
J. Jpn. Soc. Soil Phys.
»¼J
No. +*0, p. - +* ,**1 Eh *ῌ**Reaction of a Platinum Electrode for the Measurement ofRedox Potential of Paddy Soil
Daisuke MURAKAMI* and Tatsuaki KASUBUCHI*** The United Graduate School of Agricultural Science, Iwate University** Faculty of Agriculture, Yamagata University, +῏,- Wakaba-machi,
Tsuruoka, Yamagata, 331῏2///, Japan
Abstract
Redox potential (Eh) of soil has been measured to know the redox state in paddy soil. However, it was di$cult to get reliable data because the Eh values in the ﬁeld ﬂuctuated largely.
Although the measurement method had been examined to improve the problem since the +3/*’s,
it still remained to be analyzed. To improve the problem, we used the cyclic voltammetry (CV)to examine the reaction of the platinum electrode. The results obtained were as follows. The
causes that ﬂuctuated the data consisted of two factors.

One was the chemical reactions of plati-

num electrode with the surrounding materials. The other was associated with the property ofthe soil. The platinum electrode induced reaction with oxygen in the oxygenated medium andmade oxide layer in the surface of the electrode. This layer disturbed to make the Eh stable.
Polishing the sensor could remove the layer.

In the reductive state, the sensor adsorbed somematerials in the reductive state around its surface.

This also decreased the stabilizing time. In

addition, the di#usivity of ions in the soil was too small because of the large surface area andelectro double-layer of soil solid. These factors decreased the moving speed of electron or ion
transport and non-equilibrium condition was formed in the soil.
Key words : redox potential, measurement method, cyclic voltammetry, paddy soil, di#use double layer+     Eh 

 !"#$%& '() * +,-./01m +31*Dc E;deEh 'E9 nOF

89:;$%&E9 ῌ op

Eh qrstu=lgvGLtwg xE9Ty23456789:; <= +3., ; >? +32, ; @u=l z{| {G}~&3;@{|t

ABῌC +32, /0D EFE GH I$J K

E/3&E;

!LMNOP3 QRSTUTVWXLM

+3.2 ῍ qrsM@P/!&Y/! /0 Z[M\]893! ^_O +30* ; >MP/!& ^_O +30* ; >?ῌm +302 ῎

MNO/3& g! {|? +32,D  ;`ST ab/Pc E;deqrstE9deu=g!& E/3Ty

f39g!HhMiP73O9:; jkῌl9PGL/!& >?ῌm +302 /* (y
* $V : yV -*/῏**.1 fP ¡¢£¤ +0῏+ fP ¥¦ ^** >§B 331῏2/// >§¨©¡ª«¬ +῏, ¶·¸¹ºp :
 Hh ­®¯°±¯²³¦´µ°   R  +*0 ¼ [,**1\4     Eh 







     
 !" #!" $

% &'()*+, -./01

 3 45  Eh2

6

7 18 , 9: ; < =  >, !?"  @9: #A8 BCDE$F%&'G &H'(   , 9:) *I
J+K>3 ,-L, :./>,:./M0 N1O  G P
23 >QRSTUSVW"XYZT! [CV\49:]5 <=^  6 CV , > G]5,

:78:*῏+, :  Eh 3
 CV 3 [B\[A\  - :

Fig. +

Two electrodes method of Eh (A) andthree electrodes method of CV (B)7!"!! GreenKit22 [ESD[\\-=_` 4a9b

 :8 ::  :./>,:./M0 N1O  3 > [<=^c ,**,\ ,-L,3 de fg Eh   &H ;[T ,][ \ [\\, CR+*X [XW\ 4XQ!,9]W^_`]X¡ak -hi< => jk Eh  4 b¢A£¤¥sbc¦d§ 9AK¨©

9: 1O J&l< ]5efN  9:,

, 4& ª!W [ZoBell\ « ghiZ j ª!Wk«,=¬T­®,+ 

*.+ molL+]5,mE?^@^ABC@D => .E4¥±X=¬T­®¯°T¥±X=¬T­®3²

 FnG, op!qHIJ [qrs\tKL_ ,uM [LiC\ > v=>,Nw_` , mm xOyzP=4 jxOyQR{ |+,}~SG

Nl= + L [ k%_` ¯°

 +ῌ-** molL+ k%_`k«> \mi @ Eh nP* [,/ .,2 mV\   [Starkey and Wight, +3.0\ o@, + L !¬! ]5p *.1 L

F%TN 8 =q=P=rsz p,,  +* t8uv 3 z Ew³P=EKx,,+  Eh, : jz Ej´P=E µ

,U *./ mm, _ 2* mm

9:4$

:1O+KG 4: f:ῌ= V:4 , : [Wῌ+ [\ , :[\ - :3 
\ *

2

, ORP Y!" [ODIC-1 X !!![\\ 4
 Eh ,=Y:f.Gῌ

= V: =Y: )* ORP Y!"
Z+b Eh 
Eh[mV\[Z\,*0*.1[T,/\9:yv

s4 ¨¶

N(·¸@
῏ῌ : EP=E

9:yv 3

Uz Eh ¹1 ῏῍ : E9:78zP18¹yz 9:bz {|=}~
zUa

º\E

$

 »¸ Eh

*v

78

¹1 =῏῎ : , , 4 9:

Na

OP : ? Eh &"+,/ + 

#+***  , 


5 Eh   ῐῌ : 

!"# $ $ *./ mm   ,* mm %-+ mm,   2* mm % +,/ mm,  -,* mm % /** mm,  - & ' - Eh  ,(,(,CV )"* $ *./ mm,

 2* mm +, , - .,/ "#0,1

ῐ,



23.45)678"9#

Fig. ,

Eh change just after the insertion of
sensors (soil , ponded water),1 :-,*;ῌ<; =,& Eh W>῏+  ?!"* @ABCDEFGῌHIJKD
EFG HAB-+/+ L #$MN & 0,O"+, hi W

,

1W Eh  ="1 )^4*W*,&)" Eh '(  TU* ,. hW)2XB6 ] W*+V  W2X*WYZ[\]8"),^4_+ V 5*+ /* +** ,** /** +,*** mVs`+W*+,:-,O)P,!%Q" RS4`+O)P mV mine

EfH,a-b .c8d῏/0 ghi&7d῏ c¡¢£47&"
 Eh * ¤C c¥ ¦ §¨©ª«¬­B§¨®)^¤C
6 gWO"+,¯6X

jk lm nIEopqr1&3 . Ys*1°±±B Ehlm)37t6t87&"²³*[c8&´µ"ῐ῍ : u1t6TU1v3&TU,/9,#7¯6X¶t"1·bc8 L`+ῌ= +302 

|3 CV t65 6 wxyz2{
KCl/* mmol L`+ 97"]8 CV t6ῐ῏ : 9~*+

b"g1)",/*+ -(+(, 8)" Eh   Ys῏῍?EF)^4G"] ¸´9" ¹3  "#+,8hi>῏-  .+,W
8

72 >῏, hi1H  ¤C º&°±±B¥¦§¨¤Cª1«¬"g19 " ghi ¤C c§¨¤- 

Cª¯6X¬t"´µ* +,IJ8

  Eh  g8].c87&" Eh ":;<1"# ῌ=c +302 !
7 >Yst6  ?
+,

g8*8?)67,

+,wxyz2{ KCl /* mmolῐ῎ :  ,. }4Q7&,~-+* .DJI2{ Eh /9"]}

W[c8".DB,/1&b

"
-(+(-

+,TU/

 Y

s῏῎
u1FK)67 ,/9+, +,

¤C)67«¬}¹L+9»"   +, ["# Eh hi>῏.  g8]1H u1FK R@ lmg8chic¼+,

+,8)" Eh"1 ¤C c§-(+(+ , }4Q)"4 Ys῏ῌ¨¤Cª¥¦«¬7&X9 )^]G"}>῏, W1WA8v88W*u1t6,9)M&g19Nc 

XY  » +*0 ¼ &,**1+

6

ῌ-

·

Fig. -

1¸¹º/Z[1!

ῌ/XY Eh @O/DIJXY Eh @

Fig. /

Change in Soil Eh by repetitive insertion

E#ect of surface area on soil EhOaP]" Eh KLbc@

!CDE !: def:ghL
1iLbjE!!/CDJ=k! T !
1elXYf89mnoEp

q!CDE
Eh KL.> rst

-F+F/

mu$%pE mvst H
el:
`1


def Eh ghL1K

XYf Eh hL1KL :pq def!XYf!: EhhL12iw!: xdey zp ῌ.

01IJ!01"IJXY Eh @

Fig. .

E#ect of polishing on the change in Soil Eh:/ m|+



 !"#$% &'(ῌ)* +302+ ,-  .
/01234567! 01

&0{GH/G}~E!pE 

XY Eh hLU

/01gZ[1
XYf Eh :!XY

5@1"!CDE =

0!:?@H!!CDE&*E +32.+  R2pp=E

 Eh KLelXY Eh hLUp

89:; !: <= : XY

# &'(ῌ)* +302+!XYABH.>?

@AB891"!CDE
-F+F.

GH/DIJKL &MN῍ῌ+O/P 1IJ KL

! QH" &'(ῌ)*+302+ R /STU V῍/ GH/ ,

W-, cm D/XY6Z[1IJ

KL$%/\1 $%G]5f

 & +  ¡¢HU!CDE R £ E/¤¥U CV KL ¦!1CV  CV KL:§#q":-,¨~#©ª«_"p/ L¬U­2i®q  ?@¯°"  !,-©ª±²p~#p³

  !: ^_XY`12

´µ³/¬!  & 5@¶P HpE?@¯°®¯ : bcde,**, CV  

Eh °G):;< \]

7)X YZ[\]8^ _`ISG)#aQ!

I) RS bcde F<XSfG<\]8

 " #$ %&'() ()*+g")1  :;<hi()-.TU jk<)"#,-./012()34 567)"#

XSlm n)"# 



8 $)

SG)

-9,9, deopqrst :;<-9,9+ :;< =>2() CV  !?@῏ῌ/* mmol LA+AKCl BC =>CV !?@῏῍

DE# FGD

L῏1 deou ,. qrst :;<$v

E :;<HIJKL῏0  ( " JK =$ wxb yz { ?@῏ῌ #|} /* mmol LA+> 8%M N8O$4 => FG8%M

AKCl BCo

N8PQ4FRSG)"#SG) "I :;<=>()"#RS-.TU VW8F4FCV ~, _RJKCV # {

CV 

 

CV # F, 

8IFG "I/0 <

iQI8^-.QI"#SG)  CV ~,(# 8I)F,. CV L῏1K " "# :;</0 iQI=> :;<#|} J

-.TU8()"#RS-.QIS:;<I => #|FRX#+I
-9,9- deCV  !?@῏῎KCl BC DE CV

8 deR

=>Fig. 0DE#=>

CV ¥¦E#ect of polishing on CV curve

ῌῌ1Fig. 1

FGDE~,_RDE

87IFf4 S /*+,*** mV minA+ # L῏2 deῌῌ0 _R

DE CV  qr*+S_R

JK ( I)8  %&

8

  8IFR¡ CV ¢GS 18£¤ n)#CV ¥¦*. !§¨©

ª«¬­(

Change in CV curve by repetitive sweep (Numbers in the ﬁgure show the sweeping order.)JKVWX Y +*0 Z 1,**128

ῌῌ2Fig. 2

ῌῌ3>῎2

Fig. 3 ῌ  #$3GHIJK CV L-

CV curves of the soil by the change in sweeping speed

MNOPI?9!"3#$%&'Q*RSTU*I>The relation between the oxidative peak of current and square root ofsweeping speed from ﬁgure 2.



#$%&'()* +,-./0 1*2 345+

   ῍ 

67 5 1!89:; ,**,2 <+= >῎2  

?9@AB5!"6CD#$%&'EF !" :  Eh * $;<'>ΐ3     ῌ 

3 $">{|97"  5[

U1} '>3 f\ <%~lS

6!,-%#! $S6!(?'>!]

  $$%  

 #$%  $"$%  ^U

# +%,'- ./  Eh *  $;<% , - !"#$% &' () *() $%!



u!q# j_y2+ Eh %#`#0

1  234!536! !7

4:B$%,'"

"! 89    "#3.    4! 53 63:# 0 $$% $;<%3&=<'>!<?($%

 Eh * 3ab%#$;<BC $$%,) % $"#Dh5 cNPA]3('> Pd

3 '>!<?@0AB$  C ()#'$;<% Yl !\ 7"> %D' ./e3ef--  Eh 



Z $;<%gh '>

EFΐῌ EFΐ῍ EFΐ῎ EFΐ῏   
* +GH!,-#./I ,'
$% J $;<%01:A $% 6GH!2K1"$%  <%
L3!*

M%41"

$% 3: ] #i3

 m Z.-u%TZLj !kEFΐῌ EFΐ῏    Eh * +G
H



#

<'> " $;<%3G#l '>!7"$%!41"
# 89EF lm#3Q! + n3Q

N *OP?6+  6 ,-#

 Eh * !  \ 81 

L5

o- 

,)

,-!Q$%3Q Eh *R. LS6!#7TU5V*3

  -ΐ+YEF$"]3

ῌp _+302` q%rs#$% CV

Q   EW LS653:X8#

*%Crs#$%  $$3A 96 #0%' * ? Q Y Eh *t#ju*  :LS6;Y"# Z? %0!

3:%,' 81 ?=| *

1:[\%< %0!= L5C>?

5

='? *GH!2K3:%,'" ]

$%  3&=Z. ./

^@* _EFΐ῍`#g

 $;<%v# Eh *| CV *7

L! 4:AAJ abcd1" eBC   -<5!fg%Dh ? +GH!,%# E9 FG#H!&=%,'" iI
-  j* #]3GH!2K1"<% YJK!LA#?%,'"
EFΐῐ EFΐῑ  KCl 2M

Y CV *  $;< N#\kῌOP'>!&=
$% ]  "# Y CV * _EFΐῒ`  "#3 lS6!
R S6!($%! 1" $$%! ./

()#+3Q$%%CM

%,'"#N "#3mS

./w _,**,` : ./*¡ _xw` p. 2* ¢y z£¤p{|ῌ}¥~ῌ¦ _+32.` : ./*e _`¤ p. 12 §q¨_©`¤_EFΐ῎`

QX1"

3:%,'+Sῌ ªW _+32,` :  Eh *>{¤ « /- : /./ΐ/.0.
¬­j _+3.2` : /i®¤ « +3 :.-.

¯ ῌ°ῌ±²³l _+30*` : ´ZFe¤ +0  &  Eh %Z*epp. .31ΐ0.* µ§¶¤

%01:TUl!Vn $op·¸ ῌpq¹ _+31*` : 

.WqX rstS6!QX1"$%!

 5 pp. /-ΐ03 º¤

Ru%,'" $? 5YS 3v"'>wxy <%kPZz'>e¤ /¤ »C¼ _+3.,` : O` ¤ «
+0 : +*.ΐ++0.

 ¡ " +*0 ¢ ,**110ῌ +302 : Eh   -3 : /-/ῌ/.,.
 +32, :! " . #rosion of iron in soil with particular considera-$!

+  pp. +--ῌ+-3 %&'tion of the soil redox potential as indicator of
corrosiveness, +*2, (New Brunswick, N. J.).

῍( ) Eh *+,-.

Starkey, R.L. and Wight, K.M. (+3.0) : Anaerobic cor-ῌ/012345 6789:;<= >?,@A

B +CD. ( ) Eh * EFGHIJK LMC-.NOP;Q+R5 STUVWHXMYC+RCZ[\]M+,-.^_?,@A@`B
aDa +bcd`@*efghD?,@`C`B i+. j$klmn;opqmr
st/Uumrvw.xy;ghD > Gz{|}{~XF|H;`@<= B * !%S;` B+ ]* EFGHst/0m$!R , dMa@`+R;ghDa B C pqmrstj$5klM+R j$klMr>@?`+R;ghDa B : ,**0  2  +.   : ,**1  -  3 