Thermal properties of sands with different par-ticle size and shape were measured. All sands showed the similar trend for the change in heat capacity, increas-ing with increasing in water content (θ).The gradient of the thermal conductivity (λ) to θ under the dry region (θ < 0.05 〜0.10) increased with increasing particle size for sands with rough shape, indicating an increase in con-tact points per soil particle highly enhanced thermal con-duction. Oppositely, for the wet region (θ > 0.05 〜0.10), the gradient of λ to 0 were similar for sands with different particle size. Equations of λ at completely dry condition and water saturation were derived from obtained relation-ships between quartz content and Z in this study. By in-serting these equations, existing models for thermal con-ductivity were modified, which markedly improved model performances.
A multi-frequency electromagnetic sounding system (MFEM) enables non-destructive and instanta-neous measurements of soil electrical conductivity (EC) profiles. Because agricultural and forest lands are possi-ble sources of pollutant loads transported to aquatic envi-ronments, we applied MFEM to develop a procedure for conducting efficient soil environmental surveys for evalu-ation of management practices on forested lands. We in-vestigated two types of forested sites: thinning sites (TS) and delayed thinning sites (DTS). The MFEM-EC data col-lected from surface soils were well correlated with the EC data collected by a conventional sensor. MFEM-EC map-ping revealed higher EC values in surface soils of DTS. Delayed thinning had reduced understory vegetation and hydraulic conductivity of surface soils. Therefore, low plant uptake and shallow infiltration of soluble salts would have allowed them to remain in the surface soils of DTS. Forest sites that had been fertilized as farmlands could also be distinguished with an MFEM system. The proposed MFEM system would be a useful tool for creening sur-veys of forested sites prior to detailed analysis of a wider area.
Authors developed compact soil gas monitor-ing system which consisted of gas-permeable silicone rub-ber, a non-dispersive infrared CO2 gas sensor and galvanic cell O2 sensor for the purpose of evaluating changes in
soil CO2 concentration in fields. In this study, 0.5-mm-thick silicone rubber sheet was used for CO2 sensing tube,
which was reinforced with plastic and stainless mesh pipes. Time required to reach 95 % equilibrium of CO2 concen-tration of 0.5-mm-thick silicone rubber tube was 104 min-utes, while that of 4-mm-thick tube, which reported pre-viously, was 1175 minutes. The constructed system was buried in agricultural bare field and continuous monitor-ing of soil CO2 concentration was conducted through a year. Since an amplitude of seasonal changes in soil tem-perature in agricultural field is relatively large, e.g., > 25 °C at depth of 10 cm in this study field, temperature de-pendence of NDIR CO2 sensors was investigated. After temperature correction and calibration, monitored results agreed with the soil CO2 concentration which was mea-sured by conventional gas sampling method. Monitored data showed seasonal and daily changes in soil CO2 con-centration accompanied with changes in soil temperature. Quick response to increase in soil CO2 concentration fol-lowing each rainfall event was also observed. Simultane-ous decrease in O2 concentration suggested that microbial activity could be dominant factor of increase in soil CO2 concentration caused by rainfall.
The soil heat flux is an important component of heat exchange across the ground surface and is an es-sential input component used to help quantify evapotran-spiration ratio based on the heat budget. Consequently, it is useful to understand the characteristics of soil heat flux measurement methods. One objective of the current study was to compare the temperature gradient method with the heat flux plate method at a depth of 0.02 m. A second ob-jective was to assess the effect of heat storage in the soil surface layer (0.02 m thickness) under different soil water conditions. Further, the effect of the Philip’s correction on the measurement of the heat flux plate method was also as-sessed. The results indicate that the soil heat flux measured by the heat flux plate method was almost identical with the heat flux measured by the temperature gradient method when the soil thermal conductivity was approximately half of the conductivity of the heat flux plate (i.e., wet condi-tion). In contrast, the heat flux plate method overestimated the absolute value of the soil heat flux with a constant ra-tio when the soil thermal conductivity was approximately 1/10 of the conductivity of the heat flux plate (i.e., dry con-dition). In addition, the practical effect of the Philip’s cor-rection was not observed. Further, the heat storage in the surface layer showed a diurnal variation with a range com-parable to the variation of the soil heat flux at a depth of 0.02 m, whereas the net daily heat storage was quite small.
The AquaLab Vapor Sorption Analyzer (VSA) is an automatic isotherm generator to measure water po-tential for a sample with a chilled-mirror dew-point sensor while gravimetrically tracking the sample weight during wetting and drying processes. In this study, we applied the VSA to measure water retention curves for relatively dry soils ranging from —7.2 x 10 4 cm to —3.2 x 10 6 cm, and investigated the accuracy of measurement and properties of the VSA setting parameters. We confirmed that soil water potential was equilibrated with air humidity for the DVS method with 0.01 % h -1 of the weight trigger. The equi-librated water content by weight was almost identical re-gardless of the soil bulk density since the surface retention was dominant in the dry range. The newly developed DDI (Dynamic Dewpoint Isotherm) method was validated with the DVS method. The DDI method could accurately mea-sure successive retention curves for 50 h measuring time with the flow rate of 100 mL min -1. Hysteretic retention curves as well as scanning curves in a dry range could be also observed in a repeatable manner for Fujinomori silty loam soil, rokachi Andisol, and Tottori dune sand using the DDI method.