Relationship between Distributed Soil Moisture and Transpiration

Soil moisture distribution were examined under soil, crop and environmental factors. For soil factors, water retentivity index, hydraulic conductivity index and response index were defined. For crop factors root distribution and total root length per unit soil surface area, and for environmental factors daily transpiration and conductivity of lower layer were used. The simulation results showed that moisture distribution was large for 1) soil with small hydraulic conductivity index, 2) the state of root distribution under favorable moisture condition, 3) small total root length per unit soil surface area, 4) large daily transpiration, and 5) small conductivity of the lower layers. Experiment on deep (distributed moisture condition) and shallow (homogeneous moisture condition) pots was conducted to study the relationship between soil moisture distribution and transpiration. To evaluate the distributed moisture condition the averaging methods by Taylor (1952), Gardner (1964), and Karamanos (1980) were used. Both the deep and shallow pot experiment showed that transpiration rate decreased with decreased in matric potential. Mean integrated potentials by the three methods were in good agreement with each other. The relationships between relative transpiration rate and mean integrated potentials of the deep pot experiment agreed fairly well with that of the shallow pot experiment. The results of the experiment showed that for a distributed moisture system the relationship between transpiration and soil moisture can be effectively evaluated by mean integrated values