Reduction of Soil Fertility by Decontamination and Efforts for Its Recovery (2^nd report)

<p>Agricultural soil contaminated with radioactive materials due to the Tokyo Electric Power Company's (Tepco's) Fukushima Daiichi Nuclear Power Station accident was mainly decontaminated by topsoil removal and soil dressing. In such post-decontamination soils, the amount of organic matter is extremely low. Mixing dressed soil and subsurface soil layer well is recommended by local governments, but in actual fields, the mixing ratio of these soil layers is often uneven depending on locations. We investigated the effects of the difference in the ratio of the dressed soil on the growth of spinach. In addition, we conducted nitrogen fertilization using hairy vetch and chemical fertilizer (ammonium sulfate). The subsoil of Andosols was used as the subsurface soil. When spinach was cultivated in dressed soil that was not mixed with the sub-surface soil, spinach growth was extremely poor. The lack of basic physicochemical properties of dressed soil, especially phosphorus supplies, the lack of pH buffering capacity, and negative effects of accumulated ammonium in soils restricted spinach growth and its nitrogen uptake. The growth and nitrogen uptake of spinach were greatly improved by mixing the subsurface soil layer by 20% or more by volume. As a conclusion, mixing dressing soil and subsurface soil as much as possible is most important, and then it is worth to apply nitrogen fertilizers, to improve spinach growth in the decontaminated soil.</p>