Redox reactions involving structural Fe in smectite clay minerals contribute significantly to the chemistry of soils and sediments. Changes in oxidation state from Fe (III) to Fe (II) alters the clay structure, which in turn modifies the chemical nature of the smectite basal surfaces. These changes in structure are readily observed by infrared spectroscopy. Structural OH groups are progressively lost as the level of Fe (II) increases, and large shifts occur in the Si-0 stretching and bending modes of the tetrahedral sheet. The communication between octahedral and tetrahedral sheets alters the configuration of basal oxygens, as well as changing the charge, pH, and reduction potential of the surface. Infrared spectra also provide evidence for the formation of trioctahedral domains as a result of extensive Fe (III) reduction.
There is a big demand to predict water movement and solute transport in soil not only in agricultural but also in environmental fields. To predict water distribution in soil, soil hydraulic properties, i.e. a water characteristic curve and hydraulic conductivity, should be known in priori. Measurement of soil hydraulic properties, however, is usually time consuming and laborious work. Recent improvements of computing power on PC enabled us to inversely estimate hydraulic properties using a numerical simulation model along with experimental data. Spreadsheet-type software, which has a macro language and a solver, is also popular. In this study Excel was used to numerically simulate soil water movement using the finite difference method written in Visual BASIC as a macro function. The solver function of Excel successfully worked with the numerical model to estimate best-fitted values for soil hydraulic properties by comparing simulated results with temporal changes in soil water content measured. The tempo-ral changes in water content were measured with time domain reflectometry (TDR) at 20 cm below the soil surface during water infiltration into loamy sand. A water characteristic curve with parameters inversely estimated reasonably agreed with that with parameters experimentally determined. Saturated hydraulic conductivity inversely estimated also agreed well with that determined by an experiment. Excel would be alternative software to estimate soil hydraulic properties with an inverse procedure.
With the growing concern over the sustainable use of soil organic matter, it is important to know the relationship between microbial activity and the physics of soil. This study measured changes in the T-C in soil aggregate and crushed aggregate at sub-atmospheric and atmospheric pressures, following substrate incorporation, to examine the effect of decompression on microbial activity in soil. The T-C decreased rapidly in the beginning and decreased more slowly at later time stages. The decrease in T-C varied with pressure. The decrease in T-C was greatest at a gauge pressure of approximately —20 kPa. The decrease also differed between the aggregate and crushed aggregate samples. These results suggest that the chemical potential of soil water changes with decompression, affecting the vital activity of microbes. Furthermore, soil aggre-gates play an important role in this activity.
Spatial variability of soil properties was studied by using correlation analysis with landscape and geostatistical concepts on a 1.2-ha upland field in a hilly area. Soil properties of Ap horizon were examined on a square grid at 14-m intervals and on three transects at 7-m intervals. The CV values suggested that the variabilities of most soil properties were higher than the results reported at any topographical conditions. These large variables depend on the result of soil erosion and sedimentation in response to the landscape. At the eroded area, the thickness of Ap horizon had been kept constant with subsoil by tillage, as a result Ap horizon was composed of different soil materials from sedimentation and erosion effects. The spatial variability of pH, total carbon content, phosphate absorption coefficient, bulk density, stone, sand, silt and clay content could be explained with topographical features ; however, available water content was difficult to explain. Moreover, former properties were distinguished at landscape model units, these contribute to the rational soil sampling system to realize regional soil management. The multiple regression models of total carbon and stone content, using only topographic attributes calculated from a digital elevation model (DEM), matched reasonably well with the observed data.
The formation process of clathrate-hydrate in porous glass powder saturated with THF-water mixture was observed using directional cooling apparatus. When the cooling rate became lower, THF hydrate grew with excluding glass particles and formed lens -like layer of hydrate in the same manner as in the phenomenon of ice lens formation in the freezing of soil. The growth rate of hydrate lens was proportional to the supercooling degree of the growth surface and about one-twentieth the growth rate of hydrate layer in THF-water mixture without glass particles. When NaCl was added into the system, the growth of hydrate lens was inhibited depending on the NaCl concentration.
The effect of incorporation of wood bark on three-phase composition of soil, soil resistance, hydraulic conductivity, and water retention was investigated on clayey soil and sandy soil. Application of wood bark was arranged at 0.0 %, 1.0 %, 2.0 %, 3.0 %, 4.0 %, and 5.0 % of wood bark to soil (dry weight basis). Soil resistance was determined with a hand-held cone penetrometer (Yamanaka-shiki Koudokei), the hydraulic conductivity by using the variable head test technique, and water retention by the hanging water column method and centrifuge method. The remarkable result was found in sandy soil such that incorporation of 5 % wood bark produced reduction of 31 % solid phase. The soil resistance was higher in compaction stage than cutting off stage at both soils. In clayey soil, it decreased from 14.4 kgf/cm2 (0 % wood bark) to 10.5kgf/cm2 ( 5 % wood bark) in compaction stage, but it varied in cutting off stage with maximum at 9.7 kgf/cm2 ( 1 % wood bark) and minimum at 7.4 kgf/cm2 (3% wood bark). Hydraulic conductivity in clayey soil reached to the maximum ( 3.5 × 10-4 cm/s) with incorporation of 5% wood bark, however in case of sandy soil it changed inconsistently as addition of wood bark. The increase in water content by 3% wood bark was kept almost constant as 4.13% even in low suction at pF 0.8 ( -0.60 kPa) and as 4.01 % in high suction at pF 5.5 ( -31 MPa) in clayey soil, while in sandy soil, it diminished from 1.40 % at pF 0.8 ( -0.60 kPa) to 0.01% at pF 4.2 ( -1.5MPa). This study demonstrated that incorporation of wood bark influenced the physical properties of clayey and sandy soil.