The Effects of Land Restoration on Soil Fertility in Tsunami-inundated Farmlands of Miyagi Prefecture in Japan

抄録

In previous studies, a series of samples were analyzed to measure the salinity status of agricultural lands in Miyagi prefecture, where the extent of the seawater damage was the most severe among the tsunami-affected area in Northeast Japan following the Great East Japan earthquake in 2011. Since then, various restoration projects have been implemented by concerned agencies of the central and local governments. In the agricultural lands damaged by the earthquake and flooded with tsunami water, most of the technical tasks, such as the removal of debris and salts and the repair of irrigation and drainage infrastructures, were in the final stages of completion in 2016, and the efforts seems to have achieved their primary objectives. However, soil productivity in the restored farmlands remains a big issue for the local farmers. The present study was carried out in different farmlands in two adjacent towns in Miyagi Prefecture, Watari-cho and Yamamoto-cho. The major physicochemical and biological properties of soil were investigated, and the results show that the soil dressing used as topsoil in the restored farmlands had a low average cation exchange capacity (CEC) of <6 cmol(+)kg^-1, which ultimately contributed to lower average CEC values overall (<9 cmol(+)kg^-1). Moreover, carbon-to-nitrogen (C:N) ratios in the soil dressings and the restored lands showed a wider range (5 to 19), making the soil inconsistent in nutrient supply i.e., less fertile, compared to those in the farmlands where there was no top-dressing and in the farmlands at nearby inland sites. The study also suggests that issues concerned with rebuilding soil fertility and improving soil productivity in tsunami-inundated agricultural lands should be resolved through sustainable, soil-friendly methods and practices.