The purposes of this paper are to clarify the theoretical factors of food trade and to show case studies of the structural changes of food demand & supply and self-sufficiency ratio. According to trade theory, the self-sufficient ratio of food is determined by the structures of production and consumption, and price condition. In particular, the transformation of production resources in the agricultural sector is a more practical subject than that between non-agriculture and agriculture. We have to investigate the process and cost of the adjustment among sectors in agriculture.
The self-sufficient ratio has been discussed in relation to food security. According to the definition of food security, the sufficient quantity of domestic production when we are faced with an urgent food crisis is a part of food security. The ratio is rather an index that represents the conditions at ordinal situation.
The recent decrease in the ratio is related to the change of the phase from relative to absolute reduc-tion of domestic production. It is because there is an insufficient political system to evaluate the economic value of the non-market resources.
From the viewpoint of the food system, the weight of food consumption in households has been decreasing; on the other hand the weight in processing and food service sectors has been increasing drastically. Therefore providing materials for domestic production becomes more important. According to the case study of soybeans, the processing sector faces an unstable domestic market and it receives relatively less than the political support to farmers.
The self-sufficient ratio of soybeans and wheat has been affected by the set-aside program for rice. The area of paddy fields has a decreasing trend and the utilized percentage is below 100%. From the viewpoint of efficient utilization of agricultural resources, we have to reconstruct the adjustment program of paddy fields.
