Study on external economy on terraced paddy fields : economic and soil scientific approach

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This study is separated into two parts. One is economic analysis and the other is soil scientific analysis. In the former analysis, we firstly studied the current situation of terraced paddy fields in Ohtoyo-cho of Kochi prefecture. With the data of geographical and geological survey, we identified that the paddy fields stand on the landslide area. Until now the function of dam of paddy fielda is stressed as a basis for supporting the fielda. It is, however, not appropriate in this area. The space-creation function is more important. Additionally we sent out questionnaires to inhabitants in Ohtoyo-cho and Tokushima-shi, which locates on the downstream of Yoshino river and is connected to Ohtoyo-cho by the river. With the questionnaires we clarified the difference of recognition between the inhabitants and estimated the willingness to pay for maintaining the paddy field. Finally we discussed the optimal land use with using siba grass in that area. The major results of soil scientific analysis are fallowed : Monitoring of the local meteology, soil and water quality, soil microorganisms, low molecular weight organic acids in soils, under reclaimed siba (Sosiba japonica) grass land was carried out at Hanada Farm (Nahari-cho, Aki-gun, Kochi) and Saito Farm (Nankoku-shi, Kochi). Upon the utilization as siba grass land, water permeability became improved, because of the formation of root mat layr at the surface and hard-pan layr in the subsurface, and eventually, development of granular structure inbetween those two layrs. These changes in soil structure gave favorable changes for the stability of the ecosystem of reclaimed grass land in terms of the nutrient dynamics.