
J. Jpn. Soc. Soil Phys.
FRfµyNo. +*-, p. - +, ,**0

   !"#$   *The Technique for Improving Soil Physical Characteristics by Preventing theFormation of Soil Crust by Dressing the Sandy Pyroclastic Deposits
Yoshio YOKOI** Hokkaido College of Agriculture, Nishi-senbiri-,/ῌ+, honbetu, nakagawa-gun *23ῌ-01/, Japan
Abstract
E#ects of dressing pyroclastic deposits to the crust forming soils distributing in Biei hill area
are summarized as follows.
+) Crust forming soils in Biei hill area shows di$culty in plowing, which becomes the limiting
factor for the crop production. This soil is not clayey, but easily dispersed after rain fall, andreadily forms crust on drying.

This crust forming soil has remarkably large solid percentage,high bulk density, and low coarse porosity. The soil hardness also increases remarkably on
drying.
,) Pyroclastic deposits improves these soil physical properties, and the yield of ﬁeld crops
increase steadily by dressing the pyroclastic deposits to the thickness of /ῌ+* cm.

Largerdressing of pyroclastic deposit showed little e#ect on the yield of ﬁeld crops due to the decreaseof soil fertility.
-) Soil dressing decreased the speciﬁc resistance on traction when ﬁeld is plowed. Soil dressing of /ῌ+* cm thickness was e#ective enough to the decrease the speciﬁc resistance to the lowest
value.
.) Critical thresholds of the necessity of soil dressing for improving the physical properties ofsoils were evaluated. These values were (+) siltclay contents*.-/ kg kg+, (,) Crust hardness
*.2 MPa, (-) bulk density+.-/ Mg m-.

When either one of the three criteria is applicable, it isjudged that soil dressing is necessary.

The goal value of the improving soil texture was set at*.-/ kg kg+.
Key words : crust, pyroclastic deposits, soil dressing, hill area

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5

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Distribution of pyroclastic deposits covering the Biei hill area in the middle-south part of
Kamikawa district (mapped according to Ikeda and Mukaiyama, +32-).

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kg

Table +

 #The moisture content of large soil clod
and the soil hardness after plowing up.

s(kg kg+)

(MPa)

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04,
.34*

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(mm)
(,.)
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J

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-

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Table ,

E#ect of dressing pyroclastic deposits to the crust forming soils on the physical properties ofsoils.

<=>

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lcmm

c

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SCL
SL
SL

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*4,32
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z
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CL
CL

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*4,1,
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LS
LS

z
z

z
z

z
z

z
z

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z

z
z

+m Z/<=>% a T ,;<=>% b T,m Q *}0., kPa, 0.,}32.+ kPa,  32.+ kPa ~$ῌῌ- [\]^_`Ea012345EIcdefg
Table -

E#ect of dressing pyroclastic deposits to the crust forming soils on the chemical properties ofsoils.

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lcg kg+m ^uy*.+ N c

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#(%/0+123456

x +*- ¼ D,**0E

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A& 'B9:  / cm =P 1*ῌ >(<zRR#STP

 2345;<= ..+ MPa   +* cm!%*1

 *.3 MPa >?! C+ $@% "  / cm = + +* cm =[

*+?!

2345; *.2 MPa D+/ mmE s.+1#

D(ῌ,E )9:F" 

"23456

G-*0!  " 23456 -NOTd <= ,./ Mg ha+  / cm =

 H< #(+ ( IJ5K,-.+ Mg ha+  ,.ῌ $d-./L! 4MNOPQ# "IJ5K,+/ cm d?!

 +"0RS-107TU( 0RS2VG

0WX1

F YZ  ῌ- #$ 

! ! 
1#Z

f#( K\?!

0s.

 ]^_Od  / cm
>$d  +* cm = ,.20 Mg ha$@  CEC [\ ]^ 3&4_P`a

= ,2ῌ $d

5L!

 +/ cm $dPL!

>  pH b*  _P`

cde6?!

1 7 8 /f9 :!" *+ ;Kgh<= 

+ +* cm+ <! ! ]`  / cm =a$@!

P

! ! 

+* cm -Z.$d&'bc K\?}~"Us.+1

PP #(L!     ->i!" gdd <= -0.2 Mg ha+ d 1.ῌ

h"U?T )9:?j% kl

.! #(efK@mn<AT +* cm oB [\ / cm =dd ./.* Mg ha+ d]^K_P`?  ghK;p?#2*ῌ oB( ¡MI¢dd !89:< +,.+ Mg ha+ Q
$@ 5!>ha+ g-£!

 

 +* cm oB -- Mg

  +* cm $dPhiC'B9:  / cm = +/ cm =

$dP¤

¥¦6j <=P*¥§k }~!"¨l  #( %*1mnV' ©ª-F«"

UoB + 23456 .T# " ozdKMBT!

!Z/K\-?* z@m  }~T
-y-y- L¬­®z¬ j|T}~#L¬­®z¬¯}~-p°T 0 L
ῌῌ,Fig. ,

2345;»e

The relationship between the amountof dressed soil and the hardness of soil
crust.

z¬­®

±²q³r´"U µ3¶·$¸z¬¹±²sq³Q-Y - tusº!

(ῌ- £T#$ <= 0* kPa vw"U±²

sq³ $@%?!  / cm =

EF : 5+f$%Y&"a=G¹Jº58!E-&1) »¼

9

ῌ. a=-f$%Y& '& K
Table .

E#ect of dressing pyroclastic deposits to the crust forming soils on the yields of ﬁeld crops.

 9Mg ha7+;


c
9cm;

*9t;
/
+*
+/

ῌ-

@



¡¢
9O<;
9+320;£¤¡B¥
9¡?<;
9+321;¦¢§
9O<;9+322;¨©ª©
9«¬,o<;
9+32/;£¤¡B¥
9¡?<;
9+320;­©®¡
9D;9+321;

9+320;,4.2 9+**;-4++ 9+,/;,4/. 9+*,;,4.+ 9 31;+,4+ 9+**;,142 9,*-;--4- 9,1/;--4/ 9,11;,4,. 9+**;,4/3 9++0;,420 9+,2;,4.. 9+*3;-142 9+**;./4* 9++3;-342 9+*/;-/4/ 9 3.;,24+ 9+**;-,4+ 9++.;,241 9+*,;-,4/ 9++0;+*4* 9+**;+*4/ 9+*/;343 9 33;
342 9 32;

+2
1*
3,
32

+; ¯r°±!E 9

Fig. -

C9ῌ;¡¢; ,²*( c * cm 9t; J +** 8!E³tJb

8´>Le³
Relationship between the amount ofdressed soil and the speciﬁc resistanceof traction.

 .* kPa,  +* cm     
'$()

/ cm ! "# $%&*. 

ῌ.

8Bµ=¶·¸

Fig. . Change in contents of silt  clay in proportion to the amount of dressed soil.

61 cm)!/*8!0b! 9+, +33.; 35

 - -c,D0/  .d!E
8( LeTf"#gh8M/0!

0 -&1) HI ij,234Jkl

Em n5J +K o6,-+J
Kp4 q,DE8" "L, +* cm

+,-./0( 12345

1rs6c/( t8ghu7 v

5( -6/ 35 -*60* Mg m7+ 8!

8,wx@yz{J9|}~E:;% 930/ 9: +33+; 3<35

 $< ,**+; "#'=5JP+( =>?@AB( - cm

CD

1 > !0/4 UTS) 

E 9FG +323; HI( 'J +|(, '+JK?) q/

K8/L"# +, MN#5O PQ

8 L K!E# MGR!E#8 j h  ,/35 9FG +323;

ST U ) C Q! "#V@WX$%Y&Tf$%Y&~D0

WX$%Y&8!0( '-Z

E8 ,ABC WX+[0  /6+* cm, \]^(8_`a -.0./0( ya34V< 8? @  +*- ¼ ,**0

10

ῑῌ/ »
Table /

P-? @

Critical physical properties of soils indicating the necessity for the dressingof pyroclastic deposits.

 *

/6
f+

ab7dlcMdl kg kg 
4567jNkAL6 MPa
U V Mg mf-

*4-/ <)*42 <)+4-/ <);$?cHd? ). +?
@?e<"'Jf"g*P-

/ῌ ῕

ΐ

&yg"HI*45678%?^'z;?"h*9: <P^! 
+ &yg 45678%? JKL"{i ! C So'Q-|

?

=TMV }~"'!?H(1*).     +32*  ! "#$% 
" & 

+j"k4567U"8%* 45678%? ?OlU


'!$

  () ")

Vm(VnZV 4d ?jN$j"km(VG, ; @ g\*

! *+

C "h(  /F+* cm 34h+" )* ((  !,!"# ;<)4 ?opN8P3-). /0"11$2 #
3  3$45678%&'9:(.;

l8)
- H5IJKLMNq5O (  /F+* cm PQ67RG()

<)=: >" 45678% &'**+*3"?#@,-./A0 B

? @g *+* Jr"s.*)."B()-./* ῌ ab7cM
d4 *.-/ kg kgf+ <) ῍ 4567jN *.2 MPa <)

()
1 ῏. 2C

349:+4DE /F+*

cm  ) G) H5IJKLMN5O /F῎ U V +.-/ Mg mf- <) ! ;i;

X)*P-/<Z+* cm PQ67RG8P* () 9

ῐS4 :3+";/<()
G) =T>%*06 45678%U(V῏tuonv  wx a>B*

y ")Z^z{() A | )C DEFG"HI*45678%?"JY

2¡R}¢£~¤¥¦§¨£~© ª x?

@W$$XA&Z[\ K῏. "L*A& ?2]3()=: /F+* cm "^_E`
6 1./ cm  ab7 c Md4e.DE *.-/kg kgf+ ! g*0*h()

ab7cMd4#i

?45678%*.2 MPa +/ mm AL

6O ( ;<)6P-()
" lQmM?RnC ? @So1?TS?"pq( U

V +.-/

Mg mf- WX YG( ZRr ,**.  U VV-[sZ).?"^  +313 : A |?²S% HIg² VM g³ A |´µ ?2 ¢¶b· pp. ,.3῏,0-.
Asgedom, G.G. and Hasegawa, S. (,**/) : The e#ect ofraindrop impact and initial soil conditions on
surface crust. J. Jpn. Soc. Soil Phys., +** : 0/῏1/.

&2¡°>3¸ +323 : &?2¡ "'g\@,9S tu( +.-/ Mg mf-

pp. +*1῏++,.

<)g\P-() ; -./ª¤w +331 : 

A06

1῏/ ^!B() G) ]vw

x  (M^#_CῌRn`^
$?#@,ab[\; ^ 2i

C¯" s῍ ῔ ῒ ῎"/<*4567jNkAL6

C«¬­®§£~"°)Z±V^z{()

"^_45678%

pq"¹*¤¥³ 2º¤b +. : .3῏
3/.
Casagrande, A. (+3.2) : Classiﬁcation and Identiﬁc- : <9:./0wug(ov ¼;]Z  

ation of Soils. Trans. ASCE, ++-, pp. 3*+῍33+.

  +3/* :  

Tanaka, U., Yokoi, Y. and Kyuma, K. (+33,) : Mor-

+1 : +03῍+1,.



ῌ





Nutr., -2 (.) : 0//῍00..
Tanaka, U., Wada, T., Yokoi, Y. and Kyuma, K. (+33/) :ῌ +32* : 



phological characteristics of soil surface crusts
formed under simulated rainfall. Soil Sci. Plant.

 +320 : ῌ pp. +3+῍,*/  

11

 ! "#Evaluation of crusting susceptibility of someJapanese soils based on water permeability and!   ., : --῍.*.

morphology of crusts. Soil Sci.Plant Nutr., .+ :$%& ' ,**+ : ()*+,-./01 !"#$!23%& $%& ' : pp. -.῍,0-῍,1..
Tanaka, U., Yokoi, Y., Kyuma, K. and Kosaki, T.
(+331 a) : Mechanisms and processes of crust for--/.

'()*ῌ45

6 +32- : $+,!7-"8

mation : I. E#ect of initial moisture conditions

9:./0 12;3 "<=>? 23 - :on aggregate stability and crusting. ibid., .- : 33῍+0-῍+1,.

+*1.

 +323 : $4Tanaka, U., Yokoi, Y., Kyuma, K. and Kosaki, T.

 BC8 +/* : 3+῍+32.

(+331b) : Mechanisms and processes of crust for-%9= +32- :  D=EFGHI pp.

mation : II. E#ect of slaking and impact of rain-

67@;A5

0,῍2, pp. +,-῍+,..

drops on crusting under di#erent moisture con-

%23= +311 : %23J:BF;%&ῌ
pp. ,.῍,/ %23= <,K=Lῌ>?

ditions. ibid., .- : +*3῍++/.
Tanaka, U., Yokoi, Y., Kosaki, T. and Kyuma, K. (+333) :@ῌMABC ,**. : <,N

Mechanisms and processes of crust formation :O ao PQRST/UVWXYZ

III. Relations between natural rainfall character-[\D +/ EFG]YC^

!$

"8! $%BFC^HI_ $%C^`a0/ pp. ++-῍++3.
bcCJῌKL

j W % .0 - : +1῍,+.

M +32. : N?

d A

HOhV WiXj + kl mI.n(o +- : 1*῍2/.
pῌq^

g? 03 0 : 0..῍0.2.

Jῌ-

ῌr"s` ,**+ : q9:.

/0r;st" W mI.
_ῌr"s` +33. : $ab"8 "O#./0 (>Jῌkl-Iῌ?mn +332 : $o-"; p<9:./0

2 !  ! ? /, : ,--῍,-3.

bcCJῌOPQRSῌ-TU +303 : efPg

YZ[\ῌ]5

istics and degree of crusting. ibid., ./ : /-1῍/.3.

5?}~ +33+ :   h wi<Nn(o ./ , : +*/῍+++.
Jῌkl-Iῌr"s` ,**. : o-";O;cde   1* : //῍0/.

t" uOwxv Ew;Jt ,*** : ug(o!

v2hOwx

yfiXz {|jC^

g? 1+ - :$xB8 20 : /1῍0-.

yz{|} ,**/ : ]~  p. +2-.

-+/῍-+0.

῍ῌst" "Owxvug(o  ¡W4oOY¢£7@;¤¥¢Y¦ ?

§CL¨LiC ;/0r 3©] ª ¤Y«4¬­ ®¯w­(°/±aP²³]

´ µYZ¶ A · ¸Yug(o¹v¦ A ug(ov;0 ]º]»º  ¤º(LM k +*- l m,**0n12





!"#$%&'()*+,-.( /) /0+* cm 1

2345678 9 :;<=.; / >?@ABCDEFGHIJK(LMNOIP6Q)RST5UP, ῌ VWXYZ3 *.-/ kg
kg[+ \8 ῍  *] 2 MPa \8 ῎ ^'3 +.-/ Mg m[- \81 _` a_b1)

cRQTd1efghij : ,**/ h 3 i +. j
fLhij : ,**0 h , i - j