ῐ
J. Jpn. Soc. Soil Phys.
ῐ῎῍ῑῒ῏
No. 3,, p. -ῌ+0 ῍,**-῎Soil Physical Properties under Co#ee Trees with Di#erent
Weed Managements in a Hilly Humid Tropical Areaof 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, Indonesia, Jl. Sumantri Brojonegoro +,Bandar Lampung -/+./, Indonesia** Faculty of Agriculture, Gifu University, Gifu, Japan, +ῌ+ Yanagido Gifu /*+ῌ++3-, Japan*** Faculty of Environmental Science and Technology, Okayama University, Japan,-ῌ+ῌ+ Tsushimanaka Okayama 1**ῌ2/-*, Japan
Abstract
The e#ects of weed management under co#ee trees on soil physical properties were investigated during fourῌyears experiment in Lampung, South Sumatra, Indonesia. The treatments
were as follows : co#ee without cover crop (clean-weeded plot) ; co#ee with Paspalum conjugatum
as cover crop (Paspalum plot) ; and co#ee with natural weeds which was dominated by Clibadia
surinamense (natural weeds plot). Weed management was done every two weeks by clearing all
the weeds in clean-weeded plots, and cutting the weeds around the co#ee trees with diameter + m
for the weedy plots (Paspalum plot and natural weeds plot). The results showed that a better soil
physical condition was achieved when the soil surface under the co#ee trees was covered with
Paspalum conjugatum. The average soil organic-C in the soil proﬁle of Paspalum and naturalweeds plots were -, g/kg and ,1 g/kg respectively, which were higher than in clean-weeded plot
which had ,* g/kg of organic carbon. A smooth horizon boundary was found in Paspalum plot
due to the abundance of its roots which was also enhancing soil color more black, and the processof wetting and drying. A strong aggregate stability was found at the Paspalum plot as indicatedby penetrometer readings as well as water stable aggregate index. Two centimeters thickness of
hardpan which was developed at Paspalum plot made the water movement from upper layer
inhibited during the dry season. The highest porosity was found at Paspalum plot (*.0. m- mῌ-)followed by natural weeds plot (*.0, m- mῌ-) and clean-weeded plot (*.0* m- mῌ-). However, theaverage available water content was not di#erent between Paspalum plot and natural weeds plot,
and only *.+/ m- mῌ- higher than that of clean-weeded plot. The permeabilities varied among thetreatments, and this variance was biggest in the upper layer of Paspalum plot.
Key words : soil structure, co#ee, weeds, aggregate+.

Introduction

Co#ee is one of the main important exported
products of Lampung Province, Indonesia, andaccounts for about /*ῌ of Indonesian exported
co#ee (BPDῌAEKI, Lampung, +330 ; Bank Indonesia Bandar Lampung, ,***). The co#ee trees

are mostly grown in mountainous areas withhumid tropical climate, which is characterizedby high rainfall, more than ,/** mm/year(Afandi et al., +333). Due to rainfall pattern andtopographic condition, the erosion risk inco#ee areas is naturally very high. However,the soil erosion problem is more severe by the῏

4

Table +

3,,**-

Soil properties at the initial stage (+33/)

Depth
(cm)

pH
H, O

Total-N(g/kg)

Organic-C(g/kg)

CEC(cmol/kg)

Sand

*ῌ +*
+*ῌ ,*,*ῌ -/-/ῌ 0*
0*ῌ+**

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

,40
+40
*43
*41
*40

-.42
+240
243
24,
24,

+-4343
34241
241

*4,/
*4,/
*4,0
*4,0
*4,2

mismanagement of land in co#ee plantations
and cultivated land. In the future, soil erosion
from co#ee areas will be more serious due tothe rapid change of land use type from forest
areas to co#ee plantations ; in +31* the forest
occupied /1..ῌ of these areas, which was
reduced to ,+..ῌ in +33*. On the other hand,
the monoculture plantations (co#ee garden) increased from *ῌ in +31* to .+.2ῌ in +33* (Syamet al., +331).
The use of cover crop under co#ee trees isvery important to control soil loss and to maintain and improve soil structure. Beneﬁcial
e#ects of plants on improvement of soil structure usually are related to physical action ofplant roots and addition of organic matter.
Abujamin et al. (+32-) reported that the use of
Bahia grass (Paspalum notatum) strip and Bedegrass (Brachiaria decumbens) strip could suppress soil erosion to zero, and soil with stable
aggregate and higher organic matter content
was also achieved. The reduction of soil erosion was also achieved due to the increasing of
aggregate stability because of manure application (Utomo, +323). On the other hand, losing oforganic matter as much as .1ῌ occurred inbare condition due to soil erosion for two years(Suwardjo, +32+).
In Lampung areas, Indonesia, there are several ways to manage the cover crop under theco#ee trees. Some co#ee farmers used highcover crop such as Gliricidea sepium, Leucaena
leucocephala, and Pelthoporum pterocarpa as a
shading tree ; however, the most popular technology was “clean-weeded co#ee”, in which theco#ee was grown without high cover crop and

Texture (g/g)
Silt
Clay
*4,*4+0*4+*4+*4+/

*4/,
*4/3
*40+
*40+
*4/1

Bulk density(g/cm-)*430*43*433*43

by cleaning the entire surface ground cover. In
the viewpoint of co#ee production, the cleanweeded co#ee management, which was applied
for many years, had no signiﬁcant e#ect on
reducing co#ee production. However, the current use of more quantities of fertilizers by thefarmers is a#ecting the soil condition. Due tothe fact that the surface ground cover underco#ee trees (in the form of weeds) could be
used as erosion barrier and to improve soil
structure, an improvement under the existing
technology must be made. An evaluation on
rates of change in soil physical properties, especially in the long term, is necessary to conduct
the development of soil and water conservation strategies.
A fourῌyears experiment was conducted toevaluate the e#ects of weed management
under Arabika co#ee trees on soil physical properties in a hilly tropical area of Lampung,South Sumatra, Indonesia.
,.

Materials and Methods,. + Location of study site
The study ﬁeld is located at Sumber Jaya
District, Lampung Province, South Sumatra,Indonesia, with the slope gradient of around+/ and the elevation 1-/ m above the sea level(Afandi, ,**,). According to soil Taxonomy(Soil Survey Sta#, +332), this soil belongs to
Dystrudepts. Table + shows some selected soil
properties of initial conditions just after clearing all the weeds and bushes for planting theco#ee seedlings.
Table + shows that the soil was relatively
fertile with high organic matter and nitrogen ;ῐ῏ : Soil Physical Properties under Co#ee Trees with Di#erent Weed Managements in a Hilly Humid Tropical Area of Lampung, South Sumatra, Indonesia

slightly acid with moderate cation exchange
capacity. The average air temperature waslow, around ,,῎, (Afandi et al., +333), so thedecomposition rate of organic matter was relatively slow, and the soil organic carbon was
rather high compared to the other places, inwhich the elevation is lower and temperature
is higher in Lampung. In addition to that, thesoil was still relatively virgin. Although thesoil was dominated by clay fraction in all
depths, the bulk density was very low whichindicated the soil was friable and porous.
,. , Treatment
The treatments consisted of three plots with,* m slope length and 2 m width, which adjoined each other and had almost same soil
properties of initial conditions as shown in
Table +. The treatments were as follows :(+) Treatment + (clean-weeded plot) : Cleanῌ
weeded co#ee garden. Soil surface was always
keeping bare by hand weeding at two weeks
interval. This management is a general practice in this co#ee plantation area so it was
regarded as the control.
(,) Treatment , (Paspalum plot) : Co#ee
garden with Paspalum conjugatum as covercrop. Young Paspalum conjugatum was transplanted on the experiment plot in November+33/ and February +330.
(-) Treatment - (natural weeds plot) : Co#ee
garden with natural weeds as cover crop.
The plots were planted with Arabica co#ee
with planting distance +./ m by , m on November +33/. Weed management was done every
two weeks by clearing all the weeds in theco#ee plot (clean-weeded plot), and cutting theweeds around the co#ee trees with diameter +m for the weedy plots (Paspalum plot and natural weeds plot). Before and after the rainyseason, the Paspalum mats and natural weeds
were mowing at +/ῌcm height. The spray ofpesticides and the application of fertilizer havebeen adopted with the standard usual practice.
,. - Measurement of soil properties
a. Proﬁle description
A soil pit was made until +** cm depth in5

August +331 and September +333. Observationof two years time after planting was selected
because the changes in soil physical properties
took a long time. The soil color and the size ofsoil structure were observed based on JapaneseStandard Soil Color Charts.
b. Soil physical properties measurement(a) Penetration resistance (using a cone
penetrometer (DAIKI) until 3* cm depth)(b) Instantaneous soil moisture content(gravimetric method)(c) Pore size distribution or soil water content at ῍-.,ῌ῍+/2/ kPa (centrifuge
methods)(d) Permeability (using thin wall sampler
and falling head methods)
Three soil samples were taken for analyzing
the parameters of (b), (c), and (d) describedabove. Permeability and soil water content at
various soil moisture potentials at each depth
were measured at the end of the experiment in+333.
c. Changes of some dynamic soil properties(a) Organic carbon
Organic carbon was evaluated every year. A
soil sample from topsoil (*ῌ+* cm depth) was
taken in October +330 (one year after planting),
August +331, August +332, and March +333
(before the experiment ended). A composite
soil sample was taken from the upper, middle
and lower parts of the slope in each plot. Organic carbon was determined using theWalkey-Black Method.
(b) Aggregate stability index
The index of aggregate stability was measured one year after planting until the end of
the experiment by the techniques of DeBoodt
and DeLeenheer (+3/2*). About /** grams ofairῌdry aggregate was sieved through 2, ..10,,.2-, and , mm sieves (drying sieving). After
that, the aggregates from the drying sieving
are wetted with water drops until about ﬁeld
capacity ; kept in desiccators for about +,hours. Wetting sieving process was done afterwards using sieves of ..10, ,.2-, ,, +, *./ and *.,13  3,  ,**-

6mm. Aggregate stability index proposed by
DeBoodt and DeLeenheer (+3/2**) was calculated as follows.
AS+ῌMWDdryMWDwet+**ῌAS : Aggregate stability index (+*,/mm)
The mean weight diameter (MWD) was calculated with the following equation :῍

MWDdryῐ xiWi ῌWtῌ῏῎῍

xi : the mean diameter of each size fractions(mm)
Wi : the weight of each fraction (g)Wt : the total weigh of soil sample (g)The MWDwet for wetting sieving was also calculated as the above equation (,).
The values found in equation (+) could be classiﬁed as follows :,** AS : extremely stable
2* AS ,** : very stable
0* AS 2* : stable/* AS 0* : moderately stable.* AS /* : less stable
AS .* not stable-.

Results and Discussion

Field observation (soil proﬁle and soil
structure)
Field observation of soil proﬁle which wasdone in +331, two years after planting, showedthat there were very signiﬁcant changes in thesoil proﬁle, especially in upper layer, as shownin Table ,.
The abundance and distribution of weed
roots strongly a#ected the development of soil
proﬁle. Due to the fact that Paspalum roots
distributed almost in the same depth, theborder of the soil horizon was smooth (notwavy) in upper layer. The other two treatments had a wavy boundary at upper layer ofthe soil proﬁle. The type of weeds roots also
a#ected the soil color, especially under dry
conditions both directly and indirectly. The
abundance of weeds roots in Paspalum plot
made the soil color brighter under dry conditions due to the e#ect of root color. However,under wet conditions, both weedy treatments-. +had more black soil color that showed in low
chroma, which was an indication of organic
matter accumulation.
The soil structures in upper layer of bothweedy treatments were more developed thanthe clean-weeded plot. The basic type of soil
structure in all the treatments was angular
blocky, however, di#erent in size and ﬁeld consistency. The soil structure type in cleanweeded plot was ﬁne to medium angular
blocky with weak ﬁeld consistency. The abundance of Paspalum roots at upper layer (*῎,*cm) yielded a ﬁne to moderate crumb and angular blocky structure, friable but very stable,on the other hand, natural weeds plot also produced stable, medium to very coarse angular
blocky structure.
From the ﬁeld observation, it was clear thatthe development of soil structure in upper
layer in Paspalum plot was more complex thanthe other two treatments and it seemed to be
determined by three processes : mechanicalbinding of soil aggregates by root action,
cementing action by organic matter, as well as
the process of wetting and drying of the soil.
An observation that was made in the dry
season of +331 showed that the soil in Paspalum
plot was drier and harder than in the naturalweeds plot followed by clean-weeded plot because the abundance of Paspalum’s roots consumed more water than the other treatments,
so the evapotranspiration in this plot was very
high ; however under moist conditions, the aggregate was more friable than natural weeds
plot followed by clean-weeded co#ee probably
because Paspalum plot had more organic
matter.
As shown in Table ,, some cracks were
found in all the proﬁles with di#erent degrees
in length and depth. The main cause of thecracks was the existence of , : + type clay mineral. Lumbanraja et al. (+333) reported that soilin this area contained up to *.,/ g/g ofvermiculite-chlorite intergrades, a type of clay
mineral that posseses swell-shrink property.
However, the degree of cracking was di#erent῎῍ : Soil Physical Properties under Co#ee Trees with Di#erent Weed Managements in a Hilly Humid Tropical Area of Lampung, South Sumatra, Indonesia

Table ,

Soil Proﬁles two years after planting (observed in August, +331)
Treatment

Soil properties

Paspalum plot

Clean-weeded plot
Topsoil-Depth (cm)-Horizon border-Colour-Dry-Moist-Stucture
-Type
-Size
-Roots system-CrackingSubsoil-+-Depth (cm)-Horizon border-Colour(dry)-Stucture-Type-Size (dominant)-Roots system-CrackingSubsoil-,-Depth (cm)-Horizon border-Colour(dry)-Stucture-Type-Size (dominant)-Roots system-CrackingNatural weeds plot

*ῌ+*/+/
wavy, abrupt*ῌ+0smooth, clear*ῌ+*/,.
wavy, abrupt

1./ YR -/(dark brown)+* YR -/.
(dark brown)

1./ YR ./(brown)+* YR -/,
(brownish black)1./ YR -/,(brownish black)+* YR -/,
(brownish black)

Angular blocky

Crumb to Angular
blockyVery ﬁne to Medium
Paspalum roots(abundant)
Evidence(one cracks)

Angular blocky
Medium to very coarse
Various grass roots(many)
Evidence(two cracks)+*/+/ῌ-*di#use, smooth
1./ YR ./.
(brown)+0ῌ-1smooth, di#use
1./ YR //2(bright brown)+*/,.ῌ-/smooth, di#use
1./ YR ./.
(brown)

Sub angular blocky

Angular blocky

MediumCo#ee roots(less)
No

Crumb to Angular
blockyMediumPaspalum roots(less)
Evidence-*ῌ/*
di#use, smooth
1./ YR //0(bright brown)-1ῌ.1
di#use, smooth
1./ YR //0(bright brown)-/ῌ/0
di#use, smooth
1./ YR //0(bright brown)

Sub angular blocky
MediumGrass roots(small amount)
Evidence and ﬁlledwith soil from above(color 1./ YR ./.)

Angular Blocky
Fine
Grass roots (less)Angular blocky
MediumGrass roots (many)

Evidence until 1* cm
depth

Evidence until 1* cm
and ﬁlled with soil
from above (color 1./
YR -/,) and earthworm casting

Fine to Medium
Co#ee roots(less)
No

Note : Observation was done in dry condition

CoarseVarious grass roots(many)
Evidence and ﬁlledwith soil from above(color 1./ YR -/-)

7

8

Fig. +

  3,

Changes of organic carbon in topsoil
under co#ee trees with di#erent weed
managements.

among the treatments probably due to the activity of weed roots. In the clean-weeded co#ee
treatment, the cracks were found in the subsoil ;however, in both weedy treatments the cracks
were found from the upper layer until the
deeper layer. Many cracks were found in the
deeper layer of natural weeds plot, which was
dominated by woody species known as
Clibadia surinamense with deep roots. Insteadof mineral type discussed above, the existenceof root system in this layer enhanced the soil
cracking. The roots extracted more water fromthis depth, and make the process of wetting
and drying of the soil proceed at a faster rate.
Soil particles and organic matter from theabove layer, which made a form like a ﬁnger
until 1* cm depth, ﬁlled the cracks.
Soil proﬁle observation made in +333 wasquite similar to that of +331, except that thedepth of topsoil in Paspalum plot (as indicatedby the dark soil color) increased from +0 cm to,* cm. The other soil properties were almost
the same.
-. , Soil organic carbon (SOC)
The average soil organic carbon (SOC) in
Paspalum and natural weeds plots were -,.+ g/
kg and ,0./ g/kg respectively, which werehigher than in clean-weeded plot which has,*., g/kg of organic carbon (Fig. +). The valueof SOC in clean-weeded plot was almost constant, probably due to the low soil erosion
during fourῌyears of experiment which wasaround /.* mm of soil depth. However, the,**-content of SOC matter in clean-weeded plot
decreased compared to the initial stage (Table+) due to little supply of organic matter underno cover crops. The value of SOC decreased in+331 due to the long dry season, so the additionof soil organic matter decreased. As reported
by Sriyani et al. (+333), there was a sharp decrease in the number of weed species due to thelong dry season in +331.
The content of organic carbon was maintained to be as high as initial stage in Paspalum
plot. Paspalum conjugatum is a grass species ;as stated by Tisdall and Oades (+32,), organic
matter might have accumulated under good
pastures because the annual addition of phytomas was greater. The roots of grasses areshortῌlived, so each-year decomposition ofdead roots contributes to the quantity of
humiﬁed organic matter (Foth, +312).
-. - Penetrometer resistance
The penetrometer data, especially in upper
layer, gave a very di#erent result when measuring was done in dry and rainy season asshown in Fig. ,, and which supported our
proﬁle observation. It seemed that the behavior of soil water in each treatment inﬂuenced
these results because the soil water content
mainly determined the penetrometer resistance.
In the dry season measurement, a very compact and hard surface layer (,/ kgf/cm,) approximately at , cm depth was found in
Paspalum plot. Although it was not as hard asin Paspalum plot, the penetrometer resistancein natural weeds plot was also higher thanclean-weeded plot. Field observation showedthat at upper layer the soil condition was drierin weedy plots compared to clean-weeded plot
because the weedy plots consumed more water
than clean-weeded plot. Furthermore, penetrometer resistances in whole layer were higher inweedy plots than in clean-weeded plot, whichshowed that the soil conditions of weedy plots
were dry compared to clean-weeded plot due tothe soil water uptake of weed roots especiallyin dry season as shown in Fig. - described later.

ῐ῏ : Soil Physical Properties under Co#ee Trees with Di#erent Weed Managements in a Hilly Humid Tropical Area of Lampung, South Sumatra, Indonesia

Fig. ,

Fig. -

9

Soil resistance measured by penetrometer under dry condition (left : October, +333) andmoist condition (right : January, +331).
(ῌ : clean-weeded plot ; ῍ : Paspalum plot ; ῎ : natural weeds plot)

Soil moisture content under co#ee trees
with di#erent weed managements.
(ῌ : clean-weeded plot ; ῍ : Paspalum
plot ; ῎ : natural weeds plot)

Observation which was done in the rainyseason (Fig. ,) showed that the penetration resistance in Paspalum plot was less than / kgf/
cm, in the upper layer, and in natural weeds

plot and clean-weeded plot the values were /kgf/cm, and +/ kgf/cm, respectively. Thisdata showed that the soils in Paspalum andnatural weeds plots were wetter and retained
more water in upper layer during rainy season,so the soil would be more friable.
-. . Instantaneous soil water content
The proﬁles of soil water content during longdry season in +331 and normal dry season in+332 are shown in Fig. -. Soil moisture content
in this ﬁgure is the average of three soil
samples at each depth.
Both observations showed that Paspalum
plot could retain higher soil water content in
the upper layer, whereas during the long dry
season in +331, the clean-weeded plot held moresoil water content in the lower layer (,*ῌ+**cm). In normal dry season in +332, the soil
water content in the deeper layer of each plot
was almost the same.
It seems that the above phenomenon was
related to the soil surface condition as indicated by the soil resistance shown in Fig. ,.
At Paspalum plot, the evapotranspiration was
found to be higher during the dry season,
hence the soil surface became hard and about ,cm of hardpan was developed. As a consequence, during the dry season the water move-

10

Table -

3,,**-

E#ects of weed management under co#ee trees on solid, porosity and water content at
various pF (+333)
Water content

Treatment

Depth
(cm)

Solid
(m- m-)Porosity(m- m-)-., kPa

+* kPa-, kPa

+/2/ kPa(m- m-)Clean
WeededCo#ee

Co#ee
PaspalumCo#eeNatural
Weeds

/
+/
,/
-/

*4.+*
*4.**
*4-3.
*4-3.

*4/3*
*40**
*40*0
*40*0

*4.3.
*4/.0
*4//*
*4/1/

*4.02
*4/-1
*4/.+
*4/01

*4../
*4/-*
*4/-/
*4//2

*4-/,
*4..,
*4../
*4./0

Average

*4.**

*40*+

*4/.+

*4/,2

*4/+1

*4.,.

/
+/
,/
-/

*4-/0
*4--/
*4-/1
*4-1.

*40..
*400/
*40.*40,0

*4/**
*4/*3
*4/1,
*4/12

*4-00
*4.23
*4/.,
*4//-

*4-.*4.1+
*4/,1
*4/.+

*4,,*4-0+
*4.,+
*4.-3

Average

*4-/0

*40./

*4/.*

*4.22

*4.1+

*4-0+

/
+/
,/
-/

*4-13
*4-/*
*4-2/
*4.+*

*40,+
*40/*
*40+/
*4/3*

*4/,+
*4.*1
*4/*1
*4/..

*4/*,
*4-3,
*4.32
*4/-3

*4.2+
*4-1.
*4.23
*4/-+

*4-0+
*4,/0
*4-2.
*4.-1

Average

*4-2+

*40+3

*4.3/

*4.2-

*4.03

*4-0*

ment from the upper layer was inhibited, andthe roots of Paspalum as well as natural weeds
would took water from the deeper layer.
-. / Solid and soil water content
The composition of three phases of soil ispresented in Table -. The soil was clayey (clay*./+ g/g as shown in Table +) with high organic matter, so naturally the total porosity
was very high. The average total porosity
ranged from *.0*+ m- m- to *.0./ m- m-. The
highest porosity was found at Paspalum plot(*.0./ m- m-) followed by natural weeds plot(*.0+3 m- m-) and clean-weeded plot (*.0*+ mm-). As a consequence, the solid phases ofPaspalum and natural weeds plot were lower
than that of clean-weeded plot. It is interesting
to note that the existence of cover crop, especially at Paspalum plot, has changed the solidpore composition although the change wasvery small.
The existence of Paspalum and naturalweeds also a#ected the water contents of -.,,+*, -, and +/2/ kPa as shown in Table -.

The water contents at -.,, +*, and -, kPa
were lower in Paspalum and natural weeds plot
than clean-weeded plot and as a result theamount of big pore as shown in Fig. . at bothweedy plots were higher because those
porosities were higher. Both weedy plots had
aeration pore (water content between saturated and -., kPa) as much as 1/ῌ+*1ῌ higher
than clean-weeded plot ; for macro pore (watercontent between saturated and +* kPa), therange was 20ῌ++/ῌ higher ; and for coarse pore(water content between saturated and -,kPa) was 13ῌ+*1ῌ higher. Because the total
porosity was highest at Paspalum plot, themacropore and coarse pore were found to behighest for this treatment. The coarse pore in
Paspalum plot was higher as much as +*1ῌ and+0ῌ than clean-weeded plot and natural weeds
plot respectively.
The main function of large pores is anavenue for inﬁltration and drainage of water.
The aeration pore would transmit water
during saturated condition. The macro andῑῐ : Soil Physical Properties under Co#ee Trees with Di#erent Weed Managements in a Hilly Humid Tropical Area of Lampung, South Sumatra, Indonesia 11

Fig. .

E#ects of di#erent weed managements on pore composition (+333).
(῍ : clean-weeded plot ; ῎ : Paspalum plot ; ῏ : natural weeds plot)coarse pore which included aeration pore could
transmit and drain water during inﬁltration.
Macro pore could cause to drain gravitational
water quickly and coarse pore could cause todrain gravitational water slowly. Thus thenumber of these pores will a#ect surface runo#
as well as soil erosion. During the process ofdrainage under a saturation condition, thewater in aeration pore will be empty initially,
and as a consequence the natural weeds plot
which had higher aeration pore would be drierﬁrst, followed by Paspalum plot. In case of wet
condition (water content between saturated
and ﬁeld capacity), the Paspalum plot which
had highest coarse and macro pore would inﬁltrate water faster than the other treatments.
The average available water content (watercontent between ῌ-, and ῌ+/2/ kPa) for eachtreatment was almost the same, i.e. *.*3- mmῌ-, *.++* m- mῌ- and *.+*3 m- mῌ- for cleanweeded, Paspalum and natural weeds plot respectively.
The existence of weeds had
decreased the value of permanent wilting point(ῌ+/2/ kPa), however, at the same time thevalue of ﬁeld capacity (ῌ-, kPa) also decreased
simultaneously, therefore the available watercontent did not change. This situation is shownin Fig. /.
The distribution and activity of roots in eachtreatment has strongly inﬂuenced the amountof large pore in each depth as shown in Fig. ..
The abundance of Paspalum roots in the upper
layer made this plot to have bigger large pores
than the other two treatments, however, as theroots decreased with depth, the number ofpores also decreased. On the other hand, at +/cm depth, the highest big pores were found atnatural weeds plot due to the abundance ofroot system in this depth of natural weeds plot.
As the roots system decreased with depth, theamount of large pores became similar.
-. 0 Aggregate stability
It is very interesting to note that the patternof aggregate stability in each plot (Fig. 0) is
almost similar to the pattern of organic carbon,
which indicated that organic matter has a very
important role in stabilizing the soil aggregate.
The fact that the values of aggregate stability

12Fig. /



3,,**-

E#ects of di#erent weed managements
on available water content (+333).

at clean-weeded plot were almost unchanged
during fourῌyear duration of the experiment,
which supported this argument. The aggregate stability at weedy plots was higher thanclean-weeded plot, both in topsoil and subsoil.
The higher aggregate stability both in
Paspalum and natural weeds plots was mostly
related to development of soil structure
through the action of weed roots. In the lastyear observation, Paspalum, which possessed
the highest organic matter content, had thehighest aggregate stability. Instead of the existence of organic matter, ﬁeld observation also
showed that a mechanical binding by root hairof Paspalum was also responsible for increasing
aggregate stability.
The other process that was also responsible
for the development of soil structure was intermittent wetting and drying processes. The
treatments gave di#erent response to wetting
process due to rainfall events and drying process occurred by evapotranspiration events.
Fig. 1 shows the dynamics of soil moisture suction measured by self-recorded tesiometer after
rainfall events. As shown in Fig. 1, at / cm
depth, Paspalum absorbed water and the soil
become saturated very quickly due to a rainfall
event. However, when this plot started to dry,the water in upper layer depleted faster thanthe other treatments. A similar process occurred at natural weeds plot at ,/ cm depth, because many cracks were found in this depth
due to the quick wetting and drying process.

Fig. 0Aggregate stability under co#ee trees
with di#erent weed managements
measured in di#erent years.

The development of the cracks would promotesoil structure development.
-. 1 Permeability
Three soil samples were taken by cylindricalsamplers +* cm in height at each depth of /, +/,,/, and -/ cm for analyzing permeability. Alldata of the permeabilities at every depth areplotted in Fig. 2.
The maximum and minimum permeability
values were found at the same depth (+* cm
depth) of Paspalum plot, i.e. +.++*+ cm/s and,.1+*. cm/s respectively. The great variation in these data was due to several reasons,such as the properties of the soil to shrink andswell and the existence of surface crust (about, cm thick) in Paspalum plot. A thin hardpan
with about , cm thickness was found in the soil
surface of Paspalum plot ; however, the hard-῍ῌ : Soil Physical Properties under Co#ee Trees with Di#erent Weed Managements in a Hilly Humid Tropical Area of Lampung, South Sumatra, Indonesia 13

Fig. 1

Dynamics of soil moisture suction in each plot (April 0ῌ1, +330).

pan had not totally covered the soil surface.
The hard pan, which was developed due tosurface crust, had made the lowest value of
permeability at Paspalum plot ; part of the soil
surface, which was not covered with the surface crust, had a very high permeability. Sucha combination of two permeability values
would give a good e#ect on preventing soil
erosion, because the hard surface crust would
have a strong aggregate stability, and at thesame time, the surface runo# water would
enter into the soil proﬁle at a much faster rate.
Surface crust also occurred in natural weeds
and clean-weeded plot, but not as hard as inPaspalum plot.
As shown in Fig. 2, there was a tendency inall treatments that the permeability values
were lower at the upper soil and increased at+*ῌ-* cm depth, and decreased in the lower
part. The existence of surface crust was responsible for lower permeability at the upper
layer, and with increasing depth below plowlayer (+/ῌ,* cm depth), the soil tended to be
more compact and hence the permeability
decreased.
-. 2 General discussion
The above discussion proved that the soil
cover in the form of weeds could change thesoil physical properties. The process was quite
di#erent between grass weeds like Paspalum
sp. and woody weeds like Clibadia sp. in natural weeds due to the di#erent root system.
Some processes involved addition of organic
matter, evapotranspiration, and mechanicalbinding. Paspalum is a grass type of weed, andits roots are short-lived so each-year decomposition of dead roots would contribute to thequantity of humiﬁed organic matter. The root
hair of Paspalum could also bind the soil particles mechanically, and if transpiration
occurred, the soil released its water andbecame harder and much more stable. The factthat soil in Paspalum plot gave a quicker response in wetting and drying at the upper
layer also proved that the abundance ofPaspalum’s roots a#ected aggregate development. The fast process of wetting and drying
enhanced the formation of cracks and aggregates. In case of natural weeds, the wetting
and drying process occurred in deeper layer,
and materials from the above layer would ﬁll
the crack.
The results of the above process were that
Paspalum plot had much organic matter withstable aggregate stability and higher large
pores. Some soil properties in clean-weeded14

3,,**-

runo# would be less. As discussed by Afandi etal. (+333), the soil loss and runo# from Paspalum plot was very low and reached zero in
the third and fourth years of the experiment.
However since the process of wetting anddrying was quicker as this grasses consumed
more water, the use of Paspalum was not as
good as natural weeds, from the viewpoint ofwater conservation. In natural weeds plot,
cracking which occurred in the deeper layer
would make the inﬁltration water ﬂow into
deeper layer, so natural weeds was better than
Paspalum from the viewpoint of water conservation.
..

Fig. 2

E#ect of weed management underco#ee trees on soil permeability (+333).

plot were almost constant during four years,
probably because less soil erosion occurred andthe decomposition rate of organic matter was
slow due to low average temperature (,,).
The soil properties in natural weeds plot were
between the other two treatments. A ﬁngering
appeared in natural weeds plot which consisted of materials from the above layer.
From the viewpoint of soil conservation, theuse of Paspalum conjugatum as cover crops
gave many beneﬁcial e#ects for protecting soil
erosion. Stable aggregates would make the soil
strong enough against rainy drop, and highcoarse pore would enhance inﬁltration rate, so

Conclusion

The existence of weeds under co#ee trees asa cover crop has improved some soil physicalproperties, such as the increasing of soil organic carbon, aggregate stability, porosity, bigpore (macro, coarse, and aeration pore), anddecreasing the permanent wilting point. The
average soil organic carbon (SOC) in Paspalumand natural weeds plots were -,.+ g/kg and ,0./g/kg respectively, which were higher than inclean-weeded plot which was relatively constant (,*., g/kg) during four years of experiment. A thin (about , cm thick) hardpan, whichdeveloped at the soil surface in Paspalum plot,
has inﬂuenced some soil physical properties,
such as the penetrometer resistance, aggregatestability, instantaneous soil water content, andgreat variation in permeability values. The
highest porosity and large pores (macro,coarse, and aeration pore) were found at
Paspalum plot followed by natural weeds plot
and clean-weeded plot. The available watercontent was not di#erent between Paspalum
plot and natural weeds plot, and only *.+2 mm- higher than that of clean-weeded plot, because the values of ﬁeld capacity and permanent wilting point were small simultaneously
at both weedy treatments.

῍ῌ : Soil Physical Properties under Co#ee Trees with Di#erent Weed Managements in a Hilly Humid Tropical Area of Lampung, South Sumatra, Indonesia 15

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