Published 1983

CHAPTER 2C
Soil Properties and Efficient Water Use:
Water Management for Salinity Control
GLENN J. HOFFMAN AND M. TH. VAN GENUCHTEN
U.S. Salinity Laboratory, USDA-ARSRiverside, California

I. INTRODUCTION
A mixture of soluble salts is present in all soils. This mixture includes salts
originally dissolved in the applied water, applied as amendments, weatheredfrom soil minerals, or imported with subsurface water flow. If the concentration of these salts becomes excessive, crop yields will be reduced becauseof the decrease in osmotic potential of the soil water. To prevent harmful
accumulation of salts, the soil profile must be leached periodically with anamount of water in excess of that used by evapotranspiration. Thus, where
salinity is a hazard, the concept of efficient water use must be expanded toinclude an increment of water to meet the leaching requirement (L,). The
leaching requirement is defined as the minimum fraction of the total
amount of applied water that must pass through the soil root zone toprevent a reduction in crop yield from an excess accumulation of salts(USSL Staff, 1954). Leaching occurs whenever irrigation and rainfall
exceed evapotranspiration. In humid regions, rainfall is normally sufficientto periodically flush salt from the profile. In subhumid regions, additional
irrigation water must frequently be applied to assure adequate leaching. Depending on the degree of salinity control required, leaching may occur
continuously or intermittently at intervals of a few months to a few years.
Soils not only contain a mixture of salts, but distribution of those salts
is neither uniform on an area basis or with soil depth, nor constant in time.
Nonuniformity within a field is caused in large part by irrigation systems
that supply water unevenly. As a consequence of this and irrigation scheduling that exceeds evapotranspiration, a large fraction of the applied water
may leach through the root zone and be wasted as drainage. Present technology, including high-frequency irrigation, makes it possible to deliver
water more efficiently thereby reducing excessive drainage. As we
implement this technology and strive to conserve water, the minimum value
to which drainage can be reduced, the leaching requirement, becomes a vital
component in efficient water management.
Copyright 1983 © ASA-CSSA-SSSA, 677 South Segoe Road, Madison, WI 53711, USA.
Limitations to Efficient Water Use in Crop Production.
73

74

HOFFMAN & VAN GENUCHTEN

Two quantities establish the leaching requirement: the salt concentration of the applied water and the salt tolerance of the crop. The salt concentration of the applied water, including rainfall, is readily measured. Cropsalt-tolerance, however, is more difficult to measure and has traditionallybeen established by measuring yields where waters of varying salt concentrations have been applied at leaching fractions approaching 0.5. Maas andHoffman (1977) summarized salt-tolerance data for more than 60 agricultural crops. They reported salt tolerance by means of two parameters: thethreshold and the rate of yield decline as salinity increases beyond thisthreshold. The threshold value is the maximum average salt concentrationin the root zone that does not reduce yield. Where the quantity or quality of
the applied water permits, efficient salinity management should not permit
the average root-zone salinity to exceed the threshold value.
The leaching fraction, L, is defined as[1]

where q and C represent long-term average values of the volumetric flux
and the salt concentration, respectively, and the subscripts I and D refer toirrigation (including rainfall) and drainage water, respectively. Because L, isdefined as the minimum leaching fraction needed to prevent yield reduction:[2]

where the superscript ... distinguishes required from actual values (USSL
Staff, 1954). The salt concentration of a relatively dilute soil solution isroughly linearly related to the electrical conductivity (0). Because a is easily
measured, it is advantageous to express L, as:[3]

Inherent in the above equations are the assumptions that no salts precipitate, dissolve, or are removed by the crop.
Several empirical methods have been proposed to relate ab to somereadily available soil salinity value. Bernstein (1964) assumed ab to be theelectrical conductivity of the soil saturation extract (ae ) at which yield in
salt-tolerance experiments was reduced by 50070 (ae,.). Later, van Schilfgaarde et al. (1974) contended that the value of ab could be increased to thea of soil water at which roots can no longer extract water. Assuming the soil
water content to be half the saturation extract water content, this value of a
is about twice ae extrapolated to zero yield from salt tolerance data (ae,).
Concurrently Rhoades (1974) proposed that ab could be estimated from[4]

where at is taken as the salt-tolerance threshold. As will be shown later(Table 1), experimental evidence indicates that the method of BernsteinTomato
Wheat
Wheat

OrangeSorghum
Sudangrass

Lettuce
Lettuce

Alfalfa
Fescue, tall

Alfalfa

Alfalfa

Alfalfa

Crop

1.4
2.2
2.0
4.0
2.2
2.2
1.4

2.0
4.0
1.0
2.0
0.9
1.3
1.6
2.0
3.1
3.3
1.4
2.0
4.0
2.2
1.4

U[

<0.1
0.08
0.14
0.24
>0.17
0.08
0.07

0.13
0.29
0.06
0.15
<0.1
>0.1
>0.1
-0.2
>0.2
>0.2
<0.05
0.13
0.26
0.26
0.25

Lr

Experimental data

2.5
6.0
6.0

1.7
4.0
2.8

1.3
1.3

2.0
3.9

2.0

2.0

2.0

dSm- 1Threshold

7.6
13.0
13.0

4.8
11.0
14.4

5.1
5.1

8.8
13.3

8.8

8.8

8.8

aee,"

aell

12.6
20.1
20.1

8.0
36.0
26.1

9.0
9.0

15.7
22.8

15.7

15.7

15.7

Salt· tolerance data

0.29
0.20
0.14
0.28
0.29
0.17
0.11

0.23
0.45
0.11
0.23
0.10
0.15
0.18
0.23
0.35
0.38
0.16
0.15
0.30
0.43
0.27

U[/oe 50

0.09
0.03
0.04
0.08
0.09
0.05
0.03

0.06
0.13
0.03
0.06
0.03
0.04
0.05
0.06
0.10
0.11
0.04
0.04
0.09
0.12
0.08

u[I(2ue)

0.20
0.12
0.19
0.40
0.21
0.08
0.05

0.25
0.67
0.11
0.25
0.10
0.15
0.19
0.25
0.45
0.49
0.16
0.11
0.26
0.51
0.27

u j /(5u t -u[)

Lr predictions

0.15
0.10
0.13
0.22
0.16
0.07
0.04

0.17
0.26
0.09
0.17
0.08
0.12
0.14
0.17
0.23
0.24
0.13
0.10
0.18
0.24
0.18

Fig. 6

Hoffman (1980)
Hoffman et al. (1979)
Lonkert et al. (1976,
personal communica tion)

Hoffman et al. (1979)
Lonkert et al. (1976,
personal communication)
USSL Staff (1977)
Hoffman et al. (1979)
Bower et al. (1970)

USSL Staff (1977)
Bower et al. (1970)

Ingvalson et al. (1976)

Bernstein & Francois (1973)

Bower et al. (1969)

Reference

Table I-Comparisons of the leaching requirement (L r ) predicted by four models with experimentally determined leaching requirements
for several crops.

N

....
UI

t""

0

:=

.-j

z

0

("')

>
t""
Z
=l
~

(IJ

....,
0
:=

.-j

z

I:"j

I:"j

::

>
Z
>
C'l

::

:=

I:"j

>
.-j

~

I

("')

76

HOFFMAN & VAN GENUCHTEN(1964) overestimates, and the method of van Schilfgaarde et al. (1974)
underestimates, the leaching requirement. The method of Rhoades (1974)
also overestimates the leaching requirement, except at low leaching requirements.
The objectives of this discussion were to evaluate four models for predicting the mean root-zone salinity based upon experimental data, and to
determine the Lr by converting the mean root-zone salinity prediction to thecrop salt-tolerance threshold. The leaching requirement is presented as afunction of the salt concentration of the applied water and the salt-tolerance
threshold for the crop. The predicted Lr is compared with experimentally
determined leaching requirements for a number of crops.
II. MATHEMATICAl, ANAI,YSIS OF ROOT-ZONE SAUNITY
Following the analysis of Gardner (1967), which was expanded byRaats (1974), the continuity equation for one-dimensional vertical flow ofwater through soil can be expressed asa()/at = - aq/az - A,

[5]

where () is the volumetric water content of the soil, t is time, q is the volumetric flux density of water, Z is the vertical coordinate that increases positively downward and has its origin at the soil surface, and A is the rate ofwater uptake by plant roots per volume of soil, per unit time. For steadyflow, a()/at = 0 and Eq. [5] reduces todq/dz= -A.

[6]

The steady-state mass balance for salt, neglecting the effects of chemical
precipitation, dissolution, diffusion, and dispersion, isd(qC)/dz = o.

[7]

Integrating Eq. [7] and noting that at Z = 0, the salt flux equals q[C[leads
to[8]
Evaluation of Eq. [8] at the bottom of the root zone (q = qD; C = CD)leads directly to the definition of the leaching fraction (Eq. [1]). This showsthat the leaching fraction is based upon steady-state mass balance considerations. Expanding Eq. [7] by introducing Eq. [6] and [8] gives[9]
where C-l is the inverse of the concentration or alternatively the dilution

Uptakeweighted
averageroot-zone salt
Concentration

C1

L-1

<C,> = In(L)

In[L + (1 - L) exp ( - Zlo))

C1 = L + ZL

C,Linearly
averagedroot-zone salt
concentration

0C
C; = [L+(1-L) exp( -z/oW'

Concentration
vs. depth1>-, = b exp (-z/o)

T

Water
uptakefunction

VariableExponential uptake function(Raats, 1974)~T(4 - 5x)/3Z

!

2T/Z

L-'

25x2-1)/15]"'

0.2::sx<0.8
0.8::s x::s 1.0

0.0::sx<0.2
0.2::sx<0.8
0.8::s x::s 1.0
0.0::sx<0.2

<C2 >

In(L)

tan-'[3(I-L)/5L]'12[5L(1-L)/3]'12-c;- = L-1

+

C2
1
1
C1 = 5L - 2-2L In[0.6 - O.4L)

I

C2!11_2(1-L)X]-'
C = [1-(1-L)(40x-A2 =MethodTrapezoidal uptake function(W. R. Gardner, Chapter 2A)

""l

g; =

<Cs >

1/2

In(L)

1-L

= (81L-1)-c;- = L-1

a(81L> 1)Cs
lOa
C1 = 1- L [tan- ' (9a) - tan-I(a)][l-(1-L)(9x-4x2)/5]-'o......
......

I:""o..,::coz

("l

~

.Z.,

::c
r.IJ
>
I:""

..,

T
As = 5Z (9 -8x)

~
Z

t"l

>
Z
>
C'l

~

::c

t"l

..,>~

40-30-20-10 uptake function.

Table 2-Equations for the salt concentration (C) as a function of soil depth (z), the linearly averaged root-zone salt concentration (C),and the water-uptake-weighted average root-zone salt concentration ( < C» for three different water uptake functions (l>.).
The dimensionless variable x is z/Z.

N~

HOFFMAN & VAN GENUCHTEN

78(Raats, 1974). Equation [9] shows that the rate of water uptake may be calculated as the product of q[C[ and the negative of the slope of the dilution
profile, d(C-')/dz. Integration of Eq. (9] between z = 0 and any arbitrary
depth z within the soil root zone gives the cumulative water uptake (w) between the soil surface and z and can be expressed as[10]
At the bottom of the root zone (z = Z), w becomes equal to the transpiration rate (T), and C equals CD' Equation [10] then reduces to[11]

The water uptake function can be calculated from a measured steadystate salt profile using Eq. (9]. Alternatively, the steady-state salt distribution can be calculated from Eq. [10], provided the water uptake function (h)is known. Table 2 gives three models for >-. The exponential uptake function(>-, in Table 2) was first proposed by Raats (1974). The parameter 0 in thisequation is an empirical constant. The trapezoidal uptake function (>-2 inTable 2) is identical to the normalized uptake function described by W. R.
Gardner (Chapter 2A). The third uptake function (>-3) assumes that water
uptake from successively deeper quarter-fractions of the root zone is proportioned as 40, 30, 20, and 10% of the transpiration rate. This uptake pattern isreminiscent of the old "40-30-20-10" rule used by Rhoades and Merrill(1976), among others. The three water uptake functions are plotted in Fig.
1. For the exponential uptake function, the parameter () was set to 0.2 Z. In
contrast to the trapezoidal and "40-30-20-10" uptake functions, the area
under the exponential function is not exactly equal to 1.0, but to 0.993. Thisdeviation from 1.0 is a consequence of the exponential nature of this uptake
equation, and is considered insignificant.
RELATIVE WATER UPTAKE RATE
2
3
4

o

5

or----r---/"----.----,~~
I

I

I

'

/

I

/

/ '
:' ITrapezoid

l

,y'

, I

//40-30-20-10

,

I

I

I

I

I

I

I

I

I

I
1.0 LL..
__.....L-_--L_ _..I..-_--L._---'

Fig. I-Water uptake patterns as predicted by the three models presented in Table 2, relative
to an uptake rate uniform throughout the rooting depth.

79

2C-WATER MANAGEMENT FOR SALINITY CONTROLRELATIVE CONCENTRATION
OO~~~2~__4~__~6r-__~8__~IO

~ 0.2

0.

w

Q

~ 0.4

§
~

w 0.6

2:

l-

S

~ 0.8

I .0 L -__--L..__--1____...L-__--1._ _~Fig. 2-Soil salinity profiles throughout the root zone at a leaching fraction (L) of 0.1; C/> C I,
C" and C, are the salt concentrations in the irrigation water and those predicted using the
exponential, trapezoidal, and 40-30-20-10 water uptake models, respectively.

Substitution of the three uptake functions of Table 2 into Eq. [10],solving the indicated integral, and using Eq. [11] results in the salt-concentration distribution equations given in Table 2. A graphical illustration ofthese distributions for L = 0.1 is given in Fig. 2. The shapes of these curves
are similar to measured salt distributions (e.g., Bower et aI., 1969, 1970).
There are at least two possible approaches for calculating the averagesalt concentration in the root zone. The linearly averaged salt concentrationC, can be calculated as
-

1 JZ

C= Z

0

Cdz,

[12]

where Z is the depth of the root zone. Application of Eq. [12] to the equations for the salt concentration as a function of depth in Table 2 leads to expressions of C as a function of L for each of the uptake functions (see Table2). Likewise, one can calculate the average root-zone salt concentration bymeans of a water-uptake weighted function « C»,[13]
where the upper integration limit has been extended to infinity to accommodate the exponential uptake function (A2 and A3 vanish below the rootzone). Substitution of the expressions for A and C ip Table 2 into Eq. [13]results in the water-uptake-weighted average root-zone salt concentrations as given in Table 2. Note that the resulting expression for < C> isthe same for all three water uptake functions. Bernstein and Francois (1973)
showed earlier that < C> is independent of the assumed water uptake distribution.

80

HOFFMAN & VAN GENUCHTEN

z

14

0

i=
<C

0::
I-

12

Z

W

(.)

z

0

(.)

10

~

<C

II)

w

z

8

0

\
\

\

N

I-

0
0

\

6

\

0::

Z
<C

w
:E
w

4

:5
w

2

~
I-

- I

I

" ~ /c,_ c,

\
\

'\

c2 /c

'" , ----" ---::::-::::\\''-'.......

'- .....

- ..... .............::/ -- -------:::==(C >/ci
- ----::==---....
......

.......

0::

0.1
0.2
0.3
0.4
LEACHING FRACTION (L)0.5

FiL 3-Re!!tive mean root-zone salt concentrations as a function of leaching fraction (L); C;,
C" and C, are for the exponential, trapezoidal, and 40-30-20-10 water uptake models, respectively, of Table 2, and < C> is the uptake-weighted average salt concentration foreach of the three uptake models.

For comparison, the relationships between the relative mean root-zone
salt concentrations and L for all four models are given in Fig. 3. The parameter 0 for the exponential uptake function was taken as 0.2Z; the reason forthis choice will be obvious in the following section. Of interest in Fig. 3 isthe lack of sensitivity of < C> ICI to L as compared with the other models.
III. MEAN ROOT-ZONE SAUNITY
To estimate the leaching requirement based on the prediction of theaverage root-zone salinity, it is first necessary to verify the accuracy of themodels for predicting leaching fraction. For that purpose, we took soil
salinity data from the experiments of Bower et al. (1969, 1970), Bernstein
and Francois (1973), Bernstein et al. (1975), Ingvalson et al. (1976), andHoffman et al. (1979). In most, but not all, of these experiments chloride
irrigation waters were used so that precipitation at low leaching fractions
should not cause an error. For waters high in sulfate or carbonate, precipitation'could be significant at low leaching fractions and the computer model
proposed by Rhoades and Merrill (1976) may be more accurate.
For vertification of the linearly averaged expressions, the mean rootzone salinity value was calculated as the linear average of the experimentally
determined salt concentration values. Each mean salinity value was sub-81

2C-WATER MANAGEMENT FOR SALINITY CONTROL~ 0.6~---r----'----r----'----r--~
~

u
«

II::

LI.
c.!)

0.5

~
J:
U

;;S 0.4
-'

o

UJ

f-

S 0.3
:::l

u

•

-'
C(

u 0.2
~

«-'
~ 0.1
UJ

II::

o

UJ

J:

f-

O~""':::---I...----...I.----...I.-----'-----'----~

o

0.1

0.2

0.3

0.4

0.5

0.6

EXPERIMENTALLY MEASURED LEACHING FRACTION
Fig. 4-Comparison of experimentally measured leaching fractions from seven experimentswith theoretically calculated leaching fractions from c" where b = 0.2Z. Also shown are thelinear regressions for c" c" and < C> for comparison. Data points are for C, only. Larger
data points indicate more than one observation.

stituted into each of the linear-average models and the equations weresolved graphically for the "theoretical" leaching fraction. For vertificationof the uptake-weighted expression, the experimental salt concentration
values were weighted using the 40-30-20-10 water uptake function. This
procedure is valid because, as shown earlier, the uptake-weighted averagesalt concentration is independent of the particular uptake function. The"theoretical" leaching fraction was then calculated by inserting the resultant < C> value into the uptake-weighted expression. Figure 4 compares
these theoretical L-values with the experimentally measured values. With
the selection of 0 = 0.2Z, C 1 best predicts the mean root-zone salinity. The
other expressions all substantially underestimate L. The lines in Fig. 4 arestatistically fit linear regressions through the data for each model, although
only the data for C 1 are shown. The correlation coefficient of the linear regression for C 1 is 0.94.
The relatively good agreement of C 1 and C 2 with the experimental data
lends credibility to their application. A disadvantage of C, as comparedwith C 2 , is that a value must be assigned to the empirical parameter o. However, we propose the use of C because of its better correlation with the experimental data.
The mean root-zone salinity, based on C, is shown in Fig. 5 as a function of the salinity of the applied water and the leaching fraction. Note thatthe salinity is expressed in terms of the electrical conductivity of the soil
saturation extract (a e) assuming a = 2ae. Thus, the curve for L = 1.0 in
Fig. 5 does not fall on the 1: 1 line. As an example, if soil samples revealed
that the mean soil salinity was 5 dS m- I and the salinity of the applied water

82

HOFFMAN & VAN GENUCHTEN

14

s-

UI
12
"CI
IbOl

!; 10
3!:
....

:; 8
LU

Z

0

N

I-

8a::
z

c(
LU

6
4

~

2

I

234

5

SALINITY OF APPLIED WATER (OJ. dS/m)

6

Fig. 5- The mean root-zone soil salinity as a function of the salinity of the applied water andleaching fraction (L). Curves are based upon the linearly averaged root-zone salt concentration for the exponential water uptake function (C;IC[ in Table 2).

(aj) was 3 dS m- l , the leaching fraction would be estimated to be 0.21 understeady-state conditions.
The large differences between experiment and theory for C, and Cl indicate that, at least under saline conditions, the 40-30-20-10 rule of thumboften quoted as the distribution of water uptake through the root zone
underestimates the water lost from the upper portion of the root zone. The
water uptake distribution is approximately 71-21-6-1 based on C" and50-35-14-1 based on C1 • Although evaporation was ignored in the theoretical development, it may account in large part for the high proportion ofwater lost near the soil surface.

IV. I,EACHING REQUIREMENT PREDICTION
From the definition of leaching requirement as stated in Eq. [3], theunknown term in predicting L, is ab. Unfortunately, this definition is notsuited for use of the large number of experiments designed to establish thesalt tolerance of agricultural crops. A more convenient quantity for evaluating leaching requirement is the crop salinity threshold value. If mean soil
salinity is replaced by the threshold, the result is a graph similar to Fig. 5,

83

2C-WATER MANAGEMENT FOR SALINITY CONTROL
8~--~--~~~--~~--r---'

.
II:f

-6
w

:::l
...J
0:(

>

c 5

...J

o

::c

VI

~ 4

::c

I-

w
Z 3

(.)

Qli
w

...J

g2
~

~
a..

o

It:
(.)

I

234

SALINITY OF APPLIED WATER

5(OJ. dS/m)

6

Fig. 6-Graphical solution for the leaching requirement (L,) as a function of the salinity of
the applied water and the salt-tolerance threshold value for the crop.

with L replaced by L r • The resulting relationship, however, can not beapplied directly, because the mean root-zone salinity for a given salinity of
the applied water must be reduced if L is lower than Lr to prevent yield reduction or, conversely, L could be increased if the crop could tolerate moresalinity. Unfortunately, no mathematical relationship has been developed
to span this gap.
Plants adjust osmotically as soil salinity increases (Maas & Nieman,1978). In salt-tolerance trials, this adjustment is sufficient to prevent yield
loss until soil salinity surpasses the salt-tolerance threshold. Because salttolerance trials usually are designed to maintain leaching fractions approaching
0.5, the osmotic adjustment consistent with no yield loss can be estimatedby the mean soil salinity at 50070 leaching, as given in Fig. 5. As a first approximation, the leaching requirement can be expressed as a function of thethreshold value by reducing C 1 at any given L by C 1 at 50% leaching. This
relationship among salinity of the irrigation water, crop salt-tolerance
threshold, and leaching requirement is illustrated in Fig. 6.
Comparisons among calculated leaching requirements and those measured experimentally are given in Table 1. Linear regressions correlatingthese calculated and measured values are given in Fig. 7 for each of the predictive models listed in Table 2. Predicting Lr by (J[/(Je" consistently overestimates, and by (J[I2(Je. consistently underestimates, the leaching require-

84

HOFFMAN & VAN GENUCHTEN

I-

~ .25

:::iE

w

c::

~.20

w

c::

(!j

z

i: .15
u

~
c .10

...J

w

l-

S
::J

~.05

5

O~~~----~----~--~----~----~

o

.05

.10

.15

.20

.25

.30

EXPERIMENTALLY MEASURED LEACHING REQUIREMENT

Fig. 7-Comparison of experimentally measured leaching requirements for six crops with empirically calculated leaching requirements. Data for establishing the least-squares linear regressions are taken from Table I for those experiments where a precise leaching requirement
was reported.

ment. Predicting Lr from a[I(5at - a[) also overestimates the L" except at
low L,. Although not perfect, the L, predictions from Fig. 6 agree well withthe measured values throughout the range of L,'s of agricultural interest. In
view of our ability to measure the leaching fraction in the field, Fig. 6 is asuitable estimate of leaching requirement.

UTERATURE CITED
Bernstein, L. 1964. Salt tolerance of plants. USDA Info. Bull. 283. U.S. Government Printing
Office, Washington, D.C.
Bernstein, L., and L. E. Francois. 1973. Leaching requirement studies: sensitivity of alfalfa
to salinity of irrigation and drainage waters. Soil Sci. Soc. Am. Proc. 37:931-943.
Bernstein, L., L. E. Francois, and R. A. Clark. 1975. Minimal leaching with varying root
depths of alfalfa. Soil Sci. Soc. Am. Proc. 39: 112-115.
Bower, C. A., G. Ogata, and J. M. Tucker. 1969. Rootzone salt profiles and alfalfa growth as
influenced by irrigation water salinity and leaching fraction. Agron. J. 61 :783-785.
Bower, C. A., G. Ogata, and J. M. Tucker. 1970. Growth of sudan and tall fescue grasses asinfluenced by irrigation water salinity and leaching fraction. Agron. J. 62:793-794.
Gardner, W. R. 1967. Water uptake and salt-distribution patterns in saline soils. p. 335-341.
In Isotope and radiation techniques in soil physics and irrigation studies. Int. Atomic
Energy Agency Proc. Ser.
Hoffman, G. J. 1980. Leaching requirement for salinity control in agriculture. p. 277-283. In
Proc. Int. Symp. on Salt Affected Soils, Karnal, India. Feb. 1980.
Hoffman, G. J., S. L. Rawlins, J. D. Oster, J. A. Jobes, and S. D. Merrill. 1979. Leachingrequirement for salinity control: I. Wheat, sorghum, and lettuce. Agric. Water Manage.
2:177-192.
Ingvalson, R. D., J. D. Rhoades, and A. L. Page. 1976. Correlation of alfalfa yield withvarious index of salinity. Soil Sci. 122:145-153.

2C-WATER MANAGEMENT FOR SALINITY CONTROL

85

Maas, E. V., and G. J. Hoffman. 1977. Crop salt tolerance-current assessment. J. Irr. Drain.
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