Masaru Mizoguchi

Water flow and heat transport in frozen soil : Numerical solution and freeze-thaw applications

A new method is presented to account for phase changes in a fully implicit numerical model for coupled heat transport and variably saturated water flow involving conditions both above and below zero temperature. The method is based on a mixed formulation for both water flow and heat transport similar to the approach commonly used for the Richards equation. The approach enabled numerically stable, energy- and mass-conservative solutions. The model was evaluated by comparing predictions with data from laboratory column freezing experiments. These experiments involved 20-cm long soil columns with an internal diameter of 8 cm that were exposed at the top to a circulating fluid with a temperature of −6°C. Water and soil in the columns froze from the top down during the experiment, with the freezing process inducing significant water redistribution within the soil. A new function is proposed to better describe the dependency of the thermal conductivity on the ice and water contents of frozen soils. Predicted values of the total water content compared well with measured values. The model proved to be numerically stable also for a hypothetical road problem involving simultaneous heat transport and water flow. The problem was simulated using measured values of the surface temperature for the duration of almost 1 yr. Since the road was snow-plowed during winter, surface temperatures varied more rapidly, and reached much lower values, than would have been the case under a natural snow cover. The numerical experiments demonstrate the ability of the code to cope with rapidly changing boundary conditions and very nonlinear water content and pressure head distributions in the soil profile.

Amount of unfrozen water in frozen porous media saturated with solution

In porous media, such as soil, some water do not freeze when cooled below 0 � C. The amount of unfrozen water is dependent on temperature and the characteristics of the porous media and solute in water. In this study, three types each of monosized glass powder, silty soil, and clay were saturated with various concentrations of NaCl, KCl, and MgCl2 solutions and subjected to freezing temperatures. The relationship between the reduction in temperature and the amount of unfrozen water was measured using nuclear magnetic resonance (NMR) technique. The amount of unfrozen water decreased with the lowering of temperature. When a porous medium was saturated with a solution, the amount of unfrozen water increased with increasing

Physical Controls on Ebullition Losses of Methane from Peatlands

Recent studies indicate that direct escaping of CH 4 -containing gas bubbles, i.e., ebullition, plays a considerable role in determining the total CH 4 emission from peatlands into the atmosphere. Although methane is a biological product, a large bubble-storage capacity of peat leads to a partial decoupling between the production and release of methane, allowing for physical factors to act as a trigger for the ebullition. Buoyancy-induced ebullition can be controlled by (1) atmospheric pressure, (2) peat temperature, and (3) water table level. Falling atmospheric pressure exerts a dominant role in determining the timing of ebullition in some peatlands. Rapid rise in water table position by rain would result in the suppression of the bubble volume, and hence, halting ebullition. Diurnal temperature modulation might affect ebullition; however, its significance is expected to depend heavily on the position of water table, thermal characteristics of the peat, and the depth distribution of the CH 4 -containing bubbles. Wind-induced surface turbulence also gives rise to ebullition as demonstrated by eddy covariance studies. Another type of ebullition includes a release of entrapped CH 4 accumulated during winter at spring-thaw period, but its significance is largely unknown. Further technical development is necessary to examine recently suggested massive CH 4 ebullition (>g CH 4 m -2 h -1 ) in terms of surface flux monitoring. Future research also needs to address subsurface behavior of the bubbles in relation to physical characteristics of peat and other transport modes.

Social capital accumulation through public policy systems implementing paddy irrigation and rural development projects

In Japan, a developed country in Asia, the Land Improvement Act systems have worked as a measure of social capital accumulation as well as an adjective law in implementing irrigation projects since 1949. This paper illustrates the status and problems in applying the concept of social capital to agricultural and rural development policy systems in developing countries, EU and Japan. The results obtained are summarized as follows: (1) it is desirable that governments formulate public policies that are appropriate for correcting inefficiencies in resource distribution for accumulating social capital, so that the governments play a significant role in developing and supporting social capital; (2) the effect of policies in the areas, where government-supported land improvement projects have been implemented, has been improved, subsequent to which the efficient use of the national budget allocated for the projects has been improved, while the projects significantly contribute to the national land conservation and social stability by continuously promoting minimum social capital accumulation nationwide. In addition, Japan and countries in the Asian monsoon region, which hold the five elements in common that constitute the characteristics of rice field irrigation in humid climates, should take over the advantages of the land improvement project system while learning from the success achieved by the LEADER+ programme in Europe, where society precedes Asian countries concerning the problems of decline in the birth rate, and expansion of an aging society.

Formation and disappearance of Al tridecamer in the presence of low molecular weight organic ligands

Abstract Formation and disappearance of phytotoxic Al tridecamer (Al13) in the rhizosphere can be affected by root exudates such as organic ligands. We investigated the effects of organic ligands on the formation and disappearance of Alla as a function of pH and COOH / Al ratio. The aqueous Al species were analyzed by using a liquid state 27Al-NMR and an atomic absorption spectrometer and separated into four fractions, as follows; 1) Al13, 2) Al monomer and dimer (AlSYM), 3) Al complexed with organic ligands (AlORG), and 4) other undefined species (AlNON). Formation of Al13 was suppressed by acetate, oxalate, and citrate. In addition, Al13 that preexisted in a hydroxyaluminmn solution was disappeared by the introduction of acetate, oxalate, and citrate. Decrease in the concentration of Al13 at the early stage of the reaction was caused by the decomposition of Al13 along with the increase in the concentrations of AlSYM and AlORG. After 7 d of reaction, it was likely that Al13 was transformed into Al(OH)3 0 and other undefined species that could not be detected by 27Al-NMR. The ability of the carboxylic groups to suppress the occurrence of Al13 (molar-basis) was in the order of acetate << oxalate < citrate, corresponding to the ability of complexation with Al. In conclusion, the phytotoxic effects of Al13 were less pronounced because of the ubiquitous presence of organic ligands in the rhizosphere.

Feasibility of system of rice intensification practices in natural and socioeconomic contexts in Thailand

The system of rice intensification (SRI) is a set of practices in rice cultivation known for higher yields, lower water consumption, and environmentally friendly effects. However, few Thai farmers have adopted SRI even though Thailand is one of the largest rice producing nations. In this study, rice farmers in the northeastern, central, and southern regions of Thailand provided open-ended responses to descriptions of SRI prepared by the Thai government. Of the 66 rice farmers sampled, 11 positive comments were made, while 93 critical comments were directed at the time-critical and labor intensive practices necessary for SRI. Comments were especially critical of the labor intensiveness of the whole system, the slow response by rice to organic matter application, and the necessity of manual transplanting. Based on these results, it was concluded that changing the water regime would be the most feasible among the SRI practices for the farmers. The research incorporates a discussion of the natural and socioeconomic contexts in which the labor-intensive and time-consuming practices are criticized by the rice farmers.

Remediation of Paddy Soil Contaminated by Radiocesium in Iitate Village in Fukushima Prefecture

Paddy soil freezes during winter in Iitate village. The frozen soil is as hard as asphalt, and local farmers can easily peel a plate of frozen soil using an agricultural machine. The radiation level in the ground surface was demonstrated to reduce from 1.28 to 0.16 μSv/h by stripping the frozen soil in field experiments. In this chapter, two remediation methods have been introduced and the collaboration between researchers, volunteers, and farmers in Iitate Village has been discussed.

Estimation of soil moisture in paddy field using Artificial Neural Networks

In paddy field, monitoring soil moisture is required for irrigation scheduling and water resource allocation, management and planning. The current study proposes an Artificial Neural Networks (ANN) model to estimate soil moisture in paddy field with limited meteorological data. Dynamic of ANN model was adopted to estimate soil moisture with the inputs of reference evapotranspiration (ETo) and precipitation. ETo was firstly estimated using the maximum, average and minimum values of air temperature as the inputs of model. The models were performed under different weather conditions between the two paddy cultivation periods. Training process of model was carried out using the observation data in the first period, while validation process was conducted based on the observation data in the second period. Dynamic of ANN model estimated soil moisture with R 2 values of 0.80 and 0.73 for training and validation processes, respectively, indicated that tight linear correlations between observed and estimated values of soil moisture were observed. Thus, the ANN model reliably estimates soil moisture with limited meteorological data.

Spinach field monitoring for bridging Thai producer and Japanese consumer under sensor Asia

A spinach field monitoring system has been setup near Chiang Mai, Thailand which collects various sensor data and sends them to SSG server at AIT. SSG is an initiative to realize ldquosensor plug&playrdquo which covers sensor node installation, registration and visualization of sensor data. This system is an ideal example to bridge the confidence between agricultural producers in Thailand and consumers in Japan through real time sensor monitoring.

Effects of NaCl concentration on the thermal conductivity of sand and glass beads with moisture contents at levels below field capacity

Abstract Soil thermal conductivity is a key factor governing its thermal regime. In the present study, we measured the thermal conductivity of Toyoura sand and glass beads using a heat probe method to clarify the effects of gravimetric water content (w) and NaCl concentration (C) and to evaluate the estimation effectiveness of four models (Mochizuki, de Vries, Noborio and Kasubuchi). The de Vries and Kasubuchi models predict the effect of w on soil thermal conductivity, whereas the Noborio model describes the effects of solute concentration and the Mochizuki model describes both parameters. With or without NaCl, the thermal conductivity of both samples increased with increasing w, and the increase could be grouped into three ranges based on w. The upper and lower limits of each water content range were constant, even at varying NaCl concentrations, but the width of the range differed among the three ranges and between the sand and glass bead samples. Although soil thermal conductivity has previously been reported to generally decrease with increasing C, the thermal conductivities of some glass beads increased in the present study, particularly at moisture contents close to field capacity. The change in thermal conductivity as a function of C was linear in all cases. This trend was similar to that of a non-swelling clay in a previous study. The Mochizuki model, which regressed measured thermal conductivity on C and w, predicted the thermal conductivity of sand as well as previous models, but the calculations were easier and the method offers more flexibility for soils with different textures.