2023 Volume 3 Issue 2 Pages 24-29
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. A comparison of soils before and after decontamination at a farmer's field in the Yamakiya district of Kawamata revealed a large difference in total carbon (C), nitrogen (N), available N, and CEC. Especially in upland fields, the total C in the soil after decontamination was very low, and in paddy fields, the amount of available N in the soil after decontamination was undetectable. Decontamination greatly reduced the fertility of farmland soil, and recovery from soil degradation is an urgent task. Total C and available N recovered to some extent by rotary tillage. We conducted a model test examining the mixing ratio of the upper layer (top-dressed soil) and the lower layer (Andosol), changing the ratio of top-dressed soil by 0, 50, 80, and 100% (v/v). In soils with a higher ratio of top-dressed soil, N mineralization was low; plant growth was poor; and hairy vetch and N fertilizer application did not effectively change the situation. Poor basic physicochemical properties, lack of phosphorus supply, low pH buffering capacity, excessive accumulation of ammonium-N of top-dressed soil damaged plant growth. Mixing 20% or more of the lower soil by volume ratio and further fertilizer application may be expected to improve the plant growth.
