Soil thermal properties are critical to many processes. For example, germination, crop growth, and nitrification depend on soil temperature, which is determined by thermal properties. Thermal properties are usually measured in situ using specially designed probes that enclose a heat source. Here we propose and validate an alternative method for estimating soil thermal diffusivity, based on changes in temperature at the center of a soil core subjected to changing thermal boundary conditions. This method formerly required numerical analysis because no analytical solution was known ; here we present an analytical solution. Estimates of thermal diffusivity of an Andisol at various moisture levels, obtained using the new method, compared favorably to results derived with the conventional probe method, showing that the new method constitutes a viable alternative.
It is crucial to know transport properties of solute in soil when contaminants are spilled into soil. In 1990’s a procedure using a vertically-installed time domain reflectometry (TDR) probe was developed to estimate solute transport properties for the input of the Dirac delta function. We proposed a procedure for a step function input, equivalent to a contaminant breakthrough in case of a broken barrier at a final deposal site. With soil column experiments with sand, relative concentrations measured with TDR and effluent were analyzed to estimate the retardation factor, R, and the diffusion coefficient, D. For the step function input, R and D values estimated with TDR agreed well with those from effluent. For the Dirac-delta function, the R value estimated with TDR agreed with that from effluent. The proposed procedure using a vertical TDR probe to measure solute properties of soil was validated under the step function input.
We investigated the influence of the percolation pattern on the removal of soluble elements and rice plant under inundation during the cultivation with models of strati-fied layers of cadmium polluted paddy fields. At that models, plow layer and plowsole consisted of cadmium polluted soil but gravel filled subsoil is not polluted. These models had different percolation pattern in the plowsole and subsoil. In the closed system model, every layer had water flow in a closed system while the open system model had water flow in an open system in plosole and subsoil over the groundwater. The following results were obtained. At low groundwater levels, plow sole and subsoil over the groundwater had water flow an open system and hence oxidized layers. On the contrary, at high groundwater level, every layer had water flow in a closed system and hence reduced layers. The electrical conductivity values of water flow in a closed system were larger than those in water flow in an open system. In the same way, concentrations of iron, calcium and manganese in water flow in a closed system became larger than those in water flow in an open system. Plant height, number of stems and dry matter weight of rice plants under the closed system model are larger than those of open system model. But no significant difference is recognizedwhile considering leaf age and heading. The total weight of grains and filled grain ratio of rice plants under closed system treatment were better than those in open system. The root elongation depth of plants under both the models were about 60 cm. Cadmium concentration in the brown rice of plants grown under open system models are about ten times higher than that of plants grown under closed system. The above results made it clear that under inundation conditions during the cultivation period, the removal of the soluble elements, concentration of cadmium in brownrice, growth and yield of rice plant were affected by the percolation patterns.
A sandy field has the potential hazard of nitrate contamination because of its low fertilizer holding capacity. A suction controlled flux sampler (SCFS) consisting of an automated vacuum system and a sampling filter device has been developed for accurate measurement of water flux from the root zone. Knowing that water content in sandy field was highly sensitive to suction change, a buffer container was placed between the pump and a sampling bottle to apply moderate suction and avoid accidental over-sucking. A sampling device with a glass filter was placed in a dune sand column and infiltration experiments were conducted. A moderate suction was achieved and the resulting water-collecting efficiency was from 94 to 109 % under continuous rainfall. It showed that SCFS collected infiltrated water effectively without disturbing the infiltration streamline.
Accurate description of gas diffusivity in undisturbed soil is required for predicting oxygen transport in cultivated soil and the fate of greenhouse gases and volatile organic chemicals. Based on measured data for 51 undisturbed soils, we developed three types of pedotransfer models for soil-gas diffusivity : (i) a model including the effect of pore-size distribution (Campbell type soil-water characteristic, SWC); (ii) a model including the effect of pore-size distribution and inactive (isolated) air-filled pore space ; and (iii) a simple power function model for use in case limited SWC data are available. The influence of selecting the reference air-filled porosity at either —100 and —63 cm of matric potentials(ε100 and ε63)on predicting soil-gas diffusivities was also examined. The new models were compared with recent predictive models such as the Millington-Quirk (MQ) model, the Buckingham-Burdine-Campbell (BBC) model, and Macroporosity-dependent (MPD) model. The widely-used MQ model generally underpredicted data. The new models as well as the BBC model and MPD model well predicted the measured soil-gas diffusivities, with the BBC model performing slightly better. There was no significant effect of including an inactive pore space term on predicted soil-gas diffusivities. In the new models, there was a tendency that the equations using ε100 as a reference point gave a better prediction of soil-gas diffusivities compared to the equations using ε63.
A Porous Plate Tension Lysimeter (PPTL) method was used to measure the vertical water flux through a forest soil where the use of electric power is restricted. The PPTL was installed at the depth of 0.9 m in the upper, middle, and lower slopes of Katsura Headwater Catchment, and soil water flux was measured throughout the year. The vacuum pressure of PPTL was adjusted manually once a week to a target value determined by the matric potential of the adjacent natural soil profile measured by tensiometer. Annual soil water flux was 275, 608, and 601 mm for the upper, middle, and lower slopes, respectively, showing similar fluxes to annual runoff rate in the middle and lower slopes. This result shows that the PPTL method is applicable to measure annual soil water flux.