Tải bản đầy đủ - 0 (trang)
II. Characteristics of Saline and Alkali Soils

II. Characteristics of Saline and Alkali Soils

Tải bản đầy đủ - 0trang

TABLE I

Chemical Composition of Some River Waters Used for Irrigation in

Western United States a



River

Gila

Cobrado

Sacramento

Arkansas

Boise

Rio Grande

Pecos

Sevier

Columbia

Big Horn



Sampling

location



Date

sampled



P.p.m.



Eel06b



Ashurst, Ariz.

Yuma, Ariz.

Tisdale, Calif.

Ldunta, Colo.

Boise, Idaho

Eleph. B., N. Mes.

Comstock, Tex.

Delta, Utah

Wenatchee, Wn.

Thermopolis, Wyo.



4-10-32

3-21-43

2-15-47

7-21-44

11-21-38

6- -46

5- -46

10-17-45

11-29-35

7-29-35



1089

755

73

1000

99

494

2292

1634

116

428



1720

1060

94

1210

133

694

3700

2650

151

612



Ca



Mg



3.59

4.79

0.47

7.18

0.81

28 4

7.63

3 30

0.90



1.99

2.11

03 2

3.49

0.34

1.05

6.78

7.50

0.39

1.19



--



3.08



-



Milliequivalents per liter

Na

€COI



1127

4.06

022

3.47

025

3.00

23.02

1520

0.19

1.96



3.68

2.64

0.73

3.95

0.91

2.67

1.70

4.10

126

2.18



-



“These analyses were made by the U. S. Regional Salinity and Rubidoux Laboratories, Riverside, California.

ECxl06 = conductivity expressed in micromhos per centimeter.

T =trace.



G:



Na,



c1

9.95

2.05

0.09

0.62

0.05

1.10

2333

14.00

0.07

0.76

-



326

639

0.15

9.80

0.32

320

12.44

8.30

021

3.17



-



%



67.0

37.0

21.0



z



242

17.9

43.5

615

578

12.7

31.4



--



E



%



m



&-



3



m



8



E:



w



i



4



H. E. HAYWARD AND C. H. WADLEIGH



conditions ground water may contribute to the salinization of the soil.

This is particularly true if the water applied carries appreciable amounts

of dissolved salts as is frequently the case in irrigated areas. Furthermore, loss of drainage water from irrigated areas upstream and the

pick-up of saline ground water result in more salt downstream. The

range of quality in irrigation waters is shown in Table I which gives t,he

parts per million, electrical conductivity, chemical composition and

sodium percentage for a number of river waters used for irrigation in

western United States.

Although many salt problems are man-made, it should be recognized

that the occurrence of saline and alkali areas is related fundamentally

to changes in climatic conditions, the chemical composition of soil-forming materials in the primary rocks, and to geologic changes that have

taken place with time due to deposition, erosion, weathering and other

processes (Harris, 1920; Hilgard, 1906; de Sigmond, 1938).

There are numerous publications dealing with various aspects of saline

and alkali soils, some of which go back before the turn of the century

(Burgess, 1928; Gardner, 1945; Goss and Griffin, 1897; Hibbard, 1937;

Hilgard, 1886, 1895-1898; Kelley, 1937; Powers, 1946; Tinsley, 1902).

Magistad (1945) has reviewed a number of the schemes of classification

for saline and alkali soils and has reported the terminology proposed for

them. I n view of the differences in the meanings of terms as used in the

literature, the U S . Salinity Laboratory (1947) has published a terminology and description of saline and alkali soils. The terms as defined

in that publication will be followed in this review and are given below:



Alkali Soil-A soil that contains sufficient exchangeable sodium to int.erfere with the growth of most crop plants, either with or without appreciable quantities of soluble salts. (See Saline-Alkali and NomalineAlkali Soil).

Nonsaline-Alkali S o i G A soil which contains sufficient exchangeable

sodium to interfere with the growth of most crop plants and does not

contain appreciable quantities of soluble salts. The exchangeablesodium-percentage is greater than 15, the conductivity of the saturation extract is less than 4 millimhos per centimeter (at 25°C.) and the

pH of the saturated soil usually ranges between 8.5 and 10.

Saline-Alkali Soil-A soil containing sufficient exchangeable sodium to

interfere with the growth of most crop plants and containing appreciable quantities of soluble salts. The exchangeable-sodium-percentage

is greater than 15 and the conductivity of the saturation extract is

greater than 4 millimhos per centimeter (at 25°C.). The pH of the

saturated soil is usually less than 8.5.



5



PLANT GROWTH ON SALINE AND ALKALI SOILS



Saline Soil-A nonalkali soil containing soluble salts in such quantities

that they interefere with the growth of most crop plants. The conductivity of the saturation extract is greater than 4 millimhos per

centimeter (at 25"C.), the exchangeable-sodium-percentage is less than

15, and the pH of the saturated soil is usually less than 8.5.

Alkalization--A process whereby the exchangeable sodium content of

the soil is increased.

Salinization-The process of accumulation of salts in the soil.

Exchangeable-sodium-percentage-This

term indicates the degree of

saturation of the soil exchange complex with sodium and is defined as

follows:

Exchangeable sodium (m.e. per 100 g. soil)

x 100

ESP = Cation exchange capacity (m.e. per 100 g. soil)

Soluble-sodium-percentage-The proportion of sodium ions in solution in

relation to the total cation concentration, defined as follows:



SSP =



Soluble sodium concent.ration (m.e. per liter)

Total salt concentration (m.e. per liter)



x 100



This term is used in connection with irrigation waters and soil extracts.



111. PHYSIOLOGICAL

BASISOF SALTTOLERANCE

Successful agriculture on saline and alkali soils requires the use of

crops capable of producing a sat.isfactory yield under moderate intensities of salt or alkali accumulation. The question arises immediately as

to what constitutes the physiological capacity of a plant to tolerate salt

or alkali. That is, what is salt tolerance and how may it be defined?

The salt tolerance of a variety or a species may be evaluated in three

ways. Firstly, salt tolerance may be looked upon as the capacity to

persist in the presence of increasing degrees of salinity. A given species

may make little or no growth a t the higher levels of salt accumulation,

but i t does survive. That is, power of survival in increasingly saline

soils regardless of growth would be the measure of salt tolerance. This

is largely the criterion of the ecologist in evaluating halophytic environments, since the species most capable of persisting in a saline area becomes the climax vegetation of that area.

Secondly, salt tolerance may be regarded from the standpoint of

productive capacity a t a given level of salinity. For example, a number

of varieties of a given crop may be tested in a soil having a certain degree

of salinization and the highest yielding variety may be designated as the

most salt tolerant. This method of interpretation may give a differen&

evaluation of salt tolerance from the previous one, since experience has



6



H. E. HAYWARD AND C. H. WADLEIGH



shown that the capacity to produce well a t moderate levels of salinity

does not necessarily imply the ability to persist a t higher levels of salt

accumulation. This second criterion is especially useful to the agronomist

in comparing the performance of strains and varieties of a given crop.

Thirdly, the relative performance of a crop a t a given level of soil

salinity as compared to its performance on a comparable nonsaline soil

may be used as a criterion of salt tolerance. This method has certain

advantages over the previously mentioned concepts in that comparisons

between species are more readily evaluated. For example, although preference as to salt tolerance should be given to that variety of alfalfa

having the highest production on saline soil regardless of performance in

the absence of salinity, one could hardly compare salt tolerance in alfalfa

with that in cotton without taking into account the yielding power of

these respective crops when growing on comparable nonsaline soils.

Evaluating salt tolerance on the basis of relative yield will not necessarily result in the same order of classification as power of survival a t

high levels of salinity, but it will provide a more useful basis of appraising agronomic crops to be grown on moderately saline soil. I n variety

and strain testing, tshe data on relative yield should be supplemented by

data on absolute yield; ie., a strain may have a comparably poor relative

yield because of unusual vigor of growth on the nonsaline soil, and yet

yield the best of any of the strains a t the given level of salinity. Everything considered, defining salt tolerance on the basis of relative yield to

that of the nonsaline condition is to be preferred for general agronomic

use.

I n discussing the physiological basis for the various degrees of salt

tolerance which prevail among crop plants, it may be helpful to consider

the characteristics of the natural halophytes. I n a review of this group

of plants, Uphof (1941) discusses the physiological characteristics of

halophytes, but it is apparent that the specific physiology of these plants

is not well known. The early investigators concluded that halophytism

was essentially xerophytism, since both halophytes and xerophytes are

adapted physiologically or anatomically to a scarcity of water. Anatomical studies, such as those of Chermezon (1910), later revealed that

the two groups of plants must be regarded as distinct physiologically.

Halophytes tend to have relatively high values for the osmotic pressure

of the tissue fluids. Fitting (1911) used an indirect method to measure

the osmotic pressure of the cell contents of various species of plants on

the North African Desert. The highest osmotic pressures, 100 atmospheres or above, were found in plants growing on dry or highly saline

soils. Those growing on moist nonsaline soils had osmotic pressures of

10-20 atm. The osmotic pressure of the various species tended to vary



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

II. Characteristics of Saline and Alkali Soils

Tải bản đầy đủ ngay(0 tr)

×