Evaluation of the effect of groundwater condition on water and salinity stresses at crop field in Isahaya Central Polder, Japan

摘要

More than 70% of Japanese lands are classified as mountainous or hill slope land. Particularly the Nagasaki prefecture located in the south-west of Japan is well-known for its fields with steep slopes. A project to reclaim the Isahaya Bay in Nagasaki prefecture and develop prime and large-scale agricultural lands has been conducted. Cultivation in the newly reclaimed land known as Isahaya Central polder started in 2008. As the crop fields in Isahaya Central polder are flat and large-scale, agricultural productivity and farming efficiency is relatively high. However serious concerns exist on future cultivation in Isahaya Central polder because plans are made to open the gates of the reclamation dike because of seaweed crop failure. Although the present soil conditions in the root zone have been improved and agricultural productivity has been increased, the crop stress due to salinity is concerned after opening gates because of groundwater salinization. The aim of this study is to evaluate of the effect of the groundwater salinization on crop fields. A simulation model describing the soil water and solute transports was introduced. Model accuracy was verified by field observation conducted in Isahaya Central polder. The stresses due to wetness, drought and salinity were evaluated under the scenarios of groundwater salinization and drought year. Simulated result indicated that groundwater salinization produced the salinity stress and the effect was marked on the deep-rooted crops. The groundwater salinization in the drought year had significant impact on not only deep-rooted crops but also shallow-rooted crops.