In Coastal Area of Fukushima Prefecture, the fertile topsoil was stripped away during the decontamination process, which is a major problem for crop cultivation. In this study, we estimated the total soil carbon of paddy fields (32 fields with total 835 a) in Tomioka Town, Fukushima Prefecture, from hyper spectral data obtained by a tractor-mounted soil analyzing system. The results showed that there was a large spatial variation in the total soil carbon in the study area and that the total soil carbon tended to increase with increasing the number of rice cultivations after the resumption of farming. In particular, there was a significant difference in total soil carbon between fields that had not yet resumed rice cultivation and fields that had already been farmed four or more times. The results of this study will be important for the restoration of soil fertility in the resumed farming areas after decontamination in Coastal Area of Fukushima Prefecture. In the future, it is necessary to calibrate a regression model to estimate total carbon in soils from hyper spectral data using local soils, and to continue the study in the same field. This will enable us to quantify the effect of individual cultivation techniques on total carbon in soils and to provide a roadmap for the recovery of agriculture in fields after decontamination in Coastal Area of Fukushima Prefecture.

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. These processes may adversely affect fertility of agricultural soil. We conducted a research in farmer's yard in Yamakiya district, Fukushima Prefecture:1. to elucidate the effects of decontamination and 2. to restore soil fertility using three types of green manures for 2 years. As a result, 1. a significant decrease in total carbon and nitrogen content, available nitrogen content, and cation exchange capacity in the soil was observed due to the decontamination. Fertility decrease was more remarkable in paddy fields than in vegetable fields. 2. Rye grew vigorously as compared to hairy vetch and sorghum. The mass loss rate of rye and hairy vetch, measured using litter bag for 9 month, was 66 % and 83 %, respectively. Approximately 20 % of input C by green manures remained in soil after 9 months, and the carbon sequestration in soil is also an important aspect of this trial. Rye incorporation significantly increased easily decomposable carbon amount and soluble total nitrogen. Hairy vetch incorporation significantly increased soluble total nitrogen and soil microbial biomass. Fertility recovery for long-term in this region is extremely important. Green manure application may be useful to recover soil microbial available carbon and nitrogen, and it helps to recovery nutrient cycling.

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.