TEXAS AGRICULTURAL EXPERIMENT STATION

R. D. LEWIS. DIRECTOR, COLLEGE STATION, TEXAS

 

   
   
 
   
   
   
 
   

SUMMARY

Both the quality of water available and the soil management practices influence the results 
with salty irrigation waters. For most successful use of saline waters. apply the following princi
Test water and soil periodically and use these analyses as a basis for planning management - '1
TEST—DON‘T GUESS.   ’

Apply water uniformly by using a properly designed irrigation system and by leveling where n vi

Apply enough water for the crop plus enough to keep salt leached to a satisfactory level.
preplant irrigation may be desirable.

Irrigate more often than necessary under non-saline conditions. _
Provide adequate drainage. Thefree water table should be at least 5 to 6 feet below the 
Select crops tolerant to your salt conditions. I
Plant good seed under optimum moisture and temperature conditions.

Fertilize to replace nutrients lost by leaching and to maintain adequate fertility.

Use soil-improving grasses or legumes to maintain good soil structure and to aid water ' 
and penetration. 
Soil amendments. such as gypsum and sulfuric acid, do not control salt. Amendments - 
beneficial where sodium is a problem. 

Consult your county agricultural agent. experiment station or other agricultural adviser for ":17
on your problems. t»

CONTENTS y
Summary . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z Amendments Do Not Neutralize Salt . . 
Introduction . , . . . . . . . . . . . . . , , . . . . . . . . . . . . . . . . . 3 some Salls Hlgllly Tmllc " " " v v  v ' v " " " 
All Waters Contain Salts . . . . . . . . . . . . . . . . . . , . . . 3 Chemlcal Analyses °l S°ll and Walel v ' ' " " 

_ _ _ TotalDissolvedSolids................§
Salt-affected S0115 and Irrigation . . . . . . . . . . . . . . . 3 Concentration oi Specific Ions ’ H _ Q . _ D 

Characteristics of Salt-affected Soils . . . . . . . . . . , . 3 Potential Sodium Hazard . . . . . . . . . . . . . 

Saline Soils . S . . . . . . . , . . . . . . . . . . . . . . . . . . . _. 3 Exchangeable Sodium Percentage . . . . . 

Nonsaline-SodicSoils . . . . . . , . . . . . . . . . . . . ..4 

Saline-Sodic Soils . . . . . . . . . . . . . . . . . . . . . . . . . 4 Leaching Requirement . .  , . . . . . . . . . . . 

Effect of Salinity on Plant Growth . . . . . . . . . . . . . . . 4 Gypsum v v v v v v v v v v v v v v v _ 

Factors Affecting Salt Accumulation . . . , . . . . _ . . . 5 Quallly °l llllgallcln Weller " v " v " v ' v " " v " v " ' 

Large Quantities of Salt Added . . . , . . . . . . . . . 5 sclllnlly Hazard v v v v v v v v v v v v v v v v v v v v v v

Little or No Salt Evaporated . . . . . . . . . . . . . . . . 5 sodlum Hazard v v v v v v v v v v v v v v v v v v v v v ‘v

Salinity Controlled by Leaching . . . . . . . , . . . . 6 B°l°n Hazard v v v v v v v v v v v v v v v v v v 

1m p r op e} Drainage Maycause Salinity I ' _ _ g 6 Carbonate and Bicarbonate Ions Haz g
Management Practices Affecting Salinity . . . . . . . . 6 Reclamlllllln v_ v v v v v v v v v v

CropsVaryinSaltTolerance . , . . . . . . . . . . ..6 Sallllesollsvv"v"vvvvvvvvvvvvvvvvvvvvvvrtt

Leaching Requirement _ _ , A A _ _ A _ A V ’ ~ , I _ ' ‘ _ t _ 7 Saline-Sodic and Nonsaline-Sodic Soils. 

Permeable Soils Essential . . . . . . . ..§ . . . . . .. 8 Sllck Spplsvvvvvvvvvvvvvvvvvvvvvvvvvvvl

Seed and Seedlings Sensitive to Salt . . . . . . . 8 Agknqwledgments

Bed Types Influence Salt Distribution . . . . . . . 9

Irrigate More Often . . . . . . , , . . . . . . . . . . . . . . . 9 References

Sandy Soils First to “Salt Out" . . . , . . . . . . . . . 9 Appendix . . . . , . . _ .  . . . . . . . . . . . . . -. . . . . . .
Level Land for UniformvWater Application. . . .10 Definitions 4 . . . . . . . . . . . . . , . . . . . . . . . . . 
Commercial Fertilizers May Aid . . . . . . . . . . . .10 Abbreviations

Use Good Cropping Practices . . . . . , . , . . . _ . .10 Factors and Conversion Formulas . . . . . r:

u’?

Salinity Control in Irrigation Agriculture

PAUL I. LYERLY and DONALD E. LONGENECKER*

if PERMANENT, PROSPEROUS IRRIGATED AGRI-
I“ CULTURE is dependent on an adequate
. supply of irrigation water of satisfac-
quality. The terms “adequate supply” and
i isfactory quality” are difficult to define since
h is influenced by the other, and both are in-
nced by the chemical and physical nature of
i soil, climate, adequacy of drainage, crops
wn and various farming practices.

In many cases, successful irrigation farming
é ore dependent on the management practices
owed than on the quality of water available.
too often too much emphasis is placed on at-
pting to answer the question, “How good is
; water?” rather than “How can this water
used best?” Frequently, too much attention
'ven to the “toxic limits” of salt concentration
a not enough emphasis directed toward the se-
ion of suitable crops and adjustment of till-
~ and irrigation practices to the water which

:-= vailable.

ALL WATERS CONTAIN SALTS

‘ All waters from surface streams and under-

und sources contain dissolved substances
wn chemically as salts. Ocean water contains
roximately 3 percent salts, or 4O tons of salts

acre-foot of water. Waters used for irriga-
, generally contain .1 to 5 tons of salt per acre-

t of water.

In general terms, salt is thought of as table
; however, thousands of different salts are

wn. Examples of common salts in irrigation

- r are table salt (sodium chloride), Epsom salt

tgnesium sulfate), gypsum (calcium sulfate),
iate of potash (potassium chloride) and bak-
soda (sodium bicarbonate). In this publica-

, the various salts found in irrigation water
be referred to collectively as salt.

The total salt content in surface and under-
und waters varies widely. Salt is dissolved
n; the soil and rock materials through which
gwater must seep before becoming available
I irrigation. Mountain streams often contain
< than one-tenth ton of salt per acre-foot of
fer. Drainage waters and ground waters in
ert valleys may contain as much as 1O to 15
s of salt per acre-fgfoot.

I Ground waters often vary widely in total salt

tent at different locations in the same gen-
l area and at various depths in the under-
und layers of the soil profile.

pectively, superintendent and assistant agronomist,
Paso Valley Experiment Station, Ysleta, Texas.

In addition, waters differ greatly in the kinds
of salt present. Some waters are relatively high
in sodium salts, such as table salt and baking
soda, while others are relatively high in calcium
or magnesium salts. The relative proportion of
the various salts is of considerable importance.

SALT-AFFECTED SOILS AND IRRIGATION

A salt-affected soil is one in which salt has ac-
cumulated sufficiently to reduce or interfere with
crop yields. The source of the salt that accumu-
lates 1n a soil usually is the irrigation water. In
some cases, however, the soil may have been salty
1n the v1rg1n state, or the salt accumulation may
have resulted from a high water table.

Most irrigation waters do not contain a suffi-
cient concentration of salt to be greatly injurious
to plant growth. However, since all surface and
underground waters do contain salt, the applica-
tron of water by irrigation adds salt to the soil.
The salt applied remains in the soil unless it is
flushed out in the drainage water or is removed
in the harvested crop. With salt being applied
with each irrigation, any condition or combination
of conditions which allows the salt to accumulate
in the soil will produce a salty soil.

Since the development of salty soils is a proc-
ess of salt accumulation, salt-affected soils can
be associated with either good or poor quality wa-
ter. Figures 1 and 2 show the effect that soil
type and management practices may have on the
results obtained from using saline water. Ob-
viously, the more salt an irrigation water con-
tains, the greater will be the likelihood for salt
conditions to develop.

CHARACTERISTICS OF
SALT-AFFECTED SOILS

Three types of salt-affected soils occur: saline
soil, nonsaline-sodic soil and saline-sodic soil}
Since different management and reclamation
practices may be required, it is important to dis-
tinguish among these different salt conditions.

Saline Soils

A saline soil is one which contains sufficient
soluble salt to interfere with the growth of most
plants. Sodium salts are present, but in rela-
tively low concentration in comparison with cal-
cium and magnesium salts. Saline soils often
are recognized by the presence of white crusts on
the soil, by spotty stands and by stunted and ir-
regular plant growth. Ordinarily the pH is
lower than 8.5. Saline soils generally are floc-

3

culated, and the permeability is comparable with
that of similar non-saline soils.

The principal effect of salinity is t0 reduce
the availability of water t0 the plant. In cases
of extremely high salinity, there may be curling
and yellowing of the leaves, or firing in the mar-
gins 0f the leaves or actual death of the plant.
Long before such effects are observed, the gen-
eral nutrition and growth physiology of the plant
will have been altered.

Nonsaline-Sodic Soils

A nonsaline-sodic soil is relatively low in sol-
uble salts, but contains sufficient exchangeable
(adsorbed) sodium to interfere with the growth
of most plants. Exchangeable sodium differs from
soluble sodium in that it is adsorbed on the sur-
faces of the fine soil particles. It is not leached
readily until displaced by other cations such as
calcium or magnesium. These soils often are
strongly alkaline, with pH readings usually be-
tween 8.5 and 10.0. Plant nutrients, such as iron
and phosphorus, become less available to plants

  under conditions of high pH.

~»As the proportion of exchangeable sodium in-
creases, soils tend to become dispersed, less per-
meable to Water and of poorer tilth. High sod-
ium soils usually are plastic and sticky when wet,
and are prone to form clods and crusts on drying.
These conditions result in reduced plant growth
because of inadequate water penetration, poor

“root aeration and soil crusting. Nonsaline-sodic

soils occur frequently in small and irregular areas,
and often are referred to as “slick spots” or “black
alkali” areas.

lRefer to Definitions for technical descriptions. The term
“sodic” is used to describe soils high in exchangeable sod-
ium. The term “alkali” also is used in referring to such
soils.

Figure 1. High yields oi cotton were obtained in 1951
from this iield near Dateland, Arizona, with water containing
more than 5 tons oi salt per acre-ioot. The cotton was planted
and grown in the furrows. Water in excess oi that needed
by the crop was applied to prevent excessive salt accumu-
lation. This field had been in production since 1940 and
until 1950 was cropped with Sudangrass. alialia and grain
sorghum. Picture courtesy Soil Conservation Service.

4

 

    
  
   
  
   
  
   
   
   
   
  
  
   
  
    
  
   
   
   

Sodic soils usually develop because of -
sively high sodium in proportion to calciu A
magnesium. This may result from a high
centage of sodium in the irrigation water ll
cause of the precipitation of calcium and m
sium salts under certain conditions.

Saline-Sodic Soils  

'1 f. 

Saline-sodic soils contain sufficient quanl

of both total soluble salt and adsorbed sodi  
reduce the yields of most plants. As long 1
cess soluble salts are present, the physical
erties of these soils are similar to those of
soils. The pH is seldom higher than 8.5 
soil generally remains permeable to wate
the excess soluble salts are removed, these
may assume the properties of nonsaline
soils. This condition is encountered frequ
immediately following heavy rains, and 
sult in the death of young plants. 

Both nonsaline-sodic and saline-sodic soils:
be improved by the replacement of the excl
adsorbed sodium by calcium and magnesium. '
usually is done by applying soluble amend {y
which supply these cations. Acid-forming a i
ments, such as sulfur or sulfuric acid, may be AI i
on calcareous soils since they react with lime
(calcium carbonate) to form gypsum, a more
uble calcium salt. 

EFFECT OF SALINITY ON
PLANT GROWTH

Soil salinity causes poor and spotty stanl
crops, uneven and stunted growth and poor 
the extent depending on the degree of sal"
The primary effect of salinity is that it a p
make water less available to the plant, but
icity also may occur. As salinity increases, 
while still present, becomes increasingly less =-

 
     
  

Figure 2. Poor stand oi cotton on a saline soiliY
Pecos. The saline condition oi this soil developed in 3"
because oi improper management oi water containing:
tons oi salt per acre-ioot. Approximately 1.5 bales o! 
were produced the iirst year in cultivation. A he 
plant irrigation and planting in the iurrows likely
contribute to the restoration oi such land.

A i
.\»"
Q,

  
    
   
  
    
   
   
 
   
 
   
  
   
  
  
 
 
   
 
   
  
  
  
   
   
  
 
   

"BLE 1. QUANTITY OF SALT ADDED TO SOIL
, UALLY BY APPLICATION OF 3 ACRE-FEET OF
‘ ATER OF VARIOUS SALT CONCENTRATIONS

;» of salt Tons of salt added to the soil

 acre-foot
_ of 1 2 3 4 5 6

frrappfied year years years years years years
% 1% 3 4% 6 7% 9

P. 1 3 6 9 12 15 18
2 6 12 18 24 30 36
4 12 24 36 48 60 72
6 18 36 54 72 90 108

ye to the plant. This is because the osmotic
ssure of the soil solution increases as the salt
Vcentration increases. a Laboratory tests show
t the reduction in plant growth under saline
ditions is related closely to the osmotic pres-
e of the soil solution. Farmers often refer to
ine moisture as “dry moisture.” This simply
ins that the soil contains water, but the plants
j unable to extract it as readily as from non-
ine soils.

 In the case of extremely high salinity, there
y be chlorosis, or firing of the margins of the
Aves, or actual death of the plants because of
ic effects of such ions as chloride and magne-
m. Excessive concentration and absorption of
gle ions may retard the absorption of other
nerals necessary for good growth.

: There is no critical point of salinity where
nts fail to grow. As salinity increases, growth
f omes less and less until the plants become
. orotic and die. Neither is there a definite point
salinity where crop production becomes pro-
itive. With increasing salinity, the maximum
ld potential becomes progressively less. Usu-
 crop production becomes marginal or uneco-
mical at some point of salinity considerably be-
 that at which plants fail to grow.

FACTORS AFFECTING SALT
ACCUMULATION

a The net increase or decrease in salt annually

each acre of land depends on the total volume
  irrigation water applied, the salt concentration
the irrigation Water, the subsoil drainage and
p- crop grown.

o-rge Quantities of Salt Added
» Large quantities of salt may be added to the
il each year in the irrigation water, particular-

Figure 3. Salt deposit resulting from a small leak in
an evaporative cooler illustrates the process by which salts
may build up rapidly in the soil.

ily in water of high salinity, Figure 3. The quan-
tity of salt added to the soil by annual applica-
tions of 3 acre-feet of water over a 6-year period
is shown in Table 1. As the concentration of salt
in the irrigation water increases, the application

of salt to the soil increases rapidly. Thus, with I

water containing 4 tons of salt per acre-foot of
water, the application of 3-acre-feet of water re-
sults in a cumulative application of 12, 24, 36, 48,
60 and 72 tons of salt over a 6-year period. With
such water, enough salt is added to the soil each
year to approximate 0.4 percent of the soil weight
to a depth of 18 inches. This is enough salt to
create a severe salinity problem under many con-
ditions—-enough to inhibit germination of most
seed.

Little or No Salt Evaporated

Much ofthe water applied to the soil is lost
to the atmosphere by evaporation and by tran-
spiration of plants. None of the salt is so lost.
The amount of salt taken up and removed from
the soil by plant growth is small for most crops,
as shown in Table 2. Fifteen hundred pounds of
cottonseed, for instance, contain a total of only
about 34 pounds of sodium, calcium, magnesium,
sulfate and chloride. Of this total, only about 3
pounds is sodium, the element directly associated
with sodic conditions.

  

l} 2. POUNDS OF VARIOUS MINERAL-S REMOVED FROM THE SOIL BY CROPS IN THE EL PASO AREA

 

  

  
  
   
  
  

 Yield, pounds Pounds
A Cmp per acre - - - - -
_ Sodium Calcium Magnesium Sulfate Chloride Total
eetclove-r hay 8,000 17 156  104 69 33 379
dangrass hay 10,000 21 34 i 69 199 67 390
i alfa hay 8,000 42 60 49 52 55 258
Vrley straw 2,000 14 8 3 28 15 68
rn silage 30,000 72 58 103 97 103 433
rley grain 1,000 2 1 1 3 7 14
e rghum grain 3,000 6 3 5 8 17 39
ttonseed 1,500 a 2 5 s 16 34
vera 1 e 7,938 22 40 42 58 39 202

 

Salinity Controlled by Leaching

Leaching is the only way by which the salts
added in the irrigation water can be removed sat-
isfactorily. Sufficient water must be applied t0
dissolve the excess salts and carry them away by
subsurface drainage. As the quantity of salt in
the soil or irrigation water increases, increasing
amounts of water must be passed through the
root zone to keep the salinity reduced to a con-
centration low enough for crop production.

Improper Drainage May Cause Salinity

Water will rise 2 to 5 feet or more in the soil
above the water table by capillarity. The height
to which water will rise above a free water sur-
face depends on soil texture, structure and other

factors. Water reaching the surface evaporates,

leaving a salt deposit which is typical of saline
soils, Figure 4. Many saline soils have developed
as a result of a high water table or restricted
drainage.

With the necessity of using additional water
beyond the needs of the plant to provide suffi-
cient leaching, it is imperative under irrigation
that there be adequate drainage for water pass-
ing through the root zone. Natural drainage
through the underlying soil may be adequate. In
cases where subsurface drainage is inadequate,
open or tile drains may have to be provided. In
no case should the water table be permitted to
come nearer than 5 or 6 feet to the soil surface.
In some cases, clay lenses or hardpan formations
may create a perched water table, and it often
becomes necessary to break up these impervious
layers by subsoiling, deep plowing or by other
means.

Figure 4. Saline soils oiten result irom a high water
table. Water will rise 4 to 6 feet or more in the soil above
a iree water surface. A salt deposit is leit at the surface
when water evaporates.

6

  
 
 
 
 
 
 
 
 
 
   
  
  
 
  
     
 
  
    
  
  
  
  
  
 
  

MANAGEMENT PRACTICES
AFFECTING SALINITY

Although farming practices vary fromf;
irrigated region to another, many general i.
ciples have widespread application for min”
ing the effects of salinity. <

Crops Vary in Salt Tolerailnce

Some crop plants can tolerate relatively
amounts of salt. Others are more easily inj
Some may be injured by relatively small 15
of salt. The choice of crops to be grown, p
becomes highly important. Non-tolerant 
cannot be grown successfully on saline soils. p;
the salt in the water and soil increases, the 

TABLE 3. RELATIVE SALT TOLERANCE OF V,‘
OUS CROP PLANTS. GOOD GROWTH AND Yli“
OF THE LISTED CROPS CAN BE EXPECTED A
SOIL SALINITY BELOW THAT GIVEN IN 

HEADING‘ ~ ‘

Moderately Relatively High]  I
salt salt salt 

Relatively
non-tolerant

    

tolerant tolerant toleran
EC x 108 EC x 103 EC x 10* EC x 10' 
2.0 —- 4.0’ 4.0 —— 6.0’ 6.0 —-— 8.0’ 8.0 — 12.0’ i
FIELD CROPS %
Field bean Sorghum Cotton Barley (g
Cowpeas (grain) Rye (grain) Sugar beet
Corn (field) Wheat Rape 
Castorbean (grain)
Soybean Oats (grain)
Rice
FORAGE CROPS 
White clover” Tall fesque Wheat- Alkali saca 
Alsike clover Meadow grasses Bermuda Q
Red clover fesque Sudangrass Barley (ha 
Ladino clover Orchard- Sweetclover Rhodesgr
Crimson grass Alfalfa Blue _ 
clover Millet Ryegrass Pamcgra 

Rose clover Sour clover Rye (hay)
Burnet clover Birdsfoot Wheat (hay)
trefoil Oats (hay)

VEGETABLE CROPS

 

Lima bean Tomato Garden beet Asparagus  i,
Green bean Broccoli _ Kale W. ;
Celery Cabbage Spinach
Pepper Okra
Lettuce
Sweet corn
Onion
Pea
Watermelon
Cantaloupe 2
Squash . c‘
FRUIT CROPS 
Pear Olive Pomegranate Date Palm 
Apple Grape Fig ‘l
Orange
Grapefruit
Plum
Apricot
Peach g
Strawberry “i
Lemon “f
Avocado it

    
 

‘Adapted from USDA Agricultural Handbook 60, 

Salinity "Laboratory. a - 
“Conductivity of saturation extract from the soil, expr i
as millimhos/cm at 25° C. ' ‘i
“Common name formerly was White Dutch Clover.

  
   
   
    
  
   
    
 
   
    
 
   
   
 
  

l- of crops which can be grown successfully be-
mes more limited.

*   The relative salt tolerance of a number of
 p plants is shown in Table 3. The tolerance of
ops listed may vary somewhat, depending on
f; particular variety grown, the cultural prac-
 es used and the climatic factors. Cotton, for
ptance, is one of the more salt-tolerant crops,
wever, American-Egyptian varieties probably
 e somewhat more salt tolerant under most con-
tions than Upland varieties. Some crops, such
 beets, may be highly salt tolerant as mature
nts, but sensitive to salt at the time of germi-
ition. Other crops, such as corn, possess less
lerance to salt as growing plants but germinate
asonably well under moderately saline condi-
011s.

f ' aching Requirements

a a The amount of salt added to the soil is de-
i rmined by the salt content and volume of water
A plied. The amount of salt removed by leaching
; . determined, likewise, by the salt content and
l  antity of water passed below the root zone. As
  he quantity of salt in the soil or in the irrigation

  SALT CONTENT FOR LOW

  
  

FOR MODERATELY

 

water increases, increasing amounts of water
must be passed through the root zone to keep the
soil salinity low enough for crop. production. Salt-
tolerant crops can be grown with less leaching
than more sensitive crops. Soil salinity cannot
be reduced below the salinity of the water used
for leaching.

The approximate percentage of water entering
the soil which must be passed through the root
zone (leaching percent or requirementZ) to main-
tain good yields of salt-tolerant and non-tolerant
crops is shown in Figure 5. For water contain-
ing 2 tons of salt per acre-foot, approximately 29
percent leaching is required to maintain good
cotton yields. This does not mean that cotton
cannot be produced with less leaching when using
such water. If less leaching is done, however,
higher salinity may result in lower yields. Salin-
ity may not be the only cause of reduced yields.
It would be inefficient to leach in the amount in-
dicated if the fertility or other conditions were
limiting yields.

ESee page 12 for method used in determining the leaching
requirement.

APPROXIMATE LEACHING NECESSARY

FOR TOLERANT

  
 

  t IRRIGATION TOLERANT CROPS TOLERANT CROPS CROPS
  a ATER (LADINO CLOVER) (BARLEY)
1lTON PER

  ACRE-FOOT

TONS PER

  ACRE-FOOT

5 TONS PER.  NOT

    ACRE-FOOT POSSIBLE

 

Figure 5. Approximate leaching requirements—percentage of the irrigation water (white area) that must pass below the
J ot zone to prevent an appreciable reduction in crop yields because of a salt accumulation in the soil.

7

Figure 6. Saline soils result in poor and spotty stands
and irregular plant growth. Reasonably good growth of
mature plants sometimes may be obtained on soils too salty
for good seed germination.

Permeable Soils Essential

The need for applying large quantities 0f wa-
ter for leaching when using highly saline irriga-
tion water emphasizes the need for open, easily
permeable soils. Typical infiltration rates of El
Paso Valley soils are shown in Table 4. With
lOW rates of water infiltration, such as one-fourth
inch or less per hour, it would be impossible to
obtain adequate leaching without restricting
growth because of insufficient root aeration.

Clays and clay loam soils, which have very
low permeability, cannot be leached readily. Salts

 

 

TABLE 4. TYPICAL INFILTRATION RATES O
PASO VALLEY SOILS‘

Hours for water I

Soil Infiltration rate,

- penetrate 3 feet wi

Inches per hour standing water on su
Clay l/4 _- l/z 144 — 72
Clay loam 1/2 — 2 72 - 18
Sandy loam 2 —- 3 _ _ 18 —- 12
Coarse sand 7 — 9“ --, A 5 — 4

‘Courtesy of L. Freeman, So-il ‘Conservation Service.

often build up in these finer-textured soils _
when low-salt waters are applied. Permea  
may be lowered by poor soil structure resu_
from too much sodium, from excessive or 
timed tillage practices or because of poor p
ping systems. Chiseling or deep plowing mayf
in increasing soil permeability where hard i
plow soles or clay layers restrict drainage.

In many instances, the leaching requiremi
can be handled most satisfactorily by a heavy 

plant irrigation, with lighter irrigations 
throughout the growing season. The heavy-

plant irrigation also serves to lower soil sal’ 
to a minimum at the time of seed germinati  

Seed and Seedlings Sensitive to Salt 

Germinating seed and seedlings usually 
much less salt tolerant than mature plants. 

ure to obtain a good stand often is the pr’

reason for poor yields under saline conditions,  

cause mature plants sometimes thrive and
reasonably well on soil that is too saline to

 

LLI 5' § , :}:_:';§§:*,';'.'-,‘-_'.' "-_';'-,'.'.};.'-I-".'_.;§§'-_'Ii _',_
w ' 7   
Z ._,_... _ ‘g. -_._ -..
 2 r

LIJ

c:

3 #1 l‘; i1? 
oou-ooz o.o2-o.| o.| -o.2 02- 05 05-2-0
PERCENT SALT IN SOIL

Figure 7. Salt content of soil under furrow irrigation. Arrows show the direction oi the flow oi water and salt d

and sometime after irrigation.

8

 

 

 _, .',_=.~'.a .

 

   
   
    
  
  
  
  
   
  
 
    
   
   
   
  
   
   
   
  
   
  

LOW

01.5 ROW BED

 

r LE ROW BED

 
 

  PING BED

re salt accumulation is excessive.

p good seed germination, Figure 6. Manage-
pnt practices should be followed which will pro-
 a minimum of salt at the time of germination
y; in the immediate vicinity of the youngseed-
_'S. A heavy preplant irrigation or use of spe-
i types of beds for seeding may help in reduc-
i: salinity.

g Salinity usually retards seed germination, pre-
>  ably because soil moisture is less available.

ring the delay in germination, the soil sur-
nding the seed may be excessively dried by
 ds, or seed rots may set in. Hence, under sa-
,- conditions, seed should be planted under as
rly optimum moisture and temperature con-
'ons as possible.

 Difficulty may be experienced in getting
nds (even on non-saline soils) of certain salt-
rant crops, such as Rhodesgrass, which have
tively small seed and which are slow to ger-
ate and become established. On the other hand,
ps, such as Sudangrass, while possessing some-
at less salt tolerance, germinate quickly, and
.0 rapidly in the seedling stage, and may give
ch better results under moderately saline con-
IOIIS.

-- Types Influence Salt Distribution

  It is well known that salts tend to accumulate
the ridges when using a furrow type of irriga-
n. The direction-of salt movement in the soil
der furrow irrigation is shown in Figure 7.
ith each irrigation, salt leaches out of the soil
der the furrows and builds up in the ridges.
here soils and farming pract1ces permit, furrow
nting with "a lister type planter may a1d 1n ob-
‘pining stands under saline conditions.

 

SALINITY AT PLANTING TIME

MODERATE HIGH

      

"".’~.s=‘<-

is‘\—\~.-

  

 

j; Figure 8. Effect of soil salinity and bed type on salt accumulation in a seeded area. Germination is delayed or prevented

Double (cantaloupe) or sloping beds are help-
ful in getting stands under saline conditions.
Typical salt accumulation under different types
of beds is shown in Figure 8. With double beds,
most of the salt accumulates in the center of the
bed, leaving the shoulders relatively free of salt.
Sloping beds may be better on highly salty soils
because seed can be planted on the slope below
the zone of salt accumulation.

Irrigate More Often

Most plants require a continuous supply of
readily available moisture to grow normally and
produce high yields. It has been pointed out that
salinity reduces the availability of water to the
plant because of increased osmotic pressure of the
soil solution. As the soil becomes progressively
drier following an irrigation, the salt concentra-
tion in the soil solution becomes progressively
higher, Figure 9. Consequently, plant growth
declines in proportion to the increase in salinity.

Irrigations must be made more frequently to pre-

vent excessively high salt concentrations from
occurring in the soil solutlon because of low mois-
ture levels.

Plants grown on saline soils usually do not
show typical wilting or moisture-deficiency symp-
toms as readily as plants grown on non-saline
soils. Plants growing on highly saline soil often
are in need of water, although the soil appears
moist. Therefore, considerable moisture stress
may occur before the plant shows signs of need
for irrigation.

Sandy Soils First to "Salt Out"

Although permeable and readily leachable,
sandy soils often are among the first to “salt out”

v5.3 '

\

,  w’ . .-
.' l’ 4}}? g'i\'*i-"v"_'-‘.-_:
W’ -"'f§=?l?¢-"1<'i§3"5_

7 7 " “ a; v

a . - '. f" '.'-' t .
nasty r ‘*
Fad? w. x1» (olgilw-s‘
" '-' 19-‘ 1M5 }'--_¢}"'/l
"J /""’;f!/§‘f1r.é{'"’ ‘Q

   

ONE LITER WATER IO GRAMS SALT

under poor management. These coarse-textured
soils are 10W in water-holding capacity, retain-
ing only about one-half inch of available moisture
per foot of soil depth, compared" with about 2
inches for clay soils, Figure 10. With such a rel-
atively small reservoir of available moisture, re-

 

  

    
   
    

CL AYS LOAMS SANDS

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8

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5 Available
q 3o
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t-
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UJ
0.

Available

u.|
‘s’ ‘i’ z
2i <1 <1
uJ
“H; m; ‘M2’
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223-’ 2-14 %-1<
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$2 <4 <14
'$5 T3523 ‘P9531
:1: zo: on:
2o z
o<9 ooo 0&2
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Z21 Z23; I

SOIL SALINITY

Figure l0. The amount oi soil moisture available for
plant growth is influenced by both soil texture and soil
salinity. Fine-textured soils have a greater water-holding
capacity than coarse-textured soils. Saline water is less

available to plants than non-saline water.

l0

 
 
 
  
   
   
  
  
   
   
  
  
 
  
  
 
  
  
  
 
 
 
 
  
 
 
   
   
   
  
 
 
 
  
  
  

one Hatrf
WATER   EVAPO  

 \ Io
-_ ~" \ \\\l|||1;

.  -. l ' _ I“. '
cg» ad?-.~

J
9

s“)

I PERCENT
SALT SOLUTION

Figure 9. Diagrammatic effect oi water evaporation on the concentration at salt solutions.

2 PERGENT 
SALT sonata“;

moval of moisture by the plant depletes the]
able supply rapidly and results in a rapid in.
in salt concentration of the remaining so;
Figure 9. Hence, unless irrigated freq 
sandy soils may show extreme effects of 
more quickly than clay soils. F

Level Land for Uniform Water Appli it

Proper field leveling and a Well-planne
gation system are most helpful in min’
salinity. Salinity problems are aggrava 
field or soil conditions which result in 
water penetration. High areas and ridges 
fail to get sufficient Water for leaching 
develop saline conditions resulting in “salte
spots. Areas With lower than average perni
ity may develop the same condition. Lowi
in the field which are subject to drowning- 
courage the irrigator to cut off the Water-
the remainder of the field has had sufficien
gation. Water distribution and penetration;
be uniform to bring about uniform leachi
salt. '

Commercial Fertilizers May Aid

The need for periodic leaching to remo
cess salts has been stressed. Unfortunately»
process also removes soluble plant nutrients
the soil. Nitrogen is especially suscepti,
leaching. Periodic applications of commerc' 
tilizer or manures may be necessary to p
sufficient fertility for good crop produ,
When the application of large quantities of
gation water is necessary, smaller, but mor
quent fertilizer applications, may be desira

Use Good Cropping Practices a 

It is desirable with saline soils to main i
good soil structure to encourage Water i _,
tion and penetration, especially on soils 
are poor in these respects. The inclusion l,



“ABLE 5.
LANTS T0 BORON, ARRANGE-D ACCORDING TO

  mes, grasses 0r other green manure crops in

_ e rotation for this purpose may be helpful, Fig-
e 11.
i Excessive tillage operations and Working the

til While too wet or too dry tend to destroy the
q structure and should be avoided.

endments Do Not Neutralize Salt

 Common soil amendments, such as gypsum,
 lfur or sulfuric acid, do not “neutralize” or
ounteract” salinity. Under certain conditions,
ese amendments may be used to make the soil
pore permeable and thereby facilitate the leach-
i» of excess salt. Where soil and subsoil per-
eability are good, the use of amendments is not
commended generally for saline soils.

I me Salts Highly Toxic

p Under most conditions, the ill effects of salin-
yare caused largelyby the increase in osmotic

ressure of the soil solution, which increases as

e total concentration of salts in solution in-
eases. However, certain salts or ions may pro-
uce specific toxic effects. This is known as the
specific ion” effect. Boron is extremely toxic
w plants, and injury may occur if the boron con-
nt of the irrigation water exceeds 2 to 4 parts
 million, depending on the particular plants

own. The relative boron tolerance of various

I Slants is shown in Table 5.

Many of the ions commonly occurring in irri-
ation waters, such as chloride or sulfate, may
»- toxic when present in large quantities, par-

'cularily if their relative proportion to other ions

s high. The toxicity may result from the par-

‘cular ion as such, or by alteration of the gen-

al metabolism of the plant because of an un-
llanced supply or availability of other nutrients.

RELATIVE TOLERANCE OF VARIOUS
AECREASING TOLERANCE WITHIN EACH GROUP‘

I olerant Semi-tolerant Sensitive
. paragus Sunflower Pecan
Calm Potato Black walnut
.% ate palm Acala cotton Jerusalem artichoke
ugar beet Pima cotton Navy bean
angel Tomato American elm
arden beet Sweetpea Plum
a lfalfa Radish Pear
ladiolus Field pea Apple
1~ oadbean Ragged Robin rose Grape (Sultanina
a ‘ion Olive and Malaga)
urnip Barley Kado-ta fig
abbage Wheat Persimmon
i ttuce Corn Cherry
I arrot Sorghum Mgrain Peach
Oats i ' ‘ Apriwt
Zinnia Thornless blackberry
Pumpkin Orange
Bell pepper Avocado
Sweet potato a Grapefruit
Lima bean Lemon

atings made by Eaton, 1935.

Leaching of excess salts from the soil is
facilitated by soil improving crops which improve soil struc-

Figure l1.

ture and permeability. Good soil structure also lessens
crusting and cracking of the soil. This is an excellent stand
of Sweet Sudangrass.

CHEMICAL ANALYSES
OF SOIL AND WATER

Reliable soil and water analyses aid greatly
in planning and adjusting management practices
to best suit the water and soil available. Peri-
odic water analyses will provide information on
the composition and concentration of salt in the
irrigation water, which may change from time
to time. Soil analyses will indicate whether the
saline or sodic condition of the soil is improving
or is becoming worse under the farming prac-
tices followed. It is important that samples be
collected and composited in such a manner that
they will represent correctly the water or soil to
be analyzed. Soil analyses are made by the Soil
Testing Laboratory and water analyses by the
State Chemist, both at College Station, Texas.
Directions should be obtained first on how to
take and send a sample. Ordinarily a fee is
charged for these analyses. Many private lab-
oratories also make soil and water analyses.

While numerous types of laboratory tests are
available, the analyses described following are
most commonly used and most informative in rou-
tine salinity tests.

The concentration and composition of dis-
solved salts determine the suitability of water for
irrigation use. Water analyses ordinarily should
include: (1) a determination of the total dis-
solved salts, (2) a determination of the more im-
portant ions, such as sodium, calcium, chloride
and bicarbonate and (3) a determination of the
proportion of sodium to calcium and magnesium.

Routine soil analyses should include the de-
termination of: (1) concentration of salt in the
saturation extract, (2) percent of exchangeable
sodium, (3) pH and (4) calcium content of the
soil, either, as gypsum or calcium carbonate, or as
both.

ll

Figure 12. The saline condition in the soil generally is
estimated by determining the soluble salt in the “saturation
extract." A representative sample of soil is saturated with
water and part of the water is extracted by aid of a vacuum
for analysis.

The farmer generally thinks in terms of the
salt contained in the irrigation water he applies;
the plant, however, is influenced by the salt in
the soil solution. This is governed by the salt al-
ready in the soil as well as the salt in the water
applied. A saturation extract is obtained to pro-
vide an estimate of the salinity of the soil solu-
tion. This is done by saturating the soil with
water and then extracting some of the water with
the aid of a vacuum, Figure 12. The salt con-
stituents contained in the saturation extract are
then determined.

Total Dissolved Solids

The total dissolved solids (salts) may be de-
termined by evaporating a known quantity of
water to dryness after filtering to remove sus-
pended matter, then Weighing the salt residue.

Results are reported in parts per million (p.p.m.), -

percentage or other units. A more common and
faster method is to measure the electrical con-
ductivity of the solution, since the amount of elec-
trical current Water will conduct is related closely
to the dissolved salt content. The salt concen-
tration may be reported directly in terms of elec-
trical conductivity (ec), or may be converted into
approximate parts per million, tons per acre-foot
of water (t.a.f.), or other figures more readily
visualized in everyday usageyTable 6.

TABLE 6. APPROXIMATE SALINITY VALUES EX-
PRESSED IN VARIOUS TERMS

Electrical Tons per Parts per Grainsl
conductivity acre-foot million per
(ec x 10°) (t.a.f.) (p.p.m.) gallon
575 l/z 368 21
1148 1 735 43
2297 2 1470 86
4594 _4 2940 173
6891 6 4410 258

12

e-Concentration of Specific Ions

   
   
  
   
   
  
  
   
    
   
   
  
  
   
   
 
   
   
   
  
   
  
  
  
   
  
     
  

Upon dissolving, salts dissociate into p)
carrying positive charges (cations) and =1
charges (anions)- These electrically chargi
ticles are called ions. The proportion or é
tration of the various ions is especially im 3
from the standpoint of adsorbed sodium L
toxicity, or both.   

Anions commonly included in water a
analyses are: chloride (Cl), sulfate (S04):
bonate (CO3) and bicarbonate (H003). C‘
commonly analyzed for are: calcium (Ca), 
sium (Mg), sodium (Na) and potassium ( A
trates or other ions may be included. Boro
are made in areas where waters may conta’
element in harmful amounts. A



Concentrations of the various ions usu?
given in parts per million or milliequivalen
l1ter (meq/l). l

Potential Sodium Hazard

Methods commonly used for estimati 
potential sodium hazard from use of high w
water are concerned with the proportion o
ium in solution in relation to the total catio l
centration. Of the several methods in us
determination of sodium percentage is the 
and most commonly used. The sodium pe-
age may be defined as the percentage of i, A
to the total positive ions present, expressed ;
equivalent basis. A more recently develo
lation designated as the sodium-adsorption
(sar) appears to give a more reliable est
of the potential sodium hazard (17). 

Waters relatively high in carbonates or. 
bonates have an increased sodium hazard,
calcium and magnesium may be precipitaf
the soil as carbonates. Waters containing
amounts of carbonate or bicarbonate tend i
cipitate calcium and magnesium carbona
the soil becomes drier. This results in a c
ponding increase in the sodium percentage 
soil solution. The sodium percentage “po 
takes into account calcium and magnesium?
bonates that might be precipitated. The 
carbonateplus bicarbonate over. calcium plus
nesium is known as the “residual sodium ca;
ate.” Formulas for calculating the sodium.
centage, sodium adsorption ratio, sodium per
age “possible” and residual sodium carbona 
shown following. Ion concentrations are exp
ed in milliequivalents per liter: 

Sodium percentage (ssp) I

sodium >< 100
sodium + calcium + magnesium ,+ potassi

Sodium adsorption ratio (sar) I
sodium

\/ calcium + magnesium 
2 

 

 

Sodium percentage “possible” I

 sodium >< 100
odium + calcium + magnesium + potassium)
— (carbonate + bicarbonate)

Residual sodium carbonate (rsc) I

(carbonate + bicarbonate) —  
(calcium + magnesium)

a .  hangeable Sodium Percentage

The percentage of exchangeable (adsorbed)
ium in the soil may have a considerable in-
nce on soil tilth and other properties. It is
l as a criterion of a sodic soil and is useful for
ermining the amount of soil amendment needed
 reclamation purposes. While the methods of
lyses are somewhat involved, the formula for

ulating the exchangeable sodium percentage

   
   
   
  

Exchangeable sodium percentage (esp) I

Exchangeable sodium (meq/100 gm. soil)
. >< 100
tion exchange capacity (meq/10O gm. soil)

   
    
  

i. The cation exchange capacity is defined as the
. adsorptive capacity of the soil for cations.

5
i

a The term “pH” is a measure of the acidity or
linity as determined by the hydrogen ion con-
tration. Pure water with a pH of 7.0 is neu-
l-— neither acid nor alkaline. A solution with
4 (H lower than 7 .0 is acid, while a pH above 7 .0
. ylkaline. The pH scale ranges from 0 to 14 on
T ogarithmic scale. Nonsaline-sodic soils gen-
lly have pH values of 8.5 or above. Many nu-
nts become relatively unavailable to plants at
l high pH values.

  
   
  
  
  

 ching Requirement

The leaching requirement is the percentage
irrigation water entering the soil which must
z below the root zone to reduce the soil salinity
a desired level. For areas having relatively
f rainfall and rather saline irrigation water, a
ctical estimate of the amount of leaching
essary may be obtained from the following
I ula: ~

  
  
 
  
  

I (Leaching requirement I
  , ec of irrigation water

ec permissible in drainage water

. Under. certain conditions, it may be desirable
l1 use other formulas (not given here) which

_e into consideratifiofi rainfall, salt removal by

l nts, precipitation of salts in the soil and toxic
s. r

   
    
  

 The concentration of saltwhich can be toler-
a w in the soil is somewhat relative, depending
a g the varieties and crops grown, climate, fre-

quency of irrigation and other management prac-
tices, and on the yields expected. Table 3 is use-
ful for estimating the permissible soil salinity
level for various crops. To obtain good yields,
the maximum soil extract concentration probably
should be kept below a conductivity of 4
mmhos/cm for sensitivecrops, such as beans or
Ladino clover, should not exceed 8 mmhos/cm
for relatively tolerant crops, such as alfalfa and
cotton, or 12 mmhos/ cm for highly tolerant crops,
such as barley. Somewhat higher salt concen-
trations may be permissible if some reduction in
yield is acceptable or more economical.

Gypsum

Gypsum (calcium sulfate) is found in soils in
arid regions in quantities ranging from a trace to
many tons per acre-foot. Gypsum is important
in the soil as a source of soluble calcium. The
use of irrigation waters with a high sodium per-
centage is less harmful on soils of high gypsum
content. The presence of soluble calcium also is
important in reclamation processes.

Alkaline-earth carbonates (calcium and mag-
nesium carbonates) usually occur in appreciable
amounts in soils in arid areas. These materials

may occur as fine salt particles and may improve 

the physical condition of the soil, or they may oc-
cur in, hard layers, such as caliche, and restrict
water movement. Alkaline-earth carbonates are
nearly insoluble and as such have little influence
on the sodium (or sodic) status of the soil. These
carbonates, however, may be changed to more sol-
uble sulfates by the use of acid-forming soil
amendments, such as sulfur or sulfuric acid. The
alkaline earth carbonates are, therefore, impor-
tant in reclamation processes as a potential source
of soluble calcium and magnesium, and they often
influence the choice of soil amendments.

QUALITY OF IRRIGATION WATER

The quality of irrigation water used has an
important influence on the results which may be
expected under irrigation. The quality of water
is a relative matter, however, rather than a fixed
entity, since the results obtained with a given wa-
ter may be influenced greatly by the crops grown,
the soils, climate, management practices and
quantity of water available. Nevertheless, water
analyses can serve as a valuable guide in esti-
mating the saline or sodic problems which can be
expected and for determining management prac-
tices best suited for the water at hand.

The quality of irrigation water is influenced
by: ( 1) the total salt concentration or salinity
hazard, (2) the amount of sodium and its rela-
tion to other cations, (3) the concentration of
boron or other constituents that may be toxic and
(4) the bicarbonate content in relation to calcium
and magnesium.

Salinity Hazard

The salt concentration in most waters is not
sufficiently high to be injurious to plant growth.

l3

It is the salt accumulation in the soil which pro-
duces injurious saline conditions. As the concen-
tration of salt in the irrigationqwater increases,
the salinity hazard (tendency for salts to accu-
mulate in the soil) likewise increases.

Figure 13 was prepared by the USDA Salinity
Laboratory and is a useful guide for estimating
the relative salinity and sodic hazard of various
Waters. The various salinity classes are:

Class 1. Low-salinity water (C1) can be used
for irrigation with most crops on most soils with
little likelihood that soil salinity will develop.
Some leaching is required, but this occurs under
normal irrigation practices except in soils of ex-
tremely low permeability.

Class 2. Medium-salinity water (C2) can be
used if a moderate amount of leaching occurs.
Plants with moderate salt tolerance can be grown
in most cases without special practices for salin-
ity control.

Class 3. High-salinity water (C3) cannot be
used on soils with restricted drainage. Even with
adequate drainage, special management for salin-
ity control may be required and plants with good
salt tolerance should be selected.

Class 4. Very high salinity water (C4) is not
suitable for irrigation under ordinary conditions,
but may be used occasionally under special cir-
cumstances. The soils must be permeable, drain-

Ioo 2 s 4 s e 1 a I000 2 a 4 sooo
| I I I I I III I I I
so- r

HOP]
4

\ t. __ CF84 _

2O \ G2-S4

N 03-94

INCH
3
1o
O

a _ \ o4-s4 ‘
8 \\ g“ _ oI-s: \ _
5 2 -- \ -
g g § \\ oz-sa
: .5. N a IC- \\ _
s - =
a 2 cI-sz \
g \\ g l2— ~
§ l0\ oz-sz 0*“ _

I
Ol-QZ y

- G4°$2
‘ Ql-Ql i
63-8! 

4O l llllllll l ll

Q Ioo zoo no zzoo
4’ oonouonvnv - nIoaounos/ou. Isouo‘) n as‘ o.
o

I 2 3 4
LOW MEDIUM HIGH VENY HIGH
SALINIT Y HAZARD

/

Figure l3. Diagram for the classification of irrigation
water. From Handbook 6U, U. S. Salinity Laboratory.

l4

 
 
 
  
  
 
 
 
 
 
  
  
 
  
  
  
  
 
 
 
 
 
  
 
  
 
 
 
 
 
 
  
 
 
 
 
 
  
 
  
 
 
 
  
 
  
 
  
 
  
 
   
   
   
 
  
 
 
  

age must be adequate, irrigation water ll I
applied in excess to provide considerable 1
and highly salt-tolerant crops should be ~=f

Farmers in the Trans-Pecos area of T I‘
producing consistently 2 to 3 bales of co 
upland soil with irrigation Water containif
proximately 3 tons of salt per acre-foot of '_
(3500 micromhos/cm.).__, Soils of the ar
rather permeable, underground drainage is.
cotton (salt tolerant) is the principal cr
practices such as furrow planting and f q
irrigation to minimize salinity are cus
Practically all water in the area is class
Class 4, or very high saline water, accor
the guide for salinity classes, Figure 13. _
vide a better basis for differentiating I5
waters within this area, Christensen and 
(2) suggested the following classification;
I, 0-1 t.a.f.; Class II, 1-2 t.a.f.; Class III
t.a.f; Class IV, 3.5-5.5 t.a.f; Class V, abo,
t.a.f. Other research workers suggested di 
classifications for other localized areas.
classifications, which are more lenient th
devised by the U. S. Salinity Laboratory, l’:
satisfactory for the customary farming p 
and areas for which they were designed, b I
should not be extended to other areas or.
crops and management practices. “

Sodium Hazard ,

Since the physical condition of the soilv I
fluenced greatly by an increase in excha
sodium, it is necessary to consider the sodi 
ard of irrigation Water. Also, plants sensi
sodium may be injured by accumulations J
ium in the soil. Both the sodium adsorptio
and total salt concentration influence the 
hazard, as shown in Figure 13. ‘

Low-sodium water (S1) can be used f0
gation on almost all soils with little danger l,
development of harmful levels of excha q
sodium. However, sodium-sensitive crop‘,
as stone-fruit trees and avocados, may --.
late injurious concentrations of sodium. "

Medium-sodium water (S2) will pres‘
appreciable sodium hazard in fine-textur
having high cation-exchange-capacity, es,»
under low-leaching conditions, unless gyps”
present in the soil. This water may be g
coarse-textured or organic soils with nv‘
meability. 9

High-sodium water (S3) may produce ,
ful levels of exchangeable sodium in mos
and will require special soil management 
drainage, high leaching and organic matte e
tions. Gypsiferous soils may not develop’
ful levels of exchangeable sodium from su
ters. Chemical amendments may be requi 1
replacement of exchangeable sodium, exce’
amendments may not be feasible with Wa
very high salinity. 

Very high sodium water (S4) Qenerallyl-i
satisfactory for irrigation purposes except ,

id perhaps medium salinity, where the solution

calcium from the soil or use 0f gypsum or other
= endments may make the use of these waters
sible.

a Waters with a sodium percentage of less than
ut 60, and having a 10w bicarbonate content,
e probably satisfactory under most conditions.
_~ the sodium percentage increases above 60 the
dium hazard becomes progressively greater.

The occurrence of appreciable amounts of gyp-
In in the soil may permit the use of waters hav-
q an unfavorably high sodium hazard, partic-
rly if the total salt content of the water is
latively low. The sodium hazard of low saline
ters may be reduced by the addition of gypsum

. the water. Similarly, it may be advantageous

add soil amendments periodically when using
gh sodium waters. Only soil amendments con-
ining soluble calcium should be used on non-
lcareous soils, while either these or acid-form-
g amendments, such as sulfur or sulfuric acid,

, ay be used on calcareous soils. The cost of ap-

jying a sufficient amount of amendment to cor-
- t the sodium hazard of very highly saline
later may be prohibitive.

ron Hazard

While occurring in insignificant amounts in
any areas, soluble boron is extremely toxic.
lants sensitive to boron may be injured by as

le as 0.7 p.p.m. of boron in the saturation ex-
act, and more than 1.5 p.p.m. appears unsafe
cept for boron-tolerant plants, Table 5. More
ater may be required for leaching boron than
r other salts. A classification of irrigation
ater according to the boron concentration is
ven in Table 7.

prbonate and Bicarbonate Ions Hazards

" As previously indicated, the soil dries after
i: irrigation and the soil solution becomes more

'1 more concentrated. Under these conditions,

ere may be a tendency for the less soluble com-
punds to precipitate from solution. Calcium and
agnesium carbonates are much less soluble than
dium carbonate and may precipitate on drying

much is present. The precipitation of calcium
l d magnesium results in a corresponding in-
ease in the proportion of sodium in solution.

ABLE 7. PERMISSIBLE LIMITS OF BORON FOR
SEVERAL CLASSES OF IRRIGATION WATERS‘
B0 '7 l Boron- Semi-tolerant Boron-

m“ c ass sensitive crops crops tolerant crops
- — — — Parts per million — — — —

Excellent <’0.33 <0.67 <1.00
Good 0.33 to .07: 0.67 to 1.33 1.00 to 2.00
Permissible .67 to 1.050 ' 1.33 to 2.00 2.00 to 3.00
Doubtful 1.00 to 1.25 2.00 to 2.50 3.00 to 3.75
Unsuitable >“1.25 >2.50 >3.75

‘ ofield (1936).

~: than.

ore than.

The bicarbonate ion is important since it is a
source of excess carbonate.

The extent to which calcium and magnesium
carbonates will precipitate and the conditions
favoring precipitation are not clearly understood.
Waters containing 1.25-2.5 meq./l of residual
sodium carbonate are probably marginal and
those with more than 2.5 meq./l probably are un-
safe for irrigation. Therefore, waters with a
“possible” sodium percentage much higher than
actual sodium percentage possess an additional
sodium hazard.

As with high sodium waters, the effects of un-
favorably high bicarbonate may be lessened if
proper soil amendments are used or if the soil
contains an appreciable amount of gypsum.

RECLAMATION

Leaching of undesirable salts is the key to suc-
cessful improvement and reclamation of salty
soils. If an adequate supply of reasonably good
irrigation water is available, if soil permeability
is reasonably good and if drainage is adequate, it
should be possible to reclaim almost any salt-af-
fected soil.

The first step in a reclamation operation
should be the collection and analyses or repre-
sentative water and soil samples. These analyses
will provide information as to the severity of the
problem and Whether the problem involves salin-
ity, sodium or boron, or a combination of these
factors. Reclamation procedures should be plan-
ned accordingly.

Saline Soils

The reclamation of most saline soils is a rela-
tively simple operation if drainage is not restrict-
ed. Sufficient water is passed through the soil
to dissolve the excess salts and carry them away
in the drainage water. The quantity of water
needed for reclamation depends on the amount of
salt in the irrigation water and in the soil, and
also on the extent of reclamation desired. Three
to 4 acre-feet of water. or even more, may be re-
quired. The land should be leveled carefully and
borders thrown up so that the field can be flood-
ed. Water should be held on the surface until
leaching has reduced the salt concentration to a
safe level. On slowly permeable soils, it may be
desirable to obtain a partial reclamation, then
plant a salt-tolerant crop, such as Bermudagrass
or barley, to assist in opening up the soil before
further leaching. Ordinarily, saline soils are in
reasonably good tilth after reclamation and may
be farmed at once.

Saline-Sodic and Nonsaline-Sodic Soils

The reclaiming of sodic soils is more difficult
than for saline soils, since the former includes re-
placing exchangeable sodium with calcium and
improving soil tilth as well as the leaching of un-
desired salts. The calcium needed for replacing
exchangeable sodium may be supplied in the irri-

15

TABLE 8. APPROXIMATE AMOUNTS OF GYPSUM
AND SULFUR REQUIRED TO REPLACE INDICATED
AMOUNTS OF EXCHANGEABLE SODIUM‘

Exchangeable
sodium (meq. per
100 gm. of soil)

Gypsum

(caso.-2H.o) Smf“

ons per acre-foot of soil’ - -

0.32.
0.64
0.96
1.28
1.60
1.92
2.24
2.56
2.88
10 3.20

wwqmmmwuw
l-l
‘Q. Q l I O
wmqcwmwwnq

‘From USDA Agricultural Handbook 60, U.S. Salinity
Laboratory.

*1 acre-foot of soil weighs approximately 4,000,000 pounds.

gation water or perhaps from gypsum in the soil
1n some cases. Most likely the use of an appro-
priate soil amendment will be required.

Soil amendments commonly used may be di-
vided into two types: (1) amendments providing
soluble calcium, such as gypsum and calcium chlo-
ride, and (2) acid or acid-forming amendments,
such as sulfur, sulfuric acid, iron sulfate and
aluminum sulfate. Calcium polysulfides (lime-sul-
fur) are both calcium-supplying and acid-form-
ing, but are perhaps most beneficial in the latter
capacity. Applications of limestone may be of
considerable value as a source of calcium on acid
soils, but are of questionable value on alkaline
soils.

Amendments providing soluble calcium are
suitable for reclamation of all types of sodic soils.
Acid-forming amendments are most useful on
soils containing calcium carbonate since they re-
act with the latter to form calcium sulfate. The
relative value of the different acid-forming
amendments is determined largely by their sul-
fur content. The choice of amendment depends
on whether the soil contains calcium carbonate,

improving the soil structure on sodic soils.

16

Figure 14. Growing and plowing under highly salt-toler-
ant crops. such as barley. are beneficial in reclaiming and

 
 
 
 
  
 
 
  
 
   
 
  
 
 
  
  
 
 
  
 
 
  
 
 
 
 
  
  
 
 
  
  
 
  
   
 
 
 
  
  
  
  

the cost and the speed of reaction desired. .
cium chloride provides readily soluble 
but is too expensive for common use. Su__
acid and iron and aluminum sulfates are l!
ments which act quickly, while sulfur, wh’
dependent on microbial activity, acts sl,
Where possible, amendments should be 
thoroughly with the soil forsbest results. A 
ments Which are waterisdluble can be ap
easily and economically in the irrigation wa

The quantity of soil amendment need,
pends on the water quality, quantity of exc 
able sodium to be replaced, completeness of 
ical reactions in the soil and other factors.
amounts of gypsum and sulfur required 
place various amounts of exchangeable w,
are given in Table 8. Somewhat higher 
than those shown are suggested, since the rep
ment process is not complete. *

Fields should be bordered and leach,
flooding, as with saline soils. Ordinarily, ,
saline-sodic soils have low permeability,
leaching may be slow, often requiring wee 1s
months. The dispersed condition and poor. 7'
characteristic of sodic soils may persist 
leaching is completed. Farming practices 
will improve the soil structure should be 
Figure 14. The soil should not be worked  A
excessively wet, tillage operations should be , g
to a minimum and soil-improving crops s '
be grown. *

Slick Spots

Irrigated fields often contain small irre,
areas known as “slick spots.” These areas’
duce little or no growth, are hard and tight
dry and sticky when wet. These usually are 
areas of sodic soil. These areas are diffic» 
reclaim because they cannot be leached wit 
interfering with other operations in the fieldf
good treatment is to apply and work in a li .
supply of the appropriate soil amendment. 
plications of manure or other organic mate
or planting salt-tolerant crops, such as o : .8
or Bermudagrass, are useful for increasing 
meability so that leaching may be obtained. 
casionally these slick spots are underlain by l_
ized clay lenses or other impervious layers 
impede leaching. Subsoiliflg, deep plowing
establishment of deep-rooted crops maybe it
ficial in such cases. l

Digging holes through a deep, impervious
and filling with sand is an expensive process;
often the only satisfactory way in which drai
can be established. This procedure often caf
used advantageously for shade trees and of‘
mental plants. '

ACKNOWLEDGMENTS

Much of the information in this bull
based on research done at the U. S. Salinity 
oratory, Riverside, California, and also  i
findings of other research workers in this  i

  
    
  
 
  
 
  

  ther states.

LECTRICAL CONDUCTIVITY (ec):

Reference is not made in the text

O all quoted material and references. A more

chnical and complete discussion of material pre-

 is given in U. S. Department of Agricul-
re Handbook 60 and other references cited.

The authors acknowledge the many helpful

uggestions of the following men in reviewing the

 anuscript: H. E. Hayward, L. A. Richards, W.

 Gardner, C. A. Bower, L. V. Wilcox and R. C.

eeve, U. S. Salinity Laboratory; W. S. Foster,

  exas Agricultural Extension Service; and C L.
cdfrey, H. E. Joham and M. E. Bloodworth,

p Definitions
LKALI SOIL: See sodic soil.

LKALINE: A chemical term referring to a basic reac-
tion where the pH is above 7.0 as distinguished from
an acid reaction where the pH is below 7.0.

LKALINE-EARTH CARBONATES: Generally refers to
calcium and magnesium carbonates, also referred to
as lime carbonates.

VAILABLE WATER (MOISTURE): The quantity of
water retained in the soil between the limits of field
capacity and the permanent wilting percentage is
termed “available water” for plant use. It usually is
expressed in inches per foot of soil depth.

ductivity provides a rapid, useful measure of salt “con-
centration in water solutions since the amount of
current which the zsolution will conduct is closely
correlated with theaamount of dissolved salt. The
standard unit of conductivity is mhos/ cm, however,
other units often are used. A water containing ap-
proximately 1 ton of salt per acre-foot may be ex-
pressed in the following units:

ec — .0O1148 mhos/cm

ec x 10” — 1.148 millimhos/ cm or mmho/ cm

ec x 10° — 1148 micromhos/cm or a mho/cm

Electrical con-H I

10.

Grillot, Georges, 1954. The Biological and Agricultural
Problems Presented by Plants Tolerant of Saline or
Brackish Water and the Employment of Such Water
for Irrigation. UNESCO Arid Zone Programme-IV
Reviews of Research on Problems of Utilization of
Saline Water.

Hayward, H. E., 1954. Plant Growth Under Saline
Conditions. UNESCO Arid Zone Programme-IV Re-
views of Research on Problems of Utilization of Saline
Water.

Hayward, H. E. and C. H. Wadleigh, 1949. Plant
Growth on Saline and Alkali Soils. Advances in
Agronomy Vol. 1:1-38.

_ _ _ 11. Harris, Karl, 1949. Factors that Give Value to Land

exas Agrlcultural Experiment Station. The or Basic Land Values. Ariz. Agric. Expt. Sta. Bul. 223.

l 9511s expressed m th1S_ Rubhcatlon do p01,; 199995‘ 12. Lyerly, P. J ., 1957. Salinity Problems in the El Paso
arily represent the opinions of these individuals Area. Symposium on proiflems of the Upper Rig

4n the problems discussed and the recommenda- Grande River, pp. 57-62. r

011$ given. ' 13. Scofield, C. S., 1936. The Salinity of Irrigation Water.

X ‘ Smithsn, Inst. Ann. Rpt. 1935: 275-287.
RGIGIGIICGS 14. Thorne, D. W. and H. B. Peterson, 1954. dligiigated
. » . . Soils Their Fertility and Management. 2n ition.
i1. Bernstein, L., M. Fireman and R. C. Reeve, 1955. ’ - _ - -
Control of Salinity in the Imperial Valley, California, The Blaklston Company’ Phfladelphla and Torwlto:
e USDA ARS 41-4, 15. Thorne, J. P. and  W. _Thorne, 1951. Irrigation
I l2 Christensen P. D. and P. J. Lyerly 1953. Water ‘évaterss of gtellhéggihelr Quahty and Use’ Utah Agnc’

I Quality-As It Influences Irrigation Practices and . Xpt’ ta‘ u ' ' ‘ _

Crop Production—El Paso and Pecos Areas, Texas. 16.  Staff, 1955. Water, Year Book of Agriculture,
Texas Agric. Expt. Sta. Cir. 132. -

3. Dregne, H. E. and H. J . Maker, 1954. Irrigation Well 17. United States Salinity Laboratory Staff, 1954. Diag-
Waters of New Mexico—-Chemical Characteristics, I nosis and lgiprfciGnent of Saline and Alkali Soils.
Quality and Use. New Mexico Agric. Expt. Sta. Bul. USDA, Han oo o. 60.

386- I  s: 18. Wadleigh, o. H. and Milton Fireman, 194s. Salt Dis-

. Eaton, F. M., 1935. Boron in Soils and Irrigation tribution Under Furrow Irrigatgd Cotton and ItsP Ef-
Waters and Its Effect on Plants With Particular fect on Water Removal. Soil ci. Soc. Amer. roc.
Reference to the San Joaquin Valley of California. 13:527-530.

p USDA Tech‘ Bul‘ 448' 19. Wilcox, L. V., 1948. Explanation and Interpretation

ii Eaton, Frank M., 1950. Significance of Carbonates of Analyses of Irrigation Water. USDA Cir. 784.

l; in Irrigation ‘Waters’ Soil Science’ 69123433’ 20. Wilcox, L. V., 1957. Reclamation and Management of

. Eaton, F. M., 1954. Formulas for Estimating Leach- Saline and Alkali Soils. Talk presented at Western

‘ ing and Gypsum Requirements of Irrigation Waters. Cotton Irrigation Conference, Phoenix, Ariz. Mar. 4,
Tex. Agric. Expt. Sta. Misc. Pub. 111. 1957-

.. Freeman, Lawrence. USDA Soil Conservation Ser- 21. Wilcox, L. V., 1948. The Quality of Water for Irriga-

 vice, Unpublished Data. tion Use. USDA Technical Bul. 962.

APPENDIX

EQUIVALENT: A term developed by chemists to express

the unit weight of an element or ion that will react
with or be equal to another in chemical reactions.
Eight units (grams) of oxygen are used as a standard
for comparison. The equivalent weights of chemical
constituents receiving primary attention in irrigation
are:

CHEMICAL EQUIVALENT

CONSTITUENT SYMBOL WEIGHT, GRAMS
Calcium Ca a 20,04
Magnesium Mg 12.16
Sodium Na 23.00
Potassium K 39.10
Chloride C1 35.46
Carbonate CO3 30.01
Bicarbonate HCOe 61.02
Sulfate S04 48.03
Gypsum Ca SO. . 2HeO 86.05
Sulfur S 16.03
Sulfuric acid HZSO. 49,04

Iron sulfate FeSOi . 7HeO 139.01

FIELD CAPACITY: Amount of water remaining in the

soil after gravitational water has drained downward
following irrigation or period of considerable rain.
Expressed as_ inches per foot of soil depth or per-
centage of soil weight.

17

ION: Upon dissolving, salts dissociate into particles carry-
ing positive (cations) and negative (an1ons)_electr1cal
charges. These charged particles are called ions.

MILLIEQUIVALENTS PER LITER (meq/l): The milli-
equivalents of any salt or ion per liter of solution. A
milliequivalent I equivalent/ 1000.

NONSALINE-SODIC SOIL: A soil that contains suf-
ficient exchangeable sodium to interfere with the
growth of most crop plants and does not contain
appreciable quantities of soluble salt. Quantitively
defined as a soil with an exchangeable sodium per-
centage greater than 15 and a saturation extract con-
ductivity of less than 4 mmhos/ cm at 25° C.

OSMOTIC PRESSURE: A property of a solution de-
pendent on the concentration of salts or dissolved sub-
stances in the solution (and other factors) and relating
to its diffusing tendency. In plant-soil relations, two
osmotic pressures are involved. If the osmotic pres-
sure of the root cell sap is higher than that of the
soil solution, water will move from the soil into the
plant. The more nearly equal the osmotic pressures
of the cell sap and soil solution become, the more
difficult it is for plants to obtain water. (For a more
accurate definition refer to text books on plant physi-
ology or soil physics.)

PARTS PER MILLION (p.p.m.): The parts of salt or salt
constituent per million parts of solution.

PERMANENT WILTING POINT: Quantity of water re-
maining in the soil after plants have withdrawn all
they can and wilt permanently. Expressed in inches
per foot of soil depth or percentage of soil weight.

RESIDUAL SODIUM CARBONATE: See page 12.

SALINE-SODIC SOIL: A soil containing both sufficient
soluble salt and exchangeable sodium to interfere
with growth of most plants. Quantitatively defined as
a soil containing an exchangeable sodium percentage
above 15 with a saturation extract conductivity of 4
mmhos/ cm or more at 25° C.

SALINE SOIL: Soil that contains sufficient soluble salt
to interfere with the growth of most crop plants. For
the purpose of definition, soil for which the con-
ductivity of the saturation extract is 4 or more
millimhc-s per cm. at 25° C.

FORMULAS FOR CALCULATING WATER DEPTH, VOLUME AND IRRTGATING TIME. THESE FORMUL-i
NoT TAKE INTO CONSIDERATION DITCH Loss, Loss OF TAIL WATER oR UNEVEN WATER PENETRA
ALLowANCE MUST BE MADE FOR SUCH FACTORS WHERE PERTINENT.

1. Acre-inches per acre I cubic feet per second x hours gallons per minute x hours

acres x 1.008
2. Acre-feet per acre I cubic feet per second x hours
acres x 12.1

3. Acre-inches I cubic feet per second x hours gallons per minute x hours
or

 
  
 
    
 
  
  
  
  
    
   

SALT-AFFECTED SOIL: A soil that contains ei 
ficient soluble salt or exchangeable sodium,
to interfere with the growth of most, plants. 

SODIC SOIL: A soil containing sufficient exc 
sodium to interfere with the growth of y‘
plants. Quantitatively defined as a soil with‘;
changeable sodium percentage greater than 15f
with or without appreciable amounts of soluj
Also known as alkali soil. .__ 

SODIUM ADSORPTION RATlOuziiiSee page 12.
SODIUM PERCENTAGE: See page 12. 
SODIUM PERCENTAGE POSSIBLE: See page

SOIL STRUCTURE: Refers to the manner in ~~ 
soil particles are clustered together into cl
aggregates. A stable structure is highly d‘
in the finer-textured soils, since it permif
penetration of water and air. Green man f
cover crops are especially valuable for their : 
promote aggregation. 

SOIL TEXTURE: Refers to the size of the Q
particles of which the soil is composed, such : ,
silt and clay. Coarse-textured soils contain?
quantities of sand-size particles; fine-text 
contain considerable clay. Loam is a term in,
that a soil contains appreciable amounts of a. ‘ii?
size fractions. *

ABBREVIATIONS

t.a.f. z tons per acre-foot

p.p.m. I parts per million

gm. I grams

gr. I grains

c.f.s. I cubic feet per second

g.m. z gallons per minute

meq./l I milliequivalents per liter
sar. I sodium adsorption ratio

t.d.s. I total dissolved solids, generally salts
< I less than ,
> I more than

esp. I exchangeable sodium percentage
lr I leaching requirement

ec I electrical conductivity

ssp I soluble sodium percentage

gallons per minute x hours

acres x 452.5

acres x 5430

1.008

4. Acre-feet I cubic feet per second x hours gallons per
or

12.1

5. Hours irrigating time I t_o_tal acre_-feet required x 12.1

Yibic feet pergcoRd

6. Hours irrigating time I acre-inches per acre desired x acres x 1.008
cubic feet per second
or
acre-inches per acre desired x acres x 452.5

minute x hours
5,430
acre-feet required x 5430

452.5

gallons per minute

gallons per minute

EXAMPLE
(1) How many acre-feet of water are pumped per day by a well producing 2,000 gallons per minute?
Use formula 4b gallons per minute x hours 2,000 x 24 48,000 
5,430 — W I 5,430 I 8.84 acre-feet 

(2) How many hours will be required to apply 4 inches of water to 100 acres of land when using 5 cubic I‘

water per second?

Use formula 6a acre-inches per acre desired x acres x 1.008

 

cubic feet per second

l8

4 x 100 x 1.00s 403.2 l

 
 

"F ACTORS AND CONVERSION FORMULAS‘

1 cubic foot I 7.48 gallons.
1 gallonI.1337 cubic foot.

,1 liter-_I 1.057 quarts I .2642 gallon

Water Weighs: 8.34 pounds per gallon
62.43 pounds per cubic foot
2,719,450 pounds‘ per acre-foot.

Soil vveighs: 68 to 100 pounds per cubic foot
4,000,000 pounds per acre-foot (average
figure)

One acre-foot of water contains: 43,560 cubic feet
i 325,829 gallons
12 acre-inches _

1 acre-inch of water: Weighs 226,620 pounds
contains 27,152 gallons
contains 3,630 cubic feet.

1 million gallons I 3.0689 acre-feet
contains 133,680 cubic feet.

1 percent I 1/100 I 10,000 p.p.m.

10,000 p.p.m. I  »

M_eq./l x equivalent weight 2: p.p.m.

Grains per gallon x 17.1 I p.p.m.

p.p.m. x .00136 I tons per acre-foot of Water.

ec x 103 (millimhos/'cm) x 1000 I ec x 10“
(micromhos/ cm) .

Tons of salt per acre-foot (t.a.f.) of water x 735 I p.p.m.

1 cubic foot per second I 7.48 gaL/sec.

448.8 gal./min.
26,928 gaL/ hour
646,272 gaL/day

60 cu. ft./ min.

3600 cu. ft./hour
86,400 cu. ft./day
0.992 acre-inches/hour
23.8 acre-inches/ day
0.0826 acre-ft./hour
1.98 acre-ft./day

1000 gallons per minute I 60,000 gal./hour
1,440,000 gal./day
2.228 cu. ft./second
1% n8 cu ftJminute
8021‘ cu. ft./hour
192,504 cu. ft./ day
2.21 acre-inches/hour
53.03 acre-inches/day
0.184 acre-ft./hour
4.416 acre-ft./day

‘Many of the factorsgiven are in approximate figures.

APPROXIMATE WATER-HOLDING CAPACITY

OF SOILS
Moisture llilzlllfitgze Moisture 161153;?‘
Soil texture held at permanent available inches of
field 1 wilting to water to
6311361153’ pointl plants‘ wet 3 feet
of soil”
Sands 1.0 - 1.4 .2 — .4 .8 - 1.0 2.1
Sandy loams 1.9 - 2.3 .6 - .8 1.3 - 1.5 3.2
loams 2.5 - 2.9 ' .9 - 1.1 1.6 - 1.8 3.8
Silt loams 2.7 - 3.1 1.0 - 1.2 1.7- 1.9 4.1
Clay loams 3.0 - 3.4 ' 1.1 - 1.3 1.9'- 2.1 4.5
Clays 3.5 - 3.9 1.5 - 1.7 2.0 - 2.2 4.8

‘Expressed as inches of water per foot of soil.

“ikssuming three-fourths of the available Water has been
evaporated or used by plants at time of irrigation.

19

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