Cavazza L.
in
Bouchet R. (ed.).
Reuse of low quality water for irrigation Bari : CIHEAM
Options Méditerranéennes : Série A. Séminaires Méditerranéens; n. 1 1989
pages 49-57
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--- Cavazza L. Irrigation systems an d tech n iqu es for salin e water. In : Bouchet R. (ed.). Reuse of low quality water for irrigation. Bari : CIHEAM, 1989. p. 49-57 (Options Méditerranéennes : Série A.
Séminaires Méditerranéens; n. 1)
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Irrigation systems and techniques for
salinewater
CAVAZZA University of Bologna - Italy
all regions that suffer, if only seasonally, from insufficient rainfall, agriculturalists have always sought to find additional water for irrigation.
Today these efforts are increasing due to problems of increased population, the tendency toward more efficient labour and to higher standards of living.
They are favoured by the availability of capital, progress i n agricultural techniques, as well as by market expansion and organization. Under these conditions water at higher cost and of lower quality than was accepted i n the past is now being used in dry areas, while i n rainfed areas irrigation is also being extended to crops that traditionally have been coisidered in need of irrigation.
As a whole, i n semi-arid conditions, the shift from dry farming to irrigation with brackish water has led to increases in yield and profit. These
advantages, however, are lower the more saline the water is. This implies that the maximum level of water salinity actually tolerated in practical irrigation increases with aridity, management skill of the farmers and with market value of the product; it decreases with rising living standards.
For example, years ago canning tomatoes irrigated with brackish water and hand harvested were an important crop i n some areas of southern
low yield. of the same water is now used for more valuable crops (mainly autumn-to-spring vegetable crops, or capsicum, eggplant, artichoke, grapes, etc.). is possible that if the market becomes unfavourable for these
valuable crops, the area irrigated with brackish water will contract and the highest acceptable salinity for practical irrigation will drop. This
illustrates the evolving contrasts in the rush to extend the use of saline water in irrigation.
- requirements
is well known that the main in using
is to of
excessive salt levels in the soil must a given
developed of
the and many decades scientists have s t i l l b e i n g concept is well known both in its second
Lab.; see et al., is:
= E = &/
=
E c~ = of
zone;
E = the same
and =
soluble salt contents.
The second is:
= E E,, - E ,W),
but it is:
= Ecw / 2-
E,, = of
soil paste and
E c e ~ = Ece to 100% yield loss.
is
soil salinity
might be to of
FAO, No.
a steady state
is not so as in a of the salts
is leached out of
zone by following season (mostly in
of
conditions has not been sufficiently developed.
The old of
the salinity of could take into a simple way:
= (Ecr. V,
+
Ecw .VW) (Vr+
et al., 1967) is
to is not the case with the new of E,,.
liquid flow in the still too i n common of too
the soil-plant system. As a do not a
of
effect is Table
1 by Lunin et al., 1960.
to leach out of the soil the salts
become
complicated when as well a s some of
account.
- methods
The suitability of to
the use of is well known. Continuous flooding c m fields as well as
is
of
of salinized soils (this method is now mostly
low When the basin is
method a
of
conditions has many decades,
especially of
(Figure 1). One so t h a t
the is
placed in such a way
above the level of
by zone
by letting the salt accumulate on one edge of the
is by
et al., 1976);
closed at the bottom, such as
salt accumulation at the soil the conditions
of plants, i.e., by is the
to of
of the plant could
to
avoids
a of t h e d e p t h of
application and of
to small depth of single application.
a way
to a
soil-
a well known
(Figure 2; 1975).
of the of
the application of is
that salt tends to accumulate a t t h e of
zone et al.,' 1973).
(e.g.
this a at
is not likely to zone.
a
mix up the soil and, anyway, it is not easy to a
of soil.
- Water sources and irrigation methods
of the choice of should be
a) at
slightly fluctuating salinity;
b)
c )
of t h e s e c a s e s , m o s t of t h e Of m a i n is the choice of a system which
salt leaching, good (if
the is annual) and
of a well
1968). A of
of typical of
of the
usually communicates with the sea and its statics of Ghyben- (Childs, 1969; Cavazza, 1981).
A of (i.e. two
the shallow soil (1 m deep) t h a t mesozoic limestone and
salt of
on On
the bases of its
exceed the sea level by a of the thickness of
equal to Ah = (ps - pf) /pf pf and ps the of
is 1/40; i n
Ah = 1/30 1955; Cotechia, 1955;
1964).
level of to
to flow the coast. On (e.g.
climates) is a
of
on flow of
to of the
(see Figure 3).
by a well,
table, the floating balance of on the salt
is will tend to
to of 1
to 30. obvious well
below sea level
the tfie well will below by the cone of salt
will become.
to of
of all, its salinity is 1 . 5 t o 2%0) a t t h e
beginning of is
of cycle).
is double at the e n d of
is well is
low o n l y w h e n t h e l e v e l
well, hence is small. The condition was once obtained by wheels as
methods used
now the use of
well a s cost salinity of this type of is often not too high;
it might be comes
towns, due to possible of
Technicians the cheapest
of is
if to a one, of
is the health
by
by to be
at of is also used i n
is whole a m o u n t of is
volumes, inside which the of most of This usually multiplies the effects of these
on soil at
clogging ( e x a m p l e s s h o w n i n Figure 4 ) .
this type of
of the effluent (Sposito et al., 1978;
et al., 1981; et al., 1983). Usually
this implies a of the effective
adjusted as the computed one.
- Other technical aspects
Let us go back of
accumulation in the soil.
values) at not too to to keep
is a shallow,
slowly is
it is
depths, of
zone.
aluminium sesquioxides (mainly alfisols), so
is good
is applied chiefly to of
the same soil so as a
of salts the soil, was
between those of in
the Only with
2%0 is it possible
is as
of
application is usually small
(about 250
to
at peak of a
of 3,000-4,500 m3ha.
of the soil, its is usually kept so that a continuous slow of
is zone.
need to be common
is not beneficial to satisfy the whole as it
is by its
= ETC - ETo X because a n excessive
a low (low
content, delayed
shipping capacity). Usually only about 2/3 of the
whole is
aspect. This that the
of is two
is while only
of
of t h e is to choose between a
by
one caused by soil
comes to help. No now
is
by to a its
questionable.
of a non-
limiting amount of a
constant, limited flow of is also i n c h o o s i n g between the use of
as a whole of to
The has
single cases by taking into account as
a) yield of a s a function of
b) flow;
c ) cost of both volume;
application, of
e) each
The functions (a) a
way as to be by
(y = const.) in a to a given a
then techniques suitable.
is
two th.e line
the slope of
of maximum yield
one, cost of
of the saline one, the of
the volume of
is the use of the
sensitive
economical aspects should also be taken into account.
some situations a
a in
is of
is low and it is t h e n suitable
stages, when the amount of such a type of mostly in a
could to mixed
condition is
is a
has to be put in a
way. is not the flow of
of this season. The solutions of the
delay in the use of it
i n
the peak is applied by
of shifting at saline mixed)
of the canopy with
of the effects, both positive and negative, of on
conditions of
plant, while (Cavazza, 1968).
consistency,
1937).
held beliefs on tested, i.e.
to blossom becomes
A., Y. 1981. The use of gel of bound Ca and in a sewage affluent-soil systems. Shuval in
zone ecology
and Wescot, 1976.
FAO, No. 29.
L. and L.E. 1973. Leaching studies: Sensitivity of alfalfa to salinity of
Sci. Soc. 37, pp. 931-943.
E., 1975. Two-dimensional of
a Soil Sci. Soc. Am.
pp.604-617.
Cavazza, L., 1978. of
The
Ed. by W. Junk N.V. pp 53-79.
Cavazza, L., 1981. UTET.
Cotecchia, 1955.
in zone con
d'acqua Geotechnica, 2,105 p.
Childs, E.C., 1969. An to t h physical basis ofsoil London: John Wiley a.S.
1955. Some on the use of FA0,Stenciled 55-9-5602.
Ficco, N., 1961. Un con
Genio 24,pp. 753-766.
Lunin, J., Gallatin, C.A. and L.V. Wilcox, 1960.
Use of
Exp.: USA., No.
213.
V. 1983. Soil
conductivity as affected by physical of
No. 3, pp. 771-770.
E., 1937. con
Stazione 26,72 p.
and 1967. Salt to
T.W..
USA: of
pp. 998-999.
Sposito, and C.S. Lavesque 1978.
Soil Sci. Soc. Am. J., No. 42, pp.
600-706.
a n d 1950.
Co.
E. Y. Vaadia, 1973.
London: Ecologic. Studies, No.
5.
L. and C. 1964.
della salinita delle acque
del Scienza e Technica No.
4, pp. 15-28.
Table Permissible number of irrigations with brackish water between leaching rains for crops of different salt tolerance
Irrigation water
Total salts Electrical
conductivity
Parts per MiIliSiemens,
million centimeter al
Source: Lunin et al.,
Irrigations for crops having
Good salt Moderate salt Poor salt
tolerance tolerance tolerance
Number Number Number
' . 11
of = s a l t
et al., et al.,
2: in
For (% of
of
(meq/dm3 of bulk soil volume). From
? 20 cm
I
3: of
of of well salinization caused by
4: Accumulation in time of N a a n d
is also evident (?: unpublished data
m
P
l
