Studies on the Cover-Culture of Tobacco : 3. The enviromental conditions in coverings

[摘要] The environmental conditions in coverings were continuously observed in the same field in which the growth of tobacco was examined and reported previously. Two kinds of covering materials were tested. One is transparent polyethylene film whose edge is burried in furrow, the other is melamine coated paper whose one is touched on furrow surface. Results obtained were ae follows: 1) The air temperature is higher in cover of transparent polyethylene film than in cover of melamine coated paper. The relative humidity in the cover of transparent polyethylene film is almost saturated except for a few hours in the daytime, but that of melamine coated paper is almost equal to the relative humidity of the outer air. 2) As the cover of transparent polyethylene film is almost closed, there is the cycle of vapour, that is, the vapour evapotranspirated from soil and plants condenses on inside surface of film, and these water drops fall again on soil surface. The water drops protect the plants in the cover from abnormal high temperature because the water drops reflect a part of solar radiation, and transfer latent heat to outer air when the vapour condenses on inside surface of film. 3) The relationship between total solar radiation (R: cal/cm2hr) and air temperature in cover of transparent polyethylene film (T: °C) is shown in the following experimental formula. T=0.32R+6.9 4) At 10 cm depth of soil, the soil temperature ir usually higher under the cover of transparent polyethylene film than under the cover of melamine coated paper, and the difference of the maximum and minimum in diurnal change is lees under the cover of melamine coated paper than under that of transparent polyethylene film. 5) The heat flux transfered into soil and the amount of heat to warm air in covers were calculated. The former is about one third, and the latter is one several hundredth of solar radiation reached in both covers respectively.

[学科分类] 农业科学（综合）