On the property of mulch films which are effective to either soil temperature raising or weed control, several studies were made from the viewpoint of transmissrion spectrum of film and wavelength dependence of weed growth. A clear polyethylene film was very effective to raise the soil temperature but allowed a thick growth of weeds, while a black one which stained with carbon powder was almost opaque to solar radiation and the effects were just the opposit direction of the clear one (tables 1, 2 & 4). For the purpose of obtaining the more effective film, colored films were investigated. It was observed that the germination and growth of weeds were most inhibited under green light illumination as compared with the other colored lights (fig.2). This suggests that a specific green colored film can be used for the above purpose. Two types of green colored polyethylene film (fig.3), which transmits green and infrared regions, were then tested to presume the both effects of soil temperature raising and weed control. Under the mulch condition, the green films resulted in the maximum soil temperature as high as that of the clear one(fig. 4 & table2), irrespective of a considerable difference among the solar radiation transmission of their films (table 1). It may be due to the fact that water drops adhered to the inside of film were much less in the colored film mulches than in the colorless one under solar radiation (table 3 & fig.5), because the lower the transmission of film by pigmenation, the higher the film temperature by absorbing the radiation energy becomes(fig.6). The growth of weeds was remarkably suppressed by covering with the deeper green film (G) which sufficiently stopped the transmission in blue and red regions (table 4). Thus, it was concluded that green-and near infrared-transparent films like G would be of effective to both soil temperature raising and weed control when they were used for mulching.

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