Soil erosion from catchment and plot scales under coffee tree
based crop in humid tropical climate of Lampung, Indonesia
Afandi1 , Didin WIHARSO1 , Ananto AJI1 , Masateru SENGE2 and Kengo ITO2

Abstract: Problems have been widely encountered whentrying to scale erosion results from plot to catchment level.
Due to the complex hydrological response in catchment,
the soil erosion from plot level does not always correlatewith erosion measured at the catchment scale. An experiment was conducted to measure the soil erosion at both
plot and catchment levels under coffee tree based crop in
Lampung, Indonesia. Runoff and sediment were measured
at the catchment of 10.2 ha, while seven erosion plots of
75 m2 were constructed inside the catchment. The erosion
plots were designed as follows; (a) bare soil (control), (b)natural weeds (NW), (c) clean weeded coffee, (d) coffeewith Paspalumcon jugatum (PC) in spot weeding, (e) coffee with PC in strip along the contour line, (f) coffee with
NW in spot weeding, and (g) coffee with NW in strips.
After one and a half years measurement, the rate of soil
loss ranged from 0.12 t ha−1 (natural weed plot) to 0.87 t
ha−1 (bare soil plot). On the other hand, the sediment yieldfrom the catchment was 6.7 t ha−1 for 8-months measurement during the rainy season. These experiments indicate
that, the sediment yield from the catchment level is morethan ten times that of soil loss from plot scale. This is supposed, to be responsible for the gully erosion, collapse andsoil erosion from paddy field which occurred in the catchment. This result showed that the soil conservation strategy
which is now mainly focused on only cropped areas must
be revised, and the other sources of sediment yield must be
taken care of to curtail downstream soil erosion.
Key Words : catchment, coffee, Indonesia, sediment yield,
soil erosion

1. Introduction
In Indonesia, erosion research is mainly carried out at
the plot scale level and the result is used to recommend soil
conservation program at wider levels such as catchmentlevel. As a matter of concern, the on site soil erosion is of
no problem, however the problem will arise when soil erosion on plot level is scaling up to that of catchment level.
The soil erosion in catchment scale could be lower or
1 Faculty of Agriculture,Ṫhe University of Lampung, Jl. Prof. Dr. Sumantri

Brojonegoro No. 1, Lampung, 35145, Indonesia.
2 Faculty of Applied Biological Science, Gifu University, 1-1 Yanagido,
Gifu 501-1193, Japan. Corresponding author: 千家正照, 岐阜大学応用生
物科学部
2010 年 2 月 26 日受稿 2010 年 6 月 11 日受理
土壌の物理性 115 号, 15–23 (2010)

higher than soil erosion in plot scale. For example, Afandi
et al. (2002) and Dariah et al. (2004) reported that at plotlevel, the average soil loss from clean-weeded coffee at
Sumber Jaya, Lampung, Indonesia, was very small. However, in catchment scale, the Ministry of Forestry and Estate (1999) determined that the Tulangbawang watershed,in which Sumber Jaya is included, was marginal catchment
due to high sedimentation, and in 2009, it was categorized
as poor catchment (Ministry of Forestry, Republic of Indonesia, 2009a). As such, the measurement of soil erosion in both scales has become important in integrating thestrategy of soil and water conservation.
Many case studies have reported both positive and negative non-linear relationship between basin area and sediment yield. Braud et al. (2001) showed the difficulty in relating runoff volume and sediment yield to simple descriptors of the catchment such as the average slope and/or the
average vegetation cover. Ceballos and Schnabel (1998)
emphasized that the valley bottom played an important rolein sediment yield, as also shown by Steegen et al. (2001).
Using 137 Cs tracing technique, Li et al. (2009) also foundthat paddy field and caotu (a kind of cultivated land locatedat the foot of hills) were depositional areas.
Land use change from forest to the other agricultural
purposes is often seen as the main factor to increase insoil erosion and sediment yield. However, there has notbeen any significant change in discharge of the main riverat the catchment (Sihite, 2001) although it is reported that,
there has been a sharp change of land use at Sumber Jaya
areas, Lampung, Indonesia, where in 1970 the forest area
occupied 58 % of that area, which was reduced to 21 %in 1990 (Syam et al., 1997), and 12 % in 2000 (Verbist etal., 2005), while the coffee areas increase 10 fold from 7% of the total land area in 1970 to 70 % in 2000 (Verbist
et al., 2005). Afandi et al. (2002) and Dariah et al. (2004)
also reported that the average soil loss from clean-weeded
coffee was also very small. However, Rijsdijk et al.(2007a,
2007b) reported that the sediment yield from rural roads,
trails, settlements, gullies, riparian mass wasting and bankerosion, in Kali Konto catchment, Indonesia, contributed asignificant proportion of the total soil erosion.

16

第 115 号

土壌の物理性(2010)

Table 1 Soil morphology and physical properties in the study area.

∗

Soil depth (cm)Horizon

Soil structure∗

0– 6
6 – 2828 – 72
72 –104
104 –153

A
AB
Bw1
Bw2
Bw3

sab
sab
ab
ab
ab

Soil texture∗∗ (g g−1 )
sand
silt
clay
0.160
0.272
0.568
0.127
0.292
0.581
0.119
0.308
0.573
0.296
0.234
0.470
0.376
0.264
0.360

Roots

Crack
crack
crack
crack
crack
-

f-many, md-common, c-few
f-many, md-common, c-few
f-common, md-few
f-few
f-few

Soil structure: ab (angular blocky), sab (sub angular blocky); Roots: f (fine root), md (moderate root), c (coarse root) .

∗∗ Soil texture is classified by USDA method.

Table 2 Land use type and soil texture (0–20 cm depth) in the catchment.
No.
1
2
3
4
5
6
7

Area
(ha)

Area
(%)

4.55
1.13
0.75
1.40
0.11
0.10
2.15
10.19

44.6
11.1
7.4
13.7
1.1
1.0
21.1
100

Land use
Coffee with tree crops
Coffe in monoculture
Coffee with various cash crop
Coffee with vegetable crop
Chilli
Rice field
Shrub
Total

Soil texture∗ (g g−1 )
sand
silt
clay
0.232
0.127
0.641
0.152
0.114
0.734
0.266
0.121
0.613
0.180
0.210
0.610
0.198
0.157
0.645
0.167
0.197
0.636
0.160
0.090
0.750
–
–
–

∗ Soil texture is classified by USDA method.

Due to the fact that understanding the erosion and deposition rates in a catchment is important for designingsoil and water conservation measures, two simultaneous
researches which emphasizes on the measurement of soil
erosion at plot and catchment scales were conducted ontree coffee based crop. The research is aimed to measure
and compare soil erosion from both scales as the basic dataof integrated recommendation of the soil and water conservation at that region.

2. Materials and methods
2.1 Study site and soils
The soil erosion experiment was conducted in the rainyseasons of 2000/2001 and 2001/2002, while sedimentyield observation was conducted in the rainy season of
2001/2002. The research sites are located at Bodong Jaya
sub village, Sukajaya village, Sumber Jaya sub district,
West Lampung regency, Sumatra Island, Indonesia. The
geographic position is approximately situated around 105◦
26’ E and 05◦ 02’ S. According to the Soil Taxonomy
Classification (Soil Survey Staff, 1998), the soil is Vertic
Dystrudepts. This soil is dominated by clay fraction in all
depths, has high exchangeable Al (0.86 – 7.86 cmol kg−1 ),medium organic carbon (0.72 – 3.31%), acid to very acid(pH 3.9 – 4.5), high porosity (0.57 – 0.68 m3 m−3 ), andlow bulk density (0.88 – 1.09 g cm−3 ). Some selected soil
properties from representative profile are presented in Table 1.

As shown in Table 1, the fine roots still could be foundin the soil layer until 153 cm-depth. The soil texture isdominated by clay fraction, and as a consequent, cracks
were found from the topsoil until the B-horizon. The thin
A-horizon indicated that soil erosion has taken place andpart of the topsoil was carried away.
2.2 Rainfall
The amount of rainfall was observed manually and automatically. The “pulse counter type” which recorded every
rainfall event (one pulse: 0.5 mm), was used and manualombrometer was also used for recording rainfall manually.
2.3 Catchment experiment2.3.1 Catchment description
The catchment area is 10.2 ha. The areas were dominated by steep slopes, with average gradient of about 48%. Based on altimeter measurement, the highest altitude incatchment was 934 m above sea level (asl) and the lowest
was 862 m asl at the outlet of the catchment. The stream
length was 263 m, and flows between the paddy field areaand hillside, so one side of the catchment occupied by upland areas flowed directly into the creek, and the other side
flowed from paddy field areas. The land use was dominated by coffee tree with various type of management andthe main land use type is shown in Table 2 and the distribution of land use is shown in Fig. 1. The soil fraction of
the catchment from 0 to 20 cm depth in every land use typewas also dominated by clay fraction. The clay fraction ismore than 60 %.

論文：Soil erosion from catchment and plot scales under coffee tree based crop in Lampung, Indonesia

17

No. Landuse
1

Coffee with tree crops

2

Coffee in monoculture

3

Coffee with various cash crop4

Coffee with vegetable crop

5

Chilli6

Rice field

7

Shrub

Fig. 1 Land use of experimental catchment.

2.3.2 Streamflow measurement
Parshall-flume (Fig. 2) was set up at the outlet of thecatchment to monitor the streamflow leaving the catchment. The changing of water depth in Parshall flume
was monitored using an automatic water level recorder(AWLR), which was installed near the Parshall flume; thechart of the AWLR was changed daily. Based on the rating
curve derived, the stream flow was calculated.
The Parshall flume was calibrated twice, before and after installation. Calibration was done using the floating
method. However for low discharge (water level < 0.5cm), the volumetric method was applied; this was doneby measuring the volume of water, which flowed from theParshall flume a certain time. A discharge-rating curve wascalculated with the following equation:
Q = α hβ(1)where Q is discharge (L s−1 ), h is water depth in Parshall
flume (cm), α and β are constants.

Calculations of sediment yield were done by separating
into rainfall event and no rainfall event. In case of no rainfall event, the total sediment yield was calculated by averaging the sediment yield taken in the morning 7:00 and in
the afternoon 17:00 using the following equation:
Sy =Sdm + Sda
× Qd × 24 × 3600
2

where Sy is daily sediment yield (g day−1 ), Sdm is sediment concentration (g L−1 ) taken in the morning 7:00, Sda
is sediment concentration (g L−1 ) taken in the afternoon
17:00, Qd is average daily streamflow (L s−1 ).
In case of rainfall, the sediment calculation in one day
was separated into three rainfall events: before rainfall
events, during runoff event, and after runoff was over. The
following formula was used to estimate the sediment:n

Sdri
× Qri × tri + Sdo × Q0 × t0
i=1 n
(3)

Sy = Sdb × Qb × tb + ∑The mean daily flow data was calculated by averaging the water discharge from morning 7:00 to next morning 7:00. Hydrograph component was separated into baseflow and direct runoff (quick flow) using the straight-line
method.
2.3.3 Sediment yield
Water sample of about 500 mL, was taken at the outletof the Parshall flume site. The water sampling was done asfollows: (1) Two times a day around 7:00 and 17:00 if there
was no rain. (2) Several times during rainfall or runoff
event from the beginning of direct runoff until the streamflow became lower. (3) Sediment concentration was measured by sieving water sample with paper filter and ovendrying it.

(2)

Fig. 2 The Parshall flume used in the experiment.

18

土壌の物理性

where Sy is daily sediment yield (g day−1 ), Sdb is sedimentconcentration before rainfall event (g L−1 ), Sdr is sedimentconcentration during runoff (g L−1 ), Sdo is sediment concentration after runoff was over (g L−1 ), Qb is average discharge before runoff event (L s−1 ), Qr is discharge during
runoff event (L s−1 ), Qo is average discharge after runoff
was over (L s−1 ), tb is duration before runoff event (s), tri
is duration of runoff event (s), to is duration after runoff
event (second), n is the number of sediment sampling during runoff event.

第 115 号

(2010)

pacity of around 20 liters with 30 holes, one hole of which
was connected to the second unit of a bottle by vinyl pipe.
The design of erosion collection unit is shown in Fig. 5.
The erosion measurement was done every morning if
there was rainfall on the previous day. If the bucket was
full and there was water sample in the bottle, the runoff
and soil erosion was calculated as follows:

2.4 Soil erosion experiment2.4.1 Plot treatments
The slope gradient was around 50 % on average for plot
soil erosion. Seven plots were constructed and borderedwith zinc metal sheets. The plot size was 2.5 m wide and
30 m long. The treatments were as follows: (a) Bare plot:
The soil surface was always kept bare as the control plot
for the experiment. (b) Natural weeds (NW) plot: The
weeds were kept during the experiment time. The natural weed species were Ageratum conyzoides, Paspalum
con jugatum, Polugala paniculata, Hedyotis auricularia,
and Clibadia surinamense. Clibadia surinamense (woody
species), whose height reached 136 cm, was the dominant species (constitute 98 % of the total number of weed
species) in natural weed plot. (c) Clean weeded coffee:This treatment was regarded as “control” for coffee management, due to the fact that this was the most popularmanagement in this area. (d) Coffee with NW in strip
along the contour line: The weeds were managed along
the contour line, behaved like a filter strip (Fig. 3). (e)Coffee with NW in spot weeding: The weeds were cutaround the canopy of the coffee tree (Fig. 4). (f) Coffeewith Paspalum con jugatum (PC) in strip along the contour line. (g) Coffee with PC in spot weeding.
Paspalum con jugatum is one of the weed species ofgramineous perennial of South African origin. Its stalks,
hard and long, crawl over the ground, putting out irregular roots from the joints. Its growth speed is very fast andthe rhizomes are dense. This plant is widely used in bothprivate and public park areas in Indonesia. In addition tothese reason, we used Paspalum because it was abundantin that area and very easy to manage.

V +Vb × Nb
× 10−3Ap(4)

Sed + Sedb × Nb
× 10
Ap

(5)

RO =

E=

where RO is runoff (mm), V : runoff volume collectedin the bucket (cm3 ), Vb is volume of the water trapped by
the bottle (cm3 ), Ap is plot area (m2 ), E is soil erosion (kgha−1 ), Sed is oven dry weight of the sediment in bucket (g),Fig. 3 Coffee in strip along the contour linet.

Fig. 4 Coffee in spot weeding.

The coffee trees used are Arabusta type, a crossbred
between Robusta and Arabica. All the coffee trees were
three years old, with planting space of 1.5 m×2 m. The
Paspalum con jugatum seedlings were planted in October
2000. Soil erosion measurement began at early January
2001, when the Paspalum had fully covered the soil surface.
2.4.2 Measurement of soil erosion
Two-collection units were installed at the lower end ofeach plot. The first unit was a plastic bucket with the ca-

Fig. 5 Design of erosion and runoff collector.

論文：Soil erosion from catchment and plot scales under coffee tree based crop in Lampung, Indonesia

Sedb is oven dry weight of the sediment in bottle (g), Nb isthe number of hole in the bucket.

Table 3 Rainfall properties during the rainy season in
2001/2002.

1

2001.10.29

Rainfall
R(mm)
21.5

2

2001.10.30

6.5

21

18.6

3

2002. 1.16

5.0

86

3.5

4
5

2002. 1.17
2002. 1.18

13.0
47.5

87
840

9.0
3.4

6

2002. 1.22

7.0

223

1.9

7

2002. 1.23

4.5

33

8.2

8

2002. 1.24

13.0

29

26.9

9

2002. 1.25

13.0

91

8.6

10

2002. 1.27

3.0

40

4.5

11

2002. 2. 3

3.0

29

6.2

12

2002. 2.10

1.0

64

0.9

13

2002. 2.15

23.0

95

14.5

14

2002. 2.15

2.5

11

13.6

15

2002. 2.28

1.5

45

2.0

16

2002. 3. 1

28.5

53

32.3

17

2002. 3. 5

1.5

17

5.3

18

2002. 3. 5

7.5

32

14.1

19

2002. 3. 8

10.5

117

5.4

20

2002. 3. 9

9.0

112

4.8

21

2002. 3.12

19.0

66

17.3

22

2002. 3.13

22.0

38

34.7

23

2002. 3.13

5.0

212

1.4

24

2002. 3.14

5.0

16

18.8

25

2002. 3.17

40.5

82

29.6

26

2002. 3.18

12.5

104

7.2

27
28

2002. 3.27
2002. 3.28

21.5
6.0

65
12

19.8
30.0

29

2002. 3.28

13.0

101

7.7

30

2002. 4. 5

19.5

188

6.2

31

2002. 4. 6

8.0

112

4.3

32

2002. 4. 9

4.0

19

12.6

33

2002. 4.13

5.0

23

13.0

34

2002. 4.16

6.0

26

13.8

35

2002. 4.18

13.0

56

13.9

36

2002. 4.20

10.0

101

5.9

37

2002. 4.21

16.5

69

14.3

38

2002. 4.25

21.0

53

23.8

39

2002. 5. 8

9.0

28

19.3

40

2002. 5. 8

38.0

49

46.5

41

2002. 5.11

10.0

60

10.0

42

2002. 5.14

4.5

20

13.5

43

2002. 5.14

10.0

44

13.6

44

2002. 5.16

4.0

47

5.1

45

2002. 5.16

20.0

33

36.4

46

2002. 6. 3

9.5

38

15.0

47

2002. 6. 3

8.5

52

9.8

48

2002. 6. 4

9.5

21

27.1

49

2002. 6. 4

19.0

53

21.5

Date

3. Results and discussions
3.1 Rainfall
Total rainfall during the experiment period was 2975.3
mm in the year 2001 (from January to December) and
1853.5 mm in 2002 (from January to October). The
amount of rainfall in 2002 was probably normal comparedto the average rainfall in the areas. Based on 24 years
data (1974 – 1998), Afandi et al. (1999) reported that the
average rainfall from the adjacent rain gauge station wasaround 2426 mm year−1 , and the maximum rainfall was
3539.5 mm year−1 . The monthly rainfall during the experiment time is shown in Fig. 6.
Usually, the dry season starts from June until September. Average monthly rainfall of June, July, August, andSeptember from 1972 to 1998 is 136, 138, 107 and 134
mm, respectively in Sumberjaya. However, during the dry
season in 2001, the monthly rainfall amount still exceeds
100 mm as shown in Fig. 6. On the other hands, the dry
season in 2002 started at August, and it was very severe because the monthly rainfall was less than 100 mm in August,and even in September and October, the monthly rainfall
was less than 50 mm.
Table 3 shows some properties of all rainfall events thatwas more than 1 mm and contributed soil erosion during
the rainy season in 2001/2002. From October 2001 to June
2002, the maximum daily rainfall was 47.5 mm which occurred on January 18, 2002 as shown in Fig. 3. However,this rainfall had very low intensity, 3.4 mm h−1 . The maximum intensity in 2001/2002 rainy season was 46.5 mm
h−1 which occurred on May 8, 2002. This maximum intensity of rainfall had also the maximum value of 30-minutes
intensity (I30 ), in which the amount was 58 mm h−1 . From
49 selected rainfall events during 2001/2002 rainy season,
the rainfall intensity which was more than 25 mm h−1 occurred only 9 times or 18 %, and between 10 – 25 mm h−1
was 39 %, about 43 % was less than 10 mm h−1 .

Fig. 6 Monthly rainfall pattern during the experiment time.

19

Duration
T (min)46

Intensity
R/T (mm h−1 )
28.0

20

土壌の物理性第 115 号

(2010)

sia. On vegetables steep terrace, Sinukaban et al. (1994)
reported 42 – 75 t ha−1 year−1 , while on agricultural benchterrace with mixed rain-fed, van Dijk (2002) reported 40 t
ha−1 year−1 . The value of this experiment is almost similar with Bruijnzeel (2004) who reported the soil loss of 4t ha−1 year−1 for Agathis plantation forest, while Rijsdijk(2007a, b) found annual sediment yields from the two volcanic catchment areas to be 22 – 26 and 50 – 87 t ha−1
year−1 , respectively.
Fig. 7 Runoff, sediment yield, and rainfall during the observation time (from October 2001 to June 2002).

3.2 Runoff and sediment yield
Runoff from the catchment outlet is shown in Fig. 7. As
shown in Fig. 7, the monthly streamflow pattern is strongly
affected by the monthly rainfall. The maximum monthly
streamflow occurred in March when its monthly rainfall
was also the highest. The average ratio of streamflow torainfall was around 49 %, it means that more than 50 %of the monthly rainfall was stored at the catchment in theform of infiltration.
As shown in Fig. 7, the minimum runoff was about 48
mm in June and the maximum was 248 mm in October,and the ratio of max/min runoff was 5.2. It means thatthe catchment was in a good condition. For Indonesian’s
catchment, according to Mas’ud et al. (2004), if the ratio
between max/min runoff < 50, the catchment is good, andpoor if > 120.
As it has already been mentioned in the methodology,
the sediment yield estimation was divided into two categories; (i) in case of no rainfall event, and (ii) during rainfall event. During rainfall event, the calculation was also
divided into three events: (a) sediment yield before runoff
occurred, (b) the sediment yield during runoff event, and(c) the sediment yield after runoff was over. The sedimentyields from (b) to (c) reflected the sediment load, which
was carried during the soil erosion process. The results are
given in Table 4.
The total sediment yield which flowed out from thecatchment was 6.6 t ha−1 during the rainy season of
2001/2002. The total sediment yield during rainfall eventswas 4.3 t ha−1 , which contributed 64 % of total sedimentyield, and the sediment yield during no-rainfall events was
2.4 t ha−1 or 36 % of the total sediment yield. The sediment yield was far below the criterion of Ministry ofForestry (2009b) which categorized that if the sedimentyield is < 2 mm year−1 or about 20 t ha−1 year−1 , thecatchment is good, and if > 5 mm year−1 or 50 t ha−1
year−1 , it’s poor.
Various results of sediment yield have been reported
were obtained from several catchment studies in Indone-

The maximum sediment yield occurred in March 2002
which contributed 53 % of the total sediment, which also
correlated with the biggest monthly rainfall (Fig. 6). However in February and May, contribution of sediment yield
during no-rainfall events was higher than rainfall eventsas shown in Table 4. The source of no-rainfall sedimentin February was mainly due to the paddy field areas whereland was tilled and planted on 17 to 22 January, while small
collapse which occurred on the side of the creek produced”streambank erosion” during May.
Although the soil is dominated by clay fraction, the silt
and sand fraction were abundant in the sediment load (Table 5). It seemed that these soil fractions were more erodible than clay fractions, and as a consequent the clay fraction was dominant in the area as shown in Table 2.
3.3 Soil loss at erosion plot
The total soil loss from each treatment, which was observed from January 2001 until October 2002, is shownin Table 6. The lowest soil loss was from natural weeds
Table 4 Sediment yield during rainfall and no-rainfall event(from October 2001 to June 2002).
Sediment yield
Sediment yield(t ha−1 )ratio (%)
Month
Rainfall event No-rainfall
100 × SR/(SR + SN)（SR）event （SN ）October
0.11
0.04
73
November
0.60
0.19
76
December
0.24
0.22
52
January
0.31
0.11
75
February
0.15
0.40
28
March
2.28
0.53
81
April
0.44
0.32
58
May
0.10
0.53
16
June
0.06
0.03
65
Total
4.29
2.37
64
Table 5 Soil texture in the sediment yield.
Month
DecemberFebruary
March

Soil texture∗ (g g−1 )
sand
silt
0.31
0.30
0.37
0.25
0.23
0.34

∗ Soil texture is classified by USDA method.

clay
0.39
0.38
0.43

論文：Soil erosion from catchment and plot scales under coffee tree based crop in Lampung, Indonesia
Table 6 Effects of weeds management under coffee tree on soil
loss (from January 2001 to October 2002).
Land use type(a) Bare plot(b) Natural weeds(c) Clean weeded coffee(d) Coffee with natural weeds in strip(e) Coffee with natural weeds in spot(f) Coffee with Paspalum in strip(g) Coffee with Paspalum in spot

Soil Loss(t ha−1 )
0.87
0.12
0.76
0.61
0.58
0.56
0.56

plot (0.12 t ha−1 ) and the highest from the bare plot (0.87t ha−1 ), while the soil loss from coffee areas was 0.56 –0.76 t ha−1 , which ranged between the values from natural
weed plot and bare plot.
Comparing the results of this experiment to similar experiments in Indonesia, especially in Sumber Jaya, thesoil erosion was lower. The previous study by Afandi etal. (2002) showed that the average soil loss from cleanweeded coffee was 1.1 t ha−1 year−1 , while Dariah etal. (2004) found that the soil erosion from coffee withnatural grass in strip was 1.28 t ha−1 year−1 and fromclean-weeded coffee was 1.5 t ha−1 year−1 . In plot scale,Gintings (1982) found that the soil loss from 1-year old
Robusta coffee with 59 – 63 % slope gradient was 1.94 t
ha−1 , on the other hand, the soil loss from 3-years old coffee with slope gradient 62 – 66 % measured from May to
October was 1.57 t ha−1 .
In addition to the effectiveness of the conservation measures applied, the low soil loss in all treatments was probably due to the soil physical properties and the low rainfall
intensity. As shown in Table 1, the soil was deep with somecracks until 1-m depth, so the soil permeability would befast, and the infiltration would be more than runoff. Dariah
et al. (2004) also found that the soil physical properties, especially macro pore and soil permeability, was responsible
for the low soil erosion in coffee area in Sumber Jaya.
The interesting soil morphology found in the researcharea is that almost all of the soil layers have cracks vertically until the fourth layer, more or less than 100 cm fromthe soil surface. Cracks are rarely found in humid tropicalsoils, because these minerals are usually weathered intensively and directly to form low activity clays such as kaolinite or even sesquioxides that have low value of coefficientof linear extensibility. The soil cracks are probably due
to 2:1 layer silicate mineral, because Wada et al. (1999)
found that although the clay fraction in the research area
was dominated by hlloysite (66 %), it also contains 25 % of
2:1 layer silicate minerals particularly vermiculite-chlorite
intergrade.

21

3.4 Discussion
The soil erosion from the catchment level was greaterthan erosion from the plot scale. The sediment yield fromthe catchment during 8-months’ rainfall event was 4.3 t
ha−1 , while the soil erosion from coffee areas during one
and a half years was only 0.56 – 0.76 t ha−1 . It means thatthe contribution of sediment yield from agricultural areas
were very small. Other erosion sources, such as stream
bank erosion, gully erosion, collapse, and footpath were
responsible for the high soil erosion at the catchment scale,although the source of previous erosion from agricultural
fields could be entrapped inside these sites.
The other studies from Indonesian’s catchment showedvarious results. Bruijnzeel (2004) found that the erosion
from catchment roads, settlements and trails which occupied 5 % of the total area, contributed approximately 54% of the total sediment yield, while rain-fed agriculture
which occupied 20 % of the total catchment area contributed 37 % of the sediment yield. On the other hand,
Rijsdijk (2005) found that rain-fed agricultural land contributed nearly half of the soil erosion on average, whilehillside trails, settlements and roads, and non-surface erosion contributed the rest.
In this research, soil erosion was only measured fromthe plot scale and catchment, and the other sources of soil
erosion were not measured. Due to the fact that from previous studies the soil erosion from coffee areas based on
the plot level was very low (Afandi et al., 2002; Dariah etal., 2004). It was amazingly found that the sediment yieldfrom micro-catchment scale in this research was higher
than soil erosion rate at the plot scale. However, due to thefact that the sediment yield was taken on daily basis withfrequent water sampling during rainfall and calculated sediment yield on daily basis, not estimated it from sedimentdischarge rating curve equation as ordinarily used in previous research (Walling, 1977, Asselman, 2000), the accuracy of the sediment yield estimation was very high.
This research showed that at the catchment and plotscales, the soil erosion from the agricultural land is notmuch although it is dominated by steep slopes, and coffee land use with high clay soil texture. As the effects ofslope and land use in agricultural land were very small, thesoil-water conservation strategy for this catchment was directed to the other sources of sediment yield, such as road,gully, and collapse. The soil conservation practice in agricultural land strategy must be focused on how to increase
infiltration rate, so that direct runoff will be decreased before entering gullies or streams, for example by building
silt trap (Fig. 8).
This experiment also showed that the determination ofa catchment to be critical or not should be done by soil
erosion at both plot and catchment scales. In case of this22

土壌の物理性experiment where the soil erosion in agricultural land isvery low, the other factors in addition to traditional soil
erosion factors (rain, soil, slope, vegetation, and management) must be considered, such as the permeability of therock below the soil (geology).

第 115 号

(2010)

different weed managements in humid tropical hilly area of
Lampung, South Sumatra, Indonesia. J. Jpn. Soc. Soil Phys.,
91: 3 – 14.
Asselman, E.M. (2000): Fitting and interpretation of sediment
rating curves. J. Hydrol., 234 (3 – 4): 228 – 248.
Braud, I., Vich, A.I.J., Zuluaga, J., Fornero, L. and Pedrani, A.
(2001): Vegetation influence on runoff and sediment yield in
the Andes region observation and modeling. J. Hydrol., 254(1– 4): 124 – 144.
Bruijnzeel, L.A. (2004): Hydrological functions of tropicalforests: not seeing the soil for the trees? Agric. Eco. Env.,
104 (1): 185 – 228.
Ceballos, A. and Schnabel, S. (1998): Hydrological behavior of asmall catchment in the dehesa landuse system (Extremadura,
SW Spain). J. Hydrol., 210 (1-4): 146 – 160.
Dariah, A.F., Agus, S., Arsyad, Sudarsono and Maswar (2004):

Fig. 8 Silt trap in coffee plantation.

Erosion and surface runoff in a coffee area at Sumberjaya,
West-Lampung (in Indonesia). Agrivita, 26 (1): 52 – 60.

4. Conclusion

Gintings, A.Ng. (1982): Aliran permukaan dan erosi dari tanahyang tertutup tanaman kopi dan hutan alam di Sumberjaya,

This experiment strengthens the previous study that thesoil erosion from coffee areas at Sumber Jaya, Lampung,Indonesia, was very low, although the erosion factors werevery high, such as rainfall and slope. In fact, the soil erosion from catchment level was greater than erosion plotscale. The sediment yield from the catchment during 8months observation was 4.3 t ha−1 , while the soil erosion
from coffee areas during one and a half year was only 0.56
– 0.76 t ha−1 . The contribution of sediment yield fromagricultural areas was very small, less than 10 %. Other
erosion sources, such as stream bank erosion, gully erosion, collapse, and footpath were responsible for the highsoil erosion at catchment scale.

Lampung Utara. Report No. 339. Balai Penelitian Hutan,
Pusat Penelitian dan Pengembangan Kehutanan, Bogor.
Li, M., Zhanbin Li,Z., Yao, W. and Liu, P. (2009): Estimating theerosion and deposition rates in a small watershed by the 137Cs
tracing method. Appl. Radiat. Isot., 67 (2): 362 – 366.
Mas’ud, A.F., Nugroho, S.P. and Irfan, B.P. (2004): Criteria
and indicators of watershed management used for the national
movement for land and forest rehabilitation (GNRHL) in Indonesia. In : Agus, F., Farida, and van Noordwijk, M., (eds):
Hydrological impacts of forest, agroforestry and upland cropping as a basis for rewarding environmental service providers
in Indonesia, World Agroforestry Centre (ICRAF), Bogor, Indonesia: 51 – 64.

The strategies to curtail soil erosion in agricultural fieldmust be continued to reduce runoff before entering gully or
stream. This experiment also showed that the determination of a catchment to be critical or not should be done bysoil erosion estimations at the plot and catchment scales.

Ministry of Forestry and Estate (1999): Lampiran Keputusan

Acknowledgements

Ministry of Forestry (2009a): Lampiran Keputusan Menteri

Menteri Kehutanan dan Perkebunan No.284 tentang Penetapan Urutan Prioritas Daerah Aliran Sungai, The Decree of
Ministry of Forestry and Estate No.284, Republic Indonesia
about the watershed priority. Ministry of Forestry and Estate,
Republic of Indonesia, Jakarta, Indonesia: 1.

The plot soil erosion research was funded by Monbusho
under the project title “Assessment of Soil Fertility andRehabilitation of Cultivated Tropical Rain Forest in South
East Asia” led by Dr. Masanori Nonaka, Niigata University, Japan, while the catchment research was funded by
ICRAF SEA (Bogor) and ACIAR under the project of title“Micro-catchment soil loss as affected by soil management
practices”.

Kehutanan Republik Indonesia No.328 tentang Penetapan
Daerah Aliran Sungai (DAS) Prioritas Dalam Rangka Rencana
Pembangunan Jangka Menengah Tahun 2010 – 2014. The Decree of Ministry of Forestry No.328, Republic Indonesia about
the watershed priority for 2010 – 2014, Ministry of Forestry ,Republic of Indonesia, Jakarta, Indonesia: 2.
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Monitoring dan Evaluasi Daerah Aliran Sungai No.P.04/VSET/2009, The Rule of Directorate General of Rehabilita-

Referencestion and Social Forestry about Guidance of Monitoring andAfandi, Manik, T.K., Rosadi, B., Utomo, M., Senge, M., Adachi,

Evaluating of Catchment No.P.04/V-SET/2009, Ministry ofT. and Oki, Y. (2002): Soil erosion under coffee trees with

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要旨圃場レベルで実測した土壌侵食量の結果を流域レベルに拡大して適用すると問題が発生することが多い．すなわち，流域内で生起している複雑な水文現象から，圃場レベルの土壌侵食量と流域スケールで測定した侵食量は一致しないことが多い．そこで，インドネシア国ランポン州のコーヒー樹が栽培されている地域を対象に，圃場レベルと流域レベルでの土壌侵食量を実測することを目的として，10.2 ha の試験流域と，その流域内に 75 m2 の試験圃場を 7 試験区設けた．試験圃場の構成は，（a）裸地区（対照区），（b）自然植生区，（c）雑草を完全に除去したコーヒー栽培区，（d）圃場面を Paspalumcon jugatum（以下 PC）によって被覆しコーヒー樹の回りのみを除草したコーヒー栽培区，（e）等高線方向に PC を帯状に移植したコーヒー栽培区，（f）圃場面を自然植生の雑草（以下，NM）で被覆しコーヒー樹の回りのみを除草したコーヒー栽培区，（g）等高線方向に NW を帯状に移植したコーヒー栽培区，である．

1 年半の実測結果から，圃場試験区からの土壌侵食量は，0.12 t ha−1 （(b) 自然植生区）から 0.87 t ha−1（（a）裸地区）の範囲にあった．一方，8 ヶ月間の雨季における試験流域からの土壌流出量は 6.7 t ha−1であった．以上の試験結果から，流域レベルにおける単位面積当たりの土壌侵食量は，圃場レベルの侵
食量の 10 倍以上の値を示した．これは，流域からの土壌侵食量は，ガリ侵食，地滑り，流域内の水田からの土壌侵食に起因すると想定される．以上のことから，現在，耕地からの侵食対策に重点がおかれた土壌保全は再考すべきであり，他の土壌侵食発生源にも対策を講じ，下流への土壌流出を削減しなければならないことを示唆している．
キーワード：流域，コーヒー，インドネシア，土壌流出，土壌侵食