It came up with the idea of using a black solution that would absorb sunlight and so keep the water in the fields warm. But what the solution did do was starve weeds of sunlight and so prevent them from growing.
Farmers spray the liquid three or four times after the rice plants have been transplanted.
The black carbon cuts out sunlight, preventing weeds from growing, but because rice is placed into the paddy as a shoot that rises just above the water-level, it is unaffected. Indeed, the rice plants even benefit as the dark carbon does manage to absorb some sunlight and so helps raise the temperature of the water. The product is also environmentally friendly since carbon is often used as fertilizer in rice fields. While the idea is simple enough, the technology used to make the product is more complex, says Eiichi Nakayama, a senior manager at the Tokyo-based dye maker. The process involves grinding the carbon into particles measuring just one micron, or one-thousandth of a millimetre.