CONTENTS
Crop water relationships and climate
1 Introduction ..................................................................................................................................................................................................................................................... 4.1
2 Climate .................................................................................................................................................................................................................................................................. 4.1
2.1 Rainfall ................................................................................................................................................................................................................................................. 4.1
2.1.1 Rainfall parameters .............................................................................................................................................................................................. 4.1
2.1.2 Effective rainfall ...................................................................................................................................................................................................... 4.1
2.2 Evaporation .................................................................................................................................................................................................................................... 4.3
2.2.1 Evaporation measurement ........................................................................................................................................................................... 4.3
2.2.1.1 Erection .............................................................................................................................................................................................................. 4.3
2.2.1.2 Calibrating the scale .......................................................................................................................................................................... 4.3
2.2.1.3 Reading the scale ................................................................................................................................................................................... 4.4
2.2.1.4 Maintenance ................................................................................................................................................................................................. 4.6
2.3 Radiation ............................................................................................................................................................................................................................................ 4.6
2.4 Sunshine duration ................................................................................................................................................................................................................... 4.6
2.5 Temperature ................................................................................................................................................................................................................................... 4.7
2.6 Water vapour ................................................................................................................................................................................................................................ 4.7
2.7 Wind ...................................................................................................................................................................................................................................................... 4.11
2.8 Automatic weather stations .................................................................................................................................................................................... 4.11
3 Crops ....................................................................................................................................................................................................................................................................
3.1 The role played by water in plants ................................................................................................................................................................
3.2 Plant roots .....................................................................................................................................................................................................................................
3.2.1 Root systems ............................................................................................................................................................................................................
3.2.2 Factors influencing root development .....................................................................................................................................
3.3 Groundwater withdrawal patterns....................................................................................................................................................................
4.12
4.12
4.12
4.13
4.14
4.15
4 Evapotranspiration ............................................................................................................................................................................................................................. 4.15
4.1 General ............................................................................................................................................................................................................................................. 4.15
4.2 Daily and seasonal evapotranspiration .................................................................................................................................................... 4.16
4.3 Peak periods of evapotranspiration ................................................................................................................................................................ 4.16
4.4 Factors influencing evapotranspiration ..................................................................................................................................................... 4.16
4.5 Effect of groundwater levels on crop growth and harvests .............................................................................................. 4.17
4.6 Critical periods ....................................................................................................................................................................................................................... 4.17
4.7 Determination of evapotranspiration .......................................................................................................................................................... 4.18
4.7.1 A-pan evaporation and crop factors ........................................................................................................................................... 4.18
4.7.2 Relationship between short grass (ETo) and A-pan evaporation (Eo) ................................................ 4.19
4.7.3 Direct application of Penman Monteith method (short grass reference) ..................................... 4.21
5 References ..................................................................................................................................................................................................................................................... 4.42
All rights reserved
Copyright ¤ 2003 ARC-Institute for Agricultural Engineering (ARC-ILI)
ISBN 1-919849-24-6
Crop water relationships and climate
4.1
1 Introduction
The first phase in project planning and design is the determination of the crop water requirement. A plant
is actually an organic pump that withdraws water from the soil reservoir. It is, however, more than that as
it reacts to groundwater tension or a water surplus and is usually able to adapt to its water environment
within reason. Plants absorb and release moisture to the atmosphere through the transpiration process,
which takes place through stomata where water is exposed to the atmosphere and is lost as water vapour.
Only a negligible amount (less than 10%) of the water absorbed by a plant is retained in the plant fibres as
almost everything is lost during the plant cooling process. Transpiration rate is high when evaporation is
normally high, that is during dry, warm, windy conditions and low during cool, moist conditions.
Therefore the water requirement of a plant is determined by the amount of water which is absorbed and
lost through transpiration. However, the actual water requirement is not only determined by the reigning
weather conditions, but also by the type, age, health and feeding status of the plant as well as the opening
and closing of the pores as they react to light and water shortages within the plant. The size and quality of
the harvest are highly influenced by the magnitude and duration of water tension within the plant.
Furthermore it is known that most plants experience definite growth stages during which water shortages
have a higher influence on crop size than other times. On the other hand, crop size does not simply
increase with an increase in water applied to a plant, as nourishment and care also play a role.
2 Climate
Climate is influenced by the following:
2.1 Rainfall
Rainfall is the depth of rain measured in a correctly set up rain gauge for a specific period.
2.1.1 Rainfall parameters
The rainfall for an area is often characterised by the average of the total annual rainfall measured
over a long period. Usually the results of at least 30 years are used to determine an acceptable
average. As extreme values strongly influence the average, a tendency to express rainfall for an
area in terms of a median value has arisen. The median is the middle value obtained when yearly
values are arranged in ascending order.
The average annual rainfall is used in the planning of dam capacities and also in irrigation water
balance calculations. The shorter the period for which averages are determined, the less reliable
the results are.
2.1.2 Effective rainfall
All rain that falls is not available to plant roots because of interception, evaporation, run-off and
seepage. Rainfall figures are often used as if all rainfall reaches the soil surface. This is not the
case as dense foliage needs more water to wet the leaf cover to such an extent that water will move
between the leaves to wet the soil. The part of rainfall which remains on branches and leaves of
plants is known as intercepted water, which is considered only as water being lost by evaporation
and not water which may eventually trickle down the stalk.
4.2
Irrigation Design Manual
A relatively large quantity of water is therefore subtracted from the measured rainfall as
evaporation losses and depends mainly on the following:
x Density of foliage: Trees and shrubs intercept more water for the same area than strawberries
or onions.
x Leaf area: Leafy crops intercept more water than stalky crops, e.g. potatoes as opposed to
wheat.
x Rainfall duration: A short shower will have a higher percentage of interception than a long
shower.
x Rainfall intensity: High intensity showers have a lower percentage of interception and vice
versa, for the same time.
Statistics obtained from South African weather experts indicate that interception by plants makes
up no more than 10 - 15% of annual rainfall. With forests, however, the loss may be as high as
25% of total annual rainfall. There are varied opinions on the hydrological significance of
interception, but not in a plant physiological sense. Regarding plant physiologically, intercepted
rain is not a loss, as the water on the leaves help to cool the plant, thereby saving an equal amount
of groundwater.
In view hereof, interception losses should be seen as an alternative and not as additional to
transpiration.
The monthly effective rainfall is determined as follows, using long-term average rainfall figures:
Re =
where
Re
Raver
R aver - 20
2
(4.1)
= effective rainfall [mm/month]
= long-term average monthly rainfall [mm/month]
Daily effective rainfall may be determined, amongst others, by the following equation:
R e = R - 1,5 Eo
where
Re
R
Eo
(4.2)
= effective rainfall [mm/day]
= rainfall [mm/day]
= A-pan evaporation [mm/day]
Effective rainfall is zero if a negative value is obtained.
SAPWAT (Crosby, 1996) may also be consulted for determination of effective rainfall.
Crop water relationships and climate
4.3
2.2 Evaporation
Water evaporation rate depends on humidity, temperature, radiation, air movement and attitude above
sea level.
2.2.1 Evaporation measurement
Evaporation is measured by exposing free water to the atmosphere and then determining the loss
through evaporation. Therefore evaporation is not really a weather parameter but may be seen as a
combination of different influences. The South African Weather Bureau and the Department of
Agriculture make use of the American Class A evaporation pan to measure evaporation. The pan
is circular, 1,22 m in diameter and 250 mm deep. The water surface height is read off from a scale
located diagonally in the water.
As with a rain gauge the evaporation pan must be placed away from obstructions and in such a
way that sun and wind can move around it freely. Only direct rain must fall in the pan but it must
also not be screened off. The pan must never be in the shadow. The Symonds pan is not
recommended for measuring evaporation for irrigation.
2.2.1.1 Erection
The evaporation pan rests on a framework approximately 200 mm high, which is placed level
on the ground. The openings between the lower beams of the framework may be filled up but
those between the upper beams must be kept clean to promote ventilation and ease leak
detection. Grass and weeds around the pan must be kept short.
Figure 4.1: Erection of class A evaporation pan
2.2.1.2 Calibrating the scale
A stilling basin which is connected to the main pan by a hole, is provided around the scale.
When water is added to the pan, it takes about a minute for the water in the stilling basin to
reach the same level, therefore wait a few minutes before taking a reading.
4.4
Irrigation Design Manual
Figure 4.2: The class A evaporation pan scale
The scale is calibrated as follows: Once the pan has been positioned on the framework, it is
filled with water until the metal pointer at H (see Figure 4.2) is just submerged. The right
hand side of the scale is then adjusted with the nuts at B until the water surface at G gives a
scale reading of 138, and locked in position. Then the pan is filled until the scale reading is
approximately 50, this reading being recorded in column 4 (see Table 4.1). This process is
repeated whenever the pan is cleaned or moved.
Evaporation pan readings may be recorded on a form (see Table 4.1) which makes provision
for the date (column 1), rainfall (column 2), water level before regulation (column 3), water
level after regulation (column 4) and evaporation (column 5).
2.2.1.3 Reading the scale
As with all weather readings, the evaporation is measured at 08:00. The position where the
scale cuts the water surface is wetted by finger before reading the scale. The reading at the
contact point is then taken. Note that the white lines on the scale indicate EVEN values (e.g.
70, 72, 74, 76, 78) while the blue lines indicate UNEVEN values (e.g. 71, 73, 75, 77, 79). The
value to be recorded from the enlarged part of Figure 4.2 is 73. Regularly make sure that the
connecting hole between the pan and stilling basis is not blocked.
The evaporation for a specific day is determined by subtracting the reading for that day from
the value in column 4 from the previous day, dividing the difference by two and adding it to
the rainfall for the day. The unit is millimetres. Evaporation pan readings are divided by two
to allow for the enlarged scale used in the class A evaporation pan. NB: When the water level
is higher than 50 mm due to rain, water is removed until approximately the 50 level and the
value recorded in column 4. When the water level is lower than 100 due to evaporation, water
is added up to approximately 50 and the value recorded in column 4.
Crop water relationships and climate
4.5
Example 4.1:
(See Table 4.1) Reading procedure for class A evaporation pan
x Day 1:
Start with a reading of 50 and record it in column 4.
x
Day 2:
Read the water level, record the value, e.g. 72 in column 3 as well as column 4,
determine the A-pan evaporation for day 1 as indicated and record it in column 5.
x Day 3:
The same as for day 2.
x
Day 4:
Read the water level, record the value, e.g. 112 in column 3 and regulate to ± 50 by
adding water.
Water level after regulating: In this case it is 48 which is recorded in column 4, the
A-pan evaporation is determined as indicated and recorded in column 5.
x Day 5:
The same as for day 2 and 3.
x
Day 6:
Record the rainfall for day 5 in column 2. Record the water level reading in column 3
and 4, determine the evaporation as indicated and record in column 5.
Table 4.1:
An example of recording A-pan evaporation reading
1
2
3
4
5
Date
Rainfall
Water level
before
regulating
[mm]
Water level
after
regulating
[mm]
Evaporation
[mm]
1
Calculations
[mm]
50
2
72
72
11
72 - 50
= 11
2
3
97
97
12,5
97 - 72
= 12,5
2
4
112
48*
7,5
112 - 97
= 7,5
2
72
72
12
72 - 48
= 12
2
62
62
7
62 - 72
+ 12 = 7
2
5
6
12
* Water added to A-pan
4.6
Irrigation Design Manual
2.2.1.4 Maintenance
It is imperative that the pan regularly be cleaned once per month. The following procedure is
followed:
x
Record the scale reading.
x
Invert the pan and remove all accretions, silt, duckweed, etc. Ensure that the connecting
hole between the pan and stilling basin is open. Rinse the whole pan thoroughly.
x
Inspect the pan, especially the base and seams for possible leakages and rust spots. When
rusting becomes severe, the A-pan must be painted with aluminium bituminous paint.
x
Always clean the openings between the upper beams to ensure good ventilation
x
Re-erect the pan level as close as possible to the previous position on the frame. Fill with
water and calibrate the scale as indicted in 2.2.1.2.
x
Fill the pan to the starting reading prior to cleaning.
2.3 Radiation
All daily, seasonal and cyclic climate changes can be traced back to the energy that reaches the earth
in the form of electromagnetic radiation from the sun.
Radiation intensity is expressed in terms of watt per square metre [W/m2]. The intensity relates to the
rate at which energy is received. At times it may be necessary to indicate a quantity of energy. The
unit of energy is the joule [J]. An intensity of 1 W/m2 is equal to 1 J/s per m2. The intensity of full
summer sunlight is in the order of 1 000 W/m2.
It is often referred to as light intensity when radiation relates to photosynthesis. Light is the radiation
to which the human eye is sensitive. Plants, however, do not react to radiation in the same way as the
human eye. It is therefore incorrect to compare light, as observed by eye, to photosynthesis. The unit
of light intensity is the lux [lu] (1 W/m2 | 680 lx).
Radiation measurement is usually done by measuring the temperature relationship which occurs when
the sun shines on a blackened surface. Radiometers must be handled with great care.
2.4 Sunshine duration
In reality sunshine duration (when the sun shines) should be considered as the period between which
the sun just begins to appear above the horizon until it just disappears below the horizon. Weather
experts consider sunshine duration as the period of "full" sunshine. According to this definition full
sunshine occurs when the sun burns a visible mark on special paper through a glass sphere of specific
dimensions. (There are also other so-called sunshine meters, so full sunshine will depend on which
one is used.) Electronic sunshine meters are available but not widely used due to high costs. In South
Africa, the sunshine duration is measured with the Campbell-Stokes sunshine meter.
Crop water relationships and climate
4.7
2.5 Temperature
The measuring unit for temperature is Kelvin [K]. In South Africa air temperature is indicated in
degrees Celsius [ºC]. It is, however, acceptable to use ºC as the unit for temperature (K = ºC + 273).
In measuring temperature, special care must be taken to eliminate the effect of sun radiation or
radiation from the earth's surface. Temperature is measured with suitable thermometers in a Stevenson
shield. The Stevenson shield is used to house measuring instruments and is designed to shield as
many of the sun's rays and reflections from the earth's surface as possible from the instruments, while
allowing unrestricted air-flow over them. The purpose is to measure air temperature without the
influence of radiation.
The Stevenson shield is erected on a metal frame so that the instruments therein are 1,2 m above the
ground. The shield must open southwards so that the sun does not shine on the instruments when
readings are taken.
A Stevenson shield usually contains a maximum, minimum and standard or dry bulb thermometer.
The maximum and minimum thermometers are mostly only read twice per day and indicate the highest
and lowest temperatures respectively, since the previous readings. The standard thermometer indicates
the temperature at the time of reading. At times a continuous record of the temperatures is required,
which can be measured with a thermograph. Thermograph readings must always be corrected by
comparing them to the maximum and minimum thermometers.
Both extremely high and low temperatures can have an adverse effect on a crop. Cooling as well as
frost combating can be executed by application of water during critical periods and it will have an
influence on the total water requirement of the crop. It may also be necessary to install an additional
irrigation system to meet these requirements. Provision for the additional required water must
therefore be made during planning, as well as for as the costs it may implicate. See Chapter 11:
Planning.
2.6 Water vapour
The relationship between the different gases comprising the atmosphere is exceptionally constant, the
only exception being water vapour which can change from one minute to the next. The atmosphere is
saturated when the maximum water vapour is present. When saturated air is cooled, excess water
vapour will condense in the form of clouds, mist, dew or frost. Alternatively the air will become
unsaturated with an increase in temperature. Such air can become very "dry" without losing any water
vapour, depending on the temperature increase.
Relative humidity is usually measured with a hygrograph placed in a Stevenson sun shield, the
measuring element being human hair which stretches as it becomes moist. Water vapour can also be
measured with two thermometers, the bulb of one being covered with a moist cloth. The dryer it
becomes, the quicker water evaporates from the moist cloth, cooling the bulb down (like a canvas
water bag). The relative moisture can be obtained from tables (see Table 4.2) by making use of the
temperature difference between the dry and wet bulb thermometers. The cloth on the wet bulb
thermometer should ideally be moistened with distilled water.
A measure of the actual amount of moisture present in the air is the dew point. The dew point is the
temperature at which air will be saturated with water vapour provided that it is cooled down at a
constant pressure. Dew point is not dependant on temperature like relative humidity and it is also
measured in K or ºC.
Irrigation Design Manual
95
95
94
94
94
94
94
94
94
94
94
94
94
94
94
93
93
93
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
1
87
87
87
87
87
88
88
88
88
88
88
89
89
89
89
89
89
89
2
80
81
81
81
82
82
82
82
83
83
83
83
83
83
84
84
84
84
3
74
75
75
76
76
76
77
77
77
78
78
78
78
79
79
79
79
80
4
69
69
70
70
70
71
71
72
72
72
73
73
73
74
74
74
75
75
5
63
64
64
65
65
66
66
67
67
68
68
68
69
69
70
70
70
71
6
58
58
59
60
60
61
61
62
62
63
63
64
64
65
65
66
66
66
7
52
53
54
55
55
56
57
57
58
58
59
59
60
60
61
61
62
62
8
47
48
49
50
51
51
52
53
53
54
55
55
56
56
57
57
58
58
9
Difference between wet and dry bulb thermometer reading [ºC]
50
Dry bowl
[ºC]
43
44
44
45
46
47
48
48
49
50
51
51
52
52
53
53
54
54
10
38
39
40
41
42
43
44
44
45
46
47
47
48
48
49
50
50
51
11
34
35
36
37
38
39
40
40
41
42
43
43
44
45
45
46
47
47
12
29
30
32
33
34
35
36
37
37
38
39
40
41
41
42
43
43
44
13
25
26
28
29
30
31
32
33
34
35
36
36
37
38
39
39
40
41
14
21
23
24
25
26
27
28
29
30
31
32
33
34
35
35
36
37
37
15
17
19
20
21
23
24
25
26
27
28
29
30
31
31
32
33
34
34
16
Table 4.2: Percentage relative humidity, only applicable for heights from the sea level to 450 m above sea level and wind speeds < 1,5 m/s.
4.8
14
15
17
18
19
20
22
23
24
25
26
27
28
28
29
30
31
32
17
10
12
13
15
16
17
18
20
21
22
23
24
25
26
26
27
28
29
18
93
93
93
93
93
92
92
92
92
92
92
91
91
91
91
90
90
90
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
80
81
81
82
82
83
83
83
84
84
84
85
85
85
86
86
86
86
2
71
71
72
73
74
74
75
76
76
77
77
78
78
79
79
79
80
80
3
61
62
64
65
65
66
67
68
69
69
70
71
71
72
72
73
73
74
4
52
54
55
56
58
59
60
61
62
62
63
64
65
65
66
67
67
68
5
44
46
47
49
50
51
52
54
55
56
57
58
59
59
60
61
62
62
6
36
37
39
41
43
44
46
47
48
49
50
51
52
53
54
55
56
57
7
27
30
32
34
35
37
39
40
42
43
44
46
47
48
49
50
51
52
8
20
22
24
27
29
30
32
34
36
37
38
40
41
42
43
44
45
46
9
Difference between wet and dry bulb thermometer reading [ºC]
32
Dry bowl
[ºC]
Table 4.2: (continued)
12
15
17
20
22
24
26
28
30
31
33
34
36
37
38
39
41
42
10
5
8
10
13
15
18
20
22
24
26
27
29
30
32
33
34
36
37
11
-
1
4
7
9
12
14
16
18
21
22
24
25
27
28
30
31
32
12
-
-
-
-
3
6
8
11
13
15
17
19
21
22
24
25
27
28
13
-
-
-
-
-
-
3
5
8
10
12
14
16
18
19
21
22
24
14
-
-
-
-
-
-
-
-
3
5
7
9
11
13
15
17
18
20
15
-
-
-
-
-
-
-
-
-
-
3
5
7
9
11
13
14
16
16
-
-
-
-
-
-
-
-
-
-
-
-
3
5
7
9
10
12
17
Crop-water relationships and climate
-
-
-
-
-
-
-
-
-
-
-
-
-
1
3
5
7
8
18
4.9
90
89
89
88
88
88
87
87
86
86
85
84
84
83
13
12
11
10
9
8
7
6
5
4
3
2
1
1
14
Dry bowl
[ºC]
-
68
69
70
72
73
74
75
76
77
77
78
79
79
2
-
-
54
56
58
60
61
63
64
65
66
68
69
70
3
Irrigation design manual
Table 4.2: (continued)
4.10
-
-
-
42
45
47
49
51
53
54
56
57
59
60
4
-
-
-
-
32
35
37
40
42
44
46
48
49
51
5
-
-
-
-
-
23
26
29
31
34
36
38
40
42
6
-
-
-
-
-
-
14
18
21
24
26
29
31
33
7
-
-
-
-
-
-
-
7
11
14
17
20
23
25
8
-
-
-
-
-
-
-
-
1
5
8
11
14
17
9
-
-
3
6
9
10
-
-
-
2
11
-
-
-
-
12
-
-
-
-
13
-
-
-
-
14
Difference between wet and dry bulb thermometer reading [ºC]
-
-
-
-
15
-
-
-
-
16
-
-
-
-
17
-
-
-
-
18
Crop water relationships and climate
4.11
2.7 Wind
Wind originates due to differences in air pressure. Air moves from an area of high pressure to one of
low pressure. These pressure differences may occur locally or could originate in pressure systems
spanning thousands of kilometres.
Wind measurement consists of two components, namely direction and speed. At most weather stations
only speed is measured by means of an anemometer, which has three circular cups mounted on a
vertical axis. The speed with which the cups rotate is proportional to the wind speed. The axis about
which the cups rotate is connected to a mechanical counter which is read at a fixed time (always
08:00). The "distance" that the wind has moved during a period of time is measured by determining
the difference between two consecutive readings. The "distance" usually describes the wind run and
may be interpreted as the average wind speed for the particular period.
For most purposes the average wind speed, over a long period as measured with ordinary
anemometers, is of little value. The average speed and direction is usually required for a shorter
period, like an hour. In many cases, instant peak values are also important. There are various types of
wind meters using different techniques to continually measure and register wind speed and velocity.
Wind meters are erected so that air movement at a height of 2 m or 10 m is measured. It is important
to keep the area of exposure free from obstructions as wind measurement is strongly influenced by
local conditions. The recognised unit for wind speed is metres per second [m/s], although it is often
indicated in km/hour (1 m/s = 3,6 km/hour). Seafarers use knots, one knot being equal to 0,514 m/s.
With certain instruments air movement is measured over long periods of 6 hours or 24 hours, normally
referred to as wind run. Wind run is measured in kilometres and is equivalent to the distance travelled
by an air particle during the particular period at the average wind speed. Wind direction is given as
the compass direction that the wind is blowing from.
2.8 Automatic weather stations
The Weather Bureau is in the process of automising its weather station network, the advantage being
that the information will be more readily available than with manual stations. For example it will be
possible to obtain information from certain stations on the day of measurement and it will also
simplify the obtaining of hourly readings.
Unfortunately evaporation cannot be measured by commercially available automatic weather stations,
however, various equations, e.g. Penman-Monteith, exist whereby evapotranspiration can be
determined accurately by making use of radiation, moistness, temperature and wind movement.
4.12
Irrigation Design Manual
3 Crops
Crop water requirements depend on the relationship between water absorption and transpiration.
3.1 The role played by water in plants
More than half of all living fibre, as well as more than 90% of all plant fibre, consists of water,
therefore water is by far the largest plant component. Water influences the metabolism, physiological
activity and growth of plants, also functioning as a solvent in plants in which gases, minerals and
organic solutions are transported from one part to another. Water plays an important role within the
plant, with photosynthesis and many hydrological processes as well as maintaining turgor which is
imperative to cell enlargement and produces plant growth.
More than 90% of the water absorbed by a plant's roots is released in the atmosphere as water vapour.
The process is known as transpiration and is defined as the loss in water to the atmosphere from a
growing plant, which is regulated by physical and physiological processes in the plant.
Why do plants then lose such large quantities of water through transpiration? The answer lies in the
composition of a leaf. The main function of a leaf is photosynthesis, which manufactures food for the
entire plant, the required energy being obtained from sunlight. The plant must therefore expose the
largest possible transpiration area to sunlight. Sunlight is, however, only one of the requirements of
photosynthesis, as the chlorophyll also requires carbon dioxide. Carbon dioxide is normally readily
available in the air surrounding the plant, but before it can reach the plant cells by diffusion, it must be
dissolved. Carbon dioxide in the air must come into contact with a moist cell surface because the cell
walls cannot readily absorb it in a gaseous form. Evaporation occurs wherever water is exposed to air.
The evaporation of water from the leaf surface has a two-fold function, namely the absorption of
carbon dioxide as described above and plant cooling.
Plants have developed a number of special methods to limit evaporation which in turn limits carbon
dioxide absorption. Photosynthesis and loss of water through transpiration are therefore firmly bound
in the life of green plants.
3.2 Plant roots
Plant activity is normally proportional to soil water availability and therefore also the rate of water
absorption by the root system. While small quantities of water may be absorbed by external plant
components under certain conditions, the root system is usually the organ of absorption for virtually
all the water required by upper plant sections. Therefore the root system depth of each crop
determines the soil water reservoir size or the total available water in normal and deep soils. The
water withdrawal pattern is then determined by the lateral distribution and specific properties of the
roots.
Absorption of water and food substances takes place through the root hairs. Older root sections
suberise and transmit less water and dissolve food substances.
Plant roots make contact with water in two ways:
x
x
capillary movement of water to the roots and/or
root growth from dry to moist areas.
Osmosis is the process by which root hairs absorb water - it is the movement of water through a
selectively permeable membrane from a higher water potential to a lower water potential. When roots
absorb water, the soil water content reduces at that point, causing an increase in the soil water tension,
Crop water relationships and climate
4.13
binding the remaining water. The soil water tension will be at its highest when the soil moisture
content has dropped close to wilting point, in other words, the attracting or suction force of the water
in the soil is at its highest. However, rapid root growth during active growth periods maintains
sufficient water contact even though the soil water profile is decreasing as a whole and no capillary
addition occurs. In any case, root growth is more rapid than capillary water movement during active
root growth. It may eventually happen that the roots are unable to supply water to the plant fast
enough -this is called temporary wilting and if it continues too long, the plant may wilt permanently.
3.2.1 Root systems
The nature of the root system which a plant can develop under optimal soil and climatic conditions
is predetermined by its genetic code (see Table 4.3 and Figure 4.3). Therefore each plant species
has its own characteristic, natural root growth pattern. Some plants have a tap root which tends to
penetrate rapidly, deep into the subsurface layers while others have slowly growing roots which
develop a shallow, primary system with many lateral, secondary and tertiary roots. The natural
lateral root distribution of trees is normally as wide as the drip area of the tree.
Table 4.3: Natural root depth
Crop
Alfalfa
Almonds
Apricots
Avocados
Bananas
Beans
Brassicas
Citrus
Clover
Grapes
Green peas
Macadamia
Mangos
Mealies
Olives
Onions (transplanted)
Onions (seed)
Pecan nuts
Pineapple
Potatoes
Tomatoes
Wheat
Natural root depth [mm]
900+
900+
500+
900
500
600
500
900+
300
900
450
900
600+
600+
900
450
600
900
450
350
600
900+
4.14
Irrigation Design Manual
Figure 4.3: Natural root depth and distribution
3.2.2 Factors influencing root development
Root penetration is seriously deterred by dense subsurface ground layers and the root depth in
many South African soils is limited to the upper 250 mm of the profile by a plough sole. Roots
cannot penetrate a hard layer unless cracks occur and find it difficult or impossible to grow from
one to another soil layer where the texture differs drastically. A factor limiting root growth may
also be a shortage of plant food substances or an underground chemical imbalance. Root growth is
limited by a high water profile.
Figure 4.4: Root development due to physical and chemical soil limitations
Most roots will occur in the wetted area when soil is only partially irrigated, e.g. with drip
irrigation. Root depths will also be influenced by irrigation practices, e.g. with a too short cycle
length and standing time, most plants will tend to develop a shallow root system to adapt to the
shallow wetted depth.
Crop water relationships and climate
4.15
3.3 Groundwater withdrawal patterns
Figure 4.5: Typical plant water withdrawal pattern
With most plants the active roots are mainly concentrated in the upper part of the root zone (see
Figure 4.5). Therefore the most rapid water withdrawal occurs in the area of highest root
concentration under favourable temperature and aerating conditions.
The reduction of groundwater also takes place more rapidly in the upper soil layer as groundwater
evaporates directly from it. With the reduction in available water in that part of the root zone, the soil
water tension binding the remaining water increases. Plants then withdraw water at a deeper level
where it is bound with less energy.
4 Evapotranspiration
The combined loss of water from a given surface during a specific time by evaporation from the ground
surface and through plant transpiration is known as evapotranspiration.
4.1 General
Only a small part of the water which a plant absorbs from the soil is taken up by the plant cells. By far
the largest part of the water is released through the stoma to the atmosphere by transpiration. A plant's
water consumption varies during the season and with a crop increase, the water requirement also
increases to a point. Plant water absorption is also higher with a high groundwater level.
ET = E + T
where ET = evapotranspiration [mm/period]
E = evaporation from ground surface [mm/period]
T = transpiration of growing plant [mm/period]
(4.3)
4.16
Irrigation Design Manual
The estimated evapotranspiration values are very important regarding the following:
x
x
x
x
x
x
Determination of amount of irrigation water required for optimal plant growth
Planning of irrigation schemes
Design of drainage systems
Development planning of river systems
Determination of dam capacities
General catchment area management
4.2 Daily and seasonal evapotranspiration
Evapotranspiration is at its highest during the middle of the day and lowest during the night.
Seasonal evapotranspiration is used to determine the amount of water required for irrigation during
one season.
Figure 4.6: Typical seasonal evapotranspiration
4.3 Peak periods of evapotranspiration
The peak period is the plant's growth stage with the highest average evapotranspiration. An irrigation
system must be designed to supply sufficient water during the plants' peak period of
evapotranspiration. This peak consumption period usually occurs when plants start to produce their
crops.
4.4 Factors influencing evapotranspiration
The rate of groundwater withdrawal by the evapotranspiration process is mainly determined by:
x
x
climate
groundwater storage
Crop water relationships and climate
x
x
x
x
x
4.17
irrigation practice
soil texture
tilling practice
type of natural plant or crop being cultivated
salinity of soil or irrigation water
Of the above, climate is the factor which has the highest influence on evapotranspiration
x
Radiation energy:
Absorption of radiation energy by ground and leaf surfaces and the rate of evapotranspiration are
related.
x
Temperature:
The ground surface and leaves are usually warmer than the air during bright sunshine, therefore
vapour movement must take place from an area with a higher temperature and vapour pressure to
an area with lower temperature and vapour pressure.
x
Wind:
Air movement is an important contributing factor as it continually replaces air layers which would
have been nearly saturated by water vapour if they could remain upright, with unsaturated air.
The use of mulch also has an effect on evapotranspiration. The mulch may consist of organic material
(such as hay) or a permanent green crop (such as clover). In the case of dry material, the mulch can aid
in limiting evaporation from the soil and thereby reduce the evapotranspiration. The irrigation
requirement is therefore reduced. There is however a danger that the organic material may prevent the
crop from absorbing the chemicals applied to the surface. In the case of green mulch, the
evapotranspiration will increase as a result of the water utilised by the mulch crop. Provision must
therefore be made for the additional irrigation water required during system planning (see Chapter
11: Planning).
4.5 Effect of groundwater levels on crop growth and harvests
Most plants absorb water easily at a high minimum water level (low soil water depletion level)
provided that sufficient air is present in the soil. As the groundwater level reduces, the plant must use
more energy to withdraw water from the soil. Crop damage may occur if the groundwater level drops
too low and plants may wilt temporarily or even permanently if the condition continues too long.
4.6 Critical periods
Most plants have a critical period during the growth season when a high groundwater level must be
maintained for optimal production. If enough water is available for germination as well as the
development of a sufficient growth density with yearly crops, the critical period will generally occur
during the latter part of the growing season. This is during the period of flowering to fruit ripening.
4.18
Irrigation Design Manual
Table 4.4: The critical periods of crops
Crop
Almonds
Avocados
Bananas
Beans
Brassicas
Citrus
Clover
Deciduous fruit
Grapes
Macadamia
Mangos
Mealies
Olives
Onions
Peas, green
Pecan nuts
Pineapple
Potatoes
Tomatoes
Wheat
Critical period
Blossoming, shoot growth, cell division, fruit growth
Flowering, cell division, fruit growth
Flowering, cell division, fruit growth
Blossoming until fruit growth
Remaining 50 days before harvesting
Blossoming, cell division, fruit growth
Continually
Blossoming, shoot growth, cell division, fruit growth
Budding, flowering, cell division, fruit growth
Flowering, cell division, fruit growth
Flowering, cell division, fruit growth
Plum forming until beard forming
Blossoming, cell division, fruit growth
Bulb formation until harvesting
Blossoming until fruit growth
Flowering, cell division, fruit growth
Vegetative growth stage
Blossoming until harvesting
Flowering until harvesting
Ear appearance until ear completion
4.7 Determination of crop-evapotranspiration
Determination of crop-evapotranspiration is the first step in project planning and the design of
irrigation systems.
Various methods are used worldwide to determine crop-evapotranspiration, but only those used in
South Africa will be treated in this section.
4.7.1 A-pan evaporation with crop factors
This method assumes that, for a given period, crop-evapotranspiration (ETc) is directly
proportional to the A-pan evaporation (Eo).
The standard method currently in use in South Africa is based on the average monthly A-pan
evaporation and crop factors. The place and vicinity where the A-pan is erected is important in
obtaining a true reflection of the evaporation. Different crops have different crop factors which
vary during the growth season and should be adapted to suit the area as shown in Tables 4.5 to
4.10.
Figure 4.7: Direct determination of crop-evapotranspiration by using A-pan evaporation
and crop factors
Crop water relationships and climate
4.19
The equation to determine crop-evapotranspiration (ETc) directly from A-pan evaporation is as
follows:
ETc = f E o
where
ETc
f
Eo
(4.4)
= crop-evapotranspiration [mm/period]
= crop factor for direct use with A-pan evaporation [fraction]
= A-pan evaporation [mm/period]
The crop factor may be determined by the following equation:
f = kp kc
where
(4.5)
f = crop factor for direct use with A-pan evaporation [fraction]
kp = pan coefficient [fraction]
kc = crop coefficient [fraction]
The crop factors in Tables 4.5 to 4.10 for use with A-pan evaporation was recently adapted to
make provision for different climatic zones.
4.7.2 Penman-Monteith method (short grass reference)
The alternative method for the calculation of crop-evapotranspiration depends on the use of
climate data from weather stations and the amended Penman-Monteith equation. Cropevapotranspiration can be calculated by means of the following equation:
ETc = k c ETo
(4.6)
where ETc = crop-evapotranspiration [mm/period]
kc = crop coefficient [fraction]
ETo = reference evapotranspiration [mm/period]
Figure 4.8: The calculation of crop-evapotranspiration with the aid of a weather station
The computer program, SAPWAT, uses crop coefficients for the estimation of cropevapotranspiration for all crops irrigated in South Africa. A list of crop coefficients, as well as
reference evapotranspiration for weather stations over the entire country (Tables 4.11 to 4.13) is
shown. The climatic data forms part of SAPWAT. The program is available on the Internet on
http://sapwat.org.za (please note; no www address) and can be used to examine different irrigation
approaches. Training is however essential.
The reference evapotranspiration is shown in SAPWAT as average daily values per month for the
different weather stations. Figure 4.9 is an example of the screen on SAPWAT where the reference
evapotranspiration is shown for a specific weather station (Kakamas). The bottom curve on the
graph is the Penman-Monteith reference evapotranspiration (ETo) and the top curve is the A-pan
evaporation values at the same station.
4.20
Irrigation Design Manual
Figure 4.9: SAPWAT screen with reference evapotranspiration and A-pan evaporation values
The crop coefficients can also be determined with the aid of SAPWAT. There are certain
parameters from which a selection can be made to determine the coefficients for a specific crop,
such as the variety, climatic region and planting date. The crop coefficients shown in Figure 4.10
are based on a weekly irrigation cycle and a 100% wetted area.
Figure 4.10: Crop coefficients screen in SAPWAT
Crop water relationships and climate
4.21
4.7.3 Relationship between short grass reference evapotranspiration (ETo) and Apan evaporation (Eo)
Evapotranspiration for a short grass veld is determined with the aid of lysimeters and the values
are brought into relation statistically with meteorological data. The Penman-Monteith equation has
proved that it gives accurate evapotranspiration values for short grass under all climatic conditions
and the values can then be used for all crops in the surrounding area.
Evaporation from a free water level in an A-evaporation pan does not have the same
characteristics as transpiration from a living plant. It has an inherent fault when the A-pan
evaporation is used for determining crop-evapotranspiration, except if the crop factor (f) is adapted
accordingly for the local conditions.
Figure 4.11: The relation between ETo and Eo
By using reference evapotranspiration from a short grass, it takes seasonal phases of the crop as
well as climatic conditions into consideration. With this self-compensating reference values as
basis, the crop coefficient (kc) can be used more universally. The crop coefficient also differs from
crop to crop and also for the growing season.
For any specific weather station, the ETo values are normally lower than the Eo values. In the case
of hot, arid regions, the ETo values may even be half of Eo values in January. The ETo:Eo relation is
therefore 0,5. The relation varies during the season as well as over the region and a standard
conversion factor cannot be used per season.
The ETo:Eo relation is numerically equal to the pan coefficient (kp) so that the following equation
can be used to convert A-pan evaporation to reference evapotranspiration (ETo):
ETo = k p Eo
where ETo
kp
Eo
(4.6)
= reference evapotranspiration [mm/period]
= pan coefficient [fraction]
= A-pan evaporation [mm/period]
Values are available for ETo (calculated from weather data with the Penman-Monteith equation) as
well as Eo and it is now possible to adapt crop factors (f) for use with A-pan evaporation for
different climatic zones.
It is suggested that planners and designers begin to use the Penman-Monteith method and
SAPWAT under the guidance of professionals. Alternatively, A-pan evaporation and amended crop
factors (f) as used in Tables 4.5 and 4.10, can be used until they are acquainted with the new
procedures for determining crop-evapotranspiration.
4.22
Irrigation Design Manual
Example 4.2:
Calculate the expected crop-evapotranspiration for table grapes in Kakamas in December with both the Apan and Penman-Monteith methods. Assume that an A-pan evaporation of 12mm/day has been measured.
A-pan method:
From equation 4.4:
ETc
= f Eo
Eo
= 12 u 31
= 372 mm/month
f
= 0,4 (from Table 4.5)
?ETc
= 0,4 u 372
= 148 mm/month
Penman-Monteith method:
From equation 4.6:
ETc
= kcETo
kc
= 0,67 (from Table 4.11)
ETo
= 9,4 u 31 (from Table 4.13)
= 291.4 mm/month
?ETc
= 0,67 u 291,4
= 195,2 mm/month
The difference between the answers of the two methods must be further investigated to interpret it. The use of
local rather than general crop factors and coefficients will probably result in a smaller difference between
answers.
0,65
0,75
0,65
0,65
0,8
0,7
0,65
Litchi
Macadamia
Pecan nuts
Bananas
Tea
Mangos
0,7
Coffee
Frost areas
Alfalfa
0,7
0,65
Kikuyu
Pastures
-
Avocado
Rye grass
Pastures
0,50
Intensive
0,6
Early
0,25
0,6
Medium
Sub-intensive
0,5
Late
Deciduous fruit
Wine grapes
0,5
Table grapes
Jan
0,55
Description
Citrus
Perennial crops
0,65
0,7
0,8
0,65
0,65
0,75
0,65
0,65
0,7
0,7
0,50
0,50
0,25
0,60
0,60
0,6
0,6
0,60
Feb
0,65
0,7
0,8
0,65
0,65
0,75
0,65
0,65
0,70
0,7
0,7
0,30
0,20
0,20
0,40
0,50
0,6
0,65
Mar
0,65
0,7
0,8
0,65
0,65
0,75
0,65
0,65
0,50
0,7
0,7
0,20
0,20
0,20
0,20
0,20
0,4
0,70
Apr
0,65
0,7
0,8
0,35
0,65
0,75
0,65
0,65
0,40
-
0,60
0,20
0,20
0,20
0,20
0,20
0,2
0,65
May
0,65
0,7
0,8
0,35
0,65
0,75
0,65
0,65
0,30
-
0,50
0,20
0,20
0,20
0,20
0,20
0,2
0,60
Jun
0,65
0,7
0,8
0,35
0,65
0,75
0,65
0,65
0,30
-
0,50
0,20
0,20
0,20
0,20
0,20
0,12
0,45
Jul
0,65
0,7
0,8
0,65
0,65
0,75
0,65
0,65
0,40
-
1,00
0,20
0,20
0,25
0,20
0,20
0,12
0,45
Aug
Months of the year
Table 4.5: Estimated design crop factors for perennial crops in the summer rainfall areas – June 1996
0,65
0,7
0,8
0,65
0,65
0,75
0,65
0,65
0,50
0,30
0,7
0,2
0,20
0,30
0,25
0,20
0,12
0,45
Sept
0,65
0,7
0,8
0,65
0,65
0,75
0,65
0,65
0,70
0,60
0,7
0,3
0,25
0,30
0,30
0,25
0,2
0,45
Oct
0,65
0,7
0,8
0,65
0,65
0,75
0,65
0,65
0,80
0,70
0,7
0,4
0,25
0,40
0,30
0,30
0,3
0,45
Nov
Crop water relationship and climate
0,65
0,7
0,8
0,65
0,65
0,75
0,65
0,65
0,7
0,7
-
0,50
0,25
0,50
0,40
0,40
0,4
0,5
Dec
4.23
Irrigation Design Manual
1 Oct
15 Dec
15 May
15 Jun
1 Dec
1 Jan
1 Mar
1 Jun
1 Nov
15 Oct
1 Oct
Mealies
Mealies
Wheat
Wheat
Soya beans
Potatoes
Potatoes
Potatoes
Potatoes
Tobacco
Ground-nuts
1 Nov
Area C
15 Apr
30 Apr
30 Apr
31 Jan
15 Feb
15 Mar
15 Oct
15 Jul
30 Apr
15 Apr
30 Nov
15 Sept
15 Apr
15 Feb
End of growth
season
0,7
0,8
0,85
0,5
0,7
0,7
0,3
0,6
0,75
0,75
Jan
0,8
0,8
0,6
0,4
0,8
0,5
0,7
0,75
0,6
Feb
Limpopo, Eastern Transvaal, Lowveld and Northern Natal
Loskop, Rust-De Winter and Barberton
1 Nov
Area B
Area A:
Area B:
1 Oct
Area A
Cotton
Planting
date
Agronomic
crops
0,6
0,6
0,5
0,8
0,3
0,8
0,7
0,6
Mar
0,5
0,4
0,3
0,5
0,8
0,5
0,5
Apr
0,7
0,3
May
0,3
0,8
0,3
0,6
Jun
0,5
0,8
0,5
0,7
Jul
0,7
0,8
0,8
Aug
Months of the year
Table 4.6 : Estimated design crop factors for agronomic crops in the summer rainfall areas – June 1996
4.24
0,8
0,8
0,5
Sept
0,3
0,3
0,3
0,8
0,7
0,4
Oct
0,2
0,3
0,6
0,7
0,6
0,3
0,4
0,6
Nov
0,35
0,5
0,85
0,6
0,75
0,5
0,3
0,4
0,75
Dec
Vaalharts, Karoo, Eastern Cape and Transvaal middle veld
0,3
0,4
0,3
0,3
0,3
0,3
Brassicas
Cucurbits
Peas
Onions
Tomatoes
0-20
Beans
Vegetable crops
0,4
0,4
0,3
0,4
0,6
0,4
20-40
0,7
0,7
0,4
0,6
0,7
0,6
40-60
Portion of growing season [%]
Table 4.7: Estimated design crop factors for vegetables in the summer rainfall areas – June 1996
Area C:
0,7
0,7
0,7
0,7
0,7
0,6
60-80
0,7
0,7
0,6
0,7
0,7
0,7
80-100
Crop water relationship and climate
4.25
Irrigation Design Manual
0,55
0,55
0,4
Late
Medium
Early
Deciduous fruit
Kikuyu
Frost areas
Prune Aug
Pasture
Alfalfa
Guavas
0,4
0,55
0,55
0,55
0,5
Early
Mixed
0,5
Late
Intensive
Pasture
0,25
Sub-intensive
Wine grapes
0,5
Table grapes
Jan
0,4
Description
Citrus
Perennial crops
0,5
0,55
0,55
0,55
0,5
0,5
0,25
0,35
0,4
0,55
0,6
0,4
Feb
0,4
0,55
0,55
0,55
0,3
0,5
0,2
0,35
0,35
0,55
0,6
0,5
Mar
0,4
0,55
0,55
0,55
0,2
0,3
0,2
0,3
0,3
0,35
0,3
0,5
Apr
0,3
0,55
0,55
0,55
0,2
0,2
0,2
0,2
0,2
0,2
0,2
0,4
May
0,3
0,55
0,55
0,55
0,2
0,2
0,2
0,2
0,2
0,2
0,2
0,4
Jun
0,3
0,55
0,55
0,55
0,2
0,2
0,2
0,2
0,2
0,2
0,2
0,3
Jul
Months of the year
Table 4.8 Estimated design crop factors for perennial crops in the winter rainfall area – June 1990
4.26
0,2
0,55
0,55
0,55
0,2
0,2
0,2
0,25
0,25
0,25
0,2
0,3
Aug
0,2
0,55
0,55
0,55
0,2
0,2
0,2
0,3
0,3
0,3
0,2
0,4
Sept
0,2
0,55
0,55
0,55
0,3
0,3
0,2
0,4
0,4
0,4
0,3
0,4
Oct
0,3
0,55
0,55
0,55
0,4
0,4
0,25
0,45
0,45
0,45
0,4
0,4
Nov
0,4
0,55
0,55
0,55
0,5
0,5
0,25
0,5
0,5
0,5
0,5
0,4
Dec
Planting
date
1 Oct
15 May
1 Dec
1 Jan
1 Jun
1 Aug
1 Nov
Agronomic
crops
Mealies
Wheat
Soya beans
Potatoes
Potatoes
Potatoes
Potatoes
31 Jan
30 Nov
31 Sept
31 Mar
15 Apr
15 Sept
15 Feb
End of growing
season
0,6
0,4
0,6
0,55
Jan
0,7
0,7
0,4
Feb
0,6
0,55
Mar
0,55
Apr
0,25
May
0,4
0,3
Jun
0,7
0,5
Jul
0,4
0,7
0,65
Aug
Months of the year
Table 4.9: Estimated design crop factors for agronomic crops in the winter rainfall area – June 1990
0,7
0,55
0,4
Sept
0,7
0,3
Oct
0,4
0,55
0,5
Nov
Crop water relationship and climate
0,7
0,3
0,55
Dec
4.27
Irrigation Design Manual
0,25
0,3
0,25
0,25
0,25
0,25
Brassicas
Cucurbits
Peas
Onions
Tomatoes
0-20
Beans
Vegetable crops
0,3
0,3
0,3
0,3
0,5
0,3
20-40
0,5
0,5
0,3
0,4
0,5
0,5
40-60
Portion of growing season[%]
Table 4.10: Estimated design crop factors for vegetables in the winter rainfall area – June 1990
4.28
0,55
0,5
0,55
0,4
0,55
0,5
60-80
0,55
0,5
0,5
0,4
0,55
0,55
80-100
Almonds
Almonds
Apples
Apples
Apricots
Apricots
Asparagus
Avocado
Avocado
Bananas
Brambles
Cherries
Cherries
Citrus
Citrus
Coffee
Coffee
Cut flowers
Date palm
Date palm
Fescue pasture
Grapes
Grapes
Guavas
Guavas
Litchi
Litchi
Lucerne
Lucerne
Macadamia
Macadamia
Mangoes
Mangoes
Pastures
Pastures
Pawpaws
Crop
Assumptions:
Table/middle season
Wine/middle season
Mature
Young
Mature
Young
Semi-dormant
Semi-dormant
Mature
Young
Mature
Young
Summer & Winter
Summer/perennial
Mature
Mature
Young
Mature/middle season
Young/middle season
Mature/average production
Young/average production
Mature
Young
Mature
Young
Ratoon
Mature/middle season
Young/middle season
Mature/middle season
Young/middle season
Mature/middle season
Young/middle season
Crop options
All areas
All areas
All areas
All areas
All areas
All areas
All areas
Lowveld
Lowveld
Lowveld
Winter rain/Highveld
Highveld
Highveld
All areas
All areas
Lowveld
Lowveld
All areas
Karoo/North Cape
Karoo/North Cape
All areas
All areas
All areas
Winter rainfall
Winter rainfall
Lowveld
Lowveld
Areas with frost
Areas without frost
All areas
All areas
Lowveld
Lowveld
All areas
All areas
Lowveld
Climatic region
1. Weekly irrigations
2. Cover: Mature orchards/vineyards = 75%
Young orchards/vineyards = 40%
Other crops = 100%
3. Wetted area: Orchards/vineyards = 50%
Other crops = 100%
Table 4.11: Penman-Monteith Crop Factors: Perennials
Jan
0,90
0,53
0,98
0,57
0,71
0,44
0,96
0,98
0,57
0,90
1,11
0,74
0,46
0,63
0,38
0,98
0,57
1,15
0,98
0,57
0,80
0,66
0,55
0,90
0,53
0,83
0,50
0,86
0,86
0,90
0,53
0,72
0,45
0,85
0,81
0,94
Feb
0,87
0,51
0,93
0,55
0,59
0,39
0,89
0,88
0,51
0,90
1,03
0,60
0,40
0,63
0,38
0,88
0,51
1,15
0,98
0,57
0,80
0,57
0,55
0,90
0,53
0,78
0,47
0,86
0,86
0,79
0,48
0,67
0,43
0,85
0,81
0,94
Mar
0,64
0,41
0,69
0,43
0,47
0,33
0,56
0,68
0,37
0,84
0,86
0,46
0,34
0,63
0,38
0,68
0,37
1,15
0,98
0,57
0,80
0,45
0,49
0,90
0,53
0,73
0,44
0,78
0,86
0,57
0,38
0,62
0,41
0,85
0,76
0,94
Apr
0,37
0,29
0,42
0,30
0,35
0,25
0,38
0,58
0,31
0,70
0,69
0,32
0,28
0,62
0,39
0,58
0,31
0,90
0,98
0,57
0,80
0,37
0,34
0,65
0,40
0,68
0,42
0,62
0,77
0,35
0,28
0,56
0,39
0,85
0,66
0,67
May
0,24
0,23
0,28
0,23
0,28
0,24
0,38
0,58
0,31
0,56
0,61
0,25
0,24
0,61
0,39
0,58
0,31
0,62
0,79
0,45
0,76
0,26
0,26
0,38
0,25
0,65
0,40
0,47
0,61
0,24
0,23
0,51
0,37
0,85
0,55
0,39
Jun
0,24
0,23
0,28
0,23
0,28
0,24
0,38
0,58
0,31
0,49
0,61
0,25
0,24
0,61
0,39
0,58
0,31
0,62
0,59
0,32
0,72
0,26
0,26
0,38
0,25
0,72
0,44
0,38
0,52
0,24
0,23
0,53
0,37
0,85
0,50
0,39
kc
Jul
0,24
0,23
0,28
0,23
0,28
0,24
0,38
0,58
0,31
0,49
0,61
0,25
0,24
0,61
0,39
0,58
0,31
0,62
0,59
0,32
0,72
0,26
0,26
0,38
0,25
0,84
0,50
0,38
0,52
0,24
0,23
0,53
0,37
0,86
0,50
0,39
Aug
0,24
0,23
0,28
0,23
0,28
0,24
0,38
0,58
0,31
0,49
0,61
0,25
0,24
0,62
0,38
0,58
0,31
0,62
0,68
0,38
0,74
0,26
0,26
0,38
0,25
0,91
0,54
0,46
0,57
0,24
0,23
0,78
0,48
0,86
0,50
0,48
Sep
0,56
0,37
0,28
0,23
0,56
0,37
0,38
0,58
0,31
0,49
0,79
0,32
0,27
0,63
0,38
0,58
0,31
0,88
0,88
0,51
0,78
0,34
0,29
0,38
0,25
0,91
0,54
0,62
0,69
0,56
0,37
0,83
0,50
0,86
0,55
0,66
Oct
0,90
0,53
0,50
0,34
0,89
0,53
0,66
0,68
0,37
0,49
1,08
0,73
0,46
0,63
0,38
0,68
0,37
1,15
0,98
0,57
0,80
0,63
0,50
0,41
0,27
0,91
0,54
0,78
0,80
0,90
0,53
0,83
0,50
0,86
0,65
0,85
Crop water relationships and climate
Nov
0,90
0,53
0,95
0,55
0,90
0,54
0,96
0,88
0,50
0,69
1,11
0,90
0,53
0,63
0,38
0,88
0,50
1,15
0,98
0,57
0,80
0,67
0,55
0,67
0,39
0,91
0,54
0,86
0,86
0,90
0,53
0,82
0,50
0,86
0,76
0,94
Dec
0,90
0,53
0,98
0,57
0,83
0,50
0,96
0,98
0,57
0,90
1,11
0,87
0,52
0,63
0,38
0,98
0,57
1,15
0,98
0,57
0,80
0,67
0,55
0,87
0,51
0,88
0,52
0,86
0,86
0,90
0,53
0,78
0,48
0,85
0,81
0,94
4.29
Irrigation Design Manual
Young
Mature/middle season
Young/middle season
Mature/middle season
Young/middle season
Mature
Young
Mature
Young
Mature/middle season
Young/middle season
Pawpaws
Peaches
Peaches
Pears
Pears
Pecan nuts
Pecan nuts
Pistachio
Pistachio
Plums
Plums
Salt bush
Strawberries
Sugar
Sugar
Tea
Walnuts
Walnuts
Mature
Young
Winter harvest
Spring harvest
Crop options
Crop
Table 4.11: (continue)
4.30
Lowveld
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
KwaZulu-Natal/Lowveld
KwaZulu-Natal/Lowveld
Lowveld
All areas
All areas
Climatic region
Jan
0,55
0,80
0,49
0,97
0,56
0,82
0,50
0,82
0,49
0,89
0,53
0,31
0,75
1,15
1,15
0,68
0,90
0,53
Feb
0,55
0,66
0,42
0,82
0,49
0,66
0,43
0,80
0,48
0,72
0,45
0,31
0,51
1,15
1,15
0,68
0,90
0,53
Mar
0,55
0,51
0,35
0,60
0,39
0,50
0,36
0,61
0,39
0,55
0,37
0,31
0,38
1,15
1,15
0,68
0,58
0,38
Apr
0,41
0,36
0,28
0,39
0,29
0,34
0,29
0,39
0,29
0,38
0,29
0,31
0,38
1,15
1,15
0,70
0,23
0,23
May
0,26
0,29
0,24
0,28
0,23
0,25
0,25
0,28
0,24
0,29
0,24
0,29
0,38
1,12
1,15
0,72
0,23
0,23
Jun
0,26
0,29
0,24
0,28
0,23
0,25
0,25
0,28
0,24
0,29
0,24
0,26
0,38
0,68
1,15
0,75
0,23
0,23
kc
Jul
0,26
0,29
0,24
0,28
0,23
0,25
0,25
0,28
0,24
0,29
0,24
0,26
0,38
0,39
1,15
0,76
0,23
0,23
Aug
0,31
0,31
0,26
0,28
0,23
0,33
0,28
0,28
0,24
0,29
0,24
0,26
0,38
0,51
1,15
0,76
0,23
0,23
Sep
0,40
0,69
0,43
0,31
0,25
0,82
0,49
0,54
0,36
0,37
0,28
0,29
0,50
0,77
1,12
0,76
0,23
0,23
Oct
0,50
0,94
0,55
0,62
0,40
0,90
0,53
0,82
0,49
0,80
0,48
0,31
0,74
1,02
0,67
0,75
0,56
0,37
Nov
0,55
0,94
0,55
0,94
0,55
0,90
0,53
0,82
0,49
0,94
0,55
0,31
0,86
1,15
0,44
0,72
0,90
0,53
Dec
0,55
0,93
0,54
0,98
0,57
0,90
0,53
0,82
0,49
0,94
0,55
0,31
0,86
1,15
0,88
0,70
0,90
0,53
Cotton
Cow peas
Cucumbers
Cucurbits
Chicory
Chillies
Coriander
Brussels sprouts
Butternut
Cabbage Early
Canola
Carrots
Carrots
Cauliflower Main
Cauliflower Main
Cauliflower Main
Cauliflower Main
Cereals Grazing
Spring/Summer
Spring
Spring/medium
grower
Spring
Spring
Spring
Spring
Spring/Summer
Autumn/Winter
Spring
Summer
Autumn
Winter
Autumn
Autumn
Spring
Spring/Summer
Winter
Spring
Spring/Summer
Plant / Crop option
Crop
Babala
Barley
Beans Dry
Beans Green
Beetroot
Brinjals
Brocolli
1. Weekly irrigations
2. Wetted area = 100%
Assumptions:
160
100
105
130
195
110
90
120
110
75
120
100
107
100
90
120
100
190
140
140
100
90
90
140
80
Days
Warm areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
Eastern Cape
warm
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
Climatic
region
Table 4.12: Penman-Monteith Crop Factors: Annuals
0,40
0,45
0,45
0,54
0,43
0,39
0,43
0,64
0,52
0,58
0,39
0,44
0,48
0,55
0,53
0,59
0,73
0,48
Mnth
1
0,38
0,64
0,45
0,45
0,46
0,39
0,63
0,63
0,93
0,93
0,75
0,51
0,73
0,96
0,87
0,89
0,93
0,66
0,67
0,67
0,82
0,84
0,80
0,89
0,60
Mnth
2
0,65
0,82
1,02
0,91
0,94
0,66
0,86
1,01
1,06
1,09
0,93
0,76
1,09
0,93
1,07
0,98
0,99
1,10
0,94
0,92
0,99
0,99
0,98
0,99
0,88
1,09
0,81
0,75
0,93
0,90
0,75
0,90
0,98
1,00
0,99
0,99
1,00
0,99
0,90
1,01
0,82
0,72
1,07
0,90
0,90
0,93
0,90
0,80
kc Months from plant
Mnth Mnth Mnth Mnth
3
4
5
6
1,05
1,02
0,59
1,12
1,11
0,66
1,14
0,87
1,03
0,98
1,11
1,10
0,65
0,98
0,90
0,50
Mnth
7
Mnth
8
Mnth
9
Crop water relationships and climate
Remarks
4.31
Spring
Autumn
Autumn/Winter
Spring/Summer
Spring/Summer
Autumn/Winter
Spring/Summer
Autumn
Spring
Spring/short grower
Spring/medium
grower
Spring/long grower
Spring/Summer
Parsley
Pastures
Peas
Potatoes
Pumpkin
Pumpkin
Radishes
Ryegrass
Sorghum
Soybeans
Soybeans
Soybeans
Sweet melon
Maize
Oats
Onions
Paprika
Maize
Autumn/Winter
Spring/Summer
Spring
Spring
Summer
Spring
Spring
Autumn
Spring/medium
grower
Summer/short
grower
Winter
Autumn transplant
Cucurbits
Green peppers
Ground nuts
Hubbard squash
Hubbard squash
Lentils
Lettuce
Lettuce
Crop
Plant / Crop option
Irrigation Design Manual
Table 4.12 (continue)
4.32
130
140
105
270
170
110
120
125
150
45
250
170
120
120
140
160
130
135
140
110
150
140
130
170
75
100
Days
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
Climatic
region
0,44
0,43
0,64
0,49
0,45
0,49
0,29
0,38
0,39
0,72
0,61
0,45
0,43
0,36
0,64
0,58
0,51
0,39
Mnth
1
0,68
0,38
0,39
0,53
0,55
0,42
0,44
0,49
0,97
0,87
0,95
1,13
0,77
0,82
0,89
0,67
0,63
0,86
0,97
0,77
1,04
0,79
0,82
0,60
0,76
0,75
Mnth
2
0,86
0,72
0,61
0,71
0,74
0,79
0,81
0,74
1,14
1,14
0,83
1,00
0,80
1,04
1,00
0,80
1,14
1,14
1,14
0,96
1,15
0,80
1,07
1,01
0,79
0,87
1,03
1,11
0,86
1,00
1,14
1,15
0,80
1,09
1,09
0,88
0,86
1,14
1,12
0,76
0,98
1,14
0,83
0,99
1,00
0,80
0,59
0,70
1,15
0,80
0,66
0,82
1,00
0,93
1,00
0,69
1,15
0,69
0,67
kc Months from plant
Mnth Mnth Mnth Mnth
3
4
5
6
0,99
0,93
0,80
1,09
0,77
1,04
1,14
0,79
0,87
0,87
0,72
0,89
0,83
0,69
1,09
1,09
0,98
0,58
0,92
0,95
0,93
1,00
1,15
Mnth
7
1,00
1,15
Mnth
8
0,74
0,73
Mnth
9
Actually a bi-annual
plant
Remarks
Wheat
Sweet melon
Spinach
Squash
Sugarbeet
Sunflower
Sweet potatoes
Sweetcorn
Tobacco
Tomatoes
Tomatoes
Watermelon
Watermelon
Wheat
Crop
Table 12 (continue)
Autumn/Winter
Autumn
Spring
Spring
Spring/Summer
Spring
Spring/Summer
Spring/Summer
Processing
Table
Early
Late
Medium/Winter
Short/Autumn/
Spring
Plant / Crop option
80
120
190
105
240
100
150
90
120
100
160
85
100
125
Days
All areas
All areas
All areas
All areas
All areas
All areas
All areas
All areas
Warmer areas
All areas
All areas
All areas
All areas
All areas
Climatic
region
0,57
Mnth
1
0,66
0,39
0,53
0,42
0,40
0,42
0,53
0,41
0,67
0,58
0,65
0,64
0,57
1,06
Mnth
2
0,91
0,51
0,79
0,60
0,92
0,82
0,82
0,84
1,06
0,77
0,98
0,96
0,79
1,04
kc Months from plant
Mnth Mnth Mnth Mnth
3
4
5
6
1,00
0,90
0,77
0,98
0,99
0,98
0,89
0,82
0,96
1,15
1,15
1,15
1,14
0,86
1,09
1,09
1,03
0,99
1,09
0,92
1,02
0,85
0,97
1,09
1,09
1,09
0,97
0,98
0,95
1,12
1,06
1,02
1,15
0,95
Mnth
7
1,15
Mnth
8
Mnth
9
Crop water relationships and climate
Remarks
4.33
Irrigation Design Manual
ADDO OLIFANTPARK
ADDO SITRUS NS
ADELAIDE PP,
ALEXANDER BAY
ALICE
ALTO
AMALIENSTEIN
AMATIKULU
ATHOLE – AGR
AWS
BADPLAAS VYGEBOOMD
BAMBOESSPRUIT,OTTO
BARBERTON KOFFIEKO
BARBERTON SENTEEKO
BARKLY OOS
BATHURST NS.
BAVIAANSKLOOF I
BAYNESFIELD ESTATE
BEAUFORT-WEST
BEESTEKRAAL:VAALKO
BERGKWAGGA PARK
BETHAL
BETHAL:WILDEBEESFO
BETHLEHEM
BETHLEHEM;LOCH LAM
BIEN DONNE (NIVV)
BIEN DONNE PP
BLOEMENDAL,BISHOPS
BLOEMFONTEIN
BLOODRIVER:REHLING
BLOUPUTS
BOLO RESERVE
BONFOI
BOONTJIESKRAAL
BRAKSPRUIT AGR.
BUCKLANDS
BUFFELSFONTEIN
BUFFELSKLOOF
BUFFELSPOORT II AG
BULAND
BULTFONTEIN;ARBEID
BURGERSFORT MARONE
Station
Longitude
(º)
25,75
25,7
26,28
16,32
26,85
18,85
21,47
31,52
30,58
27,85
30,62
25,97
30,97
30,75
27,6
26,82
24,07
30,33
22,35
27,6
25,47
29,28
29,52
18,97
28,3
18,98
18,98
30,47
26,11
30,53
20,15
27,63
18,78
19,35
26,98
26,72
26,7
21,22
27,48
28,6
26,07
30,33
Latitude
(º)
-33,45
-33,57
-32,67
-28,34
-32,78
-34,02
-33,48
-20,03
-26,6
-28,87
-25,87
-26,95
-25,75
-25,63
-30,97
-33,52
-33,57
-29,75
-32,21
-25,18
-32,22
-26,27
-26,17
-33,92
-28,17
-33,83
-33,85
-29,53
-29,07
-27,85
-28,5
-32,38
-33,93
-34,2
-26,75
-33,1
-31,37
-33,48
-25,75
-24,42
-28,18
-24,75
Elevation
(m)
152
85
600
21
520
225
474
45
1620
1640
1100
1460
777
1300
1799
259
450
914
857
1096
1204
1640
1635
376
1631
138
138
838
1422
1234
442
880
153
128
1402
366
1783
518
1230
1000
1371
915
MAP
(mm)
406
360
460
39
570
777
294
1026
937
706
788
546
811
1151
675
683
287
852
222
544
412
754
721
1572
739
822
646
887
552
803
115
724
923
426
654
452
634
323
596
700
506
551
Jan
5,7
5,8
6,2
4,5
5,1
5,7
6,4
4,7
4,2
4,7
5,1
6,3
4,7
4,1
6,0
5,1
7,1
3,9
7,1
4,8
5,7
4,9
5,1
5,0
4,9
6,9
6,3
4,5
6,3
4,7
7,4
5,1
5,6
5,9
6,4
5,6
6,0
5,7
5,4
4,5
6,8
5,0
Feb
5,1
5,2
5,7
4,2
4,6
5,5
5,9
4,5
3,9
4,2
4,8
5,7
4,7
4,0
5,4
4,7
6,3
3,7
6,4
4,5
5,1
4,5
5,0
4,9
4,4
6,5
5,9
4,3
5,6
4,3
6,8
4,5
5,6
5,4
5,8
5,1
5,1
5,2
5,0
4,3
5,8
4,8
Mrch
4,2
4,2
4,6
3,6
3,7
4,0
4,5
4,1
3,4
3,4
4,1
4,8
4,1
3,4
4,3
4,0
5,1
3,2
5,0
3,8
4,0
3,9
4,3
3,7
3,6
5,2
4,8
3,7
4,3
3,8
5,0
4,1
4,3
4,3
4,8
4,1
4,1
3,9
4,3
3,4
4,7
4,3
April
3,2
3,3
3,7
2,9
2,9
2,9
3,1
3,4
2,6
2,5
3,5
4,0
3,3
2,9
3,2
3,4
3,7
2,6
3,8
2,9
2,9
3,2
3,6
2,6
2,7
3,3
3,1
2,9
3,3
3,1
4,3
3,4
3,2
2,9
4,1
3,3
3,1
2,8
3,6
3,2
3,6
3,5
Average daily ET0 (mm/day)
May
June
July
Aug
2,5
2,2
2,3
2,9
2,6
2,2
2,3
2,9
3,2
2,9
3,2
3,7
2,2
2,4
2,3
2,7
2,4
2,1
2,4
2,9
2,1
1,6
1,7
2,1
2,2
1,9
2,1
2,7
2,7
2,3
2,5
3,0
1,9
1,5
1,7
2,2
1,8
1,3
1,5
2,2
2,9
2,5
2,8
3,6
3,0
2,7
2,9
3,9
2,9
2,6
2,9
3,6
2,6
2,4
2,4
2,9
2,5
2,1
2,3
3,2
3,1
2,9
3,1
3,3
2,8
2,3
2,5
3,1
2,0
1,7
2,0
2,7
3,1
2,7
2,8
3,5
2,2
1,7
1,9
2,5
2,0
1,6
1,8
2,6
2,5
2,3
2,4
3,2
2,8
2,4
2,6
3,6
1,7
1,3
1,5
1,8
1,9
1,5
1,6
2,3
2,0
1,6
1,7
2,4
1,7
1,3
1,4
2,2
2,1
1,8
2,1
2,9
2,6
2,3
2,5
3,4
2,5
2,4
2,6
3,3
3,1
2,7
2,6
3,8
3,1
3,0
3,2
3,8
2,2
1,8
2,0
2,5
2,0
1,6
1,6
2,0
3,3
2,8
3,1
4,2
2,7
2,4
2,6
3,1
2,5
2,1
2,3
3,2
2,0
2,0
2,1
2,4
2,9
2,5
2,7
3,6
2,4
2,2
2,0
2,4
2,5
2,0
2,3
3,3
2,8
2,4
2,6
3,4
Table 13: Average daily reference evapotranspiration and yearly rainfall data (Source: SAPWAT)
4.34
Sept
3,7
3,8
4,5
3,3
3,7
2,8
3,7
3,5
3,0
3,1
4,6
5,6
4,3
3,5
4,4
3,8
4,3
3,2
4,4
3,5
3,7
4,2
4,8
2,6
3,2
3,3
2,8
3,6
4,4
4,3
4,8
4,4
3,3
2,9
5,8
4,0
4,2
3,2
4,6
3,8
4,6
4,5
Oct
4,5
4,4
4,9
3,8
4,2
3,7
4,6
4,0
3,5
3,8
4,8
6,2
4,4
3,7
4,9
4,1
5,1
3,4
5,4
4,2
4,4
4,7
5,2
3,7
3,9
4,9
4,2
4,1
5,3
4,4
5,7
4,5
4,3
4,1
6,2
4,5
4,8
4,1
5,2
4,9
5,7
5,1
Nov
5,2
5,1
5,6
4,4
4,7
4,3
5,6
4,3
3,8
4,5
4,8
6,6
4,6
3,9
5,5
4,6
6,2
3,7
6,4
4,6
5,2
4,9
5,4
4,5
4,5
6,0
5,2
4,3
6,2
4,7
7,1
4,7
4,8
5,1
6,5
5,0
5,4
5,0
5,5
4,9
6,4
5,3
Dec
5,7
5,7
6,1
4,4
5,1
5,1
6,2
4,6
4,1
4,8
5,0
7,0
4,7
4,0
6,3
5,0
6,8
3,9
7,1
4,6
5,7
5,1
5,2
4,9
4,9
6,4
5,7
4,7
6,6
4,9
8,1
5,0
5,3
5,8
6,7
5,5
6,0
5,5
5,5
5,2
6,9
5,1
CALVINIA
CALVINIA - TNK
CALVINIA WK.
CAPE PADRONE
CAPE ST. LUCIA
CAPE TOWN
CARNARVON PS.
CEDARA – AGR
CHILTERN DAMWAL
CITRUSDAL (NIVV)
CITRUSDAL PP
CLOCOLAN
COBHAM – BOS
COLESBERG
CONCORDIA
CRADOCK PP,
DARLING
DARNAL
DE AAR
DE AAR.
DE DOORNS (NIWW)
DE KEUR
DE KEUR (OLD)
DE RUST
DE TUIN
DE TUIN
DE VLEI
DEELVILLE
DENNEHOEK
DIE KRANS
DOHNE - AGR
DOHNE NS II
DOHNE NS.
DOUGLAS;TRONK.
DRIEFONTEIN
DRIEPLOTTE - AGR
DUIWELSKLOOF:WESTF
DUNDEE:RES.STATION
DUNGHYE PARK
DURBAN
EAST LONDON
ELANDSHEIGHTS
Station
Table 13 (continue)
Longitude
(º)
19,46
19,77
19,77
26,45
32,24
18,32
22
30,28
19,15
18,98
18,98
27,55
29,42
25,1
19,85
25,68
18,38
31,38
24,01
24,02
19,67
19,3
19,3
19,12
20,1
18,98
19,68
19,33
23,85
21,68
27,47
27,47
27,47
23,75
20,4
24,63
30,12
30,32
19,52
30,57
27,52
28,18
Latitude
(º)
-31,28
-31,47
-31,48
-33,75
-28,3
-33,54
-30,97
-29,53
-34,05
-32,57
-32,55
-28,9
-29,68
-30,7
-33,68
-32,22
-33,38
-29,27
-30,39
-30,65
-33,47
-32,98
-32,97
-34,17
-29,87
-33,13
-33,43
-33,35
-33,87
-33,55
-32,52
-32,52
-32,52
-29,07
-34,38
-29,05
-23,73
-28,17
-34,32
-29,58
-33,02
-30,85
Elevation
(m)
981
980
974
168
111
17
1280
1076
309
198
198
1600
1675
1328
937
846
110
85
1243
1243
457
945
945
330
970
80
490
480
640
229
899
899
899
1030
91
1120
750
1219
122
8
125
1830
MAP
(mm)
209
206
208
762
1292
506
215
853
879
437
281
686
1240
385
565
341
594
1084
288
320
352
782
685
797
135
546
150
582
1052
232
747
743
740
344
471
433
1049
757
521
1003
860
1120
Jan
7,1
6,0
8,9
4,8
4,6
6,1
9,4
4,3
5,2
7,0
7,2
5,0
4,2
6,7
5,5
7,1
6,7
4,7
7,1
8,0
5,8
6,2
6,2
5,0
9,7
6,5
5,7
6,2
5,0
6,0
5,2
4,7
5,1
7,3
5,5
6,2
4,2
5,3
5,8
4,3
4,5
3,3
Feb
6,6
5,6
8,0
4,5
4,3
5,7
8,0
4,1
4,8
6,3
6,3
4,5
3,9
5,8
5,1
6,2
6,4
4,4
6,4
6,6
5,3
5,5
5,8
4,8
8,7
6,1
4,8
5,9
4,7
5,4
5,0
4,4
4,9
6,0
5,0
5,0
3,9
4,9
5,5
4,3
4,4
3,4
Mrch
5,3
4,4
6,8
3,8
3,8
4,3
6,3
3,5
3,7
4,9
5,0
3,6
3,3
4,5
4,0
5,0
5,1
3,8
4,9
5,2
4,1
4,4
4,6
3,8
6,8
4,6
3,9
4,6
3,9
4,2
4,4
3,9
4,2
4,9
4,1
4,9
3,4
4,3
4,4
3,6
3,7
3,2
April
3,9
3,3
5,0
3,3
3,0
3,0
4,6
3,0
2,5
3,1
3,5
2,7
2,8
3,2
2,9
3,6
3,5
3,0
3,5
3,6
2,8
3,1
3,1
2,8
5,0
3,1
2,7
2,9
3,1
2,8
4,0
3,5
3,7
3,5
3,1
3,2
2,9
3,5
3,1
3,0
3,1
4,5
Average daily ET0 (mm/day)
May
June
July
Aug
3,0
2,6
2,6
3,1
2,6
2,1
2,2
2,7
4,0
3,1
3,2
4,1
2,9
2,7
2,8
3,1
2,5
2,1
2,3
2,8
2,1
1,7
1,8
2,4
3,4
2,6
3,0
4,1
2,4
2,0
2,2
3,0
1,8
1,5
1,6
2,0
1,8
1,3
1,4
2,2
2,3
1,2
1,7
2,1
1,9
1,4
1,6
2,3
2,3
2,0
2,3
3,0
2,2
1,7
1,9
2,9
2,2
1,8
1,9
2,3
2,8
2,3
2,5
3,4
2,0
1,4
1,5
2,2
2,3
2,0
2,1
2,7
2,8
2,4
2,6
3,3
2,6
2,1
2,3
3,4
2,0
1,6
1,9
2,4
2,1
1,3
1,4
1,9
2,2
1,7
1,8
2,4
1,8
1,5
1,3
1,7
3,6
2,9
3,1
4,2
1,8
1,3
1,4
2,0
1,9
1,8
1,8
2,2
1,8
1,4
1,4
2,0
2,4
2,1
2,3
2,7
2,1
1,9
2,2
2,6
3,8
3,6
3,5
4,1
3,1
3,0
3,2
3,5
3,5
3,4
3,5
4,0
2,6
2,1
2,3
3,3
2,2
1,8
1,8
2,3
2,7
2,2
2,3
3,6
2,4
2,1
2,3
2,8
2,9
2,7
3,0
3,8
2,2
1,7
1,8
2,2
2,5
2,1
2,2
2,8
3,1
2,8
3,1
3,3
2,8
4,1
3,0
2,8
Sept
3,9
3,6
5,2
3,4
3,3
3,1
5,3
3,4
2,7
3,1
3,0
3,3
3,7
4,2
3,0
4,6
3,2
3,2
4,3
4,7
3,4
2,6
3,2
2,3
5,5
3,0
3,1
3,0
3,4
3,6
4,5
3,9
4,6
4,5
3,2
4,3
3,5
4,8
3,1
3,2
3,4
2,4
Oct
5,2
4,7
6,4
3,8
3,7
4,1
6,9
3,7
3,5
4,6
4,4
4,1
3,8
5,1
3,9
5,4
4,7
3,7
5,4
5,9
4,4
3,4
4,2
3,4
7,1
3,9
4,0
4,2
3,9
4,6
4,7
4,1
4,5
5,7
4,1
4,4
3,8
5,0
4,1
3,8
3,6
3,7
Nov
6,0
5,4
8,0
4,2
4,2
4,9
8,2
4,1
4,5
5,9
5,3
4,8
4,2
6,0
4,8
6,3
6,0
4,2
6,3
7,1
5,2
4,7
5,1
4,2
8,5
5,0
4,8
5,2
4,5
5,4
4,8
4,5
4,9
6,7
4,8
6,0
4,0
5,3
5,1
4,2
4,3
3,0
Crop water relationships and climate
Dec
6,8
5,9
8,6
4,7
4,5
5,7
8,8
4,3
5,0
6,6
6,3
5,3
4,3
6,7
5,3
7,0
6,4
4,6
7,0
8,1
5,7
5,6
5,8
4,9
9,4
6,4
5,5
6,0
4,9
6,0
5,4
4,8
5,2
7,1
5,4
6,1
4,1
5,5
5,8
4,1
4,6
2,9
4.35
ELGIN
ELGIN (NIVV)
ELLIOT VOORLIGTING
ELSENBURG
ELSENBURG
ENDEAVOUR
ESTCOURT
ESTCRT:TABAMHLOPE
EXCELSIOR
FENFIELD
FICKSBURG;KERSIEPR
FLEURBAIX
GENL J.C.STEYN GEV
GEORGE
GERMISTON
GOEDEHOOP
GRAAFWATER KO-OP
GRASRUG
GROOT CONSTANTIA
GROOT VLAKTE
GROOTFONTEIN
GROOTFONTEIN XI,
GROOTVLAKTE
GULLEMBERG
H.L.S.AUGSBURG
HAZYVIEW BURGERSHA
HAZYVIEW, KRANSKOP
HAZYVIEW;SABIE SAN
HECTRSPRT;LAUGHING
HEIDEDAL
HELDERFONTEIN (NIV
HELDERVUE
HERTZOGVILLE;KAREE
HILLCREST:SENSAKO
HOBHOUSE.
HOEDSPRT JONGMANSP
HOPETOWN;ALFALFA.
IDEAL HILL
JAAGBAAN
JAMESTOWN
JAN KEMPDORP;VAALH
JANSENVILLE PP
Station
Longitude
(º)
19,03
19,03
27,85
18,83
18,83
26,37
29,52
29,65
19,45
27
27,85
18,83
25,33
22,25
28,09
18,77
18,6
18,83
18,42
19,62
25,02
25,02
19,62
28,97
18,9
31,08
30,87
31,13
31,58
19,07
18,88
18,72
25,3
30,75
27,13
30,8
24,18
18,88
30,68
26,78
24,83
24,7
Latitude
(º)
-34,13
-34,13
-31,35
-33,85
-33,85
-33,47
-29,01
-29,03
-32,95
-32,53
-28,87
-33,95
-33,4
-33,58
-26,15
-33,92
-32,17
-33,47
-34,03
-33,32
-31,29
-31,48
-33,33
-23,83
-32,17
-25,12
-28,97
-25,03
-25,6
-32,93
-33,92
-32,82
-28,2
-29,8
-29,52
-24,38
-29,65
-32,8
-29,35
-31,07
-27,95
-32,93
Irrigation Design Manual
Table 13 (continue)
4.36
Elevation
(m)
305
305
1463
177
177
366
1180
1450
953
1425
1640
85
200
221
1665
235
177
213
107
1155
1263
1270
1160
1100
500
722
1120
530
350
725
179
755
1326
732
1448
610
1143
152
1018
1650
1175
414
MAP
(mm)
1215
1116
744
653
596
573
738
930
443
708
710
716
368
776
708
606
288
426
1085
548
377
383
718
561
223
967
849
881
844
1179
791
811
502
817
609
514
311
286
809
574
448
290
Jan
4,8
4,8
4,9
6,2
6,1
4,6
4,8
4,6
6,5
4,4
5,0
5,4
6,8
4,2
4,9
5,3
5,8
6,7
5,1
5,0
5,9
7,2
5,9
5,3
7,0
4,1
4,3
4,4
5,1
4,5
5,8
5,5
7,1
4,1
5,0
5,0
5,3
7,8
3,9
6,6
6,3
7,1
Feb
4,5
4,4
4,4
5,9
5,7
4,3
4,4
4,3
6,1
4,1
4,5
4,9
6,2
3,7
4,5
5,2
5,3
6,5
4,6
4,7
5,3
6,1
5,3
4,9
6,2
4,0
4,1
4,2
4,8
4,2
5,7
5,1
6,1
4,1
4,3
4,9
4,9
7,1
3,7
5,5
5,5
6,3
Mrch
3,6
3,4
3,8
4,6
4,7
3,5
3,7
3,6
4,6
3,3
3,7
3,8
5,0
3,1
3,9
4,3
4,2
5,2
3,7
3,7
4,1
4,9
4,1
4,4
4,9
3,4
3,6
3,7
4,2
3,3
4,4
4,0
4,9
3,5
3,4
4,2
3,9
5,6
3,2
4,5
4,5
4,9
April
2,4
2,3
3,1
3,2
3,5
2,7
3,1
3,0
3,1
2,6
2,8
2,6
4,0
2,4
3,2
3,4
3,0
3,6
2,5
2,4
3,1
3,9
2,8
4,0
3,3
2,8
3,2
2,9
3,5
2,1
2,8
2,8
3,8
2,9
2,5
3,4
2,8
3,7
2,6
3,4
3,4
3,6
Average daily ET0 (mm/day)
May
June
July
Aug
1,8
1,4
1,6
2,0
1,8
1,5
1,7
2,0
2,8
2,5
2,7
3,3
2,1
1,7
1,8
2,3
2,2
1,7
2,1
2,4
2,4
2,3
2,4
2,7
2,3
1,8
2,3
2,8
2,5
2,0
2,3
3,0
2,1
1,7
1,8
2,3
2,1
2,0
2,2
2,7
2,0
1,6
1,7
2,5
1,7
1,4
1,4
1,9
3,4
3,0
3,3
3,8
2,0
1,9
2,0
2,3
2,7
2,5
2,6
3,4
2,4
1,8
2,0
2,4
2,1
1,7
1,8
2,3
2,4
1,7
1,7
2,2
1,8
1,7
1,8
2,2
1,6
1,1
1,2
1,8
2,4
2,3
2,2
3,0
3,3
2,6
3,0
3,8
2,1
1,5
1,2
2,0
3,0
2,9
3,1
4,1
2,0
1,6
1,6
2,3
2,2
1,8
1,9
2,4
2,9
2,7
3,0
3,5
2,4
2,0
2,2
2,7
2,9
2,7
3,0
4,0
1,4
1,0
1,1
1,6
1,9
1,6
1,8
2,3
2,0
1,7
1,8
2,2
2,9
2,3
2,6
3,7
2,4
2,1
2,5
3,0
1,7
1,2
1,4
2,0
2,6
2,3
2,4
3,2
1,8
1,3
1,5
2,2
2,3
1,6
1,5
2,2
2,0
1,7
2,0
2,6
2,6
2,2
2,4
3,3
2,4
1,9
2,1
3,1
2,9
2,4
2,7
3,3
Sept
2,6
2,7
4,0
3,0
2,9
3,2
3,9
3,9
3,3
3,4
3,6
2,7
4,6
2,6
4,6
2,9
3,2
3,1
2,9
2,6
3,7
4,9
2,3
5,3
3,4
3,1
4,1
3,4
4,9
2,3
3,1
2,9
5,2
3,5
3,0
4,2
3,2
3,4
3,1
4,5
4,4
4,2
Oct
3,8
3,4
4,2
4,2
4,2
3,7
4,4
4,4
4,6
3,6
4,2
3,8
5,2
3,2
5,0
4,0
4,3
4,6
3,8
3,5
4,6
5,6
3,2
5,7
4,8
3,5
4,0
3,8
4,9
3,4
4,5
4,0
6,1
3,6
3,7
4,6
4,2
5,1
3,4
5,2
5,4
5,0
Nov
4,2
4,2
4,7
5,4
4,8
4,3
4,9
4,5
5,7
4,2
4,7
4,5
5,9
3,8
5,3
4,4
5,1
5,9
4,6
4,3
5,2
6,5
4,2
5,9
5,9
3,8
4,3
4,1
5,1
3,8
5,1
4,7
6,9
4,1
4,6
4,8
5,0
6,5
3,8
5,9
6,2
6,2
Dec
4,2
4,6
5,1
5,9
5,6
4,8
4,9
4,9
6,2
4,4
5,1
5,1
6,7
4,1
5,3
5,1
5,5
6,5
5,0
5,0
5,9
7,1
4,7
5,8
6,5
3,9
4,3
4,2
5,0
4,3
5,5
5,3
7,4
4,2
5,0
4,7
5,6
7,4
4,1
6,7
6,4
6,9
JC STEYNGEV-LANDBO
JOHANNESBURG
JOLETTE
JONASKRAAL
JOUBERTINA
KAKAMAS
KARRINGMELKSRIVIER
KEI MOUTH
KEIMOES
KEIMOES.
KESTELL.
KIMBERLEY
KLAVER
KLAWER WYNKELDER
KLEIN BOTTELARY
KLEIN WATERVAL
KLIPFONTEIN
KLIPPAN:KOSTER
KOKSTAD
KOKSTAD - AGR
KOMATIPRT;TENBOSCH
KOSTER KOOPERASIE.
KROONSTAD
KURUMAN
KURUMAN
L.TRICHARD:LEVUBU (S
LA MOTTE
LA PLAISANTE
LANDAU
LANGGEWENS (WRS)
LANGKLOOF
LANGKLOOF (NIVV)
LE BONHEUR
LETABA LETSITELE
LETSITELE:EILAND (
LIDNEY,
LITTLE HARMONY, RI
LONGDOWN
LONGDOWN
LORRAINE
LOSKOP - PROEFSTAS
LUTZVILLE (NIWW)
Station
Table 13 (continue)
Longitude
(º)
25,35
28,03
19,55
19,9
23,87
20,62
20,77
28,15
20,97
21
28,7
24,46
18,37
18,63
18,73
19,02
25,73
26,95
29,25
29,42
31,97
26,92
27,14
23,43
23,26
30,28
19,08
19,2
18,97
18,7
23,58
23,58
18,87
30,32
30,67
26
30,32
19,17
19,17
19,05
29,4
18,43
Latitude
(º)
-33,4
-26,12
-33,5
-34,4
-33,82
-28,77
-34,13
-32,67
-28,7
-28,73
-28,32
-28,48
-31,47
-31,78
-33,9
-33,88
-32,6
-26,05
-30,32
-30,52
-25,4
-25,83
-27,4
-27,47
-27,28
-23,08
-33,88
-33,45
-33,6
-33,28
-33,78
-33,78
-33,83
-23,87
-23,67
-33,67
-29,93
-34,05
-34,05
-32,05
-25,17
-31,6
Elevation
(m)
96
1753
370
103
549
720
192
258
762
748
1707
1204
42
68
110
186
735
1561
1305
1372
189
1585
1348
1312
1300
610
206
260
122
177
722
722
260
623
457
200
869
300
340
320
945
31
MAP
(mm)
359
718
123
388
504
106
429
774
119
161
709
415
174
216
682
1134
411
608
728
832
564
620
606
356
420
842
852
633
517
415
605
632
841
714
551
551
893
687
819
251
631
144
Jan
5,7
5,1
5,6
6,1
5,4
9,5
5,8
4,8
7,6
7,3
5,3
7,0
6,9
7,0
6,1
6,9
6,3
5,5
4,5
4,4
5,3
5,9
5,8
5,6
6,4
4,9
5,9
6,5
6,7
7,1
4,5
5,3
6,2
4,3
4,7
5,2
3,9
5,4
4,7
7,0
5,3
6,4
Feb
5,2
4,8
5,0
5,7
4,9
8,3
5,4
4,5
6,4
6,6
4,9
6,2
6,6
6,8
5,6
7,2
5,8
5,3
4,0
4,1
5,1
5,4
5,3
5,0
5,8
4,6
5,6
6,1
6,2
7,1
4,1
4,9
6,1
4,1
4,4
4,9
3,8
5,0
4,9
6,6
5,1
6,1
Mrch
4,3
4,0
4,6
4,6
4,0
6,7
4,3
3,8
5,1
5,2
4,1
4,8
5,6
5,7
4,6
5,4
4,6
4,3
3,3
3,4
4,3
4,5
4,3
4,1
4,5
4,0
4,3
4,7
4,8
5,8
3,5
4,0
4,8
3,6
3,8
4,0
3,2
4,0
3,7
5,3
4,3
5,0
April
3,2
3,3
3,3
3,3
2,9
5,0
3,2
3,3
3,8
4,0
3,2
3,7
4,1
4,2
3,4
3,8
3,9
3,7
2,8
2,7
3,5
3,7
3,4
3,0
3,4
3,4
2,9
3,1
3,1
4,2
2,7
3,2
3,5
2,9
3,0
3,5
2,6
2,8
2,7
3,7
3,5
3,8
Average daily ET0 (mm/day)
May
June
July
Aug
2,6
2,3
2,5
2,8
2,7
2,5
2,5
3,4
1,9
1,7
1,6
2,7
2,3
1,8
1,8
2,3
2,2
1,8
2,0
2,5
3,6
2,8
3,2
4,2
2,6
2,1
2,1
2,4
3,1
2,8
3,1
3,6
2,8
2,3
2,7
3,4
2,8
2,3
2,6
3,6
2,8
2,6
2,7
3,3
3,0
2,6
2,9
4,0
3,2
2,7
2,7
3,3
3,0
2,2
2,4
3,2
2,3
1,7
1,7
2,2
2,4
1,8
2,0
2,4
3,2
2,7
2,9
3,5
2,8
2,5
2,7
3,6
2,1
1,8
2,1
2,6
2,2
1,8
2,0
2,7
2,8
2,4
2,8
3,7
3,1
2,6
3,0
4,0
2,8
2,6
2,6
3,5
2,3
1,8
1,9
2,6
2,4
2,0
2,3
3,1
2,9
2,6
2,6
3,3
1,8
1,5
1,7
2,2
2,0
1,7
1,8
2,3
1,9
1,4
1,5
2,1
2,8
2,1
2,0
2,5
2,3
1,7
1,9
2,4
2,7
2,4
2,5
2,8
2,2
1,5
1,7
2,1
2,3
1,9
2,0
2,5
2,3
2,0
2,1
2,7
3,2
2,9
3,0
3,3
1,9
1,5
1,7
2,3
2,0
1,7
1,8
2,2
2,1
1,4
1,5
1,7
2,4
1,8
1,9
2,7
2,7
2,3
2,5
3,3
2,8
2,3
2,4
3,0
Sept
3,9
4,5
3,6
3,2
3,3
5,5
3,2
4,0
4,7
4,6
4,4
4,9
4,1
4,3
3,1
3,4
4,4
5,1
3,5
3,4
4,6
5,2
4,7
3,6
4,2
4,2
3,0
3,2
3,1
3,5
2,8
3,4
3,1
3,2
3,6
3,8
2,8
2,9
2,5
3,8
4,5
4,1
Oct
4,5
5,1
4,7
4,5
3,9
7,1
4,1
4,1
6,1
5,7
4,9
5,9
5,1
5,8
4,2
4,6
4,8
5,8
3,8
3,8
5,1
5,9
5,5
4,5
5,2
4,5
4,2
4,5
4,6
5,1
3,9
3,9
4,3
3,8
4,2
4,3
3,2
3,7
3,4
5,2
5,0
5,0
Nov
5,4
5,3
5,1
5,4
4,6
8,5
5,2
4,5
7,2
6,6
5,3
6,8
6,1
6,5
4,8
4,2
5,6
6,0
4,4
4,2
5,3
6,5
5,9
5,3
6,3
4,7
5,0
5,6
5,7
6,2
4,0
4,6
4,8
4,0
4,5
4,6
3,5
4,6
3,8
6,2
5,2
5,8
Crop water relationships and climate
Dec
5,8
5,3
5,5
6,0
5,2
9,4
5,9
4,7
7,8
7,4
5,5
7,2
6,8
6,8
5,6
5,7
6,3
6,1
4,6
4,5
5,2
6,3
6,1
4,8
6,5
4,8
5,6
6,2
6,1
6,9
4,5
5,1
5,6
4,2
4,6
5,1
3,8
5,1
4,5
6,8
5,3
6,2
4.37
LYDENBURG LONGTOM
LYDENBURG ROSENKRA
LYDENBURG;DOORNHOE
MACUVILLE - AGR
MALELANE PROEFPLA
MALELANE VERGELEGE
MALELANE;HOECHST.L
MALELANE;KAALRUG.T
MARA – AGR
MARBLE HALL:MOOSRI
MARQUARD;SAAIPLAAS
MARQUARD;WILDEBEES
MAYFIELD, STANGER
MEERLUST
MELMOTH
MERLE I
MESSINA
MESSINA PROEFPLAAS
MHLATI
MHLUME
MIDDLETON
MONTAGU
MONTAGU POLISIE
MOORREESBURG KO-OP
MOREWAG
MORGENSTOND
MORTIMER I
MOUNTAIN VINEYARDS
MT. EDGECOMBE
NATAL EST., THORNV
NCHOSA, MUDEN
NELSPRT FRIEDENHEI
NELSPRUIT
NELSPRUIT:NISSV.
NEWCASTLE
NGOME:SAPEKOE EST.
NIETVOORBIJ
NIETVOORBIJ (NIWW)
NIVV
NKWALINI
NOOITGEDACHT
NOOITGEDACHT - CER
Station
Longitude
(º)
30,62
30,62
24,88
29,9
31,55
31,5
31,63
31,57
29,57
29,42
27,35
27,33
31,15
18,75
31,24
18,93
30,03
29,92
31,53
31,8
25,83
20,07
20,13
18,68
18,93
20,02
25,67
18,95
31,03
30,4
30,37
30,98
30,58
30,97
29,56
31,45
18,87
18,87
18,85
31,53
18,85
19,33
Latitude
(º)
-25,13
-24,9
-25,68
-22,27
-25,45
-25,5
-25,63
-25,62
-23,15
-25,02
-28,68
-28,5
-29,2
-34,02
-28,35
-33,87
-22,2
-22,23
-25,47
-26,03
-32,98
-33,47
-33,8
-33,15
-33,68
-33,93
-32,38
-33,88
-29,7
-29,75
-28,97
-25,43
-25,27
-25,45
-27,45
-27,85
-33,9
-33,9
-33,92
-28,72
-34,03
-33,22
Irrigation Design Manual
Table 13 (continue)
4.38
Elevation
(m)
2118
1525
1644
522
380
369
272
390
894
1065
1510
1450
610
33
770
180
549
700
309
280
549
223
225
158
240
140
840
362
96
860
793
671
665
660
1199
1010
146
146
160
154
343
1040
MAP
(mm)
898
614
649
310
569
578
781
845
432
515
636
600
1276
609
806
688
340
319
578
778
353
312
316
421
395
301
318
1320
1017
819
666
754
805
782
917
1424
689
768
685
740
876
845
Jan
4,0
4,3
4,7
5,8
5,3
4,7
5,4
5,1
4,9
4,9
5,4
6,6
4,2
5,9
4,8
5,4
5,9
4,8
5,0
5,0
6,1
6,6
6,5
7,0
6,0
5,9
6,7
6,0
4,4
4,3
5,0
5,0
4,8
4,9
5,3
4,6
6,2
6,1
5,2
4,8
5,3
5,5
Feb
3,7
4,1
4,6
5,5
5,1
4,5
5,1
4,9
4,6
4,6
4,7
5,8
3,9
6,0
4,5
5,1
5,8
4,5
4,8
4,7
5,5
6,1
5,9
6,7
5,6
5,2
6,1
5,8
4,2
4,2
4,6
4,8
4,7
4,7
4,8
4,4
6,2
5,9
4,9
4,6
4,9
5,1
Mrch
3,2
3,4
3,9
5,0
4,5
3,9
4,4
4,2
4,1
3,9
3,8
4,8
3,4
4,3
3,8
3,9
4,9
4,2
3,9
3,9
4,4
4,7
4,6
5,2
4,0
4,2
5,0
4,6
3,6
3,6
3,8
4,2
4,0
4,0
4,2
3,9
4,5
4,5
3,6
3,9
3,9
3,9
April
2,6
2,8
3,4
3,9
3,9
3,1
3,6
3,4
3,3
3,0
2,8
3,6
2,8
3,1
3,2
2,6
4,3
3,3
3,1
3,2
3,4
3,5
3,1
3,6
3,3
3,1
3,8
3,3
2,8
3,0
3,1
3,6
3,5
3,3
3,5
3,4
3,3
3,0
2,3
3,2
2,7
2,7
Average daily ET0 (mm/day)
May
June
July
Aug
2,0
1,6
1,7
2,3
2,1
1,7
1,8
2,4
2,6
2,3
2,5
3,2
3,0
2,5
2,7
3,5
3,4
3,3
3,4
4,1
2,4
2,2
2,4
3,0
2,9
2,6
2,8
3,8
2,7
2,5
2,8
3,7
2,6
2,1
2,3
3,0
2,2
1,8
1,9
2,6
2,0
1,5
1,6
2,3
2,7
2,2
2,4
3,3
2,1
1,9
2,1
2,7
2,1
1,8
1,9
2,3
2,6
2,2
2,4
3,3
1,6
1,2
1,3
1,7
3,7
3,3
3,4
4,1
2,5
2,0
2,2
2,8
2,4
2,0
2,2
2,9
2,4
2,0
2,2
3,1
2,7
2,3
2,7
3,2
2,9
2,4
2,5
2,9
2,1
1,6
1,7
2,4
2,3
1,7
1,7
2,3
1,9
1,5
1,4
1,9
2,1
1,8
1,6
2,2
2,9
2,6
3,0
3,7
2,2
1,8
2,0
2,5
2,1
1,8
2,0
2,5
2,3
1,9
2,2
3,0
2,4
2,0
2,3
3,1
3,1
2,8
2,9
3,5
3,0
2,9
3,0
3,6
2,9
2,5
2,6
3,3
2,9
2,7
2,8
3,6
2,9
2,6
2,9
3,5
2,1
1,7
1,9
2,1
1,9
1,6
1,7
2,3
1,4
1,2
1,3
1,7
2,4
2,0
2,2
2,9
2,0
1,9
2,0
2,2
1,8
1,5
1,5
2,0
Sept
3,1
3,2
4,2
4,5
4,7
3,8
4,8
4,5
4,0
3,5
3,6
4,7
3,3
3,0
4,0
2,4
4,9
3,6
3,7
4,0
4,1
3,5
3,5
3,3
2,2
3,0
4,7
3,3
3,0
3,7
3,9
4,3
4,6
4,1
4,7
3,7
3,0
3,2
2,4
3,7
2,9
2,7
Oct
3,4
3,8
4,7
5,4
5,0
4,2
5,1
4,8
4,4
4,1
4,1
5,5
3,7
4,0
4,3
3,6
5,8
4,1
4,2
4,4
4,8
4,6
4,5
5,0
3,8
4,2
5,5
4,6
3,6
4,0
4,3
4,5
4,8
4,3
5,3
3,9
4,2
4,5
3,7
4,2
3,9
3,7
Nov
3,7
4,0
4,6
5,7
5,2
4,5
5,2
5,0
4,7
4,5
4,8
6,1
4,0
4,5
4,7
4,1
6,3
4,6
4,6
4,6
5,5
5,6
5,7
6,1
4,2
5,3
6,3
5,4
4,0
4,3
4,7
4,5
5,0
4,5
5,5
4,2
5,0
5,4
4,6
4,4
4,8
4,5
Dec
3,8
4,2
4,5
5,9
4,9
4,7
5,3
5,1
4,9
4,7
5,3
6,8
4,2
5,4
4,9
5,0
6,1
4,8
4,9
4,9
6,0
6,4
6,4
6,7
5,8
5,8
6,8
5,7
4,3
4,4
5,0
4,7
4,8
4,7
5,6
4,4
5,6
5,8
5,1
4,7
5,0
5,1
NW KOOP MADIBOGO
OKIEP
ONSEEPKANS.
OOS LONDEN - WK
OPWAG
ORANIA:BEKER LOOPOUDTSHOORN
OUTENIQUA (WRS)
PADDOCK
PATENSIE,
PHILADELPHIA POLIS
PIETERSBURG
PIETRSBRG:UNIV.V/D
PIONEER SEED, GREY
PK LE ROUXDAM;OUKR
PLAATKOP:ALWAL NRT
PLOOYSBURG;S.A.P.
PMBURG:UKULINGA RES.
POFADDER - POL
POFFADER
PONGOLA
PORT ELIZABETH
PORTERVILLE KO-OP
POSTMASBURG
POTCHEFSTROOM AGR;
POTCHEFSTROOM;NOYO
POWERS COURT
PRESTON PARK
PRETORIA:N.I.PLANT
PRIESKA
PRINSKRAAL
PROTEM
PUNDA MILIA
QUEENSTOWN
REITZ KO-OP,
RHEBOKRANT
RICHMOND:SAPEKOE E
RICHTERSVELD
RIEBEEK-WES
RIETBRON
RIETBRON - MUN
RIETRIVIER,SANDPER
Station
Table 13 (continue)
Longitude
(º)
25,2
17,52
19,28
27,83
21,95
24,6
22,12
22,42
30,22
24,83
18,58
29,27
29,67
30,62
24,68
26,88
24,23
30,4
19,38
19,23
31,58
25,36
19,02
23
27,08
27
30,63
25,93
28,33
22,45
20,12
20,08
31,01
26,87
28,43
24,63
30,15
16,9
18,87
23,07
23,15
24,62
Latitude
(º)
-26,42
-28,36
-28,78
-33,03
-28,88
-29,88
-33,35
-33,92
-30,78
-33,78
-33,67
-23,52
-23,85
-29,03
-29,93
-30,8
-29,02
-29,67
-29,13
-29,08
-27,4
-33,59
-33,02
-28,18
-26,73
-26,78
-29,97
-33,5
-25,73
-29,4
-34,63
-34,27
-22,41
-31,9
-27,8
-34,1
-29,93
-28,13
-33,35
-32,93
-32,9
-29,07
Elevation
(m)
1311
927
305
125
884
1140
335
204
503
150
76
1230
1250
1110
1143
1349
1082
775
989
994
308
58
145
1324
1345
1370
631
330
1299
933
15
259
462
1099
1615
160
1200
42
168
820
762
1140
MAP
(mm)
427
152
85
768
190
324
254
768
1151
445
467
476
456
826
364
496
377
719
93
98
671
632
522
325
602
578
1018
452
703
232
424
463
590
527
723
842
1182
58
546
222
210
362
Jan
6,3
6,5
5,6
5,0
8,5
7,6
6,1
4,1
3,9
5,5
6,0
5,0
5,4
4,6
6,0
6,2
6,1
4,6
6,1
7,0
4,9
4,6
6,1
6,8
6,0
6,1
3,7
5,9
5,6
6,9
5,2
6,0
5,7
6,0
5,9
5,3
3,8
6,8
6,7
7,3
6,4
6,8
Feb
5,7
6,1
5,3
4,7
7,4
5,9
5,6
3,9
3,6
4,9
5,6
4,8
5,2
4,2
5,3
5,7
5,2
4,4
5,2
6,3
4,6
4,1
5,7
6,2
5,4
5,6
3,5
5,4
5,2
6,4
4,8
5,5
5,1
5,4
5,4
4,9
3,9
6,4
6,4
6,4
5,5
5,9
Mrch
4,9
5,1
4,3
3,9
6,0
4,9
4,4
3,2
3,1
3,9
4,4
4,2
4,4
3,6
4,2
4,3
4,2
3,8
4,1
5,1
3,9
3,3
4,4
4,8
4,6
4,7
3,1
4,5
4,5
5,1
4,0
4,4
4,4
4,3
4,5
4,1
3,5
5,3
5,0
5,2
4,3
4,7
April
3,8
3,4
3,0
3,6
4,5
3,6
3,0
2,6
2,7
3,1
2,9
3,5
3,7
3,0
3,0
3,0
3,0
3,1
2,9
3,5
3,0
2,9
2,9
3,6
3,7
3,9
2,7
3,7
3,6
3,5
2,9
3,2
4,0
3,5
3,5
3,7
2,9
4,3
3,3
3,7
3,0
3,4
Average daily ET0 (mm/day)
May
June
July
Aug
3,0
2,5
2,8
3,8
2,4
1,9
2,1
2,7
2,0
1,5
1,6
2,3
3,3
3,0
3,2
3,3
3,3
2,6
2,9
4,1
2,6
2,0
2,3
3,4
2,3
2,1
2,1
2,6
2,3
2,1
2,1
2,3
2,3
2,0
2,2
2,8
2,4
2,1
2,3
2,7
1,7
1,2
1,3
1,8
2,9
2,6
2,7
3,3
3,0
2,6
2,8
3,7
2,3
2,0
2,3
3,1
2,0
1,6
1,8
2,5
2,1
1,8
2,0
2,8
2,1
1,6
1,8
2,5
2,6
2,3
2,5
3,0
2,0
1,5
1,7
2,4
2,5
1,9
2,2
2,9
2,3
1,9
2,1
2,8
2,3
1,9
2,0
2,5
1,8
1,4
1,5
2,0
2,8
2,3
2,6
3,5
3,0
2,6
2,9
4,0
3,2
2,7
3,0
4,1
2,2
2,0
2,2
2,7
2,9
2,6
2,8
3,2
2,9
2,4
2,7
3,6
2,5
1,9
2,2
3,0
2,0
1,6
1,6
2,1
2,3
1,9
1,9
2,3
3,3
2,9
3,1
3,9
3,0
2,7
2,9
3,7
2,8
2,3
2,5
3,4
3,2
2,8
2,9
3,1
2,5
2,6
3,0
3,5
3,0
2,1
2,4
3,1
2,0
1,6
1,6
2,3
2,6
2,3
2,6
3,2
2,0
1,6
1,7
2,5
2,5
1,9
2,1
3,0
Sept
5,2
3,7
3,4
3,5
5,3
4,3
3,2
2,8
3,1
3,5
2,7
4,1
4,8
4,0
3,6
4,3
3,7
3,6
3,4
4,1
3,5
2,9
2,9
4,5
5,5
5,5
2,9
3,9
4,8
4,2
3,0
3,1
4,6
4,6
4,7
3,4
3,9
4,1
3,2
4,3
3,4
4,3
Oct
5,9
4,7
4,5
3,8
6,7
5,4
4,3
3,3
3,1
4,2
4,1
5,2
5,5
4,3
4,6
5,1
4,6
3,9
4,5
5,1
4,1
3,5
4,2
5,6
6,1
6,1
3,2
4,6
5,3
5,2
4,0
4,2
5,6
5,0
5,3
3,9
3,5
5,3
4,7
5,3
4,7
5,2
Nov
6,5
5,9
5,2
4,3
7,8
6,7
5,3
3,8
3,6
4,8
5,2
5,4
5,4
4,7
5,5
5,7
5,6
4,4
5,4
6,3
4,4
4,1
5,2
6,5
6,5
6,2
3,5
5,1
5,5
6,5
4,7
5,1
5,7
5,6
5,6
4,4
4,0
6,1
5,8
6,4
5,7
6,3
Crop water relationships and climate
Dec
6,6
6,5
5,7
4,7
8,4
7,6
5,9
4,1
3,8
5,4
5,8
5,2
5,3
4,8
6,2
6,5
6,0
4,6
6,2
7,0
4,8
4,7
6,0
7,1
6,5
6,4
3,7
5,7
5,5
7,2
5,2
5,7
5,9
6,1
6,0
5,0
3,9
6,7
6,3
7,0
6,4
6,7
4.39
RIVERSDAL KO-OP
ROBERTSON (NIVV)
ROBERTSON PP
ROEDTAN
ROODEHEUWEL (WRS)
ROODEPLAAT - AGR
RUSTENBURG - AGR
RUSTENHOF
SCHWEIZER RENEKE
SCOTTBURG:CROCWORL
SERJEANTSRIVIER
SETTLERS:LANDBOUSK
SEVONTEIN, ELANDSK
SITRUSBEURS GVB.
SOMERSET OOS - HOS
SPEKBOOM
SPITSKOP,PRIESKA
STELLENBOSCHVLEI
STERKSTROOM
SUGAR MILL, SEZELA
SUTHERLAND
TAUNG
TENBOSCH
THABAZIMBI
THE GRANGE, UMZIMK
TONGAAT
TOT - U - DIENS
TOWOOMBA
TWEESPRUIT;
TYGERHOEK (WRS)
UGIE
UKULINGA RES STN
UMTATA
UMZIMKULU
UNDERCHURCH
UPINGTON NS.
VAALKRANTZ
VAALWATER:ELANDSKL
VAN WYKSVLEI
VELDRESERWE
VENDA:LWAMONDO
VENDA:RABALI.
Station
Longitude
(º)
21,27
19,9
19,88
29,08
22,25
28,35
27,3
18,78
25,43
30,77
19,52
28,55
30,13
25,32
25,58
25,87
22,85
23,42
26,52
30,58
20,4
24,73
31,9
27,24
29,97
31,13
19,85
28,33
27,07
19,9
28,27
30,4
28,47
30,43
27,37
21,25
26,05
28,05
21,82
19,45
30,37
30,12
Latitude
(º)
-34,08
-33,83
-33,83
-24,57
-33,63
-25,58
-25,72
-34,05
-27,18
-30,28
-34,13
-24,95
-29,75
-33,77
-32,73
-33,45
-29,6
-32,25
-31,65
-30,33
-32,23
-27,55
-25,33
-24,37
-30,25
-29,57
-33,68
-24,9
-29,2
-34,13
-31,22
-29,67
-31,35
-30,68
-32,32
-28,45
-33,37
-24,28
-30,35
-33,65
-23,05
-22,87
Irrigation Design Manual
Table 13 (continue)
4.40
Elevation
(m)
122
156
156
973
301
1164
1157
56
1280
100
366
1050
1375
110
717
259
939
970
1297
160
1456
1097
179
1028
762
72
915
1143
1585
168
1280
775
696
180
850
793
380
1215
962
275
885
1
MAP
(mm)
455
294
360
554
249
645
614
696
499
911
557
639
930
492
506
424
236
216
478
1024
229
442
607
671
800
1026
534
635
637
498
927
678
654
1143
496
158
452
614
172
271
897
371
Jan
5,3
5,9
5,3
6,2
6,2
5,8
4,9
5,7
7,0
4,3
5,8
5,2
4,4
5,5
6,1
5,9
8,4
8,9
6,4
4,2
6,2
7,0
5,1
6,3
3,8
4,3
5,5
5,1
6,1
5,8
4,6
3,5
4,7
4,0
5,4
6,9
5,2
4,8
8,4
7,0
5,0
6,4
Feb
4,9
5,3
5,1
6,0
5,8
5,4
4,6
5,6
5,7
4,1
5,4
5,0
4,1
4,9
5,5
5,4
7,0
8,2
5,4
4,2
5,7
5,9
4,7
6,0
3,8
4,2
5,0
4,9
5,2
5,4
4,1
3,8
4,1
3,8
4,9
6,0
4,7
4,5
7,4
6,3
4,7
5,9
Mrch
3,9
4,1
3,7
5,0
4,5
4,6
3,9
4,1
4,9
3,6
4,3
4,0
3,6
4,0
4,4
4,4
5,5
6,5
4,3
3,7
4,5
4,9
3,9
4,9
3,2
3,5
4,0
4,2
4,1
4,3
3,6
3,2
3,6
3,3
4,1
4,7
3,9
3,9
5,7
4,8
4,2
5,2
April
2,8
2,9
2,7
4,0
3,0
3,8
3,0
3,1
4,0
3,0
2,9
3,2
2,9
3,3
3,5
3,5
3,9
5,1
3,2
3,2
3,3
3,9
3,1
4,0
2,5
2,7
2,9
3,3
3,0
3,0
3,0
2,6
3,0
2,5
3,4
3,4
3,1
3,2
4,1
3,3
3,5
4,4
Average daily ET0 (mm/day)
May
June
July
Aug
2,1
1,8
1,8
2,3
2,1
1,8
2,0
2,5
1,7
1,8
1,6
2,2
3,1
2,6
2,9
4,0
2,0
1,6
1,7
2,4
3,1
2,6
2,9
3,8
2,4
1,9
2,0
2,7
2,1
1,7
1,7
2,1
3,0
2,3
2,6
3,8
2,6
2,3
2,4
2,9
1,9
1,5
1,5
2,0
2,4
1,9
2,2
3,0
2,3
1,9
2,1
3,0
2,6
2,3
2,4
2,9
2,9
2,5
2,9
3,5
2,7
2,3
2,6
3,0
2,8
2,1
2,3
3,5
4,1
3,6
3,8
4,4
2,4
2,1
2,3
3,1
2,8
2,4
2,6
3,1
2,5
2,0
2,0
2,6
3,0
2,6
2,8
3,8
2,4
1,9
2,1
2,8
3,3
3,0
3,2
4,1
1,7
1,3
1,5
2,0
1,9
1,5
1,6
2,2
2,2
1,8
1,9
2,3
2,6
2,2
2,5
3,2
2,2
1,6
1,8
2,8
2,1
1,6
1,7
2,2
2,4
2,0
2,1
3,1
2,3
2,3
2,0
3,0
2,2
1,8
2,3
2,7
1,9
1,6
1,7
2,1
2,9
2,7
2,8
3,6
2,3
1,8
2,0
2,9
2,6
2,4
2,6
2,9
2,5
2,2
2,4
3,2
2,8
2,1
2,4
3,4
2,3
1,9
2,0
2,5
3,1
2,8
2,7
3,5
3,5
3,0
3,2
4,2
Sept
3,1
3,5
2,6
5,5
3,4
5,0
3,7
3,0
5,3
2,9
2,8
4,2
3,6
3,7
4,2
3,9
4,9
5,8
4,1
3,5
3,3
5,1
3,7
5,2
2,7
2,8
3,0
4,3
4,0
3,2
3,8
3,6
3,4
2,7
4,4
4,0
3,6
4,3
4,6
3,5
4,5
5,5
Oct
4,0
4,3
3,5
6,4
4,5
5,7
4,3
4,0
5,9
3,4
3,9
4,7
3,9
4,3
4,6
4,5
6,1
6,6
4,7
3,9
4,3
5,9
4,3
6,3
3,2
3,5
3,9
5,0
4,8
4,2
4,1
3,6
4,0
3,2
4,6
5,1
4,1
4,9
6,2
4,7
4,9
6,2
Nov
4,7
5,3
4,5
6,5
5,5
5,9
4,7
4,4
6,7
3,8
4,9
5,1
4,2
4,9
5,3
5,1
7,5
7,7
5,6
4,2
5,4
7,0
4,6
6,6
3,6
3,9
4,7
5,2
5,6
5,1
4,3
3,8
4,5
3,7
5,1
6,3
4,7
5,1
7,5
5,9
5,1
6,4
Dec
5,2
5,8
4,7
6,4
6,0
5,9
4,9
5,3
7,1
4,0
5,5
5,1
4,4
5,4
6,0
5,9
8,3
8,8
6,4
4,2
6,1
7,4
5,0
6,7
3,8
4,3
5,3
5,3
6,2
5,7
5,0
0,0
4,5
4,0
5,4
6,9
5,2
4,9
8,2
6,7
5,0
6,2
VENDA:SIGONDE.
VENDA:TSHIOMBO
VENTERSDORP:STERKS
VEREENIGING;RUSOORD.
VERGELEGENDRUIF
VERGELEGENVRUG
VILJOENSKROON;RIET
VILJOENSLAAGTE:KOP
VILLIERS KO-OP.
VILLIERSDORP
VREDE EN LUST
VREDENBURG KO-OP
VRYBURG;ARMOEDSVLAKT
VRYBURG;VERGELEGEN
WALKERS HOEK,LADYS
WATERFALL,UTRECHT
WELGEVALLEN II
WELKOM;SANDVET.
WELTEVREDE
WELVERDIEND AN.
WEPENER
WEPENER
WESSELSBRON;CORNEL
WESTON COLLEGE, MO
WHYTE BANK,ADELAID
WILLOWMORE.
WINTERBERG LS.
WISTARIA
WITRIVIER;MALEKUTU
WITTEKLIP
ZEBEDIELA
ZEERUST
Station
Table 13 (continue)
Longitude
(º)
30,77
30,5
26,72
28,32
18,92
18,9
26,92
27,45
28,62
19,3
18,95
18
24,63
24,2
29,67
30,25
18,85
26,68
20,62
26,72
27,03
27,02
26,45
30,03
26,23
23,5
26,63
25,05
31,2
21,83
29,27
26,05
Latitude
(º)
-22,42
-22,8
-26,47
-26,83
-34,1
-34,08
-27,17
-27,23
-27,03
-33,98
-33,85
-32,9
-26,95
-25,78
-28,47
-27,8
-33,93
-28,13
-33,93
-30,72
-29,73
-29,44
-27,7
-29,22
-32,42
-33,28
-32,78
-33,68
-25,2
-34,2
-24,3
-25,33
Elevation
(m)
405
650
1375
1450
260
80
1321
1401
1493
366
160
128
1234
1065
1200
1180
116
1295
405
1348
1438
1440
1325
1390
950
840
456
348
676
150
1250
1207
MAP
(mm)
363
824
564
562
790
740
596
621
638
697
881
326
437
372
785
704
698
519
362
582
615
626
521
800
599
267
445
514
756
449
577
590
Jan
4,8
5,2
6,1
5,2
5,2
5,3
5,5
6,2
5,1
6,0
6,4
5,8
6,6
6,1
4,6
5,2
5,6
5,1
5,4
7,9
5,4
6,3
6,5
4,1
5,6
6,9
6,5
5,0
4,8
5,0
4,5
5,7
Feb
4,7
4,9
5,5
4,9
5,1
5,1
4,9
5,7
4,7
5,5
5,9
5,6
5,4
5,3
4,2
4,8
5,3
4,6
5,0
6,1
4,4
5,4
5,7
4,0
5,2
6,1
6,0
4,5
4,7
4,5
4,9
5,3
Mrch
4,0
4,3
4,7
4,1
3,7
3,8
4,1
4,7
4,0
4,4
4,9
4,7
4,6
4,6
3,5
4,0
4,1
3,7
3,8
5,0
3,7
4,0
4,6
3,3
4,4
4,8
4,8
3,5
3,9
3,7
4,4
4,4
April
3,3
3,6
3,8
3,2
2,6
2,6
3,2
3,8
3,1
3,1
3,6
3,7
3,6
4,2
2,6
3,2
2,8
2,8
2,5
3,5
2,7
3,2
3,5
2,7
3,8
3,4
4,1
2,7
3,4
3,0
3,8
3,7
Average daily ET0 (mm/day)
May
June
July
Aug
2,5
2,1
2,2
2,8
2,9
2,7
2,8
3,5
3,0
2,6
2,9
4,0
2,4
1,9
2,1
3,0
1,8
1,4
1,3
2,2
1,7
1,6
1,6
2,1
2,3
1,9
2,1
3,0
2,8
2,3
2,6
3,7
2,3
1,9
2,1
2,9
2,3
2,0
2,3
2,5
2,3
1,6
1,8
2,1
2,7
2,2
2,2
2,6
2,5
2,0
2,2
3,2
2,7
2,2
2,5
3,6
2,0
1,6
1,8
2,5
2,6
2,3
2,6
3,5
1,9
1,6
1,6
2,1
1,9
1,4
1,6
2,2
1,7
1,2
1,3
1,9
2,6
1,9
2,3
3,3
1,9
1,5
1,7
2,4
2,5
2,2
2,4
3,4
2,6
2,0
2,3
3,5
2,1
1,8
2,0
2,6
3,4
3,4
3,6
3,9
2,4
2,1
2,2
3,0
3,4
2,9
3,2
3,8
2,0
1,8
2,0
2,3
2,6
2,4
2,4
3,3
2,5
2,1
2,2
2,5
3,1
2,7
2,9
3,4
3,1
3,0
3,1
4,0
Sept
3,7
4,6
5,4
4,5
2,7
2,7
4,3
5,0
4,0
3,4
3,3
3,5
4,6
4,6
3,3
4,4
2,9
3,2
2,8
4,6
3,3
4,2
4,7
3,4
4,5
3,9
4,6
3,0
4,3
3,1
4,9
5,2
Oct
4,2
4,9
6,2
5,1
3,6
3,5
5,3
5,8
4,6
4,3
4,6
4,6
5,5
5,4
3,8
4,8
4,3
4,0
3,8
5,7
4,3
5,2
5,7
3,8
4,7
4,9
4,9
3,6
4,8
3,8
5,4
6,0
Nov
4,6
5,2
6,6
5,6
3,7
4,0
5,7
6,1
5,0
5,2
5,0
5,3
6,3
6,1
4,3
5,1
5,0
4,7
4,8
6,8
5,0
5,8
6,3
3,9
5,2
6,1
5,6
4,4
4,9
4,4
5,3
6,2
Crop water relationships and climate
Dec
4,9
5,3
6,6
5,4
4,7
5,0
6,1
6,4
5,3
5,8
5,6
5,7
6,6
5,9
4,6
5,4
5,3
5,1
5,3
7,8
5,5
6,2
6,7
4,1
5,4
6,7
6,4
4,8
4,8
4,9
4,9
6,1
4.41
4.42
Irrigation Design Manual
5 References
1.
Crosby, C. T. 1996. SAPWAT 1.0 – A computer program for estimating irrigation requirements in
Southern Africa. WRC Report No. 379/1/96.
2.
Doorenbos, J. and Kassam, A.H. 1979. FAO. Irrigation and Drainage Paper 33. Yield response to
water. Rome.
3.
Doorenbos, J. and Pruitt, W.O. 1977. FAO. Irrigation and Drainage Paper 24. Guidelines for
predicting crop water requirements. Rome.
4.
Du Preez, M. 1990. Besproeiing van Vrugtebome: Wat weet ons? S.A. Irrigation vol. 12 no 5.
5.
Soil and Irrigation Research Institute. 1985. Beraamde Besproeiingsbehoeftes van Gewasse in SuidAfrika.
6.
Piaget, J. and Lategan, M.T. 1986. Inleiding tot Besproeiing Deel I. Stellenbosch.
7.
Scheepers, I.,
Piaget, J., Kotze, W.A.G. and Myburgh, P.A. 1991. Riglyne vir
Besproeiingskedulering van Permanente Gewasse in die Winterreëngebied. Elsenburg Agricultural
Development Institute.
8.
Smith, M. 1992. FAO. Irrigation and Drainage. Paper 46. Cropwat a computer program for
irrigation and management. Rome.