Abstract
A non-plasticized film, viz. ethylenevinyl acetate copolymer (EVA) film, has recently been in use as a covering material for horticultural use. In order to ascertain the temperature conditions under this new material, the following experiment was carried out.
During the early spring season, air and soil temperatures under tunnels covered with EVA film were compared with those under polyvinyl chloride (PVC) and polyethylene (PE) covers. In general, temperatures under PVC film were the highest through day and night, and those of PE film the lowest. It was found that the temperatures under EVA film were between those under PVC and PE films.
Seeds of turnip were sown directly into the soil under each tunnel at the beginning of the experiment. Seed germination and early growth of plants under PE cover were retarded as the result of the lower air and soil tempereratures. Yield of the turnip under EVA film, was between those under PVC and under PE films.
The spectral transmission of the unused and used films, was measured. Over the range of 6-15μ, PE film is highly transparent, but PVC film is opaque to it. Transmissibility of EVA film to the same range of wavelenghs is between those of PVC and PE films.
After the two months' use, their transmission rates of ultra-violet and visible rays were considerably reduced. However, there was no remarkable drop in transmissibility to the infra-red ray of the film.
It was confirmed that property of EVA film to reduce the nocturnal outgoing radiation was between these of PVC and PE films, mainly due to its lower transmissibility in the long wavelenghs.
