Language：English   Publishing type：Research paper (scientific journal)  

Emissions of CO2 from the soil are mainly derived from soil microbial respiration, whereas CH4 emissions originate from anaerobic degradation of organic matter via microbial processes. Kitchen waste compost is used in the agricultural sector to improve soil quality. However, abiotic CO2 and CH4 emissions from soils amended with kitchen waste compost under aerobic conditions remain uncertain. Temperature plays an important role in organic matter decomposition in both biotic and abiotic pathways. This study aimed to evaluate biotic and abiotic emissions of CO2 and CH4 from soils receiving kitchen compost at different temperatures. Ten grams of soil amended with or without 0.1 g kitchen compost (1%) were sterilized or non-sterilized. The mixture and soil-only samples were incubated in 100-mL glass bottles at 20, 30, and 35 °C for 28 d under an aerobic condition. The results showed that CO2 and CH4 emissions increased at higher temperatures and compost application rates (p < 0.05). Emissions of CO2 mainly occurred via biotic pathways. Abiotic processes were potential pathways for CH4 generation, particularly at high temperatures of 35 °C. There was 20–24% of C in kitchen compost changed to CO2 and less than 0.1% to CH4. Our results suggest that global warming enhances abiotic CO2 and CH4 emissions and may contribute to further global warming.

DOI： 10.1007/s42729-024-01919-2

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Phosphorus (P) release from sediment caused eutrophication in Kojima Lake, Japan. The efficiency of iron-added sediment microbial fuel cells (SMFCs) in regulating P release from agricultural drainage sediment was investigated in this study. Surface sediment collected from an agricultural drainage canal flowing into Kojima Lake was mixed with iron oxide (Fe2O3) or amorphous iron oxyhydroxide (FeOOH) at 50 mmol kg−1. A 14.6-cm high acrylic pipe was filled with 80 mL of deionized water after 130 g of sediment was placed. A 3 x 3 cm graphite felt was used for the anode in a dual chamber SMFC, while a carbon rod was used for the cathode. Three treatments: No Fe, Fe2O3, and FeOOH, were operated for 408 h under open or closed circuit conditions. Results showed that FeOOH addition lowered P release from sediment regardless of SMFC operational conditions, suggesting that higher P adsorption by FeOOH may mask the effect of SMFCs. Fe2O3 did not reduce total P concentration in the overlying water. In addition, electricity generation was not enhanced by Fe-added SMFCs. Although SMFCs increased sedimentary redox potential, P release was not suppressed by the SMFC operation, indicating that organic P would be released by SMFCs from P-rich sediment.

DOI： 10.2965/JWET.23-040

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.20710/dojo.94.4_245

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Although the use of kitchen waste compost is very common, GHG emissions from soil amended with kitchen waste compost have not been studied. This study aimed to determine the effects of kitchen compost age and application rates on GHG emissions to identify optimal compost management. Soil samples mixed with kitchen waste compost at three different ages: 1 month (1M), 2 months (2M), and 3 months (3M) at two application rates (1% and 2% w/w) were incubated at 25°C for 28 days under aerobic conditions. Emissions of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) were determined on days 3, 7, 14, 21, and 28. Results showed that N2O and CO2 emissions decreased with compost age (p < 0.05). Increased application rates of compost led to increased CO2 emissions and suppression of N2O emissions. Furthermore, CH4 was emitted from soil amended with kitchen compost even under aerobic conditions. This study suggests that 3M kitchen waste compost is optimal in terms of GHG emissions upon application to soil under aerobic conditions.

DOI： 10.1080/00380768.2022.2160622

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The high risk of mercury pollution in the Ratai watershed due to artisanal and small-scale gold mine activities in Pesawaran District, Lampung, Indonesia, was evaluated. Studies are needed to improve the understanding of the effect of heavy metal pollution, especially mercury (Hg), in soil and river water along the watershed because of erosion. The Universal Soil Loss Equation (USLE) integrated with Geographic Information Systems (GIS) model was used to analyze the transport of mercury (Hg) from nonpoint source pollution loads to the Way Ratai River using rainfall-based erosion. Soils and river water samplings were conducted in 2020. Biophysical conditions, the land cover, and the rainfall data of the Ratai watershed were also taken into account. The results indicated that Hg concentrations in the soil and the river water were high, ranging from 0.26-28.9 mg L-1 and from 0.08-14.1 mg L-1, respectively. The reason for the high Hg contents in the soils and the river waters was the high erosion rate in the watershed. As the study area was characterized by high rainfall erosivity and low to high soil erodibility, the erosion-caused Hg contamination in soil and water can be significant if no conservation strategies are developed.

DOI： 10.15243/jdmlm.2023.102.4233

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ejrh.2022.101225

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Rice production is an important sector of global agriculture, sustaining more than half of the world's population. However, rice production contributes significantly to global warming through increased emission of greenhouse gasses (GHGs), primarily CH4, into the atmosphere. Therefore, this study examined countermeasures to reduce GHG emissions from paddy fields without affecting rice production. A column experiment was conducted to investigate the effects of soil macroporous structure and water management on GHG emissions from flooded alluvial clay soil (paddy soil). The soils were subjected to different management regimes: with and without artificial macropores, compost, and drainage treatment. Drainage was maintained at 6.5 mm d −1 to ensure infiltration yet prevent excessive leakage from the paddy field. The measured parameters included GHG emissions, soil water content, redox potential, soil temperature, soil swelling, total carbon, total nitrogen, iron, and manganese. The results showed that the soil column with macropores and drainage had significantly lower CO2 and CH4 emissions than that without macropores and drainage. In addition, the soil level increment, and thus, the amount of gas (CH4) produced in the soil column with drainage were lower than that without drainage. The combination of drainage treatment and macropores might have effectively acted as a hydrodynamic gradient and a structure that promotes freshwater intrusion into deeper soil profiles, inhibiting absolute anaerobic methanogenic activity. The redox potential of the column with drainage and macropores was the highest. Moreover, CO2 and CH4 emissions were reduced at a relatively small drainage rate of 6.5 mm d −1 by adding macropores to the soil. The findings confirmed that GHG emissions were effectively reduced by a porous soil structure at a low drainage rate. Macropore application also exhibited effectiveness at mitigating nutrient loss (TOC and TN) through the drainage. Therefore, low tillage before flooding would be preferable to conserve the macroporous structure. However, the results also highlight an adverse effect on mineral leaching (particularly Mn) through the column with macropores.

DOI： 10.1016/j.envc.2022.100657

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/00380768.2022.2087198

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/00380768.2022.2095669

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：International Journal of Agricultural and Biological Engineering (IJABE)  

The Soil and Water Assessment Tool (SWAT) is an ecohydrological watershed-scale model which was initially developed in the early 1990s to simulate the impacts of land use, management systems, and climate on hydrology and/or water quality. First adopted in the U.S., the use of the model then spread to Europe and then later to Asia and other regions. The range of applications that SWAT has been applied to have also expanded dramatically, which influenced ongoing model development which has been virtually continuous over the past two decades. A key component of many SWAT applications in Asia is accounting for rice paddy production that is common in some subregions within the continent. However, most of these studies do not provide explicit details of how rice production was simulated in SWAT. Other research has revealed that significant problems occur when trying to represent rice paddy systems in standard versions of SWAT, due to limitations in algorithms based on the runoff curve number approach or the pothole option. In response, key modifications have been made to SWAT in recent studies that have resulted in a more accurate representation of rice paddy systems. These developments point to the need for the incorporation of an enhanced rice paddy module within SWAT to better capture rice paddy hydrological and pollutant dynamics, which would support improved use of the model in Asia and other rice production regions. Subtopics related to simulating rice production in SWAT are discussed as follows: 1) an overview of global rice production; 2) history of SWAT development; 3) typical approaches for simulating rice production; 4) problems associated with the typical approaches; 5) recent code modifications to address deficiencies in replicating rice paddy systems; 6) recommendations for developing a standard rice paddy module for future SWAT codes.

DOI： 10.25165/j.ijabe.20221501.7147

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The drought impacts in the Dakbla watershed were assessed based on a combination of hydrological modeling and drought indices. Three drought indices, the Standardized Precipitation Index (SPI), Standardized Soil Moisture Index (SSI), and Streamflow Drought Index (SDI) were utilized to evaluate the drought features of meteo-hydrology and agriculture. The results indicated that these indices are well adapted to the local conditions, especially the 12-month time scale. Evaluations of drought features on the watershed scale could provide more specific information regarding drought risk than regional-scale/district-level assessments, because a watershed is a hydrologically fundamental unit to consider water resources management. Additionally, evaluations of drought impacts using the SSI showed longer and higher trends than those using the SPI and SDI in terms of drought duration and frequency. Considering the spatial distribution of drought frequency, the areas predominated by agricultural land in the target watershed had higher drought risk. Thus, assessment of agricultural droughts along with meteo-hydrological droughts is extremely important to support realistic local drought management strategies by considering water availability, water balance, and soil characteristics, especially in specific agricultural areas.

DOI： 10.3178/hrl.15.77

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Study region: This study focuses on the Lower Limpopo River basin (LLRB) in Mozambique, Africa. Study focus: Maintaining environmental flows necessary for ecosystem sustainability represents a significant challenge to water resource management. In this study the sustainability of LLRB was evaluated by comparing hydrologic availability with ecological and anthropogenic needs. Current river ecological status was scored with a habitat integrity index verified through ground-truthing field surveys and aerial imagery data. Local stakeholder interviews were used to further evaluate the habitat index scores. Deficiencies between water availability and ecological-human requirements were assessed with a water scarcity index. New Hydrological Insights for the Region: Four environmental flow categories defined as “Excellent”, “Fair”, “Poor”, and “Degraded” coincided to approximately 50 %, 39 %, 27 %, and 14 % of the natural mean annual flow, respectively. Stakeholder interview responses indicated annual water shortages currently occur between August and November and coincide with “Poor” and “Degraded” environmental flow conditions. Water supplies appear to meet consumption needs when calculated on an annual basis with the water scarcity index. However, when calculated monthly, there is not enough to meet human water demand between August and October. This deficit period will likely expand from June to November due to projected increases in future water demands. As the greatest water use in the basin is agricultural irrigation, long-term environmental flows sustainability will likely depend upon effective irrigation management.

DOI： 10.1016/j.ejrh.2021.100843

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The main objective of this study was to evaluate various land-use input conditions in terms of the performance improvement found in consequent flow and sediment simulations. The soil and water assessment tool (SWAT) was applied to the Dakbla watershed from 2000 to 2018. After the calibration and validation processes, dissimilar effects between the input conditions on the flow and sediment simulations were confirmed. It was recognized that the impact of the land use on the sediment simulation was more sensitive than with the flow simulation. Additionally, through monthly evaluation, the effects against the flow and sediment in the rainy season were larger than those in the dry season, especially for sediment simulation in the last three months from October to December. Changing land-use conditions could improve flow and sediment simulation performance better than the performance found with static land-use conditions. Updated land-use inputs should be considered in simulations if the given land-use condition changes in a relatively short period because of frequent land-use policy changes by a local government.

DOI： 10.3390/w13050627

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© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Rice terraces in Cordillera, Philippines, a world cultural heritage site, are threatened by the risk of collapse. It is crucial to manage these rice terraces for their conservation, while simultaneously practicing traditional farming. We examined the soil environment and investigated its effects on rice terrace conservation, by focusing on the hardpan condition; infiltration process, which is related to the collapse of rice terraces; and soil nutrition conditions in these sites. Field survey and soil analysis revealed that in areas where the hardpan was not sufficiently developed and water infiltration was effectively suppressed, organic matter content was significantly high, suggesting organic matter clogging. In these rice terraces, the amounts of P, K, Ca, and Mn were significantly low, showing the mineral leaching under reductive soil conditions. Therefore, hardpan formation, rather than organic matter clogging, is essential for the suppression of infiltration and prevention of potential terrace collapse. Because hardpan formation or organic matter clogging cannot be identified from the surface of flooded rice paddies, it is difficult to identify the influencing factor. Thus, we suggest that the hard soil layer should be checked before the planting season and drainage is allowed after the cropping season in the rainy season.

DOI： 10.3390/w12113158

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© 2020, The Japanese Society of Limnology. The objective of this study was to develop a hydro-chemical model using the Soil and Water Assessment Tool (SWAT) and to evaluate the climate change impacts on discharge and nitrate-nitrogen loads from Ise Bay watersheds (the Kiso, Nagara, Ibi, and Shonai rivers). Using a regional climate model, through the dynamic downscaling approach, present and future climate data were generated at a 2 km spatial resolution. The pseudo-global warming downscaling approach under the A1B scenario was adopted for future climate prediction. Then, the optimized SWAT model, driven by the present and future climate data, was executed. The following results were obtained: (1) the significant increase of precipitation in May and June and decrease in August in the future climate scenario, and consequent discharge from the target watersheds also increased in May and June and decreased in August and September; (2) Due to the change in discharge, nitrate-nitrogen loads of the Kiso, Nagara, and Ibi rivers also increased in May and June and decreased in August and September; and (3) While nitrate-nitrogen load from deciduous forest tends to decrease, the one from evergreen forest tends to increase. The response of the model indicated the possibility of an increase in nitrogen uptake by deciduous forests.

DOI： 10.1007/s10201-020-00622-2

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

Social forestry policies grant local communities the right to access protected forest areas contingent upon certain governmental criteria. However, the adoption of social forestry is known to alter land-cover patterns and promote soil erosion. This study assessed the water quality of Sekampung Hulu and Sangharus Rivers in Lampung, Indonesia, based on their total suspended solid (TSS) concentrations. Subsequently, the extent of soil erosion in the two watersheds was determined, and best management practices (BMPs) were recommended for the study area. Water sampling was conducted in 2016 to estimate TSS levels in the two watersheds. Additionally, the Universal Soil Loss Equation (USLE) was integrated with an ArcGIS model to evaluate soil erosion in the watersheds. The results indicated that TSS concentrations in the Sekampung Hulu and Sangharus Rivers ranged from 36-813 mg L--(1) and 16-146 mg L-1, respectively. Further, the average soil erosion rates in the Sekampung Hulu and Sangharus watersheds were 12.5 Mg ha(-1) year(-1) and 5.6 Mg ha(-1) year(-1), respectively. The results indicated that young coffee trees increased soil erosion rates, especially in areas characterized by vulnerable soil. The USLE results concurred with the TSS analysis and indicated higher erosion rates for the Sekampung Hulu watershed than the Sangharus watershed. The application of BMPs, including conversion to agroforestry coffee, cover crops, and contour systems, was effective in reducing soil erosion in both the Sekampung Hulu and Sangharus watersheds.

DOI： 10.1007/s10661-019-7890-5

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This study identified seasonal water quality characteristics in two adjacent mountainous rivers (Sangharus and Sekampung Hulu Rivers) in Lampung, Indonesia and determined the impacts of fertilizer application on river chemistry as a result of social forestry management. In 2016, we measured water chemistry and conducted a farmers' questionnaire survey to obtain information on fertilizer application. The water quality results indicated that several parameters, including nitrate (NO3) and phosphate (PO4), were significantly higher in the Sangharus River than in the Sekampung Hulu River. In addition, several parameters were influenced by dilution from high river flow in the rainy season. Some parameters were likely influenced by the weathering of parent materials. By contrast, electrical conductivity (EC) and NO3 were higher in the rainy season, which was likely linked to the dominant timing of urea fertilizer application during this season. Despite the application of fertilizers in the watersheds, NO3 levels remained below the recommended standard. However, aluminum and iron concentrations were higher than the recommended level for drinking water, which was likely due to elevated soil erosion from improper land management. Therefore, we recommend that effective land management policies be implemented through the adoption of soil conservation practices for nutrient loss prevention.

DOI： 10.3390/w11112363

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© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. Climate change is a significant global issue that will affect regional agriculture and water management of irrigation supplies. In this study, we project climate change impacts on water and irrigation requirements for major crops—wheat, cotton, and apricots—in Balkh province, Afghanistan. The methodology utilizes satellite imagery to overcome limitations in ground measurements necessary to understand current crop conditions and cultivation schedules for the study site. The climate model-averaged results project an increasing trend in both crop water and irrigation requirements for the study area, with larger trends for the climate model and scenario combinations that project the largest temperature increases. Future trends in the year-to-year variability of field water requirements do not contain a clear trend for most crops. The magnitude of projected changes vary significantly between individual climate models, demonstrating the importance of applying multiple climate models to project future conditions in agricultural water management. The results demonstrate the efficacy of using globally available data, including satellite imagery and global climate model information, to overcome lack of in situ observations. The findings also highlight challenges to current agricultural paradigms in areas such as Afghanistan that are arid to semi-arid and do not have adequate irrigation infrastructure.

DOI： 10.1007/s00271-019-00638-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2018JG004513

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2018JG004513

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/lre.12221

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Contributors:
Hiroaki Somura (Corresponding author)
Hidenobu Kunii
Yasumichi Yone
Ikuo Takeda
Hirokazu Sato

DOI： 10.25165/j.ijabe.20181105.4351

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Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Other Link： http://orcid.org/0000-0002-2592-7174

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society of Irrigation, Drainage and Rural Engineering  

Iron is known to be significantly related with phosphorus runoff from watersheds, yet there is a lack of knowledge regarding this phenomenon from the viewpoint of the iron load. Therefore, we conducted a 17-month investigation on the behavior and annual mass balance of iron and phosphorus in a paddy field area where sediment of iron oxides accumulated. Most iron and phosphorus were present as particulate matter, with low concentrations of dissolved ions. Annual net-outflow loads of iron and phosphorus were 108.6 kg/ha (irrigation period: 37.3 kg/ha; non-irrigation period: 71.3 kg/ha) and 3.40 kg/ha (irrigation period: 1.49 kg/ha; non-irrigation period: 1.91 kg/ha), respectively. A possible reason that no phosphorus purification was observed at the study site despite the sufficient amount of iron, which has adsorption capacity for phosphorus, is sediment detachment and runoff due to water flow in the drainage canal. This suggests that management of phosphorus-rich sediment is an essential factor for controlling the outflow of phosphorus.

DOI： 10.11408/jsidre.84.I_57

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Research on watershed silica dynamics in Indonesia has been sparse as most of the focus on water environment has centred on suspended sediments, nitrogen and phosphorous. Thus, Si concentrations in rivers and their seasonal and spatial variations are not well understood. Silicon helps rice plants to overcome abiotic and biotic stresses by preventing lodging and increasing resistance against pests and diseases. Rice is one of the more important crops in the country, and information on Si concentrations in rivers is useful because river water is a primary irrigation source. In this study, we conducted a preliminary research on temporal and spatial variations in dissolved Si (DSi) concentrations at watershed scale to help achieve an efficient use of Si resources through irrigation water management. The Sumani Watershed, located approximately 50 km east of Padang City in West Sumatra, Indonesia, was selected as the target area. Lake Dibawah lies on the upstream end of the watershed, and water is discharged from the watershed into Lake Singkarak. The results verified that Lake Dibawah had a dam effect of naturally reducing DSi concentrations in water. In addition, the average DSi concentration from the samples obtained from rivers, small channels, and ditches from October 2013 to December 2014 did not show strong seasonal patterns at each site but revealed clear spatial differences among sub-watersheds linked to the groundwater from Mt. Talang. The watershed has a high capability of supplying DSi to paddy fields via irrigation water.

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Other Link： http://orcid.org/0000-0002-2592-7174

Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：日本教育工学会  

DOI： 10.15077/jjet.s40007

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Other Link： http://orcid.org/0000-0002-2592-7174

Language：Japanese   Publisher：THE JAPANESE FORESTRY SOCIETY  

[in Japanese]

DOI： 10.11519/jfsc.127.0_624

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

This study aimed to examine how the relationship between N-15 of nitrate (N-15(NO3)) in rivers and land use within a river basin changes with varying hydrological conditions. This information would aid in identifying the dominant source contributing to increased nitrate concentrations in rural rivers. For this, N-15(NO3) in river water was investigated monthly in the five subbasins of the Hii River basin (area: 911km(2)), western Japan, for 1year and 3months. There were significant correlations (p&lt;0.05) between N-15(NO3) and the land-use ratio (i.e. ratios of forested, agricultural and residential areas in a subbasin) for the majority of the observation days, indicating that N-15(NO3) reflected land use within the basin. N-15(NO3) ranged from +1.4 parts per thousand to +8.5 parts per thousand and was lower in a subbasin with a higher forested area ratio. We found that the absolute value of the regression slope of the relationship between N-15(NO3) and the land-use ratio decreased with increasing river discharge. This finding demonstrates that differences in N-15(NO3) among subbasins with different land-use compositions became smaller under higher flow conditions. Because N-15(NO3) decreased with increasing river discharge, the small absolute value of the regression slope under high flow conditions indicates that forested areas could be the dominant source of river nitrate during high flows in all subbasins investigated regardless of land-use composition. The results suggest that forested areas make a large contribution to the increase in nitrate concentration in downstream rivers during high flows, because the nitrate concentration increased with increasing river discharge. Copyright (c) 2014 John Wiley & Sons, Ltd.

DOI： 10.1002/rra.2756

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Thousands of Tundra Swans visit winter-flooded paddy fields in the study area, Yasugi city, Shimane Prefecture, Japan every year for overwintering from November to March. Since 2004, they have roosted in the paddy fields during the night and foraged in the paddy and surrounding fields during the day, coinciding with the time when farmers began using winter-flooded paddy fields. Before 2004, the swans visited the area for foraging during the day and roosted at nearby lakes, wetlands, and sandbars along rivers during the night. When the swans visited our target paddy fields, the water gradually became green and began to emit an ammonia-like odor. In this study, we investigated the changes in the water qualities of winter-flooded paddy fields and the influence of bird excrement on water quality in the paddy fields during winter, and then estimated the amounts of nitrogen (N) and phosphorus (P) provided by bird droppings to the paddy fields. The mean concentrations of N, P, suspended sediment, and total organic carbon were higher in the overwintering season than during the irrigation season. This trend was observed in both the first and second seasons of the study. The spatial distribution of electric conductivity (EC) measured using a GEM-2 broad-band electromagnetic sensor coincided with that of the matted sites of Tundra Swans in the paddy field, which indicated that the excrement of the swans affected the EC distribution. The total input amounts of N and P from the birds' excrement to the flooded paddy fields were estimated using a simple model that considered bird counts and probable nutrient content of feces, and the amounts were found to be equivalent to approximately 30% of those present in the standard fertilizers used for rice during the irrigation period. These results suggested that the excrement from the swans markedly influences the water qualities of winter-flooded paddy fields. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.agee.2014.07.018

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Other Link： http://orcid.org/0000-0002-2592-7174

Language：Japanese  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society of Irrigation, Drainage and Rural Engineering  

DOI： 10.11408/jsidre.82.55

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Other Link： https://agriknowledge.affrc.go.jp/RN/2010853115

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Lake Shinji lies in eastern Shimane Prefecture, and is typical of brackish lakes in Japan. Water quality of the lake does not meet the expected environmental standards for total nitrogen (TN) and total phosphorus (TP), even though the national and prefectural governments have tried to improve water quality by developing maintenance scenarios for sewage, plant effluent, agricultural activity, and forestry. Consequently, detailed data of nutrient loading to the lake from river inflows is crucial to support strategies for improving the lake water environment. The Hii River contributes approximately 80% of the discharge flowing into the lake. In this study, we examine the Hii River catchment with a focus on land uses such as paddy fields, upland fields, residential areas, and forestry. Average annual discharges of suspended sediment (SS), TN, and TP loads were determined at Otsu, near the outlet of the basin into Lake Shinji. We also determined average yield per unit area of SS, TN, and TP loads from each land use. Yields per unit area from upland areas were the greatest, whereas yields from forests were the lowest. Forests were the largest contributor of SS, TN, and TP in the basin, because of its dominant land area. Upland fields had the second largest impact on these loads in the basin, because fertilizer applied to the fields is a major source of nitrogen (N) and phosphorus (P). large differences in yields per unit area between fine and rainy day conditions were also observed, especially for SS and TP loads. Furthermore, we determined that a major pathway of N to the river was through groundwater, regardless of land use, whereas P was transported to the river with sediments, especially in paddy and upland fields. Based on these analyses, it will be difficult to reduce the SS load discharge in the basin in the future, because forestry is the major source. In contrast, N and P load reductions are straightforward, because the primary source is agricultural, and appropriate management of fertilizer application will be a key factor in reducing loads. (c) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jhydrol.2012.05.032

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DOI： 10.20660/applfor.21.2_9

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Rainwater Catchment Systems Association  

Soil infiltration process greatly contributes to the hydrological process in watershed, thus, soil infiltration water and runoff water were collected to characterize pollutant load from two planted forests. Especially, this study focused on the heavy rain which is reported to be increasing because of climate change. Glass fiber wick samplers were used to collect soil infiltration water samples, while runoff water was collected at the weir. Results showed that the wick sampler successfully collected the soil infiltration water without accumulating excess water above the device. The amounts of pollutant loads in soil infiltration water (total organic carbon; TOC, total nitrogen; TN) were positively correlated with pollutant loads in runoff water, which directly showed the contribution of soil water to runoff water. During the research period, environmental pollution load density in soil infiltration water was negatively correlated with sampled soil water volume. This could be a dilution effect caused by rainfall infiltration. However, after the heavy rainfall, soil infiltration water quality showed higher concentration than other rainfall events. The trend was clear in the long lasting strong rainfall, especially for well conductive forest slope. Because of the high permeable properties, pollutant loads from the soil surface easily reached to the depth of glass fiber wick (50cm depth), without filtering process through the soil body.

DOI： 10.7132/jrcsa.KJ00007225460

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The Soil and Water Assessment Tool (SWAT) model was applied to the Yamada River watershed to investigate the potential for using the model for watersheds characterized by circular irrigated paddy and livestock production systems in Japan. The Yamada River watershed, a typical mosaic land use in an agricultural watershed in the Ibaraki Prefecture, includes small valleys; where the paddy fields with a circular irrigation system are located along the river on lowlands and a forest, vegetable fields, and livestock barns are located in the surrounding uplands. The runoff characteristics were significantly different between the irrigation and non-irrigation periods in the study site, and the observed runoff was well simulated using the SWAT model by setting different parameters for the irrigation and non-irrigation periods. The Nash-Sutcliffe coefficient (E Ns), coefficient of determination (r 2), and relative error (RE) statistics were 0.86, 0.87, and 2.0 for the irrigation period and were 0.67, 0.68, and 2.6 for the non-irrigation period. However, the observed nutrient concentrations were not simulated well. The E NS and r 2 values were very weak and the RE values were not satisfactory. Improved estimates of storage nutrients in the vegetable fields and livestock wastes should be considered for further SWAT simulation, as well as improved algorithms for simulating rice paddy systems.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

There is a global concern that phosphorus (P) resources will be depleted in the near future, but the P flux from water to land is extremely limited, whereas the reverse flux is substantial. A new method for the recovery of P from natural water bodies was proposed using iron-oxidizing bacteria and woody biomass (heartwood of conifer) as a carrier and a practical demonstration was presented. The woody carrier was immersed in water abundant in iron-oxidizing bacteria and removed 1-10 weeks later. Our results showed that the immersed carrier collected biogenic iron (Fe) oxides produced by iron-oxidizing bacteria, and contained about 0.2 mg g(-1) of P after 3 weeks; this amount was higher than that contained in some P fertile soils used for cultivating plants. The biogenic Fe oxides on the carrier acted as a source of P for plant cultivation, and they could adsorb P from P-rich solutions (10 mg L(-1) of PO(4)-P). Although our study involved only a small-scale trial, the proposed method can potentially aid in the effective use of Pin water and in water quality improvement if conducted on a large scale. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ecoleng.2010.04.019

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DOI： 10.3759/tropics.19.29

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DOI： 10.3759/tropics.19.43

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Other Link： http://agriknowledge.affrc.go.jp/RN/2010792004

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Drainage water quality in rice paddies was strongly influenced by the puddling of soil in the paddy fields by tractors and in response to opening of drainage gates. The concentrations of contaminants in drainage water increased rapidly when the puddling process began and were maintained at high concentrations throughout the puddling period. Moreover, the high concentrations did not decrease immediately after the puddling procedures ceased. Additionally, the ratio of dissolved nitrogen and phosphorous to total nitrogen and total phosphorous increased daily during the last half of the puddling period, due to discharge of chemical fertilizers with the drainage water. Also, the loads of particulate nitrogen and phosphorus discharged during the puddling period were larger than the loads discharge during irrigation. The discharge from paddy fields during puddling also increased the total annual contaminant load. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.agwat.2008.12.005

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Other Link： http://orcid.org/0000-0002-2592-7174

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

The impacts of climate change oil water resources were analysed for the Hii River basin and downstream Lake Shinji. The variation between saline and fresh water within these systems means that they encompass diverse ecosystems. Changes in evapotranspiration (ET), snow water equivalent, discharge into the basin, and lake salinity were determined for different climate scenarios. The impact of climate change on a brackish water clam found in the lake was then examined using simulated monthly variations of lake salinity and information from prior Studies of the clam.
ET increased and snow water equivalent decreased for all scenarios incorporating temperature rise, particularly during the winter season. Furthermore, ET and snow water equivalent were not as sensitive to variations in precipitation and thus temperature rise was considered to be a major factor for these variables. Nevertheless, monthly discharge Volume was more influenced by variation in precipitation than variations in temperature. Discharge increased during both the summer and winter season, since precipitation contributed to river discharge instead of being stored as snow pack during the winter season. The magnitudes of salinity dilutions and concentrations predicted under the climate change scenarios Would not be lethal for adult clams. However, the egg-laying season of the clam would coincide with periods of strong salinity dilution in the lake. Since juveniles are less tolerant to changes in salinity, future generations of the clam may be affected and reproduction of the clam may be reduced by increasing precipitation in the future. Copyright (C) 2009 John Wiley & Sons, Ltd.

DOI： 10.1002/hyp.7321

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.11408/jsidre.77.509

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society on Water Environment  

An investigation of the water quality in an under-populated watershed was conducted over a 15-year period in which data was collected at weekly intervals. The purposes of this study were to analyze the long-term trends in water quality and to evaluate the relationship between the water quality and precipitation. Concentrations of total phosphorus (T-P), chemical oxygen demand (COD), and suspended solids (SS) reached remarkably high values under heavy precipitation conditions, and these concentrations increased exponentially with the amount of precipitation. Over the course of this study, the population, number of factories, animals (cow and pig), and area of agricultural land exhibited clearly decreasing trends, while steady progress in domestic wastewater treatment was realized. However, no clear decrease in the parameters of water quality was observed, and some nitrogen, phosphorus, and COD concentrations increased even though no significant change in precipitation occurred. A possible hypothesis explaining this lack of a clear decrease in water quality is that specific pollutant outflows from forests and agricultural lands may have increased in recent years. This is because poorly managed forests and agricultural lands in the under-populated watershed have adversely affected the water quality of the rivers.

DOI： 10.2965/jwet.2009.293

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Other Link： http://orcid.org/0000-0002-2592-7174

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society of Irrigation, Drainage and Rural Engineering  

Runoff characteristics of nitrate nitrogen (NO₃-N) concentrations of drainage water were investigated in Yatsu agricultural catchment during rainfall events. With regard to the changes in the NO₃-N concentrations for each rainfall event, the NO₃-N concentrations showed a decreased tendency according to the increases in runoff by rainfall. When the runoff and the NO₃-N concentrations for rainfall events during the irrigation or non-irrigation periods were plotted in a scattered diagram, they were significantly related to each other using a power function. The NO₃-N concentrations during the irrigation period were below those at the similar runoff during the non-irrigation period, suggesting that irrigation water and a nitrogen removal function of paddy fields affected the No₃-N concentrations during rainfall events. In special, the direct runoff was strongly related to the No₃-N concentrations. In addition, the NO₃-N concentrations decreased when the antecedent rainfall during the 5 days preceding the rainfall event (pre-5-day rainfall) was great, indicating that the pre-5-day rainfall affected the changes in the NO₃-N concentrations. The results suggested that irrigation water, direct runoff, and antecedent rainfall affected the NO₃-N concentrations of drainage water during rainfall events.

DOI： 10.11408/jsidre.77.281

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS LTD  

In order to help evaluate the trends in the NO(3)-N concentration in groundwater with a view to preventing further degradation in water quality in the future, a distributed groundwater quality model was constructed tor the Nasunogahara basin. The best fit for the groundwater table elevations by the flow component of the model was achieved with average mean absolute errors (MAEs) of 0.92 m for the calibration period and 0-83 in for the validation period. Moreover. the best fit for the NO(3)-N concentration by the water quality component was achieved with average mean relative errors (MREs) of 29-8% for the calibration period and 30.3% for the validation period. After developing a robust model. various change scenarios were tested specifically. the effects of effluent load control and a decrease in paddy field area on the NO(3)-N concentration in groundwater were predicted. The most intensively farmed area contributed about 40% of the total effluent load because of livestock fanning ill the basin. When the effluent load from this area was decreased by 50%, the average NO(3)-N concentrations at sites S1, S2 and S3 were reduced by about 15%: however, the average concentrations at S4 and S5 were reduced by only 1%. Furthermore. when the total effluent load from the concentrated livestock area was removed completely, the average groundwater NO(3)-N concentrations at SI, S2 and S3 were reduced by about 30% as compared with the original calculated results. In contrast. decreasing the area of the paddy fields in the basin did not greatly influence the groundwater NO(3)-N concentration. In the case of a 70% reduction in paddy field area, average NO(3)-N concentrations increased by about 7% at S1. S2 and S3. Copyright (C) 2008 John Wiley & Soils, Ltd.

DOI： 10.1002/hyp.7089

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

The importance of proper water management means that the consumption of irrigation water should be estimated even in areas where data are scarce. The Mekong River, particularly the lower part, is one area where irrigation water has received little research attention. Studies that seek to estimate the use of irrigation water in this area are restricted by a lack of hydrological data; consequently, alternative methods are required to obtain these data. One solution is the use of model simulations. The main difference between our approach and existing irrigation-water estimation models is that we consider agricultural data in estimating the use of irrigation water, especially that used for rice production, as these data are relatively easy to collect. As a result, rice production during the rainy season in the target area was computed for 10 years with errors of less than 30%. The average values of calculated and observed rice yields per hectare were 1.3 and 1.7 t/ha in Thailand, 2.5 and 2.7 t/ha in Lao PDR, and 1.2 and 1.3 t/ha in Cambodia, respectively. In addition, we clarified decadal fluctuations in horizontal supplied (HS) water and irrigation water. The average values of HS water supplied to the paddy fields during the simulation period were approximately 17.2 km(3)/rainy season in Thailand (388 mm), 0-81 km(3)/rainy season in Lao PDR (245 mm), and 4.4 km(3)/rainy season in Cambodia (322 mm). Comparisons with HS water (7.4 km3/rainy season) and the existing requirements for irrigation water revealed that the simulation yielded acceptable values, thus verifying the reproducibility of the model results. Finally, we calculated the average water balances during the growth period for rice. The highest amount of irrigation water per unit irrigated area during the rainy season was used in Lao PDR, though the volume of irrigation water was greatest in Thailand. Copyright (C) 2008 John Wiley & Sons, Ltd.

DOI： 10.1002/hyp.6940

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publisher：THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES  

Water management with appropriate gate operation is needed for irrigation areas where water shortages are serious. In this study, the irrigation water distributions of two irrigation projects in Northeast Thailand were analyzed and the efficiencies of water use were simulated from one day to 2 weeks. The efficiency of water distribution was calculated by using a hydraulic model under the operating schedule generated from human factors. Hydraulic structures such as a constant head orifice and spillway were included in the hydraulic model by using one-dimensional movement equations and continuity equations. The parameters of human factors were estimated from the measured data such as the gate operator density and water depth management. From the results, in the medium discharge, gate operation delays within two hours caused the error of water distribution within 5 %. However, if the gate operators operated the gates to the ideal opening height regularly every day, the error was within 5 % even in the actual density. In the high discharge, an overflow was caused regardless of gate operators density, the error of water distribution to the downstream was over 10 %

DOI： 10.3178/jjshwr.20.167

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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Language：Japanese   Publisher：Japan Rainwater Catchment Systems Association  

Relationship between diversity indexes of fishes and environmental factors were evaluated. In this study, a field investigation was carried out in a paddy-field area in the eastern part of Shimane Prefecture. Parameters of this study were water qualities, fishes, and physical environmental factors (water depth, flow velocity, vegetation coverage, soil coverage of undersurface and habitat space) in drainage canals. Eleven species of fishes were observed in the investigation sites and diversity indexes were calculated by Shannon-Wiener method. Factor analysis was conducted with the diversity indexes of fishes and the environmental factors. As a result, higher values of diversity index were found with lower concentrations of chemical oxygen demand (COD), total organic carbon (TOC), nitrogen and turbidity. In addition, the higher indexes were also found with slower flow velocity and higher levels of vegetation coverage, soil coverage of undersurface, habitat space and water depth.

DOI： 10.7132/jrcsa.KJ00004353082

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Publisher：Japan Society of Civil Engineers  

Recently, multiple functions of river riparian vegetation are attracted in biological, environmental river engineering field. The decline of riparian vegetation strongly affects the river thermal environment, which also has a large impact on the ecological systems. In this study, a model that relates stream temperature with riparian vegetation was developed. The Nam Song River, which is a tributary of the Nam Ngum River flowing through the Vientiane Metropolis, was selected for field study. Meteorological data (air temperature, relative humidity, wind speed) were used, and the sink or source terms of the heat transfer equation were estimated from that data. NDVI (normalized difference of the vegetation index) remote sensing data was used for estimation of LAI (leaf area index) seasonal change. Simulations were made with several cases of riparian vegetation density, showing that river water temperature is more sensitive to river discharge change in the case of low density condition.

DOI： 10.2208/prohe.51.1225

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DOI： 10.11408/jsidre1965.2006.249

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

Efficient management of water resources in paddy fields requires an understanding of the volume of supplementary water used. However, quantifying the volume is laborious due to the large amount of data that must be collected and analyzed. The purpose of our study was to estimate the volume of supplementary water used in paddy fields, based on several years of available statistical data, and to provide information on how much water can be supplied to paddy fields in each target area. In this study, the lower Mekong River basin of northeast Thailand, Laos, and Cambodia was selected as the study area. In the first step, we used agricultural statistics for each country, rainfall data acquired from the Mekong River Commission Secretariat (MRCS), and the value of virtual water required per unit of rice production. Because several years of data were used for dry season harvested areas and rice production in each country, the supplementary water to paddy fields in each province was calculated using virtual water and rainfall. This method made it possible to estimate changes in supplementary water in each province. Through this study, the supplementary water to paddy fields during the dry season in three countries was approximated from the minimum number of data sets. Moreover, for cases in which it is not possible to procure agricultural water use data for a hydrological model simulation, an alternative solution is proposed.

DOI： 10.1007/s10333-005-0015-5

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Language：English   Publisher：水文・水資源学会  

DOI： 10.3178/jjshwr.18.22

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Language：Japanese   Publisher：システム農学会  

This study estimated the supplementary water capacity for paddy fields by estimating the water supply in each province during the dry season. Northeast Thailand was selected for this analysis because of the availability of agricultural statistical data distinguishing irrigated rice fields and non-irrigated rice fields during the dry season. This region is in Monsoon Asia, and so the climate has two seasons: the dry season and the wet season. Since about 70% of the annual rainfall is concentrated in the wet season, rice cannot be produced using only the dry season precipitation. In other words, farmers must obtain water from some other source to supply water to their paddy fields when growing rice in the dry season. Water is supplied from dam reservoirs in the irrigated rice fields, and water is supplied to the non-irrigated rice fields by gravity and small pumps from small ponds and canals. Thus, it was assumed that the amount of water supplied to paddy fields during the dry season can be calculated by subtracting rainwater during the dry season from the amount of water used in paddy fields. Based on rice production data, the values of water resources required to produce a unit weight of rice and rainwater, attempts were made to estimate the supplementary water capacities to paddy fields from the estimated supplied water and its maximum values in each province. Because there is no data for small ponds and canals for non-irrigated paddy fields in each province, the validity of the values estimated from the agricultural statistics was examined by comparing the supply water capacities for irrigated paddy fields estimated from the statistical data with those calculated from the Royal Irrigation Department data for large- and medium-scale reservoirs in each province. As a result, both differences tended to be less than 1 mm in the provinces whose harvested area of irrigated rice was small. It was therefore considered that supplementary water capacities to the non-irrigated paddy fields in each province can be estimated by the same method as for the irrigated paddy fields because it was assumed that the actual situation was similar to the non-irrigated paddy fields even if the classification of the rice fields was "irrigated". As a result, the supplementary water capacity tended to be high in the provinces through which the Chi River flows and the province upstream of the Mun River.

DOI： 10.14962/jass.21.3_167

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Publisher：社団法人 土木学会  

Supplementary water should be estimated even in areas where data is scarce because of the importance of proper water management. The Mekong River, particularly the lower part (Lower Mekong River Basin), is one area where supplementary water has not been well researched despite the fact that this international river runs through four countries: Laos, Thailand, Cambodia and Vietnam. Studies to grasp the amount of supplementary water are restricted due to a lack of hydrological data, thus methods for obtaining these amounts are needed. One solution is model simulations. In this study, supplementary water was estimated by calculating back from rice production targeted at a macro scale. As a result, the supplementary water in Cambodia, Laos and Thailand was estimated from 1991 to 1995 through model calibration with rice production.

DOI： 10.2208/prohe.49.235

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DOI： 10.11408/jjsidre1965.73.4_281

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DOI： 10.11408/jjsidre1965.72.5_381

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Publisher：Japan Society of Civil Engineers  

The declines of river corridor vegetation density strongly affect to the river heat environment, and that change makes big impact to the ecological systems. In this study, stream temperature analysis model related with river corridor density was developed and applied to Nam Song River, Laos. Metrological data (air temperature, relative humidity, wind speed) were used, and sink or source terms of heat transfer equation were estimated from those data. Land cover GIS data was used for vegetation density analysis along the main river. As the result of simulation cases with several vegetation densities, river water temperature was more sensitive to river discharge change as decreasing of vegetation densities.

DOI： 10.2208/prohe.49.1543

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DOI： 10.11408/jjsidre1965.72.9_795

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DOI： 10.11408/jjsidre1965.71.12_1087

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DOI： 10.11408/jsidre1965.2003.455

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DOI： 10.11408/jsidre1965.2002.365

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Language：Japanese   Publisher：Society of Environmental Conservation Engineering  

The metabolic accumulation of iron oxidizing bacteria in the sediments of natural water areas contains a large amount of iron-oxidized compounds that can adsorb phosphorus content. Therefore, this accumulation can play a significant role in the recycling of phosphorus resources. However, this type of phosphorus-rich accumulation cannot be efficiently utilized because it can be easily flushed by flowing water and because it is difficult to collect the accumulation from the sediments that usually contain anaerobic and malodorous mud. In this study, an effective method has been developed, in which a wood material carrier collecting the accumulation can directly be used as phosphorus fertilizer and/or a phosphorus adsorption.

DOI： 10.5956/jriet.37.347

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Language：Japanese   Publisher：島根大学生物資源科学部  

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Event date： 2010

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An investigation of the water quality in an under-populated watershed was conducted over a 15-year period in which data was collected at weekly intervals. In the study watershed, the pollutants derived from human activities decreased, but no clear decrease in the parameters of water quality was observed, and some nitrogen and phosphorus concentrations increased even though no significant change in precipitation occurred. A possible hypothesis explaining this lack of a clear decrease in water quality is that specific pollutant outflows from forests and agricultural lands may have increased in recent years. In addition, a new method for phosphorus recovery from natural water bodies was proposed using iron-oxidizing bacteria and woody biomass.

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Event date： 2010

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A multi-frequency electro-magnetic (EM) sounding method was applied to the agriculture field to investigate the characteristics of non-point pollution load. Soil environmental properties such as differences in land management were analyzed with electrical conductivity (EC) maps. In addition, vertical EC profiles obtained from EM soundings were compared with EC in drainage ditch or river water. As results, surface soil EC maps successfully extracted the differences in land management affected by fertilizer application. Moreover, surface EC at the vertical profiles strongly related with drainage ditch or river EC.

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Event date： 2009

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A multi-frequency electro-magnetic (EM) sounding method was applied to the agriculture field to investigate the characteristics of non-point pollution load. Soil environmental properties such as differences in land management were analyzed with electrical conductivity (EC) maps. In addition, vertical EC profiles obtained from EM soundings were compared with EC in drainage river. As results, surface soil EC maps successfully extracted the differences in land management affected by fertilizer application. Moreover, surface EC at the vertical profiles strongly related with drainage river EC, showing most of the EC in the water was explained by surface EC maps at the EM sounding data. The proposed method has strength in obtaining EC data without sampling river water.

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The declines of river corridor vegetation density strongly affect to the river heat environment, and that change makes big impact to the ecological systems. In this study, stream temperature analysis model related with river corridor density was developed and applied to Nam Song River, Laos. Meteorological data (air temperature, relative humidity, wind speed) were used, and sink or source terms of heat transfer equation were estimated from those data. Land cover GIS data was used for vegetation density analysis along the main river. As the result of simulation cases with several vegetation densities, river water temperature was more sensitive to river discharge change as decreasing of vegetation densities.

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Event date： 2005

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The decline of river corridor vegetation density strongly affects the river thermal environment, which also has a large impact on the ecological systems. In this study, a stream temperature analysis model related to river corridor vegetation density was developed and applied to the Nam Song River in Laos. Meteorological data (air temperature, relative humidity, wind speed) were used, and the sink or source terms of the heat transfer equation were estimated from those data. Land cover GIS data was used for vegetation density analysis along the main river. The results of simulation with several levels of vegetation density indicate that river water temperature is more sensitive to river discharge change in the case of low vegetation density.

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Event date： 2005

I analyzed one irrigation project site in the Mekong River Basin where was the most important for rice cultivation, because the irrigation would be absolutely necessary for stable food supply against rapidly fluctuating water resource or population growth of the Asia Monsoon. KM35 Irrigation Project Site in Savannakhet Province, Laos was selected as a study area and the irrigation water volume for last rainy season was estimated from actual yields by suing FAO CROPWAT Model. Thought this model was suitable for upland crops, some modifications to be suitable for paddy cultivation were needed. Estimated irrigation days were 34 on average. The estimated volume of irrigation water for the entire KM35 site was 7% of the active capacity of the reservoir. From the relation between partition height, hardpan depth and actual yield, it was said that high partition would make high yield.

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