NaCI concentration

represents the concentration of deicing salt applied during a moderate winter and is

probably representative o f concentrations that many species would encounter in an

average Ohio winter, thus the distinction between moderately tolerant and

moderately sensitive becomes important.

A few species treated with the lowest salt level had high shoot and ro o t

ratings only at the lowest salt treatment level and will be considered salt sensitive.

Those species included: Achillea millefolium ‘Apfelblute’, Hemerocallis ‘Cherry

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cheeks’, and Solidago ‘Crown of Rays’. These plants would be able to tolerate low

amounts of salt, similar to that applied during a mild winter.

The remaining species were killed or severely damaged at even the lowest

salt level and they will be considered highly sensitive. These plants probably would

not survive the amount of deicing salt applied during even the mildest winters and

should not be planted near areas where deicing salt is applied. The final ratings,

based upon visual evaluation, for all plants are listed in Table 11.

Measurement of shoot dry weight is highly correlated with visual ratings.

Plants with high visual ratings also had more shoot weight. Plants with lower visual

ratings had less shoot weight (Table 12). Thus plants showing even some salt

tolerance were able to put on more growth vs. plants that were intolerant (Figure

17). Plants that were rated as highly sensitive showed dramatic decreases in dry

weight at even the lowest salt level, 0.05N NaCI (Figure 18). All species showed

approximately linear drops in shoot dry weight according to Sums of Squares of

Contrasts. This analysis also suggests that this general linear trend would remain

constant for most species o f ornamental plants. The fact that the trend in salt

tolerance is roughly linear, as salt levels increase, growth decreases, suggests there

exists a salt level that would kill all plants, including the most salt tolerant ones.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. This sale level could not be stated explicitly, as it would change fo r each species.

Some species would have a low salt level that would kill them, others would have a

very large level, but each would have a level at which death occurs.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Species Rating Caillardia xgrandiflora 'Goblin' HS Achillea millefolium 'Apple Blossom' Geranium sanguineum HS Achillea 'Moonshine' HS Geranium xoxonianum 'Claridge Druce' HS Armeria maritima 'Splendens' H T Hemerocallis 'Cherry Cheeks' MS Artemisia 'Powis Castle' Hemerocallis 'Stella de Oro' MT Artemisia schmidtiana 'Nana' MS Heuchera micrantha 'Palace Purple' HS Aster novi-angliae 'Purple Dome'______MS Heuchera sanguinea 'Chatterbox' HS Astilbe 'Peach Blossom' HS Hosta ‘Undulata Mediovariegata' MT Athyrium felix-femina______HS Hylotelephium ‘Herbsfruede’ S Calamagrostis xacutiflora 'Karl Foerster' Iris sibirica 'Caesar's Brother* MS Centaurea montana HS Lavandula angustifolia 'Hidcote' HS Cerastium tomentosum HS Leucanthemum xsuperbum 'Becky' M T Coreopsis grandiflora 'Early Sunrise' HS Limonium ladfolium MS Coreopsis vertidllata 'Moonbeam' HS Liriope muscari MT Dianthus deltoides 'Hashing Lights'______HS Lythrum virgatum 'Morden Gleam' HS Dianthus xallwoodii 'Helen' Monarda didyma ‘Blaustrumpf HS Echinacea purpurea 'Magnus'______HS Pennisetum alopecuroides MT Leymus arenarius Perovskia atriplidfolia HS Festuca glauca 'Elijah Blue'______MT Rudbeckia fulgida var. sullivantii 'Goldsturm' HS Solidago 'Crow n o f Rays' HS

Table 11. Tolerance of perennials to soil applied sodium chloride. H T = highly tolerant, T = tolerant, MT = moderately tolerant, MS = moderately sensitive, S = sensitive, and HS = highly sensitive. A given species must have a rating o f 3.75 or above in shoot rating AND a 3.0 in root rating to be determined to be tolerant to that particular level. A plant rating 3.75 shoots/3.0 roots at the 0.25N NaCI level is determined to be highly tolerant to soil applied N aC I. Plants with either a very high root or shoot rating at the 0.20N NaCI or 0.25 N NaCI levels were considered tolerant. A plant rating 3.75 shoots/3.0 roots at the 0.20N NaCI level is determined to be moderately tolerant. A plant rating 3.75 shoots/3.0 roots at the 0.1 ON NaCI level is determined to be moderately sensitive. Plants rating 3.75 shoots/3.0 roots at the 0.05N NaCI level, were rated as sensitive to soil applied salts. Plants rating less than 3.75 shoots/3.0 roots at the 0.05N NaCI level were rated as highly sensitive to soil applied sodium chloride.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. n BS Achillea millefolium ‘Apple Blossom’ 25.49a 24.5a 15.67b 2.73c 2.64d Achillea 'Moonshine' 25.93a 21.54b 13.57c 9.58d 6.87e Armeria maritima ‘Splendens’ 20.25a 19.59b 18.24cd 18.58c 17.52cd Artemisia 'Powis Castle' 38.41a 27.18b 25.22c 24.70d 24.66d Artemisia schmidtiana ‘Nana’ 10.34a 9.64b 5.66c l.28d 2.74e Aster novi-angliae 'Purple Dome' 17.66a 16.94a 10.65b 3.40c 2.81c Astilbe 'Peach Blossom' 8.06a 5.97b 2.68c 0.12d 0.3 Id Athyrium felix-femina 6.54a 5.83b 1.37c 0.28d 0.19d Calamagrostis xacutiflora 'Karl Foerster' 42.31a 40.98b 41.67b 37.81c 37.10c Centaurea montana 12.34a 10.08b 2.13c l.92cd I.l4d Cerastium tomentosum 8.14a 7.29b 2.37c l.96cd l.58d Coreopsis grandiflora ‘Early Sunrise’ 13.19a 5.67b 2.13c l.65d l.02d Coreopsis vertidllata 'Moonbeam' 17.00a 8.24b 6.04c 1.01 d 0.19e Dianthus dekoides ‘Flashing Lights’ 6.1 la 3.87b 1.34c 0.96d 0.65c Dianthus xallwoodii ‘Helen’ 15.67a 14.35b 13.98b 14.19b 12.2c Echinacea purpurea ‘Magnus’ 14.81 a 5.11b 2.29c 1.98c l.34d Leymus arenarius 19.98a 18.55b 18.41 b 17.64c 16.57d Festuca glauca 'Elijah Blue' 17.28a 18.3b 14.32c 14.38c 4.8 Id Gaillardia xgrandiflora ‘Goblin’ 15.47a 12.39b 8.19c 3.43d l.28e Geranium xoxonianum 'Claridge Druce’ 29.81a 10.1 lb 3.27c l.25d 0.65e Geranium sanguineum 29.01a 10.6b 3.44c 2.2d l.02e Continued on Pg. 97

Table 12. Average dry weights (12 replications) of actively growing herbaceous perennials treated three times a week for eight weeks with 250ml of one of 5 levels o f NaCI solution from 0.00N (control) to 0.25N . W ithin individual species, different letters indicate a significant difference at the 0.05 level. Each species is separate; no attem pt is made to compare different species.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 12 (continued)

Limonium latifolium 12.96a 15.81 b 14.85c 7.6 Id 8.93e Liriope muscari 10.66a 14.57b 10.36a 5.24c 5.1 Ic Lythrum virgatum ‘Morden Gleam’ 19.89a 19.67a 15.23b 1.56c 0.99d Monarda didyma ‘Blaustrumpf 15.75a 1.67b 0.35c 0.21c 0.25c Pennisetum alopecuroides 36.54a 33.25b 35.74a 27.31c 26.89c Perovskia atriplicifolia 27.85a 18.64b 5.22c l.27d l.32d Rudbeckia fulgida var. sullivantii 22.36a 5.24b 0.27c 0.65d 0.15c 'Goldsturm' Hylotelephium ‘Herbsfruede’ 14.16a 15.32b 5.44cd 5.89c 5.23d Solidago 'Crown o f Rays' 18.57a 16.52b 2.45c l.05d 0.37e Hemerocallis 'Cherry Cheeks' 12.25a 10.65b 5.74c 3.65d 0.97e Hemerocallis 'Stella de O ro' 10.09a 7.34b 1.76c 3.48d 2 .19e Heuchera micrantha ‘Palace Purple’ 21.25a 11.03b 5.24c 1.41 d 0.5 le Heuchera sanguinea ‘Chatterbox’ 22.05a 19.64b 10.22c 8.34d 2.0 le Hosta ‘Undulata Mediovariegata' 13.64a 10.27b 4.66c 4.09c 2.87d Iris sibirica ‘Caesar’s Brother’ 17.55a 17.3 la 12.65b 5.32c l.97d Lavandula angustifolia ‘Hidcote’ 12.32a 6.57b 1.89c 1.87c 1.33d Leucanthemum xsuperbum ‘Becky’ 22.34a 18.65b 17.43c 2.65d l.92d

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Arm eria Caiamagrostis Dianthus Leymus Pennisetum mariu'ma xacutiflora xallwoodii arenarius alopecuroides 'Karl Foerster1 'Helen'

□ control 00.05 00.1 E30.2 Q0.25

Figure 17. Dry weights of the five most salt tolerant perennials treated with 250ml three times a week with one of 5 different levels of NaCI solution. All species showed a statistically significant drop in dry weight, between the control plants as the highest salt level, 0.25N NaCI.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25

3 15

5 H

1 0 -M I AstUbe 'Peach Rudbeckia Centaurea Monarda Echinacea Dianthus Blossom' fulgida var. montana didyma purpurea deltoid es sulRvanbi 'Blaustrumpf 'Magnus' 'Flashing Lights’ 'Goidstumri' NaCI level (N)

0 0 .ON NaCI 0O.O5N NaCI S O .IN NaCI 0O.2N NaCI CD0 .25 N NaCI

Figure 18. Dry weights of six of the least salt tolerant perennials treated with 5 levels of NaCI solutions. All series are significandy different from control to all other levels at the 0.05 level.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DISCUSSION

During the first two repetitions of this experiment, half the plants received a

foliar spray of the various NaCI solutions rather than a soil drench. At the

completion of these two experiments it was noticed that all plants receiving the

foliar spray recovered completely within 5 weeks once the stress was removed

(Figure 19). These plants w ere very quick to display salt damage symptoms, in

some cases after only three treatments. Many species appeared dead, with no

visible living shoot tissue. However, all plants recovered. O u r area o f interest then

turned to effects of deicing chemicals on plants, rather than salt spray. In northern

states, this is most similar to the types of stress freeway and other public plantings

would encounter. At this point, we discontinued the foliar studies and

concentrated solely on soil-applied sodium chloride.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 19. Re-growth of Heuchera sanguinea ‘Chatterbox’ after salt treatments had been removed for 5 weeks. Control plant (left); the middle plant received 8 weeks of 0.25 N NaCI (approximately 5.2 g NaCI total applied) solution as a foliar application, and the far right plant had 8 weeks of 0.25 N NaCI (approximately 86.4g NaCI total applied) as a soil drench.

101

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The levels of sodium chloride solution utilized during these screening

experiments were chosen for two reasons. First, Dirr ( 1978, 1984) utilized them

in several of his studies with wood/ plants and achieved noticeable effects on the

species he tested. Second, seawater contains approximately 3.5% sodium chloride,

which calculates to approximately 98g NaCI per liter seawater. The 0.25N NaCI

solution is approximately 10-12% that of seawater, which we felt was sufficient for

most glycophytes to show damage based upon previous work with glycophytic

plants (Ungar, 1991). It is interesting to compare this with what has been found

along some roadways. In some areas in Michigan, the amount of sodium chloride in

the soil solution was as high as 13g/l_ although it was as low as 0.4g/L in other areas

(Frost, 1988). Thus the 0.25 N NaCI solution accurately represented the highest

levels of NaCI found along the roadside, and the lowest level utilized is somewhat

higher than found under minimal salt applications.

For this experiment, we based our rating system on protocols initiated by

others (Dirr, 1979, Headley, 1993). However, the placement into the various

tolerance classes seemed almost random. There is no one system fo r classifying

plants as either tolerant or sensitive. To that end, we created a system that we

found rational from both a “people perspective" as well as from a horticultural

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. perspective. The classification system was described earlier. The rationale for this

system is described in the following paragraphs. W e present this system as a

potential method to provide consistency to any other researchers looking into this

topic.

People looking at plants report a given plants’ health based upon the

appearance of the shoots and leaves. Roots must be healthy if the plant is to

perform well in the landscape. Although more damage was apparent in the root

systems of all plants, most plants w ere able to recover from a seemingly large

amount of damage. Plants showed damage but then w ere able to recover. By

observing which plants recovered and correlating this data to root damage, it was

determined that plants with an average root rating of 3.0 or above would recover

in sufficient tim e to perform well during the growing season. Plants with an average

root rating below 3.0 did eventually recover, but the process took much longer and

the plants never performed well: flowering was decreased, plants were stunted,

and foliage color was visually lighter than th eir control counterparts. Some

individual plants never did recover. Based upon the observations with the plants

we developed the rating system described in the materials and methods.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. It is interesting to note that the only plant to receive the highly tolerant

rating was the halophyte Armeria maritima. This rating should not be surprising, as

the native habitat ofArmeria maritima is the salt marshes and rocky outcroppings o f

coastal regions o f northern European countries such as Scotland (Phillips and Rix,

1991, and Heywood, 1994), where it has adapted to saline conditions. One theory

put forth for the development of this adaptation is thatArmeria maritima is not a

good competitor, and when placed into non-saline conditions, it is unable to

compete (Ungar, 19 9 1). Although the plant displays very high tolerance to salinity,

under non-saline conditions the plant puts on more mass and has greatly increased

photosynthesis (Cooper, 1982). Thus, salt tolerance may have developed in this

species as a mechanism fo r reducing competition. This hypothesis has been

suggested for several facultative halophytes to attempt to explain the development

o f high salt tolerance certain plants that prefer non-saline conditions (Ungar, 199 1,

Cooper, 1982, and LeHouerou, 1996).

Many grasses also display high salt tolerance levels (Ungar, 199 1), and this

was evident in the strong tolerance of Calamagrostis and Leymus, although in our

study, grasses such as Festuca and Pennisetum showed only minimal tolerance to soil

applied sodium chloride. Within the genera Calamagrostis, Festuca and Leymus there

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. are several species o f halophytes (Ungar, 1991). Monocots also have a very

different morphology from dicots as well as several key differences in physiology. It

is these differences that perhaps also confer relatively high levels of salt tolerance in

this group o f plants, and indirectly to the species represented here.

The low ratings for Umonium latifolium were surprising; given this plant is a

known halophyte. Umonium is native to brackish waters in southern Europe and

Asia, and is also found in deserts, (Heywood, 1993) indicating the plant should have

a high degree of both salt and drought tolerance. Previous research has shown that

Umonium accumulates both sodium and chloride then excretes them through the

leaves as levels become too high in the tissues (Ungar, 1991). This process,

although not studied during this experiment, was noticed (Figure 20), and this

corroborates previous w ork with this species. Given the halophytic nature of

Umonium, it was expected that this plant would receive higher ratings than many

other species. In our study it was rated as moderately sensitive to sodium chloride.

Perhaps Umonium is sensitive to sodium chloride, but is not sensitive to other types

o f salt. Perhaps Umonium utilizes these other salts in osmotic adjustment, and

cannot tolerate sodium chloride alone. Perhaps it is simply not as well adjusted to

high salinity levels as other species o f halophytes. Le Houerou (1996) states that

105

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Umonium is indeed a facultative halophyte that has adapted to sporadic low levels of

brackish water, but suffers under continual salinity, and in fact, prefers a non-saline

habitat. He further states that it is not a highly competitive plant, and perhaps has

evolved this limited salt tolerance as a means of avoiding competition.

Figure 20. Umonium latifolium showing salt excretion from the leaves. The small white dots on the leaves are excreted sodium chloride.

106

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The relatively high tolerance of Dianthus xallwoodii ‘Helen’ was unexpected,

and this should be looked at more closely to determine its mechanism fo r

tolerance. It is not listed anywhere in the literature as a halophyte, yet its tolerance

was very close to Armeria, a known halophyte, and better than Umonium latifolium,

another known halophytic plant. The closely related Dianthus deltoides ‘Flashing

Lights’ was highly sensitive to soil applied sodium chloride. Dianthus xallwoodii is a

cross between Dianthus plumarius and Dianthus caryophyllus (Still, 1994). There have

been no studies with 0. plumarius, thus its contribution to the hybrid’s salt

tolerance cannot be assessed. The one study with D. caryophyllus shows it to be

fairly sensitive to soil applied salts when grown in sand (Ishida, 1979). Any

assumption that D. caryophyllus was the parent responsible for salt tolerance in the

hybrid would be suspect. Dianthus plumarius would be a good candidate for another

screening study to determine its salt tolerance. However, it could be as simple as

hybrid vigor that explains the unexpected salt tolerance in Dianthus xallwoodii

‘Helen’.

By correlating the tolerance ratings with shoot dry weight, several other

anomalies also emerge. Many researchers have illustrated the relationship between

107

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. salt tolerance and shoot dry weight and this measure has now become an accepted

estimate of salt tolerance, although it is not without problems.

Two of the plants that warrant a closer look based upon their dry weights

are Artemisia ‘Powis Castle and Hylotelephium ‘Herbsfreude’ (Figure 21). Both these

plants w ere rated as salt sensitive, and th eir dry weights dropped significantly at the

highest salt levels. However, the drops are not as dramatic as with any of the other

sensitive species when other variables are considered. All raters thought the plants

looked good, but were simply stunted. N either species showed marginal necrosis,

wilting o r any other symptom of drought o r salt damage typical of sensitive and

moderately sensitive species. The only visible symptom was stunting, which, judging

from the dramatic drop in shoot dry weight, was severe. This might indicate

reduced photosynthesis. Most salt tolerant plants with reduced photosynthesis

have lower amounts of chlorophyll and reduced transpiration (Terry, 1984). These

results might indicate these plants are far more tolerant than the visual ratings

would show. Even Armeria had a significant lowering of dry weight. Perhaps these

species w ere able to adjust osmotically. Perhaps energy was being expended

sequestering one or more ions, resulting in decreased growth. Perhaps one o r

108

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. more plant hormones were affected, impacting growth in a negative manner, which

is a recent suggestion in the literature.

Although Artemisia ‘Powis Castle’ is a hybrid, its lineage can be traced to

Mediterranean native species (Heywood, 1993). Plants native to this area are often

highly drought tolerant, and this Artemisia is no exception (Sill, 1994). The

mechanisms for drought tolerance may also confer limited salt tolerance to the

plant, as the tw o stresses often cause similar changes physiologically.

Figure 2 1. Symptoms o f salt damage to Sedum ‘Herbsfruede’ after 8 weeks of soil applied NaCI. Plants received 250ml of one of five NaCI solutions three times per week. From left to right plants received 0.25N, 0.20N, 0.1 ON 0.05N and 0.0N (control) NaCI. Note the obvious stunting on the plants receiving the most levels of salt, but also the lack of other visible symptoms.

109

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Hylotelephium ‘Herbsfruede’ was developed from Hylotelephium spectabile,

(syn. Sedum spectabile) and other closely allied species, most of which are native to

low altitude areas of northern China and Korea (Stephenson, 1994). This group of

Hylotelephium exhibit CAM metabolism and close their stomata during the day. This

would reduce water loss and decrease photosynthetic rates, but also allow the

plants to survive extreme drought. This type of metabolism is also found in many

species of halophytic plants (Gorham, 1996). It is perhaps this reduction in water

loss, which in turn reduces photosynthesis, which may allow the plant to survive

times o f stress, including excessive soil salts. It has already been mentioned that

Armeria maritima exhibits reduced photosynthesis under salt stress, (Cooper, 1982)

however, Armeria is a plant whose height doesn’t change much during the growing

season. Stunting would not necessarily be visible with this species. However, when

plants that should be two to three feet tall become stunted, the change is dramatic.

This may cause a human rater to be biased and rate the plants low er than they

would Armeria, whose height wouldn’t have changed as dramatically. Both Artemisia

‘Powis Castle’ and Hylotelephium ‘Herbsfruede’ may indeed be far more salt tolerant

than the low ratings would otherwise indicate. There is no literature on the

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mechanisms of salt tolerance fo r either o f these two species; they should be studied

further to determine their method(s) of salt tolerance.

By concentrating on the visual ratings of the 5 most salt tolerant species

(Figure 22), it is possible to see that at the highest salt levels, even these species had

dramatic reductions in growth and developed visual symptoms. These changes,

while not significant between individual salt treatments was significant between the

control plants and the highest salt levels. These tolerant species did recover once

the stress was removed. By comparing these plants with 6 of the most salt

sensitive plants (Figure 23), it becomes apparent that the drops in visual ratings

were far more dramatic than for the tolerant species. In addition these drops

tended to occur at lower levels than for the tolerant species. Most of the salt

sensitive plants did not recover once the stress was removed. Others showed only

marginal recovery, a single shoot, o r one o r tw o green leaves.

Ill

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Armeria maritima Calamagrostis Dianthus Leymus arenarius Pennisetum xacutiflara ‘Kart xallwoodii Helen' alopecuroides Foerster*

Armeria Calamagrostis Dianthus Leymus Pennisetum maritima xacutiflora 'Karl xallwoodii arenarius (syn. alopecuroides Foerster* 'Helen* Elymus glauca)

Bo 00.05 Qo.i Bo.2 00.25

Figure 22. Visual ratings of roots and shoots of five of the most salt tolerant herbaceous perennials treated with 5 levels of NaCI. X-axis is the Normality of the salt solution applied. Y-axis is the average visual rating fo r each species. This average was taken from 3 observers across all the replications for each species. Differences are significant at the 0.05 level.

112

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6

□ O.OON Nad 0O.O5N Nad CDO.ION Nad C30.20N Nad a0.25N Nad

Figure 23. Visual ratings o f shoots and roots o f six o f the least salt tolerant herbaceous perennials treated with 5 levels of NaCI. X-axis is the species of plant. Y-axis is the average visual rating for each species. This average was taken from 3 observers across all the replications for each species. Differences are significant at the 0.05 level.

113

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. As mentioned above, there would be a salt level that would kill even the

most salt tolerant of plants, although this level would change for different species.

This level might even change for different cultivars. The changes for different

cultivars are suggested by the different performance of the two cultivars of

Hemerocallis, ‘Stella de Oro’ and ‘Cherry Cheeks’. The cultivar ‘Cherry Cheeks’

was unable to maintain shoot mass at the higher salt levels and its dry weight

dropped precipitously. The cultivar ‘Stella de Oro’ was able to maintain a greatly

reduced amount of shoot mass across all salt levels. Visually there are differences

between these tw o cultivars. ‘Stella de O ro ’ is a small plant with small, thin leaves.

‘Cherry Cheeks’ is a much larger plant with large thick leaves. Perhaps the general

trend would be for the smaller daylilies to prove slightly more salt tolerant than the

larger ones.

There are several possible explanations fo r the divergent responses of the

two cultivars. The first would be the genetic differences between the cultivars,

something that provided one cultivar with a given characteristic, happened to also

confer limited salt tolerance. There could be genetic differences in salt tolerance in

the genus Hemerocallis, such as exists for Taxodium distichum, as mentioned

previously. These variations in ecotype might have been passed along through the

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. breeding of the various cultivars. There might also be morphological differences

between the two cultivars, such as cuticle thickness, that might make one cultivar

more tolerant than another. The differences might be physiological. One cultivar

grows faster than the other, is better able to sequester problem ions, or is simply

better at w ater uptake. Finally, it is possible that the breeding ofHemerocallis, and

the development of the many cultivars is so complex that no one method of salt

tolerance could ever be elucidated fo r this genus and the many cultivars and hybrids

available.

Even salt tolerant plants showed effects from soil applied sodium chloride.

Armeria maritima, showed significant decreases in shoot dry weight. There is an

energy cost to the plant for salt tolerance. It is already known thatArmeria lowers

its photosynthetic rate to allow it to maintain its osmotic potential while under salt

stress. It also expends energy in uptake of both Na+ and K+, to maintain higher

levels of ions within its tissue than the surrounding soil. Uptake of these two ions is

an active process, which utilizes energy (Ungar, 1992). Thus the cost to the plant is

decreased shoot mass.

By rearranging Table 11 to show the plants by tolerance rating (rather than

alphabetically), several interesting trends appear (Table 13). The number of plants

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in the three sensitive categories (highly sensitive, sensitive and moderately sensitive)

is twenty-eight. Of these 28, 12 (43%) are from the Asteraceae family. This is a

group o f plants that most horticulturalists consider highly tough and durable plants.

They are often listed as “clay busters” and are capable of handling dry, windy,

infertile situations. Yet, a large percentage of this family is also apparently highly

intolerant to soil applied sodium chloride. There was only one member of this

family that rated higher than moderately sensitive, Leucanthemum xsuperbum

‘Becky’, which we rated as moderately tolerant.

This experiment was conducted with actively growing plants. The results

obtained may relate direcdy to salt spray applications to perennials in seaside

conditions during the growing season. It might also indicate survival during a late

season salt application. Plants have already emerged from the ground when the

weather conditions necessitate salt application, thus applying salt to actively growing

plants.

116

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Species Rating Astilbe 'Peach Blossom' HS

Armeria maritima 'Splendens' HT Athyrium felix-femina HS

Calamagrostis xacutiflora 'Karl Centaurea montana HS Foerster' Cerastium tomentosum HS Dianthus xallwoodii 'Helen' Coreopsis grandiflora 'Early Leymus arenarius HS Sunrise' Festuca glauca 'Elijah Blue’ MT Coreopsis verticillata 'Moonbeam' HS

Hemerocallis 'Stella de O ro' MT Dianthus deltoides 'Hashing Ughts' HS

Hosta ‘Undulata Mediovariegata' MT Echinacea purpurea 'Magnus' HS

Leucanthemum xsuperbum 'Becky' MT Gaillardia xgrandiflora 'Goblin' HS

Liriope muscari MT Geranium sanguineum HS Pennisetum alopecuroides Geranium xoxonianum 'Claridge MT HS Druce' Artemisia schmidtiana 'Nana' MS Heuchera micrantha 'Palace Purple' HS Aster novi-angliae 'Purple Dome' MS Heuchera sanguinea 'Chatterbox' HS Hemerocallis 'Cherry Cheeks' MS Lavandula angustifolia 'Hidcote' HS Iris sibirica 'Caesar's Brother' MS Lythrum virgatum 'Morden Gleam' HS Umonium latifolium MS Monarda didyma ‘Blaustrumpf HS Achillea millefolium 'Apple Perovskia atriplicifolia Blossom' HS Artemisia 'Powis Castle' Rudbeckia fulgida var. sullivantii HS 'Goldsturm' Hylotelephium 'Herbsfruede' Solidago 'Crown of Rays' HS Achillea 'Moonshine' HS

Table 12. Tolerance of herbaceous ornamental perennials to soil applied sodium chloride, listed by rating. HT = highly tolerant, T = tolerant, MT = moderately tolerant, MS = moderately sensitive, S = sensitive, and HS = highly sensitive.

117

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Another factor that must be studied is the effect o f soil on survival as these

plants w ere all grown in soil-less, peat based media. W hile a peat-based media will

hold sodium chloride well, it also drains very well compared to clay soils, which

would also have a large capacity for holding salt ions. Thus, the conditions may not

accurately reflect field conditions, where the soil is very different and behaves in a

very different manner. A prime example of the effect of soil on plant survival is

seen in Figure 24. This shows Achillea millefolium growing approximately 15m from

the Atlantic Ocean. This is obviously a sandy soil and the plant is flowering

normally. However, the plant is also stunted compared to specimens growing along

the freeway system in Central Ohio. This is a plant that we rated as moderately

sensitive, but grows in the salt spray of the Atlantic Ocean, which might indicate a

higher tolerance in a more sandy soil. Sandy soils drain very quickly and would not

retain many o f the damaging ions, which would leach through the soil profile

quickly. Soil may play a greater role for some species than fo r others.

There are, however, other explanations for this difference in both height

and survival of this species. The straight species, Achillea millefolium, while closely

allied to the cultivar A millefolium ‘Apfelblute’ may be vastly different genetically, and

these differences may account for the different survival. The process of breeding

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. for one characteristic or another may alter the relationship of many different genes

within the plant. There may also be ecotypes of this species, whereby some types

are capable o f survival in salt spray and others are not.

Figure 24. Achillea millefolium growing on the ocean-facing primary dune. This plant is approximately 15m from the shore and is flowering normally, although its height is somewhat reduced compared to landscape plants.

Hemerocallis ‘Cherry Cheeks’ and Hemerocallis ‘Stella de Oro’ are two plants

that are closely related that showed different levels of salt tolerance. This shows

that we cannot assume that different cultivars o f the same genus will provide us

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. with the same landscape performance. However, their ratings were very close

together, one being sensitive and the other being moderately sensitive. It would

probably be safe to assume that most, if not all daylilies were approximately

moderately sensitive, with some cultivars perhaps slightly less so.

The dichotomous performance o f the tw o species of Dianthus, however,

shows that we cannot assume that all plants of a given genus will perform in a

similar manner. This does not imply that we must screen all available cultivars and

species, however. W hat it does mean is, we must exercise caution when applying

the data presented here to plants with very different morphology. Plants with an

appearance similar to Dianthus xallwoodii ‘Helen’, i.e. stiff gray leaves with a glaucous

coating, (Dianthus gratianopolitanus, Dianthus plumarius etc) might perform in a

similar manner and show good tolerance. Plants along the roadside may need to be

replaced after a w inter with heavy snowfall.

Distance from the road plays a major role in damage to plant materials.

D ’ltri (1992) showed that a sensitive species ( Pinus strobus) was susceptible to salt

damage up to 1000m away from the freeway. The area closest to the roadside is

the most susceptible to high amounts o f salt and the salt levels decrease as distance

to the road increases. Thus plants that have been shown here to be highly sensitive

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to roadside deicing salts should be planted as far away from the roadside as

conditions will allow. Those plants that are more tolerant can be planted closer to

the edge of the road. Only those species that are the most tolerant should be

planted at the edge of the road, sidewalk, parking lo t etc. More screenings should

be done to generate a longer list of plants that are tolerant to the highest levels of

deicing chemicals.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 2

GROWTH AND SURVIVAL OF HERBACEOUS PERENNIALS (Armeria maritima, Leucanthemum xsuperbum ‘Becky’, and Monarda didyma ‘Blaustrumpf) TO WINTER APPLICATIONS OF NACL AND ITS EFFECT O N SOIL PHYSICAL PROPERTIES IN A CROSBY CLAY-LOAM

INTRODUCTION

There is a dearth of information on the sensitivity of herbaceous ornamental

plants to high levels o f sodium chloride that may remain in the soil after application of

deicing sodium chloride in northern climates. There are studies o f field soils and the

effects of deicing chemicals on roadside weed populations and ecology (Cusick, 1982,

Jones, 1998). Enumerable studies exist on the salinization of cropland due to irrigation

and/or limited rainfall (Ungar, 1991, Staples, 1983). Crops are expected to produce

food at a certain level, thus anything that changes the output of these plants is

intensively studied. The ecology of roadside weeds may change due to the addition of

sodium chloride, which may be a cause for environmental concern; however, the

performance of either of these groups of plants is generally not a major concern to

ornamental horticulturalists.

A preliminary greenhouse screening o f 38 species and cultivars fo r salt

sensitivity (chapter I), identified plants that were tolerant or susceptible to soil applied

sodium chloride. Therefore, three different experiments were conducted to study the 122

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. effects o f w inter applications o f sodium chloride on selected soil physical properties as

well as on three species o f herbaceous perennials. From the results of experiments

mentioned in chapter I, three species were selected based upon their final salt

tolerance ratings, highly tolerant, moderately tolerant and highly sensitive, for a study.

Although greenhouse studies are convenient and allow the researcher to control many

variables, they may not accurately correspond to field conditions. Greenhouse studies

are generally carried out with actively growing plants; deicing chemicals are typically

applied when plants are dormant. Most herbaceous perennials die to the soil level in

the foil, leaving few to no shoots above ground. Therefore, it was important to

compare the results obtained in the greenhouse with those obtained in a field soil with

dormant plants.

Soil-less media are predominantly peat moss, to which sodium binds quite

tightly. In addition, peat moss slows down surface evaporation, which allows more

time for salts to leach more thoroughly (Brady, 1990). Therefore the use of soil-less

media may not reflect field conditions and plants may indeed perform very differently

when grown in clay than in potting media.

Deicing chemicals can have a deleterious impact on soil physical properties. In

1998 the US Geologic Survey published the results of a three-year study on the effects

o f deicing chemicals on groundwater (jones, 1998). The researchers also measured

ion content in the soil. The results show that it can take up to 3 years to leach from

the soil the deicing chemicals from a single season’s application. Because deicing

chemicals are applied every year, this means the overall trend would be to build up

123

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. levels of salt in the soil. Despite the dormant nature o f roadside plants during the

winter, these chemicals may have a detrimental effect on plant growth.

Salts accumulate in soils in many areas around the world. In arid regions salts

accumulate because of lack of sufficient rainfall to leach them from the soil. In other

areas, salts accumulate from irrigation water, and again there is insufficient rainfall or

irrigation to leach these salts from the soil (Brady, 1990). Most plants cannot tolerate

this buildup of salts in the soil and this has made a certain percentage of otherwise

arable cropland unsuitable for agriculture. Several other physical changes occur in salt

laden soils. Highly saline soils are poorly drained and often develop hardpans. Excess

salts can also cause exosmosis from plants as w ater moves from the plants to the soil

system (Kim, 1988)

The movement of cars during w inter is one way deicing salt moves into soil

alongside the freeway. The rate of travel gready impacts the distance salt solution will

travel; the faster vehicles are traveling, the further away from the roadside salt is found

(D’ltri, 1992). Pinus strobus showed damage in the Morton Arboretum up to 1400m

from the freeway during a particularly harsh winter (Hootman and Kelsey, 1992). The

highest levels of sodium chloride along roadways were in the I m closest to the road

and amounts decreased as distance from the road increased, with minimal levels

occurring approximately 3m from the roadside (Allison and Sroka, 1997). However,

the researchers also acknowledged the levels w ere highly variable, depending upon

many factors, including average traffic speed, the amount o f sodium chloride applied

during the winter, soil type and even slope. Other researchers have also confirmed

124

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. that damage to plants decreased as distance from the road increased, but highly

sensitive plants continued to show damage at distances up to 1400m, as was shown by

the study previously mentioned from Morton Arboretum (Hofstra and Lumis, 1978).

W ith this in mind, three studies w ere designed. The first would involve

sampling soil from various roadsides and analyzing these soils for N a* content,

electrical conductivity of the soil solution and pH. This would determine if there were

effects o f deicing chemicals to Central Ohio's roadways. The second was a field study

involving w inter NaCI applications o f salt to dormant plants growing in soil, which

would confirm or deny the results of the greenhouse study in terms of the tolerance

ratings determined for herbaceous ornamental plants. This third study looked at the

effects o f this NaCI application on soil physical properties of the field soil, which would

determine if there was an effect of sodium chloride application to a soil where no

deicing chemicals had ever been applied. The field soil studies could then also be

compared to the freeway soils to determ ine if deleterious effects of deicing chemicals

are occurring along Central Ohio’s freeways.

There were four objectives. The first was to determine the amount of salt

remaining in the soil in several roadside situations. The second was to study the

changes in soil physical properties after one w inter of salt application and compare the

results to the freeway soils that have had sodium chloride applied for many

consecutive seasons. The third objective was to determine how dormant applications

of salt affect herbaceous perennials. The final objective was to compare these field

125

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. studies with the greenhouse studies to determine if the greenhouse studies accurately

predicted dormant plant survival.

MATERIALS AND METHODS

Roadside observations. Nine soil samples w ere collected from three different sites in

the Columbus area. The speed limit was different at each site. The first site was along

1-71, a north and south major freeway with a speed lim it o f 65mph. The second site

was along SR 16 1 (East Dublin Granville Rd.), which runs east and west at the north

end of town. The speed limit in this sampling area is 35mph. The final site was on The

Ohio State University campus, directly behind the horticulture building along John

Herrick Dr. This is an infrequently traveled road where the speed limit is 25mph.

Several species of plants, including several species o f Graminaceae, Plantaginaceae and

Asteraceae were noted at each site, although many were obviously dormant. Nine

different samples were taken at each site. Samples w ere collected at 0.25m, I m and

3m from the edge of the road. There were approximately 1.5m of horizontal distance

between each sample. Thus at each site approximately 4.5m of distance along the road

was sampled (Figure 25). Samples were collected during April of the 1996 winter

season. Each sample was analyzed for Na+ content, electrical conductivity and pH per

methods described below. There was not enough of each sample to conduct bulk

density and soil texture analysis.

126

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.5m

3.0m Q 1.5m

1.0m

0.25m roadway

Figure 25. Sampling locations fo r soil samples taking along various roadways in Central Ohio. The circles represent the location of the soil sample taken. No direction is implied as tw o samples w ere taken from N/S roadways, and one from an E/W roadway. The distribution o f samples was the same from each location.

Soil Field Experiments. For the field experiments, three species of herbaceous

perennials were planted into the field plots at the Waterman Farms research plots at

The Ohio State University in Columbus, OH. The plot size was 4.5m x 6.1 m, and its

layout was as described below (Field Plant Experiments). Starting January I, 2000,

4.5kg of a mix of # l and FC rock salt was applied with a rotary spreader every week

fo r 10 weeks. Soil samples w ere taken at planting time, again at 3 weeks and 7 weeks,

and a final series o f samples was collected in April, approximately 2 weeks after the

last salt application. During each sampling session, there w ere a total of 6 samples

127

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. taken from each type o f plot, control, high salt and mid-level salt. Once the samples

were collected they were wrapped in plastic wrap to prevent further crumbling until

they could be weighed again. A fter weighing all samples, they w ere dried fo r 48 hours

at IOO°C. Once dry, all samples w ere weighed again and bulk density and other

physical properties could be measured (all equations are included in Appendix B).

After bulk density was measured, 50g samples were taken and ground with

m ortar and pestle fo r texture analysis. Each sample was mixed with 400ml o f double

distilled water and had 40ml of hexametaphosphate added. Samples were then put on

a milkshake mixer and mixed for 10 minutes. Each sample was then poured into a

I OOOml-graduated cylinder and double distilled w ater was added to bring the level to

1000ml. They were then stirred for several seconds and a soil hydrometer (Figure 26)

was slowly lowered into the mix. After 45 seconds a first reading was taken. The

samples then stood for I hr and 45min and a second reading was taken with the

hydrometer. This allowed soil texture to be calculated.

128

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Read level •Thermometer here A — I Hydrometer

g—Soil Suspension Sediment"

Figure 26. Apparatus for determining particle size distribution by the hydrometer method (adapted from Bingham, 1999)

Approximately 500g o f each sample were taken for further analysis. Soil

salinity was measured by the following procedure as recommended in the manual

Recommended Chemical Soil Test Procedures for the North Central Region (Walsh

and Dahnke eds. 1988). The saturated paste method was utilized, as it is the

recommended method for assessing soil salinity in relation to plant growth, and there

is no adjustment needed for soil texture. Distilled water was added to each sample

while stirring. The amount of water added varies with the sample, but the paste will

glisten and flow slowly when the container is tipped. Samples were allowed to stand

for I hour. Any samples with standing w ater at the top had more soil added, and

samples that had stiffened had more w ater added. Each sample was then vacuum

filtered and the extract was tested with EC meters (Hach Company, Loveland CO).

Ion measurements w ere also performed on the samples prepared in the same manner 129

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. as above. To measure pH, 5g samples had 5ml o f distilled w ater added and stirred

vigorously for 5 minutes. After standing for 10 minutes the pH was read utilizing a pH

electrode (Hach Company, Loveland CO).

Sodium analysis was done according to the procedures in Recommended

Chemical Soil Test Procedures (1988). Four Ig samples w ere taken from each of the

18 samples and mixed with 10ml of IM calcium chloride in a 50ml Erlenmeyer flask.

The flasks were mechanically stirred for 5 minutes. Ten ml of deionized water was

added and the ion probe was placed into the solution and allowed to stabilize, for 10-

15 minutes per sample.

Plant Field Experiments. The three species chosen for field studies represent the range

of salt tolerance found in the greenhouse screening experiments (chapterI). Armeria

maritima was selected as the only plant to rate highly tolerant. Leucanthemum

xsuperbum ‘Becky’ was selected due to its moderately tolerant rating and Monarda

didyma ‘Blaustrumpf was selected due to its being highly sensitive to soil applied

sodium chloride. Twenty-four plants in one-liter containers were purchased from

Millcreek Gardens and planted on August 2, 1999. The location is described above. A

diagram of the experimental layout is shown in Figure 27 and a photograph of the

experiment is shown in Figure 28.

130

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.45n i

0.15m

9m 6.1m

4.5m

Edge effect plants surround entire setup Three plants o f each species randomly planted in each ro w for a total of 6 replications per block

Figure 27. Experimental layout of the field plots for testing dormant applications of sodium chloride on three species of herbaceous perennials differing in salt tolerance.

131

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure. 28. Photograph of field trials one week after planting. The two rock piles were placed to delineate the center aisle. Salt was applied with a rotary spreader from the center isle. The arrows point to the two rows o f plants in line with the rocks and these rows were the high salt rows.

132

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A high rate of application to a I -lane, 1.6km section o f road is 272kg NaCI

(Field and O ’Shea, 1970). Based on this level of application, this 4.5m by 6 .1 m would

receive 1.04kg NaCI during a moderate to severe winter. To ensure a salt level high

enough for plants to show damage, this was doubled. During a severe winter, trucks

may be applying salt as many as 4-5 times per week. Thus our experiment simulated a

severe winter.

Salt was applied with a rotary spreader fo r 10 weeks w ith the last application

being made in mid-March. N o further applications were made after this date. Practice

runs with the spreader showed it had a maximum spread of 0.9m per side. A t this

distance, the amount of rock salt being spread was visually low er than at 0.3m and

0.5m. Spacing for the rows was based upon these trials with the spreader (Figure 27).

The first row to either side of the center aisle received the most amount of salt, the

second row to either side received a minimum amount of salt and the last row on

either side were control rows and received no salt.

Tests with the spreader showed that approximately 2/3’s of the salt was

applied at 0.3 — 0.5 and approximately 1/3 was applied between 1.2 and 1.8m. This

translates to approximately 0.93kg applied to each of the high salt rows and

approximately 0.47kg applied to each o f the low salt rows. Applications of sodium

chloride were made to the field by pushing a rotary spreader through the middle of

the plot until the required amount of rock salt was applied. Generally, this required

four back and forth trips. Tw o large piles of rocks were placed on either side of the

center isle to denote this walkway during the winter months. When snow was deeper

133

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. than 6”, the center isle was cleared with a show shovel prior to application to ensure

proper functioning of the spreader and for ease of application. No snow was removed

from the plots themselves.

RESULTS

Roadside Observations. The pH of these soils remained relatively constant from site to

site and from sample to sample. Electrical conductivity showed that these soils are

slighdy to moderately saline close to the roadside and slightly to non-saline at the

greater distances. Sodium content fo r these samples is also consistent w ith a slighdy

to moderately saline soil for those samples taken close to the edge of the road and

with a non-saline soil fo r those samples taken at 3m from the road. For these soils,

there is some effect from the addition of sodium chloride as a deicing chemical.

Figures 29 and 30 show these results.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9

l-71a 1-71 b 1-71 c 161a 161b 161c JHa JHb JHc Sample location

SpH DEC

Figure 29. Results of pH and EC analysis done on samples taken from three locations in the Columbus area. Error bars indicate significant differences across that particular parameter only. JH indicates samples from John Herrick D r., I6 I indicates samples taken from SR I6 I and I-7 I indicates samples taken from I- 7 I. The letters following the street indicator is the distance from the edge of the road in meters thus a = 0.25M, b = I m and c = 3m from the road.

135

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 300

E 250

E 200

1-71 a 1-71 b 1-71 c 161a 161 b 161 c JHa JHb JHc Sample location

Figure 30. Measurements of sodium content from soil samples taken in three different sites in the Columbus area during the 1996 winter. JH indicates samples from John Herrick D r., I6 I indicates samples taken from SR I6 I and I-7 I indicates samples taken from I-71. The letters following the street indicator is the distance from the edge of the road in meters thus a = 0.25m, b = 1.0m and c = 3.0m from the edge o f the road.

136

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Soil Field Experiments. Bulk density show some changes with added rock salt; however,

the changes were not statistically significant and could have been due to random

sampling. The bulk density was slighdy lower in the control plots than in either the

mid-level o r high salt level plots. The bulk density did not change between the high

salt and the mid-level salt plots. Since sodium has a tendency to break up soil

aggregates into smaller particles there is a trend toward less pore space in a heavily

saline soil. However, the amount o f salt applied to this field over one w in ter season

was not enough to affect bulk density to a significant degree (Figure 3 1).

1.7 1.65 1.6 1.55 1.5 Bulk Density . (g/cm3) 145 1.4 1.35 1.3 1.25 1.2 high mid-level control NaCI Level

Figure 3 1. Bulk density of a Crosby soil after one season of winter rock salt application applied with a rotary spreader.

137

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Each soil sample also had textural analysis done. According to the Franklin

Country Soil Survey (1975), the textural classification for Central Ohio is generally

day-loam. The samples taken at the beginning of the experiment were mostly

classified as loam, which is slighdy different from the County Soil Survey. Th ere was

no noticeable change in texture until the conclusion of the experiment, when several

samples w ere classified as day-loam. The average classification over all samples

remained loam (Figure 32). However, there was a general pattern seen. The higher

salt levels were more likely to be categorized as day-loam, whereas the samples taken

from the control plot had a higher percentage of loam (Table 14). The mid-level plots

w ere a m ixture o f both. Although the results are not statistically significant, they do

indicate a trend that could continue given yearly applications of rock salt to this field.

This is supported by the US Geological Survey ( 1998) study showing a gradual buildup

o f sodium chloride along roadsides in 4 O h io locations. Cusick (1984) also showed a

gradual increase in soil salinity along Ohio roadsides accompanied by a change in flora

associated with increased salinity. These soil changes, although not significant after

one year, could cause significant changes in naturalized plant populations as well as

changes in planted landscape plant performance as the soil changes over several years.

138

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. % silt 37%

Figure 32. Soil texture averaged over all samples taken from a field plot after one season o f w inter application o f rock salt with a rotary spreader. Textural classification based upon these percentages is loam.

139

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. H -R -l 26.4 36 37.6 Clay loam H-R-2 24.4 36 39.6 Clay loam H-R-3 24.4 38 37.6 Loam H -L -l 28.4 36 35.6 Clay loam H-L-2 30.4 34 35.6 Clay loam H-L-3 22.4 36 41.6 Loam M -L-l 26.4 34 39.6 Clay loam M-L-2 22.4 38 39.6 Loam M-L-3 30.4 34 35.6 Clay loam M -R -l 25.1 38 36.9 Clay loam M-R-2 23.1 38 38.9 Loam M-R-3 23.8 41.3 34.9 Loam C-R-3 26.4 38 35.6 Loam C-R-2 26.4 36 37.6 Clay loam C -R -l 24.4 38 37.6 Loam C -L -l 22.4 38 39.6 Loam C-L-2 24.4 40 37.6 Loam C-L-3 24.4 40 37.6 Loam

Table 14. Classification of 18 soil cores taken after I winter of applying rock salt with a rotary spreader. H-R indicates the sample was taken from the High Level plot on the right side. H-L was taken from the High Level plot on the left side. M-L and M-R are Mid Level left and right and C -L and C-R and control left and right.

Two of the three other parameters tested showed significant changes due to

the addition o f sodium chloride. Electrical conductivity fo r the control plots averaged

0.99mmhos/cm, which is typical for soils where salinity is not a problem (Brady, 1990).

As sodium chloride levels increased, so did EC. The change was most dramatic for the

high salt section of the plot, where the EC averaged 4.03mmhos/cm. This would

indicate only a moderately saline soil, however, this increase is just over 400% from

the control plots (Figure 33).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. High NaCI Mid NaCI Control NaCI level received during treatment

Figure 33. Average electrical conductivity of a Crosby soil after one season of winter NaCI application (mmhos/cm)

Native Ohio soils have very little natural sodium present (Eckert, 1998,

personal communication). As sodium levels increased, so did EC. The amount of

sodium in the soil was considerably higher after application than before. It was also

considerably higher than the control plots. Thus the assumption can be made that the

change in EC was mostly due to applied rock salt (Figure 34).

141

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. High NaCI Mid NaCI Control Treatment level

Figure 34. Average sodium content of a Crosby soil after one season of NaCI application (mg/g)

The only parameter not greatly affected after one season of rock salt

application was soil pH. There was a general trend toward an increasing pH, but this is

a trend only; the changes seen were not enough to be due to the added sodium

chloride, and could have been due to random sampling. It would be interesting to

continue to apply sodium to these soils for two to three subsequent seasons and

determine if there w ere any significant changes. The trend toward increasing pH

coupled with the dramatic changes in Na* content and EC would indicate potential fo r

this particular soil becoming sodic and perhaps no longer arable (Figure 35). The pH

o f this soil would need to rise into approximately 8.5 and above for this to happen, this

142

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. dramatic change in pH is unlikely. The pH o f a given soil can be very difficult to modify

permanently (Brady, 1990), and even many season’s application did not change the pH

significantly in samples taken from several roadside locations as reported above.

8.2 8 7.8 7.6 5 . 7.4 7.2 7 6.8 6.6 High NaCI Mid NaCI Control NaCI level received during treatment

Figure 35. Average pH of a Crosby soil after one season of winter NaCI applications.

Plant Field Experiments. All control plants survived the winter. This would indicate they

had sufficient moisture and time to grow a healthy root system. This would also give

credence to the theory that plants in the salt blocks that did not survive were killed

from the application of rock salt, and not from other environmental factors. All

control plants appeared visually healthy and growth was as expected for the tim e of

year and the species. Several specimens o f Armeria were flowering, which is normal

fo r this plant during early spring (Figures 36, 37 and 38).

143

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figures 36, 37, and 38. Control plants from field trials. Note overall health, size and color o f all plants.

The only plant to survive the high salt application level was Armeria maritima

‘Splendens’. This plant is a highly salt tolerant halophyte native to coastal regions of

Scotland (Heywood, 1993). Neither of the other two species treated with the highest

salt application emerged in spring. This would indicate that dormant applications of

rock salt (sodium chloride) can be highly detrimental to plant survival and performance

in the landscape (Figures 39, 40, and 41).

144

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figures 39, 40, and 4 1. Field photos of high salt level Leucanthemum xsuperbum ‘Becky’, Armeria maritima ‘Splendens’, and Monarda didyma ‘Blue Stocking’. These plants were planted 0.45m away from the center aisle and received the highest levels o f rock salt.

All replications of Armeria in the mid-level salt treatm ent survived and were

flowering at the proper time. Visually, there was little difference between the control

plants and the plants that received the mid-level of NaCI. The plants visually seemed

to have fewer flowers, but no official flower count was conducted. This difference

could have been due to species variation. Among the Leucanthemum there were

several differences. Visually the plants were not a healthy deep green but had several

yellow leaves, and often weren’t as tall o r as wide as the control plants. Leaves 145

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. appeared smaller, although no formal leaf size analysis was performed. Several plants

failed to emerge from the ground by mid-April, which is a time when all three of these

species should be actively growing. Most specimens did emerge; however, they w ere

not visually as healthy in appearance as the control plants. All but tw o Monarda w ere

killed. The two surviving specimens that had a total o f 6 shoots. Among these 6

shoots, the leaves w ere small compared to the control plants, although their color

appeared normal. One month after salt applications had stopped, theseMonarda w ere

still small and had not grown as tall as control plants (Figures 42,43, and 44).

Figures 42, 43, and 44. Plants from the mid-salt level field trials. Notice thatArmeria is flowering and appears healthy and robust. Leucanthemum is healthy overall, but there are signs o f damage: yellow leaves, smaller leaves, overall less green in color compared with control plants. One of the two Monarda that did have shoots emerge from the ground. Note the overall lack of vigor and the small leaves. 146

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Measurements of height corroborated visual results. The control plants of all

three species were visually healthy in appearance during the month after treatments

stopped. Although visually there was litde difference between the control Armeria and

the other two treatments, there was a small difference in height. This difference was

not statistically significant however. Armeria is not a plant that changes dramatically in

height during the course o f a growing season (Still, 1994).

For the other two species, there was a dramatic decrease in plant height even

between control and mid-level salt concentrations. The height reduction was

significant for both species (Figure 46). Measurements w ere taken fo r five consecutive

weeks, although only the beginning and ending measurements are shown fo r ail

species. Monarda and Leucanthemum are tw o species whose height would vary

significantly as the growing season progressed. The height increase fo r Monarda was

approximately 16cm during the month of April. During the same time frame the

increase for Leucanthemum was approximately 4cm. These changes are normal for

these species. There was no tissue to measure for salt treatedMonarda as none

emerged from the ground. Leucanthemum plants receiving the high salt level grew only

0.5cm during the same month the control plants grew 4cm, which is an 87% decrease

in growth rate. The mid-salt level Leucanthemum grew approximately 2.5cm during

this same time frame. Although this particular number doesn’t appear to be a large

change, it is significant. The mid-salt level Leucanthemum had approximately 62% less

growth than the control plants did. It must also be remembered that many

Leucanthemum did not emerge from the ground at all.

147

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25

I 15 19

o 10

/ ✓ V V^ / / V ^ N? y > ^ Species and NaCI Concentration

□ 1 -Apr □ 3-May

Figure 45. Height measurements for three species of perennials after 10 weeks of NaCI application. A = Armeria maritima ‘Splendens’, M = Monarda didyma ‘Blaustrumpf, L = Leucanthemum xsuperbum ‘Becky’, (c) = control, (m) = mid- level NaCI, and (h) - high level NaCI applied. Dates are when the beginning and ending dates when measurements were taken.

148

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dry weights for the three species were also consistent with visual and height

data. Armeria had very little difference in visual appearance between high salt

treatment and the control; however, the drop in dry weight was significant. For the

other two species dry weight dropped dramatically, and fo r the high salt level Monarda

was O.OOg as all plants were dead (Figure 46).

pfcl I * a t il

v!vX I ! II mu — Armeria Leucanthemum Monarda □ control 12.5 8.6 8.4 □ mid-level 11.7 5.2 0.32 II high-level 9 .8 0 .6 9 NaCI level

Figure 46. Average dry weights of three species of perennials after 10 weeks of dormant season NaCI application. Error bars show significant differences at the 0.01 level. Differences shown are significant for each individual species only and not between species.

149

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DISCUSSION

Although EC levels are consistent with low to moderately saline soils, sodium is

not the only ion responsible for the results. There are many salts present in the soil

and the city o f Columbus does not exclusively utilize sodium chloride fo r deicing

roadsides. There are many ions that would contribute to these numbers. The

measurements of pH and Na* content provide a far better measure of the viability of

these soils. If the pH o f these soils was found to be 9.0 and above, a problem with

sodic soils might be indicated and the soils would not be conducive to plant growth.

However, the diversity of plant life along the streets of Columbus proves these soils

are capable of sustaining plant growth. The pH for these samples are well within what

is considered normal for this area of the state. The rainfall in the state is generally high

enough to ensure leaching of detrimental ions, which would account for the pH

remaining stable despite the sodium content o f these soils being relatively high fo r this

area.

One surprising result from this experiment was the amount of sodium present

in the SR 161 site at 3m from the edge of the road. It was expected that the 1-71 site,

with its faster speeds would prove to have the highest amounts o f sodium the furthest

from the road. The speed of traffic along SR 161 is 35 mph along the area sampled;

yet the amount of sodium present in the soil was considerably higher further from the

road. There are several factors that might account fo r this however. One possible

answer is that traffic is not traveling the speed limit and once a certain threshold is

reached the distance salt solution travels remains relatively constant. It is also possible

150

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. this area of road, which is very heavily traveled, received more salt than the section of

freeway sampled. There is also a sidewalk along the SR 161 site and this might also

have received deicing chemicals, which might also account for more salt further away

from the road. The stop and go nature of traffic along this stretch of road might also

account for unexpected results. There are no studies showing how city traffic

patterns affects the pattern of salt solution distribution at any distance from the road.

Less plausible, but not impossible is the possibility of a salt truck, stopped in traffic, not

halting the spinning o f the spreader, thus more salt was applied to this particular

section of road.

It is also interesting to note the amount of salt in all three areas was very

similar at short distances from the edge of the road. The amount of salt at 0.25m

from the road was remarkably similar for both the freeway and the city section of

street. The less traveled John H errick D r. had significantly less sodium content in the

soil, and these numbers were even more gready decreased at Im and 3m from the

road. Again, there are several factors that could account for these results. John

Herrick is on The Ohio State University campus and the campus is responsible for the

clearing of snow and ice. It is possible there was less salt applied on this stretch of

road. It is also possible that due to its being less traveled, there simply wasn’t enough

traffic to cause the salt solution to disperse into the soil. The similarities between the

other tw o sites could be due to reasons discussed above.

Although the change in pH may be unlikely due to the application o f rock salt,

the soil did change from non-saline to moderately saline after one season. A saline soil

151

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is easier to w ork with than a sodic soil. W h ile a highly saline soil is unproductive,

there are measures that can be taken to reduce salinity levels. Leaching is the best

solution and it would seem that with the rainfall received during the average spring in

Central Ohio (approximately 180mm) (www.worlddimate.org) the amount of leaching

naturally occurring is enough to maintain low levels of salinity. As long as the pH

remains relatively low, natural rainfall should be enough to maintain viable soils.

The major problem will come when there is not sufficient rainfall to leach these

detrimental ions from the soil. Generally, soils in Central Ohio have large enough

quantities o f calcium and magnesium (Franklin County Soil Survey, 1975) to counteract

the small amounts o f sodium added due to deicing chemicals (Brady, 1990). However,

as sodium levels continue to rise, the sodium can displace both calcium and magnesium

on the cation exchange. This subtle change brings about far-reaching changes in soil

physical properties. As sodium levels begin to rise, there is a corresponding increase

in pH. Generally, the pH must increase to above 8.5 for deleterious effects to occur

to a great degree. Table 14 shows the general properties for several soil types. At

this point, there is no cause for alarm. Further, long term studies need to be

conducted to determine the long-term effects of rock salt on Central Ohio soils.

Measurements of Sodium Absorption Ratio SAR, as well as Exchangable Sodium

Percentage (ESP) need to be done.

152

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Normal 6.S-7.2 <4 <13-15 Acidic <6.5 <4 <13-15 Saline <8.5 >4 <13-15 Saline-sodic <8.5 >4 >13-15 Sodic >8.5 <4 >13-15

Table 14. Properties o f Normal Soils compared to Acid, Saline, Sodic and Saline-sodic soils. (Brady, 1990).

The decreases in height and dry weight o f Armeria maritima ‘Splendens’

indicates that although this plant is adapted to growing in saline conditions, the

presence of NaCI impacts the plant’s growth. Previous work with Armeria shows

decreased photosynthesis under highly saline conditions (Ungar, 1991). The plant is

tolerant to these types of growing conditions, but grows better on non-saline soils.

This adaptive mechanism may have evolved as a means to allowArmeria to survive.

Fewer plants can survive highly saline growing conditions; thus, competition from

other species would be limited. The high salt tolerance of Armeria may simply be a

response to competition from other species. Competition studies with Armeria and

inland species of glycophytes could prove interesting.

The results of this study indicate that greenhouse studies were effective at

predicting field salt tolerance for these three species. Greenhouse experiments

indicated Armeria maritima ‘Splendens’ was highly salt tolerant, Leucanthemum

xsuperbum ‘Becky’ was moderately salt tolerant and Monarda didyma ‘Blaustrumpf

153

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (Blue Stocking) was highly intolerant to soil applied sodium chloride. Although there is

no research with Monarda nor with Leucanthemum, this supports previous research

with Armeria (Ungar, 1991).

The results of this study also indicate that high levels of sodium chloride can

have a deleterious effect on dormant perennials. It is also interesting to note that

weed growth was also significandy impacted during this experiment (Figure. 47), and

that weeds were only present in the control rows. No measurement of numbers or

species of weeds was recorded, but it is obvious from the photograph that weed

numbers were visually, dramatically reduced after one season of salt application.

For people who make decisions about roadside plantings, this information is

important. Knowing which species are likely to survive salt applications or salt

solution runoff in the winter may mean the difference between plantings that look

good during the growing season, especially in the early spring and those that need to

be replaced. It also confirms the results of the previous greenhouse studies, which

indicated the salt tolerance of the three selected herbaceous perennials.

154

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 47. Photograph of field trials. Note weed growth is almost absent in the middle of the plot, near where the plants received the most salt. Weeds were also suppressed in the area with mid-level salt, but not to the same degree, and weeds were not suppressed at all in the control areas.

155

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 3

OSMOTIC RELATIONS AND NA*. CL', K* AND CA2+ UPTAKE IN THREE SPECIES OF SALT STRESSED PERENNIALS (Armeria maritima MILL ‘SPLENDENS1, Leucanthemum xsuperbum INGRAM ‘BECKY* AND Monarda didyma L ‘Blaustrumpf)

INTRODUCTION

As our use o f perennials increases, so should our knowledge. Nutrient

interactions within ornamental plants are one area of research that has not received

much attention; and nutrient interactions within stressed plants have received even

less. N utrient interaction includes the use o f deicing chemicals, the most common of

which is still sodium chloride.

In order to better utilize plants in the landscape it is important to understand

the underlying mechanisms responsible fo r plant growth. W ith that in mind, this

research focused on ionic as well as osmotic effects of plants grown under salt (NaCI)

stress. Sodium chloride ionizes to Na+ and C l' in water. Uptake o f the Na* ion often

interferes with the uptake of several other plant nutrients, including K*. Mg2*, and Ca2+

(Headley, 1990). The number of leaves or rosettes produced during the experiment,

and plant heights w ere also investigated as measurements of overall plant health.

Plants that produce new growth and are able to grow taller are generally considered

to be relatively healthy plants. Thus, these two basic measurements were used to 156

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. compare the growth between control and salt stressed plants, and provided a basis for

comparison between unstressed plants and salt stressed plants.

The chloride ion is generally thought to be the more directly toxic of the two

ions (D irr, 1978), but it can interfere with uptake, N 0 3‘ and P 0 42 uptake. Changes in

nutrient interactions can dramatically impact plant health. Soils high in magnesium and

sodium sulfates are generally considered poor soils for good plant growth. Plants

grown on these soils show dramatically decreased levels o f calcium in their tissues

(Marschner, 1995). Phosphorous interacts with zinc such that plants receiving an

excess of phosphorous may also show dramatically decreased levels of zinc and even

display symptoms of zinc deficiency (Robson and Pitman, 1983). Brownell (1965)

showed that the sodium ion interfered with potassium uptake inAtriplex. Despite the

possibilities for deleterious interactions there are many species that are relatively

unaffected by some of these interactions, especially those involving sodium and

chloride ions (Davison, 1971 and Greenway, 1973).

Although some plants are more resistant to sodium and chloride induced

nutrient interactions, most are affected by changes in osmotic potential.

Osmoregulation is used to describe the ability of plants to regulate the number and/or

concentration of intracellular solutes. This process was noted as far back as 1936

(Hoagland and Broyer, 1936). In 1972, Mott and Steward determined there are

several solutes plants used for osmotic adjustment, depending upon nutrient availability

and other environmental pressures, including potassium, several sugars and chemicals

such as mannitol.

157

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Osmotic potential in plants is generally expressed in the form:

'i'w = + V,

*FW is water potential ‘Fp is turgor and is osmotic potential. The units are Mega Pascal’s or MPa. (-2.48 MPa = I osmol/kg)

Seawater is nearly -2.48 MPa, and a saturated sodium chloride solution is

approximately —39.5 MPa (Wyn-Jones and Gorham, 1983). In plant cells the

maintenance of turgor pressure is vital to the normal life cycle of the cell. Thus, water

relations plays a key role for plants and measurements of osmotic pressure become

important for stressed plants as this is a component of plant growth that is uniquely

sensitive to environmental changes.

The osmotic potential for many species o f plants is between -0.8 and - 1. 1 MPa

(Raven, 1980). Several researchers have shown that K+ makes a major contribution to

osmotic pressure (Cram, 1976, Wyn-Jones, 1979, and Raven, 1980). K+ flux is coupled

to net anion flux electrically. Thus, although the cell wall is highly permeable to IO, the

ion cannot leave the cell passively (Hastings and Gutknecht, 1978). Potassium isn’t the

only solute available for osmotic regulation. Many species have substantial sugar

accumulation in response to osmotic stress (Eaton and Ergle, 1948 and Barlow, 1976).

In the glycophytic species Helianthus annuus L, sugars as well as K+ and amino acids all

play a role in osmotic adjustment. If NaCI is available in the medium, it is taken up

preferentially over other solutes (Wyn-Jones and Gorham, 1983). Waisel (1972)

showed that a large proportion of halophytic species accumulate N a \ Cl', or both for

regulation of osmotic pressure, particularly in dicots. Monocots tend toward lower

158

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. amounts of these tw o ions and higher levels o f sugars in their tissues. It is interesting

to note that while many halophytes actively accumulate Na* and Cl', they generally also

have mechanisms for excretion of these two ions.

Our research studied two important components of salt tolerance: ion uptake

and osmotic potential. It also looked at plant symptomology including: height and

number o f leaves/rosettes as measures of overall plant health in an effort to better

understand the interactions that Na* and Cl' have within ornamental plants.

MATERIALS AND METHODS

A fter initially screening several perennial species for tolerance to sodium

chloride, three species were chosen for further study based upon their range salt

tolerance. Armeria maritima ‘Splendens’ was chosen for its high tolerance,

Leucanthemum xsuperbum ‘Becky’ for its moderate tolerance and Monarda didyma

‘Purple Mildew Resistant’ for its intolerance to soil applied sodium chloride. Field

studies with these three plans confirmed their greenhouse tolerance ratings (chapter

2).

These experiments were replicated 4 times over a 6-month period. To ensure

a reliable supply o fMonarda (which has a vernalization requirement) during the winter

months, the seed grown strain Purple Mildew Resistant was chosen. This strain is

similar to the previously utilized Monarda cultivar ‘Blaustrumpf in many respects. Both

grow to a height of approximately 3 feet; have light purple flowers in mid summer, and

are resistant to powdery mildew. The difference is ‘Blaustrumpf is a cutting-grown 159

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cultivar with a vernalization requirement and ‘Purple Mildew Resistant’ is seed grown

without a vernalization requirement (Hamemick, 1999). Selection of ‘Purple Mildew

Resistant’ allowed actively growing plants to be received from the nursery during the

winter months.

Plants arrived from Bluestone Perennials in 50 cell plug trays and were planted

into l-L containers. The growing medium was a Crosby clay loam mixed with peat

moss to the currently recommended rate for perennials: 30% by volume (DiSabato-

Aust, 1999). This would duplicate previously utilized field conditions as well as ‘typical’

homeowner conditions in Central O hio. Plants w ere then placed into a growth

chamber set at 21° C and 13-hour days. Both 6 0 W incandescent and F I0 -4 0 W cool

white fluorescent lights were utilized. Plants were given one week in the growth

chamber to acclimate prior to the beginning of treatments.

The experiment was arranged as a two-way factorial with 12 replicates of 3

species by 2 salt treatments (3 x 2 x 12 = 72 plants or experimental units) in a

completely randomized design. Each plant was given two treatments weekly of 125 ml

of either tap water with no salt added (tap water in Central Ohio has a natural NaCI

content of < 25mg/L (Columbus W ater Treatment Facility, 2001) or a 0.25N NaCI

added solution. Total NaCI loading over the 4 weeks of experimental treatment was

2l.7g NaCI applied per pot. Plants w ere also watered as required with tap w ater,

generally once per day. Measurements of height, width, leaf counts, Na*. Cl', K*, and

Ca2+ content as well as leaf osmotic potential were taken weekly during the course of

the experiments, which ran for 4 weeks. For Armeria maritima ‘Splendens’ rosettes,

160

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. rather than leaves, were counted. This is a plant that is comprised of a large quantity

o f small, grass-like leaves and counting o f individual leaves is complicated and

inaccurate at best. Leaves are organized into small rosettes, and each plant is

comprised of several rosettes (Figure 48). Samples were taken weekly to perform the

ionic and osmotic tests. Each time a sample was taken for analysis, the number of

leaves or rosettes removed was recorded. Thus at the end of the experiment the

total number of leaves/rosettes could be compared to the number present at the

beginning o f the experiment. In addition, visual ratings and notations of symptoms

present and when they first appeared were recorded. The experiment was repeated a

total of four times and results shown are compilations of the four experiments. Paired

t-test and A N O V A was performed using Jandel Scientifics’ Sigma Stat and graphs were

created using Microsoft Excel.

Ionic Analysis. Enough leaves to make 0 .15g-dried sample w ere removed from each

species each week to be analyzed for Na+, C l' 1C and Ca2+ content. Hach Company’s

(Loveland, C O ) ion sensitive electrodes w ere utilized to measure the various ion

contents of the leaves. Each sample was oven dried and ground with a m ortar and

pestle. Enough deionized water was added to make a paste, generally a few drops per

sample was sufficient Then 40ml o f one o f several different reagents was added,

depending upon the ion being measured. 10ml o f 0.5N K O H was added to raise the

pH of the sample (depending upon the ion being tested). The total procedure for each

ion is outline in Hach Co’s manual. The probes were calibrated prior to testing each

161

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sample as recommended in Hach’s manual. The probe was then left in the sample

approximately 15 minutes until the reading stabilized.

Figure 49 Armeria maritima ‘Splendens’ showing location of one newly forming rosette.

Osmotic Analysis. Leaf samples were taken each week and osmotic potentials were

recorded. Six samples were analyzed at one time. Samples were taken fresh from the

plant, and small disks were cut from Leucanthemum and Monarda with a sterilized hole

punch. For Armeria, a small section of leaf was cut, since the anatomy o f this plant 162

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. prevented disks from being taken. The disks w ere placed into a W escor

hygrometer/psychrometer (Wescor, Inc. Logan, UT). The disks were left for 3 hours

to allow sufficient time for thermal and vapor equilibration and then readings were

taken. The proportionality constant for this method is -0.47 pvolt/bar. Osmotic

potential is the reading from the psychrometer divided by the proportionality constant.

Corrections were also made if the temperature varied from 25° C. The equation for a

corrected reading is as follows:

CR = R/(0.325 + 0.027T) where T is temperature in Centigrade, CR is corrected reading and R is original reading in |xvolt/bar.

RESULTS

Plants treated with salt water did not grow as tall as control plants and had

fewer leaves, with the exception of Armeria maritima ‘Splendens’. Control plants

generally added several centimeters to th eir height and width while salt stressed plants

added no new growth after the first week (Figure 49). During the first week, several

new shoots were seen to be emerging, but these never fully expanded. By the end of

4 weeks of treatment, both Monarda and Leucanthemum actually had decreased in

height and width as leaves abscised (Figure 49). The changes in height were

statistically significant for Monarda and Leucanthemum, especially during the last two

weeks. Data for width measurements were unchanged over the four weeks.

163

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Armeria did not put on any new rosettes during the treatment period (data not

presented). During the first week of treatment, both Leucanthemum and Monarda

added foliage. A fter this time, new leaf production ceased and the remaining leaves

began to show signs o f stress. The foliage o fLeucanthemum generally remained on the

plant, while the foliage of Monarda typically abscised after becoming necrotic (Figures

50, and 51). At the end of 4 weeks of treatment, there were several specimens of

Leucanthemum with no remaining live tissue, although several individuals showed small

amounts o f green tissue. There w ere no remaining leaves on any specimen o f

Monarda.

Visual symptoms of salt stress corresponded to increasing salt levels except in

Armeria, which showed no visible symptoms. The salt treated Armeria w ere visually

similar to the control plants at the end o f 4 weeks. There was no visible necrosis, no

change in leaf color, and no noticeable change in plant height o r width. Plants flowered

normally.

Leucanthemum showed a wide range o f visual symptoms. Necrotic margins

appeared on the lower leaves after two weeks. From there, symptoms progressed

rapidly. Larger necrotic areas appeared, entire leaves turned brown, and the apical

meristem stopped growing. Stressed plants were a lighter green and the foliage lost its

glaucous sheen. Marginal necrosis occasionally developed after these symptoms in

some individuals, while others wilted and died without the appearance of necrotic

lesions. None o f the leaves abscised from any o f the plants. Control plants were a

deep green and foliage was glossy.

164

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Monarda responded still differently to salt stress. During the second week,

large areas o f marginal necrosis appeared. This was quickly followed by leaf death and

abscission. The apical meristem quickly became necrotic and new leaf production

ceased after the second week of salt application. By the end of the four weeks, there

w ere few to no leaves left on any salt treated plants (Figures 50, and 5 1).

Osmotic potentials of Armeria changed dramatically over the course of the 4

weeks, suggesting that Armeria, which is a known Na* accumulator (Ungar, 1991), is

using Na* to adjust its osmotic potential for continued w ater uptake under salt stress.

Osmotic potentials for the other tw o species did not change significantly during the

course of the experiments although osmotic potential was lowered somewhat by salt

application (Figure 53). It would appear that neither Leucanthemum nor Monarda was

able to adjust osmotic potential in response to salt application. Osmotic potential

remained relatively constant for both control plants and for salt stressed plants (Figure

53). Data for Monarda are compilations of 3 weeks of data since after that there was

not enough live tissue remaining to ensure an accurate reading.

Calcium uptake is also often decreased in the presence of the sodium ion

(Ungar, 1991), but calcium uptake was unaffected in Armeria over the course of this

experiment (Figure 53). Chloride content also remained relatively unchanged for

Armeria.

N either Leucanthemum nor Monarda had high levels of sodium in their leaf tissue.

Control plants o f Leucanthemum and Monarda also had high levels of potassium in their

leaf tissue, but salt stressed plants had significantly lower levels. Calcium levels

165

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. remained unaffected for both these species as well. Chloride measurements were

inconsistent for both Leucanthemum and Monarda, with some specimens showing very

high levels of C l- in the leaves and other specimens showing litde to no C l- in the

leaves (data not presented). D irr (1974) showed that Cl' was a highly toxic ion to salt

tolerant Gleditsia traicanthos var. inermis W illd. seedlings. Damage in this woody plant

was strongly correlated to levels of Cl' found in leaf tissue.

The progression o f symptoms in salt stressed plants varied in these three

species. In Monarda the first visual symptom was marginal necrosis. From the ionic

and osmotic data, it would appear that the tissues simply dried out. The plant rapidly

progressed from marginal necrosis through complete leaf death and finally leaf

abscission. The apical meristems produced no new growth after the first week of salt

application, although some new growth was seen during that first week (Figure 50).

Plant height dropped significantly vs. control plants, and by the end of four weeks there

w ere very few leaves left on the salt treated plants compared to the control plants.

Monarda didyma ‘Purple Mildew Resistant’ was reaffirmed to be highly sensitive to soil

applied salts and even small amounts can kill the plant.

In the moderately tolerant Leucanthemum, the situation would seem more

complicated, since some plants showed marginal necrosis and others never developed

necrotic areas and still others changed color then developed necrotic areas. There

would appear to be no specific cause and effect relationship between physiology and

visual symptoms at this point with this particular species. The overall trend is toward

increasing amounts of damage as salt is applied to the plants, up to and including death,

166

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. but the symptoms of such damage may vary from plant to plant. Leucanthemum

appears to be incapable o f osmotic regulation (Figure 52) o r to have the ability to

uptake K+ under saline conditions (Figure 54). As with Monarda, it is unknown at this

time if this is a toxic ionic effect on the roots, or an osmotic effect in the shoots due

to the growing media utilized. Further studies should be done to begin to isolate the

true cause o f the damage.

Armeria never developed any visually noticeable symptoms of stress, such as

necrotic lesions, marginal necrosis, wilting o r reduction in flowering. Although

previous work shows reduced photosynthesis and growth, in this experiment there

was no noticeable effect measured. Height and width remained constant and although

no new rosettes were produced over the four weeks, this does not mean that growth

was impaired as there may simply not have been enough time for new rosettes to be

produced. There may well have been new foliage initiated, however, this was not

observed during the course of this experiment since rosettes, and not leaves, were

counted.

167

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ,<>*■ & ✓ / & N?' v«y

□planting Qweek2 Bweek4

Figure. 49. Effects of no salt and 0.25N NaCI treatments on plant height of three species of herbaceous perennials over a four-week application period. The letter ‘c’ after species name indicates control plant; the letter ‘s’ indicates salt treatment plant.

168

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 120

• 100

80 a . 60

£ 20 - —

planting week 1 week 2 week 3 week 4 Time of Measurement □ Monarda c □Monarda s

Figure. 50. Number of fully expanded leaves o f Monarda didyma ‘Purple Mildew Resistant’ in no salt and 0.25N NaCI salt stressed plants over the course of four weeks of treatment, c = control plants, s = salt stressed plants.

169

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced at n 02N NC sl tesd lns vr h cus o orwes rament treatm f o weeks four of course the plants. stressed salt over = s plants, plants stressed control salt = c NaCI 0.25N and salt Figure 5 1. Number of fully expanded leaves o f f o leaves expanded fully of Number 1. 5 Figure

Number of Leaves 20 25 planting □ Leucanthemum c □Leucanthem um s um □Leucanthem c Leucanthemum □ week 1 week Time o f Measurement f o Time week 2 week 3 week 2 week 170 Leucanthemum xsuperbum week 4 week Bcy i no in ‘Becky’

-4 Species □beginning potential (0.25) Pending potential (0.25) □beginning potential (0.00)______Bending potential (0.00)

Figure 52. Osmotic potentials for three species of herbaceous perennials differing in salt tolerance after four weeks of treatment with either no salt (control) or with a 0.25N NaCI solution.

171

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60

a 50 a t E 40 c o 30 S c 8 20 c o o

r*n m s * r n rMU____ Control NaCI Na Control K NaCI K Control NaCI Ca Control NaCI Cl Na Ca Cl Ion Measured

□ Armeria maritima 'Splendens' O Leucanthemum xsuperbum 'Becky' □ Monarda didyma Purple Mldew Resistenf

Figure S3. Effect of four weeks of either water or 0.25 N NaCI solutions on the content Na*, Cl', K* and Ca2* ions in the leaves of three species of herbaceous perennials with varying salt tolerance.

DISCUSSION

Ionic content for Armeria corroborates previous work with the species (Ungar, 1991).

It accumulated Na* in large quantities in the foliage. Stressed plants also accumulated

K* at the same rate as the control plants suggesting a high affinity uptake mechanism

fo r K* in the presence o f Na* for this species. This is in addition to its other apparent 172

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mechanisms fo r tolerating salt, which include decreased photosynthesis and decreased

growth rate (Ungar, 1991). In 1982, Cooper showed that Armeria was able to

continue potassium uptake under saline conditions, and this study corroborated this

previous study. Many halophytic species have mechanisms for continued uptake of IC*

in the presence of large quantities of Na*(Ungar, 1991). Although these plants are

generally monocots, the phenomenon is not unknown in dicots, although it is

somewhat less common.

This work disputes other results showing that levels of Cl- in the shoot tissue

had a direct correlation to plant salt tolerant (D irr, 1979). For these species o f

herbaceous plants, some specimens showed greatly increased levels of Cl' and others

showed very little increase in tissue Cl'. Concentration of Cl* in the shoot tissue

appears to have no direct bearing on visual symptomology with these species o f plants.

However it is difficult to compare seedling woody species with herbaceous perennials.

The seedling stage o f plants, including haiophytes, is typically one of the most sensitive

stages to soil applied salts (Ungar, 199 1), woody plants also have a different anatomy

than herbaceous plants including secondary growth and slower life cycles. These

differences may account fo r the varied response between these species. O th er

researchers have also found C l' to be highly damaging to some woody plants. Headley

(1990) showed large quantities of Cl* were taken up into leaf tissue in 33 different

cultivars of Hedera helix L Even salt tolerant cuitivars acquired large quantities o f Cl* in

the leaf tissue, indicating some mechanism for regulating this amount of Cl* in tolerant

173

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cultivars, such as Cl* exclusion in the endodermis, or a Cl' ion pump, although this has

not been documented at this time (Headley, 1990).

Previous w ork with Armeria shows it to be a Na* accumulator that also has

reduced photosynthesis (Ungar, 1991) under salt stress. This work suggests that

Armeria also has a mechanism for continued uptake of K* in the presence of Na*. which

is often a source of problems for many species (Figure 53). Potassium uptake in many

species of glycophytes is often inhibited in the presence of sodium (Ungar, 1991).

Receptors for K+ uptake in the roots seem incapable of differentiating between K* and

Na* in many species (Ungar, 19 9 1). There are several species o f halophytes where this

process can potentially cause physiological problems due to limited availability o f IC;

however, these plants also have mechanisms for regulation o f excess Na* in their

tissues. Halophytic monocots in particular, have developed mechanisms for continued

K* uptake in the presence of sodium (Ungar, 1991).

Finally, it would also appear that Armeria is capable o f adjusting its osmotic

potential, in order to continue to uptake water in the presence of salt (Figure 54).

The large quantities of Na+ present in shoot tissue might indicate the plant is utilizing

Na+ in osmoregulation. This phenomenon is known to occur in several species of

halophytes including many members o f the Cheopodiaceae family and also in the family

Plantaginaceae, o f which Armeria is a member (Still, 1994). In studies w ith other

members of the Piantanginaceae, it was found that several species accumulated large

quantities o f Na*. but these w ere also very low in other organic substances within

their tissues (Albert and Kinzel, 1973). These plants may also incorporate other

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mechanisms to regulate excess salt in their tissues including succulence, salt glands

and/or abscission of tissues with excess salts. It would appear that Armeria maritima

has several mechanisms for adapting to situations o f elevated salt levels, including

reduced photosynthesis, the ability to sustain K* uptake in the presence of Na*, and

finally the ability to utilize Na* to regulate water relations within the plant.

The tw o sensitive plants showed dramatic changes both in morphology as well

as physiologically. This would further imply a need for closer look at other popular

species. In addition, w ork could be done with the sensitive species to determine if

amelioration techniques (such as amending the soil with gypsum) would allow these

species to be grown along roadsides and in other areas where large quantities of

deicing salts are utilized. Finally, work to specifically separate the toxic effects from

osmotic effects could be conducted. Plants could be grown in Turface™ or other

substrate in order to better study the effects of NaCI on root growth and physiology.

From this study, neither Leucanthemum nor Monarda appeared able to adjust

their osmotic potentials as soil salt levels increased (Figure 52). Since neither the

sodium nor the chloride ion was found in leaf tissue in significant quantities, it would

appear that problems with osmotic adjustment are what killed these species rather

than specific ion effects (Figure 54). The fact that both these species had reduced

potassium uptake would only exacerbate this situation since potassium is utilized for

opening and closing the guard cells. However, it is also possible that toxic effects were

seen in the roots. If the roots were severely damaged by excess salt, w ater uptake

would cease, causing drought symptoms in the foliage, which appear very similar to salt

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. damage: necrotic lesions, early leaf abscission, wilting and death o f the plant (Jaiwal, P

et al, 1997). The lack of osmotic adjustment could have been a secondary result of

toxic ion effects in ro o t tissue. In order to best simulate “typical” growing conditions,

plants w ere grown in soil rather than media. The heavy clay soil prevented any

analysis of root material and this is something that could be looked at in future studies.

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SOIL PHYSICAL PROPERTIES

W HAT IS SOIL?

Plants make life possible on earth, and yet they depend upon soil fo r life. The

process by which soil forms provides plants with physical support, water, air and

nutrients. Soils have distinct physical and chemical properties that distinguish them

from the parent material from which they are formed. Human life also revolves

around soil, from farming and agriculture, to roads and even waste disposal.

Historians believe civilization was possible because o f the fertile soil around the Nile

River Valley. This soil allowed for large-scale agriculture, which supported a growing

population. This gave people the opportunity to have the leisure time to develop

civilization. Organized communities thus replaced a more nomadic life style.

For centuries, people recognized the importance of soil and water for plant

health. Mesopotamian civilizations had irrigation systems in place as early as 3500 BC.

The Minoans (2500 BC), Romans and Phoenicians (1000 BC) all had roads, aqueducts,

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sewer and drainage systems, all dependent on soil properties; many of these structures

are still standing today. The Greek historian Xenophon first espoused the importance

of green manure, “But then whatever weeds are upon the ground, being turned into

the earth, enrich the soil as much as dung.” (C arter and Dale, 1974). Others also

knew the importance of adding manure to the soil. Cato and Columella both realized

the impact that legumes had on corn crop if planted in rotation. Litde else was

learned about the soil and its effects on plants until Justus von Leibig came up with the

Law of the Minimum. The Law o f the Minimum states that the growth of plants is

limited by the essential element present in the least relative amount. He also came up

with the first list o f essential plant nutrients. And in 1855, J. B. Lawes and J.H. Gilbert

drew the following conclusions from several experiments;

1. Crops require salts o f potassium and phosphorus, but the amounts of each found in the plant ash are invalid for estimating the relative amounts needed for normal growth. 2. Crops need a source of nitrogen in the soil, although leguminous crops can sometimes grow will without much nitrogen in the soil. 3. Artificial manures added to the soil can maintain soil fertility for many years. (Donahue, et al., 1977)

In the latter half o f the 19th century, Russian scientists began to study and

classify soils apart from how they affect plants. Since the 1940’s the knowledge o f soil

has grown exponentially. Soil is many things to many people. A farmer looks upon

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. soil as a habitat for plants. A homeowner might share this viewpoint. An engineer

looks upon soil as a substance that may need removing to prepare the area for

building. All are correct. Yet, this fails to answer the question of what is soil? “Soil is

a life-supporting layer o f material” (Plaster, 1985). A t its most basic, soil “is the

natural medium for the growth of land plants...it has a thickness determined by the

depth o f rooting plants” (Soil Survey Staff, 1975). Although engineers and farmers

think o f soil in different ways, it is all a complex biogeochemical material that has many

complex properties that allow humans to utilize it in so many different ways.

SOIL COMPONENTS

Although all soils are different, they share many common features. Soil is a

three-phase system consisting of soil air, soil solids and soil w ater (Figure 55). This

figure is only representative; an actual soil will contain varying amounts of the different

phases.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ORGANIC MATERIAL 5% Figure 55. The soil system, showing the three phases. Between the solid particles are pores that contain air and/or water. (Donahue, 1975)

The gaseous phase, also known as soil air, is the channel for movement of

oxygen and other gasses. It differs from the atmosphere in several respects. Its

composition can vary from place to place, due to the activity of microorganisms and

plant roots. Typically, soil air also has a higher moisture content, and the carbon

dioxide content often approaches several hundred times that of the atmosphere. The

composition o f the gaseous phase is closely tied to the liquid phase. After a rain, pore

spaces become filled with water, which then moves in response to gravity, evaporation

and transpiration. “W a te r is held in the soil pores w ith varying degrees of tenacity,

depending on the amount of water present and the size of the pores. Together with

its soluble constituents... soil water makes up the soil solution...” (Brady, 1990).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W ater can move downward in response to gravity, upward in response to evaporation

or in any direction toward plant roots. Plants will remove some of the water, but

when pore spaces are small, they are not able to remove all of the water. Even after

plants have died from lack of water, as much as 2/3s of the soil moisture may still

remain, depending upon the soil. The soil solution contains the essential plant

nutrients, as well as other chemicals and compounds. These elements, whether

essential o r not, all come from the solid phase.

The solid phase consists o f inorganic minerals and organic matter. The

inorganic minerals are small rock fragments, which are remnants of the underlying

parent material. Soils typically contain stones and small gravel pieces, reminiscent o f

the parent material, as well as sand, silt and clay. These terms, sand, silt and clay,

describe nothing more than the size of the particles in the soil. Sand particles are the

largest, 0.05 - 2mm in diameter, clay is the smallest, <0.002mm, and silt is in-between

the two, 0.002 - 0.05mm in diameter.

Sand is quite coarse, and does not stick together. Silt, although powdery when

dry, also does not stick together when wet. Clay will form a sticky mass when wet

and hard clods when dry. It binds together in aggregates. These aggregates, which

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. also typically have silt and sand bound to them as well, determine the properties of a

soil. The relative amount of each particle size determines the texture (Figure 56).

'v-C5 ♦ t l / V s \ V J • V \

Figure 56. Soil texture classification scheme illustrating the percentages o f sand, silt and clay in a given soil type. (Brady, 1990)

Organic matter is plant and animal m atter as microorganisms decompose it.

Although the ‘average’ soil contains approximately 3-5% organic m atter, this

component is very transitory. Environmental factors affect the ability and speed with

which microorganisms decompose the plant and animal matter, as well as the

availability of matter for decomposition. Organic matter binds minerals as well as

water in the soil. It greatly increases the amount of water a soil can hold, and is the

major source o f sulfur, phosphorus, and nitrogen in soil. In addition, it is the source of

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. energy for microorganisms in the soil, without which, biochemical activity would come

to a standstill. W hen the organic matter in a soil is sufficiently high enough, it can

significantly change the properties. To be classified as organic, a soil must have one of

the following occur

1. the mineral fraction has 50% o r more clay, and there is 30 % or more organic matter 2. the mineral fraction has no clay, and there is 20% or more organic matter 3. the clay percentage is between 0 and 50%, and the amount o f organic matter is proportionately between 20 and 30 % (Donahue, 1977)

SOIL PROFILE

Humans have recognized the organization o f soils into profiles, caused by

horizontal layering during soil formation processes, and visible only by vertically

sectioning the soil to reveal the subsurface layers. Each layer is termed a horizon, of

which there are five major categories: O, A, E, B, and C. A ‘typical’ horizon is shown

in Figure 57.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Oi Organic, slightly decomposed Oe Organic, moderately decomposed Oa Organic, highly decomposed A Mineral, mixed with humus, dark colored

^ Horizon of maximum eluviation of silicate clays, Fe, Ai oxides, etc. AB or EB Transition to B, more like A or E than B BA or BE Transition to A or E, more like B than A or E

B Most clearly expressed portion o f B horizon

BC Transition to C, more like B than C

Zone of least weathering, accumulation of Ca and Mg carbonates, cementation, sometimes high bulk density

Bedrocks

Figure 57. Typical’ soil profile, illustrating the major horizons that are present in a well-drained soil in a temperate region. N o t all soils exhibit all profiles, and the depth of the horizons varies widely. (Adapted from Brady, 1990)

The O horizon is the organic layer, and is above the mineral soils. There are

three subdivisions based upon the amount of decomposition, ranging from slightly

decomposed (still possible to identify the fragments) to highly decomposed (impossible

to recognize any fragments). The topmost mineral layer is the A-horizon. This

horizon is usually mixed with decomposing organic matter and is often darker in color

than the other horizons. The horizon of maximum leaching is the E horizon (from

eluviation — Latin e, meaning out and lavere, meaning to wash). The particles in this

horizon are typically sand and silt, the clays being washed down further into the

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. profile. The B-horizon is the layer of illuviation (from Latin //, meaning in andlavere, to

wash). This is the layer where aluminum and iron oxides accumulate, both from the

top and from the bottom in temperate regions. In arid regions, salts such as calcium

carbonate as well as others, also accumulate. The C-horizon is the unconsolidated

parent material. There is little biological activity and this horizon is usually unaffected

by the process that affect the upper layers. It is highly unlikely that any given soil will

show all the profiles, as the character of the profile is highly dependent upon climate,

vegetation, topography, and time. Soils from forested regions have a much different

profile than those from grasslands in temperate zones, and soils from arid regions are

different altogether (Figures 58 and 59).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 58. A soil profile from a Figure 59. A grassland soil from forested region in Minnesota. The A- Minnesota. The A-horizon is dark and horizon is highly leached and the B- quite deep, and the B-horizon is almost horizon is very will developed. absent. (From USDA soil Conservation Compare this to Figure 57. (From Service) USDA Soil Conservation Service)

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Under ideal conditions, a soil profile can develop in under 200 years. “Soil

development proceeds at a rate that is a combination of the effects of time plus the

intensities of climate and biota, further modified by the effect of land relief on which

the soil is situated and the kind of parent material from which the soil is developing”

(Donahue, 1977). There are many factors that retard soil development, including:

1. Low rainfall and low relative humidity 2. High lime content of the parent material 3. Resistant parent materials, such as granite, which weather very slowly 4. Steep slopes 5. Cold temperatures 6. Mixing by animals and humans

Soil is a complex system o f chemicals and particles that when combined, allow

plants to flourish o r perish, allow humans to build roads and buildings, have

recreational areas such as golf courses, dispose of everyday waste products and have

building materials, such as clay. It serves as the interface between the Earth’s crust and

the atmosphere, supplies w ater and nutrients to plants and finally, people use the soil

in a number of different ways, all of which ultimately requires some knowledge of soil.

This paper is meant to provide a basic understanding o f the physical properties that

affect how soil behaves, especially as it relates to plants. Topics will include the basic

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. physical properties, soil water, soil air, cation exchange, minerals and nutrients, soil

pH, and soil compaction. Figures and charts are used to supplement the text.

SOIL PHYSICAL PROPERTIES

Soils all have several properties in common, no matter how different they are,

no matter how fertile they are, and no matter how useful they are to humans. An

understanding of these properties will aid in understanding how soils function, which

will help us understand not only how to grow plants better, but also to decide if a

given soil is even suited for growing plants, o r if it would be better suited for

something else, such as a foundation, or a road, or even a wetland. These properties

affect all aspects of the soil, from drainage, to compaction, to erosion.

SOIL TEXTURE

Soil texture and soil structure are two properties that affect the other

properties, and are easily confused. As previously mentioned, soil texture is the

relative percentages of the different sizes of particles present in the soil. Soil structure

is the arrangement of those particles. Soil texture is the one that most influences

other properties since it is relatively unchanging. A sandy soil is one where at least

70% of the particles are sand. Sandy soils are classified as either sands o r loamy sand.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A soil with at least 80% silt is named silt. To be classified as a clay soil, a soil must

have at least 35 % clay. Clays can be sandy-day, silty-day o r clay, depending upon the

amount of the other two particle sizes. Many homeowners claim to want a loam soil.

However, in practice there are many subdivisions o f the category loam. A true loam is

one with equal proportions of sand, silt and clay. Most soils however, are not true

loams. They are one o f the many types o f loam, including silt-loams, silty-day-loam,

sandy-day-loam or day-loam. To determine the type of soil, find the percentage of

two of the sizes on the texture triangle, which automatically provides the third. Then

the classification of soil can be determined (Figure 56)

Size of particle greatly influences the other properties by affecting the size and

number of pore spaces as well as the total surface area. The coarse fragments in a soil

include gravel, pebbles and stones, which are all larger than 2mm, the size of the

largest sand grain (Figure. 60)

D ia m e te r D ia m e te r d m Range (mm) Range (In.) Gravel 2-75 1/12-3 Cobbles 75-254 3-10 Slones More Chan 254 More than 10

Figure 60. Coarse particle size distribution. From USDA soil classification for stones in the soil (Plaster, 1985)

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sand particles are not sticky when wet, cannot be molded and are not plastic.

Due to the large pore size, sand has very low water holding capacity. This makes a

sandy soil very well drained, but drought prone. Sand also has little to no nutrient

holding capacity.

Silt particles are intermediate in size between sand and clay. They can be sticky

or powdery, and generally do not stick together. Occasionally, they have a layer of

clay particles adhering to them, which provides plasticity, cohesion and adsorptive

capacity. Silt has the best capacity to hold water and nutrients of all the particles.

However, it can cause the surface o f a soil to become crusty unless there is plenty of

sand and clay present as well.

Clay, the smallest fraction o f a soil has the highest surface area o f all the

particles. It is this high surface area that accounts for its high reactivity. The

adsorption of water, nutrients and gas as well as the attraction of particles to one

another are all surface phenomenon, thus, clays are very significant in determining the

other physical properties. Clay particles, or colloids, have several properties that

should be considered separately.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. coarse sand

medium sand very fine fine sand silt sand

cla

Figure 61 Diagram of the relative sizes of soil particles, from coarse sand down to clay (Plaster, 1985)

First, as previously mentioned, colloids are extremely small (Figure 61), and

because of their small size, they have an extrem ely high surface area. Some o f them

also have internal surface area. These areas are typically charged, generally negative,

although some are positive. The nature o f these charges is very important and more

details will be presented later in the paper. For now, it is more important to

remember that the attraction of these charges to the opposite charge. It is these

charges that attract hundreds of ions in the soil. Thus the particle becomes a double

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. layer of charges, with the inner layer being the particle itself, with generally a net

negative charge, and the outer layer is the layer of ions, held (adsorbed) rather loosely

by the attraction to the negative surface of the particle. W a te r can also be adsorbed

to particles. Some of the water molecules are attracted directly to the particle due to

the polarity of the water molecule, others are attracted to the ions, which then

become hydrated (Brady, 1990).

Soil minerals form from the silica and oxygen in the soil. Minerals are either

crystalline or amorphous. Crystals are arranged in a definite and repeating order.

Amorphous particles do not have this order. The kinds o f minerals in the soil

influences how the soil is formed and it nutrient holding capacity. It also influences

how a soil erodes over time. Although there are many types of minerals and clays in

the soil, the vast majority are of 4 major types: silicate clays, iron and aluminum

oxides, allophane and associated amorphous clays, and humus. Silicate clays are layer

like in structure, and is much like a book in arrangement. The silicon, aluminum

magnesium and iron atoms are held horizontally by oxygen and hydroxy groups.

There are many different compositions of these clays and the composition determines

properties, but they are the most predominandy particles in soils all around the globe.

Iron and aluminum oxides are dominant in highly weathered soils, and are mostly seen

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in the tropics and subtropics. This type o f soil displays a characteristic red color.

They generally are not sticky nor are they plastic. They can be crystalline or

amorphous, and their properties vary widely with pH. At high pH, the colloids carry a

negative charge; whereas, at a low pH, they carry a positive charge. Thus, the types of

ions they attract can be vastly different. Allophane typically lacks an ordered, 3-

dimensional structure. It is typically poorly defined aluminum silicate and is prevalent

in soils from volcanic ash. It adsorbs cations and anions almost equally. Humus has

many similarities to clay. The particles are surrounded by cations, which like iron and

aluminum oxides varies with pH, but are not crystalline in structure. Humus has an

extrem ely high capacity for holding w ater and other essential plant elements.

Since particle size is such an im portant component of soils, a brief mention of

how to do a particle size analysis is included here. The results o f such an analyses then

gives information about the texture and the soil can then be classified via the textural

chart seen in figure 56. Stokes’ Law is the basis fo r particle size analysis, and works on

the basis of determining the terminal velocity of a particle in a fluid settling under the

force of gravity. According to Stokes’ Law, “the terminal velocity of a spherical

particle settling under the influence of gravity in a fluid of a given density and viscosity

is proportional to the square of the particle’s radius” (Hillel, 1990). The equation is

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. written as: V = 2gr2(D, - (Ail equations are found in appendix B and a symbol

explanation is found on page xiv). The use of Stokes* Law is dependent upon certain

assumptions:

1. The particles are sufficiently large to be unaffected by the thermal (Brownian) motion of the fluid molecules. 2. The particles are rigid, spherical and smooth. 3. All particles have the same density. 4. The suspension is sufficiently dilute that particles do not interfere with one another and each settles independently. 5. The flow of the fluid around the particles is such that no particle exceeds the critical velocity for the onset of turbulence (Hillel, 1990).

In reality, particles are neither rigid, nor spherical, nor smooth. In addition, not

all particles actually have the same density. The biggest drawback though, is that the

law fails to take into account the differences in clay particles, which can greatly

influence soil behavior. Therefore, Stokes’ Law should only be used as a method for

estimating particle sizes.

SOIL STRUCTURE AND AGGREGATION

Soil structure is the arrangement of the particles within the soil. Are they

independent of each other, o r formed together in aggregates? Aggregation is the

formation o f soils into secondary granules composed o f many smaller, primary soil

particles, which are held together by chemical bonds between the particles, organic

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. matter, iron oxides, carbonates, clays and/or silica. Two processes contribute to the

aggregation of soils although they are notoriously hard to separate. First are the

physical processes that directly contribute to the formation of aggregates, and second

are the processes that make those aggregates stable. Physical processes that

contribute to aggregation include wetting and drying, freezing and thawing, ro o t

extension, and the actions o f soils organisms. If the aggregates are formed from

human processes such as tillage, they are termed clods, if they are formed naturally,

they are termed peds. Although occasionally soil particles are found independent o f

one another, aggregation is by far the most common situation, and good aggregation is

considered to be of prime importance for horticulture.

The major component that contributes to aggregation as well as aggregate

stability is organic matter. The microorganisms that break down organic matter also

exude many types of viscous substances, which all help to ‘glue’ particles together and

encourage aggregate formation (Emerson e t al. 1986). Figures 58 and 59 show tw o

different soils, one with good aggregation, and one with very poor aggregation; note

the large quantity of roots in the soil on the left Organic compounds tend to orient

soil particles along a common plane, then to form bridges between these smaller

particles eventually forming stable aggregates. In addition to organic matter, certain

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cations also promote aggregate formation, including Ca2\ Mg2*, and Al3*. These ions

bind soil particles together, but they do not stabilize them in the way that organic

matter does. Thus, the binding of particles by cations is called flocculation due to this

lack of stabilization.

Organic matter provides aggregate stability. Stability is highly important to the

growing of plants. Some aggregates degenerate easily under the influence of wind or

rain, others are able to withstand even plowing and tilling. Aggregate stability is

promoted by three factors:

1. The temporary mechanical binding action o f microorganisms, especially the thread-like mycelia of fungi. These effects are pronounced when fresh organic matter is added to soils and are at a maximum a few weeks or months after the application. 2. The cementing action of the intermediate products of microbial synthesis and decay, such as microbiaily produced gums and certain polysaccharides. 3. The cementing action of the more resistant stable humus components aided by similar action of certain inorganic compounds, such as iron oxides. These materials provide most of the long-term aggregate stability (Brady, 1990)

Although organics play a very important role in aggregate stability, it is not the

only factor that affects stability. Ions in the soil are constantly interacting with soil

particles and with each other. Iron oxide exerts a particularly important influence on

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. aggregate stability. Size o f the aggregates also plays an important role. Generally

speaking, the larger the aggregate, the less stable and more prone to destruction, it is.

Humus is soil organic matter that decomposes very slowly. It is the humus that

provides a large portion of the ‘glue’ that holds aggregates together due to several

properties. First, like clay, it is highly charged and has a very large surface area. Thus

it is reactive in soils. Polysaccharides such as glucose, cellulose, hemicellulose and

especially lignin all form large parts of humus. Lignin is highly important due in part to

its size. It is a very large molecule with many chains and hydrogen ions. These H* are

readily lost o r gained giving the molecule a charge. These charges may be different at

different ends o f the molecule; as a result, they attract oppositely charged soil

particles. It is these very attractions that bind soil particles together as aggregates

(Figure 62). The formation and stability of aggregates provides for another soil

property known as tilth.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 62. Two soils with different aggregation. The one on the left shows excellent aggregation, while the right side shows litde to no aggregation. N ote the number of plant roots in the sample on the left. Roots tend to encourage aggregation as structure in a soil (Adapted from Brady, 1990 and the USDA Soil Conservation Service).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Prismatic (Level tops)

Columnar (Rounded tops)

ffl Blocky (Cube-like)

Blocky (Subangular)

Granular (Porous)

Crumb (Very porous) Platy-leafy and Flaky also found

Figure 63. Various structural types found in soils, and their ‘typical’ shape (adapted from Brady, 1990).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Although a given profile may have more than one type of aggregate, there are

four main classifications fo r soil structure: spheroid, platy, prism-like and block-like

(Figure 63).

Soil structure also has three major classification schemes. Figure 9 shows

structural types, which refers to the shape o f the aggregate. Soil classes refers to the

size of the aggregates: very fine, very thin, fine, thin, medium, coarse, thick, and very

coarse or very thick. Finally there are several grades of soil structure. A structure

less soil has no distinguishable aggregation. This may simply be a very sandy soil, o r it

may be a mass of soil that has cemented together. Weak structure means the

aggregates can barely be distinguished. Moderate structure means the aggregates can

readily be seen and sometimes handled. Strong structure means the aggregates are

very well formed and are easily handled (Soil Survey Staff, 1975).

Soil structure influences many different soil properties, including water

infiltration rate, heat transfer, aeration and porosity. It is not well known how soils

form. Structure comes about from a number of different forces, including swelling and

shrinking, and cementation. Plant roots also tend to break up larger soil particles and

compress smaller ones. Roots also secrete sticky substances that bind the soil

together into aggregates (Esau, 1977).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Although many ions contribute to soil structure, the one ion that exerts the

most influence on soil structure is sodium (N a*). Sodium is a large, hydrated ion with

a low charge. Therefore it does not effectively neutralize the negative charge o f the

soil particles, with the result being a repulsion and destruction of the aggregates and

peds. As the aggregates are broken down into smaller and smaller particles, they

move easily with the soil water lodging in the soil pores. This effectively seals the soil

and makes it impermeable to water. Thus soils high in sodium are almost

impenetrable to water and have a thick crust on the surface (Donahue, 1977 and

Hillel, 1990).

PARTICLE DENSITY

Particle density is another property common to all soils. The size of particles

and their arrangement have absolutely nothing to do with their density. Density is the

mass of a volume of soil solids and is usually measured in grams per centimeter cubed

(g/cm3) or mega grams per meter cubed (Mg/m3). Particle density is simply a measure

of the mass of the soil without the pore space included. Interestingly enough, particle

densities of soils around the world are surprisingly similar, ranging from 2.60 to 2.75

Mg/m3 with 2.65 Mg/m3 being the standard used in calculations. The reason fo r this

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. similarity is due to the fact that most soils have silica clays as their most abundant

mineral. If there are large quantities of denser minerals, such as magnetite or zircon,

then the density will be higher. Large quantities of organic matter in the soil makes

the particle density lighter as the density of organic matter ranges from 1.1 - 1.4 Mg/m3

(Handbook of Chemistry and Physics, 1994). Particle density is expressed as the mass

o f the solids divided by the volume o f the solids o r Ps = M ,/Vs.

BULK DENSITY

Bulk density is the density of the soil including any air spaces and organic

matter; however, water content is not measured as a part o f bulk density. Bulk

densities can readily be used to determine the level o f compaction in a given soil. A

soil that is loose and contains many pore spaces has a much smaller weight per given

area than it does after compaction. Thus soils with many pores have a smaller bulk

density than do soils with few pore spaces.

The density of surface soils can range, but generally falls between 1.00 Mg./m3

to 1.60 Mg/m3. A soil that is highly compacted might have a bulk density as high as

2.00 Mg/m3. These soils are typically found much low er in the soil profile and are

usually impervious to roots. A soil that has a bulk density higher that l.60Mg/m3 is

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. considered highly compacted and not conducive to plant growth. The bulk densities

for several soils are shown in Tables 15 and 16.

soil treatment and identification bulk density g/cc

Tilled surface soil o f a cotton field 1.3 Trafficked interrows where wheels passed surface 1.67 Traffic pan at about 25 cm deep 1.7 Undisturbed subsoil below traffic pan, clay loam 1.5 Rocky silt loam soil under aspen forest 1.62 Loamy sand surface soil 1.5 Decomposed peat 0.55

Table 15. Representative bulk densities o f soils as affected by texture, compaction (Trouse, 1971)

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Plow layer 1.72 1.28 1.33 1.24 0.95 Upper subsoil 1.74 1.41 1.46 1.36 N A Lower subsoil 1.8 1.43 2.02 1.51 1 Parent material 1.85 1.49 N A 1.61 NA

Table 16. Bulk density for several soil profiles Mg/m3 (Dawud e t al. 1979, Larson, e t al. 1980, Nelson etal., 1941 and Yule etal., 1980)

Soil bulk density is a ratio o f the mass o f solids to its total volume. Bulk density

is affected by the looseness o f a soil, as well as by compaction, swelling and shrinking,

and clay content. The equation for calculating bulk density is as follows: Pb = M,/Vt =

MJ(VS + V, + Vw) (Hillel, 1982).

PORE SPACE

The pore space o f a soil is the amount of area taken up by air and water, and is

commonly called soil porosity. These spaces are usually irregular in size because of

the nature of the particles themselves. Sand grains have the largest pore spaces and

clay soils tend to have the smallest. In soils with a very high clay content the spaces

may become filled with water and prevent any air movement. These soils may not

have enough air in them for root growth. Obviously, the best and most rapid

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. movement o f air and water is through sandy soils. Sandy soils can be as high as 50%,

whereas a compact clay soil may only be 20% or less pore space. Pore spaces in

uncropped lands remain relatively constant over time, as the amount of organic matter

is relatively unchanging. However, in cropping situations, the percentage of pore

spaces is continually declining, due to a gradual decrease in organic m atter content o f

cropped soils (Wilson, 1947).

There are two types of pore spaces: micro and macropores. The macropores

allow for water and air movement and the micropores hold water. For plants, it is the

balance o f pore sizes that are important and not necessarily the number o r percentage

of pores. W ater drains from the macropores via gravity, but is held in the micropores

by attraction to the aggregates.

Since porosity is expressed as a percentage it is also relatively simple to

calculate. A soil sample is oven dried and its weight measured. Then the sample is

soaked in a pan o f w ater until all the pore spaces fill. The difference in weight is the

pore space. The equation is as follows: f = V/Vt = (V, + VW)/(V, + V, + Vw). Another

method for calculating porosity is: f = [(W wet - W dry)/VJ x 100. Although soil porosity

varies greatly from soil to soil, ‘typical’ values are often in the range of 30 - 60 percent.

It is im portant to remember that porosity is highly variable, especially in soils with a

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. high clay content, as the soil swells, shrinks, cracks and aggregates. In addition,

porosity reveals absolutely nothing about the size distribution of the pores and this is

far more im portant to plants than is total porosity.

TILTH

Soil tilth is the physical condition of the soil specifically as it relates to plant

growth. W ith good tilth a soil is arable, loose, friable, and porous, aggregation is good,

permitting w ater and air movement, and cultivation of the land is easy. Bulk density,

aeration, rate of water infiltration, and drainage are all factors that affect tilth.

The factor that affects tilth the most is tillage. Tillage promotes tilth, and in

turn good crop production. Conventional tillage has several immediate benefits: crop

residues are broken down more quickly, pore space is higher right after tilling, and it is

a good method for weed control. However, soil erosion is increased, via wind and

water erosion. Tillage, although good for the short-term productivity of a soil tends

to cause a gradual decrease in aeration as well as soil structure (Wilson, 1947).

Although there are other deleterious effects, it is this increase in erosion, especially

over the long term that makes conventional tillage undesirable. Although tilth is not

an inherent property of soils, it is important to anyone growing plants.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CONSISTENTCE

Soil consistence describes the ability of a soil to resist mechanical stresses

and/or manipulations, or more simply put it is a soil’s ability to stick together. It is

usually described at three moisture levels: wet, moist and dry. Consistence can often

be determined by hand or by the action of a tilling instrument through the soil. The

terms used to describe consistence are shown in Table 17. These terms are common

everyday words for which most people already have an inherent meaning in their

minds. An example o f common usage follows: a w et clay soil could be termed slightly

sticky, sticky or very sticky, whereas a wet sand could be non-sticky. The amount of

w ater in the soil changes the terms slightly, but the hand can feel all o f these terms.

Plasticity is simply how easily and how much the soil can be molded between the

fingers. Pressing a sample between the thumb and first finger and observing the

amount o f soil stuck to the fingers measure stickiness. Friable refers to materials that

are readily crushed under pressure. Consistence is very important when estimating

soil strength under a given set of forces, such as compaction by farming equipment,

building weight o r traffic pressure and vibration.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WET MOIST DRY Stickiness Plasticity

Non sticky Non plastic Loose Loose Slightly sticky Slightly plastic Very friable Soft Sticky Plastic Friable Slightly hard Very sticky Very plastic Firm Hard Very firm Very hard Extremely firm Extremely hard

Table 17. Consistence terms for soils at the three moisture levels. Cohesion of the soil increases going down the table. (Adapted from Brady, 1990 and Donahue, 1977).

The relationships between the three phases o f soil are highly variable,

depending upon the type of soil, environmental conditions, and other features

mentioned above. However, a general representation can be derived for many soils

regarding the mass and volume o f the three phases. This relationship is shown in

Figure 64. Any measurement for mass can easily be converted to a weight by

multiplying the mass by the acceleration of gravity, 9.8m2. Particle density, dry bulk

density, and porosity have been discussed already. Two other relationships can be

worked out from this figure: void ratio and soil wetness, which includes mass wetness,

volume wetness, and degree of saturation.

208

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. volume relationships mass relationships

l ~ ~ Va Ma-0 ,L_ — J- Vf

Vw Mw Mt Vt

Vs Ms

fig. £4 representation of the relationships between the three phases of the soil system. (taken from Hillel, 1980)

The void ratio is also an indicator of the volume of soil air, but it relates to the

volume o f the solids rather than total volume. Void ratio is generally used only in

engineering and mechanics whereas porosity is the more accepted term for

agricultural situations. The equation for void ratio is as follows:

e = (V, + Vw)/Vs = V/(Vt - Vf)

Soil wetness refers to the relative water content of the soil. It can be relative

to the mass of the solids, total mass, the volume o f the solids, total volume, as well as

to the volume of pores. These equations are stated below.

The mass wetness is the mass of the water relative to the mass of oven dry

solids. In the literature, this term is also called the gravimetric water content. This

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. term generally ranges from 25 - 60% depending upon the soil, with clay soils usually

having a higher value than sandy soils. In a highly organic soil, it may be as high as 100

percent.

w = M JM ,

Volume wetness is also referred to as volumetric water content or volume

fraction of the soil water in the literature. It is based upon the total volume of the soil.

It also represents the depth of the w ater per unit depth o f the solids.

q = v¥yvt= vw/(vJ + vf)

The degree of saturation relates the relative water content to the volume of

pores in the soil. It can range from 0 - 100 percent in a soil with complete saturation,

which is extremely rare. There is usually some air trapped within the soil even when

it is very wet.

S = VJV, = VJQ/t + Vw) (Hillel. 1980)

SOIL W A TER

Soil water is a concern for horticulturists because there must be enough water

to allow plant to survive, yet not so much as to drown them. Since w ater is

continually lost via evaporation as well as transpiration the main goal of horticulturists

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is to ensure enough water to satisfy plant needs. W a te r is not only used direcdy by

plants, it also is the solvent fo r ions and minerals required by plants. In addition, water

landing on the surface of a soil is one of the main methods fo r soil erosion. Finally

water helps to control soil temperature. In fact, water participates in most of the

chemical reactions that take place in the soil due to the nature o f the water molecule

and its physical properties.

CAPILLARITY

The main property of w ater that affects the soil as well as plants is capillarity.

This is a familiar function of water and is the cause of water rising up a wick or tube

placed into a tub of water. This property is due to the forces of cohesion and

adhesion. Adhesion is the attraction of the water molecules to other objects (the sides

of a tube for example) and cohesion is the attraction of water molecules for other

water molecules. The height of rise in a tube is inversely proportional to the diameter

of the tube and proportional to the surface tension of the water, a measure of its

cohesion. It is given by the equation: h = 0.15/r, where r is the radius of the tube.

Although capillary movement is soils is common, the distances are not great.

The reason for this is the pores in soils, while they are adjoining, do not join in a

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. straight line. In a clay soil capillary movement is greater than in a sandy soil because o f

the pores in sandy soils are generally too large for this type o f movement.

Several terms need to be defined at this point. Soil is held in the soil against

several forces, and these forces define the different classifications of soil water.

G ra v ita tio n a l w a te r is w ater that will drain freely from the soil simply due to the

force o f gravity. Gravity plays an important role in removing w ater from the soil after

heavy rains or irrigation. The movement of the water is relatively rapid (depending

upon the soil texture) and through the large, continuous pores. Available w ater is

defined in relation to water that plants have access to. It must be able to be absorbed

fast enough to maintain plants. This represents most o f the w ater that plants use,

although gravitational w ater is also plant available IF there is enough air in the soil as

well. The permanent wilting point is the point where plants cannot pull enough

water out of the soil to counter transpiration. It is the point where plants will not

recover unless more water is added to the system. Field capacity is defined as the

greatest amount of water a soil will hold AFTER the gravitational water has drained

from the system. It is difficult to determine when a soil has reached field capacity

because plants are continually transpiring water, water is evaporating into the air and it

is also moving downward into the deeper layers of the soil.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WATER MOVEMENT

There are tw o types of w ater movement in soils, saturated flow and

unsaturated flow. Water moving due to gravitational force is saturated flow.

Following a heaving rain or irrigation, soil is often saturated, that is all the pores are

filled with water. As the water infiltrates the soil, it percolates (moves downward)

through the soil eventually reaching the groundwater. Movement into the large pores

is relatively quick, but can be slowed by a number of factors, which are listed below.

1. The percentage of sand, silt and clay. Coarse sands permit rapid infiltration. 2. The soil structure. Fine textured soils with large water stable aggregates have higher infiltration rates than unstructured soils. 3. The amount of organic matter in the soil. The greater the amount of organic matter and the coarser it is, the more water that enters the soil. Organic surface mulches are especially helpful in keeping infiltration high because they protect soil aggregates from breakdown by reducing the impact of raindrops and by continuing to supply the cementing agents fo r aggregates as they decompose. 4. The depth of the soil to the hardpan bedrock or other impervious layers. Shallow soils do not perm it as much water to enter, as do deep soils, if they are similar in other respects, such as texture and structure. 5. The amount of water in the soil. W et soils do not have as high an infiltration rate as do moist o r dry soils. This is partly because pores o r cracks are few er o r smaller because clays have already wetted and swelled. 6. Soil temperature. W arm soils take in w ater faster than do cold ones. Frozen soils may or may not be capable to absorbing water, depending upon the kind o f freezing that has taken place.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Water flow in unsaturated soils is a bit more complicated. The macropores

are filled with air, leaving only the micropores filled with water. Movement from these

pores is quite slow. W ater moves down the water gradient, which is from areas of

higher water content to areas of lower water content. Water can move in response

to plants pulling the water out, as well as in response to evaporation into the air. Both

of these are movement from an area of higher water content (the soil) into an area of

lower water content (either the plant or the air).

Most soil water movement discussions are based upon the assumption that the

soil consists of one homogeneous layer, which is rarely, if ever, the case in the field.

The different horizons can have a profound impact on the movement o f soil water.

The one general assumption about w ater in the soil horizons is that anytime the soil

changes dramatically, water movement is impeded. Horticulturists tend to think of a

sand soil as having good drainage. However, if the layer of sand is under a layer of

topsoil, water movement will be restricted until the topsoil is saturated (figure 65). It

is only when the gradient is sufficiently large enough (i.e., when the top layer is

saturated) that water is permitted to move downward into the sandy layer (Gardner,

1921).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I

(C)

Figure 65. Downward water movement in a soil with obvious layering. A) Water is applied to the surface and after 40 minutes downward movement is the same as lateral movement. B) After 110 minutes, the downward movement is impeded by the layer of sand, note that no w ater has moved into the sandy layer, but lateral movement still continues. C) After 400 minutes the gradient is sufficiently large enough to allow water to move into the sand layer, and downward movement continues. This proves that sand, as well as compacted soils can provide a barrier to water movement (Gardner, 1921).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WATER VAPOR MOVEMENT

W a te r not only moves in the soil during its liquid phase, but also during its

gaseous phase. W ate r vapor can move within the soil, in the pores, and also along the

surface of the soil, where it can also be lost to evaporation. Again, it is a gradient that

drives the movement of water vapor in the soil. Water vapor movement though, is

also highly regulated by soil temperature. W here temperatures are high, movement

will be from areas of higher temperatures to lower temperatures. Generally the

amount o f water vapor in the soil at any given point is 10 kg in the upper 15 cm of a

hectare o f soil (Brady, 1990). In dry soils, many plants can survive on only water vapor

for a considerable period of time, especially those that are highly drought tolerant.

WATER POTENTIAL

The above discussion all relates to w ater movement in the soil. Everything

mentioned so far can be explained by a difference in gradient. However, another

method of explain w ater movement is to look at the changes in energy that are

involved. Potential, kinetic and electrical energies are all involved in the movement of

water within the soil system. This change in energy is also movement along a gradient,

a gradient of higher energy to one of lower energy. Knowing these differences allows

one to predict the direction of water movement. There are three major forces that

216

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. drive w ater movement; matric forces (the attraction o f w ater for the soil solids),

osmotic forces (the attraction of water fo r other ions in the soil solution) and

gravitational forces, which will pull the water downward. Soil water potential is the

standard reference point that compares the difference in energy in the soil water and

pure water. Although the forces act simultaneously within a soil, they are not

technically additive, as each comes from a different source of energy.

Matric potential (ym) is the result of adhesion and capillarity. The net effect of

these two forces is to reduce the free energy of water when compared to pure water.

Matric potentials are always negative. Differences between matric potentials of two

adjacent soils horizons aids water movement; however, this movement is very slow.

Osmotic potential (y0) comes from the soil solution, not just the water, but all

the ions dissolved in the water, which reduce the free energy of water. However,

osmotic potential has little overall effect on water movement, but a dramatic effect on

water uptake by plant roots. In soils with high concentrations of soluble salts or

inorganic ions, the osmotic potential of the soil may be considerably higher that in the

roots, thus preventing water from moving into the roots, and may in fact, cause water

to move out of the roots.

217

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Gravitational potential (y j is simply the force exerted on soil water by gravity.

This force is the same as for every other object on the planet and it movement is

always toward the center of the Earth. A reference point is generally chosen to be

below the observed elevation simply so the number will always be positive. This has

no effect on the direction of the force, simply on the sign of the number. Remember

that gravity is independent of any chemical reactions that may be occurring within the

soil; it is solely dependent upon elevation and relationship to the chosen reference

point.

The units for pressure are variable depending upon the date of the literature.

More recent papers tend to use MegaPascals as the unit of pressure for water

potential, but older papers commonly utilize bars, or atmospheres (atm). One bar is

approximately I atm (14.7 Ib/in2 or 760 mm Hg). O ne MegaPascal (MPa) is

approximately ten bars. The relationships between these units are shown in Table 18.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Height of column water potential water potential (cm) (bars) (MPa)

0 0 0

10.2 - 0.01 - 0.001 ______!

102 - 0.1 - 0.001 306 -0.3 -0.03

1020 -1 - 0.1 15300 -15 -1.5 31700 -31 -3.1 102000 -100 -10

Table 18. Approximate equivalents o f the different methods o f expressing soil energy levels (Brady, 1990).

SOIL AIR

Soil air is important because it is necessary fo r microorganisms as well as plant

roots. Soil aeration is the process by which carbon dioxide is exchanged fo r oxygen

between the soil system and the atmosphere. Poor aeration occurs when one (o r

both) o f tw o things happens: I) when the moisture content is sufficiently high such

that the pores are filled with water and little to no air, 2) when the exchange of gasses

between the soil system and the atmosphere is impeded to the point where toxic

gasses are allowed to build up, o r desirable levels o f oxygen cannot be maintained.

219

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Condition number one often occurs when the soil is saturated with water.

This could be due to heavy rains, poor drainage, a low spot in the topography or

compaction. The second condition can also occur during times of flooding, but it can

also occur during periods of intense plant respiration. The result is an oxygen deficit

in the soil and finally a slowing o f respiration as oxygen becomes limiting. Soil oxygen

can range from 20% (just under the atmosphere content) to as low as 5 percent or

lower in area of poor drainage. Following periods of heavy rainfall, oxygen content is

decreased as the pores fill with water. This water contains approximately 3 percent

dissolved oxygen, which some microorganisms are able to utilize. However, if the

water fails to drain, even the microbes are put at risk. The best measurement of soil

aeration is the oxygen diffusion rate (ODR), which determines the rate that oxygen

can be replaced once it is utilized by plants o r other organisms. Root growth ceases if

the ODR drops below 20 x 10-8 g/cm2/min (Patrick W „ 1977).

Although soil air is very similar in many respects to the Earth’s atmosphere, it

varies in a couple of important ways. First, there is more carbon dioxide in soil air

than in the atmosphere. A well-aerated soil contains in the vicinity of 205 mL Oz/L of

air, but this dramatically drops in half at I m below the surface. Near roots, this level

drops even further, to 20mL o r less. The levels o f C O z near the surface are near 30

220

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mL/L of air, but at Im depth, this increases to almost lOOmL/L air (Sposito, 1989).

Also, soil air is generally saturated with water vapor all the time. This means the

relative humidity is close to 99 - 100 percent all the time. In the atmosphere it varies

from very low in deserts to very high in tropical areas.

Soil air moves through tw o main methods: diffusion and bulk flow. Diffusion is

responsible fo r the exchange of carbon dioxide and oxygen between the soil and the

atmosphere. The rate o f diffusion is dependent upon a number of variables:

temperature, w ater content, size and number of pores as well as the kind o f molecule

diffusing. Bulk flow seems to be less important in soil air movement, but occurs when

the gas molecules respond to changes in pressure. This change may be due to an

increase/decrease in soil temperature, or if the atmospheric pressure changes. Also,

plants extract w ater from the soil and air moves into the spaces occupied by the water

(Stolzy, 1961)

For a soil to become aerated, water must drain through the profile. Air can

only enter the soil when water exits, either though evaporation, transpiration or

drainage. Physical properties all determine how well water drains though the soil.

However, aeration influences soil reactions, which in turn, influences physical

221

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. properties. Most of the reactions influenced have to do with soil microbes and how

fast they are able to break down organic matter.

Different plants have differing abilities to handle poor aeration. Some crops

require good aeration, such as Oats and Peas, but some crops, notably clover and

fescue are able to handle very low amounts of oxygen in the soil (Table 19). However,

most plants are probably going to face growth limitations if porosity goes below 10

percent (Williamson and Kriz, 1970).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Plants tolerant to constant table at each depth

15 - 30cm 40 - 60cm 75 - 90cm 100+ cm Clover Alfalfa Corn Wheat Orchard grass Potatoes Peas Barley Fescue Sorghum Tomato Oats Mustard Millet Peas Cabbage Beans Snap beans Horse beans Sugar beats

Table 19. Ability of certain crop plants to withstand restricted aeration. Numbers represent height of the water table, which provides the source of poor aeration (Williamson and Kriz, 1970).

SOIL TEMPERATURE

In cold soils, chemical processes slow. In contrast, as soils warm, chemical

processes are sped up. Plants respond to cold temperatures in many ways.

Photosynthesis is slowed, as is growth. Nutrient uptake is also affected. However, it

is microbial processes that greatly influence other properties as well as plant growth as

soil temperatures fluctuate.

One of the most studied topics in fertilizations programs results from a

decrease in soil temperature. The process of converting ammonium ions to nitrate

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. comes to a standstill at temperatures below 10 degrees Celsius. Once this was

determined, fertilizer applications could be made more efficiently. Anhydrous

ammonia is now injected into the soil in the spring, but will not be converted to

nitrate until the soil temperature rises. The optimum temperature for this is

approximately 27 - 32 degrees Celsius. This has become a widely accepted practice in

temperate regions because anhydrous ammonia does not leach through the soil, but

nitrate does. By preventing the conversion of ammonia to nitrate, the nitrogen is kept

in the soil longer and converted slowly, as the plants need it (Fluker, 1958).

Disease control can also be achieved by controlling the soil temperature.

Fusarium and Vertidllium, two highly destructive pests of many crops, can readily be

controlled by covering the soil with clear plastic. This can raise the temperature to

well above 50 degrees Celsius, which prevents growth of the fungi. This reduces the

need for pesticides and can cut costs fo r producers.

Alternations of freezing and thawing has dramatic effects on soil. Aggregates

are broken apart by the action of ice crystals. This alters the structure of the soil.

Many such alternations causes heaving o f some plants. Shallow rooted ornamental

crops such as Armeria maritima can be killed by such action.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Considerable variation in soil temperature occurs throughout the season.

Fluctuations occurring on a daily basis while not usually great, are measurable. Most of

the variation comes from the upper layers of the soil. Surface layers are typically

warmer than the air, but approximately 2cm below the surface, the temperatures are

generally that of air temperature (Fluker, 1958). Only a few centimeters below the

surface of the soil, the fluctuations are not as dramatic and occur over longer periods

of time. Fluker notes that in March, the upper centimeters are rapidly responding to

the warm er air temperatures; however, the subsoil is still cooling due to effects of

winter temperatures. Thus during the winter, subsoil temperatures are warm and

during the summer, they are cold. The decreased variability of deep soils to changes

in temperature provides protection for plant roots as well as building foundations.

Although people cannot regulate soil temperature to any great extant, there

are two practices which are helpful, at least as far as plant production is concerned.

The first is mulching, and the second is anything that decreases soil moisture. Mulches

are used extensively throughout horticulture to regulate soil temperatures and buffer

the soil against extreme soil temperatures. The concept o f conservation tillage, where

crop residue is left on the field is simply mulching (Brady, 1990).

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Practices that reduce soil moisture is another means for controlling soil

temperature to some extent. Soils that are full of water can be as much as 3-6 degrees

Celsius lower than dry soils. Thus, by removing the excess water, the temperature

can be somewhat regulated. W a te r can be removed via several means, ridging

systems, (raised beds) underground tiles, or the addition of organic matter, or sand to

a heavy soil to improve texture. There are also situations where soil temperatures

might need to be raised in order to control diseases, o r prom ote germination. In

these cases, simply covering the soil with clear plastic can raise the temperature as

much as 10 degrees Celsius, and these changes can be noted at a depth o f up to 30 cm

in the soil (Rykbost, 1975).

SOIL COLLOIDS

As discussed previously, there are four main types o f soil colloids: humus,

allophane and amorphous clays, layer silicate clays, and iron and aluminum oxides.

Layer silicate clays are crystalline in structure, and are composed o f sheets o f silicon,

magnesium, aluminum, and/or iron held together by hydroxy groups. The exact

chemical composition varies from clay to clay, but all have many positively charged

cations and a smaller number of negative anions attached. The overall charge of the

clay colloid is negative, although there are isolated patches of positive charge.

226

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Aluminum and iron oxides dominate in old, highly weathered soils. They

account for the deep red coloration o f soils in the tropics and even in the southern

Untied States.. Some are crystalline in structure, but others are amorphous. Their

charge attraction is highly dependent upon the pH of the soil. At high pH, these clays

attract positive cations due to a small negative charge, but at a low pH, they are highly

positively charged and therefore attract negative anions.

The other two types of colloids, amorphous, and humus have varying

properties. Some resemble those of clay, others are difficult to predict, and therefore

less is known about them. Humus tends to have high water absorption capacity, and

behaves much in the same manner as clay, but it is not crystalline in structure. Once

again, the surrounding charges are highly dependent upon the pH of the soil.

CATION EXCHANGE CAPACITY AND pH

The cations that are held on the surface o f the colloids are subject to change.

They are exchanged with other cations in the soil solution. There are tw o factors that

determine the likeliness of a given cations’ exchangeability. First, there are varying

degrees o f bonding, with some being held for more tightly than others. The second is

the relative concentration of the ions in the solution. If the concentrations of the

cations is equal, the strength of adsorption is as follows: Al3+ > Ca2+ > Mg2* > K* =

227

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. NH4+ > Na+ (Brady, 1990). Concentrations of cations is often dependent upon the pH

o f the soil. Soils with low pH tend to be dominated by A l3* and H +. A t high pH, Ca2+

and Mg2+ typically dominate soils. Some soils become saturated with salts and

become sodic in nature. These are dominated by the cation Na+.

The cation exchange capacity (CEC) then deals with the total exchangeable

cations that a soil can adsorb. To measure CEC, the cations are replaced by another

common ion (barium for example), then the total amount of barium is determined.

The CEC varies from soil to soil. On sandy soils, it is quite low, whereas, on clay soils

it is relatively high. They types o f clay will also determine CEC, but in general terms,

clays have the highest CEC.

The CEC o f a soil greatly influences plant available nutrients. For example, K*

is held tightly in the soil if the soil is alkaline and rather loosely in the soil if it is acidic.

This is simply due to the strength of adsorption mentioned earlier (see the order of

adsorption above). However, the soil pH, is the largest factor contributing to CEC.

A t a given pH, some nutrients are more available than others. For example, at pH

roughly 5.5, sulfur is readily available, but Ca and Mg are not so available, and boron is

very difficult fo r plants to obtain (see figure 66).

228

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. pH 4 5 6 7 8 9

! • • ‘ A -.L it 1 - 1. :* -T- f "• i.* i 1 L" '.‘ • >

•k«sa

Figure 66. (Adapted from Brady, 1990). The relationship between soil pH and the availability o f selected plant nutrients. W ide bands indicate greatest availability or activity, and narrow bands indicate limited availability/activity.

There are also many known antagonistic relationships between these nutrients.

For example, if high levels of Ca2* exist in the soil K* uptake is restricted. Also high

levels o f K* limits uptake of Mg2*, even in soils w here Mg2* is not limiting. O ther

examples o f these antagonisms are abundant. Phosphorus can restrict the uptake of

several nutrients including Zn*, as well as both forms of iron (Fe2* and Fe3*). Copper

229

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. uptake is negatively affected by high levels o f molybdenum as well as calcium (Sydnor,

1996).

Soil pH is a measure of alkalinity or acidity of the soil. Simply put, it measures

the number of H * ions in the soil. The scale goes from 0-14 with the lower numbers

representing a low, or acidic pH, and the higher numbers representing an alkaline pH.

A pH of 7 is considered neutral. As previously mentioned, soil pH greatly influences

the availability of nutrients. Soils with a very low pH often have toxic concentrations

o f aluminum. By raising the pH o f these soils, the aluminum becomes bound in the soil

and is no longer a threat to plants. Soils become acidic over time through leaching of

basic cations (Ca2+, Mg2*, K* and Na*), which often get replaced by H+. Weathering,

also tends to low er soil pH. Plants will also excrete H + into the soil. These ions are

then adsorbed onto the CEC and exchanged for other ions that are then absorbed by

the plants (Donahue, 1977). Thus, H* and A l3* exert the most influence on soil acidity.

Soil pH doesn’t generally have a direct affect on plant growth unless it is

extremely high o r low. However, it greatly influences the availability of nutrients.

Most minerals are more soluble in acidic soils than in alkaline soils. In addition,

although soil pH refers to acidity in both the solid and liquid phases, the vast majority

o f acidity is located in the solid phase (Eckert, 1998).

230

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Soil pH is highly resistant to changes. This is due to buffering mechanisms in

the soil. Clays soils are more able to resist changes than sandy soils due to a higher

CEC, but in general, it is very difficult to change the pH of a given soil. In soils in the

Midwest, the ‘magic’ number for pH is approximately 5.5. Attempts to raise or lower

the pH from this number are usually foiled by the strong buffering capacity o f the soil.

To be an effective buffer, a soil must remove H+ from acids o r the O H - o f bases. This

is all accomplished by exchanges on the CEC. For a soil with pH<5.5 Al+3 is the major

source o f buffering:

Al+3 -> <- A I(H 20 ) 6+3 -> < r AI(0H)(H20 )5*2 + HjO* AI(0H)(H20 )5+2 -»<- AI(OH)2(H20 ) / + h3o + at pH = 5.5 AI(0H)(H20)«* ->«- AI(OH)3 + h3ct

AI(OH)3 (gibbsite) precipitates out and is insoluble (Adams, 1984).

Aluminum binds so tightly to oxygen that H+ can come off the CEC. Most Al

exists as Al3* coordinated by six water molecules. As the pH increases, water

becomes hydrolyzed and this kicks hydronium into the system. The precipitation of

gibbsite removes soluble Al form the system. At low pH, aluminum is soluble and can

become toxic to plants. At higher pH, it is precipitated out as gibbsite and is no

longer toxic. Although Al can be chelated with organic matter, soils with very low pH

231

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (below 5.5) also show toxic levels of Mn (jenny, 1968). If hydronium ions are added to

the system, then some gets precipitated. Ideal pH fo r many agronomic and

horticultural crops is 5.5 simply because there is no toxic aluminum present, and it is

the pH at which all of the nutrient are readily available, with the lowest amount of

interactions between nutrients. Not much is known about the mechanisms for

lowering soil pH as in many agronomic areas, this isn’t the problem. Many highly

productive areas of the world need to raise the pH, and this phenomenon has been

more intensively studied.

In an agronomic situation, if the pH needs to be raised, then tons per acre of

material, generally lime, need to be added. After 4-5 years, the pH has generally been

changed for several years. The amount of lime needed will neutralize the acidity in the

soil. Although every soil is different, approximately 2-3 tons per acre, for 4-5 years is

enough to change the pH (Nobel, et. al, 1988). Choice of liming material is highly

important. The effectiveness is based upon tw o properties: chemical composition and

fineness. The chemical composition determines acid neutralizing power relative to

pure CaC03. This will determine the quantity of acidity neutralized. Fineness

measures the particle size distribution. This determines the rate and duration of the

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reaction. A range of particle sizes is best. This will not only prolong the length of

effectiveness but decrease the amount of time before changes are noticed.

Another effect of soil pH is to regulate soil microorganisms. A t a low pH,

many microorganisms don’t function well. Nitrogen fixing rhizobia need a pH of

approximately 7.0 or slightly above to be able to nodulate properly. Thus for many

legumes, the recommended pH is slightly higher than for other crops. Bacteria tend to

prefer a slighdy acidic soil, but this can vary with species. Therefore, the

recommendations for ideal soil pH vary with many factors (Brady, 1990). The

availability of nutrients, the types of nutrients that a given plant is susceptible to

deficiency (Iron in Quercus palustris fo r example), and the microorganisms in the soil all

impact the soil pH and its effect on the plants growing in that location.

CONCLUSION

Many problems face anyone who attempts to utilize the soil (and this is just

about everyone). World population is expanding at an exponential rate. Food must

be produced to feed all these people. This means agricultural practices that are

sustainable fo r many generations. Science is partly responsible for this increase.

Scientists have developed medicines and vaccines for diseases that used to be life

threatening; they have bred crops to produce at high yield rates and for disease

233

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. resistance. Insects (as well as bacteria and viruses) that carry or cause potentially fatal

diseases have been eliminated or their numbers greatly reduced. Has the planet’s

carrying capacity already been reached? Although the population is increasing, the

amount of arable land will remain, at best, unchanged. In a worst-case scenario, it will

decrease dramatically.

Fertilizers greatly increase the productivity of a given soil, but they are

expensive, and many formers in underdeveloped countries simply can’t afford them.

Farmers in countries with highly weathered soils have been through hundreds of

generations of slash and burn forming. Do others have the right to tell them how to

produce their food, when they are producing only enough to live on? These questions

will present future generations with many challenges. Many of these can be solved

with proper soil management. To manage soil properly, a thorough understanding of

the physical properties o f soil will be extremely beneficial.

W ill people be able to sustain food production or will the Earth’s human

population crash due to starvation brought on by poor soil management? Only time

will tell for sure. Humans have the potential fo r supplying the world with food, as well

as the ingenuity to be able to do this for many generations to come. Plants provide

life; soil provides plants. Proper soil management will provide food for all.

234

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX B

LIST OF EQUATIONS

Problem Equation

P, = M JV% ...... Particle density

Pb = M/V, = M ^V, + V, + Vw) ...... Bulk density

f = V/Vt = (V, + VW)/(V, + V,+ Vw) Porosity

f= [(W wet-W dry)/VJxlO O ...... Porosity

V = Igr^D, - D J/9n ...... Stokes’ Law

S = VJVf = Vw/(V 1 + Vw) ...... Degree of Saturation

= V7Vt= V w/(VI + Vf) ...... Volume wetness

w = M ^/M j...... Mass wetness

e = (V +V W =V/(Vt-Vf) ...... Void ratio

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPEMDIX C

RELATIVE SALT TOLERANCE OF WOODY ORNAMENTAL PLANT SPECIES IN ALPHABETICAL ORDER.

VT = Very Tolerant, T = Tolerant, MT = Moderately Tolerant, S = Sensitive and VS = Very Sensitive. This list applies to established plants only; young plants, newly transplanted plants, and seedlings behave differently from established plants, and in general, are far more sensitive to salinity than established plants. This list also applies to plants that are N O T under any other stresses, and assumes proper cultural conditions are met. (Adapted from Lumis, 1973, 1975, Johnson, 1999, D irr, 1974, 1975, 1976, 1990, Hanes, 1970, Hofstra, 1975, Monk, 1961, 1970, Pellett, 1972, Shortle, 1970, W yman, 1965, 1969, Francois, 1982, 1978, Buschbom, 1968, Carpenter, 1970, Allen, 1994, Bernstein, 1972, Perry, 1998, Fitzgerald, 1995, Michigan State University Cooperative Extension Service, 1996, Colorado State Cooperative Extension Service, 1997, and USDA Salinity Research Lab, 1990.)

Abies balsamea S Abies concolor MT Acer campestre MT Acer ginnala MT Acer griseum MT Acer miyabei MT Acer negundo MT Acer nigrum MT Acer palmatum MT Acer platanoides T Acer pseudoplatanus T

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Acer rubrum MT Acer saccharinum T Acer saccharum S Acer tataricum S Acer truncation MT Acer xfreemanii MT Aesculus flava MT Aesculus glabra VT Aesculus hippocastanum T Aesculus xcamea MT Ailanthus altissima T Alnus glutinosa S Alnus incana S Alnus rugosa MT Amelanchier arborea MT A melanchier canadensis T Amelanchier laevis MT Amelanchier sp. S Amelanchier xgrandiflora MT Asimina triloba MT Berberis koreana MT Berberis thunbergii S Betula allegheniensis T Betula lenta T Betula nigra MT Betula papyrifera MT Betula pendula MT Betula populifolia T Bougainvillea spectabilis VT Buxus microphylla var. japonica S Buxus sempervirens S Carpinus betulus S Carpinus caroliniana S Carya cordiformis MT Carya illinoensis MT Carya ovata S Carya sp. S Castanea dentata MT Catalpa bignonioides MT Catalpa spedosa MT 237

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Celtis laevigata S Celtis ocddentalis S Celtis reticulata MT Cerddiphyllum japonicum MT Cerds canadensis S Celtis ocddentalis S Chaenomeles spedosa S Chamaecyparis pisifera S Cladrastis kentukea MT Comus sericea S Comus altemifolia MT Comus florida MT Comus mas S Comus racemosa S Comus stolonifera S Corylus avellana S Corylus columa S Corylus sp. S Cotoneaster congestus S Crataegus crus-galli MT Crataegus laevigata S Crataegus mollis S Crataegus monogyna MT Crataegus oxyacantha S Crataegus phaenopyrum T Crataegus punctata S Crataegus Vaughn' s Crataegus viridis W in te r King' s Crataegus xlavallei s Diospyros virginiana s Elaeagnus angustifolia T Elaeagnus pungens MT Euonymus alata VT Euonymus europaeus S Euonymus japonica var. grandiflora T Fagus grandifolia S Fagus sylvatica S Fraxinus excelsior T Forsythia xintermedia T

2 3 8

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fraxinus americana T Fraxinus excelsior MT Fraxinus pennsylvanica T Fraxinus quadrangulata S Ginkgo biloba MT Gleditsia triacanthos T Gymnodadus dioicus S Hamamelis virginiana MT Hibiscus rosa-sinensis S Ilex comuta VS Ilex opaca T Ilex vertidllata T fuglans anerea T fuglans nigra S fuglans regia S funiperus chinensis MT funiperus communis T funiperus horizontalis MT funiperus horizontalis 'Plumosa' MT funiperus scopulorum T funiperus sp. MT funiperus virginiana T Koelreuteria paniculata MT Lantana camara MT Larix deddua T Larix laridna T Larix leptolepsis T Ugustrum amurense MT Ligustrum sp. MT Ugustrum vulgare S Uquidambar styradflua MT Uriodendron tulipifera S Lonicera japonica S Lonicera tatarica VT Madura pomifera MT Magnolia acuminata MT Magnolia grandiflora S Mahonia aquifolium VS Malus sp. S

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Metasequoia glyptostroboides S Morus alba T Morus rubra T Nyssa sylvatica MT Ostrya virginiana S Parthenodssus quinquefolia VT Phellodendron amurense MT Philadelphus coronarius T Photinia sp. VS Photinia xfraseri s Picea abies MT Picea asperata T Picea glauca S Picea mariana S Picea pungens VT Picea pungens var. glauca T Pinus banksiana MT Pinus cembra T Pinus mugo T Pinus nigra VT Pinus pinea T Pinus ponderosa MT Pinus resinosa S Pinus rigida T Pinus strobus VS Pinus sylvestris s Pinus thunbergiana s Platanus ocddentalis s Platanus xacerifolia vs Platanus xhybrida s Populus alba VT Populus deltoides VT Populus grandidentata MT Populus nigra 'Italica' S Populus tremuloides MT Potentilla fruiticosa VT Prunus americana S Prunus avium MT Prunus cerasifera MT

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Prunus padus T Prunus pennsylvanica S Prunus sargentii T Prunus serrotina T Prunus virginiana T Pseudotsuga menziesii T Pyracantha graberii MT Pyrus calleryana 'Bradford' MT Pyrus kawakamii VT Pyrus sp. MT Quercus alba S Quercus bicolor S Quercus coccinea S Quercus ellipsoidalis MT Quercus imbricaria MT Quercus macrocarpa MT Quercus muehlenbergii S Quercus palustris S Quercus prinus S Quercus robur S Quercus rubra S Quercus stellata MT Quercus velutina S Rhamnus cathartica T Rhamnus frangula MT Rhamnus sp. T Rhodotypos scandens VT Rhus aromatica T Rhus glabra T Rhus typhina T Ribes alpinum T Robinia pseudoacacia VT Robinia pseudoacada 'Umbraculifera' T Rosa multiflora S Rosa rugosa VT Rosa sp. S Rosmarinus ofjpanalis MT Salix alba 'Tristis' T

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Salix alba MT Salix alba Vitellina' T Salix discolor T Salix matsudana ’Tortuosa’ T Salix nigra MT Salix purpurea 'Nana' S Salix sp. MT Sambucus canadensis S Sassafras albidum S Sophora japonica T Sorbus americana MT Sorbus aucuparia T Sorbus decora T Sorbus sp. MT Spiraea xvanhouttei T Symphoricarpos albus VT Symphoricarpos orbiculatus S Syringa amurensis var. japonica T Syringa pekinensis T Syringa reticulata MT Syringa vulgaris VT Tamarix pentandra VT Taxodium distichum MT Taxus cuspidata MT Taxus sp. T Thuja ocddentalis S Tilia americana S Tilia cordata s Tilia euchlora s Tilia platyphyllos T Tsuga canadensis VS Ulmus americana MT Ulmus glabra T Ulmus parvifolia MT Ulmus pumila T Ulmus rubra MT Viburnum americanum T Viburnum dentatum MT

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Viburnum lentago MT Viburnum lantana S Viburnum prunifolium MT Viburnum sieboldii MT Viburnum trilobum MT Weigela florida 'Eva Rathke' MT XCupressocyparis leylandii T Yucca filamentosa T Zelkova serrata T

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX D

RELATIVE SALT TOLERANCE OF HERBACEOUS PLANT SPECIES IN ALPHABETICAL ORDER.

VT = very tolerant, T = tolerant, MT = Moderately tolerant, S = sensitive, VS = very sensitive. * Means the plant is utilized ornamentally. As before, this information is for established plants, young plants and seedlings have different sensitivities than established plants. (Adapted from Colorado State Cooperative Extension, 1997, USDA Salinity Research Lab, 1999, Franco, 1993, Reggiani, 1994, Mendlinger, 1992, Francois, 1988, Kenkel, 1991, Mendlinger, 1993, Graifenberg, 1993, Francois, 1994, Ungar, 1991, Zuryak, 1993, Ishida, 1979, Sonneveld, 1983, Pitelka, 1979, N erd, 1991, Matoh, 1988, Catling, 1980, Braidek, 1984, Reznicek, 1980, Greub, 1985, Cusick, 1984)

Agropyron cristatum VT Agropyron elongatum VT Agropyron repens VT Agropyron riparium T *Agropyron smithii MT *Agropyron trachycaulum T Agrostis alba VT *Allium sativum T Alopecurus arundinaceus 'Garrison' T *Amaranthus retroflexus T Ambrosia psilostachya VT *Ammophila arenaria VT Anthurium andreanum VT Aquilegia micrantha S 244

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Argemone sp. T *Armeria maritima S Arrhenatherum elatium T Artemisia frigida MT *Arundinaria gigantea VT Aster brachyactis MT Aster ericoides VT Aster hesperius VT Aster laevis VT Aster paudflorous VT Aster subulatus VT Atriplex hastata VT A triplex nuttallii VT Atriplex patula VT *Begonia sp VT *Bromus inermis S *Bromus inermis 'Lincold' VT *6 romus inermis 'Polar' T Bromus marginatus T Buchloe dactylaides MT Calamagrostis inexpansa MT Calamagrostis negtecta VT Calochortus sp VT Corex atrubae S *Carex distans T Carex tyngbyei T Carex palaecea MT Carex pluriflora MT *Carex remenskii T *Carex praegradlis T Chenopodium album VT Chenopodium berlandieri VT Chenopodium glaucum VT Chenopodium rubrum VT Chenopodium salinum VT Chlorophytum sp. VT *Chrysanthemum 'H orim ' MT *Chrysanthemum 'Spider' MT Chrysothamnus nauseous MT *Chyrsopsis villosa VT Cirsium arvense S *Coleus blumei VT Coronilla varia 'Penngift' MT

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cucumis melo 'BG' vs Cucumis melo 'Galia' T Cucumis melo 'Revigal' MT Cucumis melo Topm ark' MT Cynara scolymus T ero m ' MT Cynodon sp. S Dactylis glomerata 'Frode' VT *Delosperma alba T *Dianthus caryophyllus 'Coral' VT *Dianthus caryophyllus 'Nora Barlow' MT *Dianthus caryophyllus 'Scania' MT Distichlis stricta MT Drosanthemum hispidum VT Elymus triticoides VT Festuca arundinacea VT Festuca elatior MT *Festuca rubra S Gaillardia pennatifido S Galium mollugo S Gentiana critina var. critina VT *Gerbera jamesonii 'Fabiola' VT *Gerbera jamesonii 'Mandarine' S Grindelias squarrosa S *Gunnera albocarpa VT *Helianthus annuus S Helianthus nuttallii S *Hippeastrum vittatum 'Diana' VT *Hippeastrum vittatum 'Red L on' S Hordeum jubatum S Hymenocyclus croceus VT *lmperata cylindrica VT *Juncus bakicus MT Kochia scoparia VT Lampranthus productus VT *Lathyrus palustris VT Lepidium densiflorum MT Lepidium ramosissium VT Liatris ligulistylis VT Limonium axillare VT Limonium vulgare MT Lolium perenne T Lolium perenne MT Lolium perenne 'N K 20' MT

246

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. *Lotus comkulatus 'Leo' S Machaeranthera xylorrhiza MT Malva pussilla T Matricaria maritima VT Medicago sativa VT Medicago sativa Travois' MT Medicago sativa T e to n ' S Melilotus alba MT Melilotus officinalis MT Mesembryanthemum sp. M T Monolepis nutalliana VT *Muhlenbergia asperifolia VT *Nicotiana retusa VT Oenothera caespitosa S Onobrychis vidaefolia 'Eski' M l *Opuntia ficus-indica MT *Opuntia humifusa S *Opuntia polyacantha MT *Panicum virgatum VT Poa pratensis 'Nugget' VS *Pelargonium xhortorum S *Phalaris arundinacea MT Phleum pratense 'Lorain' MT *Phragmites australis T *Phragmites communis VT *Pisum sativum VT Plantago major S Poa glaudfolia VT Poa pratensis 'Fylking' VT Poa pratensis 'M erion' S Poa pratensis 'N ew p o rt' S Poa pratensis 'Park' S Poa pratensis 'Pennstar' S Poa trivialis S Polygonum aviculare MT *Potentilla anserina VT Psilstrophe bakerii VT Puccinellia airoides T Pucdnellia distans T Puccinellia lemmoni T Pucdnellia sp. T Ranunculus cymblaria T Ridnus communis VT

247

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. *Rumex crispus S Salicomia rubra MT Sdrpus americanus VT Scirpus paludosus VT Secale cereale VonLochow' VT Silene gallica S Silene maritima S *Solidago canadensis T *Solidago juncea VT Solidago nemoralis T *Solidago sempervirens VT *Sorghastrum nutans VT Sorghum halapense VT Spartina patens MT *Spartina pectinata VT Spergularia marina VT Sporobolus airoides VT Stanley pinnata T Sueda cakeoliformis T Trifolium fragiferum VT Trifolium repens 'M erit' MT *Typha glauca S *Uniola paniculata MT Vitis sp. T *Yucca elata S *Yucca glauca MT Zea mays MT Zoysia micrantha S

248

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX E

COMMONLY SEEN UNTIS OF MEASUREMENT FOR ELECTROCONDUCTIVITY

Unit Common Designation Equivalency

Siemens dS/m o r mS/cm I dS/m = 1,000,000mmhos/cm

Part per Million ppm I mmhos/cm = 640ppm I ppm = I mg/L

249

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Acer tataricum subsp. ginnala subsp. tataricum Acer Boxelder maple Boxelder white fir white

APPENDIX F Maxim maple Amur Lindl ex Hildebr ex Lindl L maple hedge (Gordon & Glend) & (Gordon (Andre) Rehd(Andre) Mill(L) abelia glossy fir balsam negundo L griseum Pax (Franch) maple paperpark ginnala concolor balsamea LISTING OF PLANTPROPER NAMES W ITHAUTHORITY PROPER maintainted maintainted theby USDA theand Agricultural www.ars-grin.gov/npgs/tax/indexService, Research Acer Acer Acer miyabei Maxim maple Miyabei Acer Acer campestre Abies Abeliagrandiflora x Abies Proper nomenclature taken from Dr.H. J. Wiersema (site manager) at the National Germplasm Plant System

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Elytrigia elongata Elytrigia repens Elytrigia

hybrid wheatgrass tall horsechestnut horsechestnut wheatgrass wheatgrass crested Ohio buckeye Ohio Tatarian maple Tatarian fernleaf Moonshine yarrow Blosoom Apple yarrow common yarrow common buckeye yellow sugar maple sugar Japanese maple Japanese maple red Norway maple Norway maple Planetree maple silver Apfelblute _ L L Willd A.E. MurrayA.E. LSol Moonshine maple Freeman Marshall L Thunb L Michx maple black x camea x Hayne elongatum Nevksi (Host) glabra hippocastanum sp. cristatum Gaertn (L) truncatum Bunge maple blow purple millefolium L tataricum L saccharum millefolium L rubrum saccharinum platanoides pseudoplatanus L nigrum Agropyron repens L wheatgrass couch Aesculus Agropyron Agropyron Agropyron Aesculus Aesculus Acer Achillea Achillea Aesculus flava AcerAchillea freemanii x Acer Acer Acer Acer palmatum Acer Acer Acer Acer

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Elymus lancelatus subsp. lancelatus Elymus lanceolatus smithii Pascopyrum gigantea Agrostis

grass anthurium celery serviceberry serviceberry serviceberry beech European serviceberry Canadian black bent grass bent black garlic wheatgrass wheatgrass western streambank wheatgrass alder European alder weed alligator root red streambank

Rehdr serviceberry apple (L) Medik (L) Wiegand Link (L) L (Michx) Fem (Michx) Roth Swingle(Mill) Gaertn (L) Spreng (Duroi) Poirheaven of tree DC Garrisonfoxtail creeping ragweed perennial Gould Moench(L) alder black (Scribon & J.G. Sm.) J.G. & (Scribon laevis sp. L andreanum Andre canadensis graveolens alba rugosa retroflexus L sativum L glutinosa incana smithiitrachycaulum Love A. (Rydb) Vasey altissima arundinaceus philoxeroides Mart riparium Amelanchier grandifiora x Amelanchier Amelanchier Ammophila arenaria Amelanchier Anthurium Apium Amelanchier arborea Agrostis Ailanthus Alopecurus Amaranthus Ambrosia psilostachya Allium Alnus Alnus Agropyron Alnus Altemanthera Agropyron Agropyron to cn to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Aster tongolensis Aster Heteropappus hispidus Heteropappus

aster Blossom Peach fern lady false spirea false sea aster sea giant cane giant smooth aster smooth artemisia dwarf silver mound silver dwarf sagewort prairie heath aster heath wormwood pinks Castle Powis arabidopsis sea Splendens groundnut Purple DomePurple aster Dome Purple Powis Castle Powis Splendens _ L L L Buch Blossom Peach L Franch MaximWilld Muhl (Walter) Nana Franch L (L) Dunal(L) pawpaw L L MillMill pinks sea A. Gray A. sp. felix-femina novi-angliae subcaeruleus tripolium gigantea paucidendatus Muell F. paucidentatus Oleanta laevis L triloba brachytrichus ericoides hispidusLoss (Thunb) micrantha Regel columbine hypogaea maritima maritima elatium Aster Astilbe Aster Athyrium Aster Aster ArtemisiaArtemisiaArundinaria schmidtiana frigida Aster Aster Aster Asimina Aster Aster Artemisia ArabidopsisArgemoneArmeria thaliana Armaria sp Arrhenatherum Arachis Aquilegia N) u>

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Atriplex gardneri var. aptena var. gardneri Atriplex

Lincold smooth Lincold brome brome smooth Polar brome mountain rutabega brome smooth gray birch gray bougainvillea birch European white European paper birch paper begonia barberry Korean barberry Japanese birch black birch river beets spreaing orache spreaing salt bush salt bush salt giant saltbush giant four-winged saltbush Lincold Polar Moq) Oietr Moq) _ _ Leyss Leyss Leyss Marshall Willd Roth Marshall L L Britton birch yellow lutea Betula marginatus Steud ex Nees inermis inermis inermis napus L populifolia spectabilis pendula papyrifera sp. koreanavulgaris Palib allegheniensis lenta triangularis L nummularia Lindl patula nuttallii sp. hastata Bromus Bromus Bromus Bromus Brassica Betula Bougainvillea Betula Betula Berberis BerberisBetula thunbergiiBetula DC nigra Atriplex Atriplex Begonia Beta Betuta Atriplex Atriplex Atriplex Atriplex Ui N)

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Carex acuta var. nigra var. acuta Carex inexpansa subsp stricta Calamagrostis stricta Calamagrostis stricta subsp stricta Calamagrostis

Nutt) Columbus Nutt) (Mill) K. Koch K. (Mill) L Walter Holten L Homem Greene Greene (Ehrh) P. Gaertn P. (Ehrh) grass reed feather L (A. Gray) C.W. Gray) (A. Rehdr&E.H. Wilson L (Mull. Arg. Miq) Ex Arg. (Mull.

ovata caroliniana aponica praegracillis Boott remenskii panicea L spatrubae Reichard (L) L sp neglecta inexpansa x acutiflorax Rchb (Schrad) microphylla var. microphylla sempervirens dactyloides Carya Carpinus Carpinus betulus Carex Carex pluriflora Carex Carex Carex Carex Carex lyngbyei Calamagrostis Calamagrostis Calochortus Calamagrostis Carex distans Buxus Buxus Buchloe U» N>

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oak leaf goosefoot leaf oak lamb's quarters lamb's falsecypress red bud red quince flowering common hackberry common bluet mountain snow-in-summer Northern catalpa Northern hackberry sugar Southern catalpa Southern hickory bittemut hickory bittemut American chestnut American

Marshall) Borkh Marshall) L Wangenh) K. Koch K. Wangenh) L _ Wangenh) K. Koch K. Wangenh) pecan Moq Endl L Nakai (Sucut) (Siebold & Zucc) & (Siebold Torr hackberry netted L L (Warder ex Barney) ex (Warder Warder ex Engelm ex Warder Willd Walter aevigata glaucum album speciosa pisifera berlandieri canadensis llinoinensis reticulata iaponicumZucc & Siebold katsuratree montana tomentosum occidentalis L speciosa bignonioides dentata sp. cordiformis Chenopodium Chenopodium Chamaecyparis Chenopodium Cercis Chaenomeles Cercidiphyllum Celtis Centaurea Cerastium Celtis Catalpa Celtis Catalpa Castanea Carya Carya Carya ON to

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Moonbeam Comeliancherry dogwood dogwood panicled red-osier dogwood Cornus serecia subsp. sericea dogwood subsp. serecia red-osier Cornus Pagoda dogwood Pagoda dogwood flowering red-osier dogwood red-osier Early Sunrise Early tickseed threadleaf tickseed threadleaf Canada thistle Canada mums mums rabbitbush rubber red goosefoot red plant spider Moonbeam Horim Spider Pall) Britton Pall) Lam _ (L) Codd(L) L coleus Hogg ex Sweet ex Hogg Sunrise Early (Michx) K. Koch K. (Michx) yellowwood (L) Scop (L) Ramat Ramat stolonifera L masracemosa L Florida L altemifolia L.f, sericea L blumei grandiflora verticillata kentukea nauseous arvense x morifoiium x morifoiium x morifoiiumx Ramat mums salinum rubrum Comus Comus Comus Comus Cornus Comus Coleus Coreopsis Coreopsis Cladrastis Cirsium Dendranthema Dendranthema Dendranthema Chrysothamnus Chenopodium Chlorophytum sp Jacq J. Thunb) Chenopodium '-J U\ N)

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Cynara cardunculuc subsp. cardunculuc Cynara cardunculus Cratageus laevigata Cratageus Cotoneaster microphyllus var. microphyllus Cotoneaster glacialis

hawthorne melon melon melon artichoke hawthorne Winter King Winter Washington hawthorne hawthorne English hawthorne English hawthorne English hawthorne English hawthorne downy Turkish filbert Turkish hawthorne cockspur cotoneaster American filbert American filbert Topmark Terom VaughnKing Winter hawthorne Penngift

_ Herincq ex Lavallee ex Herincq L Jacq (L.f) Medik (L.f) Jacq DC (Poir) (Torr & A. Gray) A. & (Torr Scheele L DC (Poir) L Hook melo L BG x lavallei x melomeloscolymus L L L Revigal viridis L melo L Galia melon punctata phaenopyrum oxycantha monogyna mollis laevigata crus-galli corluma sp.congestus L varia avellana Crataegus Cucumis Cucumis Cucumis Cynara Crataegus Cucumis Crataegus Crataegus Crataegus Crataegus Crataegus Crataegus Crataegus Cotoneaster Crataegus Corylus Corylus Coronilla Corylus to i/i 00

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euonymus desert salt grass salt desert stricta var spicata Distichlis European euonymus Flashing Lights Flashing pinks cottage persimmon flower dew olive Russian wheatgrass slender bush burning maiden pinks maiden Flashing Lights Flashing Helen pinks Allwood Helen Coral BarlowNora Scania carnation carnation carnation Coral carnation Coral

Rehdr VillL pinks Cheddar Shinners L L L L L (Link) Gould ex Gould (Link) L (L) Pers(L) LL Bermudagrass iceplant

japonica var japonica grandiflora strictahispidumGreene (L) Haw deltoides x allwoodii x gratianopolitanus virginiana L pungens Thunb alatusSiebold (Thunb) plumarius L caryophyllus caryophyllus caryophyllus triticoides Pilg (Buckley) wheatgrass triticoides Leymus alba caryophyllus sp. glomerata L Frode Bermudagrass Euonymus Distichlis Drosanthemum Dianthus Dianthus Dianthus Diospyros ElaeagnusElaeagnus Elymus angustifolia Euonymus Euonymus europaeus Dianthus Dianthus Dianthus Dianthus Elymus trachycaulos Delosperma Dianthus Cynodon Dactylis to Oi VO

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Acca sellowiana Acca Gerbera daisy Gerbera bloodred cranesbill bloodred blanketflower green ash green ash blue white ash white Elijah Blue fescue Blue Elijah ash European red fescue red fescue fescue red forsythia pineapple guava pineapple European beech European American beech American Fabiola daisy Gerbera Goblinblanketflower Goblin Elijah Blue Elijah Bol ex. Adlam ex. Bol (Eckl & Zeyh) Druce Zeyh) & (Eckl L Holm L Marshall Michx L L L (0. Burret Berg) jamesonii jamesonii Adlam ex. Bol Mandarine sanguineum x grandiflora x Houtte Van ex hort. pubescens critina var critina pennatifida L pennsylvanica americana L quadrangulata glauca Vill sp. excelsior rubra intermediax Zeb arundinacea Schreb elatior Schreb arundinaceae Festuca sp. sylvatica L grandifolia Ehrs Gerbera Gerbera Galenia GaliumGaliumGauxGentiana Geranium sp. mollugo maritima L L Gaillardia Gaillardia Fraxinus Fraxinus Festuca Festuca Festuca Fraxinus Fraxinus Festuca Forsythia Feijoa Festuca Fagus Fagus Q\ o N)

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hibiscus hippeastrum

vittatum riacanthos var. riacanthos sp. L nermis rosa-sinensis LSharon of Rose nuttallii sanguinea annuus L helixsp. L L strobilacuemvirginiana M. Bieb (Pall) albocarpa dioicus Koch K (L) biloba squarrosa tinctoria Hibiscus Hippeastrum Hibiscus Heuchera micrantha HemerocallisHeuchera L Hemerocallis Helianthus Helianthus Hedera Helianthus Halocnemum Hamamelis Gunnera Gymnocladus Grindelias Ginkgo Gunnera Gleditsia Gerbera Gerbera (jamesonii to ON

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Rocky Mountain Rocky juniper Mediovariegata creeping juniper creeping common juniper common black walnut black rush Chinese juniper Chinese butternut walnut Carpatian Caesar's Brother Caesar's iris Siberian holly grass Kogon American holly American holly winterberry hippeastrum barley hosta holly foxtail barley foxtail Wediovariegata Plumosajuniper creeping Caesar's Brother Caesar's Undulata- Red Lion Red hippeastrum ex Aiton ex ndl & Paxton & ndl ail L) A. Gray A. L) _ Moench Moench Willd rush Baltic L'Herit ubatum scopulorum Surg horizontalis horizontalis nigra sp. balticus communis cinerea regia cylindrica sp. cornuta opaca vittatumvulgare L'Herit vittatum Juniperus Juniperus Juniperus Juniperus Juncus Juncus Juglans Juniperus chinensis Juglans Juglans Iris sibirica Ilex Imperata Ilex verticillata Ilex Hordeum Hosta HymenocyclusIlex croceus Hippeastrum Hordeum Hippeastrum ON N) N)

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Ligustrum obtusifolium subsp. obtusifolium Ligustrum suave

uniper Eastern red cedar red Eastern Chinese ’fitzer uniper antana wild rye wild rye wild beach privet Amur gayfeather prairie peppergrass prairie Hidcote English Hidcote lavender larch vetchling marsh kaempferi Larix Eastern larch Eastern iceplant burning bushburning scoparia Brassica Hidcote (Kitag) Kitag (Kitag) Moenchjuniper creeping _ L Hochst (L) A. NelsonA. peppergrass bushy Schrad L Mill larch (Haw) N.E. Br. N.E. (Haw) L antana (DuRoi) K. Koch K. (DuRoi) L arenarius amurense x superbumx Ingram Becky daisy shasta Becky ligulistylis Walter ramosissium densiflorum angustifolia Mill sp. palustris L productus decidua leptolepsisCarreire (Lamb) laricina scoparia (L)A.J. Scott paniculata Laxmsp raintree golden sp. chinensishorizontalis L 5fitzeriana virginiana Leymus Ligustrum Leucanthemum Leymus Liatris Lepidium Lepidium Lavandula Lathyrus Lathyrus Lampranthus Larix Larix Larix Juniperus Kochia Koelreuteria LantanaLantana camara Juniperus Juniperus Juniperus ON U> NJ

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Morden Gleam Morden purple loosestrife purple tomato Tatarian honeysuckle Japanese honeysuckle American sweetgum American English NK20 ryegrass sea lavender sea lilyturf ryegrass English privet common privet common Morden Gleam Morden NK20 _ Ruprhoneysuckle Amur Mill tomato Thunb Sm Sm Decne Sm LL privet common maackii virgatum comiculatusesculentum Leotrefoil foot bird's cheesmanii styracifiua vulgare latifolium Soldano muscari tulipiferatree tulip sp. LoniceraLonicera tatarica Machaeranthera xylorrhiza Lotus Lycopersicon Lythrum Lycopersicon Lonicera japonica Liquidambar LimoniumLimonium axillare Liriodendron Lolium perenne Liriope Lolium perenne LigustrumLimoniumLimonium vulgare sp. Ligustrum Ligustrum vulgare K) ON

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subsp. maritimum subsp. Tripleurospermum maritimum Tripleurospermum

tobacco red mulberry red scratch grass scratch iceplant iceplant white mulberry white Blue Stocking bee Stocking Blue balm mayweed alfalfa alfalfa crabapple coastal scentless coastal magnolia magnolia southern grapeholly Oregon cucumber tree cucumber mallow dwarf Blaustrumpf Teton alfalfa Travois

Trin) Parodi Trin) L (Nees & Meyon ex Meyon & (Nees (Schult) Greene(Schult) weed poverty L L W.C. Cheng & Hu redwood dawn MedikLam honey-clover meliot field L L (L) W.D.J. Koch W.D.J. (L) L L Nutt (Pursh) Sm retusa L tobacco rubraasperifolia L tabacum Sp. crystallinum nutalliana alba L didyma L albus officinalis sativa L sativa L maritima sativa acuminata sp pussilla grandiflora aquifolium Nicotiana Morns Muhlenbergia Nicotiana Monolepis Morus Mesembryanthemum Mesembryanthemum Melilotus Melilotus MetasequoiaMonarda glyptostroboides Medicago Medicago Medicago Malus Matricaria Malva Magnolia Mahonia Magnolia to ON

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Amur corktree Amur mockorange sweet perennial fountain perennial grass ribbon geranium grass switch grass switch geranium zonal prickly pear prickly American hophombeam grass switch primrose tufted evening tufted prickly pear prickly pear prickly humifusa Opuntia black tupelo black Nugget cattail meadow Eski clover holy Rupr ThunbDress photinia photinia tip red BenthHillL sage Russian parsley L'Herit (L) Planch(L) creeper Virginia L Haw Mill (L) Koch K. (Mill) pear prickly pratense L arundinacea L sp. virgatumquinquefolia hortorumx L Bailey L.H. odoratumpolyacantha Scop (L) virginiana woodruff sweet viciifolia Scop humifusa Raf (Raf) sylvatica Marshall PhellodendronPhiladelphus amurense Phleum Photinia coronarius Photinia sp fraseri x PennisetumPerovskiaPetroselinum alopecuroidesPhalaris L atriplicifolia sp. Pelargonium Panicum Parthenocissus Pelargonium Opuntia Ostrya Panicum sp. Onobrychis Galium OpuntiaOpuntia ficus-indica Oenothera caespitosa Nutt Opuntia compressa Raf (Rat) Nyssa ON ON to

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Japanese black Japanese black Japanese pine Scotch pine Scotch pine White Pine White Ponderosa pine Ponderosa Austrian pine Austrian Norway spruce Norway white pine white pine jack spruce Colorado Blue Colorado dragon spruce dragon common reed common common reed common

Cav) Trin ex Steud Trin Cav) reed common Pari L Mill Aiton pine red Japanese Lawson Turra Arnold J.F. pine mugo P. Lawson & C & Lawson P. Lamb (L) H. H. Karst (L) Englem Voss (Moench) spruce White Mast (Cav) Trin ex Steud ex Trin (Cav) thunbergiana thunbergii Pari strobussylvestris L resinosa nigra ponderosa cembra L pine stone Swiss abies strobus L glauca pungens var glauca var pungens asperata communis australis Steud ex Trin Cav) communis Pinus Pinus Pinus Pinus PinusPinus rigida Pinus pinea L Pinus Pinus Pinus Pinus mugo Pinus banksiana Pinus Picea Picea Picea Picea Phragmites Phragmites Phragmites "4 ON

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Poa glauca Poa Kentucky bluegrass Kentucky knotgrass poplar white cottonwood rough bluegrass rough Kentucky bluegrass Kentucky bluegrass Kentucky London planetree London planetreeglaucantha bluegrass acerifolia x Platanus Sycamore pea broadleaf plantain broadleaf maritime pine maritime Pennstarbluegrass Kentucky Newport Parkbluegrass Kentucky Flykingbluegrass Kentucky

W Bartram ex Bartram W Marshall (Aiton) Willd (Aiton) Vahl (Aiton) Willd (Aiton) Banks ex Gaertn ex Banks Aiton pratensis pratensis trlvialis pratensis pratensis pratensispratensis Merion glaucifolia x acerifolia x majoroccidentalis L L pinaster sativum L sp PolygonumPopulus aviculare deltoides Poa Populus alba Poa Poa Poa Poa Poa Poa Poa Platanushybrida x Platanus Plantago Platanus Pinus Pisum Pittosporum N) 00 C\

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callery pear callery Bradford pear Bradford Lemmon's alkali Lemmon's grass Nuttall's alkali grass alkali Nuttall's douglasfir grass European alkali European black cherry black chokecherry Sargent cherry Sargent bird cherry bird bird cherry bird fire cherry fire American plum American sandcherry poplar cinquefoil grass goose quaking aspen quaking talica poplar Lombardy Decne Roem firethom Maxim firethom _ _ Nutt grass alkali (Schult) Hitchc (Schult) (Jacq) Pari (Jacq) Ehrs L.f. Rehdr Ehrh Michx Michx Marshall calleryana Decne Bradford sp. nuttaliana L grass alkali Nuttall's bakerii menziesii Franco (Mirb) serrotina virginiana sargentii padus aviumcerasifera (L)L grandidentata nigra L americana tremuloides Pyrus kawakamii PyracanthaPyrus sp. Pyracantha graberii Puccinellia Puccinellia Puccinellia lemmoni Hitchc (Vasey) Psilstrophe Puccinellia airoides Puccinellia distans Prunus Prunus Pseudotsuga Prunus Prunus pennsylvanica Prunus Potentilla fruticosa Prunus Prunus PotentillaPrunus anserina Populus Populus Populus n N) O NO

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Frangula alnus Frangula Quercus montana Quercus black locust black apline currant apline castor bean castor staghom sumac staghom fragran sumac fragran sumac shining buckthorn buckthorn English oak English chestnut oak chestnut oak red Hill's oak Hill's white oak white swamp white oak white swamp Mill buckthorn glossy ThunbAiton jetbead black LamPurshoak black buttercup marsh Wangenhoak post Munchh oak pin Michxoak bur Michx oak shingle Munchhoak scarlet E.J. Hill E.J. Decne pear Willd pseudoacacia alpinum communis frangula aromatica typhina cathartica sp scandens stellata velutina rubra robur muehlenbergiipalustris Englemoak chinkapin prinus macrocarpa bicolorellipsoidalis Willd sp. alba Ricinis Robinia Ribes Rhamnus Rhus RhusRhus glabra Rhamnus Rhodotypos RanunculusRhamnus cymblaria Quercus Quercus Quercus Quercus Quercus Quercus Quercus Quercus mbricaria Quercus Quercus QuercusQuercus coccinea Quercus Pyrus ->) N1 O

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elderberry black willow black purpleosier dwarf willow lyebush corkscrew willow corkscrew willow pussy willow pussy locust weeping willow weeping willow white Goldsturm black Goldsturm Susan eyed rosemary dock umbrella black umbrella rugosa rose rugosa Tortuosa Vitellinawillow white Vitellina Tristis Goldsturm Rehdr Marshall L Muhl Boynt & Bendle & Boynt Torrglasswort dwarf L rose Thunb rosa multiflora sp.canadensis L L.f. nigra purpurea L Nana discolor pseudoacacia L Umbraculifera fulgida var. sullivantii var. fulgida bigelovii rubra alba rubra crispus officinalis L europaeafruticosa chickenclaus rugosasp Thunb multiflora Sambucus Salix Salix Salix SalixSalix matsudana Salsola sp. Salix alba Rumex SalixSalix alba Salicomia Rosmarinus Rudbeckia Salicomia Salicomia Salicomia Salicomia Rosa Rosa Rosa Robinia

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Japanese pagodatree goldentod Crown of Rays of Crown goldenrod goldenrod dune goldenrod Canadian goldenrod Canadian goldentod goldenrod catchfly catchfly French campion sea American bullrush americanus American Schoenoplectus rye cereal VonLochnow

Marshall ash mountain Unofficial - not yet - not Unofficial attributed Aiton LRays of Crown Roth (L) Roem & Schult. & Roem (L) L Ohba H. (Boreau) Herbstfreude 'Herbsfreude' sedumJoy Hylotelephium Autumn palustris rush spike Eleocharis common (Nutt) Nees(Nutt) ex Volkart (Pers) Keller R. & Schinz sassafras Ohba H. (Boreau) stonecrop americana japonica Schott (L) sempervirens L junceanemoralis goldentod canadensis L sempervirenssp. L L maritima juncea paludosus sp.gallica L L americanus cereale albidum Sorbus Sophora Solidago Solidago Solidago Solidago Solidago Solidago Solidago Solidago Scirpus Sedum Silene Silene Silene Scirpus Secale Sedum spectabile Sassafras Scirpus sp. N) S)

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reticulata subsp. reticulata Syringa pekinensis Syringa reticulata subsp. reticulata Syringa ndian grass ndian common lilac common alkali sakaton alkali snowberry Japanese spirea Japanese lesser sea spray sea lesser spirea Vanhout mountain ash mountain grass saltwater cordgrass marshgrass marshgrass mountain ash mountain ash mountain sorghum Sarg) C.K. Schneid C.K. Sarg) Aiton) Muhl Aiton) _ Rupr lilac Peking (Blume) H. H. Hara(Blume) lilac tree Japanese _ L.f. (Torr)Torr S.F. Blake (L) Link cordgrass prairie

pekinensis vulgaris L japonica amurense var. amurense arioides pinnata depressaorbiculatus L Moench coralberry calceoliformis L albus marina Griseb (L) x vanhouttei x Zabel (Briot) anglica Hubb CE altemiflora Loisel halepense Moenchpatens pectinata ohnsongrass sp. nutansbicolorsp. Nash L) Moench aucuparia decora Syringa Syringa Syringa Sporobolus Stanely Sueda Sueda Symphoricarpos Symphoricarpos Spiraea japonica Spergularia Spiraea Sorghastrum Spartina Spartina Spartina Sorghum Spartina Sorbus Sorbus Sorghum Spartina Sorbus ^1 u» N>

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North American sea American North oats Canadian hemlock Canadian cattail elm smooth angustifolia Typha elm Siberian strawberry clover strawberry wheat big leaf linden leaf big Japanese yew Japanese littleleaf linden littleleaf Eastern arborvitae Eastern bald cypress bald yew Japanese tree lilac tree Japanese American linden American L Muhl elm red L LJacq elm American elm lacebark K. KochK. Lem linden Crimean L Mill Ledeb Rich(L) Rich Zucc & Siebold cedar salt cypress bald (Blume) H. H. Hara (Blume) Ledebcedar salt ramosissima Tamarix paniculata L canadensis glaucaamericana parvifolia L pumila rubra fragiferumaestivum L L glabra Huds euchlora platyphyllos Scop cuspidata ramosissima americana sp Nutt sp. pentandra reticulata occidentalis L Tsuga Typha Ulmus Ulmus Ulmus Ulmus Uniola Trifolium Triticum Ulmus Tilia Tilia Trachelospermum sp. Taxus Taxus Tamarix Tilia cordata Thuja Tilia TaxodiumTaxodium distichum Tamarix Syringa N) -4

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americanum Viburnum opulus var. opulus Viburnum zoysia grass zoysia small soapweed small yucca com Leyland cypress Leyland viburnum viburnum weigela American cranberrybush sevenbarkarrowwood arborescens Hydrangea Nannyberry viburnum viburnum blackhaw viburnum siebold viburnum viburnum wayfaringtree Eva Rathke Eva

Hance EngelmNutt palmilla (Thunb) Makino (Thunb) zelkova Japanese (AB Jacko & Dallim) & Jacko (AB Dallim L Michx vines grape Aiton Miq micrantha elata Filamentosa L maysserrata L leylandii florida Wenge weigela Florida DC A. (Bunge) lentago prunifolium sp. sp americanum dentatum trilobum sieboldii Yucca Yucca Yucca glauca Zoysia Zea Zelkova Weigela Xcupressosyparis Viburnum Viburnum Viburnum Vitis Weigela Viburnum Viburnum Viburnum Viburnum lantana Viburnum Ul •o to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GENERAL DISCUSSION

Sodium chloride affects plants in many ways. It can cause osmotic changes

within the plant and affect how the plant interacts with soil water. It can change

nutrient relations within the plant, affecting the availability o f nutrients by changing the

composition o f the ions on the cation exchange, by changing the pH of the soil, or by

disrupting the natural chemical and physical properties of the soil. Both ions can be

toxic to plants. These effects are by no means mutually exclusive. Therefore it is

difficult to separate toxic effects from osmotic effects in practice. In the literature on

salinity tolerance in plants, there exist many examples o f apparently misleading

evidence for various mechanisms on salt tolerance. For example, one researcher may

conclude a given species’ salt tolerance is directly correlated to its ability to tolerate

sodium in the shoot tissue (Dirr, 1974, 1975). At the same time, another researcher

will conclude exactly the opposite for a different species (Franco. 1993). This same

pattern follows with any given conclusion for the ability o f plants to tolerate salt.

W hat is to be concluded from this contradictory evidence? The ability o f plants to

tolerate various levels of salt in the soil may be almost as varied as the number of plant

species on the planet! Unfortunately, there is no simple answer to this question.

Environmental factors will also affect plant salt tolerance. A plant may be determined

2 7 6

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to be salt tolerant under certain environmental conditions; however, a small change in

any external factor may dramatically alter that tolerance. This research concluded that

tw o species o f Coreopsis were highly sensitive to soil applied sodium chloride. Y et

these same species are also listed as salt tolerant by observation of the plants growing

along the seaside (Heriteau, 1992). The difference between these two citations may

be the growing media. A small change in soil texture, soil pH, or any other physical

property may impact plant survival. Plants stressed fo r other reasons may also exhibit

increased susceptibility to what otherwise would be non-lethal levels of salt in the soil

(Levitt, 1972).

There has been considerable discussion on what exactly constitutes salt

tolerance in plants. Are the plants tolerating, resisting, avoiding or adapting to salt in

the environment? The correct answer is “yes”- In some cases, they are avoiding.

Most glycophytes practice this method. They grow in locations were salt is not a

factor in their immediate environment. Several species o f halophytes also practice a

variation of this technique. They may be able to tolerate salt in the soil during the

vegetative stage, for example, but be highly sensitive to those same salt levels during

seed germination, early growth, or flowering. These plants will avoid salt by a subtle

change in life cycle, having their most sensitive stage occurring at a time when the salt

levels are the lowest. O ther species produce seeds that are capable of remaining

dormant and viable until the salt levels decrease. Many factors may play a role in plant

avoidance o f salt: rapid growth during times o f high salt levels, soil pH,

presence/absence of other nutrients, amount of moisture in the soil, and competition.

277

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The question of whether the plants utilized in this study are resistant to salt or

tolerant to salt is a reasonable one to ask. Accepted terminology in the literature is to

term the plants “salt tolerant”. However, resistance and tolerance are closely related.

Therefore, the answer to the question, “Are the plants salt resistant or salt tolerant?”

is, “Yes”.

There are several types o f resistance seen in plants (to any disease, biotic or

abiotic). The basic definition of resistance is the ability to “oppose the perturbation

through the expression of pre-existing mechanisms of defense while maintaining their

initial and internal physiological mode” (Ungar, 1991). There are several types of

resistance. True resistance is genetically controlled by one o r more genes.

Horizontal resistance is controlled by a multitude o f genes working in conjunction

with each other. This type of resistance confers a limited ability to overcome a

diverse array of diseases and stressors. Vertical resistance confers limited

susceptibility to one disease, but provides no ability to resist other diseases. This type

o r resistance is usually controlled by one gene. Complete resistance is a

combination of both horizontal and vertical resistance. The plant has several genes

that provide vertical resistance against several diseases (Agrios, 1988).

The basic definition of tolerance is “the ability o f a plant to sustain the effects

o f a disease o r other factor without dying o r suffering serious injury or crop loss”

(Agrios, 1988). Both result from specific, heritable characteristics and are difficult to

separate on a genetic basis. Tolerance may simply be a strong form of horizontal

resistance. Some have labeled tolerance a type of resistance, termed apparent

278

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. resistan ce (Agrios, 1988). Another basic difference is tolerant plants will produce a

better crop without the stress, although they will produce a good crop with it. Are

the plants in this study tolerant o r resistant to salt? In some species tolerance may be

more correctly called a resistance, however, with many species the strict definition of

tolerance will suffice.

Many species are perhaps more accurately labeled ad aptors. They have some

internal, physiological change to adapt to the presence of salt in the environment.

Adaptation involves one o r several changes within the plant; some o f these changes

may be visible, others are not. Many species will switch from C4 metabolism to CAM

metabolism in the presence of salt (Bonnert, 2000). Others will retranslocate the

various ions back to the roots (Matoh, 1988). Others compartmentalize the salt in

various locations (glands, hairs, vacuole) (Ungar, 1991). Again, there are almost as

many adaptations as there are species o f plants, none of which are mutually exclusive

and many species will utilize several methods, often at the same time. On the genetic

level there are plants with one gene that confers salt tolerance and the presence or

absence o f this gene would indicate if the plant was salt tolerant or not (W u, 1996).

There are other species where tolerance is conferred by several genes. Finally there

are species that are facultative halophytes; plants that are salt tolerant, but only the

presence of salt will “turn on” the genes that confer tolerance (Bonnert, 2000). Many

species are tolerant of low levels o f salt if given time to adapt to the stress. If the

stress is applied quickly, the plants are killed (Ungar, 1991). None of these

mechanisms are mutually exclusive.

279

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The results of this study indicate the need for more work to be done with

herbaceous ornamentals. There is a high degree of variance for this diverse group of

plants. This is evidenced by the genus Dianthus where D. xallwoodii ‘Helen’ was

tolerant to soil applied salts but D. deltoides ‘Flashing Lights’ was very sensitive. W ould

species morphologically similar to D. xallwoodii be as tolerant? The variable tolerance

within the two cultivars of Hemerocallis would also lead us to believe there could be a

huge variation between cultivars of the same species.

Tw o species showed few external symptoms save for stunting. W as

photosynthesis reduced in these species? Was growth reduced due to the action of

one or more hormones within the plants? W ere these plants compartmentalizing or

retranslocating the salt at the expense of tissue production? These two species both

showed a lack of any symptom save for stunting. In a landscape situation, this may be

an acceptable response, as the plants would still flow er and look healthy to passersby.

However, what would the effect of several severe winters have on these species?

Does the tolerance come at such a great expense that several seasons of high salt

levels would kill the plants? Clearly, these plants should be looked at more closely.

Testing of additional species will provide landscape planners with a more

complete list of plants that would survive in situations of potentially high salt

applications. From a practical point of view, homeowners, landscape contractors,

nurserymen, and others with an interest in plant landscape performance need a bigger

list o f plants to choose from when making planting design decisions. N o t only is it

important to know which plants are likely to survive, but also it is equally important to

280

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. be aware of plants that are highly sensitive so they can be avoided. The field study

results correlated to greenhouse results, indicating that fo r the three species studies

the results of the greenhouse study predicted the survival of these plants in the

landscape. It may be a far leap to assume they would be accurate fo r all species, but

greenhouse studies have the advantage of not causing damage to field soils. In

addition, greenhouse studies are better able to isolate and control other

environmental conditions. The changes in physiology involved in a phase change would

indicate that studies on seeds, seedlings and perhaps even flowers would not prove the

most accurate. Greenhouse screenings remain, at this point in time, the fastest and

most reliable method of discerning which plants are tolerant to salt and which are not.

In addition, field tests of more than one winter season, would be greatly helpful in

discerning long-term salt tolerance fo r any group of plants.

Understanding the physiology behind salt tolerance is more complicated.

There are many mechanisms for salt tolerance, even among halophytes. The

dichotomous conclusions of a variety of researchers only illustrate the variety of

methods at work. Although some researchers feel there is little evidence for either

sodium or chloride toxicity in plants, this work has generally been conducted in vitro

and extrapolation to in vivo situations is, at best, difficult. It is known that NaCI can

and does significantly impact several aspects of plant physiology, ranging from tissue

production to photosynthesis to nutrient uptake. However, the impact on water

relations is perhaps the greatest challenge for plants, since all plants need w ater. The

difficulty in separating the two is two-fold. Plants with lowered water uptake (or other

281

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. osmotic problems) will also have slower growth, lowered photosynthetic rates etc.

Species where photosynthesis is directly impacted by the presence o f salt will also have

slower growth rates. Thus, although the route to slower growth is different and the

physiological impact cannot be seen visually, both plants will exhibit the same visual

symptom, reduced growth. An additional challenge arises when the method of

tolerance is a physiological change involving reduced photosynthesis. Finally,

experimental conditions can lead to misleading results. Plants in growth chambers are

subject to lowered light intensity, which ultimately is stressful for plants. W hole

response o f plants to salt is best studied in a greenhouse, although environmental

conditions are harder to control compared to the growth chamber.

A recently proposed hypothesis suggests the solution to plant response to

salinity is directly related to a disruption in plant hormones rather than other

physiological mechanisms (Amzallag, 2001). All species tested w ere able to overcome

the effects of a sub-lethal dosage of NaCI by the application of one or more

phytohormones. This is a relatively new area of salt studies and it deserves a closer

look.

There are several things a homeowner can do to combat high levels of salt in

the soil. The best is to reduce the level o f deicing salt applied in the winter, however,

when faced with ice and snow on sidewalks and driveways, this may not seem feasible.

Anything that can be done to improve drainage will help alleviate the problem. This

allows w ater to move below the root zone and also helps damaging chemicals move

through the soil profile that much faster. Organic m atter in the soil will also help. It

282

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. improves drainage; it slows down surface percolation and keeps the pH at a moderate

to acidic level, which makes other nutrients more available. If the pH is below 8.5 the

use o f gypsum will also cause a more rapid leaching o f sodium through the soil. If the

pH is acidic already, the use of lime has the same effect. Both the chemical methods

assume a soil with otherwise good physical properties. Finally, a homeowner can

provide large quantities o f w ater through the area during the spring. This, combined

with proper bed preparation techniques, leaches salt through the soil solution at a

time when many plants are susceptible to salt damage. The best thing, however, is to

plant highly susceptible species away from areas that receive salt as a deicing chemical.

For managers of large landscapes, the above solutions may not be practical. In

some areas, the use of snow fencing, raised beds, or windbreaks of tolerant plants may

prove helpful. Golf courses, arboreta, cemeteries and city plantings may find these

solutions viable, as the square footage is manageable. Again the best solution would be

to plant tolerant plants in locations most impacted by salt.

Due to the amount of land covered by transportation departments, the only

viable solution is to plant tolerant plants along the freeway and to hope the spring

rains are sufficient enough to leach salt through the soil profile. W hile a reduction in

the amount of deicing chemicals used on the roads would seem to be an obvious

solution, which would not only save plants, but cars, and other infrastructures, but also

money as well, it is not a likely solution in the foreseeable future. Motorists have

come to expect snow- and ice-free road surfaces. Until an environmentally safe and

inexpensive solution is found, rock salt will be continued to provide the best solution

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to maintaining safe winter driving conditions. By combining salt tolerant species with

other preventative measures, such as snow fencing, raised beds, o r even wind breaks

of tolerant plants, the list of plants suitable for public areas is almost unlimited.

The results of the field study show there can be considerable effects to the

plants from rock salt application, up to and including death. This settles the question

of lack of effect on herbaceous plants due to dormancy. Two of the three species

tested would have needed replacing in a public planting after a moderate to severe

winter. By utilizing species with proven salt tolerance, that need is eliminated.

The effects on the soil are subtler and more difficult to extrapolate. Long-term

studies on the effects of rock salt still need to be done. One season of rock salt

application was not enough to change many properties of the soil to a great degree.

The USDA has shown there are changes within some soils in Ohio after one year, but

this particular soil was more resistant to change (Jones, 1997). W ould the changes be

greater with 2 or more seasons o f application? The trends seen in this study would

indicate that several seasons o f salt application, in the absence o f leaching, could greatly

impact soil physical properties, which would, in turn, impact plant growth.

284

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