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J. Jpn. Soc. Soil Phys.
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No. 33, p. 0/1, ,**/

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 +*ῌ**ῌ **On the Decrease of NO--N Concentration of Flow Water in Paddy Field Plots
Toshio TABUCHI*, Hisao KURODA** and Yasuji SHINODA*** Former professor of The University of Tokyo** College of Agriculture, Ibaraki University, Chuo -ῌ,+ῌ+, Ami-machi, Inashiki-gun,Ibaraki, -**ῌ*-3- Japan
Abstract
We continue the long term experiment on nitrate removal in the paddy ﬁeld plots. Natural
water with high nitrate concentration of approximately ,* mg L + was supplied to each plot
continuously more than ten years.

Nitrate removal rates gradually decreased in the ﬁrst few

years, but now they keep the ability of nitrate removal. In this paper, the decrease of nitrateconcentration and water temperature in the ﬂow process was measured at - hours intervals.
Water temperature was lowest in the ﬁrst block and it gradually increased through ﬂow process(Fig. ,).

The values of nitrate concentration decreased linearly and did not change so much bytime as shown in Fig. ..

Average nitrate removal rate (R) of non-plant plot was *.0+ g m , d +.

The coe$cients of nitrate removal rate (a) were calculated by the equation (3) and the average
coe$cient of nitrate removal rate (a) was *.*-2 m d +.

The coe$cient of nitrate removal rate of

the ﬁrst block was smaller than the values of other blocks due to low water temperature (Fig. 3).
Key words : Nitrate removal, Paddy ﬁeld, Temperature+    
 +33+  /  
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 0123^_`a<= /bcd +N *+ST

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 $ABCDEFGH@I J0.,/ mK
 / LMNO PQ JRῌ+K S / NO 2 T -*UV 0 ?

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3 NO--N

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-+ 

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14 OZoGpqo4 r , NOs1
Whi4 atuvGX1 %$gwxyzZhi +1o4 ahid{!"#$y|g}m $@~9:ZB>d4!"#$Zo%$y|g -. +1S%y1U o01
O

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1^)* 1ῌ,-, 

Fig. ,!"#$ NO--N {B1+4 Y?fῌ+
Fig. +

$

Experimental plot.

ῌFig. -ZB>d

Changes of water temperature in ﬂow
process.

$9:ZcZ

Changes of average water temperature.

ab : c%?Y@defgh*+    

 - mg L+   NO--N 

67 pH ?Y"ZP[\]5  %&'($II0 RPQA3

!"#$ %&'($)  *+,-./
%&'($0123 435$6789:!"#;:123 <=ῌ/>-ῌ-pH ῍ῐ῎pH ;?@A3 BCA

 <=ῌ0>  

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 ῏ῌ.

῏ῌ/^_` NO--N !"#

Fig. /

Changes of average NO--N concentration.

Fig. 0Changes of pH values in ﬂow process.

NO--N ?Y"Z

Fig. . Decrease of NO--N concentration in ﬂow
process.

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pH ?Y"Z¥¦&§¨U  33 © ,**/

68

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 ῒ1 

!"# $%&

3  +,  +/ '( %)( *( & DO

+ 2,+- mg L-+./ 01)%)(

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6o BcLῌ., Lc,/ m &

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Fig. 1

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Changes of DO values in ﬂow process.

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>/iC

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Fig. 2

jk#¤FG DO +&HI

Changes of average DO values of eachplot.

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Xt_XoῌexpLatῌHO῍

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Fig. 3

Average values of nitrate removal rateR, coe$cient of nitrate removal (a) and(ao), and ﬁeld coe$cient (f) of each plot.

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

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,B«¬2ΐ

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U + *.*,2 m d+ +HIJ

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+ *.*+. m d+ U

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in ﬂow process in non-plant plot measured in ,**-.

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Tabuchi, T. (,**+) : Nitrate removal in the ﬂooded,) *Tn ji o% :( l$=4

paddy ﬁeld. Proceedings of the International+ pKD'"$& &'(

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Workshop on E$ciency of Puriﬁcation Proc-a 0bc?qrs) /7'tuS

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