沙漠研究 22-1, 211 -214 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－

Trial on Supplemental Irrigation Technology during Rainy Season
in Semi-Arid Area of Ethiopia
Tetsuji OYA*1), Kozo INADA2), Yoshitoshi TSUTSUI2), Girma LEMMA3), Birhanu KEBEBEW4),
Shinji SUZUKI5) and Satoru TAKAHASHI5)
Abstract: To stabilize and increase crop yield in semi-arid area, where rainfall is insufficient and unreliable even during rainy season,
supplemental irrigation is essential. A verification experiment was carried out in the field located in Zway, Oromia Region, Ethiopia
to examine the effect of supplemental irrigation on yield of cabbage and tomato. Application of irrigation was decided based oneither effective rainfall (5 mm/day) or soil moisture content (25% at 20 cm depth, volume %). Two levels of water amount (5.6, 11.2mm/day) were applied as supplemental irrigation. The effects of Furrow and Watering Can irrigation were also compared.
Cabbage yield was increased by supplemental irrigation, however, no substantial increase was observed in tomato yield. Two levelsof water amount for irrigation gave no consistent effect on yield of cabbage and tomato. Decision of irrigation application based on
soil moisture content was more effective compared to effective rainfall when water was applied to the cabbage plots with the amountof 5.6 mm/day. Irrigation efficiency in terms of crop yield was relatively higher with Furrow irrigation compared to Watering Can
irrigation. This result was consistent with our previous one during dry season that showed Watering Can and drip irrigation were lesseffective compared to basin and Furrow irrigation if irrigation was not applied frequently. Together with the improvement in water
harvesting technologies, such as spate irrigation and farming pond, supplemental irrigation will become a more important technology
in semi-arid agriculture.
Key Words: Crop yield, Irrigation efficiency, Soil moisture, Supplemental irrigation, Water use efficiency

1. Introduction
Ethiopia has great agricultural potential based on its vast
areas of fertile land, diverse climate, generally adequate rainfall,and large labor pool. Despite this potential, however,Ethiopian agriculture has remained underdeveloped. The
agricultural sector suffers from frequent drought and poor
cultivation practices. Some of the very precious rainfall in thedry lands is wasted through evaporation and runoff.
Insufficient and unreliable rainfall, drought, and low
diversification of crops have resulted in natural resources
degradation, low production, and low water use efficiency.
Improving water use efficiency through the implementation ofappropriate technologies may lead to poverty mitigation
through the increased crop productivity. Although this can beachieved through different agronomic practices, irrigation
development has a great and decisive role to play.
Based on this background, after conducting several
development studies, Japan International Cooperation Agency(JICA) conducted “The project for irrigation farming

improvement” for three years from September 2005 toSeptember 2008. Its objective was that water utilization
technology is improved by the farmers in the project target area,
which will make small holder farmers to increase theirproduction using the available moisture in those areas.
To maximize crop yield, irrigation will be applied
according to crop water requirement shown by FAO (1998).
A verification experiment was carried out during dry season in
the field located in Zway, Oromia Region to examine suitable
irrigation type and optimum irrigation amount that can beeasily applicable by farmers (Inada et al., 2009). However,even during rainy season, rainfall is not sufficient in this area
for crop optimum growth. Therefore, supplemental irrigation
should be applied to fulfill crop water requirement.
Necessity of irrigation application can be judged byavailable water such as rainfall pattern and soil moisture
content, or crop state such as wilting and stomatal behavior.
To examine when and what amount irrigation should apply, averification experiment was carried out during rainy season inthe same field as the previous dry season experiment.

* Corresponding Author: oyatet@affrc.go.jp
1-1 Ohwashi, Tsukuba, Ibaraki, 305-8686, JAPAN
1) Japan International Research Center for Agricultural Sciences (JIRCAS), Tsukuba, Japan4) Oromia Water Resources Bureau, Addis Ababa, Ethiopia

2) Japan International Cooperation Agency (JICA), Addis Ababa, Ethiopia

5) Tokyo University of Agriculture, Setagaya, Tokyo, Japan3) Oromia Rural and Agricultural Development Bureau, Addis Ababa, Ethiopia

2. Materials and Methods
Experiment was carried out during rainy season in Zway
(N08o01’, E38o43’, 1622 masl.).
Cabbage (Variety:Copenhagen) and tomato (Variety: RomaVF) seedlings weretransplanted to the experimental field (Farmer Training Center
demonstration field) on 9 and 10 August 2008. Plot size was
3 m × 3 m, and planting density was 40 cm × 60 cm forcabbage and 40 cm × 75 cm for tomato.
Soil type was sandy loam. Ten and twenty g/m2 ofdiammonium phosphate was applied to cabbage and tomato,respectively, on the day of transplanting. Twenty g/m2 of urea
was applied on the day of the initiation of irrigation treatment.
Weeding was made manually as needed. Fungicide andinsecticide were applied once during vegetative stage.
Daily rainfall was recorded manually with a rain gauge
installed by the experimental field.
Soil moisture content at 10, 20, 30 cm depth, 10 cm apartfrom the plant grown center of the plot was measured with soil
moisture sensor (Profile probe, PR2/4, Delta-T) during 7 to 9a.m. every day before irrigation.
The timing to apply irrigation was decided based on thefollowing conditions. 1) Rain-based irrigation treatment:
Irrigation was applied every day except the following day ofeffective rainfall (more than 5 mm/day). 2) Moisture-based
irrigation treatment: Irrigation was applied when soil moisture
content at 10cm depth was below 25% (volume). Two levelsof water amount were applied (50 liter/plot/day and 100
liter/plot/day, equal to 5.6 and 11.2 mm/day, respectively)
To compare the effects of irrigation type on crop growthand yield, irrigation was applied as furrow and watering can.
Water was applied to a furrow plot from the bottom of a barrel
through a hose. Irrigated water was not so clear with somesilt and its pH was around 8.
For yield analysis of cabbage, five average plants wereharvested from mid area of each plot on November 9 todetermine mean fresh weight. For tomato, the whole
products during harvesting period (from 9 to 29 November)were taken from each plot for yield analysis.
There were three replication plots, however, due to thelimitation in number of the tubes, soil moisture was measured
without replications.

3. Results and Discussion
Rainfall pattern during experiment is shown in Figure 1.
Days with effective rainfall were observed constantly but withcertain intervals until 50 days after transplanting (DAT, lateSeptember). After this period, there was a dry spell for one
month until 80 DAT (late October). After that, considerable

Fig. 1. Pattern of rainfall during experimental period.

Transplanting

date was 10 August 2008.
Table 1. Number of days with irrigation during experimental period.
Cabbage

Treatment
Control
R50
R100
M50
M100Tomato

Furrow

Watering Can

Furrow

Watering Can

065654822065653127071713614071713913

Table 2. Cabbage yield (kg Fresh Weight/head).
Treatment

Furrow

Watering Can

Control
R50
R100
M50
M100

1.28±0.39
1.46±0.25
1.72±0.14
2.00±0.31
1.10±0.47

1.08±0.36
1.57±0.20
1.21±0.21
1.57±0.33
1.47±0.10

Data are shown as means of three replications±SE.

amount of rainfall was concentrated in a short period until
harvest (90 DAT for cabbage, 110 DAT for tomato).
According to the decision based on rainfall pattern and soil
moisture content, number of days with irrigation varied bytreatment (Table 1). Rain-based irrigation with 100 liter(R100) treatment received the largest irrigation amount during
the experimental period, followed by Rain-based irrigation
with 50 liter (R50) treatment, Moisture-based irrigation with 50liter (M50) treatment, and Moisture-based irrigation with 100
liter (M100), in this order.
Cabbage yield tended to increase with supplemental
irrigation in both cases applied by furrow and watering can(Table 2). Furrow irrigation showed slightly higher yieldcompared with Watering Can irrigation, which suggests thatwater use efficiency or irrigation efficiency in terms of crop
yield is higher with Furrow irrigation compared to Watering
can irrigation. Similar result had been obtained in ourprevious experiment carried out during dry season (Inada et al.,2009). It was considered that R50 treatment would havebrought the highest yield, because our previous results
recommended 5 mm/day of irrigation was optimum for yieldof cabbage (Inada et al., 2009). However, the highest yieldWatering CanControl
R50
R100M50
M1000.92±0.13
1.08±0.04
0.94±0.10
0.98±0.14
1.07±0.19

0.90±0.22
0.76±0.14
0.74±0.12
0.80±0.11
0.90±0.30

Data are shown as means of three replications±SE.

was shown by M50 treatment with smaller amount of
supplemental irrigation compared with R50 treatment, whichsuggests the possibility of water saving with monitoring of soil
moisture. Yield in M100 treatment with Furrow irrigation
was relatively low probably because it received smallest
amount of water by irrigation.
Different from cabbage, no substantial yield increase wasobserved with supplemental irrigation in tomato (Table 3).
Similar to cabbage, Furrow irrigation showed slightly higher
yield compared with Watering Can irrigation.
Soil moisture content at 10 cm depth with cabbage wasmore affected by rainfall and irrigation than those at 20 cm andat 30 cm depths (Figs. 2 and 3). That in control plot at 10 cm
depth reflected rainfall pattern, showing a considerable decline
during dry spell period and a subsequent increase with rainfall
after the period (Figs. 1, 2 and 3). Decision for irrigation
application based on the soil moisture content at 10 cm depth
was effective to maintain soil moisture content higher in M50
and M100 treatment plots compared to control plot, although
M100 treatment plot received irrigation with longer interval
and less frequency than M50 plots as is shown in Table 1.
R50 and R100 irrigation treatments made soil moisture content
higher than M50 and M100 treatments at 10cm depth. It is
presumably because of larger amount of water applied more
frequently to those treatments (Table 1).
In our previous experiment during dry season, soil
moisture contents at 20cm and 30cm depths also declined as
crop grew (Inada et al., 2009), however, those in thisexperiment were maintained almost constant. This differenceby season may suggest that optimum irrigation amount during
rainy season should be smaller than that during dry season
when atmosphere is extremely dry without any rainfall. This
fact may explain why R50 treatment that received 5.6 mm/day
water constantly during the experimental period did not show
the highest yield in cabbage (Table 2).
Trend of soil moisture content with tomato was similar tothat with cabbage (data not shown for tomato). However, soil
moisture content at 20cm depth with tomato showed a decline
during dry spell period, which was not observed with cabbage
in this experiment. Maynard (1997) reported that effective
rooting depth is deeper in tomato than in cabbage. This may

60

10 cm
50
Soil moisture content (volume %)Furrow

40

30

20

1000

102030

40

50

60

7080

60

70

80

6070

80

Days after transplanting (d)

60

20 cm
50
Soil moisture content (volume %)Treatment

be one of the possible reasons why tomato did not respond tosupplemental irrigation.

40302010001020304050

Days after transplanting (d)7030 cm
60
Soil moisture content (volume %)Table 3. Tomato fruits yield (kg Fresh Weight/m2).

5040302010001020304050

Days after transplanting (d)Fig. 2. Change in soil moisture content in Furrow irrigation plot
during experimental period. ◇:Control, □:R50, △:R100,×:M50,＊:M100.

This experiment was conducted in the final year of theproject, that is, only in one rainy season. Further repeatedexperiments may be necessary to confirm the obtained results.

4510 cm

40

Soil moisture content (volume %)354. Conclusion

30
2520
1510500102030

4050607080

Days after transplanting (d)5020 cm

45

Soil moisture content (volume %)

40
35
30
2520References

15
10
500

1020

30

40

50

60

70

80

60

70

80

Days after transplanting (d)

80

30 cm
70

Soil moisture content (volume %)It is considered that supplemental irrigation is effective toincrease cabbage yield during rainy season. Decision madefor irrigation by soil moisture content will be more effective
and efficient than by rainfall pattern, which will be more watersaving technology in semi-arid area of Ethiopia. Simple
index for farmers that shows critical soil moisture content
should be developed. Therefore, a trial should be done
further on farmers’ field with their management as a process ofextension like Yusuf and Muluken (2008) to make them more
confident of its practical applicability.
Without water source, supplemental irrigation will not beapplicable. Water harvesting pond that collects runoff fromroads or other water ways may be a good source. Besides it,
spate irrigation system that utilizes unused floods to irrigate
fields will be also a good source in Ethiopia (Geleta et al., 2009,Negussie et al., 2009).

605040302010001020304050

Days after transplanting (d)Fig. 3. Change in soil moisture content in Watering Can irrigation plot
during experimental period. ◇:Control, □:R50, △:R100,×:M50,＊:M100.

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