Methane (CH₄) generated from paddy fields accounts for about 25% of total greenhouse gas emissions (measured in carbon dioxide equivalents) in Vietnam. Therefore, balancing rice production levels and CH₄ emission reduction is an important issue for Vietnam. We performed rice cultivation experiments in the Mekong Delta by using two types of water-saving irrigation, or alternate wetting and drying (AWD) irrigation: one is recommended by the International Rice Research Institute (IRRI-AWD) and the other is customarily used by farmers (FAWD). Both irrigation systems successfully reduced year-round CH₄ emissions without decreasing rice yields. In the dry season, there was a strong correlation between total CH₄ emission and the number of cumulative days on which water levels were below the paddy-field soil surface. Farmers preferred FAWD to IRRI-AWD because of its simplicity. Therefore, we intend to establish methods for measuring, reporting, and evaluating CH₄ emission reduction by FAWD and to utilize them in CH₄ reduction measures formulated by the Vietnamese Government and the Joint Crediting Mechanism between Vietnam and Japan. Through this, we will be able to encourage the widespread use of FAWD and thus to CH₄ emission reduction.

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Recently the population of red dragonflies has declined nationwide in Japan. It is pointed out that the change of paddy field-management is one of the main causes for it. In order to mitigate the influence of such changes, it is necessary to introduce a proper management method suitably adaptable to farmland. To examine the effects of difference in cultivation management, we introduced the program of risk assessment mitigation and conducted of census of red dragonfly and cultivation management in paddy fields in Tajiri, Osaki City, Miyagi Prefecture from 2009 until 2013. We investigated the correlation between the emergence status of the red dragonflies and cultivation methods for paddy fields together with local farmers. The husks of red dragonflies were more sparsely found in the paddy fields where dinotefuran were applied. For conservation of red dragonflies, we started to employ the different pesticides with lower effects on red dragonflies and applied the pesticides only in the peripheral zone of each patch and successfully reduced the insecticidal effects on red dragonflies compared to broadcast application over the entire fields. Each technique was observed that suppress the decrease of red dragonflies.

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Recently liners have been used for the rehabilitation of deteriorated agricultural pipes. Existing pipes have not been considered in the design of the liners, although existing pipes influence the behavior of the liners in practice. Model tests using liners are conducted, and the influences of deteriorated existing pipes on liners are investigated in this work. The results show that large earth pressures do not act on liners until the existing pipes divide and existing pipes are still sustained parts of earth pressure after division. Distribution of earth pressures acting on the liners is estimated from the strain distribution. Maximum stress and horizontal deflection are calculated from the distribution of the earth pressure. The calculated and experimental values are compared, and the effectiveness of the estimated distribution of the earth pressure is evaluated. When designing liners for a particular earth pressure, feasible designs must consider that the existing pipe sections sustain the applied earth pressure.

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Rooted soils can prevent plants from lodging by supporting the above-ground parts of the plants in cultivated land areas. They can also enhance the stability of natural slopes and soil structures. Understanding the fundamental mechanical behavior of the root-soil interface is necessary for predicting the behavior of rooted soils. To this end, an apparatus for measuring the shear strength on the root-soil interface was developed and applied to three combinations of root-soil materials, namely, steel-silica sand, balsa-silica sand, and barley root-paddy soil. The test results have revealed that the Coulomb criterion is well applicable to the interfacial shear strength in the above three combinations. The results are interpreted in terms of contact mechanics and the modeling of the interfacial shear behavior provides a constitutive equation to describe the relationship between the shear stress and the displacement on the root-soil interface.

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The hydraulic performance decline of the concrete agriculture irrigation canal often depends on roughness coefficients the evaluation criteria. The arithmetic mean roughness of the concrete surface is applied to the estimate of the roughness coefficient. In this study, we focused on that the aerial ultrasonic reflection wave has the feature of the peak to peak value varies according to the roughness of the wall surface. We suggested the measurement method of the roughness of the degraded concrete wall surface using the aerial ultrasonic wave. We conducted a series of experiments about relation of arithmetic mean roughness with the peak to peak value of the reflection wave. Next we verified about the measuring range. As a result, following became clear. The peak to peak value of reflection wave could estimate arithmetic mean roughness of concrete surface well. In addition, the calculated results by Kirchhoff theory predicted the peak to peak values well. We can get the root mean square surface roughness and the correlation length of the wall surface by applying Kirchhoff theory to the peak to peak value.

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In recent years, many irrigation pipelines require a repair work by the deterioration. The aging pipelines have a risk for a leakage, a decrease of a capacity of flow and a serious damage during earthquake. As the repair work for aging pipelines, pipe rehabilitation has been used. However, the dynamic behavior of the rehabilitated pipe during earthquake has not been cleared. In this study, in order to clarify an influence of a shear deformation of grounds on the behavior of the buried rehabilitated pipe, shear tests and DEM analyses were conducted. As the results, it was revealed that the degree of the influence of the aging host pipe on the deformation of the rehabilitated pipe was divided into three types according to the damage levels of the host pipe and the relative density of the backfill material. In addition, the prediction equation on the deformation of the rehabilitated pipe to the shear deformation was proposed in consideration of the damage levels of the host pipe, the deformation modulus of the backfill material and the bending ring stiffness of the rehabilitated pipe.

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For the purpose of utilization of paper sludge generated from pulp/paper manufacturing company as base material for greening slope, this study investigated base physical properties and rainfall erosion resistance of a base material for greening slope manipulating mix ratio of paper sludge, and conducted a growth test of plant under the condition using the base material. Additionally, this study examined the workability and long-term growth test of plant on a test field. As a result, we found that the increase in the number of pore related to an air permeability and permeability, and the favorable growth condition of plant when a base material for greening slope was mixed a paper sludge. Moreover, we showed improvement of the rainfall erosion resistance when a base material for greening slope was mixed with paper sludge of 6～10%. As a results of the test field, we found no construction failure, and showed excellent growth of plant after six years from the execution. These results showed a high possibility that paper sludge is utilized as material for the base material for greening slope.

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We investigated land consolidation projects of paddy fields during recovery and reconstruction processes after the Great East Japan Earthquake in Miyagi Prefecture. Transitions in decision making and consensus building for restart of farming after a Tsunami disaster were analyzed, challenges in each stage extracted, and corresponding cases compared. Through a series of investigations, we verified usage and effect of various support measures prepared by the national and local governments based on the stage and work progress of the recovery and reconstruction processes. Measures that contributed to the recovery and reconstruction were as follows; 1) preparation of basic GIS data on agricultural infrastructure, 2) maintenance and formation of regional communities, 3) presentation of plans and goals by the national and local governments, and 4) provision of funds, human resources, know-how from outside, including financial support from the national and local governments. Through this study, we determined it is necessary to maintain and activate regional communities to prepare for large disasters.

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Reduction scales in rice yield, which show the decrease in both weight and quality of rice grains caused by flooding, were formulated. A pseudo-flooding experiment of rice plants was conducted for three years to collect basic data of the scales. In the experiment, a paddy field was dug to three depths to construct a flood zone. Therefore, the zone can reproduce a variety of flood conditions without water management. Reduction of the weight of whole rice grains, which is calculated by multiplying the gross weight of brown rice by the weight ratio of whole rice under each flooding condition, was used as fundamental data for making the scales. As a result, the scales indicated that flooding caused damage to rice yields at all growth stages, but the degree of yield reduction differed significantly depending on the stages. In particular, the booting and heading stages of rice were vulnerable to submergence, the yields reduced approximately 50% from just 1 day of flooding at these stages. At the same time, flooding with incomplete submergence mitigated damage to yields. Assessing these flooding conditions is important in order to use the scales to estimate damage on rice. The scales are available for easy estimation of basin scale flood damage to rice, and are also useful tools for risk assessment of climate change impact on agriculture by applying them to output of flood analysis.

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The rice terrace in the Shiraito plateau, Kumamoto prefecture, is designated as a cultural landscape by Agency for Cultural Affairs and suggested to be conserved with further understanding the canal system role for rice terrace. In this context, we analyzed the historical change of Tsujun-yousui canal system (established in 1855) using historical documents, documents kept by land improvement district, and our survey data. As a result, we classified Tsujun-yousui canal system into three type according to the time-series. The Type1 is spring water usage before the construction of Tsujun-yousui canal system, the Type2 is wide expansion of water supply system by construction of Tsujun-yousui canal system, the Type3 is the modified type based on Type2. In the process of transition from the Type1 to the Type2, Type2 stage was improved based on Type1 water use methods and enabled wide expansion of paddy fields area by increasing irrigation water which Tsujun-yousui supply. The Type3 has been developed by modern technology, such as pumps and gates, and enable further expansion of paddy fields area.

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The relative dynamic modulus of elasticity is used when carrying out a diagnosis of frost damage deterioration of concrete structure as a general index. However, there are only a few studies that have been examined about the relationship between the mechanical properties of concrete and relative dynamic modulus of elasticity. In this research, this relationship was clarified in the examination using concrete specimens of various mix proportion and core specimens that collected from a structure. In addition, a flow chart to estimate the dynamic modulus of elasticity by on-site non-destructive test was drawn up. The flow chart is intended to measure for thin-walled members. From the results, in the case of multiple members, considerations about dynamic modulus of elasticity evaluation based on the flow chart were carried out. The on-site tests that were carried out on an RC open channel, which deteriorated by frost damage by non-destructive test.
As a result, it was confirmed that the relationship between the mechanical properties ratio and relative dynamic modulus of elasticity can show a linear relationship, and the value of mechanical properties that deteriorated due to frost damage is verifiable through using a relative dynamic modulus of elasticity. Furthermore, it was confirmed that the proposed flow chart is applicable to concrete in the incubation period and advanced period of frost damage deterioration.

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This paper discusses resilience of coastal agricultural fields for applying the concept of resilience to agricultural structure improvement projects in near future. We interpreted recovery of the coastal agricultural fields which affected by the 2004 Indian Ocean Tsunami in terms of resilience theory. It was revealed that paddy system depending on inherent hydraulic regime possesses desalinization function. In this study, we showed that the function can be defined as general resilience before the tsunami, and then it changed to specified resilience after the tsunami. This dynamic change of resilience definition of the function sheds light on building resilience of the coastal agricultural fields. From these findings, knowledge and technologies established by agricultural engineering can be interpreted as elements which elicit beneficial effects on recovery of the fields from natural disasters.

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This study aimed to identify barriers that prevent rural community from taking residents' collective action to chase off monkeys employing conceptual decision-making process model as an analytical framework, and discussed possible supports by local government to overcome the barriers identified and to increase the community engagement in collective action to chase off monkeys. The data was collected through intensive interview with representatives of 19 rural communities in Iga city that have not carried out collective action to chase off monkeys.
Our analysis clarified a set of barriers in the each stage of decision-making process that prevent rural residents from taking collective action to drive away monkeys. There are three major barriers identified through this study. The first is the lack of problem recognition. Many interviewees in this study showed poor recognition about damages caused by monkeys. The second is the negative evaluation about the effectiveness of collective chase-off of monkeys. The third is the lack of labors participating in collecting chase-off of monkeys. The government should provide correct information about the effectiveness of collective action to chase off monkeys, and solve the misunderstanding that women and elderly people are ineffective labors to chase off monkeys.

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It is widely reported that durability of concrete decreases readily due to such effects, as salt, chemical attack or freezing-thawing process. In service structures, mechanical damage of concrete has been practically inspected from the strength by a compression test. For effective maintenance of concrete structures, it is necessary to evaluate not only the strength but also the degree of damage. By the authors, quantitative damage evaluation of structural concrete is proposed by applying acoustic emission (AE) technique and damage mechanics. In experiments, core-samples were collected from a slab portion of a reinforced concrete road bridge that had been in service for 87 years. Compressive strengths and Young's moduli were measured during the compression test along with AE monitoring. Thus, the λ and β values were successfully evaluated by ultrasonic velocity.

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The abrasion test using water jet with sand is now considered as a standard material test for construction and repair materials for agricultural water channels. Since the only one tester for this method is available and a test needs more than 10 hours, the Taber type abrasion test, which is widely used and needs only 20 minutes for a test, is examined as an alternative testing method. Mortar specimens with different particle sizes of aggregate, as well as specimens of hardened cement paste without aggregate, are tested by abrasion tests using water jet with sand and tests of Taber type. With abrasion tests using water jet with sand specimens with smaller size of aggregate are abraded more, but little difference in abrasion depth is observed by Taber type abrasion tests. Abraded surfaces of specimens show different mechanisms of abrasion in two kinds of tests, separations of aggregate in tests using water jet with sand, and scraping of aggregate in Taber type tests. Since abrasion in agricultural water channels consists of separation of aggregate, it is concluded that Taber type abrasion tests are not suitable especially to construction and repair materials for water channels.

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In April 2014, the Geospatial Information Authority of Japan publicized The GSIGEO2011, putting GNSS leveling into practice nationwide to enable leveling for Grade 3 benchmarks. Our study started with installation of a new benchmark on an about 920-m-high mountain existing about 5 km from 3 benchmarks in Karuizawa, Nagano. Concerning the new benchmark, we performed two methods, i.e. GNSS leveling and direct leveling, to survey the elevation, conducted check of misclosures and discrepancies and rigorous network adjustment for those two methods, and compared the elevations obtained by those two methods. In GNSS leveling, the following things were investigated, a streamlined survey process, the influence on most probable value and standard deviation by the difference of using satellite “GPS-only” and “GPS and GLONASS” and the influence on most probable value and standard deviation by the difference of observation duration. As the results, our tests found that dramatically streamlined survey process, “GPS-only” can mitigate the variation among most probable value that results from different observation duration, and can obtain an elevation value that is consistent with the value from direct leveling.

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We investigated the amount of water used for the cultivation management of summer-sown radish in an upland field on a sand dune on the coast of the Sea of Japan. The sowing season, which is early-to-mid-August, is hot and dry with little rain. To prevent a lack of soil moisture, which can cause the malformation of roots, farmers irrigate the soil for an hour once a day for 10 days before seeding. The amount of water used for this seeding preparation is 95 mm. After seeding, the ridges are covered with white cheesecloth until early September, in conjunction with sprinkler irrigation, to mitigate drying and high temperatures in August. Some of the irrigation water adheres to the cheesecloth and evaporates, suppressing the rise in soil temperature. The amount of water that adhered to the cheesecloth is 26 mm. To prevent the blowing of sand by the strong föhn wind, the soil must be irrigated for two consecutive days. The amount of water to prevent blowing sand is 20 mm. Thus, the amount of water used for cultivation management is 141 mm, which accounts for 38 % of the irrigation water (377 mm) used for summer-sowing cultivation.

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The neutralization depth of cementitious coating materials used for surface repair methods is shallow because their superior neutralization resistance. Conventional measurement methods are inadequate to evaluate the neutralization depth of such materials. Therefore, a new measurement method that simplifies the in situ measurement of shallow neutralization depth is now required. This paper examines the applicability of the core bit method as a neutralization depth measurement method. The core bit method is a simple method based on the color reaction to spraying of a phenolphthalein solution into a groove made in the coating material surface using a core bit. The values measured by proposed method were compared with those obtained by the conventional method using a core split surface, on a cementitious coating material that had been exposed atmospherically for about 8 years. The mean neutralization depth according to the proposed method was almost equal to that by the conventional method. However, the individual values measured by the proposed method tended to be slightly larger than those obtained by the conventional method. Considering reasons for this from the perspectives of the color reaction characteristics of the material and the proposed procedure has shown that the proposed core bit method can be applied to neutralization depth measurement.

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In order to improve the roughness of concrete surfaces and prevent factors causing their deterioration, deteriorated concrete surfaces of open channels have been repaired using various cementitious surface coating materials. But the service period of these materials has not been sufficiently verified because for a long time, there has been little data about aged materials exposed in irrigation channels. In this study, the authors measured the neutralization depth of several cementitious surface coating materials that had been exposed for about 10 years. They measured the neutralization depth at the cutting section of small 25 mm diameter concrete cores. In addition, the authors developed and tried a new method measuring the neutralization depth easily on site using a core bit. The results showed that the measured neutralization depth by both methods were almost identical in the part of the sidewall above the water surface. The maximum neutralization velocity is 0.62 mm per square root year, therefore, the predicted neutralization depth after 20 years exposure is a maximum of 3 mm.

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FOEAS (Farm Oriented Enhancing Aquatic System) consists of a buried porous tube which is connected to supply and drain control equipment to manage water table depth. The system can activate irrigation and drainage events to control soil water content to counter both drought and wet injury.
The objective of the work reported in this paper were to characterize fluctuations in surface soil water content (0-20 cm depth) before and after precipitation under FOEAS management (-30 cm depth) during soybean cultivation by continuous field measurements, and to propose a simple model formula which can be used by farmers for estimating the soil water content at surface layer after precipitation. The results show that the soil water content at 0-10 cm layer fluctuated widely corresponding to rainfall events, but the one at 10-20 cm layer stayed constant than 0-10 cm layer under the FOEAS management condition. And a relation between the increase in the soil water content at 0-10 cm layer and the total rainfall can be explained by linear regression to a degree, and the daily decrease rates in the soil water content at 0-10 cm layer after precipitation events were assumed to be monotonous decreasing functions. Finally, a new simple empirical formula to estimate the soil water content at 0-10 cm layer was proposed by using the results obtained above.

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Partial deformation in buried pipes occurs as a result of considerable pressure because of ground deformation or unequal setting. In this study, the external and three-point pressure tests are conducted to compare the bending strains measured using bending strain method and ones measured by the strain gages. We describe how the applicability of the bending strain estimation method, which was developed as a diagnostic tool for partially deformed pipes, was verified for fiberglass-reinforced plastic mortar pipes. When the bending strain estimation method is applied, it is assumed that bending strain is estimated using standard values of pipe thickness and curvature radius before deformation. Thus, the influence of the standard value and real value errors on the estimated value is clarified. And the influence of errors of measured length on bending strains are estimated to propose an optimal base length for each pipe diameter.

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Continuous irrigation with running water (CIRW) experiments during nighttime were conducted in an conventional paddy field, to obtain the relationship between irrigation conditions (amount of irrigation water, irrigation rate and irrigation water temperature) and distributions of the nighttime average water temperature and lowest water temperature. At first, 18 CIRW experiments were conducted under the various irrigation and climate conditions in 2013, 2014, and the water temperature distributions of these conditions were obtained. Then, from the observed temperature, empirical equations were developed for the distribution of nighttime average and minimum water temperature as a function of irrigation water amount and temperature, air temperature and water temperature at the start of irrigation. Predictions of the equations were in good agreement with the observed distribution; root mean square errors (RMSE) for nighttime average and minimum water temperature were 0.47 and 0.62 °C, respectively. Finally, we calculated the irrigation water requirement and cooling effect of CIRW on paddy water temperature and then found that CIRW using normal irrigation water amount can not provide sufficient cooling effect for a whole paddy field.

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We conducted centrifuge model testing with upper seepage flow along with some different subsurface ground conditions. The hydraulic gradient in the upper ground tended to be higher because the void ratio in the subsurface ground was lower. Additionally, the hydraulic gradient in the upper ground of the single-layer ground condition with a loaded filter and the single-layer ground condition with groundwater remained low. Residual vertical effective stresses were present. Saturated ground settlement near the critical hydraulic gradient was remarkable, but settlement of the one-layered ground condition with a loaded filter and a single-layer ground condition with groundwater remained low.

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This report deals with the dredged sludge from the farm ponds, and the fundamental properties are clarified to promote the use of the sludge for the agricultural use. Particularly, the change of the chemical and physical properties with the desiccation is discussed. The previous works including authors' works already have clarified the property change with desiccation, while, in this report, the more variety of factors are examined, namely, the repeat of the desiccating and wetting, and several drying temperatures are tested. Concluding remarks are as follows. The repeat of the desiccating and wetting reduces drastically the liquid limit, and the first repeat has the predominant effect. The permeability increases with desiccation, and the increase tendency is clearer with the higher temperature. The total dissolved suspension increases with the temperature.

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Production increase of rice is a problem in Sub-Sahara Africa. Maintenance of irrigation facilities is needed to produce rice in stable way. But many canals are earth canal, and the function falls. Therefore canal protection measure with less initial cost should be installed. It was considered in this report to protect a canal using laterite contained soil easily available on site. A brick made by laterite contained soil is immediately collapse if nothing obtains in it. Therefore measures to improve erosion resistance against water and the effectiveness of the measures were considered. As a result, erosion resistance against water improve, in case that ashes of shell or palm is mixed, light burning is treated and oil is mixed.

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In this paper, methane fermentation plants that produce less than 3,000m³ of digested slurry in a year are defined as small plants. Transportation and application of digested slurry to paddy fields from a small plant were planned using a model developed by the authors. A pouring method was employed for application of the digested slurry in this plant.
Pre-calculation results indicate that α (the ratio of slurry application area as basal fertilization to total slurry application area) between 0.12 and 0.62 would yield the minimum slurry storage tank volume. Although the values for α that minimize tank volume depend on the specific application conditions, these results show that the optimal values of α have a range of values rather than a single optimal ratio.
Comparisons of the pouring method to applications with a spreader for basal fertilization showed that quantities of labors and vehicles for the pouring method were lower than for application with spreaders.

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The comparisons of the compressive strength of hardened geopolymer pastes using 4 types of fly ash which were different in discharge lot were examined. As for the principal chemical components of these fly ashes, the differences in the amounts of Fe₂O₃, CaO, TiO₂ and MgO were approved. Although the differences of ignition loss, particle size distribution and pH were also recognized, the difference of Blaine value was not assessed. Then the polymerization by dehydration of geopolymer using fly ash without self-hardening property might be exerted as the strength increase after 28 days of material age. As the result of a multiple regression analysis, the material age was consequently determined as the most influential factor for the compressive strength of geopolymer, whereas the basicity of fly ash was also found as a considerable influential factor.

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In the rural communities of Japan, the aging population and increase in mixed inhabitation have reduced the workforce available for maintaining irrigation/drainage canals. Therefore, the cooperation of non-farmers is required. To promote the participation of non-farmers in maintenance activities, the efficacy of factors that influence their participation needs to be effectively improved. From this viewpoint, previous studies have analyzed the multiple factors to identify the influencing factors. However, when we analyzed the factors in other areas based on the knowledge of previous studies, it was difficult to judge which factors we should analyze because not the same factors were identified as influencing factors in all the studies we examined. Therefore, this study focuses on 10 cases from 7 previous studies that statistically analyzed questionnaire survey data. Then, we examined the present state and problems of the influencing factor analysis. The following results were observed in 8 cases of the previous studies using the statistical significant difference to identify influencing factors: (1) in an average of 64% of the cases, a reason to influence (causality) is not shown, (2) we cannot distinguish “influence is small” from “there is no causality” because of (1), and (3) therefore, a reason to influence must be given.

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We investigated the effects of bamboo (Phyllostachys edulis) forest expansion on the soil physical properties, such as hydraulic conductivity, water retention, and water repellency. We also examined the pathways of water movement in soil using a dye tracer experiment. Moreover, we surveyed the effects of the expansion on snow accumulation and melt. Soil physical characteristics in the bamboo forest expansion and deciduous plots were quite different with respect to the soil surface; the bamboo forest has much more root mass and lower dry bulk density. As root mass increases, volumetric water content at the same matric potential decreases. Therefore, it can be concluded that water retention is reduced as the bamboo forest expands. Results of the dye tracer experiment indicate that water moves through roots and cracks, and the dye was observed in the soil from the surface to a depth of 30 cm. Moreover, soil water repellency was observed in the bamboo forest expansion and this contributed to the concentration of rainwater pathways. Snow period and snow depth in a bamboo expansion plot were less than those of deciduous plot by 14%, indicating that bamboo forest expansion has a significant effect on water resources in snowy areas.

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In regions with heavy snowfall like Aomori prefecture, where orchards are covered with snow during the winter, the spring fertilization is often recommended in order to avoid leaching of fertilizer from main root zone under the snow. It is useful to measure the electrical conductivity (EC) and the soil water content using soil sensors to detect the leaching after fertilization. In this study, the authors collaborated with farmers in Tsuruta, Aomori prefecture, to monitor the soil environment (soil water content, EC of soil solution and soil temperature) after fertilizing in apple orchards using the Field Monitoring System (FMS).
As a result of 6 years monitoring, we found that 1) Severe leaching was not observed in the investigated orchard during the period of lingering snows. It was found that seepage of melting snow, at higher temperature, has a significant effect on the dynamic state of fertilizer. After the period of snow melting, EC attenuated to the level before fertilization. 2) Penetration of fertilizer in spring was strongly affected by precipitation. Heavy rains may cause sever leaching of fertilizer components, and light rains make fertilizer remain close to the surface. 3) We visualized the penetration of fertilizer by installed soil sensors in the orchard and helped farmers' decision-making for fertilization timing.

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