Phytoextraction with rice cultivar IR8 in a cadmium-contaminated paddy field

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  • AZUMA Hideo
    Toyama Prefectural Agricultural, Forestry and Fisheries Research Center:National Agricultural Research Center
  • ISHIKURO Tetsuya
    Toyama Prefectural Agricultural, Forestry and Fisheries Research Center:Toyama Prefecture Office
  • YAMADA Munetaka
    Toyama Prefectural Agricultural, Forestry and Fisheries Research Center:Niikawa Agricultural Extension Service Center
  • OGAWA Youko
    Toyama Prefectural Agricultural, Forestry and Fisheries Research Center:Toyama Prefecture Office
  • INAHARA Makoto
    Toyama Prefectural Agricultural, Forestry and Fisheries Research Center

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Other Title
  • 水稲品種「IR8」を用いたカドミウム汚染水田における土壌浄化
  • スイトウ ヒンシュ 「 IR8 」 オ モチイタ カドミウム オセン スイデン ニ オケル ドジョウ ジョウカ

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Abstract

The rice (Oryza sativa L.) cultivar IR8 is one of the most promising plants for the decontamination of cadmium (Cd) from paddy soil. In this study, the effect of phytoextraction with IR8 was examined for 4 years in a paddy field in the Jinzu River basin. The coarse gley soil was kept under aerobic condition after midsummer drainage by the restriction of irrigation to increase Cd uptake by IR8. Before the experiment, 0.1 mol L^<-1> HCl-extractable Cd in the topsoil ranged from 0.27 to 0.65 mg kg^<-1> (average, 0.40 mg kg^<-1>). Cd uptake by IR8 and HCl-extractable Cd were measured by using grid sampling every year (24 points in the first year, 36 points in subsequent years). A grain rice (cv. Koshihikari) was grown from the second year onward in 36 small plots (1.2 m × 0.6 m) where IR8 had been sampled in the previous year. Koshihikari was also grown in the entire field after the phytoextraction experiment to ensure the decontamination of Cd. The Cd uptake by IR8 was 13.0 mg m^<-2> in the first year and decreased each year thereafter. HCl-extractable Cd in soil and its variation across the field decreased during phytoextraction. Over the 4 years, 36.8 mg Cd m^<-2> was taken up by IR8, and HCl-extractable Cd decreased to 0.22 mg kg^<-1> on average. The Cd uptake by IR8 was positively correlated with HCl-extractable Cd within this field. The average Cd concentration in Koshihikari brown rice was 0.44 mg kg^<-1> in the second year and 0.22 mg kg^<-1> by the fourth year. After phytoextraction, the Cd concentration in all Koshihikari brown rice samples was less than the Japanese regulatory value of 0.4 mg kg^<-1>. Because the Cd concentration of Koshihikari brown rice and Cd uptake by IR8 measured in the previous year were positively correlated with the Cd concentration of Koshihikari brown rice, these values could be useful indices for judging the success of phytoextraction. The estimated cost of phytoextraction over 4 years was lower than that for soil dressing, which is performed in many contaminated areas. Further studies related to the durability of the decontamination effect and improvement of soil fertility after phytoextraction are necessary.

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