Estimation of total nitrogen content in surface paddy soils by measuring their electrical conductivity after hydrogen peroxide treatment

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  • 過酸化水素処理後の電気伝導度測定による水田表層土壌の全窒素含量の推定
  • カサンカスイソ ショリ ゴ ノ デンキ デンドウド ソクテイ ニ ヨル スイデン ヒョウソウ ドジョウ ノ ゼン チッソ ガンリョウ ノ スイテイ

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<p>We proposed a simple, inexpensive method for estimating total nitrogen (N) content in surface paddy soils by measuring their electrical conductivity after a hydrogen peroxide treatment. In this method, 5 g of air-dried, 2-mm sieved soil was extracted with 100 mL of a commercially available oxydol (approximately 3％ H2O2). After extraction with oxydol at 25°C for 40 h, the electrical conductivity of the soil extract [EC (H2O2)] was measured. For the six paddy soil samples, the coefficient of variation for the average of five repeated analyses of EC (H2O2) was less than approximately 2％, indicating a high reproducibility of the method. The temperature during the extraction significantly influenced EC (H2O2) values, and the temperature at 25°C was found more suitable than either 20°C or 30°C. Furthermore, the relationship between EC (H2O2) and total N content was evaluated at two sampling scales: 1) the national scale, with samples collected from paddy fields throughout Japan (n=83) and 2) the field scale, with samples collected from eight fields in Mifune town (n=39) and five fields in Takatsuki city (n=246). The coefficient of determination between EC (H2O2) and total N content was 0.70 for the nationwide samples, excluding 11 volcanic ash soils, whereas it was 0.68 and 0.23 for the Mifune and Takatsuki samples, respectively. The low accuracy of estimation for volcanic ash soils and some of the Takatsuki samples was mainly due to the low rate of mineralization of soil organic N by the oxydol treatment. Compared with the soil lightness (L* value), as measured by a soil color reader, EC (H2O2) could estimate the total N content with greater accuracy for both the nationwide and field-scale samples, provided that the volcanic ash soils were excluded.</p>

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