1. Adaptation and improvement of the
seed-plot technique in smallholder
potato production
Presentation by
Z.M. Kinyua
Plant Pathologist & National Coordinator
Crop Health Programme
Kenya Agricultural Research Institute
kinyuazm@gmail.com
+254 (0)733 999444
Presentation during the 9th Triennial African Potato Association Conference
The Great Rift Valley Lodge, Naivasha, Kenya
30 June-4 July 2013

2. Common sources of seed potato
Farmers commonly obtain seed potato for planting from:
• own previous crop harvests
• ‘neighbours’
• market places
• Distant potato-producing areas (high altitude zones)
Other sources (Kenya)
• KARI (e.g. Tigoni station & its sub-centres)
• Agricultural Development Corporation -Molo
• Individual private companies (e.g. Kisima Farm, Midlands Ltd)
• Farmer groups/CBOs producing clean seed potato
• Individual farmers with reputable seed potato
> 95%
< 5%

3. Different inputs, different expectations
Poor quality seed
Good quality seed

4. Bacterial wilt - a consequence of planting
infected seed tubers
A devastated potato field
A healthy, promising
potato crop

5. The principle
Improving seed potato quality through a
seed-plot technique

6. Site selection for seed-plot establishment
Might be contaminated, especially if low-lying!
Probable sites (bush
land, other crops,
homestead, etc.)

7. Schematic presentation of seed-plot practice
Seed plot
Seed plot
Seed plot
Seed plot Main field
Main field
Main field
Market or
home
consumption
Market or
home
consumption
Market or
home
consumption
Season 1
Season 2
Season 3
Season 4
(Initial multiplication)

8. 1. Adaptation of potato seedplot technique
10 seed-plot trial sites in Kenya, managed by farmer groups:
• Kianthumbi - 3 seed plots
• Mutethia Mbuyene - 3 seed plots
• Kibaranyaki - 3 seed plots
• Muchicha - 3 seed plots
Done during the 2010 long rains season (April-July)
Repeated during the 2010 short rains (October-December)
5 seed plots hosted by farmer groups for three seasons (2010-2011)in Uganda:
• Rushebeya
• Kayanga
• Kyambura
• Burema
• Mpangango
Productivity assessed by determining tuber yields (number & weight per unit
area)
Methodology

9. Active participation of a farmer group in
establishment of a potato seed plot
Establishing a potato seed plot
• A well-dug bed
(loosened soil)
• Narrow bed marked
(1.8m width) to avoid
stepping in when
working.
• Fertilizer applied
(DAP - 18: 46: 0) and
raked in.
• Furrows made and
tubers placed at a
spacing of 30cm by
30cm.
Methodology (cont’d)

10. Established potato seed plots

11. 2. Effect of fertilizer application in potato seed plots
General information
Cultivar used: Asante
Trial location: Abo West Division, Meru Central District, Kenya.
Seedplot size: 2.4m by 1.8m
Spacing: 30x30cm
thus accommodating 8 rows of 6 tubers (48 plants) per plot.
Two fertilizer types:
diammonium phosphate, DAP (18: 46: 0)
Mavuno Planting (10: 26: 10)
Three fertilizer rates:
no fertilizer application (0kg N/ha),
DAP low level (45kg N/ha)
DAP high level (90kg N/ha)
Methodology (cont’d)

12. CountryTrial site (Group name or
host farmer)
%
Small
tubers
%
Medium
tubers
%
Large
tubers
Tubers/
m2
Multipl
ication
ratio
Yield
(t/ha)
Kenya Muchicha (Munyugi P) 5.99 54.43 39.58 49.4 4.5 41.7
Kenya Muchicha (Bundi H) 7.16 61.30 31.54 48.5 4.4 32.1
Kenya Kianthumbi (Kimathi S) 10.33 70.41 12.37 54.4 4.9 28.4
Kenya Kianthumbi (Kaimenyi E) 5.27 71.14 23.60 62.7 5.6 40.7
Kenya Kianthumbi (Kinoti R) 5.51 60.64 33.84 44.5 4.0 45.1
Kenya Mutethia Mbuyene (Wambui) 6.84 56.16 36.94 65.9 5.9 69.8
Kenya M Mbuyene (Mbijiwe T) 7.45 54.02 33.69 41.5 3.7 44.6
Kenya M Mbuyene (Kinya M) 5.85 67.02 26.61 60.4 5.4 40.7
Kenya Kibaranyaki (Murithi I) 8.96 66.92 24.12 28.6 2.6 21.6
Kenya Kibaranyaki (Agwima S) 8.52 67.41 27.58 39.7 3.6 30.9
Uganda Kyambura 20.16 75.22 4.63 54.7 4.9 45.1
Uganda Kayanga 26.45 66.19 7.36 69.6 6.3 74.1
Uganda Rushebeya 20.35 73.74 5.91 40.0 3.6 21.6
Uganda Burema 29.49 61.22 9.29 63.6 5.7 66.4
Uganda Mpangango 49.35 45.86 4.79 47.2 4.3 15.1
Results
Seed-plot potato yields in various sites in Kenya and Uganda

13. • Productivity of seed plots: 28.6 to 69.6 tubers/m2
• Mean multiplication ratio: up to 6 tubers per plant.
• Yield in most of the sites was above 40 tonnes/ha.
indicating that the technique was easily adaptable
in many areas
• Sites that had low yields also had poor tuber
multiplication ratios.
Results (cont’d)

14. Fertilizer
regime
Number of tubers by
size
Total
tubers
Total
tuber
yield
(kg)
Average
weight
per
tuber (g)
Tuber
multipli
cation
rate
Small Medium Large
Zero 32.25a 102.50a 12.50a 147.25a 3.80a 25.82a 4.09a
DAP-Low 23.25a 163.25b 33.75ab 220.25b 10.16b 46.12b 6.12b
DAP-High 31.50a 162.00b 43.00b 236.50b 12.04b 50.93b 6.57b
Mavuno-
Low
29.75a 155.75b 30.75ab 216.25b 10.35b 47.85b 6.01b
Mavuno-
High
26.75a 133.50ab 49.25b 209.50b 11.14b 53.19b 5.82b
Note: The parameters are taken from plots measuring 1.8 x 2.4m (4.32m2)
Tuber productivity in seed plots with different fertilizer
application regimes
Results (cont’d)

15. 0
10
20
30
40
50
60
70
80
Small Medium Large
Seed size categories
Proportionoftotaltubers(%) Zero
DAP-Low
DAP-High
Mavuno-Low
Mavuno-High
Potato tuber sizes under different fertilizer application regimes
Results (cont’d)

16. • Seed-size (medium) tubers
low DAP & low Mavuno more than DAP-high and Mavuno
Planting-high
• Ware-size (large) tubers:
high DAP and high Mavuno Planting more than DAP-low and
Mavuno Planting-low
No. of tubers and corresponding total tuber yield
in plots without fertilizer was significantly lower
than fertilized plots.
The fertilized plots did not differ significantly
across all the treatments
Results (cont’d)

17. Conclusion
The seed-plot technology, with improved productivity
through fertilizer application, can increase the availability
of quality seed potato.
Recommendation
The seed-plot technology should be widely promoted,
especially in smallholder farming systems where frequent
replenishment of seed stocks is hampered by financial
inadequacies.

18. Discussions/clarifications

19. Seed plot
measurements
Estimated amount of seed to
plant in a seed plot
Size of ware potato field
to be covered with seed
from a seed plot
Width
(m)
Length
(m)
Number of
tubers
Weight (kg) Acres Hectares
1.8
1.8
1.8
1.8
1.8
1.8
1.8
4.5
9
21
32
43
64
86
90
180
420
640
860
1280
1720
6-7
12-15
28-35
43-53
58-71
86-106
115-143
0.1
0.2
0.5
0.75
1
1.5
2
0.04
0.08
0.20
0.30
0.40
0.61
0.81
Approximate seedplot sizes to produce adequate seed
tubers for ware fields

20. Thank you
• ASARECA
• KARI and other host institutions
• Participating farmer groups
• Organizers, 9th Triennial APA Conference
• Sponsors, 9th Triennial APA Conference
• The Session Participants
Z.M. Kinyua