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Abstract

 

This article in SSSAJ

  1. Vol. 74 No. 5, p. 1562-1567
     
    Received: Nov 16, 2009


    * Corresponding author(s): k_tagami@nirs.go.jp
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doi:10.2136/sssaj2009.0423

Estimation of Plant-Unavailable Iodine Concentrations in Agricultural Fields

  1. Keiko Tagami *a,
  2. Shigeo Uchidaa,
  3. Akira Takedab and
  4. Shin-ichi Yamasakic
  1. a Office of Biospheric Assessment for Waste Disposal, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
    b Dep. of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi Rokkasho-mura, Kamikita-gun, Aomori, 039-3212, Japan
    c  Noriyoshi Tsuchiya, Graduate School of Environmental Studies, Tohoku Univ., 6-6-20 Aramaki-aza-Aoba, Aoba-ku, Sendai 980-8579, Japan

Abstract

In this study, a method for the estimation of plant-unavailable I concentrations in soils was developed. Concentrations of total I and potentially plant-available I (i.e., water-soluble and organically bound I) were measured in 141 agricultural soil samples. For total I measurements, pressed powder pellets were prepared from soil samples, and concentrations of I were measured by energy dispersive x-ray fluorescence. Potentially plant-available I contents were measured by inductively coupled plasma mass spectrometry after the soil samples had been extracted with tetramethyl ammonium hydroxide and their soluble and organically bound I concentrations had been measured (TMAH-extractable I). The results showed a high correlation between the total and TMAH-extractable I concentrations. The geometric means of total and TMAH-extractable I in the paddy field samples were 1.9 and 1.1 mg kg−1 dry weight, respectively, while those in the upland field soil samples were 5.7 and 4.2 mg kg−1 dry weight, respectively. For the agricultural soils having <5 mg kg−1 total I, it was estimated that the average concentrations of plant-unavailable I in paddy fields and upland fields were 0.7 ± 0.2 and 0.7 ± 0.4 mg kg−1 dry weight, respectively. The different total I concentrations for the fields from the two agricultural uses could be explained by the differences in their redox conditions; I is mobile under reducing conditions so that it was removed from the paddy fields by leaching from the plowed layer or by I volatilization from the soil.

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