水田における農家の水需要曲線

Demand for water use in rice paddy fields in Japan has traditionally been measured according to a unit known as "Gensuishin" However, it does not consider farmer decisions on how much water to use in rice production, while the quantity of water measured by "Gensuishin" takes into account biologocal and physical conditions. This paper reports that analysis of water demand in rice production ought to incorporate a farmer's subjective equilibrium and water demand quantity. The water demand curve on a paddy field that is specified here associates with three factors. The first, the farmer's subjective equilibrium of how much water to use in rice production. The second is the two major roles of water playing in rice production. The third is a consideration of the stages of rice growing. There are two important roles which water plays during a rice production cycle. The first words, water is involved in protecting the growth level achieved for each stage, as well as to help the plant in starting its new growth stage. A proper evaluation of the economic values of water in rice production must take into account those two roles. The economic value of water for surviving rice plant increases consistently through growth stages. The value of water for contributing in rice growth should depend on the marginal value product of water inputted into rice production at each growing stage.