ῐ
J. Jpn. Soc. Soil Phys.
ῐ῎῍ῑῒ῏
No. +*1, p. -ῌ+0 ῍,**1῎Field Evaluation of Compost, Sawdust and Rice Straw
Biomass on Soil Physical and Hydraulic Properties
Moniruzzaman Khan EUSUFZAI*, Takeki MAEDA** and Katsumi FUJII*** The United Graduate School of Agricultural Sciences, Iwate University,-ῌ+2ῌ2 Ueda, Morioka, Iwate *,*ῌ2//*, Japan** Dept. of Environmental Sciences, Faculty of Agriculture, Iwate University,-ῌ+2ῌ2 Ueda, Morioka, Iwate *,*ῌ2//*, Japan
Abstract
A ﬁeld experiment was carried out to investigate the e#ects of compost, sawdust and rice straw
biomass on soil three-phase composition, soil resistance to penetration, bulk density, nearsaturated hydraulic conductivity, K (h), and soil water retention characteristics. The experimental design involved ten split blocks such that the non-amended one plot was considered as control
and other nine plots were under each of compost, sawdust and straw treatments at application
rates of *.+, *., and *.- m- mῌ- of apparent soil volume. Addition of compost, sawdust and straw
showed potential for improvement of surface soil physical and hydraulic properties, then its
e#ectiveness was partly dependent on amendment types and application rates. Three-phasecomposition of all amended soils showed solid-phase reductions and increase of total porosity.
Generally, soil resistance and bulk density at all amendment plots were decreased, which was
likely due to reduction in soil solid phases. A good correlation between soil resistance and bulk
density was also observed. Except for sawdust applied at higher rate, the K (h) generally increased at any level of compost and straw incorporations, and this was attributed to the of
reduction in solid phase of amended soils. Soil water content was relatively high at higher suction
for compost amended soils, while improvement in soil water retention was limited at lower
suction for sawdust, and gradually increased from low to high suction for straw amended soils,
respectively.
Key words : Biomass, bulk density, near-saturated hydraulic conductivity, soil resistance, soil
three-phase composition, soil water retention+.

Introduction

Application of crop and plant biomass for
improving soil organic matter (SOM) and enhancing soil quality is well recognized in sustainable agriculture (Carter et al., +332 ; Kay,
+332). Although these biomasses are often regarded as agricultural wastes, development ofagricultural conservation practices aimed atenhanced soil quality, however, have resulted
in very diverse methods of organic residue
management. Recycling of these surplus agri-

cultural byproducts has the advantage to meet
nutrient requirements for the crop and expanded use as e#ective soil amendments. Manure and composted manure have been studied
for long time as the organic amendments. Dueto labor shortages as well as increasing farmmechanization, application of manure andcomposted manure has been gradually decreased over the last few decades. At the same time,
direct application of crop and plant biomass as
soil amendments has received considerable interest. Among these types of biomass, com-

῏

4



post, sawdust and rice straw can be used ase#ective soil amendments. Rice straw is usually left in the ﬁeld after harvest and is subsequently burnt or used as animal feed. Sawdust
obtained as byproducts of lumber mill is usually thrown into the ground or simply burned up.
During the last several decades, much attention has been paid to the utilization of crop andplant residues as soil amendments, as well as toevaluate the e#ects of existing organic matterson soil physical properties such as soil structure and aggregate stability (Tisdal and Oades,+32, ; Oades, +32. ; Martens and Frankenberger, +33, ; Carter and Stewart, +330 ; Debosz etal., ,**,), porosity and pore size distribution(Pagliai et al., +321 ; Boyle et al., +323 ; Martensand Frankenberger, +33, ; Schjonning et al.,+33. ; ,**, ; ,**/), bulk density (BD) (Gupta etal., +311) and water holding capacity (Khaleel etal., +32+ ; Miller et al., ,**, ; Rawls et al., ,**-).
Addition of organic matter decreases bulk density due to the dilution e#ect of added organic
matter with the denser mineral fraction (Gupta
et al., +311). From their report, yearly additionof ./* t ha+ of anaerobically digested sewage
sludge for two consecutive years decreased thebulk density of ﬁeld coarse sandy soils by ,2ῌ.
The e#ect of residue management on soil bulk
density and soil resistance expressed as cone
index has been found to be variable (Mandal etal., ,**.). On the contrary, Bhagat and Verma(+33+) observed that incorporation of rice straw
at an application rate of / t ha+ yr+ to a wheatrice crop sequence, reduced ﬁeld bulk densityfrom +.-, to +.,/ Mg m-. Debosz et al. (,**,) reported the ,/ῌ increase in water stable aggregates of sandy loam soil amended with household compost at constant temperature (+*).
Several studies demonstrated with biosolids
and composted biosolids suggested increased
soil water retention and aggregate stability insilt loam soils (Epstein, +31/ ; Epteien et al.,+310 ; Wei et al., +32/ ; Lindsay and Logan, +332).
For evaluating the e#ects of manure additionon pore-size distribution, Schjonning et al. (+33.)
observed that farmyard manure or slurry sig-

+*1

,**1

niﬁcantly increased the volume of pores for *., and *., to *.- mm within ,* cm depth fromthe soil surface while they noticed no e#ect onpores for  -* mm. In another study, Pagliai etal. (+321) reported that poultry manure increased pores for -* to /** mm and those for /** mm. Addition of animal manure has greater
e#ect on macroporosity and conductivity insubsoil below plowing layer compared to plowlayer (Schjonning et al., ,**/). For a long-term
manure amended soil, Miller et al. (,**,) reported that soil water retention was signiﬁcantly increased by / to .2ῌ (*ῌ/ cm and +*ῌ
+/ cm soil depths) compared with the control
at di#erent matric potentials between * and+/** kPa.
The increased SOM with organic amendments applied to agricultural ﬁelds, as indicated by Boyle et al. (+323), improves the soil
aggregation, and this improvement of soil
structure favors the downward soil water ﬂow.
Although manure and composted manure asorganic amendments have been addressed inseveral studies, very little research has been
done in order to observe the e#ects of sawdust
and straw as soil amendments on soil physicalproperties. To date there is little informationon the e#ect straw and sawdust soil amendments on the hydraulic conductivity of soils(Garnier et al., ,**.). In particular, there might
have not been any reported ﬁeld studies forevaluating the unsaturated hydraulic conductivity under straw and sawdust application.
For optimal land application of these biomasses as soil amendments, understanding of theinﬂuence of these amendments on soil physicaland hydraulic properties is essential. Therefore, the purpose of this study was to evaluate
the e#ects of compost, sawdust and straw incorporated as amendments on the three-phasecomposition of soil, bulk density and soil resistance, the hydraulic conductivity and soil water
retention characteristics.

῎῍ : Field Evaluation of Compost, Sawdust and Rice Straw Biomass on Soil Physical and Hydraulic Properties,.

Materials and Methods

Site Description and Experimental Design
The experiment was conducted in an uplandfallow ﬁeld at the Iwate University Experimental Station, Morioka, Japan. The ﬁeld was not
subject to under tillage practices during thelast two decades. Before cultivation the ﬁeld
was prepared to cut tall grass down to groundlevel. The soil is volcanic ash soil, andisol andclay loam in texture (.-.2ῌ sand, .,.+ῌ silt &+..+ῌ clay). The average values of soil properties measured at the beginning of the experiment within *ῌ/ cm soil depth were as follows :particle density ,.1+ Mg mῌ- ; bulk density +.,*
Mg mῌ- ; total carbon +*0 g kgῌ+ ; and total nitrogen +.02 g kgῌ+ (dry soil basis).
The rectangular ﬁeld of approximately +**m, was arranged as a split block design. Totalten plots each comprising an area of +./ by ,.*m were established in this study. Amendment
types and rates were considered as treatments
in nine plots and the other one non-amended
control plot was used for measurement andresult comparison purposes. Field experiment
was performed from July ,**/ to June ,**0.
Amendments were applied once in the middleof July ,**/ to these nine plots. We did notcultivate any crop but periodical weeding management was performed in every three months
interval. Sampling and measurements of soil
physical and hydraulic properties were carriedout in June ,**0, i.e. at the end of one year.
,. , Amendment Types and Application
Rates
Amendment types applied to treatment plots
included three di#erent biomasses : compost,
sawdust and fresh rice straw. Compost used assoil amendment in this study was a mixture ofrice straw, cow excrement and wood bark.
Sawdust obtained from a lumber mill was predominantly Japanese cedar waste, and used assoil amendment in this study. Water content
and particle density of compost and sawdust
was *.1/ kg kgῌ+, ,.1* Mg mῌ- and *..- kg kgῌ+,,. +5+.1+ Mg mῌ-, respectively. Rice straw (Japonica)
was collected from the farm at Takizawa, aneighboring village of Morioka. Straw was airdried and then cut into +ῌ, cm pieces. The
values of water content and particle density ofrice straw were *.+3 kg kgῌ+ and +.0* Mg mῌ-.
Water content was measured on dry-weightbasis.
All soil amendments using compost, sawdust
and rice straw were applied on apparent soilvolume basis and spread manually over eachamendment treatment plot. The amendment
volume was calculated for each plot by multiplying the plot area with a constant incorporation plow depth of +/ cm. Amendments wereapplied on a random basis to all nine treatment
plots. Each of compost, sawdust and straw incorporated amendments was applied to threetreatment plots. Three application rates expressed as *.+, *., and *.- m- mῌ- of the soil volume (apparent) were assigned to these threetreatment plots of each amendment, respectively. Brieﬂy, we calculated the apparent soilvolume of each plot by multiplying the area tothe depth of incorporation. Then we incorporated each biomass (volume basis) to the *.*, *.+,*., and *.- m- mῌ- of apparent soil volume ofeach plot. A small tractor implemented with arotavator was used to incorporate amendments
into the top +/ cm of the soil proﬁle. The nonamendment control plot was also tilled to thesame soil depth as the treatment plots. As ourstudy was limited to the changes of physicaland hydraulic properties due to compost, sawdust and straw amendment, therefore, we did
not investigate crop yield response to theseamendments.
,. - Measurement of Soil Physical and Hydraulic Properties
Bulk density for all plots was determinedfrom soil core samples. Samples were collectedfrom top / cm of each plot, by commercial coresamplers of / cm diameter, and /.+ cm in length.
However, for each plot bulk density were notmeasured for several sample series. Collected
samples were dried in a force-vent oven at +*/6 for ,. h and dry weights were recorded forbulk density computations. In-situ soil resistance was measured for each plot within the top/ cm soil depth using a Yamanaka hand-heldcone penetrometer, and measurements weretaken at ﬁve points following on a circulararray. For each plot, changes in the phase composition of soil matrix were estimated fromcollected undisturbed soil cores. Approximately + cm of the topsoil was scraped and one undisturbed core was taken at the top 0 cm soil
depth for each plot. Disturbed soil samples
were also collected at the same time for gravimetric water content measurements. Collected
samples were weighted immediately and wereoven-dried for determining the solid mass. The
mass of solid, water and amendments were
estimated for +** cm- total soil sample using
the average water content obtained from disturbed soil samples. This mass weight wasconverted to volume proportion of solid, waterand organic amendments by using the particle
density of soil amendments mixture. Subtracting the volume of solid, water and amendmentsfrom the total sample volume of +** cm- resulted in an estimate of the gas phase volume.
The volume proportion of solid, water, gas andamendments was then converted into percentage.
In this study, the near-saturated hydraulicconductivity was determined for all plots. A
disc permeameter (Perroux and White, +322)
was used for in-situ measurements of the unsaturated hydraulic conductivity, referred to as K(h) (cm s+),where h is the suction (cm). The
advantage of disc permeameter is that, the instrument is relatively simple, minimal disturbance of soil and in situ estimation of hydraulicconductivity is possible at or near saturated
condition. The disc permeameter consisted of areservoir tower, a bubble tower with movableair-entry point and a disc (,* cm in diameter),covered with a highly permeable nylon membrane. The air-entry tube allowed to impose
the constant pressure head conditions with apressure head being below the atmospheric+*1  ,**1

pressure. A thin layer of highly permeable
coarse sand was used to ensure good hydrauliccontact between the disc and the soil. Since
removal of surface crust, soil clods and roots
from the soil surface was reported e#ective forachieving a leveled surface for tension inﬁltrometer (Ankeney, +33,), the top + cm soil was
removed before the measurement of inﬁltration. Inﬁltration was recorded by measuring
the water level drop in the reservoir for a sequence of preset time step. The time step was
set at +/ seconds for few initial readings and at
the end water levels in the reservoir tower
were recorded for every /-minute intervals
until the steady state condition was attained.
Steady state ﬂow rates, Q (cm- s+), were determined for successive suctions of 2, ., ,
cm and 0 mm of water, because these suctions
were reported to be best for describing biological activities in soils (White et al., +33, ; Murphy et al., +33-). However, as the suctions approached close to saturation it was very di$cult to notice, because the steady state condition prevailed during very short run time.
Therefore, data observed at suctions of , cm
and 0 mm of water were not presented in thisstudy.
The K (h) was determined using steady state
ﬂow data from the disc permeameter under thedi#erent suctions applied (Reynolds and Elrick, +33+). According to their study, the piecewise slope and intercept can be described by :axylnQxῌQy
hxhyῌ

Kxy

GdaxyQxr+GdaxyprQxῌQyP

῍

where Phx/(hxhy) ; Kxy is the piecewise intercept (cm s+) ; axy (cm+) is the piecewiseslope of the plots of lnQ against h ; Q is the ﬂow
rate (cm- s+) ; Gd is the dimensionless shapefactor for tension inﬁltration from a surface
disc and is equal to *.,/ ; and r is the radius of
the disc (cm). The values x (+, ,, -, - - -) and y(x+) are integers, which are used to denotepiecewise sequences. By assuming a simple

ῑῐ : Field Evaluation of Compost, Sawdust and Rice Straw Biomass on Soil Physical and Hydraulic Properties

exponential relationship between the hydraulic conductivity and pressure head (Gardner,+3/2), the K (h) is given by :Kῌh῍῏Kxyexpῌaxyh῍ῌThe K (h) was calculated as the average of ῎2and ῎. cm of water of applied suctions. SteadyState ﬂow rate (Q) for each suctions were ob-

7tained as the slope of the curve of cumulative
inﬁltration volume versus elapsed time, whichis shown in Fig. +. Assuming that the sorptive
number a is constant over the interval between
the two successive suctions, the piecewise linear regression analysis were carried out whichis shown in Fig. ,. The slope and intercept
value of piecewise regression plot were taken

Fig. +

Cumulative inﬁltration at successive supply pressure head measured at each treatment plotusing disc permeameter. Steady state ﬂow rate (Q) is taken as slope of the linear portion of
the curve.

Fig. ,Natural logarithm of steady state ﬂow rate (Q) versus supply pressure head (h) for obtaining the a based on the piecewise exponential relationship expressed in the Eq.-. The
values of a and Kxy in Eq.- are the slope and intercept of two successive pressure heads,
respectively.



8

as equal to the value of axy and Kxy in Eq.+ andEq.,. Unsaturated hydraulic conductivity, K(h) were calculated using Eq.- as the average of2 and . cm of water of applied suctions.
Soil water retention characteristics for eachplot were determined from the undisturbed
core samples (/.+ cm length and /.* cm diameter) using the hanging water column and centrifuge method. It is to be mentioned that, water retention characteristics were not measured
for several sample series. Saturated cores weretransferred to the hanging water column andplaced on a porous ceramic plate. Lowering ahanging water column connected to the plate
induced a step change in suction at the bottomof the plate. The water column was setup as
lower as at ../ cm, /*.+ cm and 30.* cm measured
from the mid-point of the sample. High suctions such as /.*+*,, +.*+*- and ,./+*- cm
were applied by centrifuge and suctions at -.+0
+*/ and +.*+*1 cm were taken as air dry andoven dry condition. Volumetric water content
at fully saturated condition was calculated
from the three-phase composition such that thesoil matrix is perfectly saturated with water,
and then assumed as * cm suction. So the air
volume at each mixing level was assumed to be
zero and the volumetric soil water content wascalculated by subtracting the solid volume
from the total volume.
-.

+*1

,**1

Fig. -

Soil three-phase composition of compost incorporated plots at *.+, *., and *.- m- mῌ- ofapparent soil volume

Fig. .

Soil three-phase composition of sawdust incorporated plots at *.+, *., and *.- m- mῌ- ofapparent soil volume

Fig. /

Soil three-phase composition of straw incorporated plots at *.+, *., and *.- m- mῌ- ofapparent soil volume

Results and Discussion-. + Three-Phase Composition of Soil
Compared to the non-amended control plot
(represented by *.* application rate), soil threephase compositions (solid, water and air) ofcompost, sawdust and rice straw amended
plots incorporated at application rates of *.+, *.,and *.- m- m- (volume basis) were shown in
Fig. -, Fig. . and Fig. /, respectively. Despite
application rates of compost, sawdust andstraw incorporation, the soil phase composition, as shown in Figs. -ῌ/, generally changed
in all amended treatment plots compared to thecontrol. However, the most distinct change ofsolid, water and air phases was observed incompost incorporated amended plots. The solid phase was markedly reduced with the application rate of compost incorporation (Fig. -)ῑῐ : Field Evaluation of Compost, Sawdust and Rice Straw Biomass on Soil Physical and Hydraulic Properties

For compost, application rate at *.- m- m῏yields ,.,*ῌ composition of the total volume.
At this application rate the solid phase reduced
up to /.0*ῌ, while the air phase increases to
1.0.ῌ (Fig. -). This may be attributed to thecomposition of compost, which was made ofstraw, cow excrement and wood bark. Generally cow excrement is more decomposable thanstraw and wood bark ; as a result it may leavea blend of ﬁbrous materials that occupies morepore space.
Sawdust amended at *.+, *., and *.- m- m῏-,
shown in Fig. ., indicated the similar trend ascompost incorporations. However, the reduction of the soil solid phase at *.- m- m῏- level ofincorporation was slightly less. The *.- m- m῏of sawdust incorporation corresponded to ,.*,
ῌ of the total volume, which causes /.+0ῌ
reduction in the soil solid phase. The air phaseof sawdust-amended soils also increases to /.0,
ῌ compared to the control plot. For straw
amendments, the trend of phase changes varied abruptly at di#erent level of incorporation.
As shown in Fig. /, the soil solid phase decreased by ,./*ῌ (from .*.0ῌ to -2.+ῌ) at *.+ mm῏- incorporation level ; remained almost constant (.*.0ῌ to .*.-ῌ) at *., m- m῏- and thenreduced to /.+*ῌ (from .*.0ῌ to -/./ῌ) at *.- mm῏- level of straw incorporation.
-. , Soil Resistance and Bulk Density
Table + showed values of soil resistance andbulk density at di#erent level of compost, sawdust and straw amendment. Soil resistanceand bulk density generally decreased due tocompost, sawdust and straw amendments,

Table +

compared to the non-amended soil. Averagesoil resistance decreased from /1, kPa to -10
kPa, and bulk density decreased from +.,* Mgm῏- to *.3/ Mg m῏- as a#ected by the incorporation of *.+ m- m῏- compost (Table +). Similarly,
soil resistance and bulk density for the incorporation of *.- m- m῏- compost decreased sharply to 20.* kPa and *.2. Mg m῏-, respectively,
compared with the control plot.
Soil resistance and bulk density did notdecreased gradually for di#erent level of sawdust incorporation (Table +), compared to thecontrol plot. For instance, both soil resistanceand bulk density decreased to ,22 kPa and +.*0
Mg m῏- at *.+ m- m῏- sawdust, and to +*3 kPa
and *.2. Mg m῏- at *., m- m῏- sawdust incorporations, respectively. On the contrary, soil resistance and bulk density increased to -10 kPa
and *.32 Mg m῏-, respectively, for the additionof *.- m- m῏- sawdust. As shown in Table +, addition of straw at any level, sharply decreased
soil resistance and bulk density. For instance,
both soil resistance and bulk density decreased
to 01./ kPa and *.1- Mg m῏-, respectively, at of*.- m- m῏- incorporation level.
Figures 0, 1 and 2 showed the relationships
between soil resistance and bulk density for all
treatment plots derived from simple linear regression analysis, indicating a good correlation
between soil resistance and bulk density at all
applied amendments. For compost and straw
amendments soil resistance decreased gradually with the decrease in bulk density at any
level of incorporation. However, sawdust incorporated at *., m- m῏- application rate re-

Average soil resistance and bulk density for compost, sawdust, and straw incorporation

Application
rate (ῌ)

*
+*
,*
-*

9

Bulk density (Mg m῏-)

Soil resistance (kPa)
ControlCompostSawdustStraw

ControlCompostSawdustStraw/1, ῍014*῎ῌῌῌῌ-10 ῍2-40῎++0 ῍1-4-῎
204* ῍--4*῎ῌ
,22 ῍1+4*῎+*3 ῍-+4*῎-10 ῍2.4*῎ῌ.** ῍+1*῎
134* ῍+*4*῎
014/ ῍,04*῎

+4,
ῌ
ῌ
ῌ

ῌ
*43/
*43,
*42.

ῌ
+4*0
*42.
*432

ῌ
*432
*43*
*41-

Values in parentheses are standard deviation of the sample meanΐῐ῎῔῕ῑ ῒ +*1 ῏ ῌ,**1῍

10Fig. 0Relationship between soil resistance and bulk density for compost amended
soils incorporated at application rates of *.+, *., and *.- m- mῌ-.

Fig. 1

Relationship between soil resistance and bulk density for sawdust amended
soils incorporated at application rates of *.+, *., and *.- m- mῌ-.

Fig. 2

Relationship between soil resistance and bulk density for rice straw amended
soils incorporated at application rates of *.+, *., and *.- m- mῌ-.

῏῎ : Field Evaluation of Compost, Sawdust and Rice Straw Biomass on Soil Physical and Hydraulic Properties 11

sulted the maximum reduction in soil resistance and bulk density values compared toother *.+ m- mῌ- and *.- m- mῌ- of sawdust incorporations. Relatively better correlation (R,῍*.1+.2) between soil resistance and bulk density obtained for straw amended soils. Variations in the reduction of soil resistance andbulk density values for compost, straw andsawdust amended soils may be explained fromthe changes of their phase compositions at
di#erent level of incorporations (section -. +).
Bulk density is inversely proportional to total
porosity (Carter and Ball, +33-), which provides
a measure of the total pore space left in the soil
for air and water movement. Lower bulk density generally reduces the soil resistance because of relatively less unconﬁned compressive
strength of the soil. The reduction in the solid
phase at any level of compost, sawdust andstraw incorporations was higher than the nonamended control soils. The decrease in solid
phase increased the air phase resulted a subsequent increase in total porosity. For instance,at *.- m- mῌ- additions as compost, sawdust
and straw incorporations reduced soil solid
phases by /.0*, ..*2 and /.+0ῌ, and thereby
increasing the total porosity by ., - and .ῌ,respectively. In addition, decomposition rates

Fig. 3of these biomasses may be a reason of variablesoil resistance and bulk density of amended
soils, which is evident in sawdust amendments.
-. - Near-Saturated Hydraulic Conductivity
The e#ect of compost, sawdust and straw
incorporations on near-saturated hydraulic conductivity, K (h), was shown in Fig. 3. Since thesimilar trend was observed under di#erent applied suctions, the e#ect of compost, sawdust
and straw incorporation on near-saturated hydraulic conductivity, K (h), at ῌ0 cm of watersuction (average of ῌ2 and ῌ. cm suction) was
demonstratively shown. The ability of soil totransmit water depends on the porosity andthe arrangement of soil particles. Addition oforganic amendments usually leads to an increase in soil aggregation and porosity, therefore, K (h) is expected to be greater in organic
matter amended soils. As shown in Fig. 3, bothcompost and straw incorporations increased K(h) remarkably at di#erent application rates
though signiﬁcant di#erence in data among
treatment variables were not tested. For compost amended soils, the K (h) sharply increased
to ,/.. cm dῌ+ at level of *.+ m- mῌ- incorporation and then gradually increased to maximum.*.. cm dῌ+ at *.- m- mῌ- addition (compared toE#ect of the di#erent incorporation rates of compost, sawdust and straw
amendments on the near-saturated hydraulic conductivity of the soil, K (h),observed at a suction of 0 cm of water.

12

the non-amended control plot). Straw incorporations showed the similar trends. Comparedto the control plot, a steep increase of the K (h)was observed at *.+ m- m- straw incorporation(+2.- cm d+) and then exhibited the maximum--./ cm d+ at *.- m- m- incorporation. In contrast, the trends of the K (h) increments withincreasing sawdust additions were not consistent. As shown in Fig. 3, the K (h) gradually
increased from 0.+* cm d+ (control plot) to 3..*and to +-.- cm d+ at *.+ m- m- and *., m- mincorporation levels, respectively, and thensuddenly decreased to /..* cm d+ at *.- m- mincorporation level. This sudden decrease in
the K (h) for sawdust amended soil at higher
application rate may be attributed to either
measurement error or at higher rate appliedand suspended solids or microorganisms which
may likely to block the water conducting pores(McAuli#e at al., +32, ; Lehrsch et al., +330).
Notably, as shown in Fig. 3, K (h) values forsawdust amended soils was also lower thancompost and straw amended soils incorporated
at *.+ m- m- and *., m- m- rates.
Incorporations of compost, sawdust andstraw to soils generally decreased the solid
phase and increased the water and gas phase(Fig. -, Fig. ., and Fig. /, respectively). Hence,
the total porosity increased with the increase
in incorporation rates. The increase in the total
porosity might have an e#ect on the increasing
trend of the K (h) for compost, straw and sawdust amended soils. As water ﬂow rates in soil
pores (cylindrical) is proportional to the fourth
power of the radius, near saturated porosity
would account for most of the water movement in unsaturated condition (Brady, +31.).
The total porosity ratio for compost, straw andsawdust amended soils at *.- m- m- incorporation was +.*0, +.*/ and +.*0, respectively, compared with control plot. At the same level ofincorporation, the K (h) increased by 0.0, /./ and*.3 times than non amended soil, thus indicating that the K (h) change was much higher thanthe porosity expansion. Therefore, it is clearthat the e#ect of organic matter incorporations

+*1

,**1

on the K (h) may be attributed to the porosity
along with pore radius expansion.
-. . Soil Water Retention Characteristics
Soil water retention curves for di#erent application rates of compost, sawdust and straw
amended soils compared to the control plot
were presented in Fig. +*, Fig. ++, and Fig. +,,respectively. Compared to the control plot,
compost incorporation at higher application
rate retained larger amount of water than sawdust and straw. For instance, the *.- m- mincorporation of compost caused *.*0 m- m(from *..1 m- m- to *./- m- m-) increase in water content at a low suction (at ../ cm) ; remained almost constant at *.*/ m- m- (from *.-/ mm- to *..* m- m-) at /.*+*, cm suction, andthen increased to *.+. m- m- (from *.+/ m- mto *.,3 m- m-) at -.+0+*/ cm suction (Fig. +*).
However, sawdust incorporation e#ect waslimited to relatively at low suction. As shownin Fig. ++, at *.- m- m- sawdust incorporationlevel, water content increased by *.*. m- m(from *..2 m- m- to *./, m- m-) at ../ cm ; remained constant *.*. m- m- (*.-/ m- m- to *.-3m- m-) at /.*+*, cm and then decreased by*.*+ m- m- (*.+/ m- m- to *.+0 m- m-) at -.+0
+*/ cm suction. For straw amended soils (Fig.
+,) increments in water content was lower
than compost amended soils at higher suction.
However, at relatively lower suction, volumetric water content of straw and compost
amended soils were almost same. For instance,
addition of straw at the *.- m- m- incorporation level increased water content by *.*/ mm- at ../ cm, remained constant at *.*/ m- mat /.*+*, cm, and then increased to *.*0 m- mat -.+0+*/ cm suction, respectively.
The e#ect of compost, sawdust and straw
incorporations on changes in soil water retention behaviors may be explained from the capillary pore size and porosity expansion considerations of amended soils. Assuming that thesoil is behaving as a bundle of capillary tubes,
then capillarity would be su$cient to describe
the relationships between the capillary pressure head and soil pore radii. According to the῍ῌ : Field Evaluation of Compost, Sawdust and Rice Straw Biomass on Soil Physical and Hydraulic Properties 13

Fig. +*

Soil water retention curve of compost amended treatment plots at di#erent suctions.

Fig. ++

Soil water retention curve of sawdust amended treatment plots at di#erent suctions.

Fig. +,

Soil water retention curve of straw amended treatment plots at di#erent suctions.



14

Young-Laplace equation, the capillary pressure
head in a capillary tube is proportional to theheight of h above the free water surface andinversely proportional to the capillary radius r,which is given as follows :,gcosavῌgr+rgrwhere rg is the density of gas (generally neglected), r+ is the density of water, g is the surface tension, g is the acceleration due to gravity and av is the contact angle. The equivalentcapillary tube radius re at di#erent suctions
can be estimated using this Young-Laplace,such as re*.,. mm for ../ cm, and +../ mm for/.*+*, cm suction. However, at high suction
such as at -.+0+*/ cm, the equivalent capillaryradius drops down to ,.-/ nm, which is not an
actual capillary size but surface adsorption
scale that forms a hydration envelope over theparticle surface. As the soil was predominantly
clay in this study, the incorporation e#ect oforganic matters appears in ﬁne pore system ofnm scales, and enlarges its porosity to at least+.1.ῌ. The porosity expansion is also evident
from three-phase compositions of compost andsawdust amended soils (Fig. - and Fig. ., respectively), such that, the *.- m- m- incorporation caused -..*ῌ and -.+-ῌ increase in theporosity, respectively. In contrast, straw incorporation at the same *.- m- m- application rateincreased the porosity to ,.1.ῌ. Among threebiomasses incorporated to the clay soils in thisstudy, compost and sawdust amendments
showed an increase in capillary pore sizes ofthe soil.
hc..

Conclusion

The ﬁeld experiment conducted in this study
showed that additions of plant and composted
biomass such as compost, sawdust and ricestraw at di#erent application rates of *.+, *.,,and *.- m- m- (apparent soil volume basis) toclay loam soils led to a substantial improvement of soil physical and hydraulic properties.
The extent of their e#ectiveness for improving
soil physical and hydraulic properties was par-+*1

,**1

tially dependent on application rate ; in suchas way that higher application rate of thesebiomasses provided greater improvement insoil properties. Compared to the control plot,
three-phase compositions of compost, sawdust
and straw amended soils showed the reduction
in soil solid phases, and thereby increased thetotal porosity. Additions of all amendments
also decreased soil resistance and bulk density,
which were likely due to the reduction in solid
phases of amended soils. A good correlation
between soil resistance and bulk density wasobserved for all amended plots. Except forsawdust addition only at higher application
rate, near-saturated hydraulic conductivity, K(h), increased for all application rates of compost and straw incorporations. The incrementin the K (h) might be attributed to the reduction in solid phases of compost, sawdust andstraw amended soils and thus the increase in
the total porosity. Improvements in soil water
retention were varied among amendment
types and application rate. Compost amended
soils retained large amount of water even at
higher suctions. However, improvement in soil
water retention characteristics for sawdustamended soils was limited at lower suction.
For straw amended soils, water retention capacity increased steadily from low to high suction.
This ﬁeld study showed that compost, sawdust and straw had di#erent interactions to thebasic soil physical and hydraulic properties
when incorporated to clayey loam soil. Although di#erent agricultural practices andcrop yields under applied biomass incorporations have not been considered as indicators,
results concerned with the e#ect of incorporated compost, sawdust and straw biomass
amendments on soil physical and hydraulicproperties investigated and presented in thisstudy will extend our ideas for the e#ective application of these biomasses in order to improve soil quality.

῍ῌ : Field Evaluation of Compost, Sawdust and Rice Straw Biomass on Soil Physical and Hydraulic Properties 15

Acknowledgments
We would like to express our appreciation to
the Ministry of Education, Science, Sports andCulture, Japan for proving the scholarship,
which lead to this study.
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