Interception of Rainfall at Different (Growth Stages by Canopy of Tobacco Plant

Abstract

To reveal the interception of rainfall by the canopy of tobacco at various growth stages and know the effects of rain strikes on the quality of flue-cured tobacco, the experiments were carried out in 1966-1967 at the Hatano Tobacco Experiment Station. The variety Bright Yellow was used in this experiment. The rainfall which is caught by the tobacco canopy is redistributed as throughfall, stalk-flow and by evaporation and absorption. It is obvious that tobacco canopy gives an influence on the soil environment by changing the distribution of ground rainfall. Results obtained were as follows : 1) The shaded area by the canopy was measured quantitatively by the use of photogarph and planimeter. Methods for measureing the number and size of raindrops were done by means of photographic paper spread with developer. There was a high degree of positive correlation between the diameter of raindrop and the size of trace on the catch photographic paper. The number of raindrop counted on the shaded area of the canopy per second were 282 at moulding time, 527 at topping time. 2) The dissolution of raindrops due to the collision with leaf surface differed by the position on the leaf inclination angle of leaf, condition of surface and collision angle between drops and the leaf. The above facts were ascertained by photographing with 8mm cinema camera. A drop of water (the diameter was 4.1 mm) fell from the height of 11 m and hit the surface of the leaf was divided into many micro droplets and the diameter of the largest droplet was about 2.0 mm. 3) The interception was found to increase directly with the growth of vegetative cover and the distribution of ground rainfall was influenced by the character of vegetative growth. The amount of water attached to the leaf after rainfall was about 50 g per plant at budding stage and this water was absorbed by the leaf or evaporated into the atmosphere after about 50 minutes. 4) It was found that the amount of water ran down along the tobacco stalks was relatively smaller than those reached to the ground directly through the gaps in the canopy or dripped from leaves. About one third of the water attached to the leaf flowed down from the tip and about two third from the basal part of the leaf. At the budding time the water dropped on the surface of row to the distance of 30 cm and at the topping time to the distance of 40 cm from the plant. 5) The content of petroleum ether extract reduced by excessive rainfall or by irrigation as reported by Darkis et al. Thus the excessive rainfall gives an inferior effect on the leaf quality of flue-cured tobacco.