This document describes the design, development, and testing of a manually operated multi-row weeder for System of Rice Intensification (SRI) fields in Sri Lanka. The weeder was modified three times to improve performance. The final three-row design had the highest field capacity of 0.034 hectares/hour compared to other manual weeders, though weed destruction was still slightly lower. It was effective at controlling weeds with less labor than other methods while keeping damaged plants low at 3.1-3.5%. The total cost of the final three-row weeder was 5,000 LKR.

1. Design, Development and Performance
evaluation of a manually operated multi
row weeder for SRI rice in Sri Lanka
P.D. Kahandage and G.A.S. Ginigaddara
Faculty of Agriculture,
Rajarata University of Sri Lanka,
Puliyankulama,
Anuradhapuraand

2. Introduction
• Rice is the staple food for nearly a half of the
world’s population
• Rice production is to be increased by another 50 %
to fulfill the demand which will arise by 2025.
• Increasing the productivity of existing lands
• Improving the crop
may give a satisfactory approach to increase the
production

3. •System of Rice Intensification (SRI) is a
technology which was revamped recently for
increasing the productivity of irrigated rice while
reducing the burden on environment.
•Weed growth in wider gaps between and within
rows of paddy has been recognized as one of the
major obstacles faced by rice farmers.

4. Barriers for increasing the farmer adoption of the
SRI
•Labour consuming activities like,
marking the rows before transplanting
transplanting
Weeding (highly affect to the yield)
•Mechanization of weeding in SRI fields might be a
good solution for the labour consuming nature of
weeding in SRI.

5. •Presently,
single row cono-weeder
double row cono-weeder
separate markers - manually operated
manually operated
•Yet there is no a two-in-one machine developed
for the marking and the weeding in SRI fields.
•The ability of using the same machine for several
purposes with slight adjustments is convenient and
economical investment for the SRI farmers.

6. •Most of the SRI farmers in Sri Lanka are
holding small sized lands and involving the family
labour in farming.
•In order to suit for these conditions, a dual
purpose machine was designed, developed and
tested in SRI fields.

7. Methodology
Designing the weeder

8. •The most salient features of this design are,
 arrangement of wheels
 the frame with adjustable ground clearance
(to reduce damages to the plants)
adjustable operating handle to provide a
(convenient operation)
easily detachable marker.
•In this design, five weeding wheels are arranged
in such a way that paddy plants do not get crashed
in between two weeding wheels.
•The operator has to push and pull the device

9. •After completing one set of rows, operator has
to lift the device with the frame and move into
another set of rows.
•Here, the convenient directions for force
applying have been considered.

10. •The first trail of the prototype was carried out in
the experimental paddy field of Rajarata University.
•eight plots with 50 m2 area
•two rice seedlings in one hole with 20 cm x 20 cm
spacing.

11. •Before testing the machine in the field,
 conditions of field and soil
 type and characters of soil (soil moisture on
dry basis, depth of standing water, bulk
density (g/cm3), cone index, cone apex
angle and base diameter)
 conditions of weeds (types, weed number,
average height of each weed type,
number of leaves)
 conditions of operator (age, height, weight,
skills and wage per head)

12. Nursery
Manual marking Manual transplanting

13. •First, second, and the third weeding were made
between 8 -10, 18-20, 28-30 days after date
of transplanting.
•At each and every weeding of the plots,
 weeding efficiency
 damaged plant percentage
 actual and theoretical field capacities
 suitable traveling speed of the machines
during operation was measured.

14. Following equations were used
Weeding Efficiency
WE = (N1-N2)/N1 x 100
N1 is the number of weeds before weeding
N2 is the number of weeds after weeding
(Remesan et al., 2007)
Damaged Plant Percentage
DP = (Pt/Pd) x 100
Pt is the number of total plants in 1m2
Pd is the number of damage plants in 1m2.

15. Effective Field capacity
CE- hah-1 = (s.w)/10
s - the traveling speed (kmh-1)
w - is the width of work (m)
(Hunt, 1995):
Field efficiency
FE-% = (Te/Tt) x 100
Te - the useful working time (h)
Tt - the total working time (h)
(Hunt, 1995):
Work capacity
WC- hha-1 =WC = 1/ CE
(Hunt, 1995):

16. Results
Device characteristics
Total length of the device =125 cm
Total width of the device =100 cm
Total height of the device =147 cm
Maximum height between frame and ground =45 cm
Minimum height between frame and ground =24 cm
Total weight =30 kg
Calculations:
Theoretical Field Capacity = 0.0064 ha/h
Actual Field Capacity = 0.0048 ha/h
Field Efficiency = 75%
Weed Destroying Percentage = 87%
Damaged paddy plant percentage = 21%

17. •After the first trail, numbers of practical
problems were recognized,
 higher weight which created problems in handling
 lower field capacities
 high damaged plant percentages
•It was also realized that, length of the
machine, 125 cm makes difficulties for the
operator to control the machine in the rice
rows and it increases the damaged plants
percentage.
•Similarly higher weight of the machine has
caused to reduce the field capacity.

18. Modifications -01
•The machine was modified in order to reduce the
weight and obtained the optimum dimensions
•In this new design, the size of the frame was
reduced and marker attachment was removed.
FLOATER

19. •The performance of the new design was evaluated
as previous design and followings are the results.
Calculations:
Theoretical Field Capacity = 0.038 ha/h
Actual Field Capacity = 0.025 ha/h (12 mins for
50 m2)
Field Efficiency = 65.78%
Weed Destroying Percentage = 90 %
Damaged paddy plant percentage = 16%

20. •Although it achieved a satisfactory field capacity,
the damaged paddy plant percentage was still the
same.
•Reducing the dimensions and changing the shape
had reduced the weight to 14.5 kg.
•After this trial it was realized that, controlling
the five weeding wheels simultaneously is still
difficult in Sri Lankan field conditions due to
poor land preparation, marking and
transplanting.

21. Modifications -02
•To address the problems encountered in the fist
modifications, it was decided to reduce the number
of weeding wheels up to three and reconstruct the
machine

22. •The performances of this three- row weeder
were evaluated compared to the single row cono-weeeder,
double row cono-weeder and manual
weeding.

23. Weeding with
single row cono
weeder
Weeding with double
row cono weeder
Weeding with
three
row weeder

24. Results
Device characteristics
Total length of the device = 105 cm
Total width of the device = 70 cm
Total height of the device = 90 cm
Maximum height between frame and ground =40 cm
Minimum height between frame and ground =28 cm
Total weight = 12.5 kg

25. Table 01: Comparison of weeders for the efficiency
Weeding
Weeds
method
destroying
%
Damaged
paddy
plant %
Work
capacity,
hr/ha
Actual
Field
capacity
(ha/hr)
Field
efficiency, %
Single row
cono- weeder
94.55 1.531 65.5 0.0153 76.72
Double row
cono- weeder
91.82 3.053 38.5 0.026 65.07
Three row
weeder
86 4.02 29.4 0.034 76.62
Manual
weeding
98.06 1.042 130 0.0077

26. Modifications -03
•Although, the three row weeder has been
modified up to a satisfactory level, it was realized
that the weed destroying percentage should be
further developed.
•Because other manually operated weeders have
achieved higher weed destroying percentages
than three row weeder

27. •Therefore, the handle was modified and three
floaters were attached in front of each
weeding wheel to improve the weeding
percentage
•The total weight of the weeder was reduced up
to 10.1 kg.
•After these modifications, the performance of
the weeder was evaluated with male operators
and female operators separately.

32. Results
Device characteristics
Total length of the device = 55 cm
Total width of the device = 60 cm
Total height of the device = 90 cm
Height between frame and ground = 25 cm
Total weight = 10.1 kg

33. Table 02: Performances of the three row weeder against sex
Male Female
Theoretical field capacity 0.043 ha/hr 0.043 ha/hr
Actual Field Capacity 0.034 ha/hr (9 mins
for 50 m2)
0.028 ha/hr (11 mins for
50 m2)
Field Efficiency 76.5% 65.1 %
Weed Destroying
89 % 91%
Percentage
Damaged paddy plant
percentage
3.5% 3.1%

34. Conclusions
•The final version of the multi row weeder (Three row
weeder) has shown the highest field capacity (0.034
ha/hr) amongst manually operated other weeders which are
mostly been used in Sri Lanka.
•The weed destroying percentage of three row weeder is
still lower (Table 01) than other manually operated
weeders.
•Although the damaged paddy plant percentage of three
row weeder is bit higher in three row weeder than other
manually operated weeders, it can be used effectively to
control weeds in SRI fields with less labour usage.

35. Acknowledgement
• This is one of the outcome of the on going
collaborative research program between
Oxfam in Sri Lanka and Rajarata University in
Sri Lanka
• Financial assistance and other numerous
assistances for developing and testing the
machine was given by Oxfam –Australia in Sri
Lanka is greatly acknowledged

37. Cost
• Cost for first five row weeder= 12,000.00LKR
• Cost for last three row weeder = 5,000.00 LKR