The use of alkaline and saline waters for irrigation

GIFT OF

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Aerie. Deo t.

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Agric. Dept.

United States Dtet^ettt W Agriculture,

BUREAU OF Sto£$-ili$jfi&ff!ATt NO. 10.
MILTON WHITNEY, Chief of Bureau.

THE USE OF ALKALINE AND SALINE WATERS FOR IRRIGATION.

During the summer of 1902 a representative of the Bureau of Soils
visited the oases of the Oued Rihr country in the Desert of Sahara in
Eastern Algeria. In these oases artesian waters carrying very large
quantities of soluble matter are used successfully for irrigation. From
the information gathered there, and from experience in this country, it
seems that the amount of soluble matter allowable in an irrigation water
has been greatly underestimated by American writers, and that many
sources of water which have been condemned can be used with safety
and success, provided the proper precautions are taken to prevent the
accumulation of the salts. As the precautions are those which should
be taken by every irrigator, even if pure water is used, it seems an
important matter to bring before the American people the methods in
use in the Sahara.

The staple crop grown by the Arabs in the oasis country is the date,
the fruit of a palm tree known to be one of the plants most resistant to
alkaline or saline conditions of the soil, but in addition to this consid-
erable quantities of the deciduous fruits, garden vegetables, and alfalfa
are produced for home consumption.

Some of the vegetables successfully grown are those considered sensi-
tive to alkali, and yet they were being irrigated with water containing
in some instances as much as 800 parts of soluble salts to 100,000
parts of water, sometimes as high as 50 per cent of the salts being
sodium chloride.

The limit of concentration for irrigation water in the United States,
even where only the most resistant field crops are to be grown, has
been placed by some authorities at 30 parts sodium chloride (common
salt) or sodium carbonate (black alkali), and at from 170 to 300 parts
of the less harmful salts, per 100,000 of water. The Bureau of Soils,
however, several years ago insisted that water of a somewhat higher
salt content might be used if the soil had good natural drainage, or
artificial drainage were supplied, and the methods of irrigation were
modified to suit the different conditions. Thus in 1899 1 the following
statements were made after a study of soils and alkali conditions in the
Pecos Valley, New Mexico :

Next to the ownership of the land and the labor questions, the most important
cause of the trouble in the larger portion of the Pecos Valley is the high salt con-
tent of the irrigation water, especially in certain seasons.

At Roswell the principal water supply contains about 76 parts of soluble mat-
ter in 100,000 parts of water. At Hagerman this is increased to about 200 parts ;
at Carlsbad, to 240 parts ; at Florence, to 280 parts ; Red Bluff, 316 parts ; at
Pecos City, Tex., to 400 parts; and below Pecos City to over 500 parts. Five

!Rept. 64, Field Operations, Division of Soils, 1899.

hundred parts of soluble matter maybe taken as the extreme limit of endurance
for plants, while 250 or 300 parts mark the danger point at which the results of

the use of the water are very uncertain.

*******

The limit of endurance for most cultivated plants in a water solution is about
1 per cent or 1,000 parts of the readily soluble salts in 100,000 parts of water,
but it must be remembered that in field culture the water is applied to soils
already containing more or less of these salts, and also that evaporation and
consequent concentration immediately set in after the application of water. It
was found at Carlsbad that about 300 parts of soluble matter per 100,000 parts

of water marked the extreme limit of safetv of the use of water at that place.
* * * * * * *

One thing should be said in connection with the Carlsbad area, which seems
rather anomalous in view of the statements of other investigators, namely, that
with a water supply so near the limit of crop endurance as this becomes at times
and in those areas in which there is already a large accumulation of salts,
economy in the use of irrigation water, which is generally recommended in alkali
regions, is one of the worst methods which can be practiced. Where the soil
contains a relatively large amount of salt and but little water containing much
salt is frequently applied, the ordinary evaporation will increase the salt content
of the soil to such an extent that crops can no longer survive, whereas if ade-
quate drainage is provided, and a large amount of water is used, the excess of
salt resulting from the evaporation of previous applications of water, may be
removed, and the soil moisture be maintained at nearly the same concentration
as the water supply.

The fact that the Arabs in Algerian oases are actually growing sensi-
tive plants by the aid of irrigation waters containing from 400 to 800
parts of soluble salts, in some instances 50 per cent sodium chloride,
shows that the Bureau has been on the conservative side in its esti-
mates, and should encourage a more hopeful feeling among the people
occupying areas where only alkali water is available for irrigation.

The prerequisite to the use of water of high salt content in irrigation
is the knowledge that the methods employed are opposed to the teach-
ings of most American writers on the subject. Those who place the
low limit of safety for alkaline irrigation waters have taught that where
water was badly alkaline irrigation should be sparing. They have not
insisted on thorough drainage, and they have warned irrigators against
too frequent irrigation. With such practices the limit of concentration
which they set is probably high enough, and even then all except the
most sandy soils or those with exceptionally good natural drainage
would ultimately be damaged.

The methods in the oases are quite different. The Arab gardens are
divided into small plots, about 20 feet square, between which run drain-
age ditches dug to a depth of about 3 feet. The soils being very light
and sandy, this ditching at short intervals insures the most rapid and
thorough drainage. Irrigation is by the check method, and application
is made at least once a week, though often two wettings a week are
deemed necessary. A large quantity of water is used at each irrigation.
Thus a continuous movement of the water downward is maintained,
there is little opportunity for the soil water to become more concentrated
than the water as applied, and the interval between irrigations being so
short but little accumulation of salt from evaporation at the surface
takes place. What concentration or accumulation does occur is quickly
corrected by the succeeding irrigation.

The native gardens are situated in the date palm groves and the
vegetables and fruit are grown in the partial shade cast by these trees.
The natives not only have the question of very saline irrigation waters
to contend with, but the soils originally are often very alkaline. In
three years they reclaim land too salty to grow the minor crops, using
the saline water for that purpose, following the same plan of drainage
and weekly irrigation as where crops are growing. One garden situated
on the side of a salt flat and originally very saline was visited. Here
alfalfa was in very good condition, and fig, pomegranate, melon, tomato,
cabbage, pepper, and other plants were growing luxuriantly. The
reclamation of this plot by irrigation twice a week had taken three
years.

The native gardeners exercise great judgment in adapting their crops
to the soil conditions. Where most alkaline the date palm alone is
found ; in other parts of the grove are grown the fig and pomegranate,
and in other parts the vegetables less resistant to alkali. The amount
of salt in the soil sufficient to injure the palm was not determined, but
the French were unsuccessful in an attempt to establish a grove, the
water used in irrigation being taken from a salt pond and containing,
according to field determinations, 3 parts sodium carbonate, 5 parts
sodium bicarbonate, and 1,036 parts sodium chloride in 100,000 parts.

The irrigation water is all drawn from artesian wells. A number of
samples were sent in to the laboratory for analysis, the results of which
are shown in the following table. These are fair average samples of the
irrigation waters in use, and do not represent by any means the maximum
of salinity. Field tests showed as high as 816 parts to 100,000 water
in actual use on soils growing vegetables.

Chemical analyses of artesian water used in irrigating gardens in Sahara Oases,

Algeria.

Constituent.

Well at
oasis Ta-
bes-best.

Well at
oasis Kudi
Asli.

Well at gar-
den of Ben
Hadriah.

Ions:
Calcium (Ca) .

Per cent.
9.92

Per cent.
4.19

Per cent.

9.86

Magnesium (Mg)-_ ._ - --

4.52

6.02

4.26

Sodium (Na)

14.03

20.48

14.18

Potassium (K)

4.27

2.35

2.72

Sulphuric acid (804)

34.38

29.43

17.59

Chlorine (CD

28.06

36.21

27.05

Bicarbonic acid (HCOs)

5.02

1.32

24.34

Conventional combinations :
Calcium sulphate (CaSO4>

33.04

14.23

24.90

Magnesium sulphate (MgSO.j)

13.63

24.29

7.04

Magnesium chloride (MgCte) -

7.23

4.41

16.72

Potassium chloride (KC1)

8.12

4.48

5.19

Sodium bicarbonate (NaHCO1))

6.92

1.81

33.54

Sodium chloride (NaCl)

31.06

50.78

12.61

Total solids in 100 000 parts water

601.50

408.10

571.90

Enough has been written to show that much more can be done with
alkaline irrigation water than has hitherto been generally thought possi-
ble, and while the intensive culture of the Algerian gardeners is not
suited to our Western conditions, there is believed to be no reason why
their methods can not be adapted, even with an improvement in point
of economy, to more extensive cropping of the soil.

The soils in the Pecos Valley are not unlike those of the oases, and
the general conditions in the two places are somewhat similar, although
the irrigation water, even at the lowest stage of the Pecos River, is not
as alkaline as the artesian water of the desert, nor are the soils natur-
ally as alkaline. Employing the Algerian method of frequent irriga-
tion with generous amounts of water on land well drained by open
ditches or tile drains, large areas now out of cultivation might be used
to grow alfalfa, truck, and other crops.

It is believed that the information conveyed in this circular will be
of great value to the people of this country residing in regions affected
with alkali, and that it will result ultimately in bringing into cultiva-
tion much land that has hitherto been thought worthless because of the
character of the water available for irrigation.

THOMAS H. MEANS,
In Charge of Alkali Reclamation Work.

Approved :

JAMES WILSON,

Secretary of Agriculture.

. WASHINGTON, D. C., July 1, 1903.

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