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Permeability and Water Retentivity of Peat Soil
Soil Physical Properties of Bibai Peat Land (ῌ) 
Hiromi IMOTO*,Tsuyoshi MIYAZAKI*, Hirotaka SAITO* and Masashi NAKANO*** The University of Tokyo** Faculty of Agriculture, Kobe University
Abstract
We measured saturated hydraulic conductivities, unsaturated hydraulic conductivities andwater retentivities of Bibai peat soils, consisted of highmoor peat (natural moss), transitional peatand lowmoor peat.
The transitional moor soils exhibited remarkable anisotropy of permeability. The verticalsaturated hydraulic conductivity was utmost about .** times more than its horizontal saturated
hydraulic conductivity probably due to the horizontal sedimentation of plant ﬁber.

Thisanisotropy was most remarkable in the subsoil of a paddy ﬁeld under the dressed soil and was lessin the undisturbed soils under windbreak.

Soil dressings and continuous cultivations may havea#ected the appearance of the intensive anisotropy.
The unsaturated hydraulic conductivities of transitional peat and highmoor peat were quite
small and were less than those of sand.

This feature caused the necessity of relatively long time

for the equilibration of water retention.
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Water charactaristics curve (hanging water column method, (a) lowmoor peat, (b) transition
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Unsaturated hydraulic conductivity.

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Boelter, D. H.(+30/) : HYDRAULIC CONDUCTIVITY
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J. Jpn. Soc. Soil Phys.
/No. 22, p. +++2 ,**+





*ῌ **ῌJanya SANGῌARUN***ῌ

*

E#ect of Grass Strips on Reduction of Sediment Loss from Upland Field
Takashi UENO*, Machito MIHARA**, Janya SANGῌARUN*** and Yukiko DOKIYA** Tokyo University of Agriculture and Technology, -ῌ/ῌ2 Saiwaiocho Fuchuoshi Tokyo, Japan** Tokyo University of Agriculture, +ῌ+ῌ+ Sakuragaoka Setagayaoku Tokyo, Japan*** Mae Fah Luang University, --- Moo. +. Tasud subodistrict, Muang district,
Chiang Rai, Thailand
Abstract
The e#ect of grass strips on the reduction of sediment and eutrophic salt loads is been widely
recognized.

However, there is very little knowledge of the e#ect of grass strips on the reductionof sediment and eutrophic salt losses.

Attention was hence focused on the investigation of what

grass strips should be managed.
Soil suspension was supplied to the experimental plots under simulated rainfall. During theexperiment, surface discharge and sediment concentration were measured.

In order to observe

the e#ect of grass strips on the reduction of sediment loss, the di#erence between the amounts of
sediment supplied and sediment loss was investigated in each plot.
While the sediment concentration and load from the bare upland ﬁeld exceeded the concentration and load of the soil suspension supplied, the sediment concentration and load from all thegrass strips were lower than the concentration and load of the supplied soil suspension.

The

di#erence between the sediment supplied and the sediment loss from the cutting weeds plot forpest control was approximately equivalent to that of the plot with the natural weeds.

Therefore,

it was concluded that cutting weeds for pest control can be applied to the grass strip for reductionof the sediment loss.

There was little di#erence between the reduction of the sediment loss fromthe plot with 2** stems/m, and that from the plot with +,.2* stems/m, of Tall Fescue (F.
arundinacea).

However the plot with ,,--* stems/m, of Tall Fescue was e#ective for the reduc-tion of sediment loss comparing with 2** stems/m, and +,.2* stems/m,.

It suggests that stem

density for grass strips should be maintain ,,--* stems/m, to control soil loss from upland ﬁeld.
Key words : Grass strips, Sediment loss , Surface runo#, UplandJU56V%0WX34'56 =YZ( +33/(+    

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12

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Simulated rainfall system and experimental plots.

<<$@

Physical properties of soil

Particle size distribution* (ῌ)

Speciﬁcgravity

GravelCoarse sandFine sand

Silt

Clay

Dispersion
ratio (ῌ)

Ignitionloss (ῌ)

Soiltexture

,40*

*4*

241

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,/40

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Table ,

13

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Vegetation and management in plots

Plot

Vegetation (scientiﬁc name)rd(g/cm-)

Density of stems (W+)(stems/m,)

Management

Plot I
Plot II
Plot IIIPlot IV
Plot V
Plot VI

None
Weed (10ῌ with Setaria viridis)
Weed (2-ῌ with Setaria viridis)
Tall Fescue (F. arundinacea)
Tall Fescue (F. arundinacea)
Tall Fescue (F. arundinacea)*42*421*42*42,
*42.
*42-

X
,5.2* 1,5//*:,5-2* 1,52.*:
2**
+5.2*
,5--*

Bare
Cutting
None
None
None
None

W+

: , weeks after the cutting weed of plot II.

ῌῌ+

YZ[\]^_'("`a7bcde#'5cf*# 1gh23 Plot ῌi:Fig. +

Changes in cumulative surface runo#
and soil loss under simulated rainfall(before the cutting weed in plot II).

cm 



Plot

 Plotῌῌ,

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Fig. ,

Changes in cumulative surface runo#
and soil loss under simulated rainfall(just after the cutting weed in plot II).

4'563/07῏, 8 & Plot 9,*+,῍῎  !"#$%

-./0

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14

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@AB.

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Fig. -

Changes in cumulative surface runo#
and soil loss under simulated rainfall (,weeks after the cutting weed in plot II).

w_tumpq©ª ¸<·zg{ |p -Plot ῌ789:=B.

Fig. .

Changes in cumulative surface runo#
and soil loss under simulated rainfallwith additional suspended water supply(just after the cutting weed in plot II).

  Plots ῌ ῍ /ῌ   Plot ῌ
῍

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%&'()*+, -Setaria&
0 PlotM&pq45 ,. rAs K

viridis. /0110ῌ 2-ῌ 23456 Plots ῌB .2 mm/h tuv  -* 4Aw_tuxy5;῍ zg{ |p }~5K789:5;<=>

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 789: 8 Plot ῌ

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ῌpq ¡¢p £5J¤¥4 K,

stems/m, %? [\_,`Q&abcbd/ +*** stems/m, e %&Lf
Plot ῎/[\_M&8ghijk5llm

n8 Plots ῏ ῐ/jk5on?&L/Sf¦ 5xKB   §K¨/5©ªK¦ 5« h? ¦m USLE `¬yM& +331 ­0 ®¯°r±²³´µ -Mihara ,**+.

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Changes in cumulative surface runo#
and soil loss under simulated rainfallwith additional suspended water supply(, weeks after the cutting weed in plotII).

-'(*+ῒῌ0/012345#$%&CD6789:$EF)': z{|}~

Fig. 0Changes in cumulative surface runo#
and soil loss under simulated rainfall(Tall Fescue).

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  22  P,**+-

16

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6789-

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Changes in cumulative surface runo#
and soil loss under simulated rainfallwith additional suspended water supply(Tall Fescue).

ῌῌ2 Plot II er
h;< U:a*Fig. 2Comparison between amount of soil
supplied and of soil loss under simulated rainfall with additional suspended
water supply (just after the cutting
weed in plot II).

EF Plot ῍ Z_L` /ῌ _abc

ῌd+,  Ee Plot ῎ :S0T ;

  +* cm   !"#$

%&'()*+,,- ./0 123456789 :

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Plot !ghiIjO+ PQ῏

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;MlOABmnEe +2

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@ABCD EFABGHIJKL ;MCD!NO+ PQ῏0 1-,abcd+, ./0 2** stems/m,v,--* stems/m,Plots ῌ P2** stems/m,- ῍ P+.2* stems/m,- ῎?@ABR :S0T ;<P,--* stems/m,-

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:

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{`' +*** stems/m,|0 ./0 V;<'em- +/- g/m- 'O+, _L` /ῌ V Plot ῌ  CDGHV ,--* stems/m, |0./Plot ῍0!stkZ_aVbcd2O+ ./0 ,--* stems/m,Plot ῎:;< UV Plot+,}!~dhª« : KLM+,¬9 Er­®¯

17

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

Fig. 3Comparison between amount of soil
supplied and of soil loss under simulated rainfall with additional suspended
water supply (, weeks after the cutting
weed in plot II).

Fig. +*

Comparison between amount of soil
supplied and of soil loss under simulated rainfall with additional suspended
water supply (Tall Fescue).



&,--* stems/m,- 

X7  
! Plot "# $% '()*&L, "#

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pnoefghijk+yzC(.  YZ
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W/3* g/m X7,;!VW/02 YZ[\.]^F++;_= .`abF.G=c.;d"U,5 ef

PlotghijkKLMX( Plots ῏ &2** stems/m,¤/,5 9¡¢'7 +* cm p¥mῐ&+.2* stems/m, :  :.`W0,, g/m, XU,;l`mLno p Plot ῑ "#)* ¡¢£ 'N +O7PQ+

TU,KLM'N¦O7PQ KLM: Plot "#. Plot"#'7)*, L 22 ¼ ,**+

18   

   Plot 

tiveness of grass strips for the control of sediment and associated pollutant transport in !"# $" %&'() 

runo#, The Role of Erosion and Sediment Trans-  *+ ,- .

port in Nutrient and Contaminant Transfer, pp.

/ 0 %&'() 1234567!89 "# :+;<)& =>?@A"BCDE!F. GH
IJK *A"#LM

QRS T "U >C PV7 WXYZ[\] ^!F_-"# >C P

2**`,--* stems/m, ab"T-F Plot Ec

dPe  fg" hijdPklA"# + >C P 2** stems/m E)m,+.1* stems/m,  Plot dPe  .no+7*A" ,--*

stems/m, BCDEc

dP 2** stems/m, E)

m +.2* stems/m BCD)&p , 

E!F.)&:*A"#:+;<)& qrsEc & tQR
K

Science Press, U.K..
Mihara, M. (,**+) : Nitrogen and phosphorus losses
due to soil erosion during a typhoon, Japan,

N O "BCD>C P !F2-ῌ3+, International Association of Hydrological+*** stems/m, uP>CPBCD

NJK& + ,--* stems/m, uP>C Pvwg :Nxyz+ :*A"#

Journal of Agricultural Engineering Research,
12 (,) : ,*3ῌ,+0.
UusiῌKamppa, J. and Ylaranta, T. (+33,) : Reductionof sediment, phosphorus and nitrogen transport
on vegetated bu#er strips, Agric.Sci.Finl. + : /03ῌ/1/.
`

Parsons, J.E., Gilliam, J.W., MunozῌCarpena, R.,
Daniels, R.B. and Dillaha, T.A. (+33.) : Nutrientand sediment removal by grass and riparianbu#ers, Environmentally sound agriculture proceedings of the second conference : +.1ῌ+/..

>{|}ῌ~ῌ +33. : =>?] pp. +/ῌ,3   +33/ : "U>r 

E)m

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 1+ : -1ῌ.*.

ῌ ῏ ῎ ῍
Dalton, P.A., Smith, R. J. and Truong, P.N.V. (+330) :  ¡¢ +33* : & ts a£ῌ¤s¥ pp. +30ῌ+32 ¦§¨©¡¢ ª«¬­®ῌy¯° +333 : Ec

Vetiver grass hedges for erosion control on a

±²E)m³´    µ¢

cropped ﬂood plain : hedge hydraulics, Agricul-¨¶ ,** : 1ῌ+..

tural Water Management, -+ : 3+ῌ+*..
Ghadiri, H., Hogarth, B. and Rose, C. (,***) : The e#ec-·¸¹º» : ,*** ¹ 3 º +- »·¹º» : ,**+ ¹ - º ,- »
J. Jpn. Soc. Soil Phys.
 ῍
No. 22, p. +3,/ ,**+

ῌ

 PDE    *Application of a General PDE Solver for Analyzing
Water and Solute Transport in Soil
Kosuke NOBORIO** Faculty of Agriculture, Iwate University, Morioka *,*ῌ2//*, Japan
Abstract
For the proper management of water and fertilizer resources, distributions of water and solutein soil should be precisely predicted.

The movement of water and solute in soil may be expressedwith partial di#erential equations (PDEs).

The PDEs should be numerically solved for real world

applications because of complex initial and boundary conditions and high non-linearity in somecases.

The recent development of a general PDE solver using the ﬁnite element method enabled

us to more easily solve these PDEs governing water and solute transport in soil. FlexPDE Lite
can be freely obtained through the Internet, and its applicability to solve water and solutetransport in soil was investigated. FlexPDE Lite successfully simulated water inﬁltration into
Haverkamp’s sandy soil with ῍,῎ of mass balance errors.

However, it failed to calculate waterinﬁltration into dry loamy sand when initial pressure head was 0* cm.

Results of simulating

solute transport with FlexPDE Lite also agreed well with analytical solutions especially when theconvective transport was not dominant. Therefore, FlexPDE Lite, although its performanceswere purposely limited, could be an ideal tool for a training purpose or a smalloscale simulation.
Keywords : numerical solution, ﬁnite element method, soil water movement, solute transport,
simulation model+    

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Comparison of water distribution calculated by FlexPDE Lite, FEM (Noborio etal., +330), and FDM with results ofHaverkamp et al. (+311) during waterinﬁltration under (A) the Dirichlet, and(B) the Neumann boundary conditions.

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῏῍ῌῐῑ῎
No. 22, p. ,1ῌ-/ ῍,**+῎Application of Electromagnetic Technique to
Identify Recharge and Discharge Areas for
Reforestation in Northeastern Thailand
Chaiyanam DISSATAPORN*, Hajime NARIOKA**, Pramot YAMCLEE* and Somsri ARUNIN** Land Development Department, Bangkok, Thailand** Okayama University, Okayama, Japan
Abstract
Areas a#ected by salinization in northeastern Thailand were studied using data obtained fromground geophysics methods, multi frequency electromagnetic induction terrain conductivity
meter, and hydrological data from the routine piezometer method. The electromagnetic technique is not only a useful tool for identifying the spatial distribution of salt content in landscapes,
but it may also be applicable for delineating local recharge and discharge areas by comparing
results with hydrological data. It could also aid in reforestation planning in large-scale areas forrehabilitation of salt-a#ected soils.
Keywords : Electromagnetic induction terrain conductivity meter (EITCM), Salinization, Recharge and discharge areas, Reforestation, Northeastern Thailand

Introduction
Secondary salinization of salt-a#ected soils
in northeastern Thailand is mainly due to therising of shallow saline groundwater in discharge areas after clearing of native Dipterocarpus forest in recharge areas. The source ofadditional recharge to groundwater discharge
aquifers is rainfall, which percolates throughthe root zone of annual, short-rooted and lowwater-use cash crops in cleared lands. Salt isthen transported and accumulated on soil surfaces by evapotranspiration and capillaryaction from rising shallow saline groundwaterin discharge areas. Halite, of the Mahasarakram Formation founded at the depth of 0* to+** m from soil surface, is widely accepted as asource of salt in the process of soil salinization.
A remedial measure for controlling shallow
saline groundwater in discharge areas is toutilize recharge water before it reaches groundwater aquifers (Williamson et al., +323).
Reforestation in recharge areas is recognized

as one land management technique for minimizing groundwater recharge. Perennial, deeprooted, fast-growing and high-water-use trees
are planted in recharge areas where groundwater tables rapidly respond to rainfall. The
goal of this technique is to intercept and utilize
precipitation before it percolates through theroot zone to groundwater aquifers (Sedgley etal. +32+).
Regarding this method, it is necessary todeﬁne signiﬁcant recharge areas before reforestation schemes are begun (Bullock andWilliams, +321). They can be roughly delineated from topographic, soil and land surface
properties but the most accurate, althoughcostly and time-consuming technique, is to
study groundwater characteristics (Freeze andCherry, +313).
The electromagnetic terrain conductivity
technique is a simple and rapid method fordelineating the distribution of salt on surface
and subsurface soils at depth of 1./, +/ and -* mfrom the soil surface (McNeil, +32*). The low῏28  22

conductivity of upland soils indicates recharge
areas while high conductivity indicates a salinity hazard as well as discharge areas (Bullock
and Williams, +321, and Engle et al.,+321).
Williams and Arunin (+33*) employed the
EITCM for predicting recharge and discharge
areas from the empirical average ratio of deep
to shallow depths of sounding at Nakorn
Ratchasima in northeast Thailand. Ratios ofgreater than or less than one indicate recharge
and discharge areas, respectively. Area where
terrain conductivity increases with reading
depth indicates recharge areas due to adequate
leaching of salt and nutrients. In the discharge
areas, where salt moves from shallow saline
groundwater to soil surfaces, readings decrease
with depth of transverse.
The objective of this research was to study
the application of the EITCM for delineating
recharge areas to be reforested for salinity control.
Study area and methodology
Salt a#ected soils in Ubonrachathani province were selected for studying the applicationof electromagnetic terrain conductivity formapping recharge areas.
The study area
covers -0* square km. Annual average rainfall
and evaporation is +,/11 and ,,*/. mm, respectively. Soil proﬁle description and type ofrocks from soil surface to -* m depth wererecorded during the installation of piezometer.
Soils in high terrace were silt and sand while
low elevated area soils were silt with increased
in clay content. It was founded that soils were
underlain with shale, sandstone and siltstoneof the Mahasarakram Formation but no salt
layers were detected.
The hydraulic head of groundwater fromnested piezometers at depths of /, +*, +/, ,* and-* meters from soil surface (U+U3*) was used
for mapping recharge and discharge areas.
The horizontal hydraulic gradients of groundwater at a depth of / meter from soil surfaces
were contoured and ﬂow lines of groundwater
were drawn (Surfer for Windows, +330). The,**+

vertical hydraulic gradient between each
depth of nested piezometer was calculated.
The downward and upward vertical hydraulicgradient was identiﬁed as recharge and discharge areas, respectively (Freeze and Cherry,+313).
The EITCM measures the bulk apparent electromagnetic terrain conductivity (Eca) of soluble salt concentrations in soils (mS/m) to
depths of 1./, +/ and -* m from the soil surface.
The instrument consists of transmitter and receiver coil with diameter of 0- cm and weightof - and 1., kg, respectively. They are connected to transmitter and receiver meter, respectively. The coil conﬁgurations are either vertical or horizontal and are +*, ,* and .* meterapart (Fig. +). The transmitter coil generates
primary electromagnetic currents in the soil
proﬁle, which induce the secondary magnetic
ﬁeld from soluble salts in the soil proﬁle. The
magnitude of secondary magnetic ﬁeld depends on the concentration of soluble salts,
moisture and clay contents. The receiver coildetermines the primary and secondary magnetic ﬁeld and calculates the ratio between the
two. This ratio yields the apparent electricalconductivity of the soil proﬁle. The depth ofsoil measured depends on the current frequency, distance between the transmitter and receiver coils and the coil arrangement relative
to the soil surface. The coils in the horizontal
dipole mode provide the depth of sounding of
1./, +/ and -* m from the soil surface (McNeil,+32-).
The EITCM survey was carried out at grid of+ km and at each nested piezometer using a +*,,* and .* m coil separation and horizontal
dipoles. The apparent electromagnetic conductivity at depths of 1./, +/ and -* m was obtained. Surfer for Windows was used for contouring the apparent electromagnetic conductivity of the soil proﬁle at depths of 1./, +/ and-* m from soil surface (Surfer for Windows,+330). Salinity is classed into non-salt-a#ectedsoils (*2* mS/m), slightly salt-a#ected soils(2*+,* mS/m), moderately salt-a#ected soils

ῒῑ : Application of Electromagnetic Technique to Identify Recharge and Discharge Areas for Reforestation in Northeastern Thailand 29

Results

Fig. +

Electromagnetic induction terrain conductivity meter (EITCM), in horizontal
and vertical dipole mode.

(+,*ῌ+0* mS/m), severely salt-a#ected soils(+0*ῌ,** mS/m) and very severely salta#ected soil (ῐ,** mS/m).
Williams and Arunin (+33*) proposed thatsalinity at di#erent depths in the soil proﬁledetermined from EITCM measurements could
predict recharge and discharge areas. Areas inwhich Em values increase or decrease with thedepth of the soil proﬁle can be identiﬁed asrecharge and discharge areas, respectively.
Thus, the EM slope can be derived as
EM slope῎((EM-*/EM+/)῍(EM-*/EM1./)
῍(EM+//1./))/ῌ
Recharge area EM slope ῐ +῍Discharge area EM slope ῏ +῎EM1./ : Apparent electrical conductivity
from soil surface to 1./ m depth
EM+/ : Apparent electrical conductivity
from soil surface to +/ m depth
EM-* : Apparent electrical conductivity
from soil surface to -* m depth
The EM slope formulated from this formula
was then contoured using Surfer for Windows.
The contour of the EM slope was overlain on
the recharge and discharge area, which delineated the vertical and horizontal hydraulicgradient of groundwater from the same area.

Groundwater hydrology and the electromagnetic technique was used for investigation of
the development of salt-a#ected soil in northeastern Thailand
Groundwater hydrology
Data from nested piezometers was collectedfrom April +330 to March +332. The distribution of horizontal hydraulic head and groundwater ﬂow lines at a depth / meter from soil
surfaces were drawn using data gathered in
April +331. Groundwater moved from the elevated areas (+-*ῌ+.* m above mean sea level)to the lower areas of the study area. The
pattern of groundwater ﬂows were the same
during the period of study. The vertical hydraulic gradients between nested piezometer
were calculated.
Nested piezometers withdownward and upward vertical hydraulic gradients were identiﬁed as recharge and discharge areas, respectively. It was found thatmost of the recharge areas were situated primarily over the horizontal hydraulic head of+,, meter. The depth of ground water ranged
from ,.. to /.+* m from the soil surface in therecharge areas, while that of the discharge
areas was in the range of +.3/ to -.2 m from soil
surface (Fig. ,).
Electromagnetic technique
Soil salinity maps of the study area wereprepared and are shown in Fig. -. The measured apparent electromagnetic terrain conductivity from soil surface to 1./ m depth ranged
from 0 mS/m in the recharge areas to +3/ mS/
m in the discharge areas. All recharge areas
identiﬁed by the groundwater hydrology wereclassiﬁed as non-salt a#ected soils, while thedischarge areas were classiﬁed as slightly toseverely salt-a#ected soils. The severely salta#ected soil occurred in small areas in thevicinity of U-3 and U+/ and U+0. The bulk
apparent electromagnetic terrain conductivityof soils located +/ and -* m from soil surface
ranged from +*ῌ+3/ and 2ῌ,,* mS/m, respectively. The boundary of salt a#ected area atΐῐ῎῔῕ῑ ῒ 22 ῏ ῌ,**+῍

30

Fig. ,

Distribution of horizontal hydraulic head (m), ﬂow lines of groundwater measured inpiezometers at a depth of / m from soil surface in April +331 and recharge [R] anddischarge area [D]. Discharge area identiﬁed from vertical hydraulic gradient (map scale isin meter).

῍ῌ : Application of Electromagnetic Technique to Identify Recharge and Discharge Areas for Reforestation in Northeastern Thailand 31

Fig. - a, b, c

The apparent electromagnetic terrain conductivity (mS/m) from soil surface to 1./ m(a), +/ (b) and -* m (c) depth (map scale is in meter).

the depth of +/ and -* m from soil surface
increased with the depth of investigation. The
boundary of severely salt a#ected soil was
found at the depth of -* m.
Recharge and discharge evaluation
The frequency distribution of EM slopes
ranged from *.1/ to -./*. The EM slope wasdistributed around +.,2. The relationship between the recharge areas and EM slope is il-lustrated in Fig. .. The result of this overlay
shows that the EM slopes in the recharge areas
were more than + and could be classiﬁed asrecharge areas. The EM slopes which werelower than + were situated in the salt-a#ectedareas near U.+, U., and U/+. But in the rest of
the salt-a#ected soils or discharge areas, EM
slopes were greater than +.
High values of EM slopes were found in veryΐῐ῎῔῕ῑ ῒ 22 ῏ ῌ,**+῍

32

Fig. .

The distribution of EM slope (map scale is in meter).

low apparent electromagnetic terrain conductivity upland areas which were classiﬁed as
non-salt-a#ected soils, while the EM slopes insalt-a#ected soils ranged from *.1, to +./2. The
frequency distribution of EM slopes in the discharge areas showed that only +*ῌ were lessthan +.
Discussion
Salinization process
The salinization process is a#ected by waterand salt sources, as well as the mechanism of
salinization. The major source of water in local
recharge areas is rainfall. Recharge occurredin upland areas where coarse-texture-soil, sandand silt exist in the soil proﬁle. The distribution of vertical hydraulic gradient shows thedownward movement for the period of time,
which is longer than the upward vertical hydraulic gradient. The electrical conductivity ofgroundwater in the recharge area is low.
Groundwater salinity increases along the path-῍ῌ : Application of Electromagnetic Technique to Identify Recharge and Discharge Areas for Reforestation in Northeastern Thailand 33

way of groundwater ﬂow. The ionic composition of salty groundwater is dominated by Na
and Cl. The ratio of Na and Cl toward + withincreasing the total dissolved solid (TDS) indicates that halite (NaCl mineral) dissolution is
the major source of salt (Williamson et al.,+323).
Groundwater in the discharge area rises towards the soil surface to the depth where capillary rise can occur because of the upward
hydraulic gradient. The evaporation of saltwater leaves salt in the soil proﬁle. The horizontal
hydraulic gradient of salty groundwater insalt-a#ected soil was very low, which allowed
time for the salinization process. The di#erence in the salinity hazard of salt-a#ected soil
is due to the magnitude of the vertical andhorizontal hydraulic gradient in the recharge
and discharge areas, the period of upward anddownward hydraulic gradient, and the depthof groundwater from the soil surface. Excesswater in discharge areas needs to be manipulated by minimizing water input in the recharge areas and water output in the discharge
areas.
Salinity level
The EITCM was adopted for delineating saltstorage in the landscape. Low Eca readings
were found in the upland areas indicating thatrecharge is dominant in these areas. High apparent electrical conductivity was found in thelower slopes and alluvial plains, indicating thatsalt was discharged and accumulated after
evaporation in the surface or near-surface soil.
Three depths of sounding provided the distribution of salt content in the soil proﬁle. The
increasing Eca reading with the depth of sounding in the upland recharge area indicates leaching of soluble salts or nutrients in the soil
proﬁle. The reverse of this phenomenon is seenin discharge areas where shallow salty groundwater is discharged to soil surface (Williams
and Arunin, +33*). From this study it wasdetermined that salinity in discharge areas increased with depth of sounding. This is probably because these areas are underlain withhighly electrically conductive material which
is being mobilized from the depth deeper than-* m to the soil surface by groundwater.
The empirical EM slope is developed forpractical determination of salt content in recharge and discharge areas. All of the identiﬁed local recharge areas had EM slope values
greater than + and apparent electromagnetic
terrain conductivity of non-salt-a#ected soil.
The EM slope in the salt-a#ected soils ranged
from less than + to more than + due to a highsalt concentration in the deeper depths. These
areas may be interpreted as recharge areas.
From the results presented here, it can be seenthat EM slope is not the proper tool for identifying recharge areas because the value of the
EM slope, which is used to divide recharge anddischarge areas, varies from place to place.
The distribution of the EM slope and the salt
concentration in the soil proﬁle should be examined and rejected when the EM slope isgreater than + in salt-a#ected soil. In addition,
one should consider the relationship of highEM slopes and the amount of recharge togroundwater aquifers. Even though the electromagnetic technique is not successful for
identifying recharge areas properly, salt distribution in the soil proﬁle is important data forreforestation program.
Conclusion
The process of salinization can be determined from routine piezometer method thatrecharge from rainfall occurred in the uplandarea and discharged to the alluvium plain
where upward hydraulic gradient was dominated phenomenon. The source of salt mightcome from the Mahasarakram formation
which underlies salt-a#ected areas.
The geophysics technique was adopted toinvestigate hydrosalinity in salt-a#ected soils.
The mapping of soil salinity by EITCM wasproven to be very useful in detecting anddelineating salinity in landscape where it can
not be noticed on the surface soil.
In addition, the empirical approach, usingΐῐ῎῔῕ῑ ῒ 22 ῏ ῌ,**+῍34ratios of deep to shallow sounding for identifying recharge and discharge areas did not accurately handle the assumption due to the increasing of Eca value with increasing depth ofsounding in the discharge area. As the accumulation of soluble salt in the deeper soil
proﬁle. Such situation lead to interpret as arecharge area instead of discharge area. This
exception can be solved by rejecting the highEM slope data which is in the high salt content
proﬁle.
Acknowledgement
The authors wish to thank Prof. Makoto
ANASE and Prof. Rokuro YASUTOMI at TUA
for their guidance and advice as well as Dr.
Mastur Koeshadi of Watershed Management
Technology Center, Indonesia for his conﬁrmation of this paper.
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Surfer for Windows. +330. Surfer Mapping System.
Golden Software, Inc.
Williamson, D.R., Peck, A. J., Turner, J.V. andArunin, S. (+323) : Groundwater hydrology andsalinity in a valley in Northeast Thailand. In‘Groundwater Contamination’. IAHS Publ. no.
+2/.
Williams, B.G. and Arunin, S. (+33*) : Inferring recharge/discharge areas from multi frequency
electromagnetic induction method. Technical
Memorandum 3*/++, CSIRO.
Williams B.G. and Baker, G.C. (+32,) : An electromagnetic induction technique for reconnaissance survey for salinity hazards. Aust. J. Soil
Res. ,* : +*1ῌ+2.

p : Application of Electromagnetic Technique to Identify Recharge and Discharge Areas for Reforestation in Northeastern Thailand 35

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E#ects of Opener-Type Subsoil Improvements with Amendment Matter on
Hardsetting Soils in the Kamikawa District of Hokkaido
Yoshio YOKOI*, Iwao KITAGAWA**, Eiji GOTOU*** and Hiroyuki TAMARU**** Hokkaido Pref. Kitami Agric. Exp. Stn, /, Aza Yayoi Kunneppu-cho
Hokkaido *33ῌ+.30, Japan** Hokkaido Pref. Central Agric. Exp. Stn, Kita +/ Higashi 0 Sen Naganuma-cho
Hokkaido *03ῌ+-3/, Japan*** Hokkaido Pref. Kamikawa Agric. Exp. Stn, / Minami + Sen Pippu-cho
Hokkaido *12ῌ+-31, Japan
Abstract
The e#ects of subsoil improvements were examined on hardsetting soils in Kamikawa,
Hokkaido. The soils were ﬁne-textured gray terrace soils. They are clayey, hard, and compacted and have a shallow soil layer.
For subsoil improvement, a new technique has been developed that makes use of soil amendments.

The technique is a modiﬁed method of subsoiling.

It requires the construction of trenches that are +*cm wide and ,/ῌ// cm deep at 0*ῌ+,* cmintervals. Soil amendments are put into the trench.

The e#ects of the subsoil improvements andthe construction standards for the trenches are as follows :+.

Three years after the subsoil was amended, soil hardness and bulk density decreased along

the trench, and air ﬁlled porosity was maintained at around *.+* m- m--.

Penetration resistancewas greater than ,../ MPa at a depth of ,/ cm before treatment ; however, it decreased to *.32 to+..1 MPa after the treatment.
,.

The amended parts of the ﬁeld worked as a supplementary underground drain in the uplandﬁeld and by the improvements agricultural machinery can be operated more e#ectively even after
rainfall.
-.

The subsoil improvements caused the root zone of crops to expand.

improved remarkably, and yields increased.

Nutrient absorption

The improvements were especially e#ective todeep-rooted crops which are susceptible to wet injury.
..

The trench intervals were set at 0* cm when soil hardness was greater than +.+0 MPa ;however, the intervals were expanded to +,* cm when the soil hardness was *./- to +.+0 MPa.
Key Words : subsoil improvement, hardsetting soils, soil hardness, bulk density.

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Soil physical properties of hardsetting soils

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«¬­ 0* cm ij
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Crop yield in the ﬁeld experiment

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The management evaluation of openertype subsoil improvement

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J. Jpn. Soc. Soil Phys.
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*E#ects of Subsoil Breaking on Surface Runo#, Pressure Headand Soil Temperature in a Sloping Field
Toshitsugu MOROIZUMI*, Yuichi SATO**, Koichi SATO** and Takeshi MIURA** Faculty of Environmental Science and Technology,
Okayama University, Okayama 1**ῌ2/-*, JAPAN** School of Veterinary Medicine and Animal Sciences, Kitasato University,
Aomori *-.ῌ20,2, JAPAN
Abstract
This paper discusses the e#ects of subsoil breaking on the change of pressure head, soil
temperature and runo# discharge in space and time in a sloping ﬁeld.

A controlled comparison

experiment was conducted in a subsoil breaking ﬁeld and a no-subsoil breaking ﬁeld.

The results

showed that the runo# ratio of the subsoil-breaking ﬁeld was about +/+* of that in the no-subsoil
breaking ﬁeld.

This indicates that subsoil breaking promotes the inﬁltration of rainfall into thesoil and can reduce the surface runo# discharge.

The spatial distribution of the equi-pressure

heads during rainfall was complicated, and the coe$cients of variation were large.

However,that of the equi-pressure heads before and after rainfall showed the similar patterns of variationin both ﬁelds.

As for soil temperatures, we didn’t observe a large di#erence between the subsoil

breaking ﬁeld and the no-subsoil breaking ﬁeld, and the spatial variation was smaller than that ofthe pressure head.
Key words : Subsoil breaking, Pressure head, Soil temperature, Surface runo# discharge, Coe$cient of variation+    

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Soil moisture characteristic curves for the subsoil breaking ﬁeld and theno-subsoil breaking ﬁeld.

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Fig. .

BCDῌEῌF'HI=>?

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Temporal changes of the equivalent pressure heads (Unit : cm H, O).

ΐῌ+ ghi&[ jk
Table +

Physical properties of soils

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cg cmN-fpqno
cg cmN-f

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ῌῌ/Fig. /W

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49

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Coe$cients of variation for pressure heads in (a) subsoil breaking ﬁeld and (b) no-subsoil
breaking ﬁeld.

 

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50

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Fig. 0Observed discharges and distribution rate of pressure heads in (a) subsoil breaking ﬁeldand (b) no-subsoil breaking ﬁeld. The arrows (cd) show the date of Fig. ..

Fig. 1

Temporal changes in soil temperatures and air temperature in (a) subsoil breaking ﬁeld and(b) no-subsoil breaking ﬁled.

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J. Jpn. Soc. Soil Phys.
῏῍ῌῐῑ῎
No. 22, p. /-ῌ0* ῍,**+῎E#ect of Roots on Formation of Internal Fissures in
Clayey Paddy Soil during Desiccation
Shuichiro YOSHIDA and Kazuhide ADACHINational Agricultural Research Center, NARO Inada +ῌ,ῌ+, Joetsu, Niigata, 3.-ῌ*+3-, Japan
Abstrct

Internal ﬁssures in clayey soil are important for tillage e$ciency. The roots reinforce thesoil and absorb soil moisture, resulting in shrinkage and fractures in the massive soil structure.
The objective of this study is to clarify the inﬂuence of roots on the prevention of wide cracks
and the formation of small ﬁssures during desiccation. Soil samples were taken from thesurface layer of inter-row spaces of a clayey paddy three weeks after the release of ponding
water in the summer +332. In half of the sampling sites, the stems and leaves of the rice plants
were cut away just before the release of the ponding water, in order to compare the e#ects ofthe two resulting water absorption conditions. After measurement of the volume fractions of
the solid, liquid, and air phases, the oven-dried samples were soaked in water and then scoured
with tap water in a sieve. The remaining roots were dried and weighed. The relationships
among volumetric air ratio, moisture ratio, and root density were statistically analyzed, withthe volumetric air ratio being regarded as the ratio of newly formed ﬁssures due to desiccation.
Positive direct correlations were observed between root density and air ratio for all plots. In
the plots with transpiration, since the moisture ratio correlated with root density and air ratio,a large proportion of the variances in air ratio explained by moisture ratio and root density
were shared. These results lead to the following conclusion : Rice plant roots inhibit theformation of wide cracks and induce small ﬁssures in clayey well-puddled soil during desiccation. With transpiration, these e#ects are attributed to the compound functions of roots :absorption of water and soil reinforcement. However, even without transpiration, soil reinforcement by roots uniquely contributes to the development of small ﬁssures.
Key words : Soil shrinkage, Root density, Internal ﬁssure, Soil reinforcement, Absorption ofsoil moisture+.

Introduction

Internal micro-cracks in soil are practicallyimportant for tillage e$ciency, because soil’s
tensile strength depends on the number andextent of ﬁssures from which fractures would
begin. Utomo and Dexter (+32+) proposed thatthe friability of soil clods can be expressed by
the linear relationship between the logarithmof aggregate volume and the logarithm of tensile strength. The slope of the relationship is ameasure of the dispersion of the strengths of
micro-cracks and ﬂaws. Major processes in theformation of aggregates in soils are desiccation, shear failure, and biological activity(Wilding and Hallmark +32.). Micro-cracks insoil are also considered to be formed by the
combination of such factors or by previous
tillage.
Desiccation causes soil shrinkage and brings
the particles closer together, but if the movement of soil particles is constrained, tensile῏54ΐῐ῎῔῕ῑ ῒ 22 ῏ ῌ,**+῍stress is generated between the particles,
resulting in tensile failure. The shrinkage
characteristic of soil depends not only on theproperties of the soil, but also on the rate ofdesiccation or substances that hinder the homogeneous movement of soil particles. Rootsin soil exert large e#ects on soil shrinkage
behavior, because they increase the rate ofdesiccation and reinforce the soil. Mitchell andvan Genuchten (+33-) clariﬁed the e#ects ofroots on an in situ soil shrinkage rate. Afterobserving greater shrinkage volume in fallow
ﬁelds than in wheat and alfalfa ﬁelds, they
concluded that soil’s shrinkage characteristic
may change, depending on the cropping condition.
Waldron et al. (+32-) measured the shear resistance of soil reinforced by alfalfa and pineroots, and observed a signiﬁcant increase compared to the soils without roots. Waldron andDakessian (+32+) measured the mechanical properties of roots, and related them to increased
soil shear resistance. Their analysis showedthat the elastic behavior of roots enhances resistance against the shear stress. Thus, it isnaturally deduced that roots also increase thetensile strength of soil, and inhibit homogeneous shrinkage.
The e#ects of roots on soil’s shrinkage behavior include not only reinforcement but also
water absorption. It should be noted that roots
reinforce the soil against the tensile stressgenerated by the depletion of water, which theroots themselves cause. Yoshida et al. (+331)
pointed out that the introduction of wintercrops into paddy ﬁelds enhances the macropores in soil in spring, when the crops begin togrow again. Pillai and McGarry (+333) compared the e#ect of crops on the structural
repair of compacted soil. They concluded thatlablab [Lablab purpureus (L.) Sweet] and mungbean [Vigna radiata (L.) R. Wilezek] lead to therapid repair of soil structures due to the great
cyclic variation in wetting and drying induced
by a large evapotranspiration rate. Thesestudies suggest that the absorption of water byroots may also contribute to the formation ofsoil structure because roots inhomogeneously
distribute suction and tensile stress, possibly
inducing micro-cracks.
The present study examines the relationshipbetween the internal ﬁssures and root densitywith respect to water content, aiming to discriminate between the two di#erent e#ects ofroots on soil shrinkage : water absorption andsoil reinforcement. Such discrimination ispractically useful to estimate the di#erence between the e#ects of living and remaining roots
on soil structure during desiccation.
,.

Materials and Methods

The experimental paddy ﬁeld used for thisstudy is located at the Hokuriku Agricultural
Experiment Station in Niigata Prefecture,
Japan. It has been utilized as an irrigatedpaddy for more than ,* years. The soil isclayey, montomorillonitic, mesic, typic Epiaquepts, and contains -2ῌ clay, -1ῌ silt, and,/ῌ sand. The experiment was performed in+332. The rice seedlings were transplanted inrows by hand from sca#olds that had been set
up around and across the sample site in order
to avoid disturbing the surface of the soil. The
row spacings were set as -* cm or 0* cm. The
ponding water was maintained on the surfaceof the ﬁeld until ++ August +332. In half of thesampling sites, the stems and leaves of the rice
plants were cut away just before the release of
the ponding water, in order to compare thee#ect of water absorption on soil shrinkage
behavior. In these sites, only the roots, whichhardly absorb water, remained in the soil.
Sampling of the soil was performed on +* and++ September. Undisturbed core samples, eachwith a diameter of /* mm and a thickness of ,/mm, were taken from the surface layer in theinter-row space, avoiding the wide visible
cracks. The distances from the plants werereferred to in determining the sampling sites,
since samples with large deviations in root
density were desirable for the analysis. Aftermeasuring volume fractions in the solid, liquid,῎῍ : E#ect of roots on formation of internal ﬁssures in clayey paddy soil during desiccation55

and air phases, the oven-dried samples were
soaked in water for a day and then scoured
with tap water in a sieve with a *..,-mm mesh.
The remaining roots were picked up, dried for,. hr. in an oven at 2/ῌ, then weighed.
-.

Results and Discussion

Figure + provides a typical shrinkage characteristic curve, representing decreasing soil void
ratio with decreasing soil moisture ratio. The
structure of the well-puddled paddy soil shows
little stability. Most of the pores are plastic
and shrink easily within the stress range induced by low suction. Thus the entry of air
into stable macro-pores, usually observed instructured soils (a), is negligible for puddled
clay soils (b, c). In the normal shrinkage range,
cracks or small internal ﬁssures are easily produced in the in situ puddled soils (b), while inthe conventional shrinkage tests in the laboratory, puddled samples packed in the testing
dishes exhibit volume decreases that arealmost equal to the water losses (c). This isbecause the horizontal movement of soil is notallowed in the ﬁelds but is allowed in the laboratory test. The formation of cracks or manysmall ﬁssures is the only process in which theincreasing horizontal stress is released. At ahigher suction range, soil exhibits residual
shrinkage or zero shrinkage. These shrinkage
regimes are relatively less important for theformation of structures, since the entry of air
into pores precedes the deformation of pores.
In soils reinforced by many roots, crack formation tends to be inhibited and instead smallﬁssures are induced. To compare the e#ect ofroots on such ﬁssures induced by desiccation,
we used the volumetric ratio of air with respect
to the volume of a solid, assuming that all the
air-ﬁlled pores are newly made by fractures.
This hypothesis seems to be reasonable because the puddled pasty clayey soil never initially has large stable pores subject to air entry,
due to low suction. The pores between larger
clods would be ﬁlled with small particles
during the sedimentation process after puddl-

Fig. +

Typical shrinkage characteristic curvesfor (a) structured non-swelling soils, (b)well-puddled swelling soils in situ, and(c) well-puddled swelling soils in conventional shrinkage tests.

ing.
Fig. , (a) through (c) show the relationships
among root density, volumetric moisture ratio(Vw/Vs), and volumetric air ratio (Va/Vs) for
the samples in the plots with transpiration.
According to the shrinkage characteristic observed in the disturbed samples of the sameﬁeld, the maximum and minimum moisture
ratios of ,., and +.- shown in Fig. , correspond
approximately to suction levels of + kPa and+** kPa, respectively. All the samples are
therefore considered to be within the normal
shrinkage range. Negative signiﬁcant correlations are observed between volumetric moisture ratio and volumetric air ratio (a) and between root density and volumetric moisture
ratio (c) ; and a positive signiﬁcant correlation
is observed between root density and volumetric air ratio (b). The negative correlation between moisture ratio and air ratio, shown in (a),can be naturally accepted by regarding typicalshrinkage characteristics discussed in the preceding section : the increase in air ratio, representing the formation of internal ﬁssures, is
induced by a decrease in the moisture ratio, in
other words, ‘desiccation’. On the other hand,56  22,**+

Fig. -

Concept of shared and unique varianceexplained by two inter-correlated factors.

the positive correlation between root density
and air ratio does not necessarily demonstratethat roots mechanically reinforce the soil
resulting in the formation of ﬁssures by shrinkage, because roots simultaneously reduce themoisture ratio, resulting in the observed increase in the air ratio. Thus we should
delineate the e#ect of root density on air ratio
by calculating the unique and shared variances
between these independent variables. The concept is summarized in Fig. - after Hair et al.
+332. The total variance in the volumetric air
ratio consists of the variance uniquely explained by moisture ratio (S+ ), the variance
uniquely explained by root density (S, ), thevariance explained jointly by both factors(S+,), and the variance not explained by thesefactors, i.e., error (SE). The procedure of calculation is provided in the Appendix. The results
are shown in Table +. All these variances arecalculated for the standardized data : the total
variance in the air ratio is equal to one, and theFig. ,

Relations between (a) volumetric moisture ratio (Vw/Vs) and volumetric air
ratio (Va/Vs), (b) root density andvolumetric air ratio (Va/Vs), and (c)root density and volumetric moisture
ratio (Vw/Vs) for the samples in theplots with transpiration.
*, ** : Signiﬁcant at the *.*/ and *.*+
probability levels, respectively.

ῐ῏ : E#ect of roots on formation of internal ﬁssures in clayey paddy soil during desiccation

Table +

57

Direct correlation coe$cient between the variables and composition of variances ofstandardized Va/Vs (With Transpiration)

R : Direct correlation
coe$cient-* cm row
spacing
Variances ofstandarized Va/Vs

R : Direct correlation
coe$cient

0* cm row
spacing
Variances ofstandardized Va/Vs

Volumetric moisture
ratio (Vw/Vs)

Root
density῍*42,/1***41,1**

Volumetric moisture
ratio (Vw/Vs)ῌ῍*42/13**(S+) : Unique varianceexplained by Vw/Vs*4+/.0(S,) : Unique varianceexplained by root density*4**+-(S+῎,) : Shared variance*4/,1,(S+῎,) : Total varianceexplained by these factors*402-*Air ratio (Va/Vs)

Volumetric moisture
ratio (Vw/Vs)

Root
density῍*40-12**41113**

Volumetric moisture
ratio (Vw/Vs)ῌ῍*42/+-**(S+) : Unique varianceexplained by Vw/Vs*4**,,(S,) : Unique varianceexplained by root density*4,**.

(S+῎,) : Shared variance*4.*.1(S+῎,) : Total varianceexplained by these factors*40*1-Air ratio (Va/Vs)*, ** : Signiﬁcant at the *.*/ and *.*+ probability levels, respectively.

total variance explained by factors (S+῎,) is
identical to the coe$cient of determination (R,)
after the multivariate analysis. It should be
noted that the shared variance is substantial
compared to the unique variances of thefactors. Therefore, while the roots absorb soil
moisture, the compound function of roots :water absorption and reinforcement, is exerted
on the increase in internal ﬁssures during
shrinking. The variances not explained bythese factors may include experimental errors
and e#ects of unknown variation in propertiesof the soil or the roots.
Fig. . (a) through (c) show the relationships
between the factors for the samples in the plots
without transpiration. No correlations wereobserved between moisture ratio and air ratio ;however, positive signiﬁcant correlations be-

tween root density and air ratio were observed.
Although the moisture ratio is slightly correlated with root density in the 0* cm row spacing plot, this might be due to the di#erence indrainage e$ciency between the row and therow-middle, and has no signiﬁcant meaning.
Thus we regard that no correlations exist between the root density and the moisture ratio
in the following discussion. The signiﬁcant
positive correlations between root density andair ratio without the e#ect of moisture ratio
prove that the mechanical reinforcement of theroots induces small ﬁssures after desiccationeven when the roots do not absorb soil moisture. In other words, during desiccation due
solely to evaporation, roots mechanicallyinduce internal ﬁssures in soil by meshing andﬁxing the soil particles together, against the

58ΐῐ῎῔῕ῑ ῒ 22 ῏ ῌ,**+῍

fracturing forces generated by shrinkage.
The e#ect of root density on the increase in
air ratio is considerably less in the plots without transpiration than in the plots with transpiration, according to the slope of the relationship shown in Fig. , (b) and Fig. . (b). Therefore, the e#ect of roots on the development offriable structures of soil is better exerted
during the period when rice plants activelytranspire. However, these ﬁndings may also
aid in controlling the structure of clayey soils
after harvesting rice. If the roots remain until
the next spring and become enmeshed in thesoil, they can contribute to the creation of ﬁssures as the soil dries. The clayey paddy soil
just after rice harvesting is so sticky that large
clods would be produced if tillage were performed then. Such clods would shrink with
few internal fractures the next spring, becoming extremely hard with poor friability. If no
mechanical procedures are performed until thenext spring, many ﬁssures can be naturally
produced as the soil dries.
The increase in the volume of minute ﬁssures depresses the development of wide
cracks. These ﬁndings therefore suggest thatroot density controls the distribution of thetotal shrinkage volume to the wide cracks andsmall ﬁssures. Root density varies with respect
to the distance from the plant. The regions inwhich roots extend sparsely are subject towide cracks, while the regions near the plants
are not. Soil reinforcement by roots also
a#ects the cracking patterns between the rows
in this manner.

Fig. .

Relations between (a) volumetric moisture ratio (Vw/Vs) and volumetric air
ratio (Va/Vs), (b) root density andvolumetric air ratio (Va/Vs), and (c)root density and volumetric moisture
ratio (Vw/Vs) for the samples in theplots without transpiration.
*, ** : Signiﬁcant at the *.*/ and *.*+
probability levels, respectively.

῔ΐ : E#ect of roots on formation of internal ﬁssures in clayey paddy soil during desiccation..

Conclusion

The roots of rice plants inhibit the formationof wide cracks and induce small ﬁssures inclayey well-puddled soil during desiccation.
This e#ect of roots on soil is exerted even when
the roots do not absorb soil moisture. Thisﬁnding is important in regard to the physicalfunction of the roots that remain after crops
are harvested.
Acknowledgment
We thank Dr. Noburo Haraguchi for his
advice on statistical analysis. We also thankMr. Yoichi Wakai and Mr. Yuji Yokoyama of
the ﬁeld management section in our institutefor their experimental assistance and technicaladvice.
References
Hair, Jr., J.F., Anderson, R.E., Tatham, R.L., andBlack, W.C. (+332) : Multivariate data analysis,
Prentice-hall Internatinal, Inc., p. +3*ῒ+3+.
Mitchell, A.R. and van Genuchten, M. Th. (+33-) :Flood irrigation of cracked soil, Soil Sci. Soc.

59

Am. J., /1 : .3*ῒ.31.
Pillai, U.P. and McGarry, D. (+333) : Structure repairof a compacted vertisol with wet-dry cycles
and crops, Soil Sci. Soc. Am. J., 0- : ,*+ῒ,+*.
Utomo, W.H. and Dexter, A.R. (+32+) : Soil Friability, J. Soil Sci., -, : ,*-ῒ,+-.
Waldron, L. J. and Dakessian, S. (+32+) : Soil reinforcement by roots : calculation of increased
soil shear resistance from root properties, Soil
Sci., +-, : .,1ῒ.-/.
Waldron, L. J., Dakessian, S., and Nemson, J.A.
(+32-) : Shear resistance enhancement of +.,,ῒ
meter diameter soil cross sections by pine andalfalfa roots, Soil Sci. Soc. Am. J., .1 : 3ῒ+..
Wilding, L.P. and Hallmark, C.T. (+32.) : Development of structural and microfabric properties
in shrinking and swelling clays. In Proceedings ISSS Symposium on water and solute
movement in heavy clay soils. J.Bouma and P.
A.C.Raats (eds.) ILRI Publ. No. -1, Wageningen,the Netherlands, p. +ῒ,,.
Yoshida. S., Itoh, K. and Adachi, K. (+331) : Improvement of drainage in clayey rotational
ﬁeld by introducing winter crops after conversion from paddy, Soil Phys. Cond. Plant
Growth, Jpn., 10 : -ῒ+,. (in Japanese with English abstract)

Appendix (after Hair et al. +332)
The analyst can determine the shared andunique variance for inter-correlated independent variables using direct correlation coe$cients. Part correlation of Y, X+, given X, canbe calculated as :rY, X+ (X,)ῐ

rY, X+῎(rY, X,῏rX+, X,)
ῌ+῎rX+, X,,ῌwhere ra, b denotes a direct correlation coe$cient between variables a and b ; and Y denotes the dependent variable. X+ and X,
denote independent variables, inter-correlatedwith each other. The unique standardized variance predicted by X + is equal to the square of
the part correlation :S+ῐr,
Y, X+ (X,)῍

The unique variance explained by X, is also
written as :S,ῐrYῌX, (X+),῎

The amount of shared variance can be conﬁrmed by subtracting the standardized uniquevariance from the square of the direct correlation coe$cient between Y and Xi :S+ῒ,ῐrY, X+,῎S+orS+ῒ,ῐrY, X,,῎S,

῏ῐBoth equations lead to the same result. The
summation of these variances yields total variances explained by these independent variables :S+ῑ,ῐS+῍S,῍S+ῒ,ῑThis value exactly corresponds to the coe$cient of determination R, after the performanceof multivariate analysis.

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Journal of the Japanese Societyof
Soil Physics
October ῎ῌῌ῍

No. 22
Contents

Foreword ῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍T. MIYAZAKI῍ +Original Papers
Permeability and Water Retentivity of Peat Soil ῌSoil Physical Properties of Bibai
Peat Land(ῌ)ῌ῍῍῍῍῍῍῍῍῍῍H. IMOTO, T. MIYAZAKI, H. SAITO and M. NAKANO῍ E#ect of Grass Strips on Reduction of Sediment Loss from Upland Field῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍T. UENO, M. MIHARA, J. S. ARUN and Y. DOKIYA῍++
Application of a General PDE Solver for Analyzing Water and Solute Transport inSoil῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍K. NOBORIO῍+3Application of Electromagnetic Technique to Identify Recharge and Discharge Areasfor Reforestation in Northeastern Thailand῍῍῍῍῍῍῍῍῍῍῍῍῍C. DISSATAPORN, H. NARIOKA, P. YAMCLEE and S. ARUNIN῍,1
E#ects of Opener῍Type Subsoil Improvements with Amendment Matter on Hardsetting Soils in the Kamikawa District of Hokkaido῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍Y. YOKOI, I. KITAGAWA, E. GOTOU and H. TAMARU῍-1
E#ects of Subsoil Breaking on Surface Runo#, Pressure Head and Soil Temperature
in a Sloping Field῍῍῍῍῍῍῍῍῍῍T. MOROIZUMI, Y. SATO, K. SATO and T. MIURA῍./
E#ects of Roots on Formation of Internal Fissures in Clayey Paddy Soil during
Desiccation ῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍S. YOSHIDA and K. ADACHI῍/Announcements ῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍0+Editor’s Postscript ῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍0-Japanese Society of Soil Physics
Department Biological and Environmental Engineering
Graduate School of Agricultural and Life Sciences, The University of Tokyo+῍+῍+ Yayoi Bunkyooku, Tokyo ++-῍20/1, Japan