The physiological adaptation responses in plants to environmental stress, such as water stress and salt stress induce changes in physicochemical conditions of the plant, since formation of osmotic-regulatory substances can be formed during the environmental adaptation responses. Strong electrolytes, amino acids, proteins and saccharides are well-known as osmoregulatory substances. Since these substances are ionic conductors and their molecules are lectrically dipolar, it can be considered that these substances cause changes in the dielectric properties of the plant, which can be detected by microwave sensing. The dielectric properties (0.3 to 3 GHz), water content and water potential of plant leaves which reflect the physiological condition of the plant under salt stress were measured and analyzed. Experimental results showed the potential of the microwave sensing as a method for monitoring adaptation responses in plants under saline environment and that suggested the saline environment in rhizosphere can be detected non-invasively and quantitatively by the microwave sensing which detects the changes in complex dielectric properties of the plant.
Some new field techniques for measuring unsaturated soil hydraulic properties by using soil water content measured from dielectric properties of unsaturated soils are proposed. Firstly in-situ permeability tests for unsaturated soils are developed. The constant head infiltration test and the gravity drainage test were performed continuously. The transient soil water content data during these tests were measured by a portable soil moisture device. The vertical soil moisture profiles during the drainage test were used to determine the unsaturated hydraulic conductivity. The inverse solution of unsaturated soil hydraulic functions was applied to independently measured transient water content for wetting and drying process to consider hysteresis phenomenon of unsaturated soil hydraulic properties. Secondly surface ground-penetrating radar (GPR) system is employed to estimate the average soil water content profiles in the survey region as a function of the dielectric constant measured by electromagnetic wave velocities. GPR offers a simple and nondestructive approach for in-situ determination of soil water content. The utilities of proposed methods are demonstrated by using field experimental data for unsaturated dune sands.
The stem flow is volumetrically much less than through fall and it was believed to be less wet around a tree stem than the other part of the forest floor because of rainfall resistance of a tree canopy and little contribution of stem flow. In the present study, the continuous resistivity survey was conducted at the experimental deciduous forest along the one selected line for about 1.5 years’ intervals to observe the seasonal change of soil water content under the tree canopy. The observation results were applied to evaluate the effect of the stem flow on the shallow soil water content around the selected trees. The results clearly show that the downward soil water flux under the tree canopy is 2.2 times larger than that of the no tree area in the study forest. By using this downward flux data with tree density in the study forest, the groundwater recharge rate was calculated. The groundwater recharge through the stem flow is nearly 39.1% in the total groundwater recharge in the study forest, which is completely larger than the tree density of the study forest (0.115m2/m2(1.15%)). This result clearly supports the effect of stem flow on the groundwater recharge in the forested area.
The surveys using the high-frequency CSMT system were carried out to make clear the electrical conductivity structures in the landslide area in Izumi and in the test-field of Shirasu banks in Satuma-sendai. Although the survey in Izumi was conducted along a short line in a narrow flat area, relatively good data were obtained because of the short span of electrodes in this system. The 2-D resistivity model indicates that a high-conductive layer possibly highly satisfied with water lies just upon impermeable tuff breccia. Beneath the test-field of Shirasu banks, it is found that the deep layers on March are rather dry than those on January after rainfall test. These results indicate that the high-frequency CSMT method is relatively effective to survey shallow subsurface structures.
Time domain reflectometry (TDR) has been drawing a lot more attention as a way to identify the interfaces in between different dielectric media. To monitor water level (hw) with electrical conductivity (σw) and sediment surface level (hsed) in river by applying TDR, we developed a mathematical model to evaluate these properties and verified its effectiveness by measuring the dielectric constant of conductive fluid media and a soil material (sand) using TDR probes with different lengths. Although the determination of hw in extremely high-conductive media was technically incompleted, we could successfully determine hw,σw, and hsed with a probe in moderateconductive media. Judging from the relatively good agreement between properties evaluated from the model and observed data, we concluded the TDR measurement could be useful to evaluate hw, σw, and hsed with sufficient accuracy for practical use within an appropriate conductive range. In actual application of TDR to a river monitoring, the calibration of the probe used must be required to conduct accurate measurement based of the model.
The use of composted organic matter as soil surface cover is recently viewed as a potential application for erosion control similarly to straw cover. However, limited information on the effect of these cover materials on erosion from bare soil is available. This study evaluates two cover materials, rice straw and cattle manure compost, with a focus on the relationship between soil surface coverage (expressed in areal%) and soil loss from bare upland field. A clay loam Andisol was packed into a 1.2 m X 0.35 m X 0.12 m soil box with a slope of 14% and subjected to simulated rainfall of 45.1 mm hr-1 for 100 minutes. The soil surface was either left bare or was covered with rice straw (Oryza Sativa L.) or cattle manure compost at a surface coverage of 30 areal % for straw, 35 areal% for compost, and 60 areal% for both materials. During the simulated rainfall, surface runoff was periodically collected to determine sediment concentration and infiltration rate. As the coverage rate increased from 30 or 35 to 60 areal%, the straw and compost covers acted to significantly reduce the sediment concentration. The observed reduction in sediment loss from the covered soils resulted from the direct interception of raindrops and trapping of sediment by the cover ; however, neither cover material was able to reduce the runoff rate. The total runoff volume was higher for compost-covered soils than for bare or straw-covered soils. This result may reflect the development of a depositional crust over the soil surface. Such crusts formed in sediment-trap areas close to pieces of the covering material.
To establish a method to investigate leakage from small earth dams by measuring ground temperature at a depth of one meter, its daily range and seasonal variation and the surface temperature of the small earth dam body were measured at the Aoike Irrigation Pond in Kagawa Prefecture. The relationship between the ground temperature at a depth of one meter and the conditions of the small earth dam body surfaces, leakage paths and seepage surfaces was investigated through simulation. The results indicate that ground temperature anomalies caused by partial leakage from a low-height small earth dam can be detected by the measurement of the ground temperature at a depth of one meter on the crest of the small earth dam during summer or winter, when ground temperature differences are more likely to occur. A method to set leakage paths, seepage surfaces and fixed temperature boundaries for simulation is also presented. From the simulation of ground temperature at a depth of one meter, the width and depth of leakage paths can be estimated by determining the conditions of leakage paths and seepage surfaces that are concordant with the measured temperature values.
A field experiment in a pineapple plantation at Lampung Province of Indonesia was conducted for 15 months to investigate the effect of rice husk and tapioca wastes (cassava bagasse and cassava peel) used as organic amendments, on soil physical and biological properties. The treatments included control, rice husk mulch, cassava bagasse mulch, cassava peel mulch, cassava peel-soil mixture and black polyethylene film mulch. The organic materials were applied manually at a rate of 30 kg m-2. The soil physical and biological properties at the initial and final stages of the experiment were measured and compared. The results showed that the moderate rate of rice husk’s decomposition process slightly increased SOM of surface layer that may had led to somewhat decreased particle density and available water content enhancement. On the other hand, cassava bagasse mulch decomposed within very short period after application and thus its roles especially in soil physical properties were no more noticeable in 15 months after its application. Due to the slow decomposition rate,15 months was probably too short for cassava peel to contribute in SOM enhancement as well as other soil physical properties. However, the application of investigated organic materials for soil amendment resulted in the more abundance earthworm populations, bulk density decreasing, and the increases of macro pores and WSA in general. The existence of earthworms in the soil is certainly contributed positive effects in the soil properties, especially physical soil properties. But which soil properties that were most affected by the earthworm activities cannot be concluded, since other factors such as soil microorganisms could also play a role in promoting soil properties enhancement.
Measurement of soil heat flux using a thermo-module was examined. The measuring principle is almost the same to a traditional heat flux plate method, however, the measurement accuracy of the temperature difference of the thermo-module is much higher than that of the traditional thermo-pile. It was considered that the utilization of thermo-module allowed to measure the soil heat flux accurately even under the soil layer of small temperature gradients. Relation between the thermo-module output and one-dimensional steady heat flux was examined in agar-gel. As a result, the thermo-module output was proportional to the heat flux in a wide range. Using this relation, the soil heat flux in a field was determined. In order to confirm the reliability of the thermo-module method, the heat storage flux in soil layer was compared between the thermomodule method and the calorimetric method. Both results corresponded closely. These showed that the thermo-module method was effective as the heat flux meter.