沙漠研究 19-1, 295- 298 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

Meteorological and Soil Characteristics in the Central Ethiopia
Shinji SUZUKI1, Masku DERESSA2, Fumio WATANABE1, Kiyoshi SHIRATORI3, Iwao MATSUMOTO3,Berhanu S. JABESSA2, Satoru TAKAHASHI1
Abstract: Crop production systems in the Central Ethiopia are mostly under rainfed condition.
Although the mean amount of annual rainfall is still much for crop growth (400 to 800 mm),the crop production systems often suffer from severe drought stress resulting in unstable foodsecurity. This is in part due to erratic and fluctuated rainfall distribution patterns in the region.
However, it is required to investigate soil infiltration characteristics, soil water holding capacity,and meteorological condition other than precipitation (ex. evaporation) in order to know how
much rainfall can be utilized for crop growth. In the current study, changes in soil watercontent associated with irrigation or subsequent rainfall were monitored in both dry and rainyseason in an experimental field established in the Central Ethiopia. Meteorologicalobservation system was also established. In the dry season, the applied water did not reachdown to 25 cm due to poor permeability associated with dry soil condition. In contrast, initialirrigation and subsequent rainfall increased soil water content and infiltrated into the depths in
the rainy season. Even in the rainy season, evaporation affected on moistening of deeper soil
depths associated with infiltration and redistribution. The meteorological observation
revealed that intense solar radiation, high temperature, low relative humidity, and constant windspeed would accelerate evaporation from soil surface.
Keywords: Central Ethiopia, Infiltration, Micro meteorology, Soil water dynamics

1. Introduction
Crop production systems in the Central Ethiopia are mostly under rainfed condition. Although themean amount of annual rainfall is still much for crop growth (400 to 800 mm), the crop production systems
often suffer from severe drought stress resulting in unstable food security. This is in part due to erratic
and fluctuated rainfall distribution patterns in the region. However, it is necessary to investigate soil
infiltration characteristics, soil water holding capacity, and meteorological condition other thanprecipitation (ex. evaporation) in order to know how much rainfall can be utilized for crop growth. In thecurrent study, characteristics of changes in soil water content associated with the infiltration and themeteorological condition is reported.
2. Materials and Methods
The experimental site is located in Adami-tulu Agricultural Research Center, Oromia region of thecentral Ethiopia (7˚52’N, 38˚43’E, 1649 m alt.). Rainy season is during June to September, and dry
season is other months. Soil texture of the experimental field was Loamy Sand.
In an upland cropping field, a single pair of 1 m × 1 m monitoring plot was prepared. In each plot,changes in soil water content were recorded at a depth of 5, 15, 25, and 35 cm using ECH2O and Em50
(type EC5, Decagon Devices, Inc., Pullman, WA, USA). In Dec. 2007 (dry season), 45 mm of water was
initially applied to the plots by a hand sprinkler, thereafter one plot was exposed to the atmosphere(thereafter termed as ‘bare condition’) and the other was covered by a plastic sheet (thereafter ‘coveredcondition’). In June 2008 (rainy season), similar observation was undertaken, namely; 30 mm of water
was applied to both plot, thereafter one plot was monitored under bare condition and the other was covered
for initial 3 weeks, then the plastic sheet was removed (initially covered condition). Temperature, relative
humidity, wind speed, solar radiation, and precipitation have been recorded since Feb. 2008 by HOBO
Weather station (Onset Computer Co., Bourne, MA, USA).

1

Tokyo University of Agriculture, 1-1-1, Sakuragaoka, Setagaya, Tokyo, 156-8502, Japan.
E-mail: s4suzuki@nodai.ac.jp
2Adami Tulu Agricultural Research Center, P. O. Box 35, East Shewa Zone, Ziway, Ethiopia.
3Japan International Cooperation Agency, P. O. Box 436, Adama, Ethiopia.

296

35

Max
Min

252015Air temperature (℃)

Air temperature (℃)

30

10530
252028-Feb

1528-Aug

100:00 4:00 8:00 12:00 16:00 20:00
Time0FebMar

AprMayJunJul

AugSepFig. 1. Temperature change in 2008.

30

20
15
1051200

Solar radiation (W m-2)

Solar radiation (MJ/m2)

25

1000
800
600
40028-Feb
28-Aug

200
00:00

4:00

8:000FebMar

Apr

12:00
Time

16:00

May

20:00

JunJulAug

Sep

Fig. 2. Solar radiation in 2008.
90

70

50

100

Relative humidity (%)

Relative humidity (%)

3. Results and Discussion
The air temperature observed
was characterized by large diurnal
range in the dry season and small
diurnal range in the rainy season withthe mean daily air temperature
ranging from 17 to 25 ˚C (Fig. 1).
That is to say, the daily maximum airtemperature in the dry season
exceeded > 30 ˚C and decreased inthe rainy season (20 to 25 ˚C). Thedaily minimum air temperature in thedry season reaches down to 10 ˚C,while the temperature in the rainyseason is relatively constant (15 ˚C).
The solar radiation in the dry season
was considerably high (>25 MJ m-2)
(Fig. 2).
In contrast, the solar
radiation decreases in the rainyseason. This is because the sun
shine is interrupted by clouds in therainy season (Fig. 2). Concomitantwith this, the daily mean relative
humidity was < 50% in the dry
season and increased up to 80% in
the rainy season (Fig. 3). The
relative humidity was decreased indaytime and increased in nighttime(Fig. 3).
The wind speed wasmoderate and constant (Fig. 4).
The wind speed in dry season was
relatively higher than that in rainy

3080604028-Feb
28-Aug

20
00:00

4:00

8:00

12:00
Time

16:00

20:00

10Feb

Mar

AprMayJunJul

Fig. 3. Relative humidity in 2008.

AugSep297

Wind speed (m s-1)

528-Feb
28-Aug

4
32
1
00:00

12:00
16:00
20:00
TimeFig. 4. Comparison of wind speed between dry (Feb.) andrainy (Aug.) seasons in 2008.

Volumetric water content (m3 m-3)

0.4

4:00

8:00

45 mm irrigated.

a. Bare condition
5 cm
15 cm

0.3

25 cm
35 cm
0.2

0.1

022
December

0.4

Volumetric water content (m3 m-3)

season (Fig. 4).
The result of the infiltration
experiment undertaken in the dry
season is presented in Figure 5.
In case of the experiment in the dry
season, the soil profile wasconsiderably dry with soil watercontent at 5 cm of depth being <0.05 m3 m-3. For both bare andcovered condition, the irrigation
caused a steep rise of the soil watercontent at depth of 5 cm, and thesoil water content at depth of 15 cm
gradually increased (Fig. 5).
However, the applied water did notreach down to 25 cm. The result
indicates
poor
infiltration
characteristics of the soil associatedwith dry initial condition. Since thesoil water content at depth of 5 cm
became constant for coveredcondition, dominant reason ofdecreases in the soil water content
at depth of 5 cm observed for thebare condition is suggested to beevaporation.
The result of the infiltration
observation undertaken in the rainyseason is presented in Figure 6.
In this case, the initial soil watercontent of the soil profile was >0.15 m3 m-3. Initial irrigation andsubsequent rainfall increased soil
water content and infiltrated into
the depths. For the bare condition,soil water content increased over awhole profile but did not exceed
0.40 m3 m-3. In contrast, the soil
water contents at depths of 15, 25,
and 35 cm were relatively constantranging from 0.37 to 0.42 m3 m-3
after the plastic sheet was removed,
while the soil water content at depthof 5 cm was lower than that ofdeeper depths by more than 0.10 m3m-3. A reason of the difference insoil water profiles between the bareand initially covered conditions issuggested to be as follows; for the
initially covered condition, applied
water was redistributed in the soil
profile resulting in decreases in the

24

26

2830

1
January3545 mm irrigated.

b. Covered condition
5 cm
15 cm

0.3

25 cm
35 cm
0.20.1022December

24

26

28

30

1
January

35Fig. 5. Comparison of changes in soil water content associated withirrigation between bare (a) and covered (b) conditionsobserved in dry season from 2007 to 2008.

298

Rainfall (mm)010203040

Volumetric water content (m3 m-3)

500.530 mm irrigated.

a. Bare condition

0.4

0.35 cm
15 cm
25 cm
35 cm

0.2

0.1
13June19251July7131925

316August121824

soil water content at the shallower
depth (i.e. 5 cm) and increases atdeeper depths under a condition
without evaporation (Hillel, 2000).
Therefore, the soil water content atdeeperdepthsremainedhighrepeating increases and decreases by
the evaporation and rainfall, evenafter the plastic sheet was removed.
For bare condition, the water
infiltrated into the soil profiles wasimmediately extracted by theevaporation before increasing soil
water content in deeper depths
sufficiently.

30
September

4. Conclusions
The infiltration experiment
30 mm irrigated.
showedcontrast results between dryb. Initially covered condition
and wet seasons. The results of theSurface was coveredby a plastic sheet.
0.4
current study suggest that low soil
permeability of upland cropping
fields of the Central Ethiopia
0.3
associated with low soil water content
results in the difficulty of rainwater to5 cm
0.2
wet the soil profile at the onset of the15 cm
25 cm
rainy season.
Comparison of35 cm
changes in soil water contents
0.1
1319251713192531
612182430
between the bared and covered
June
July
SeptemberAugustconditions, particularly observation inFig. 6. Comparison of changes in soil water content
the rainy season indicates that theassociated with irrigation and subsequentevaporation affects on redistribution
rainfall between bare (a) and initially covered (b)of water in the soil profile before
conditions observed in rainy season of 2008.
moistening deeper depths sufficiently.
Intense solar radiation, high temperature, low relative humidity and constant wind speed would accelerate
evaporation from soil surface. Concomitant with this, the results also suggest a potential of mulching toretain water in the soils.
Volumetric water content (m3 m-3)

0.5

Acknowledgement
Authors are grateful to Mr. K. Nakamura of Japan Overseas Cooperative Volunteer, Mr. Y. Kobayashi
of Tokyo University of Agriculture (TUA), Mr. T. Ishibashi (TUA), and Dr. A. Sanada (TUA) for theirhelpful support to the research.
ReferenceHillel D. (2000): Redistribution of water in soil. In Environmental Soil Physics, Academic Press, San Diego, 449-470.