Studies on the relation between soil moisture and growth of tobacco plant. : 1. On the change of the rate of transpiration from tobacco plant (variety, Bright Yellow).

Abstract

1. The effects of soil moisture on the rate of transpiration from tobacco plant (variety, Bright Yellow) were studied. The plant was maintained in an air conditioned glasshouse in a 1/5, 000 Wagner's pot packed with soil kept at a constant moisture. The moisture levels, 20, 40, 60. and 80 volume %, were designed in all. The rate of transpiration was measurd by means of the weighing method during the whole growth stages. The transpiration per plant and per unit energy of radiation showed a peak in every moisture level before the stage of the maximum leaf area, and this peak appeared higher and earlier under the high moisture level than the others. 2. The rate of transpiration per unit leaf area showed a peak in earlier stage than above mentioned. The difference was clearly seen between different moisture levels, but it became indistinct after the topping. This may be due to that the rate of transpiration per unit area from each leaf has a peak in considerably early stage of its expansion and that the moisture of a leaf is usually increased with that of the soil. 3. "The water requirement" per unit leaf weight was higher with the high moisture levels and the delay of the harvest. The time of harvest especially of the tobacco plant, affected largely on "the water requirement".