On the Micrometeorological Characteristics and the Heat Balance of the Nursery Beds covered with Polyethylene Film and Oil Paper

Abstract

This paper aims to clarify the micrometeorological characteristics and heat balance of the nursery beds covered with polyethylene film and oil paper. The transmissivity of solar radiation, temperature and amont of evaporation in these nurseries were observed and compared with the naked one.Following results were derived through the observations:(1) The air temperature in the polyethylene nursery was 5.5°C less in fine weather or 2°C less in average of the whole term observed than that of the oil paper nursery.(2) These results were caused by the fact that transmissivity of solar radiation in the polyethylene nursery was a little bit less than that in the oil paper one, i.e. the former was 50-60 per cent and the latter 57-60 per cent. In spite of the better transparency of the polyethylene film, the decrease in transmissivity of film is caused from reflection of water drops adhered to the inside of polyethylene film.(3) Referring to the amount of evaporation, the oil paper nursery amounted to 1/5th less, comparing with the naked one, and evaporation could not be observed in the polyethylene nursery.(4) As a result, the sensible heat flux reached to the maximum in the polyethylene nursery with a range from 228 to 319ly/day, being followed by the oil paper and with a range from 201 to 285. The amount in the naked nursery showed the least, with a rang from 34 to 64. the ratio of latent heat flux to sensible heat flux were 1:4 in the oil paper nursery and 7:1 in the naked nursery.(5) It seems that the heat transfer in the space formed between the polyethylene cover and the soil surface is attributed to the molecular conductivity, accompanyed with the water vapor that affected it as a mediator.