Drag line irrigation: Practical experiences with sugar cane

Agricultural Water Management, 17 (1990) 25-35

25

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

DRAG LINE IRRIGATION: PRACTICALEXPERIENCES WITH SUGARCANE H. ZADRAZIL Head office: Lonrho PIc, 138 Cheapside House, London EC 2V 6BL U.K. Correspondence and home address: Neuriesgasse 18, A-2484 Weigelsdorf (Austria)

ABSTRACT Zadrazil,H.,1990.Draglineirrigation:practicalexperienceswBh sugarcane.Agric. WeterManoge.,17:25-35. Drag l i n e i r r i g a t i o n i s d e f i n e d a s an o v e r h e a d s p r i n k l e r system, where sprinklers a r e c o n n e c t e d by means o f p o r t a b l e h o s e s and p e r m a n e n t or semi-permanent pipes to a pressurized water supply. The system h a s been d e r i v e d from t h e c o n v e n t i o n a l s p r i n k l e r system o f p o r t a b l e p i p e s in o r d e r t o reduce labour requirement for its operation. T h i s h a s been a c h i e v e d w i t h a modest i n c r e a s e o f c a p i t a l c o s t s , well below t h e c o m p a r a t i v e c o s t s o f o t h e r k i n d s o f more a u t o m a t i c i r r i g a t i o n s y s t e m s . P a r t i c u l a r r e f e r e n c e i s made t o S w a z i l a n d , S o u t h A f r i c a and Kwa-Zulu, where d r a g l i n e i r r i g a t i o n for sugar c a n e h a s been i n o p e r a t i o n f o r many y e a r s . According to climatic conditions, a p p l i c a t i o n r a t e s have been d e s i g n e d f o r v a l u e s between 0 . 5 and 1.0 1 / s / h a . Alternative lay-outs are described with varying lengths of hoses, for p e r m a n e n t PVC l a t e r a l s o r s e m i - p e r m a n e n t p o r t a b l e p i p e s and t e c h n i c a l d e t a i l s are discussed. Drag l i n e i r r i g a t i o n can be well a d a p t e d f o r t h e i r r i g a t i o n o f l a r g e a r e a s o f b i g e s t a t e s o r f o r s m a l l h o l d e r i r r i g a t i o n w i t h p l o t s i z e s a s s m a l l as 1 ha and l e s s . I t can be s u c c e s s f u l l y integrated with a conservation contour l a y - o u t a s r e q u i r e d in h i l l y a r e a s f o r e r o s i o n c o n t r o l . Labour r e q u i r e m e n t s f o r t h e o p e r a t i o n , s u i t a b l y e x p r e s s e d in m3 i r r i g a t e d p e r man-day a r e i n d i c a t e d and compared t o l a b o u r r e q u i r e m e n t s f o r some o t h e r irrigation systems. Details of a particularly practical design for the a p p l i c a t i o n o f 60 mm i r r i g a t i o n w i t h a s p r i n k l e r s p a c i n g o f 18 x 18 m and 2 s p r i n k l e r moves in 24 h o u r s a r e p r e s e n t e d . R e f e r e n c e i s made t o power demand and a d v a n t a g e s t o be g a i n e d by s u b - d i v i d i n g t h e scheme in 2 o r more p r e s s u r e z o n e s in h i l l y a r e a s a r e p o i n t e d o u t .

INTRODUCTION Ever s i n c e t h e e a r l y days o f c o n v e n t i o n a l s p r i n k l e r

irrigation

systems,

it

has been recognised that the many advantages of this system are opposed by the need of high labour demand for the moving of irrigation pipes. remedy

this

problem

have resulted

in designs

with

smaller

Attempts to

size

laterals,

longer standing times, the hop-along system and eventually higher degrees of automation

such as center

eliminated completely.

and

linear pivots,

where

pipe moves

have been

This development has resulted in higher capital costs

for the equipment and the need of better qualified

labour.

Both of these

requirements are, however, not always readily available, particularly in many developing countries. half

way

solution:

0378-3774/90/$03.50

The drag line irrigation system can be described as a by

placing

lateral

lines

at

greater

© 1990 Elsevier Science Publishers B.V.

intervals

and

26

H. ZADRAZIL

connecting

sprinklers

by means of hose pipes,

the need

for pipe moves have

been eliminated completely and only sprinklers and hoses have to be moved.

At

the same time, the additional

capital requirement

as compared to conventional

sprinkler

moderate.

this

systems

successfully

irrigation

is

only

Today

system

is

in many countries and some examples are presented

in Swaziland,

operating

for sugar cane

Kwa-Zulu and South Africa.

DESCRIPTION AND DISCUSSION i)

The

principle

of

drag

line

irrigation.

Figure

lay-out consisting of a main llne with hydrants deeding

i

shows

a

typical

into laterals.

These

can be buried PVC pipes with flushing valves at the end, or light weight steel

or aluminium pipes placed on the soil surface and only removed

for harvest.

Laterals are equipped with valves for the connection of the drag line hose. long life time - up to i0 years - can be achieved material yarn

for the hose,

reinforcing

foldable

e.g. PVC inner

in between.

tripods.

Hoses

Frequently,

liner,

the correct

outer cover with polyester and

are connected

20 mm hoses

by selecting

A

are

to sprinklers

mounted

in use with varying

on

lengths

according to the spacing of laterals. 2)

Examples

of sprinkler

different

groups

depending

if priority

supervision,

within

or

the

presented

combinations.

given

system

Sprinklers as

can

demonstrated

is given to the cost of equipment, walking

system of 21 sprinklers combinations

a

distance

for

irrigation

be in

arranged Figures

in 2-5,

or the facility of

labour.

Comparing

a

at 0.56 i/s and a spacing of 18.3 m for the various in Figures

2-5, pipe sizes and corresponding

friction

head losses would be as follows: a)

3)

the full line system : 89 ms pipe at 5.9 m loss

b)

the half line system : 76 mm pipe at 6.4 m loss

c)

the all lines system : 70 mm pipe at 2.5 m loss

d)

the interspaced system : 76 mm pipe at 4.3 m loss

Direction of cane rows.

relation

to the drag

The lay-out of the sugar cane plantation

line system can be oriented

in the following

ways

in (see

also Figure 6): -

the drag

line operates

line is eliminated -

the drag

in the direction

one cane

(no cane planted) for every sprinkler path

line operates

at right angles to the cane rows:

wide path is provided for sprinkler moves. planting

of the cane rows:

with a small

rotary

tiller

a two meter

This path can be constructed after

or similar

equipment

by destroying

the

cane stools along this line -

two

the cane meter

wide

lines follow a contour path

for

the

drag

lay-out as required

lines

disregarding the direction of cane lines.

is opened

with

in hilly areas: a a

rotary

tiller,

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29

DRAG LINE IRRIGATION

36x

--

~

~

Fig. 5.

~

~

~

ZO,3 = 7 3 0 , 6 m

~

~

to

~

Sprinkler combinations - interspaced

--

H. ZADRAZIL

3O Fig.

6.

Direction

of cane

rows

"t3 e-,

.o

~ u

o

Lateral

A

Cane rows in s a m e d i r e c t i o n

as

cane

-----', ~

~

row

Lat eral

o l

1

I Cane

drag l i n e

rows

at

1

right

angles

to drag l i n e

c

,L,a t e r a l

cane

Cane

rows

following

contour

lay

out

row

DRAG LINE IRRIGATION

4)

31

Irrigation of small

cane farms.

Small

holder

irrigation has been

successfully implemented in the Umvoty valley in Kwa-Zulu (Fig. 7): sprinklers travel

first across and then down the lateral,

until they have covered 24

positions and are then returned to the starting position.

A system of 18 x

18 m spacing with a sprinkler output of 0.448 I/s results in an application rate of 5.0 mm/h.

On soils with good storage capacity, 60 mm irrigation can

be applied in 12 days with a standing time of 12 hours (2 sprinkler moves per day).

On shallow or sandy soils, 40 mm can be applied in 8 days with an 8

hour standing time (3 sprinkler moves per day).

Ideally, farm sizes should be

7776

area

m2 or

multiples,

corresponding

to

the

covered

per

sprinkler.

However, where farmers have been reluctant to adjust their boundaries to fit the regular block system, it has been observed that cane growers soon learned to overcome the problem by sharing sprinklers along common boundaries and still follow the principles of the lay-out. 5)

Labour

requirements

for

sprinkler

moves.

The

objective

of

the

irrigation scheme is the even distribution of a certain volume of water over a given area and therefore, labour efficiency to carry out this distribution can conveniently be expressed in volume of water distributed per unit of labour. Obviously, the bigger the volume of water distributed in one irrigation cycle, the less labour is required.

In many soil types, an application of 50 to

75 mm per cycle can be achieved.

Shallow or sandy soils have significantly

less storage capacity so that more labour is required for the distribution of the same amount of water. The

following examples of a drag

influence of various

systems on

line

irrigation

lay-out should demonstrate the labour.

They are based on a

spacing of 18.3 x 20.3 m, a field width of 21 sprinklers equal to 384.3 m and a field length of 72 positlons equal to 1461.3 m, resulting in an area of 56.17 ha.

Sprinkler output

is 2.0 m31h and the precipitation rate is 5.4

mm/h. With 3 sprinkler positions per lateral, 24 laterals will be required to be placed in distance of 60.9 m and drag llne hoses wlll be 20.3 m long. Walking distances for the move of 84 sprinklers have been calculated for the systems referred to earlier in Figures 2-5 and are given in Table i.

TABLE 1 Walking distances - 24 laterals System

Short move

Long move

Full cycle

Mean

full line half lines all lines interspace

5.8 6.0 6.4 7.3

12.3 12.1 11.3 13.4

143.5 144.5 144.4 168.0

8.0 8.0 8.0 9.3

km km km km

km km km km

km km km km

km km km km

32

H. ZADRAZIL Fig.

7.

Small

grower

system

Flushing valve

J F i

O

O

O

O

O

O

O

O

0

0

0

1

O

O

0

Hose

O

-0'

--

-0

O

.

.

.

.

Far m

O

0----

--

-0

O

O

0

O

O

O

O

O

O

0

0

0

1 Farm

~ 0

I

0

13

0

_.J

H~se

023 0

0

O

0

0

14

o

----0----

022 0

0

15

O

--

21

O--

- - - - 0

020

16

O

0

17

O

19

18 1 Far m

~ o12

18 x 18 x 24 = 011

Hose

010

o9

08

4

03

---O

S

. . . .

O--

7776

07

m2

6 --

--O

Valve Main l i n e

Tee

i

Scale 4

100meter t---

#

i

i

i

I

DRAG LINE IRRIGATION

Short

moves

33

can

be carried

required for long moves, the next.

out by i

labour unit,

whilst

2 units are

when the drag line hose changes from one lateral to

One full cycle requires 12 short moves and 6 long moves,

total labour demand will be 12 +(2 x 6)= 24 units. of water distributed,

so that

In relation to the volume

labour performance are given in Table 2.

TABLE 2 Labour efficiency related to soil type Storage capacity of soil low average high

Irrigation applied

Cycle time

Water appl. per cycle

mm

days

m3

6 x 5.4 = 32 8 x 5.4 = 43 12 x 5.4 = 64

4.5 6 9

18144 24192 36288

Labour units required

m3 water per unit of labour

24 24 24

756 1008 1512

Depending on the storage capacity of the soil, various irrigation regimes can be selected, A

applying the same amount of water overall.

considerable

positions

are

parameters.

saving

connected

Only 12

in to

laterals 1

can

lateral,

be

achieved,

without

when

modifying

any

laterals will be required at distances

121.8 m and drag line hoses will be 50.75 m long.

6

sprinkler irrigation

of 6 x 20.3 =

Walking distances for the

sprinkler move will increase only insignificantly as demonstrated in Table 3.

TABLE 3 Walking distances - 12 laterals System

Short move

Long move

Full cycle

Mean

full line half lines all lines interspace

5.8 6.3 6.8 7.3

22.0 km 22.0 km 21.4 km 14.5/15.4

153.3 161.2 166.7 177.2

8.5 9.0 9.3 9.8

km km km km

km km km km

km km km km

Short moves can be carried out by 1 labour unit, whilst long moves require 3 units for the full line, half line and all lines system and 2 units for the interspaced system,

so that 24 units will be required again for a full cycle

and relative labour output is equal to the 24 lateral system. These

figures

can

be

supported

with

practical

results

from

Swaziland,

where irrigation of soils with low and average storage capacity is carried out with a labour input between 700 and ii00 m3 per man-day. for other schemes:

types

of

irrigation

Sprinkler irrigation,

indicate

the good

conventional system:

Mkwasine, Zimbabwe - 275 m3/man-day Mafambisse, Mozambique - 330 m3/man-day

Comparative results

performance

of drag

line

34

H. ZADRAZIL

Sprinkler irrigation, hop-along system:

Sucoma, Malawi - 535 m3/man-day Surface irrigation, syphon system: Mkwaslne, Zimbabwe - 775 m3/man-day Dwangwa, Malawi - 732 m3/man-day Surface irrigation,

low spill system:

Ubombo Ranches, Swaziland - 530 m3/man-day Sprinkler irrigation, drag line system: Ubombo Ranches, Swaziland - 855 m3/man-day 6)

Power demand.

Power is required for the operation of an irrigation

scheme in accordance with the volume of water to be pumped (design capacity), the required pressure head and the efficiency of the pumping unit.

Whilst

design capacity is a function of given climatic conditions, mainly rainfall and evaporation, the components of pressure requirements can be influenced by various design criteria: static head is defined as the difference between the water level at the point of supply and the highest sprinkler nozzle in the field.

Savings can be

achieved by eliminating certain high areas from irrigation altogether and by subdividing

the

scheme

into

different

pressure

zones

according

to

the

topography of the land, sometimes at the expense of additional main lines; -

friction head is required to overcome pressure losses in suction lines,

main lines, hydrants,

laterals, drag line hoses and riser pipes.

Savings can

be achieved by the design of adequate sizes for pipes and hoses. field.

nozzle pressure is required for the distribution of water over the Various types of irrigation differ greatly in their requirements of

nozzle pressure: conventional sprinkler irrigation, hop-along, drag line-

300-350 kPa

large scale sprinklers-

400-800 kPa

travelling guns, at nozzle - 400-600 kPa at inlet center pivot-

150-300 kPa

drip irrigationThe

influence

- 600-900 kPa

50-200 kPa of

the

various

components

on

total

power

demand

is

highlighted in Table 4 on two examples of drag line schemes actually installed in Kwa-Zulu and Swaziland.

DRAG LINE IRRIGATION

35

TABLE 4 Power demand for 2 drag line schemes Kwa-Zulu s t a t i c head f r i c t i o n head nozzle pressure

79 m 61% 15 m 12k 35 m 27k

Swaziland 25 m 12 m 35 m

35% 16k 49%

total pressure head

129 m lOOk

72 m

lOOk

design capacity

0.576 I/s,ha

0.85 I/s,ha

power demand for 75k pump efficiency

0.99 kW/ha

0.82 kW/ha

Power requirements between 0.8 and 1.0 kW/ha are considered economically Justified for both schemes, when compared to dry land cane production. CONCLUSION Drag line Irrigation schemes have found wide acceptance, particularly in developing countries, as a step from conventional

sprinkler systems towards

higher degrees of mechanisation, with the following main features: -

-

-

-

elimination of movement of pipes employment of low skilled labour energy requirement similar to conventional system adaptable

equally to large estates and small plots, flat lands and

hilly areas. ACKNOWLEDGEMENTS Thanks Swaziland,

are

due

to the

management

of

Lonrho

Sugar

Corporation

Ubombo Ranches Ltd., Swaziland and Glendale Sugar Millers

Ltd., South Africa, for the use of lnformation presented in this paper.

Ltd., (Pty)