ῐ
J. Jpn. Soc. Soil Phys.
ῐ῎῍ῑῒ῏
No. 3+, p. -ῌ+. ῍,**,῎Soil Erosion under Co#ee Trees with Di#erent Weed
Managements in Humid Tropical Hilly Area of
Lampung, South Sumatra, Indonesia
AFANDI*, Tumiar Katarina MANIK*, Bustomi ROSADI*,
Muhajir UTOMO*, Masateru SENGE**, Tadashi ADACHI***and Yoko OKI**** Faculty of Agriculture, University of Lampung, Jl. Sumantri Brojonegoro
No. +Bandar Lampung -/+./, Lampung Province, Indonesia** Faculty of Agriculture, Gifu University, +ῌ+ Yanagido Gifu /*+ῌ++3-, Japan*** Faculty of Environmental Science and Technology, Okayama University,-ῌ+ῌ+ Tsushimanaka Okayama 1**ῌ2/-*, Japan
Abstract
Soil loss and surface runo# from farmland under co#ee trees with di#erent weed managements
were investigated in Lampung, South Sumatra, Indonesia during rainy seasons from +330 to +333.
Three treatment practices investigated were as follows : co#ee without cover crop ; co#ee with
Paspalum conjugatum sp. as cover crop, and co#ee with natural weeds. Weed management wasdone every two week by clearing all the weeds in co#ee plot, and cutting the weeds around theco#ee trees with diameter + m for the weedy plots. The results showed that the maximum daily
rainfall and intensity based on +* minutes observation were 2, mm/day and +,* mm/h, however,
only +..,ῌ of rainfall intensities was greater than ,/ mm/h (classiﬁed as erosive rainfall intensity).
A relationship between erosivity index (R) and daily rainfall (X) was found as follows : Rῌ+.0,.
(Xῌ+*.3), where R : daily erosivity index (m, · t/ha/h) and X : daily rainfall (mm/day). The runo#
ratio for cleanoweeded co#ee ranged from 1.* to +/.3ῌ, and decreased after the second year
because of the co#ee canopy growth. The presence of Paspalum conjugatum had reduced runo#
until zero after the third year, whereas in natural weeds plot, runo# became zero after the fourthyear. The highest soil loss was found in cleanoweeded co#ee which reached ,,.1 t/ha in thesecond year of experiment. The use of cover crop could suppress soil loss until zero after the thirdyear in Paspalum plot and after the fourth year in natural weeds plot.

However the goodmanagement of weeds as cover crops is necessary due to the bad performance of co#ee growth atboth weedy plots. The average soil loss from cleanoweeded co#ee plot was +.,. mm per year
which was below the soil formation rate in Indonesia.
Key words : co#ee, soil erosion, runo#, erosivity index+.

Introduction

Lampung, located in the southern part of
Sumatra Island, is one of the biggest co#ee
producing districts in Indonesia. About /*ῌ ofco#ee production of Indonesia occurs in
Lampung. From +33* to +33., the average ex-port of co#ee bean from Lampung was +/3,31*
tons out of -,3,*1* tons of total Indonesian’s
co#ee export (BPD-AEKI, Lampung, +330). In+333, the co#ee export from Lampung
amounted to +1/,2** tons out of -/.,*** tons
(Bank Indonesia Bandar Lampung, ,***).
The major problem of the co#ee manage-

῏4

ment in Lampung is that the co#ee trees were
mostly planted in steep areas where the soil
conservation is usually not applied very well.
Clearing up all the ground cover under theco#ee plants is the most popular practice forweeding management. The farmers perform
such a management practice due to the factthat the co#ee root system is abundant aroundthe upper part of the soil surface, so even small
weeds like grass type will inﬂuence the co#ee
growth. This reﬂects on the nutrient component of the co#ee leaves due to competition
between co#ees and weeds if the weeds wereleft unclear. However, clearing all the weeds
promotes soil erosion since this area possesses
a humid tropical climate, characterized by abundant rainfall and high rainfall intensity concentrated on rainy season.
It is well known that cropping systems withground cover maintenance, especially in rainyseason, are recommended for farming on slopesin order to reduce soil erosion. Unfortunately,
the study of soil loss under co#ee plants in thetropics is limited, and a little information isavailable about soil erosion from co#ee areas
in Indonesia. An erosion study by Gintings(+32,) in Sumber Jaya areas, Lampung, measured soil loss in Robusta co#ee under natural
condition without any other management. The
co#ee tree used was +0ῌyr old for 2ῌmonths
measurement, and +ῌyr and -ῌyr old for 0ῌ
month measurement.
A 0ῌmonth erosion
study was also conducted in Bali by Pudjiharta
and Pramono (+322) in +/ῌyr old co#ee trees.
The information derived from the studies wasjust the amount of soil loss from co#ee plantation in a short period. Some researchers inIndonesia also have used some grasses as cover
crop, but it was limited for horticultural cropor annual crops, for example Abujamin et al.
(+32-) used Bahia and Bede grass, and Utomo(+323) reported the using of King grass in sandy
soil in Indonesia.
Lately, the problem of soil erosion in
Lampung, Indonesia, has accelerated the following political changes. Due to weak law

3+

,**,

enforcement during the reformation period in+332, the public was encouraged to open the
Calliandra reforestation areas. In a very shortperiod during +333, thousand of hectares ofprotected forest in Sumber Jaya were converted into co#ee plantation. The increasing of
co#ee bean price more than three times alsoenhanced the forest squattering in +332.
The current controversies on soil erosion in
the co#eeῌgrowing areas in Lampung persist
due to lack of comprehensive research. Since
most co#ee farmers in these areas apply clean
weeding management, a prompt evaluation ofsoil loss under existing methods of farming
and other alternatives of weed management
was in need. Thus, the objective of this four
years study was to measure the e#ects of
di#erent weed managements under Arabica
co#ee plants on the extent of surface runo#
and soil loss.
,.

Materials and Methods,. + Study site
This study was conducted during the rainyseasons from +33/ to +333. The study site was
located at Sumber Jaya District, Lampung
Province, South Sumatra, Indonesia. Geographically, it is located at +*/*+’ EL and *.-.’
SL. The slope gradient was around +/with theelevation of 12*m above the sea level. The
average rainfall recorded from +31. to +332 wasaround ,/** mm/year and the air temperature
was around ,, (Afandi et al., +333).
The soil had the initial properties as shownin Table +. The soil was dominated by clay
fraction in all depths, however the soil bulk
density was very low, which is indicating thatthe soil was friable and porous. The color ofsoil proﬁle (up to +** cm soil depth) was
dominated by brown to red color which indicated that the internal drainage was very
good. The soil reaction is slightly acid withmoderate cation exchange capacity. The soilorganic carbon was quite high probably due tothe fact that the decomposition rate of organic
matter was relatively slow. Based on the aboveῐ῏ : Soil Erosion under Co#ee Trees with Di#erent Weed Managements in Humid Tropical Hilly Area of Lampung, South Sumatra, Indonesia

Table +
Depth
(cm)

pH
H,O

*῍+*
+*῍,*
,*῍-/
-/῍0*
0*῍+**

.43,
.423
.43+
.421
.42/

5

Initial soil characteristics prior to planting

Total-N Organic-C
CEC
Texture (ῌ)(ῌ)(ῌ)(cmol/kg) Sand
Silt
Clay
*4,0
*4+0
*4*3
*4*1
*4*0

Fig. +

-4.2
+420
*423
*42,
*42,

+-4343
34241
241

,/
,/
,0
,0
,2

,+0
+++/

/,
/3
0+
0+
/1

Bulk density(g/cm-)*430*43*433*43ῌ

The design of experimental plot.

soil properties, the soil could be classiﬁed as
Latosol (Indonesian soil classiﬁcation system)
or Dystrudepts (Soil Survey Sta#, +332).
,. , Treatment plot
The erosion plots were consisted of threeplots with +/῎gradient, ,* m slope length and /m width, and bordered by -*ῌcm height zincmetal sheets. Two collection units were installed at the lower end of each plot. The ﬁrst
unit was a ditch with the capacity of *.+ m-,
which was connected to the second unit (a tank
and water reservoir) by seven pipes. One pipe,
which was in the center, was connected to atank by a siphon and the others overﬂowed
into the water reservoir box in which a triangle
weir and a water gauge were installed. The
detailed design of the plot was shown in Fig. +.
The treatments were as followed :(+) Treatment + (cleanoweeded plot) : Groundsurface was always keeping bare by hand
weeding at two weeks interval. This management is a general practice in this co#ee plantation area so that this treatment is regarded as acontrol.
(,) Treatment , (Paspalum plot) : Co#ee with
Paspalum conjugatum as cover crop. Young
Paspalum conjugatum was transplanted to theexperiment plot in November +33/ and February +330.
Paspalum conjugatum is one of weed species,
gramineous perennial of the South Africa
origin. Its stalks, hard and long, are crawled
over the ground, putting out an irregular roots
from joints. Its growth speed is very fast andthe rhizomes are dense. This plant was widelyused in both private and public park areas in6Indonesia.
Instead of these reason, we used Paspalum
because it was abundant in that area and very
easy to manage.
(-) Treatment - (natural weeds plot) : Co#ee
with natural weeds as cover crop.
In each plot, seedlings of Arabica co#ee wereplanted with planting distance +./ m by , m on
November +33/. Weed management was done
every two weeks by clearing all the weeds incleanoweeded plot, and cutting the weeds
around the co#ee tree with diameter + m forthe weedy plots. Before and after rainy season,
the Paspalum mats and natural weeds were
mowed at +/-cm height. Application of fertilizer and pesticides had been adopted according
to the standard usual practice.
,. - Rainfall erosivity
Rainfall was measured by automatic weather station, which recorded every ten minutes.
We selected +,- rainfall event data from +330 to+333.
The rainfall energy factor was calculatedusing the equation of Wischmeier and Smith(+312) as follows :EIEI-*ῌWhere E : total rainfall energy in metricoton
meter per hectare (t · m/ha)
I-* : the maximum -*-min rainfall intensity(cm/h)E was calculated as follows :EEkr῍Ek,+*23 logI῎
Where Ek : kinetic energy in metricoton meter
per hectare per centimeter of rain(t · m/ha/cm)
I : rainfall intensity (cm/h)r : rainfall(cm)Rain shower less than *./ inch and separated
from the other rain periods by more than 0
hours was omitted from the erosion index,
unless as much as *.,/ inch of rain fell in +/minutes. According to Wischmeier and Smith(+312), the value of ,23 (t · m/ha/cm) was applied for all intensities greater than 1.0 cm/h, so
equation (-) will be

3+  ,**,

Ek,+*23 log I for I1.0 cm/h
῏
Ek,23for I1.0 cm/h
ῐBecause energy computed in EI equation isexpressed in hundreds of metricoton per ha (t ·m,/ha/h), the erosivity index (R)becomes :R(EI-*)+*,ῑ,. . Soil loss measurement
The sediment in the ditch was pulled out into
a drum with a siphon, thoroughly stirring thecontents in the drum and quickly extracting/** ml sample with plastic bottle. By measuring the dry weight and the volume of runo#
water stored in the ditch, the soil loss in theditch was calculated as follows :Sd(A//**)Vd+,***
ῒ
Sd : total soil loss in the ditch (g), A : dryweight of /** ml water sample (g), Vd : volume
of runo# water in the ditch (liter), +,*** : conversion factor from ml to liter
The sediment in the tank was sampled andthe total soil loss in a tank (Sdr) was calculatedusing the same procedure as mentioned above.
Total soil loss from erosion plot in an individual measurement was converted into kg/ha as
follows :Soil loss(SdSdr1)+**+*ΐ+** : conversion factor from +** m*, to + ha,+*- : conversion factor from g to kg,. / Supporting data
Supporting data which also had been collected in this study were rainfall and co#ee growthparameters. Rainfall data were collected using
automatic rainfall recorder every ten minutes ;while co#ee growth parameters (height, diameter of canopy, and co#ee yield) were measured
directly in the ﬁeld for evaluating the competition between co#ees and weeds. The type of
weeds and co#ee growth parameter were observed by Sriyani et al. (+333).
,. /. + Weed vegetation
Although the weeds were cut regularly
every two weeks, some weed species were still
appeared in cleanoweeded plot. As presented
in Table , reported by Sriyani et al. (+333), thedominant weed species in cleanoweeded plot
was Ageratum conyzoides which was an annual῍ῌ : Soil Erosion under Co#ee Trees with Di#erent Weed Managements in Humid Tropical Hilly Area of Lampung, South Sumatra, Indonesia

Table ,

7

Type of weeds species found in each treatment

Clean-weeded plot

Paspalum plot

Natural weeds plot

Ageratum conyzoides
Borreria repens
Erechtites valeriaifolia
Imperata cylindrica
Oxalis barrelieri

Paspalum conjugatum
Polygala paniculata
Hedyotis auricularia
Ageratum conyzoides
Borreria repens

Clibadia surinamense
Clidemia herta
Chromolaena odorata
Melastoma a$ne
Imperata cylindrica

herb. Instead of Paspalum conjugatum, a few
weed species also occurred in Paspalum plot
including Polygala paniculata, Hedyotis auricularia, and Ageratum conyzoides. Clibadia
surinamense (woody species) whose mean plantheight reached +-0 cm was the dominant species (occupy 32ῌ of the total number of weed
species) in natural weeds plot. The photos ofdominant weed species were shown in Fig. ,.
The weeds started to cover the entire groundsurface (+**ῌ covered) around March +330 at
Paspalum plot and on April +330 at naturalweeds plot.
After that, the weeds weremanaged by spot weeding with diameter + maround the co#ee tree, and the coverage of
weeds, the ratio of the area occupied by weeds
to total areas, was calculated as 03ῌ. So,
during the experiment period, the weeds covered the soil surface between 03ῌ (after spot
weeding) and +**ῌ (before spot weeding).
,. /. , Co#ee growth
The existence of weeds has inﬂuenced on theco#ee growth. The conventional weed management (cleaning up weed) gave the best performance of co#ee growth as shown in plantheight, canopy diameter and coverage. The
weeds had suppressed the co#ee height at
Paspalum plot about .*ῌ and at natural weeds
plot about -*ῌ. The canopy diameter was also
suppressed as much as /1 ῌ at Paspalum plot
and /. ῌ at natural weeds plot.
Due to the bad performance of co#ee growthat both weedy plots, the co#ee yields of theweedy plots were very low. As reported by
Sriyani et al. (,***), the yield reduction ofco#ee beans in weedy plots in +333 was .*ῌ at
Paspalum plot and 1/ῌ at natural weeds plot

Fig. ,

Dominant species of weed in each experimental plot.



8

Table -

3+,**,Rain erosivity data during . years experiment

Year ofexperimentR(t · m,/ha/hr)

Rainfall
(mm)

+st
,nd
-rd
.th
Total
Average

-2/40
/++40
+/.1423,,4*--014*
2.+42./04++*1.4,+10242+,.24/./.140++-043

Average Rainfall
from nearest
rainfall station*
(mm)+23-42* Calculated from , rainfall stations (Pajar Bulan and SumberJaya) for rainy season data (Nov4 to May) from +31.+332

compared to cleanoweeded plot.
-.

Results and Discussion-. + Rainfall Pattern
Table - shows that the total rainfall during
four years of experimental period was ./.1.0
mm, with ++-0.3 mm per rainy season. This
rainfall was lower than average rainfall occurring in this area, i.e. +23- mm per rainy season(Afandi et al., +333) since El Nino’s occurrencein +331 caused a long dry season with low
rainfall. In addition, due to plot construction
during the ﬁrst year, the experiment beganlate, in February +33/, whereas the rainyseason usually occurred from October to April
or May.
The daily rainfall distribution (Fig. -)showed that .2ῌ of the rainfalls occurred lessthan / mm/day or about 0-ῌ was less than +*mm/day. Based on the equation (3) describedlater, about -1ῌ of the daily rainfall could be
categorized as the daily erosive rain (+*.3
mm/day).
The maximum intensity was ,* mm in +*minutes or +,* mm/h, which occurred at March0, +333. According to Hudson (+310), the soil
erosion will be occurred if rainfall intensity,/ mm/h, and as it was shown in Fig. ., only+.ῌ of the rainfall intensities which were calculated based on +*-minutes time interval
could be classiﬁed as erosive (,/ mm/h).
The maximum daily rainfall was 2, mm/day
occurred at January +1, +332, which almost con-Fig. -

Distribution of daily rainfall.

Fig. .

Distribution of rainfall intensities basedon +*-minutes time interval of rainfall.

Fig. /

Pattern of rainfall Indonesia, occurredat January +1th, +332.

centrated in two hours and its maximum intensity was +-./ mm in +* minutes or 2+ mm/hr.
As shown in Fig. /, this rainfall was fallen in /῏῎ : Soil Erosion under Co#ee Trees with Di#erent Weed Managements in Humid Tropical Hilly Area of Lampung, South Sumatra, Indonesia

hours, with intermittent pattern ; twenty
minutes after the rain started, it stopped, andbegan again for about two hours and ten
minutes. The intermittent pattern is a typicalrainfall in this area, so several rainfall events
could occur in one day. Due to this rainfall
character, the rain which fell later could be
more erosive although smaller than the previous rainfall, because the soil has been alreadywet and easy to disperse.
-. ,. Erosivity Index
The value of erosivity index ranged between-2/.0῏+/.1.2 and was tabulated in Table -.
Since the measurement period for each rainyseason is not the same, the erosivity values
di#er much. In the ﬁrst year experiment, themeasurement period was only two months dueto the erosion plot construction. A long dry
season due to El-Nino occurred during thesecond year of experiment until the end of +331,
thus the amount of rainfall was meager although the length of the rainy season was
normal. Hence, normal value was probably
found in the third and fourth year of measurement, and the values were +,/.1.2 and 3,,.* (ton· m,/h/ha) respectively.
The rainfall erosivity index as calculated inequation (0) proved to be the optimal rain parameter in Indonesia as indicated by Suwardjo(+32+) and Utomo (+323). Utomo (+323) reported
the values between 3+-῏+,0-- (ton · m,/h/ha) for
several areas in Indonesia which agreed with
the normal values in this experiment.
-. - Relationship between daily rainfall
and erosivity index
Based on +,- rainfall events from +33/ to +333
(Fig 0), a relationship between erosivity index
which was calculated using equation (.), (/),
and (0) and observed daily rainfall was derived
as follows :R῍+.0,. (Xῌ+*.3)
ῌ,with r ῍*.2,
Where R : daily erosivity index (t · m,/h/ha)
X : daily rainfall (mm)From this equation which shows the linear
relationship between R and X, it can be in-Fig. 09

Relationship between daily rainfall anderosivity index.

ferred that the rainfall will be erosive if theamount of rainfall exceeded +*.3 mm per day.
Due to the fact that the rainfall data available
in Indonesia was mostly daily rainfall, someresearchers had proposed rain erosivity index
using daily rainfall data. The rainfall erosion
index widely used in Indonesia as rainerosivity factor for applying USLE was introduced by Bols (+312) as follows :EIm῍0.++3 (CHb)+.,+ (HH)ῌ*..1 (CH,.)*./῎
῍
where :
EIm : monthly rain erosivity index (t · m,/h/ha)
CHb : monthly rainfall data (cm)
HH : monthly rainfall event (days)
CH,. : the amount of maximum rainfall in ,.
hours during one month (cm)
Applying the observed rainfall data to equation (+*), the values of EIm between /-, and-,-1* (t · m,/h/ha) with a mean of +,2./(t · m,/h/ha) were obtained in this experiment. These
values were two fold higher than Wischmeierand Smith’s rain erosivity index (equation (.)
and (/)). As shown in Table -, the Wischmeierand Smith’s rain erosivity index ranged from
-2/.0 to +/.1.2(t · m,/h/ha) with a mean of 2.+.2(t · m,/h/ha). An estimated rain erosivity index
between 3** and ,,/** (t · m,/h/ha) were also
found for Lampung areas (Manik and Afandi,+332) that were also higher than the values
found in this experiment.
-.. Surface runo#
The presence of weeds as well as the diameter of co#ee canopy inﬂuenced the runo# ratio
very signiﬁcantly. As shown in Table ., in the  3+

10

Table .
Rainy
SeasonPeriodRuno# and runo# ratio of each rainy season

Rainfall
(mm)

Runo#
(mm)
Cleanweeded

+st
,nd
-rd
.th
Total

30 Jan.30 Apr.
30 Oct.31 Apr.
32 Jan.32 Jun.
33 Jan.33 Jun.

,**,

Runo# Ratio(ῌ)

Paspalum

Naturalweeds

Cleanweeded
+/43
34*
340
14*

.0140
+*124,+1034.
+,.24/

1.4/
314/+034214-

042
*4/
*4*
*4*

.,4+
-4024*4*./0-41

.,240

14-

++-41

ﬁrst year of experiment, the average runo#
ratio was very high (+/.3ῌ, +./ ῌ, and 3.* ῌ forcleanoweeded plot, Paspalum plot, and naturalweeds plot respectively) compared to the otheryears, since the soil surface was relatively
open. The runo# ratio from the second to
fourth year experiment was 3.* ῌ, 3.0 ῌ and1.*ῌ for cleanoweeded plot ; *ῌ for Paspalum
plot ; and *.-ῌ, -.3ῌ and *ῌ for natural weeds
plot.
Although the total runo# of cleanoweeded
plot increased during the second year of experiment, its runo# ratio decreased due to theincrease of the co#ee tree canopy. The increasein co#ee coverage also reduced the runo# ratio
in the fourth year of experiment although therainfall was fairly high.
The runo# ratio for cleanoweeded plot was
higher than that found by Gintings(+32,) in
Sumber Jaya areas. Without cover crops, hefound a runo# ratio of +.12ῌ for +ῌyears old
co#ee with /30-ῌ slope gradient, and -.-3 ῌ
for -ῌyears old co#ee with slope gradient 0,00ῌ.
It was interesting to note that the Paspalum
conjugatum and natural weeds could reduce thesurface runo# drastically.
Paspalum conjugatum is a grass weed type, so the canopy
fully crept over the ground surface and its rootsystem was very dense and large. As a consequence, Paspalum conjugatum could intercept
the rainfall e#ectively and would act as runo#
barrier, thereby inhibiting the surface runo#
signiﬁcantly. Since the internal drainage ofPaspalum
+4/
*4*
*4*
*4*

Natural
weeds
34*
*4-43
*4*

soil proﬁle was very good, the runo# water
would inﬁltrate into the soil.
As shown in Table ,, a weed of tree typecalled Clibadia surinamense was present at natural weeds plot and could behave as a shadingtree. As consequence, the soil surface was not
fully covered with grass weeds type, so thesurface runo# was greater than Paspalum plot.
The e#ectiveness of cover crop in reducing
runo# was clearly shown in Table ..
In
Paspalum and natural weeds plot, the increasing of rainfall did not increase runo# height.
However, there exists a tendency in cleanῌ
weeded plot that runo# height would increase
with rainfall.
-. / Soil loss
The amount of soil loss in every month andthe total soil loss during the experimental
period are shown in Fig. 1, Fig. 2, and Table /.
In the ﬁrst year of experiment, the soil loss
from each treatment during the three months
observational period (FebῌApril +330) was asfollows : 2.2 t/ha in cleanoweeded plot, ,.1 t/ha
in Paspalum plot, and +./ t/ha in natural weeds
plot. Before the weeds covered the groundsurface, there was a little di#erence in soil loss
as shown in February +330 ; soil loss from
Paspalum plot was higher than the other plots
due to the fact that the ground surface was notcovered yet and was disturbed by transplanting Paspalum seedlings at this plot. One month
later (March +330), this situation was changed
drastically after the weeds began to cover the
ground surface ; the soil erosion from clean-῍ῌ : Soil Erosion under Co#ee Trees with Di#erent Weed Managements in Humid Tropical Hilly Area of Lampung, South Sumatra, Indonesia

Fig. 1

Fig. 211Monthly soil loss under co#ee tree with di#erent weed management.

Soil under co#ee tree with di#eremt
weeds management.

oweeded plot increased sharply.
The second year experiment began in October +330 and continued until April +331. The
soil loss from co#ee plot with general weed
management (cleanoweeded plot) in the second
year of experiment was ,,.1 t/ha, however it
could be *.*,2 t/ha if covered with Paspalum
conjugatum and *.+0 t/ha in natural weeds plot.
The weeds had already covered totally theground surface in Paspalum plot and naturalweeds plot (+**ῌ covered). However there
were big di#erences in weeds species (Table ,),which a#ected the amount of soil loss.
Paspalum plot was dominated by Paspalum
conjugatum, which was very e#ective in preventing soil erosion due to the fact that groundsurface was covered densely with Paspalum
whose canopy and root system would act as

runo# barrier and catch the direct raindrops
and prevent surface runo# from ﬂowing overthe ground surface. The natural weeds were
dominated by woody species and not so dense
compared to Paspalum plot. Thus, a chance forrainfall to pass the canopy and overﬂow on the
ground surface among the weeds existed.
Due to the long dry season in +331 because of
El-Nino e#ects, the third observation began in+332 for rainy season of +331/+332 and thefourth observation began in +333 for rainyseason of +332/+333. The soil loss from co#ee
with weeds was very small compared to cleanoweeded plot. The soil loss in +332 from cleanoweeded plot was 3.+ t/ha followed by naturalweeds plot *.01 t/ha, and no erosion was foundin Paspalum plot. In +333, the soil loss fromcleanoweeded plot was ..2 t/ha, and there wasno soil loss in both weedy plots.
Compared to the other research data with
di#erent crops in Indonesia, the soil loss fromthe co#ee areas was meager. However, comparing with the ﬁndings of Gintings (+32,) in
co#ee areas in Sumber Jaya, soil loss appeared
higher. The maximum soil loss in this experiment was found in cleanoweeded co#ee asmuch as ,,.1 t/ha. Utomo (+323) reported thatthe soil loss from a bare plot could be .,- t/ha.
During the four years experimental period
from +310 to+32*, Abujamin et al. (+32-) foundsoil loss from bare plot to be +3-./ῌ./, t/ha.

12



However, they also reported that the use of
Bahia grass (Paspalum notatum) strip with + m
width could suppress soil erosion to zero in thesecond and third year of experiment, whereas*./ m strip of Bede grass (Brachiara decumbens)
suppressed soil erosion until zero after the
fourth year of experiment.
Gintings (+32,) found that the soil loss from+ῌyear old Robusta co#ee with /30-ῌ slope
gradient was +.3. t/ha which was very low
compared to the soil loss from cleanoweededco#ee (,,.1 t/ha). On the other hand, the soil
loss from -ῌyears old co#ee with slope gradient0,00ῌ measured from May to October was+./1 t/ha (Gintings, +32,), which was lower than
the soil loss from cleanoweeded co#ee withsimilar age which was 3.+ and ..2 t/ha.
The e#ect of co#ee canopy on reducing soil
loss was demonstrated clearly in Fig. 2 and Fig.
3. Table . showed that in cleanoweeded plot,
runo# was ﬂuctuated but almost constantfrom the second to the fourth year of experiment. However, the soil loss tended to decrease
as shown in Fig. 2. It means that although theruno# ratio was relatively unchanged after thesecond year, the sediment which carried byruno# became smaller year by year as shownin Fig. 3. Increasing the co#ee canopy was the
major factor that was responsible of these phenomena. The co#ee canopy intercepted therainfall, hence the raindrops did not directly
strike the soil surface and soil aggregate did
not disperse, so runo# would carry less sediment.
-. 0 Soil loss tolerance
As shown in Table /, the soil loss from thisexperiment was very low ; the total soil loss
from cleanoweeded plot was around ..30 mm
for four years experiment or +.,. mm per year.
This value is below the soil formation rate inIndonesia, which is estimated about , mm per
year (Shah, +32,). If we took the average soil
loss only for three years observation (because
the +st experiment started too late), the average soil loss was around +,.31 t/ha or +.-/ mm/
yr. This value was also lower than the soil loss

3+

,**,

Fig. 3

Sedimentation of each plot.

Table / Total soil loss under co#ee with
di#erent weed management
Unit (mm)Year of
Clean-weeded
observation
plot

Paspalum
plot

Natural weeds
plot

+st
,nd
-rd
.th

*43+
,4-0
*4/*
+4+3

*4,2
*4**
*4**
*4**

*4+0
*4*,
*4**
*4*1

Total

.430

*4,2

*4,/

Average(mm/year)

+4,.

*4*1

*4*0

tolerance for that area which was estimatedbetween ,./-.1 mm per year (Manik et al.,+331) or ,,.. t/ha per year for Indonesia (Utomo,+33.).
..

Conclusion

The four years soil erosion research conducted in a hilly humid tropical area of
Lampung, Indonesia, showed that only +..,ῌ
of rainfall intensities could be categorized as
the erosive intensity (,/ mm/h). The maximum rainfall intensity was +,* mm/h, and the
maximum daily rainfall was 2, mm. A relationship between rainfall erosivity index (R : t · m,/ha/h) and daily rainfall (X : mm) was determined as follows :R+.0,. (Xῌ+*.3)
Soil loss from cleanoweeded plot ranged
from ..2 t/ha to ,,.1 t/ha. The total soil loss
from cleanoweeded plot was ..1* mm during
the four years experimental period, and +.+1῍ῌ : Soil Erosion under Co#ee Trees with Di#erent Weed Managements in Humid Tropical Hilly Area of Lampung, South Sumatra, Indonesia

mm/year was lower than the soil formation
rate in Indonesia.
The use of Paspalum conjugatum and naturalweeds as cover crop under co#ee trees wasvery e#ective in controlling soil erosion. The
soil loss from Paspalum plot was ,.1 t/haduring the ﬁrst year of experiment and becamezero after the third year. However, the soil loss
from natural weeds plot in the ﬁrst year was +./t/ha and zero after four years. Instead ofweeds coverage, the reduction of soil loss after
three years experiment was also caused byco#ee canopy through its rainfall interception.
The presence of weeds and the increasing of
co#ee canopy as the co#ee growth inﬂuenced
the runo# signiﬁcantly. Paspalum conjugatum
could suppress runo# until zero after the thirdyear of experiment, and in case of naturalweeds it suppressed until zero after four years.
Runo# in cleanoweeded co#ee decreased year
by year due to co#ee canopy growth, andruno# ratio became almost constant around 1ῌ
+*ῌ after the second year of experiment.
Both weedy plots showed the bad performance of co#ee growth. However, the use of
Paspalum conjugatum as cover crop in co#ee
garden was promising if managed optimally.
Since Paspalum has a shallow roots, it competes with co#ee’s root, thus these species haveto be introduced when the co#ee trees havegained enough height (about three years old).
Paspalum could be planted along strips between the co#ee plants or around the co#ee
canopy.
Acknowledgments
Appreciation is extended to Ministry of Education, Culture, and Sport of Japan, for funding
this study, and also to Dr. N. Sriyani, Mr. H.
Suprapto, Mr. H. Susanto, and Mr. A.T. Lubis
for supporting the weeds and some co#ee data.
Reference
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14

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