Time domain transmissiometry (TDT), a method of measuring transmitted broadband signal in microwave frequency, has been drawing a lot of attention more than ever as an alternative method to monitor water content and solute concentration in soils. To establish the monitoring method by applying TDT, we measured travel time and amplitude of impulse-signal transmitted through several types of fluid media using TDT probes with different lengths, and verified the effectiveness of TDT for the estimation of apparent permittivity and electrical conductivity of the media. Although the determination of apparent permittivity and electrical conductivity of an extremely high-conductive medium was not completed due to the inadmissible loss of the transmitted signal, we successfully determined both properties by TDT in moderate-conductive media. Judging from their distribution from referential values in literature, we concluded that the longer probes provided more accurate estimations of apparent permittivity and electrical conductivity.
Time domain reflectometry (TDR), measuring dielectric properties, has widely been applied to monitor volumetric water content (θ) and bulk electrical conductivity (σb) in soil. TDR is, however, not applicable to clays due to the inadmissible energy loss of emitted microwave signals. To reveal the response of the clays to the signals, by using a vector network analyzer we measured the spectra of real (ε') and imaginary (ε") part of complex permittivity in the frequency of 0.1 to 3.0 GHz for kaolinite and bentonite having di erentθ-values. Besides the distinctε"- and ε"-spectra for θ, for kaolinite we found that the relation of ε' versus θ can be given by a unique expression within a range of examined frequency, and can be estimated from ε" -values at around 3.0 GHz with relatively small errors. Although the σb values for the bentonite, estimated by the present method, included unacceptable large errors, the relations of ε' versus θ were adequately determined in whole examined frequencies. Judging from the gradient of ε' - θ relations for bentonite, we suggested that the signals with higher frequency should provide more sensitive determination of than θ that with lower frequencies.
Pozzolanic materials, either naturally occurring or artificially made, have long been in practice for soil stabilization. Of the artificial pozzolans, the ordinary portland cement is the most commonly used globally. Literature review indicates that, to date, the percentage of the cement used to improve the properties of soil is 4 to 14% or more. For the sake of cost saving in soilcement construction works, it is crucial to scrutinize the efficacy of an incredibly diminutive amount of cement on the engineering properties of soils. In this paper, efforts have been made to study the usefulness of nominal dosage rate of the ordinary portland cement on the bearing capacity and permeability of a clayey soil in Mie prefecture. Laboratory tests were conducted on California Bearing Ratio (CBR), unconfined compressive strength and the permeability coefficient of the clayey soil with the cement content of 0.0, 0.2, 0.4 and 0.6% in the ratio of mass. On the basis of the test results, it was concluded that both the CBR and compressive strength, a measure of bearing capacity of a soil, increased with the increase in the amount of cement. The stressstrain relationships of the soil under the unconfined compression tests indicated that the addition of the nominal dosage rate of ordinary portland cement reduced the strain at which the ultimate compressive strength occurred noticing the increase in the rigidity of soil. The modulus of deformation, a measure of deformation characteristics of a soil, was also found to increase with the increase in the quantity of cement content. Permeability tests revealed that the coefficient of permeability increased with the increase in the amount of cement.
Currently, various types of livestock manure composts have been developing for application to farmlands as an organic fertilizer. Nutrients released from these newly developed composts play an important role in the overall chemical dynamics in soils. In the traditional methods, such as an incubation method, the nutrient release patterns were measured under soil-compost mixing conditions, in which the major cations and anions were not analyzed precisely. Thus, in this study, a new method for measuring early nutrient release pattern from composts was developed using sand column mixed with manure compost and was applied for analyzing the nutrient release patterns for four kinds of cattle manure compost. A sand column of 9.3 cm height and of 5 cm diameter, having the unsaturated sand layer of 2.3 cm height mixed with compost overlain the saturated sand layer of 7 cm height, was prepared. Distilled water was supplied to the top of the column at a constant rate and the pattern of the nutrient concentration in drained water was measured. This could be evaluated as BTC normalized with pore volume. This method performed well in detecting the delayed release of nutrients and the increase in the released K in the pelletized composts compared with the traditional ones.
The anionic polyacrylamide (PAM) is recently used to rehabilitate saline and sodic soils. It is also applied to control soil erosion ; however, few researches have tested the effectiveness of anionic PAM along with source of electrolytes application to control artificial sodic soil erosion. An experiment was conducted to study the effects of anionic PAM with and without gypsum on the erosion of sodic soils under saline rain water conditions. A clay loam soil was prepared to achieve three levels of exchangeable sodium percentage (ESP); 0.5, 9.9 and 25.5 with appropriate salts solutions. Soil samples were air-dried and packed in the trays. Powdered PAM, gypsum or a mixture of both were applied to the salt treated soils. Soils were subjected to simulated rainstorm of 40 mm h_1 by a fixed rainfall simulator. Saline waters with different levels of electrical conductivity (EC); 0.13, 2, 5, and 8dSm_1 were used for simulated rains during the study. It seems that the artificial soil showed fairly similar soil erosion characteristics as that reported on a natural sodic soil. It was found that the soil sodicity enhanced soil erosion under non-saline water. It seems that the effects of electrolyte source on soil erosion were affected by the soil initial electrical conductivity (ECe) rather than by the ESP level of soil. PAM amendment substantially increased the surface runoff while at the same time controlled the soil losses. A reduction in surface runoff was found by applying gypsum or saline water on the soil treated with PAM. However, it seems that the mixed addition of PAM with gypsum or salts enhanced detachments of soil particles by raindrop impact.
Thermal conductivity (K) as functions of water content (w) is not so well known for swelling soils as that for non-swelling soils. We measured K and thermal diffusivity of a swelling soil taken from paddy fields in Indonesia, together with its shrinkage-swelling characteristic. The soil showed remarkable shrinkage-swelling nature ; void ratio of the soil in-situ exceeded 2.0 when flooded condition whereas it became less then 1.0 when the soil was dry. Observed K increased from 0.60 to 1.28 W m-1 K-1 with w increased from zero to 0.24 gg-1. However, for w greater than
0.24 gg-1, K decreased gradually with increase in w, differently from non-swelling soil that shows monotonic increase with w. The decrease in K with increase in w must be produced by increased void ratio. As a result, the value of K for the soil of most dry condition in the field (K = 0.99 W m-1K-1) was almost the same as the value of K for flooded condition. Consequently, drying of the swelling soil has no effects of reducing heat conduction from surface into the soil when it is exposed to sunshine.