Abstract
Transpiration of sugar beet plant was measured as a loss in weight of detached leaf blade. A leaf blade (100-300 cm2) randomly sampled from the field plant was weighed by a top pan balance immediately after sampling. After direct exposure horizontally to the sun on the balance for five minutes, the leaf blade was weighed again. In preliminary experiments, it was ascertained that behavior of stomata and temparature of detached leaf were scarcely changed for about 20 minutes after detaching. The difference between the first and the second weight may be regarded as a loss mainly due to transpiration. Among several evironmental factors, the horizontal solar radiation seemed to have a predominant influence on transpiration. When thn loss in weight was plotted against the horizontal solar radiation, a linear relation was observed and the points were fitted by a regression line. The relation of transpiration to the horizontal solar radiation was by the following equation. t/dm-2. 5 minutes=(0.35x+0.02 where t=quantity of transpiration x=mean horizontal solar radiation (cal) for five minutes This equation was applied to estimate transpiration of a whole plant and of plants in unit field area. t/plant. 5 minutes=(0.35·x·R+0.02) L/plant t/unit field area·5 minutes=(0.35·x·R+0.02) L/unit field area where L=leaf area exposed to light R=mean solar radiation in all leaves exposed to light/horizontal solar radiation
