ῐ
J. Jpn. Soc. Soil Phys.

No. +*2, p. 2+ῌ3* ῍,**2῎Amendment of Soil Physical and Biological Properties
Using Rice Husk and Tapioca Wastes
KOMARIAH*, Kengo ITO**, Masateru SENGE**,John Tawiah ADOMAKO** and AFANDI**** Graduate School of Agriculture, Gifu University, Yanagido +ῌ+, Gifu City, Japan** Faculty of Applied Biological Science, Gifu University, Yanagido +ῌ+, Gifu City, Japan*** Soil Science Department of Lampung University, Jl. Sumantri
Brojonegoro No. + , Bandar Lampung, Indonesia
Abstract
A ﬁeld experiment in a pineapple plantation at Lampung Province of Indonesia was conducted
for +/ months to investigate the e#ect of rice husk and tapioca wastes (cassava bagasse andcassava peel) used as organic amendments, on soil physical and biological properties. The
treatments included control, rice husk mulch, cassava bagasse mulch, cassava peel mulch, cassava
peel-soil mixture and black polyethylene ﬁlm mulch. The organic materials were applied
manually at a rate of -* kg m,. The soil physical and biological properties at the initial and ﬁnal
stages of the experiment were measured and compared. The results showed that the moderate
rate of rice husk’s decomposition process slightly increased SOM of surface layer that may had led
to somewhat decreased particle density and available water content enhancement. On the other
hand, cassava bagasse mulch decomposed within very short period after application and thus its
roles especially in soil physical properties were no more noticeable in +/ months after its
application. Due to the slow decomposition rate, +/ months was probably too short for cassava
peel to contribute in SOM enhancement as well as other soil physical properties. However, theapplication of investigated organic materials for soil amendment resulted in the more abundance
earthworm populations, bulk density decreasing, and the increases of macro pores and WSA in
general. The existence of earthworms in the soil is certainly contributed positive e#ects in the soil
properties, especially physical soil properties. But which soil properties that were most a#ected by
the earthworm activities cannot be concluded, since other factors such as soil microorganisms
could also play a role in promoting soil properties enhancement.
Key words : Indonesia, soil organic matter, Red-Yellow Podzolic, organic mulch, tapioca wastes,
earthworm+.

Introduction

Soil deterioration is an important problem inpineapple plantation areas, such as Indonesia,
due to the long period of pineapple life cycle
and the tropical monsoon climate. The ﬁrst
harvest time could take about +/ to +2 months
from seedlings, and optimum production could
still be obtained at the third harvest time, which

could take about three years. Long culture
period, high annual rainfall and high mean
temperature all year long in tropical monsoon
climatic countries result in decreasing of soil
physical, chemical and biological properties.
Erenstein (,**-) stated that soil degradation
process could be arrested by the application oforganic mulching. Organic mulching also gradually improves the soil physical and biological

῏

82



properties. Crop residues have also been widely used for organic mulching studies. Straw
mulches contributed organic matter to the soil,
hence increasing inﬁltration and reducing mechanical impedance (Tindall et al., +33+). Furthermore, Lal et al. (+32*) showed that applying+., kg m, straw mulch was e#ective in suppressing soil erosion up to *ῌ after deforestation. Application of plant residues as mulch in
the tropics is known to improve the soil microclimate, besides providing food for earthworms(Tian et al., +33-). Many studies have shown
the importance of worm activity to soil productivity and thereby to plant growth.
Organic mulching materials could be obtained not only from the crop residues of postharvest, but also from the waste of agriculturalindustries. For example, cassava peel and cassava bagasse wastes are generated in the tapioca industries during tapioca production process. Generally, in the tapioca production, +,***
kg of cassava would produce about ,** kg tapioca and almost 2** kg solid wastes (Trade andIndustry Dept. of Indonesia, ,**-). Meanwhile,
the area for cassava cultivation in Lampung
province, Indonesia in ,**. was ,00,/20 ha, andthe total cassava production was ..01 +*3 kg(Lukita G., ,**/). It means that there are abundant tapioca wastes, which sometimes evoke
environmental problem by spreading o#ensive
smell in the surroundings. The daily production of tapioca wastes is relatively high but
their utilization for industries and livestock
feed is limited. Therefore, the utilization of
those wastes for environmental conservationmust be developed, especially to improve soil
properties as soil amendment.
The studies and investigations of industrial
wastes amendment as alternatives for wastes
disposal and environment enhancement havebeen widely conducted. The application of waste
paper product by Brauer and Aiken (,**0) for
soil amendment near Booneville (USA) to decrease the risk of phosphorus (P) transport tosurface water showed an increase of soil
carbon content (i.e. organic matter) and the+*2

,**2

decreasing of soil bulk density, but had noe#ect on soil test P value. Seth et al. (,**/)
utilized +/ t ha+ of composted sugar industry
waste (pressmud) in a sodic soil to evaluate thesoil properties and rice growth and found thatthe pressmud and its di#erent composts signiﬁcantly increased the plant height, grain andyield. Zheljazkov (,**/) investigated that wool
and hair wastes decompose slowly under bothof ﬁeld and greenhouse conditions, and theirapplication of only -.- g kg+ for soil amendment may support crop yield, which became
double to ﬁve times bigger and would improvesoil biological and chemical characteristics.
Foley and Cooperband (,**,) found that amending soil with paper mill residuals signiﬁcantly
increased total soil C and increased plantavailable water by / to ./ῌ. The experiment
by Mantovi, P. et al. (,**/) using composted
sewage sludge for long-term application on soil
resulted in the increasing of organic matter,
total N and available P in the soil. Signiﬁcant
increases in total organic carbon and aggregatestability were observed in the plots amended
with two-phase olive-mill waste on degradedagricultural soil (Lopez-Pineiro et al., ,**1).
The researches about the utilization of various organic materials mentioned above, including industrial wastes for soil amendment resulted in di#erent e#ects. But, in spite of theabundance of tapioca production in South-East
Asia, especially Indonesia, the application oftapioca wastes as an alternative for soil amendment and their e#ects on soil physical andbiological properties are not covered in literatures. Therefore, the aim of this experiment
was to investigate the inﬂuence of crop residue(rice husk) and tapioca wastes (cassava peeland cassava bagasse) in particular, on the amendment of soil physical and biological properties.
,.

Materials and methods

The experimental ﬁeld was located in a pineapple plantation owned by Great Giant Pineapple Company (GGPC) in Lampung province ofIndonesia, lying on latitude ./3῍ S and longi- : Amendment of Soil Physical and Biological Properties Using Rice Husk and Tapioca Wastes

tude +*/+-῎ E. The site consisted of Red-Yellow
Podzolic soil with predominantly sandy loam
texture. The site used had previously beencultivated with pineapple for three continuous
years followed by one-year cassava cultivation.
The investigation was conducted from July,**+ to September ,**,. The experiment waslaid out in a randomized complete block design
with three replications. Each plot consisted of
two beds, measuring *.0 m+/ m, and a heightof *.+/ῌ*., m. Each bed was planted with 0*
smooth cayenne pineapple seedlings in two rows.
The experimental treatments were : control,
rice husk mulch, cassava bagasse mulch, cassava peel mulch, cassava peel-soil mixture andblack polyethylene ﬁlm mulch. The typicalsize of rice husk used in the experiment was 2ῌ
+* mm in length, ,ῌ- mm in width and about *.,mm in thickness. Cassava bagasse was in granular form with the diameter of bigger than *.2.
mm. Cassava peel was chopped in irregularshape with *.,ῌ*.- mm in thickness and /ῌ,*mm in diameter. The rice husk, cassava bagasse and cassava peel mulches were manuallyapplied by hand at a rate of -* kg m, based on
wet basis, and this resulted in mulch height of,ῌ/ cm. The rate of -* kg m, of application
was adjustable to the abundant availability oforganic amendments in the surounding. Regarding the cassava peel-soil mixture, cassava
peel was thoroughly mixed with the soil toapproximately -* cm depth in the middle ofJune ,**+. The seedlings were transplanted inlate June ,**+ and mulching was completely
applied on soil surface in late July ,**+. Pineapple fruits were harvested in September ,**,.
Total rainfall was ,,22- mm and total evaporation from evaporation pan class A was +,12,mm during +/ months of experiment period.
Maximum air temperature was ./.2 and thisoccurred on January -+st ,**,, while the minimum air temperature of +1.+ was observed on
August +/th ,**,.
Initial soil sampling was performed to obtain
the disturbed and undisturbed samples in late
July ,**+, just after mulching application ac-

83

complished. The ﬁnal soil sampling was conducted in the early of October ,**,, soon after
the pineapples were harvested. Soil sampling
was taken in the depths of *ῌ/ cm, /ῌ+* cm, +*ῌ
+/ cm and +/ῌ,/ cm with three samples for each
depth of each treatment. Undisturbed soil
samples were performed with +** cc soil coresto determine bulk density and soil water potentials, and disturbed soil samples were taken to
determine particle size distribution especiallyclay fraction distribution, particle density, totalsoil organic matter (SOM) content and waterstable aggregate (WSA).
The soil water retention curve at +*, -*,+**, -** and +,/** kPa was determinedusing a centrifuge apparatus (Kokusan H-,***B). Based on the standard methods of soil
physical analysis described in JSSMFE (+33+),
particle density and particle size distribution
were determined using pycnometer and thehydrometer methods, respectively. Clay fraction distribution with the particle size of*.**,
mm was classiﬁed according to the International Soil Science System (Foth, +32.). WSA wasdetermined using a set of wet-sieving cylinder
having , mm, + mm, /** mm, ,/* mm and +** mmmesh sieves arranged in that order. The WSA
was expressed as the percentage of soil mass
with the aggregate fraction of ῌ*.,/ mm. The
loss on ignition method was used to determine
the SOM content (JSSMFE, +33+). The physicalsoil properties mentioned above were analyzed
statistically using Mann-Whitney U-Test at 3/῍probability level.
Soil temperatures were measured using thesilver-copper thermocouple cords at the depthof *ῌ,/ cm, and soil moistures were measured
at *ῌ-* cm of depth with the Time Domain
Reﬂectometer (TDR) probes. Both of soil temperature and soil moisture measurements wereconnected to a CR,-X data logger and recorded
every ten minutes, the data were taken only at
one point at each treatment.
Soil biological property observed was earthworm population at each rainy and dry season.
Soil pits of *.- m*.- m size were dug in each



84

Table +

Treatment

Control(No mulch)

Changes of soil physical properties under various treatments

Clay Fraction
SOM
Particle Density
Depth
initial ﬁnal initial ﬁnal
initial
ﬁnal
(cm)
,
+
+
+* kg kg
+* kg kg
+* kg m-

initial

*ῌ /
/ῌ+*
+*ῌ+/
+/ῌ,/

+4+.
+4+1
+4+1
+4,-

,*4*
,*4*
,*4*
+04*

Signiﬁcance within treat4

Rice husk
mulch

*ῌ /
/ῌ+*
+*ῌ+/
+/ῌ,/

*ῌ /
/ῌ+*
+*ῌ+/
+/ῌ,/

04,
+/4*
+*42
+,4*

*ῌ /
/ῌ+*
+*ῌ+/
+/ῌ,/

*ῌ /
/ῌ+*
+*ῌ+/
+/ῌ,/

Signiﬁcance within treat4

-+
-,
-,
-+

//
.+
-0
-3
S

,4/+,
,4/.2
,4.-3
,4//1

*4,3
*4-*
*4-0
*4-/

*4/*4.3
*4.1
*4.S

+4+/
+4+.
+4,3
+4-*

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

*4/.
*4/.
*4/.
*4/,
S

+4*2
+4*1
+4++4,-

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

*4-0
*4.0
*4.*4..

*4.1*4-/*4-*4-+

*4-.
*4,1
*4,1
*4+.

NS
,400.
,4010
,4003
,4002

S

*4-/
*4-1
*4-2
*4-,

S
,401/
,41+*
,4002
,401.

*4-*4.3
*4.1
*4..

S
+4*+
+4*2
+4,2
+4,/

+4++4+3
+4-/
+4-1

NS
-+
,2
,3
--

*4,2
*4-.
*4-*
*4,3
S

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

+4+/
+4+2
+4,+4+2

ﬁnal

kg kg+

NS
,401+
,402*
,4003
,400.

,40/,4011
,40/.
,402*

S
+*4*
342
04+*4.

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

S
,1
,1
,2
,1

initialS,401,401+
,4013
,402-

,40/,40/,
,40.3
,40/,

+4+*
+4+/
+4,.
+4-,

WSA

NS
,401+
,402*
,4010
,403*

,400,
,4003
,4003
,400,

-

+* kg m

S
,1
,2
,3
,2

-,
-,
-,
-,

S

S

-+
,1
,1
,0

ﬁnal

-

NS

S
.4*
.4*
14+
04.

+34*
,*4*
,*4*
,*4*

,4021
,403*
,402.
,402-

S
.4,
04*
14.
14.

,4021
,403,
,4022
,4022

Bulk Density

S
-0
,3
-,3

--.
-/
--

S

Signiﬁcance within treat4

Cassava peel-soil
mixture

--/
-.
-.

S

+.41
+*4+
+.4/
140

,401*
,4012
,4023
,4023

NS
.43
042
+-4+
++4-

+/4*
+,4*
+/4*
+24*

,2
,2
,3
-*
S

.4*
/4+
34*
34*

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

Signiﬁcance within treat4
*ῌ /
Black
/ῌ+*
polyethylene ﬁlm
+*ῌ+/
mulch
+/ῌ,/

-.
-.
-/
-+

S

Signiﬁcance within treat4

Cassava bagasse
mulch

24.
.4,
/4*
/42
S

Signiﬁcance within treat4

Cassava peelmulch+*2  ,**2

*4.0
*4.*
*4.0
*4/,
S

*41+
+4*.
+4,3
+4-,

*4-*
*4,.
*4,/
*4-+

NS

*4/2
*40*
*4/2
*4/3
S

Note : Initial sampling : July ,**+ ; Final sampling : October ,**,
*S : Signiﬁcant di#erent at Pῌ*4*/ using Mann-Whitney U-Test ; n++, ; n,+,

treatment and the earthworm population (individual m,) at depths of *ῌ+/, +/ῌ-* and -*ῌ./cm with three replications were sampled andobserved using hand-sorting method (Svendsen,+3//). The earthworm population was thenanalyzed statistically using ANOVA followedby Duncan’s Least Signiﬁcant Di#erence (LSD)
test at 3/῍ probability level.
-.

Results and discussion-. + Clay Fraction Distribution
The clay fraction changes at *ῌ/, /ῌ+*, +*ῌ+/῕῔ : Amendment of Soil Physical and Biological Properties Using Rice Husk and Tapioca Wastes

Fig. +

85

Clay fraction change at *-,/ cm depth for +/ months(Initial sampling : July ,**+ ; Final sampling : October ,**,)and +/ῌ,/ cm of depths in Table + shows thatclay fractions decreased in all treatments at all
depths. From Table +, it is di$cult to informthe decreasing trend of clay fraction at each
depth between treatments since they do notshow a particular tendency in detail. Therefore, Fig. + that shows the percentage of clay
fraction at *ῌ,/ cm depth at initial and +/months later, is also presented to simply understand the changes. It is shown that the clay
fractions signiﬁcantly decreased in all treatments at *ῌ,/ cm of soil depth. It was assumed
that the clay was leached into deeper soil
layers. Water inﬁltration through the soil surface during rainy days may have caused theﬁne particles dispersion, therefore clay fractions leached into deeper layers through cracks
and soil pores. This clay leaching had caused
texture change from sandy loam to loamy sandsoil in the whole treatments. The degradationof soil physicochemical properties due to clay
particle leaching has been an inherent big problem in and around the study site. Due to thefragile nature of the soil, deep plowing is usually undertaken before the next plantation cycle
to bring the clay particles up to surface andthus improve soil physical properties. The

practice of amending the soil with organic materials at the experiment site was also aimed atpreventing clay-leaching problem. But, it has
been shown distinctly that irrespective of thetreatments applied, the clay content signiﬁcantly decreased in all treatments. Vinyl mulchthat completely protected soil surface fromwater inﬁltration during precipitation shouldhave prevented clay from leaching into deeper
layer. But the vinyl mulch, just as the organic
mulches, in this study could not prevent theclay loss because water dripping through theopen spaces of plant stands during rainfalls
transported the ﬁne particles from surface into
deeper layer.
The rates of clay content decreases especially under rice husk mulch were smaller thancassava peel, yet the organic amendment materials investigated could not play any betterrole in preventing clay leaching in this study.
Therefore, further study of other methods would
be required to overcome the clay-leaching problem during pineapple cultivation in the experiment site.
-. , Soil Organic Matter (SOM)
Organic materials are the main source of soilorganic matter (SOM), hence one of the aims of

86



organic amendment is to increase the SOM,
which will improve soil physical, chemical andbiological properties. But Table + shows thatwith the exception of rice husk mulching especially at *ῌ/ cm depth, SOM signiﬁcantly decreased in all the soil layers under the various
treatments. The rate of decomposition and theamount of organic materials are the keys todetermining the availability of SOM in the soil.
Fifteen months after application, the cassava
peel-soil mixture and cassava peel mulch treatments had not undergone decomposition andcould be seen physically in its original form
with the naked eyes. This indicates that +/months was probably too short for cassava
peel to decompose to contribute to the enhancement of SOM.
On the other hand, there was a speedy decomposition of cassava bagasse within a very
short period after application. In that case, thedecomposed SOM had already been mineralized
into nutrients and used by the plants, hence
SOM decreased at the end of the observation
period.
In the meantime, +/ months after its application, the rice husks had been partially decomposed with the remnant still covering soil
surface. Although insigniﬁcant, the partiallydecomposed rice husk may have slightly increased SOM at the upper layer (*ῌ/ cm). It is
expected that the remaining rice husks would
continue to decompose beyond the +/ months
study period to enhance SOM at the sub-layers.
According to the period and the rate ofdecomposition of each organic material andtheir role in SOM enhancement discussed above,rice husk can be recommended for use as organic amendment with a moderate decomposition rate.
-. - Particle Density and Bulk Density
It is shown in Table + that particle density
insigniﬁcantly decreased under rice husk mulching, while it signiﬁcantly increased in the othertreatments as well as the control, which experienced a negligible decrease at +*ῌ,/ cm depth.
However, the slight increase in the SOM at+*2

,**2

surface layer (*-/ cm) under rice husk mulching
had somehow improved the soil physical properties and consequently decreased the particle density. On the other hand, the increased
particle density under control and the othertreatments was accordingly due to the decrease of SOM.
It is also shown that bulk density signiﬁcantly decreased in rice husk mulch and cassava bagasse mulch. However, despite insigniﬁcant, bulk density in other treatments also generally decreased. That is probably due to soil
cracks that occurred during the dry season(low rainfall) when soil moisture was extremely low. Also, the decreased bulk density could
be the result of earthworms burrowing activities. Beside the burrows formation, earthworm casts could also played a role in thesigniﬁcant general increase of water-stable aggregate (WSA), as shown in Table +. Thus, thedecrease of bulk density and the increase of
WSA could be the results of earthworms burrowing activities.
-. . Soil Gravitational Water and Available Water Content (AWC)
Table , shows that the total soil water contents from saturation (* kPa) to ﬁeld capacity( +* kPa) at ﬁnal stage were generally higher
compared to the initial stage. The total soil
water content from * to+* kPa positively
relates to the soil macro pores. Macro porescause gravitational water to drain quickly andthe total soil water content within * to +* kPa
is called the gravitational water.
Except under rice husk mulch, there were no
signiﬁcant di#erences in gravitational water
increasing in all treatments. The general increase of gravitational water nevertheless showthat soil macro pores also increased in all thetreatments, which was probably due to thegeneral decline of bulk density and the increaseof WSA. Especially in the organic amendment
treatments, the di#erences of macro pores atinitial to ﬁnal stage were bigger at all layers
than the other treatments. Among all the organic amendments investigated, rice husk : Amendment of Soil Physical and Biological Properties Using Rice Husk and Tapioca Wastes

Table ,

87

Changes of Soil Gravitational and Available Water Content
Soil water content (m- m-)Treatment

Control

Soil
depth
(cm)
*῏ /
/῏+*
+*῏+/
+/῏,/

ῌ
* kPa

῍
+* kPa῎
+/** kPaῌ῏῍῍῏῎Gravitational Water Available Water

Initialﬁnal

Initialﬁnal

Initialﬁnal

Initialﬁnal

Initial

ﬁnal

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

*4/3
*4/1
*4/.
*4/+

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

*4-,
*4-3
*4.*
*4.,

*4,/
*4,3
*4,2
*4,3

*4,*4-**4-+*4-,*4,*4+0
*4+2
*4+-

*4,1
*4+3
*4+.
*4*3

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

*4*3
*4*3
*4*3
*4+*

Signiﬁcance within treat4

Rice husk mulch

*῏ /
/῏+*
+*῏+/
+/῏,/

*40+
*4/.
*4/+
*4.3

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

*4-1
*4..
*4.,
*4.0

NS

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

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

*4,+
*4,0
*4,,
*4-,

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

Signiﬁcance within treat4

Cassava peel
mulch

*῏ /
/῏+*
+*῏+/
+/῏,/

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

*40,
*40*
*4/,
*4/-

*4-.
*4-0
*4-3
*4-2

*῏ /
/῏+*
+*῏+/
+/῏,/

*4/1
*4//
*4.3
*4.2

*40*
*40*
*4/2
*4/.

*4-.
*4-.
*4..
*4.-

*4-.
*4-,
*4.+
*4-1

*4,.
*4,0
*4,2
*4,0

*4,.
*4,.
*4-+
*4,1

*4,*4,*
*4+/
*4+2

*῏ /
/῏+*
+*῏+/
+/῏,/

*40,
*4/1
*4.0
*4/+

*4/1
*4/2
*4/,
*4/+

*4-+
*4-1
*4.*4.-

*4-,
*4-+
*4-/
*4-0

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

*῏ /
/῏+*
+*῏+/
+/῏,/

*4/3
*4/0
*4.1
*4.2

*40+
*4/2
*4//
*4/+

*4-+
*4-.
*4-,
*4-+

*4,+
*4,1
*4-*4--*4,0*4,/*4-*4-**4,1*4,3*4,*4+2*4-+*4,**4**4*1

*4,,
*4,.
*4,2
*4,1

*4+2
*4,,
*4-+
*4-*

*4*3
*4*3
*4++
*4+*

*4*3
*4*3
*4*3
*4+*
NS

*4,+
*4,.
*4+*
*4++

*4,2
*4,+
*4+/
*4+1

*4+*
*4*2
*4*3
*4+*
NS

*4+*
*4*3
*4+*
*4++

NS

*4,3
*4-,
*4.,
*4.,

Signiﬁcance within treat4

*4+*
*4+*
*4+,
*4+,

NS

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

*4+3
*4*3
*4+*
*4+*
NS

*4,2
*4,2
*4+,
*4+0

*4,*4,+*4*/*4*/

Signiﬁcance within treat4

Cassava peel-soil
mixture

*4+.
*4+2
*4+,
*4+,

NS

Signiﬁcance within treat4Blackpolyethylene
mulch

*4,+
*4,.
*4,3
*4*3
S

Signiﬁcance within treat4

Cassava bagasse
mulch

S

*4+*
*4*3
*4*3
*4++
NS

*4-,
*4,1
*4+*4*3
NS

*4+*
*4++
*4*.
*4*.

*4++
*4*3
*4++
*4+,
S

Note : Initial sampling : July ,**+ ; Final sampling : October ,**,
*S : Signiﬁcantly di#erent at Pῌ*4*/ using Mann-Whitney U-Test ; n++, ; n,+,mulch resulted in signiﬁcantly more macropores than cassava bagasse and cassava peel
application treatments.
The available water contents (AWC) decreased
or stable in general, except at the surface layerof rice husk mulching and in the deeper layerof cassava peel-soil mixture treatment. The
increased AWC at surface layer of rice husk
mulching is assumed due to the slight SOM
increasing. It is generally shown that the in-

88

Fig. ,+*2

,**2Population of earthworms at each season(nῌ3 ; rainy season sampling ; February ,**, ; dry season sampling : July, ,**, ;a,b,c,d : Means with di#erent letters in the same depth for earthworm population
are signiﬁcantly di#erent with Duncan’s statistical test at Pῌ*.*/)

vestigated organic amendments, especially forsoil mulching insigniﬁcantly a#ected AWC.
However, the current results show that amending cassava peel by mixing it into soil greatly
enhanced the AWC especially at deeper layers.
-. / Water-Stable Aggregate (WSA) and
Earthworms Population
The percentage of soil mass with the aggregate fraction ῌ*.,/mm (water-stable aggregate/
WSA) signiﬁcantly increased in all the treatments including control and black polyethylene ﬁlm mulch as shown in Table +. Since
WSA is also derived from earthworm casts, thesigniﬁcant general WSA increase in the present study somehow related to the earthworm
activities (Fig. ,).
Figure , shows the earthworm populations
in each treatment at three depths (*ῌ+/, +/ῌ-*,-*ῌ./ cm) during the rainy season and dry
season, respectively. Soil moisture and soil
temperature (Table -) are the soil properties
that might be most a#ected by the seasons.
But it is shown that those of the properties do
not correlate well to that of the earthworm
populations. However, earthworm populations
were signiﬁcantly higher in the organic : Amendment of Soil Physical and Biological Properties Using Rice Husk and Tapioca Wastes

89

Table - Mean Soil Moisture and Soil Temperature During Each Season
Soil moisture (m- m-)Treatment
Control (No mulch)
Rice husk mulch
Cassava peel mulch
Cassava bagasse mulchBlack polyethylene mulch
Cassava peel-soil mixture

Soil temperature ()Rainy season

Dry season

Rainy season

Dry season

*4-.3
*4-./
*4--.
*4-1*
*4--1
*4-.+

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

,04,
,040
,041
,040
,14,04-,04,04+
,04/
,04,
,043
,/43

Note : Soil moisture was measured at *ῌ-* cm depth ; soil temperature was measured
at *ῌ,/ cm depth4
Rainy season is Feb4 ,**, ; dry season is Jul4 ,**,

amendment treatments within *ῌ+/ cm depth
during rainy season. The earthworm populations were also rather higher in the organic
amendment treatments during dry season although insigniﬁcant. The higher earthworm
populations in both seasons in organic amendment treatments showed that organic amendments provided food source for earthworms.
The abundance of earthworms in general positively a#ected soil physical properties.
..

Conclusions

Each investigated organic material for soil
amendment resulted in di#erent e#ects on soil
properties +/ months after their application in
the experimental ﬁeld. Speciﬁcally, the moderate rate of rice husk’s decomposition processslightly increased SOM of surface layer that
may had led to somewhat decreased particle
density and available water content enhancement. On the other hand, cassava bagassemulch decomposed within very short period
after application, and thus its roles especiallyin soil physical properties were no more noticeable in +/ months after its application. Due tothe slow decomposition rate, +/ months wasprobably too short for cassava peel to contribute in SOM enhancement as well as other soil
physical properties. However, the applicationof investigated organic materials for soil
amendment resulted in the more abundance
earthworm populations, bulk density decreas-ing, and the increases of macro pores and WSA
in general.
Organic amendments provided food sourcefor earthworms, and thus the earthworm populations were rather higher in those treatments.
The existence and activities of earthworms inthe soil certainly contributed positive e#ects inthe soil properties, especially soil physical properties enhancement.
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