CHAPTER VII: DATE PALM IRRIGATION

By P.J. Liebenberg and A. Zaid
Date Production
Support Programme

This chapter describes date palm irrigation and aims to calculate water
requirements of this species as well as schedule irrigation to ensure that the
date palm gets the necessary quantity of water when needed.

1. Introduction

Like any other fruit tree, date palm needs suffi cient water of acceptable
quality to reach its potential yield. In Table 48 quantities of water made
available to date palm around the world can be seen. It is worth mentioning that
all these countries use fl ood irrigation, except for Israel, which uses drip
irrigation.

Table 48
Date palm irrigation around the world

Place

Quantity (m3/ha)

Algeria

15,000 - 35,000

California, USA

27,000 - 36,000

Egypt

22,300

India

22,000 - 25,000

Iraq

15,000 - 20,000

Jordan Valley, Israel

25,000 - 32,000

Morocco

13,000 - 20,000

South Africa

25,000

Tunisia

23,600

Table 49 shows differences in summer and winter requirements in Tunisia.
Summer water requirements (July, August and September) are about 7,154
m3/ha, while only 4,372 m3/ha are needed for the winter
period (December, January and February). Summer requirements are almost double
the winter ones and constitute 1/3 of the total annual
consumption. Note these values are made available to the trees through fl ood
irrigation.

Differences in water requirements between different regions of the same
country are common as illustrated in the case of Algeria (Table 50). The date
growing area of the Sahara needs approximately 34,190
m3/ha/year,while Ziran region needs only 15,000.

Table 49
Water quantity consumed per ha of Deglet Nour date palm
at Tozeur (Tunisia)

Month

Consumed Quantity (m3/ha)

January

1339.2

February

1693.4

March

1874.8

April

2073.6

May

2142.7

June

2073.6

July

2410.5

August

2410.5

September

2332.8

October

2142.7

November

1814.4

December

1339.2

Annual consumption

23,647.4

Table 50
Approximate water requirements of date palm at
different regions of Algeria

Scientist (Year)

Region

Number of
trees per ha

Approximate
needs
(m3/ha/year)

Rolland
(1894)

Sahara
(Algeria)

130

34190

Rose
(1898)

Ziban
(Algeria)

144

10368

Jus
(1900)

Oved Rhir
(Algeria)

130

22750

Wertheimer
(1957)

Ziran
(Algeria)

120

15000

2. Factors infl uencing water requirements

It is necessary to take certain aspects into consideration in order to
calculate the volume of water required by a palm. The following aspects play a
major role in this calculation:

a. Soil salinity: If the soil is saline, more water must be given to
enable a leaching process for clearing the salt from the soil.

b. Temperature: The higher the temperature, the higher the rate of
evaporation and the more water the plant needs.

c. Humidity: The lower the humidity level, the more water
needed.

d. Wind (speed and occurrence): Higher constant wind speeds cause
higher evaporation and thus higher water demands.

e. Cloud cover: More water is required during periods of less cloud
cover.

It is worth mentioning that all above factors infl uence evapotranspiration,
which strongly determines the water requirements.

Irrigation

Irrigation is the timely application of water to a crop in need of water. Any
water applied when not necessary, is a waste of a precious commodity. For
example: if water is applied too late in the season, then it is useless because
the crop is already dead or the production suffered so much that there will be
no fruit, even though defi cient water is then applied over the growing period.
The opposite is also true; if too much water is applied, the plant may also
suffer. The crop may die due to waterlogging. Usually date palms do not suffer
from too much water although, as illustrated, i t is possible in uncontrolled fl
ow from artesian wells at Qatif, Saudi Arabia (Dowson, 1982). It, will however,
still be waste of water, as the farmer could use this water to irrigate other
palms or crops.

Irrigation must take place where the roots of the plant can easily reach it.
It is of no use to the plant if water is applied where the roots cannot reach
it. Let us look at the root development of a date palm tree. If the soil is
divided into four layers of equal depth from top to bottom, 40 % of all roots
can be found in the top layer, 30 % in the second layer, 20 % in the third layer
and the remaining 10 % in the last layer. The same percentages apply in
concentric rings around the plant (Figure 62). The same percentage of water will
also be extracted from the soil in the different layers due to the presence of
the roots in these respective layers.

For mature date palms, the depth is about 5 m,and 3 m radius around the
trunk. Thus, it is seen that for dates 40 % of all water is extracted from the
first 50 cm, 70 % is from the first 100 cm, 90 % is from the top 150 cm and only
10 % is from the last layer or 150 to 200 cm and deeper. For young date
plantlets this depth can vary from 25 to 50 cm and the radius from 10 to 30 cm,
depending on the size of the plant. This means that the irrigation water must be
applied within these boundaries to enable the plant to reach it. However, it is
important to apply water be applied in such a way that it does not reach the
deeper soil levels in order to ensure proper root development of the date
palms.

Localised irrigation (e.g. drip and micro) will therefore be more effi cient
than non- localised one (e.g. fl ood irrigation).

After planting small tissue culture-derived date palms, the volume of soil
from which it can extract water is very small. If a person is not careful, suffi
cient water may be applied, but not enough will be available to the plant for
optimum growth. It is thus necessary to ensure that enough water reaches the
area where the roots are. Irrigation must preferably be done by basin, micro or
drip methods. Due to the shallow root depth at this stage, frequent irrigation
is also necessary to ensure that the palm does not suffer from water deficiency.
Even more care should be given if the palm is planted in a very sandy soil.

3. Different irrigation techniques

Different irrigation techniques are available to irrigate crops, but not all
of them are suitable for date palm irrigation. The following methods are of
importance and each has its own advantages and disadvantages:

a. Flood irrigation

This irrigation method is the oldest method known, and is also the method
most widely used in date palm culture. It has, however, advantages as well as
disadvantages which are outlined below:

i. Advantages:

(1) running costs are low;
(2) easy to apply; and
(3) initial costs
are low if the area is fairly flat.

ii. Disadvantages:

(1) diffi cult to achieve a high effi ciency rate;
(2) labour
intensive;
(3) irrigates areas in between where no palms are planted;
and
(4) not well suited for sandy soils.

b. Furrow and basin irrigation

It is basically a redesign of fl ood irrigation to eliminate some of the
disadvantages listed above and thus make it more effi cient.

i. Advantages:

(1) running costs are low;
(2) easy to apply; and
(3) initial costs
are low if the area is fairly flat,

ii. Disadvantages:

(1) labour intensive; and
(2) interferes with mechanical
operations.

c. Sprinkler irrigation

This is the oldest modern irrigation method and was introduced to enhance
effi ciency and to enable automation.

i. Advantages:

(1) more effi cient use of water is possible;
(2) easy to schedule -
manage;
(3) less labour is needed; and
(4) tpography is not a
limitation.

ii. Disadvantages:

(1) expensive (installation);

(2) running costs are high;

(3) heavily influenced by wind and temperature (spray pattern and
evaporation);

(4) not well suited for small palms because water can enter from above
into the growth point of the palm.

d. Micro irrigation

This method was more recently introduced and was developed in South Africa to
irrigate mine dumps to prevent the wind from blowing the sand away. It was then
adapted for irrigation of trees and other crops.

i. Advantages:

(1) more effi cient use of water is possible;

(2) running costs are lower than sprinkler irrigation (lower pressure
needed);

(3) easy to schedule - manage;

(4) only areas that need water are irrigated;

(5) topography is not a limitation;

(6) It is easy to automate;

(7) It is not labour intensive; and

(8) several spray patterns are available to suit date palms (e.g. gaps in
the spray pattern so as not to wet the growth point or the trunk of the
palm.)

ii. Disadvantages:

(1) Installation costs are high;
(2) needs clean water; and
(3)
infl uenced by wind and temperature (spray pattern and
evaporation).

e. Drip irrigation

This is the latest irrigation method introduced and was developed in Israel
where there is scarcity of water (Figure 62).

i. Advantages:

(1) more effi cient use of water;
(2) running costs are low;
(3)
easy to schedule/manage;
(4) topography is not a limitation;
(5) only
the water needed by the palm is applied;
(6) not infl uenced by
wind;
(7) easy to automate; and
(8) not labour
intensive.

ii. Disadvantages:

(1) expensive (Installation);

(2) requires very clean water; and

(3) sometimes difficult to determine if the correct amount of water has
been applied by the system, and when it becomes clear that it is too little,
it may be too late.

4. Methods for calculating date palm water
requirements

From the earliest times, different methods were used to calculate the water
requirements of different crops. As a result, numerous methods have been
developed and adopted for date palms. Some of these methods are more accurate
than others and some more convenient to use than others, because of the
availability of information for the site where the date trees will be planted.
The following are a few of the methods available:

- Evapotranspiration/Class A Pan Method;
- Penman's Equation;
-
Blaney-Criddle Equation; and
- Solomon and Kodama's
Equation.

a. ETP Class A Pan

In Israel, USA and Southern Africa, the evapotranspiration/Class A Pan Method
is frequently used because the needed information, is readily available.

Where:

AWR = Amount of water required during period under
observation.
ETpan = Evaporation for period in mm as measured
with Class A Pan.
CFpan = Crop Factor for that period.
h =
Efficiency of irrigation system (in decimal).

Table 51 shows in more detail the calculations done to forecast water
requirements of the palms for the 12 months of the year and using different
irrigation methods for Naute - Namibia. (Note that this is for the Southern
Hemisphere harvesting period is March to April)

b. Revised Penman-Monteith Method

The Penman method is widely accepted as the most accurate method of
calculating water requirements for crops. This method makes use of daily
climatic information (e.g. maximum and minimum temperatures, wind velocity,
humidity and radiation per day) to calculate the reference evaporation ETo. Due
to the relative complexity of the formula, it is best used with the help of a
computer program. The reference crop evaporation (Eto) is first determined and
then the water requirement is calculated using the following formula:

Where:

kc = Crop Factor
Eto = Reference Evaporation
mm/day
Etcrop = Crop Evapotranspiration mm/day

ETcrop = kc * ET0
[mm/day]

In Tables 52, 53 and 54, calculations done with Cropwat 7 can be seen.
Cropwat 7 is a computer programme based on the revised Penman-Monteith method,
to calculate crop water requrements (Smith, 1992)

TABLE 51
Water requirements for date palm at Naute,
Namibia

MONTH

N. of days

kci ii

ETpan

ETa NETT

AWRnett TOTAL for

GROSS APPLICATION FOR DIFFERENT SYSTEMS

MONTH

Micro irrigation

Drip irrigation

Flood irrigation

mm/day

mm/day

mm

mm/day

mm/month

mm/day

mm/month

mm/day

mm/month

JAN

31

0.67

15.30

10.3

317.8

12.1

373.9

11.4

353.1

17.1

529.6

FEB

28

0.61

13.20

8.1

225.5

9.5

265.2

8.9

250.5

13.4

375.8

MAR

31

0.55

10.80

5.9

184.1

7.0

216.6

6.6

204.6

9.9

306.9

APR

30

0.49

9.00

4.4

132.3

5.2

155.6

4.9

147.0

7.4

220.5

MAY

31

0.43

8.10

3.5

108.0

4.1

127.0

3.9

120.0

5.8

180.0

JUN

30

0.37

6.30

2.3

69.9

2.7

82.3

2.6

77.7

3.9

116.6

JUL

31

0.37

6.70

2.5

76.8

2.9

90.4

2.8

85.4

4.1

128.1

AUG

31

0.43

7.90

3.4

105.3

4.0

123.9

3.8

117.0

5.7

175.5

SEP

30

0.49

9.90

4.9

145.5

5.7

171.2

5.4

161.7

8.1

242.6

OCT

31

0.55

12.30

6.8

209.7

8.0

246.7

7.5

233.0

11.3

349.5

NOV

30

0.61

14.40

8.8

263.5

10.3

310.0

9.8

292.8

14.6

439.2

DEC

31

0.69

14.90

10.3

318.7

12.1

375.0

11.4

354.1

17.1

531.2

TOTAL APPLICATION PER YEAR (mm)

2,157.2

2537.9

2,396.9

3,595.4

Flood Irrigation ® h = 60%
Micro Irrigation ® h = 85%
Drip Irrigation
® h = 90%
i - This is an estimate according to some desk study by the
authors of this chapter - 1989.
ii - Use this crop factor only with class A
evaporation pan fi gures.

TABLE 52
Monthly reference evapotranspiration (revised Penman
Montheith)

Meteostation: NAUTE

Country: NAMIBIA

Altitude: 700 m

Coordinates: -26.57 South 17.55 East

Month

MinTemp
°C

MaxTemp
°C

Humid.
%

Wind
km/day

Sunshine
Hours

Radiation
MJ/m2/day

ETo-PenMon
mm/mon

Eto
mm/day

January

18.6

35.1

28

345

11.3

28.6

303.6

9.8

February

18.5

33.7

36

302

10.6

26.4

233.0

8.3

March

17.5

31.8

40

294

9.7

22.6

218.9

7.1

April

13.7

28.1

40

302

10.2

19.8

175.2

5.8

May

9.8

24.1

38

328

9.8

16.3

151.6

4.9

June

7.2

21.2

39

372

9.6

14.6

133.5

4.5

July

6.2

21.2

36

380

9.9

15.6

146.6

4.7

August

7.2

23.4

31

389

10.3

18.8

180.1

5.8

September

10.5

27.4

27

363

10.5

22.5

215.1

7.2

October

13.1

29.9

24

380

10.6

25.6

265.7

8.6

November

15.6

32.6

24

371

11.6

28.7

288.0

9.6

December

17.3

34.4

25

354

12.0

29.9

310.3

10.0

Year

12.9

28.6

32

348

10.5

22.5

218.5

TABLE 53
Crop data

Growth stage

Crop name: DATEPALM

Init

Devel

Mid

Late

Total

Length

days

150

35

150

30

365

Crop coefficient

coeff.

0.80

0.80-1.00

1.00

0.80

Rooting depth

meter

2.00

2.00

2.00

2.00

Depletion level

fraction

0.50

0.50

0.50

0.50

Yield response factor

coeff.

0.80

0.80

0.80

0.80

0.80

TABLE 54
Crop evapotranspiration and irrigation
requirements

Rain climate station: NAUTE
ETo climate
station: NAUTE

Crop: DATEPALM
Planting date:
01/04

Month

Dec

Stage

Coeff

ETcrop

ETcrop

Eff.Rain

IrReq

IrReq.

Apr

1

Init

0.80

5.00

50.0

0.0

5.00

50.0

Apr

2

Init

0.80

4.67

46.7

0.0

4.67

46.7

Apr

3

Init

0.80

4.42

44.2

0.0

4.42

44.2

May

1

Init

0.80

4.17

41.7

0.0

4.17

41.7

May

2

Init

0.80

3.91

39.1

0.0

3.91

39.1

May

3

Init

0.80

3.79

41.7

0.0

3.79

41.7

Jun

1

Init

0.80

3.68

36.8

0.0

3.68

36.8

Jun

2

Init

0.80

3.56

35.6

0.0

3.56

35.6

Jun

3

Init

0.80

3.63

36.3

0.0

3.63

36.3

Jul

1

Init

0.80

3.71

37.1

0.0

3.71

37.1

Jul

2

Init

0.80

3.78

37.8

0.0

3.78

37.8

Jul

3

Init

0.80

4.07

44.8

0.0

4.07

44.8

Aug

1

Init

0.80

4.36

43.6

0.0

4.36

43.6

Aug

2

Init

0.80

4.65

46.5

0.0

4.65

46.5

Aug

3

Init/Dev

0.81

5.06

55.7

0.0

5.06

55.7

Sep

1

Dev

0.85

5.68

56.8

0.0

5.68

56.8

Sep

2

Dev

0.90

6.47

64.7

0.0

6.47

64.7

Sep

3

Dev

0.96

7.33

73.3

0.0

7.33

73.3

Oct

1

Dev/Mid

0.99

8.06

80.6

0.0

8.06

80.6

Oct

2

Mid

1.00

8.57

85.7

0.0

8.57

85.7

Oct

3

Mid

1.00

8.91

98.0

0.0

8.91

98.0

Nov

1

Mid

1.00

9.26

92.6

0.0

9.26

92.6

Nov

2

Mid

1.00

9.60

96.0

0.0

9.60

96.0

Nov

3

Mid

1.00

9.74

97.4

0.0

9.74

97.4

Dec

1

Mid

1.00

9.87

98.7

0.0

9.87

98.7

Dec

2

Mid

1.00

10.01

100.1

0.0

10.01

100.1

Dec

3

Mid

1.00

9.94

109.3

0.0

9.94

109.3

Jan

1

Mid

1.00

9.93

99.3

0.0

9.93

99.3

Jan

2

Mid

1.00

9.89

98.9

0.0

9.89

98.9

Jan

3

Mid

1.00

9.37

103.0

0.0

9.37

103.0

Feb

1

Mid

1.00

8.81

88.1

0.0

8.81

88.1

Feb

2

Mid

1.00

8.32

83.2

0.0

8.32

83.2

Feb

3

Mid

1.00

7.90

63.2

0.0

7.90

63.2

Mar

1

Mid/Late

0.97

7.26

72.6

0.0

7.26

72.6

Mar

2

Late

0.91

6.40

64.0

0.0

6.40

64.0

Mar

3

Late

0.84

5.57

55.7

0.0

5.57

55.7

Total

2,418

0.0

2,418

From tables 51 & 54 it is clear that the date palms at Naute (Namibia)
need between 2,157 and 2,419 mm Nett irrigation per annum to fulfi l their
needs.

5. Leaching

As mentioned earlier, the date palm needs suffi cient water of acceptable
quality to enable it to reach its full yield potential. To reach this aim,
if all agricultural practices are catered for, (except water), then the average
electric conductivity of the soil (ECe) must not exceed 4 dS/m (Ayers and
Westcot, 1985), and that of the water (Ecw) not 2.7 dS/m. If situations occur
where these values are exceeded then leaching must be practised to overcome this
problem. However, due to the scarcity of water or the high cost of water, it
will not always be viable to meet the leaching requirements. In such a case it
may be viable to opt for a lower yield which may be more economical. In Table
55, ECe and ECw values corresponding to % of yield for date palm are shown.

TABLE 55
ECe and ECw values corresponding to yield
percentage

YIELD %

ECe (dS/m)

ECw (dS/m)

100

4.0

2.7

90

6.8

4.5

75

11.0

7.3

50

18.0

12.0

0

32.0

21.0

However, to calculate the quantity of water needed for leaching, the
following formula is used:

Where:

LR = Leaching Requirement (fraction).
Ecw = Electric conductivity of the
water (dS/m).
Ece = Electric conductivity of the soil at % yield to be
obtained (dS/m).

This quantity of water is over and above the nett irrigation required by the
crop during the season. The total annual requirement is then calculated from the
following formula:

Where:

AW = Depth of water supply (mm/yr).
ET = Total annual water demand
(mm/yr).
LR = Leaching requirement.

6. Scheduling

Once it is known how much water to apply, it is also important to know when
to apply it. To determine this, knowledge of the type of soil and how deep it
is, is required. This gives an indication of how much water is in the soil and
how much is available for the palm. This information, combined with the daily
usage of water by the palm, enables the determination of when the next
irrigation cycle is due.

The following fi gures are mean values of available water for the three major
soil types:

Light soils

- 100 mm/m

Medium soils

- 140 mm/m

Heavy soils

- 180 mm/m

The best approach is to determine, through laboratory tests, the water
holding capacity of the specifi c soil under consideration and then to establish
an effective scheduling program.

To ensure that the palm will not be put under water stress, it is the normal
practice to allow for only a fraction of the available water to be extracted.
For date palm, as illustrated below, this fraction equals 0.4 or 40 % of the
available soil water.

EXAMPLE

The water usage of date palm for a certain period is 8.7 mm/day. Table 56
shows that the available water for the soil is 140 mm/m depth. The rooting depth
of a full grown date palm is 2 m. Thus:

Available water

= 2 × 140

= 280mm

Extraction allowed

= 0.4 × 280

= 112mm

Cycle period

= 112 ÷ 8.7

= 12.87 days. 13 days (Practically)

In Tables 57 and 58, an example of a fi xed scheduling programme can be seen
for date palm at Naute (Namibia) as done by Cropwat 7. For this example, note
that no rainfall is taken into consideration.

TABLE 56
Soil data

Soil type: Medium

Total Available Soil Moisture (TAM)

140.0 mm/m

Maximum Rain Infiltration Rate

60 mm/day

Maximum Rooting Depth

200 cm

Initial Soil Moisture Depletion (% TAM)

0 %

® Initial Available Soil Moisture

140.0 mm/m

TABLE 57
Irrigation scheduling

Rain station: NAUTE

Crop: DATEPALM

Plant date: 01/04

ETo station: NAUTE

Soil: Medium

Timing: Fixed intervals (7, 7, 7, 7 days)

Application: Refill up to Field Capacity

Field Efficiency: 85 %

No. Irr

Int days

Date

Stage

Deplet %

TX %

ETa %

Net Gift mm

Deficit mm

Loss mm

Gr.Gift mm

Flow l/s/ha

1

7

8 Apr

A

12

100

100

35.0

0.0

0.0

41.2

0.68

2

7

15 Apr

A

12

100

100

33.7

0.0

0.0

39.6

0.66

3

7

22 Apr

A

12

100

100

32.5

0.0

0.0

38.2

0.63

4

7

29 Apr

A

11

100

100

30.9

0.0

0.0

36.4

0.60

5

7

6 May

A

11

100

100

29.7

0.0

0.0

34.9

0.58

6

7

13 May

A

10

100

100

28.7

0.0

0.0

33.7

0.56

7

7

20 May

A

10

100

100

27.4

0.0

0.0

32.2

0.53

8

7

27 May

A

10

100

100

26.7

0.0

0.0

31.4

0.52

9

7

3 Jun

A

9

100

100

26.3

0.0

0.0

31.0

0.51

10

7

10 Jun

A

9

100

100

25.7

0.0

0.0

30.3

0.50

11

7

17 Jun

A

9

100

100

25.0

0.0

0.0

29.5

0.49

12

7

24 Jun

A

9

100

100

25.1

0.0

0.0

29.6

0.49

13

7

1 Jul

A

9

100

100

25.4

0.0

0.0

29.9

0.49

14

7

8 Jul

A

9

100

100

26.0

0.0

0.0

30.5

0.51

15

7

15 Jul

A

9

100

100

26.3

0.0

0.0

30.9

0.51

16

7

22 Jul

A

10

100

100

26.8

0.0

0.0

31.5

0.52

17

7

29 Jul

A

10

100

100

28.7

0.0

0.0

33.8

0.56

18

7

5 Aug

B

11

100

100

30.6

0.0

0.0

36.0

0.60

19

7

12 Aug

B

12

100

100

32.7

0.0

0.0

38.4

0.64

20

7

19 Aug

B

13

100

100

36.5

0.0

0.0

42.9

0.71

21

7

26 Aug

B

14

100

100

40.4

0.0

0.0

47.5

0.79

22

7

2 Sep

B

15

100

100

42.6

0.0

0.0

50.2

0.83

23

7

9 Sep

C

17

100

100

46.7

0.0

0.0

55.0

0.91

24

7

16 Sep

C

18

100

100

49.2

0.0

0.0

57.9

0.96

25

7

23 Sep

C

18

100

100

51.1

0.0

0.0

60.1

0.99

26

7

30 Sep

C

19

100

100

53.5

0.0

0.0

62.9

1.04

27

7

7 Oct

C

20

100

100

56.3

0.0

0.0

66.2

1.09

28

7

14 Oct

C

21

100

100

58.1

0.0

0.0

68.4

1.13

29

7

21 Oct

C

21

100

100

60.0

0.0

0.0

70.6

1.17

30

7

28 Oct

C

22

100

100

62.4

0.0

0.0

73.4

1.21

31

7

4 Nov

C

23

100

100

63.4

0.0

0.0

74.6

1.23

32

7

11 Nov

C

23

100

100

64.8

0.0

0.0

76.2

1.26

33

7

18 Nov

C

24

100

100

67.2

0.0

0.0

79.1

1.31

34

7

25 Nov

C

24

100

100

67.7

0.0

0.0

79.7

1.32

35

7

2 Dec

C

24

100

100

68.3

0.0

0.0

80.3

1.33

36

7

9 Dec

C

25

100

100

69.1

0.0

0.0

81.3

1.34

37

7

16 Dec

C

25

100

100

69.8

0.0

0.0

82.1

1.36

38

7

23 Dec

C

25

100

100

69.9

0.0

0.0

82.3

1.36

39

7

30 Dec

C

25

100

100

69.6

0.0

0.0

81.8

1.35

40

7

6 Jan

C

25

100

100

69.5

0.0

0.0

81.8

1.35

41

7

13 Jan

C

25

100

100

69.5

0.0

0.0

81.7

1.35

42

7

20 Jan

C

25

100

100

69.3

0.0

0.0

81.5

1.35

43

7

27 Jan

C

24

100

100

66.1

0.0

0.0

77.8

1.29

44

7

3 Feb

C

23

100

100

64.5

0.0

0.0

75.8

1.25

45

7

10 Feb

C

22

100

100

61.7

0.0

0.0

72.6

1.20

46

7

17 Feb

C

21

100

100

58.7

0.0

0.0

69.1

1.14

47

7

24 Feb

C

20

100

100

57.0

0.0

0.0

67.0

1.11

48

7

3 Mar

D

19

100

100

54.0

0.0

0.0

63.5

1.05

49

7

10 Mar

D

18

100

100

50.8

0.0

0.0

59.8

0.99

50

7

17 Mar

D

16

100

100

45.7

0.0

0.0

53.7

0.89

51

7

24 Mar

D

15

100

100

42.3

0.0

0.0

49.8

0.82

52

7

31 Mar

D

14

100

100

39.0

0.0

0.0

45.8

0.76

END

2

1 Apr

D

2

100

100

CROPWAT 7.0 (The information in the last column is only valid for fl ood
irrigation.)

TABLE 58
Water requirement using cropWat 7

Total Net Irrigation

2457.8 mm

No yield reductions

Total Irrigation Losses

0.0 mm

Effective Rain

0.0 mm

Moist Deficit at harvest

5.6 mm

Total Rain Loss

0.0 mm

Actual Water Use by Crop

2463.4 mm

Actual Irrigation Requirement

2463.4 mm

Efficiency Irrigation. Schedule

100.0 %

Potential Water Use by Crop

2463.4 mm

Deficiency Irr. Schedule

0.0%

Efficiency Rain

- %

7. Layout of date palm orchard and irrigation

The spacing between date palms differs worldwide. This can be ascribed to
differences in variety as well as climatic conditions. In Namibia, the trend is
to a 10 × 8 m spacing, 10 m between rows and 8 m in the rows. Some private
farmers also use a 8 × 8 m spacing but, it is not advisable to use a narrower
spacing.

The usage of micro irrigation is recommended due to the sandy soils where
date palm is commonly grown, and the efficiency of this type of irrigation. Care
should however be taken that no water is sprayed into the crown of the small
palm. To this effect, micro's with a 300° - 320° spray pattern should be used.
Furthermore, to optimise the efficient usage of water it was decided to change
the type of micro's during the initial growing period of the date palm to ensure
100 % coverage of the drip area (rooting area). As stated before, due to
shallower rooting in the first years of development, a more frequent irrigation
schedule is recommended during these years than in the later ones. From planting
to year (4) the area covered is about 12 m2 and the flow rate 96
l/h/palm, from year (5) to year (10) the area covered = 18 m2
and the flow rate 104 l/h/palm and from year ten the area covered = 28
m2 and the flow rate 156 l/h/palm (Figure 63). This bigger
area covered in the initial years (0 -3 and 5 - 8) will lead to waste of water,
but on the other hand it will serve as a leaching operation that will benefit
the date palm as a whole. Due to shallower rooting in the first years of
development a more frequent irrigation schedule is required in those years

Figure 62. Drip area of adult date palm tree and root
distribution

Figure 63. Wetting pattern of Micro's