Masaru Sakai

A complete soil hydraulic model accounting for capillary and adsorptive water retention, capillary and film conductivity, and hysteresis

A soil hydraulic model that considers capillary hysteretic and adsorptive water retention as well as capillary and film conductivity covering the complete soil moisture range is presented. The model was obtained by incorporating the capillary hysteresis model of Parker and Lenhard into the hydraulic model of Peters-Durner-Iden (PDI) as formulated for the van Genuchten (VG) retention equation. The formulation includes the following processes: capillary hysteresis accounting for air entrapment, closed scanning curves, nonhysteretic sorption of water retention onto mineral surfaces, a hysteretic function for the capillary conductivity, a nonhysteretic function for the film conductivity, and a nearly nonhysteretic function of the conductivity as a function of water content (θ) for the entire range of water contents. The proposed model only requires two additional parameters to describe hysteresis. The model was found to accurately describe observed hysteretic water retention and conductivity data for a dune sand. Using a range of published data sets, relationships could be established between the capillary water retention and film conductivity parameters. Including vapor conductivity improved conductivity descriptions in the very dry range. The resulting model allows predictions of the hydraulic conductivity from saturation until complete dryness using water retention parameters.

Freezing experiments on unsaturated sand, loam and silt loam

Abstarct Estimating soil-water flow during ground freezing is important for understanding factors affecting spring farming, soil microbial activity below the frozen soil, and permafrost thawing behavior. In this study, we performed a column freezing experiment using three different unsaturated soils (sand, loam and silt loam) to obtain a detailed dataset of temperature, water-content and pressure-head change under freezing conditions. The liquid water content and pressure head in the three soils decreased with decreasing temperature. Three soil temperature stages were found: unfrozen, stagnating near 0˚C and frozen. The temperature and duration of the stagnation stage differed among the soil types. The changes in liquid water content and pressure head during the freezing process were highly dependent on the soil-water retention curve. Water flowed through the frozen area in silt loam and sand, but no water flux was observed in the frozen loam. The freezing soil columns tended to contain more liquid water than estimated from retention curves measured at room temperature, especially at the early stage of freezing.

A Multi-Functional Penta-Needle Thermo-Dielectric Sensor for Porous Media Sensing

There is growing interest in multifunctional sensors that expand sensing capabilities, especially for environmental measurement needs. This paper aims to develop a multifunctional penta-needle thermo-dielectric sensor (MPTDS) by coupling an electromagnetic (EM) sensor for determining water content with a penta-needle heat pulse probe (PHPP) for determining thermal properties. The thermal properties were inverse fit to the measured temperature rise at four surrounding thermistor needles from an 8-s heat pulse on a central heater needle. The dielectric permittivity was obtained from an impedance measurement made on the heater needle and two adjacent thermistor needles, leading to water content estimates. To determine water content and thermal properties for porous media, a two-step permittivity calibration and an in-situ effective needle spacing calibration were also made. The prototype MPTDS was evaluated in fine quartz sand across a range of water contents from dry to saturated to determine dielectric permittivity, thermal conductivity, and thermal diffusivity, followed by the accurate calculation of water content and soil heat capacity. The limited comparison here demonstrates substantially improved substrate water content determination accuracy from the EM sensor (RSME = 0.012 cm3/cm3) when compared with heat-pulse estimates (RSME = 0.042 cm3/cm3).

Bulk density effects on soil hydrologic and thermal characteristics: A numerical investigation

Department of Civil Engineering, Gifu University, 1‐1 Yanagido, Gifu City, Gifu 501‐ 1193, Japan Department of Crop and Soil Science, North Carolina State University, Raleigh, NC 27695, USA Graduate School of Bioresources, Mie University, 1577 Kurimamachiya‐cho, Tsu, Mie 514‐8507, Japan Department of Agricultural and Environmental Engineering, Hirosaki University, 3 Bunkyo‐cho, Hirosaki, Aomori 036‐8561, Japan Department of Agronomy, Iowa State University, Ames, IA 50011, USA Correspondence Yuki Kojima, Department of Civil Engineering, Gifu University, 1‐1 Yanagido, Gifu City, Gifu 501‐1193, Japan. Email: kojima@gifu‐u.ac.jp