On the Soil Moisture Characteristic Curve of Sandy Soil and Its Temperature Dependence

The soil moisture characteristic curves of sandy soils were determined by using the soil column method and their temperature dependence was examined. An analytical expression fitting the observed data is: Sℯ＝1/{1+(αh)ⁿ} m where Sℯ is the effective saturation，h is the matric suction head，and α，m，n are the parameters to be determined experimentally. The temperature coefficient of matric suction，which was calculated from the experimentally determined expression，greatly exceeded the values expected from the c1assical surface tension-temperature relationship. Larger values of temperature coefficient were obtained in decomposed granite in comparison to dune sand. The trapped air in the unsaturated soi1 system was considered to have resulted in the discrepancy between the observed and calculated temperature coefficients

A New Method of Determining the Dispersion Coefficient of Salt in Soil

To determine the dispersion coefficient of salt in soil，improving the measuring apparatus was attempted. The salt content of supplied water to the soil surface could be rapidly changed by keeping a uniform moisture distribution in the soiI column by means of this method. The obtained results showed good agreement with the experimentaI results of the paper described by ColIins (1961). The effect of air flow in the soiI column was discussed based on the theory of a two-phase air-water fIow through the soil

The Effects of Environmental Factors on the Estimation of Stomatal Diffusion Resistance

A physical mathematical model of water transportation in the soil-plant-atmosphere continuum have been developed recently. To predict daily actual transpiration，much more detailed studies on the behavior of stomata are needed. To make a behavior model of stomatal resistance，concurrent measurements of irradiance，leaf water potential，air temperature，leaf temperature，net radiation，CO₂ concentration， humidity， wind speed and stomatal resistance were obtained in cucumbers under wet soil conditions. The same measurements were made in soybeans under dry and wet conditions. The results indicated that light is likely to have an important role on stomatal behavior under any soil water status. The relationship between stomatal resistance and light fits a hyperbolic curve as shown in Fig. 2. But the duirnal change in leaf water potential did not measurably affect stomatal resistance