In north part of Japan, it is important to consider the temperature-rising of irrigation water in paddy field. Some methods to rise the temperature of water have been usually practised, but these effects are not enough.
To establish the effective method, thermal ballance in the field fill with water must be first cleared up. of water and soil, and evaporation.
On October, amount of energy reflected from water surface is about a tenth of whole incoming energy, and about 50% is expended for evaporation, exchange, and back-going radiation, so only about 40% of heat energy is used to rise the temperature of water and soil.
We spread the carbon-black powder on the surface of water and examined the effect of the extinction of reflection, but the result is contrary to expection, the temperature of water is always lower than that of normal.
The effect of prevention of evaporation by using an oil membrane on water surface is very remarkable.