Methane fermentation under lower temperature conditions than normal (35 °C) and the use of digested sludge as a fertilizer are promising as an energy efficiency improvement technology. However, there is little information available on the influence of digestion under low temperature condition on the compositions and characteristics of sludge as a fertilizer. In this study, we conducted incubation testing to examine the characteristics of methane production and nitrogen mineralization in paddy soil treated with the low-temperature anaerobically digested sludge.

Relatively more methane was produced in soil treated with sludge digested at 15 °C, because organic matter that is not decomposed under anaerobic digestion is used as a substrate for methane production in soil. On the other hand, little methane production was observed in soil treated with sludge digested at more than 25 °C. Moreover, only a small amount of ammonium nitrogen (3 to 13%) was released from anaerobically digested sludge after application under all low temperature conditions. Therefore, an appropriate rate of application of anaerobically digested sludge can be determined based on the ammonium nitrogen in the sludge.

We propose a simple measurement method employing a depth gauge as a quantitative abrasion measurement technique for agricultural irrigation canal surfaces. As the first step in this method, anchors are installed at two locations on the surface to serve as reference points. A measuring plate is placed on the top of the two anchors and the distance from the measuring plate surface to the surface is measured in 5 places with a depth gauge. The average distance to the surface is obtained as the average of 5 measurement values. By determining the difference between two values at different times, it is possible to estimate the progress of the average abrasion amount during that period.

In order to clarify the influence of each factor on the measured values, we conducted laboratory tests and field measurements on a channel with coated surfaces using a high-precision laser displacement meter and we compared the average distance to the coated surface using the laser displacement meter and the depth gauge.

As a result, the error of the abrasion measurement value using the depth gauge was estimated to be 0.4 mm for the laser measurement value of a channel with coated surface. The accuracy of a single measurement of the average abrasion depth estimated by the field measurement results was the laser measurement value ± 0.4 mm. When the average value of three iterations is used, the measurement accuracy is improved to ± 0.3 mm for the laser measurement value.

The multi-functionality payment grant, entitled TAMENTEKI KINOU SHIHARAI, aims to prolong the lifespan of agricultural infrastructures with participation of residents. In this activity, participants construct and repair facilities by themselves or order the repair to the construction companies. Such facility maintenance can create new services and revitalize the local economy.

This study evaluated the backward linkage and income linkage effects by using a 47-prefecture inter-regional Input/Output model and the spending content data on different types of activities. The results demonstrated that (i) the induced production and induced value-added vary in the way of doing an activity for repair, and (ii) the incidence rates of induced value added within the execution areas were about 30～32% (in the case of self-repair) and 27% (in the case of ordering to construction companies) of the grant spending.

We have proposed a generation method for heavy rainfall that reflects the uncertainty of climate projection extracted from a number of climate scenarios. First, we extracted heavy rainfall events from each collected climate scenario, and determined their occurrence frequency, average amount of rainfall, and coefficient of variation. These statistical values were used as estimates for the characteristics of heavy rainfall in each scenario. Next, variability of the values among climate scenarios for each estimate was defined as the uncertainty of the climate projection, and we applied the normal distribution to express the probability of occurrence for each value. The values extracted from the distributions, defined as the change of parameters of the normal distribution, were combined to generate a quasi-climate scenario. This process was repeated many times to create a variety of scenarios, each with different characteristics; the results are based on the uncertainties considering the distributions. The methodology was applied to both present and future climate scenarios. Heavy rainfall groups were generated under the quasi-scenario and used for estimation of present and future rainfall probability distributions. The results show that the rainfall intensity will increase in the future, and the proposed method could express distributions of probability rainfalls in the future with uncertainty of climate projection. The results are expected to be useful for climate change risk assessment for flooding and safety assessment of reservoirs and sediment-related disasters caused by heavy rainfall.

We developed a method to evaluate regional flood risk in low-lying paddy areas and its uncertainty. First, the uncertainties of heavy rainfall characteristics were extracted from several climate scenarios obtained from GCMs, which were used in the calculation of rainfall probability distributions. Next, the shapes of the distributions were used to estimate river flood risk and the risk of damage to rice paddy fields through a flood analysis. The shapes of these distributions, compared in a time series, defined the uncertainty of the risk assessment of climate change. The results show that the mean value and peak position of the risk distributions increased, indicating that the flood risk would rise in the future. Additionally, the values of the expected shortfall (ES) for rice reduction with more than 50%, 90%, and 99% of each distribution were calculated to characterize each of them. The risk was quantitatively evaluated by comparing the ES values, and the risk increased in the future and in the higher-order RCP scenario. By using this method we can quantitatively evaluate the uncertainty of climate risk assessment. The results can provide useful information for setting specific goals, such as the scale of drainage facilities, to prevent and/or reduce damage from the heavy rainfall disasters that are expected both in the short-, the medium- and long-term future.

To quantify the influence of agricultural water use on streams, we developed a hydrological model incorporating diversion and return flow processes. To rigorously validate the model, we applied it to the Kinu River watershed with intensive observation of streamflow on both the main and branch channels, all of which experience substantial human influences. We sequentially applied the information related to agricultural water use with different details, trying to identify the details in the operational rules necessary for modelling watersheds. The operational and management rules were divided into eight steps, including the initial model, two for reservoir operation, four for water diversion, and one for water allocation in the irrigation areas. The accuracies of the simulated streamflow along the main stream improved by introducing the first rule on reservoir operation related to the seasonal variation of maximum water levels, whereas detailed information related to the integrated operation of multiple reservoirs was not as effective at improving accuracy. Each rule on water diversion from the main stream improved the accuracies and water balances, suggesting the diversion volume in the initial model was overestimated. The sequential screening also revealed the issues regarding the structural errors in the current model and their potential direction for improvement.

The hydraulic performance of irrigation and drainage canals is relied on roughness of concrete surface. The aerial ultrasonic sensor is effective tool of measuring the roughness of concrete surface. In this paper, we focused on the influence of wind velocity when using the aerial ultrasonic sensor. We measured the peak to peak of the reflected wave by a wind tunnel experiment. Consideration was given to the influence of wind velocity on the peak to peak, as well as the influence of wind on the estimate of arithmetical mean roughness, and the theoretical value and measured value were compared. As a result, the followings became clear. As the wind velocity increased, the peak to peak decreased. When we set the wind velocity as 10 m/s, the decreasing rate from peak to peak of wind velocity as 0 m/s was: smooth board (Ra: 0.04 mm): 4.4%, rough board (Ra: 0.32 mm): 7.2%, and rough board (Ra: 1.04 mm): 11.1%. As a result of estimating of the arithmetical mean roughness of each wind velocity, the following became clear. When we set the wind velocity as 4 m/s, the influence of wind velocity was small. When we set the wind velocity as 8 m/s, the estimate of arithmetical mean roughness increased by about 0.1 mm compared with the estimate of arithmetical mean roughness at 0 m/s. When we set the smooth board, the theoretical value and measured value were in relatively good agreement. When we set the rough board, the peak to peak distance was decreased below the theoretical rate due to the influence of the scattered wave.

We conducted this research to clarify the new framework to control the conversion of agricultural lands and land development without the control of the City Planning Act (CPA), as well as the influence of the abolition of zoning under the CPA considering conversions of agricultural lands in an area defined by the Act on Establishment of Agricultural Promotion Areas (AEAPA) and the Agricultural Land Law (ALL). As results, we found the distinguished influence upon the conversion of the Class 2 agricultural lands in the former urbanization control area. Within the former urbanization control area, the Class 2 agricultural lands converted to stores by land leasehold as a relatively large project, as well as houses by ownership transfer as small projects. Conversion of the agricultural lands to small apartments was supply-side controlled conversion and would not meet the demands of housing for rural migrants. The Class 2 agricultural lands in the suburban area without the land development control by the CPA, the agricultural lands converted to different types of land use. The AEAPA and ALL need to have acts to control land use of converted agricultural lands by zoning of rural area.

This study proposed a new method for hydraulic analysis of pipelines using a rigid water column model. This method was developed based on the concept of HSMAC method which is a method for numerical analysis of incompressible flow. The pressure term in the motion equation of pipelines and the continuous equation at junctions were solved by an implicit method, and the others were solved by an explicit method. In this way, the velocity of pipelines and the pressure head at nodes including junctions could be calculated simultaneously without the preprocessing which is essential to existing methods. The proposed method was applied to the benchmark tests of water distribution systems which includes junctions, pipe networks, and water supplies expressed as non-linear functions of pressure head. As a result, it was found that this method had sufficient precision, stability, and efficiency as a method for hydraulic analysis of pipelines using a rigid water column model.

To study the Tokyo Daruma pond frog's habitat conservation, investigation was conducted in early spring to identify the configuration of the holes made by the frogs crawling out from under the ground, determine the period of the frogs' crawling out, and evaluate the relationship between soil temperature and precipitation with such crawling out events in chive-growing and bare fields. The crawling out of the frogs in the site occurred from middle April to late May, and showed bimodal peaks. When the mean daily number of crawling holes was used to represent the number of individuals crawling out, and the daily maximum and minimum soil temperature and the maximum rainfall during a period of continuous rainfall were used as meteorological indicators for the periods of investigation, it was found that crawling out started when the daily maximum soil temperature was between 12 and 15 °C. The mean daily number of individual frogs crawling out was positively correlated with the maximum rainfall during the period of continuous rainfall in both the fields. Therefore, it is suggested that this species of frog tends to end its hibernation and crawls out from under the ground when precipitation occurs and the daily minimum soil temperature is above a certain range.

This study conducted research on the water requirement and labor for water management throughout the cropping season for paddy fields where the field water management system introduced water saving and labor required. The system was allowed the maintenance of stable water levels specified by users automatically. The system enabled irrigation according to the necessary water volume and timing. The irrigation water volume used by the system 53% compared to manual control. The labor required for water management decreased by 85%. The system did not affect the crop yields. The introduction of the system led to the water saving and labor reduction without sacrificing the crop yields.

This study presented maximum daily flow rates, average daily flow rates and minimum daily flow rates with examination of fitting non-excess probability distribution in order to comprehend the actual situation of sewerage flow rates on observed rural sewerage facilities. The discussion on influence factors of daily flow rates variation is based on real time data measured by flow meters installed in observed rural sewerage facilities. The daily flow rates is confirmed to be influenced by the land use and site conditions of rural sewerage facilities. Therefore, daily flow rate can be estimated with high accuracy from the multiple regression equation in which drinking water and precipitation are considered explanatory variables as well as land use and site conditions. Besides, it is clarified that hourly flow rate fluctuations and peak coefficients was influenced by the duct line length, utilization rate and floating population rate, so they can be derived accurately by multiple regression equation with these three factors. The results of this study are expected to be reflected in setting appropriate design units and management methods of rural sewerage facilities in the future.

The ultimate goal of the present study was to identify the factors determining the occurrence of tuber damages in Chinese yam in the large-scale agricultural land in the Byobusan-area, Aomori Prefecture developed by the agricultural land development and reclamation project by the government enterprise. To identify effect on anions and cations distribution in soil under excess irrigation, control and test plots were settled. The latter was subjected to excessive irrigation in a Chinese-yam-planting field of the Shariki construction field, where a deep underdrainage system has been installed. Moreover, the tubes with porous cup to collect the soil pore water were installed at depths of 10, 30, 50, 70, 100, and 150 cm in the plots. To understand the anions and cations dynamics of the cropped soil, the concentration of water-soluble ions (e.g., NO₃^-, SO₄^2-, Ca²⁺), pH, and electrical conductivity (EC) of the soil pore water at each depth during the growing period of Chinese yam was measured. Consequently, the NO₃^- content exceeded 100 mg/L at the depth of 10-30 cm in the control plot in mid-August, owing to leaching and accumulation of solutes depending on rainfall and irrigation patterns. However, in the treatment plot subjected to excessive irrigation, the NO₃^- content exceeded 100 mg/L at a depth of approximately 50 cm from late August to early September. The spatiotemporal dynamics of soil water quality corresponding to precipitation and irrigation patterns during the growth period of the Chinese yam became clear.

This study clarifies the pumping performance of Irrigation Water Wheel (IWW) by using full scale, 2,000 mm diameter wheel, hydraulic model experiment. As a result, principal losses of pumping discharge depend upon the installation angle of the bucket and water volume in the bucket to fallen water volume for gutter. If the impact of these losses tends to be minimum, then the pumping efficiency, that is the ratio of measured pumping discharge and no-loss pumping discharge is 70∼80%, and pumping discharge in this experiment condition is about 50∼150 m³/d. Therefore, to reduce these losses, it is important to determine the bucket condition in consideration of submerged area of blade and circumferential velocity, and to install the bucket optimum angle. The revolution of IWW depends on back water, which is caused as the result of install IWW. The greater the installed bucket volume, the greater is the back water necessary for running IWW. And, the larger submerged area of blade, the easier it becomes for the backwater to run IWW. Flowchart that can judge the applicability of the IWW is developed using clarified pumping performance of IWW.

Paddy fields are used not only for rice cultivation but also for cultivation of upland field crops such as barley and soybean. The cultivation of these upland field crops in paddy fields often involves wet damage. A tillage technique using chisel plows is thought to be a countermeasure for the wet damage at paddy field which is used for cultivation of both rice and upland field crops in the crop rotation system. We examined the effect of the chisel plow tillage by comparing water suctions of soil in root zone at a field with the chisel plow tillage and a field without during barley cropping season and soybean cropping season. As a result, we confirmed that the chisel plow tillage kept the water suctions of soil in ridge larger, and that can be used as a mitigation technique of the wet damage.

Since groundwater is used as the major water supply source in the Kumamoto area, groundwater maintenance is a significant problem. As the water diffusing from the fields of the OOKIKU land improvement district in the middle stream of the Shirakawa basin is an important source for groundwater augmentation, the summer seasonal flooding, which inundates fields in the fallow period, with water permeating into the fields, is performed to intensify groundwater cultivation. It causes a shift from water usage for paddy-rice monocrop agriculture to new uses of water enabled by the summer flooding. However, details of the water usage situation in this area are unclear. Therefore, we investigated the situation by conducting fieldwork and used a numerical computation method. Consequently, we clarified that the fields with high water requirement rates were located over the middle basin in the water usage system and that ample water was needed from June to August. In addition, results of the numerical computation revealed that the level of water intake and discharge in the upper fields of the water usage system was less in comparison with that in lower fields. Thus, it is important to understand the present situation of water usage by utilizing GIS and numerical computation in order to cope with the requirement of water for new uses.

Adsorption of humic acids (HA) on a synthesized imogolite with different pH was characterized. Adsorbed mass of HA on the imogolite was measured in a pH range of 4.5 to 11.0. The maximum adsorption mass was decreased with an increase of pH. This trend can be explained by an alternation of charge amounts of imogolite and HA as a result of pH change. Wetting of imogolite-HA complex membrane fabricated by a drying of retentate of imogolite-HA mixed solution with different pH was examined. Contact angle of water droplet on the membrane was increased with an increase of the adsorbed mass of HA. However, the higher the pH in the fabrication process, the smaller its increment. This difference can be attributed to a difference in a charging state of HA caused by solution condition when HA was adsorbed by surface of imogolite in the fabrication process.

The authors made two test models for case of measurement of the volume of biogas produced by laboratory-scale methane fermentation experiments. Both models measure gas volume based on downward displacement of water, and confirm that the gas pressure is equal to atmospheric pressure by the water level indicated in the models. The measurement capacity of Model 1 is through to approximately 100 mL and that of Model 2 is through to approximately 450 mL.

The accuracy and precision of the test models were verified by injecting air into the models using a syringe. Test results for Model 1 were a difference of -3.0 to -4.3% and a standard deviation of 0.3 to 0.8% whereas for Model 2, the difference and standard deviation were -2.7 to -3.2% and 0.3 to 0.7% respectively.

The accuracy and precision of the test models will allow their application for comparison biogas production among laboratory-scale methane fermentation experimental cases.

Many weirs for irrigation are distributed in upstream area of river fans. They have risks of piping and structural unstableness by their downstream scouring from downstream riverbed declination that occurred by riverbed excavation. Severe damage of weirs is caused by less frequent large floods. It is required to make maximum scouring depth right downstream of the weir apron through less frequent large floods clear for the protection of weir from damages caused by the large floods. In this paper, the scouring depth and mechanism in site conditions of irrigation weirs was evaluated by two-dimensional hydraulic model experiments. Scouring proceeded with fluctuated scouring depth and flow regimes between wavy flow and submerged jet flow. Temporal changes in maximum scouring depth was calculated within an error of 10% by proposed experimental formulas in this paper.

In the sixteen years between 2001 and 2016, we analyzed the nitrate-nitrogen concentration change, as well as the frequency distribution of fluctuation patterns (rising, descending, and leveling) of the nitrate-nitrogen concentration of groundwater in the Miyakonojo Basin. We also analyzed and summarized the trends of the nitrate-nitrogen concentration where the concentration at the measurement points exceeded 10 mg･L^-1. The relative frequency of the high nitrate-nitrogen concentration in the groundwater has decreased and the fluctuation pattern showed that the leveling-off pattern decreased, and the descending pattern has increased. These changes seem to have occurred in the past 16 years. However, in the past 5 years, many measurement points indicated that the concentrations were leveling-off. Also, it was found that in 64% of measurement points where the nitrate-nitrogen concentration of the groundwater exceeded 10 mg･L^-1, the concentration had improved to 10 mg･L^-1 or less by 2016. However, during the 16-year period, it was found that 2.2% of the measurement points were consistently and significantly over 10 mg･L^-1, while 2.8% of measurement points indicated fluctuations of measurements above and below 10 mg･L^-1.

In apple production in the cold snowy region, Aomori prefecture, changes of soil temperature in the snow-melting period are important for farm work and field conservation. So, we aimed to clarify the characteristics of soil temperature in an apple orchard in this period. We have been monitoring soil temperature of the orchard for 7 years, particularly during the winter seasons. The results are: 1) There was little fluctuation in soil temperature, which was maintained above 0℃, due to the fact that the accumulated snow functions as insulation. 2) During the investigated periods, two types of soil temperature profile were found. In the first type, the nearer the soil layer was from the surface, the lower the temperature was; we called this Type I. Meanwhile, there were 2 years in these periods in which the shallow layer (8cm) was maintained almost as warm as the middle layer (32cm) until the snow-melting. We called this Type II. 3) This feature of Type II was caused in years when air temperature was relatively high in the beginning of the winter, and when there was only a short time lag between the first snow fall and when we started to have lingering snow.

Loach inhabiting paddy fields is an important species as a food resource for higher-level consumers, and the quantity of the resource is of great concern for environmental conservation. However, in ordinary paddy fields undergoing active farming, it is nearly impossible to validate the estimated population size. This difficulty occurs, simply because the true population value is unknown. We conducted an experiment to estimate population size by using a closed experimental paddy field where barriers were installed to prevent individuals' migration. At the onset there were no fish in the field. We released 1,185 loaches into the field so the number of individuals was considered nearly fixed. In the experiment, we selected 75 sampling points located at regular intervals to set the gear (wired trap) for an area of 300 m² and sampled 7 times with removal of captured individuals each time. We calculated population size based on all 75 points and on the 36 peripheral points of the sampling grid. Based on the results we obtained, it is suggested that application of such high-density sampling, repetitive removal, and application of DeLury's first model or the program CAPTURE have sufficient validity on the practical level. Further, our results suggest that approximating population size using limited data from peripheral sampling points may indicate the future possibility of a simple approach to population estimation.