Effects of Internal Water Content of Plant on the Growth and Yield of Soybean
To establish the irrigation criterion according to variation of internal water contents, the study on effects of relative turgidity of soybean leaves was conducted in Fall 1967 and Spring 1968. Late variety, Acadian, medium variety Taita-Kaohsiong No. 5 and early variety Hsih-hsih were used. The results were as follows:
1. The value of relative turgidity of soybean leaves showed significant variation according to the times of sampling, age of leaves, and varieties. On the daytime, the value was maximum at sunrise, then decreased toward the minimum at 1 to 2 pm, and increased again toward sunset. The leaves near the top showed higher relative turgid than the leaves near the ground. Variety Acadian showed higher value and less fluctuation than the other varieties.
2. The correlation coefficient between relative turgidity and soil moisture content was (+) 0.4391 to (+) 0.5684. Relative turgidity was related to atmospheric condition. The correlation coefficients with air temperature, relative humidity, and pan evaporation were (－) 0.7788, (+) 0.6955 and (－) 0.8002, respectively. These results indicated atmospheric condition has more effect in regulating the internal water balance of plant than the soil moisture condition.
3. Soybean grown under high relative turgidity (above 75% between 1 to 2 pm) showed higher plant height, number of branch, number of matured pod, 1,000 seed weight, and grain yield than the lower relative turgidity. There were no significant different on growth and yield between different criterions as relative turgidity, soil moisture, or pan evaporation.
Since the value of relative turgidity were varied according to time of sampling, age of leaves, and varieties, and the procedure was time and labor costing, using relative turgidity for scheduling soybean irrigation may not exceed the conventional soil moisture criterion or evaporation criterion.