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Macropores resulting from soil pedogenesis, biological activity, and agricultural practices play important roles in soil water, chemical and gas transport; however, seldom studies focus on the effect of soil macropores on CO2 behavior. In this study, a 150-day soil column incubation experiment was conducted to investigate the CO2 behavior in a homogeneous soil column and a soil column with an artificial macropore, which have the same total porosity. The results showed that the cumulative CO2 fluxes observed in the soil with a macropore (57.2 g m−2) were higher than those in the homogeneous soil (52.7 g m−2). The soil cumulative CO2 fluxes measured using column incubation can fit the kinetic model, and a higher carbon mineralization rate in the soil with the macropore was found. The results of the incubation experiment also suggest that macropore increased the gas diffusivities, and thus decreased the CO2 concentrations in the soil profile. This study proposed a simulation experiment and quantified the effect of macropore on soil CO2 behavior, which could help to understand the mechanism of CO2 emission from soil with macropores especially caused by agricultural practices.

Accurate quantification of soil gas diffusion is essential to understand the gas transport mechanism in soils, especially for soil greenhouse gas emissions. To date, the performance of soil gas diffusivity (Dp/D0, where Dp is the soil gas diffusion coefficient and D0 is the diffusion coefficient in free air) models has seldom been evaluated for no-tilled and tilled volcanic ash soils. In the present study, six commonly used models were evaluated for volcanic ash soils under two treatments by comparing the predicted and measured soil gas diffusivities at water potentials of pF 1.3–3. The Buckingham-Burdine-Campbell (BBC), soil-water-characteristic-dependent (SWC-dependent), and two-region extended Archie’s Law (2EAL) models showed better performance for both no-tilled and tilled volcanic ash soils, which is likely because porosity and pore size parameters of bimodal soils were taken into consideration in these models. Since the BBC model showed better accuracy than the SWC-dependent and 2EAL models...

Agricultural management plays an important role in the storage of carbon in soils. The behavior of soil CO2 in an Andisol in two different tillage systems (no tillage and tillage) was studied. Soil-column incubation experiments were performed for a period of 150 days to conduct this study. Soil CO2 flux, under no-tillage and tillage treatments, was observed to be 0.557 and 0.616 gCO2-C m−2 d−1, respectively. The cumulative CO2 flux under tillage treatment was observed to be higher than that under no-tillage treatment, but no distinct difference in the soil carbon stock was observed between both treatments. The soil CO2 concentration under no-tillage treatment was clearly much higher than that under tillage treatment, except at a depth of 2.5 cm. Tillage decreased soil dry bulk density and enhanced soil air-filled porosity. Soil gas diffusivity, which depends on air-filled porosity, was increased by tillage at a depth of 0–15 cm, which contributed to their lower soil CO2 concentration. CO2 flux through the soil profile, calculated from the CO2 concentration, decreased with depth. Compared to the deep soils, the surface soil (0–5 cm) showed greater variation in CO2 flux. The CO2 production at depths of 0–10 cm accounted for 62.2 and 51.7 % of the whole CO2 production of the 0–30-cm soil profile for no-tillage and tillage treatments. CO2 production was higher for soil under no tillage at depths of 0–10 cm, but contrary results were observed for soil at depths of 10–30 cm.

Rising saline shallow groundwater and associated soil salinization problems are widespread especially in arid and semiarid areas. There have been numerous studies on groundwater-associated salinity, but more information is required on the effects of groundwater frequent and high fluctuations on soil salinization. In the present study, laboratory experiments and numerical simulations using HYDRUS-1D model were carried out for this purpose. The experimental and modeling results showed that groundwater fluctuation caused not only the accumulation of more salt in the soil profile compared to stable groundwater, but also an enhancement of the mechanism. Water table fluctuation induced a much greater spreading of the bromide (Br) tracer within the column than the constant water table. The Br content was on average five orders of magnitude greater under a fluctuating water table than under a constant one. Further, the numerical simulations showed that an increase in the groundwater fluctuation frequency brought about an increase in soil surface salinization under the same evaporation boundary conditions. Additional simulations with HYDRUS-1D were used to study the effects of various management strategies on soil salinization induced by shallow groundwater. Hence, by reducing the evaporation rate through the application of surface mulching, a significant reduction of salt concentration at the soil surface was observed. Moreover, frequent irrigations with small quantities were effective to reduce soil surface salt accumulation induced by saline shallow groundwater.

Predicting the effects of climate change on the vadose zone is a new and important application of the analysis of simultaneous heat and water movement between the atmosphere and the vadose zone. The HYDRUS-1D software system, with meteorological submodels that evaluate the surface water and energy balance, has been reported to be a useful tool for predicting field thermal and moisture conditions in semiarid regions. Application of the physical model to a humid climate and all types of soils is necessary because this climate has pronounced biological activity and thus significantly contributes to the global environment. The purpose of this study was to evaluate the usefulness of HYDRUS in predicting annual changes in soil moisture and temperature in the vadose zone under a monsoon climate. The model was evaluated using observed data from a western suburb of Tokyo. The soil properties utilized in the simulation were obtained using laboratory experiments. Climate data for the meteorological submodels were obtained from open-access climate records. The observed surface heat flux agreed well with the predicted surface heat flux produced by the meteorological submodels. The numerical results produced by HYDRUS using the meteorological submodels represented annual changes in soil thermal and moisture conditions fairly well. Our results show that the meteorological submodels of HYDRUS are appropriate to produce thermal and water boundary conditions under a monsoon climate. This suggests that HYDRUS has the potential to simulate the physical conditions of the vadose zone by using forecast climate data coupled with global circulation models.

In this study, artificial rainfall was applied to a partially frozen Andisol soil, and the effects of the subsoil's physical conditions, prefreeze moisture condition, and soil compaction on surface runoff and soil loss were studied. The soil, an Andisol from a mountainous region of Japan, was packed into a plastic box to a thickness of 0.08 m to attain a predetermined moisture condition and dry bulk density, then stored in a freezer at -30°C overnight to create a sample representative of frozen subsoil. Twenty millimeters of unfrozen soil were added on top of the frozen subsoil to simulate a thawing surface layer. During the simulated rainfall (42 mm h ―1 ) experiment, surface runoff, soil loss, and seepage from outlets at the front wall of the downslope end of the box were sampled periodically. In the early stage of rainfall, the impermeable frozen subsoil increased surface runoff and soil loss, and seepage occurred at the downslope end of the box, indicating saturation of the near-surface, unfrozen soil. During the early stage of the rainfall, soil loss was particularly greater than during the latter half of the rainfall experiment although both showed a similar surface runoff rate. Saturation of the near-surface soil was the reason for the greater soil loss rate, while a surface seal restricted soil loss by surface runoff during the latter half of the rainfall experiment.

Water-saving rice-winter crop rotation systems were repeated for 4 cycles from 2000 to 2004 in an urban area, Nishitokyo, Japan, to assess the effects of water-saving (i.e. non-flooded vs. flooded) on grain yield of rice (Oryza sativa L.) and chemical constituents of percolating water. The effects of pre-rice winter cropping compared with fallow on rice yield were also examined. The pre-cultivated crops were wheat (Triticum aestivum L.), italian ryegrass (Lolium multiflorum Lam.) or spinach (Spinacea oleracea L.) with their above-ground parts removed, chinese milk vetch (Astragalus sinicus L.) or rapeseed (Brassica napus L.) with their above-ground parts incorporated before rice transplanting. Neither winter cropping effects nor its interaction with water-saving were significant for rice yield, although the yield after rapeseed incorporation tended to be 9 % higher than that after fallow. In 2001, 2003 and 2004, when more than 70% of irrigation water was saved in the non-flooded trial, average yield in non-flooded trial was 58 % of flooded trial, but water productivity increased (from 0.10 to 0.16 kg m-3). Among the 3 years, yield in non-flooded trial was highest in 2004 when the amounts of irrigation and total water supply was larger, the frequency of dry spells was the lowest, and 2 seedlings were transplanted per hill. The nitrate and nitrite concentrations in the percolating water were far below the environmental standard values by WHO. The study showed that incorporation of winter crops had no negative effects on water-saving rice production at least for the first 4 years, and that under extreme water-saving, irrigation and planting methods could minimize yield reduction.

A Deep Root System May Be A Desirable Plant Characteristic In Upland Rice Because It Improves The Plant’s Water Extraction Capacity. The Objective of The Present Study Was To Assess The Deep Root Development of Rice Cultivars In Relation To Soil Moisture Change and Plant Water Status Under Upland Conditions With Moderate Water Deficits In The Field and In Simple Lysimeter Experiments. We Used One Upland Cultivar (‘Yumeno-Hatamochi [Yhm]) and Two Lowland Cultivars (‘Lemont’ [Lmt] and 'Nipponbare’ [Npb]) In The Field Experiment, With No Supplemental Water From 88 To 106 Days After Sowing (Das) and 116 To 145 Das. In The Lysimeter Experiment, We Used Yhm and Npb and Imposed Two Water Stress Periods During The Late Vegetative Stages (71 To 104 Das and 88 To 104 Das). In The Lysimeter Experiment, A Higher Deep-Root Length Ratio (Proportion of The Length of Deep Roots To The Total Root Length) In Yhm Was Associated With A Greater Deep-Root Length Than In Npb. The Difference In Deep Root Development Was Associated With Change In Soil Water Content At The Depths of 45 To 70 Cm Between The Two Cultivars Under The Above Conditions. The Drought In The Field Experiment Was Less Intense Than In The Lysimeter Experiment, and We Observed Greater Varietal Differences In Total Aboveground Biomass Than In Root System Development; This Was Associated With The Change In Soil Water Content During The Initial Drought Period. Lmt, With Smaller Shoots, Tended To Save Water and Maintain Higher Leaf Water Potential and Lower Diffusion Resistance As The Drought Progressed. Our Results Suggest That Deep Root Development of Rice Was Primarily Advantageous For Soil Water Extraction and Plant Water Status Under Moderate Water Stress In Uplands, But That The Advantage of A Deep Root System Was Affected By Total Aboveground Biomass, Which Had Strong Effects On Plant Water Status Under These Conditions.

Wedge-shaped defects are frequently observed on the cervical region of the human tooth. Previously, most studies explained that improper toothbrushing causes such defects. However, recent clinical obsarvation suggested that the repeated stress due to occlusal force may induce the formation of these wedge-shaped defects. In this study, a two-dimensional human tooth model after a wedge-shaped defect is restored with the composite resin is analyzed by using the finite element method. To obtain the intensity of the singular stress field accurately, a method of analysis is discussed for calculating generalized stress intensity factors, which control the singular stress around the tip of the defect. Then, the relationships between the stress intensity and occlusion are discussed.

Soil carbon evolution under the lowest moisture conditions varies considerably among experimental systems/techniques, leading to discrepancies in the estimations from carbon dynamics models under low moisture conditions. We focused our study on clarifying the regulating factors of soil carbon evolution under the lowest moisture conditions by conducting laboratory experiments under precisely controlled conditions. Nanoscale porosity and surface properties of these soils were determined to analyze the role of residual water in the carbon evolution processes in dry soils. Laboratory incubation showed that the carbon evolution from a microporous (D < 2 n m) volcanic soil proceeded even at -100 U kg-1 water potential (INT) in contrast to the carbon evolution from a phyllosilicate alluvial soil. Pore-size estimation and 1H-NMR spectroscopy showed that the carbon evolution at -100 U kg-1 WP proceeded through the utilization of nanopore-water in soils. Batch sorption experiment suggested that the surface...

Recently, carbon capture and storage by soils is recognized as an important function of agricultural fields. When discussing global warming mitigation such as proper agricultural practices and/or an appropriate depth of composting in agricultural lands for soil carbon storage, not only CO2 efflux, but also profiles of CO2 concentrations in soil air, are important. This study evaluated the performance of the SOILCO2 model in predicting soil CO2 dynamics, especially CO2 concentrations at various depths in an arable bare land of Andisol. We attempted to experimentally determine two soil parameters required for the CO2 production model, the optimal CO2 production rate and the parameter of a depth-dependent CO2 production function by measuring CO2 efflux from the surface and a vertical distribution of concentration of dissolved organic carbon, respectively. Soil CO2 concentrations, water contents and temperatures were continuously monitored for approximately one year at three different depths, and simu...

Seven sites ranging from 15 to 135 km from Mount St. Helens were selected to study the impact of air-fall tephra on the growth of Abiesamabilis (Dougl.) Forbes, A. procera Rehd., Pseudotsugamenziesii (Mirb.) Franco, Tsugaheterophylla (Raf.) Sarg., and T. mertensiana (Bong.) Carr. As tephra depth increased, there was a corresponding increase in visible foliar damage and associated decreases in diameter and height growth. Reduction in diameter growth was greater than reduction in height growth. The reduction in diameter growth approached 50% in both trees and saplings of A. amabilis. Growth reduction in true firs was greater than in associated species. This difference was related to their greater capacity for interception and retention of air-fall tephra. Damage to trees, and resulting growth reductions, were due to tephra coverage of both the foliage and the soil. Coverage of the foliage resulted in foliar damage, foliage abscission and reduction of total tree foliar area, and increased fine root mortality. Tephra coverage of the soil had the potential to restrict oxygen diffusion into the soil. However, soil oxygen concentrations less than 10% were measured only once over a 2-year period.