Elsevier BV Acta Medica Okayama 2772-4271 21 2026 Assessing water resources availability and crop performance under climate change in Kenya's Bura irrigation scheme using SWAT and AquaCrop 100624 EN Daniel Mwendwa Wambua Graduate School of Environmental and Life Science, Okayama University Hiroaki Somura Graduate School of Environmental and Life Science, Okayama University Toshitsugu Moroizumi Graduate School of Environmental and Life Science, Okayama University Morihiro Maeda Graduate School of Environmental and Life Science, Okayama University The current study focused on Tana River Basin in Kenya, home to the Bura irrigation scheme (BIS). The BIS faces water supply shortages during critical months of crop development. This study aimed to evaluate the available water resources and crop performance using the Soil and Water Assessment Tool (SWAT) and AquaCrop, respectively, under historical and future shared socioeconomic pathways (SSPs) at the BIS. SWAT estimated the total available flows (TAF) at the BIS intake, whereas AquaCrop estimated crop water requirements (CWR), yields, and water productivity (Wpet) of rice and maize at various carbon (IV) oxide (CO2) levels. The study suggested that the TAF will remain relatively low during the early critical crop development stages in the main cropping season, August-October. Maize yields remained steady over the two cropping seasons under both constant and elevated CO2 levels in the historical and future periods, as opposed to those of rice. Elevated CO2 levels led to diminishing CWR. Moreover, rice showed a stronger response to elevated CO2 than maize. As a result, maize which is less affected by variations in CO2 and temperatures and has less crop water requirements will be better suited than rice for cultivation in the BIS under climate change. To ensure a sustainable water supply in the scheme, the government should increase rainwater harvesting during periods of high TAF. Moreover, there should be a focus on introducing crops that are tolerant to water and temperature stresses and that can reap the most from the elevated CO2 levels. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 0361-5995 89 3 2025 Autoclaved lightweight aerated concrete suppressed N2O and CO2 emissions from paddy soil e70091 EN Nagoda R. R. W. S. Rathnayake Department of Soil Science, Faculty of Agriculture, University of Ruhuna Morihiro Maeda Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Dewpura A. L. Leelamanie Department of Soil Science, Faculty of Agriculture, University of Ruhuna Atsushi Yatagai Clion Co. Ltd Autoclaved lightweight aerated concrete (AAC), a construction waste that is utilized as a soil amendment, can influence terrestrial carbon dioxide (CO2) emissions. Still, no evidence exists regarding its impact on the emission of nitrous oxide (N2O), which has a higher global warming potential. This study examined effects of AAC on CO2 and N2O emissions from paddy soil under compacted and non-compacted conditions, under 60% and 100% water-holding capacity (WHC). Samples were incubated in glass vials (25°C) for 21 days. Emissions of CO2 and N2O were measured on days 0, 1, 3, 7, 14, and 21 using gas chromatography. The results revealed that AAC significantly (p < 0.05) lowered N2O emission rate during the whole period of incubation, while it suppressed CO2 emission rate only at the early stages (∼7 days) of incubation. In compacted soil, the emissions of CO2 were significantly lower, while N2O was significantly higher than that in non-compacted soil, showing the influence of soil physical conditions. The emissions of CO2 and N2O were significantly lower at 100% WHC than those at 60% WHC. AAC suppressed both CO2 and N2O emissions under both compaction and WHC levels. The results confirm that AAC supports suppressing terrestrial emission of both CO2 and N2O, indicating that AAC has a potential as a sustainable soil amendment that enhances the climate change resilience. No potential conflict of interest relevant to this article was reported.

MDPI AG Acta Medica Okayama 2504-3129 6 4 2025 Drip Fertigation in Greenhouse Eggplant Cultivation: Reducing N2O Emissions and Nitrate Leaching 116 EN Wataru Shiraishi Kochi Prefectural Agricultural Research Center Shion Nishimura Department of Bioresource Production Science, United Graduate School of Agriculture, Ehime University Morihiro Maeda Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Hideto Ueno Department of Bioresource Production Science, United Graduate School of Agriculture, Ehime University Drip fertigation (DF) is a sustainable agricultural management technique that optimizes water and nutrient usage, enhances crop productivity, and reduces environmental impact. Herein, we compared the effects of DF and conventional fertilization (CF) with a basal fertilizer on yield, soil inorganic nitrogen dynamics, N2O emissions, and nitrogen leaching during facility-grown eggplant cultivation. The experiment was conducted in a greenhouse from September 2023 to May 2024, with treatments arranged in three rows and three replicates. Soil, gas, and water samples were collected and analyzed throughout the growing season. The results revealed that the DF treatment produced yields comparable to those obtained with the CF treatment while significantly reducing nitrogen and phosphorus inputs. DF effectively prevented excessive nitrogen accumulation in the soil and reduced nitrogen loss through leaching and gas emissions. N2O emissions were significantly lower by more than 60% under DF than under CF. Precise nutrient management in DF suppressed nitrification and denitrification processes, mitigating N2O emissions. DF also significantly reduced nitrogen leaching by more than 70% compared with that in CF. These findings demonstrate that DF effectively enhances agricultural sustainability by improving nutrient use efficiency, reducing greenhouse gas emissions, and minimizing nitrogen leaching during the cultivation of facility-grown eggplant. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0341-8162 254 2025 Cellulose nanofibers boost soil water availability, plant growth, and irrigation water use efficiency under deficit irrigation 108998 EN An Thuy Ngo Graduate School of Environmental and Life Science, Okayama University Manh Cong Nguyen Nong Lam University Morihiro Maeda Graduate School of Environmental and Life Science, Okayama University Yasushi Mori Graduate School of Environmental and Life Science, Okayama University Under climate change, even previously rainfall-prone areas may experience droughts, and effective strategies are vital for soil conservation. Owing to their cutting-edge water absorption and storage properties, cellulose nanofibers (CNF) are expected to increase soil water availability and help plants resist water stress. However, the role of CNF in improving plant growth and soil water retention under various irrigation regimes is not yet known. We evaluated the effects of CNFs on plant available water (PAW), germination, plant growth, and irrigation water use efficiency (IWUE) under both adequate and deficit irrigation conditions. Plant cultivation experiments were conducted using different CNF dosages (0%, 0.1%, 0.5%, and 1.0%), irrigation levels (I100, I50, and I25), and soil types (sandy and silty loam). The results indicated that CNF significantly increased field capacity (FC) and PAW in both soil types, with PAW in CNF-amended soils increasing by up to 110% and 88% in sandy and silty loam soil, respectively, at 1% CNF dosage. In germination tests, CNF showed no phytotoxicity and supported the germination process during water stress, with enhancements of up to 64% and 163% at I50 and up to 125% and 214% at I25 in germination percentage and germination index, respectively. Plant growth experiments revealed that CNF addition helped plants resist water stress, maintaining plant height and weight close to those under full irrigation, while using 50% less water. IWUE analyses demonstrated that CNF enhanced IWUE, with increases of up to 56% under sufficient watering (I100), 169% under moderate water stress (I50), and 120% under severe water stress (I25), at 1% CNF dosage. These findings highlight the potential of CNF as a multifaceted amendment, offering practical solutions for addressing water scarcity challenges and contributing to more resilient and sustainable agricultural practices. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 1439-0108 2025 Coupling effects of biochar and sediment microbial fuel cells on CH4 and CO2 emissions from straw-amended paddy soil EN Adhena Tesfau Bekele Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Morihiro Maeda Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Nozomi Nakahara Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Ayumi Hashiguchi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Hiroaki Somura Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Satoshi Akao Faculty of Science and Engineering, Doshisha University Chiyu Nakano Department of Comprehensive Technical Solutions, Okayama University Yuta Nishina Research Institute for Interdisciplinary Science, Okayama University Purpose The independent incorporation of biochar and sediment microbial fuel cells (SMFCs) into paddy soil has been shown to reduce methane (CH4) emissions. However, the application of rice straw into paddy soil enhances the availability of labile carbon that stimulates methanogen growth, counteracting the mitigation effects of both methods. This study, therefore, aimed to investigate the effect of coupling biochar and SMFC on CH4 and CO2 emissions from straw-amended paddy soil.<br> Materials and methods Single chamber SMFC setups constructed using acrylic columns (height, 25 cm; inner diameter, 9 cm) with six treatments were established using soil amended with 0% (0BC), 1% (1BC), and 2% (2BC) biochar: with and without SMFC conditions. Stainless steel mesh (15 × 3 cm) and graphite felt (6 × 5 cm) were used as anode and cathode materials, respectively.<br> Results Cumulative emission of CH4 in the 0BC treatment with SMFC was 39% less than in that without SMFC. Biochar addition and SMFC operation together further reduced CH4 emission by 57% and 60% in 1BC and 2BC treatments, respectively, compared to that in the 0BC treatment without SMFC operation. The relative abundance of microbial communities indicated methane-oxidizing bacteria were enriched in the presence of biochar and hydrogenotrophic Methanoregula were suppressed by SMFC operation. This suggested that SMFC mainly inhibited CH4 production by outcompeting hydrogenotrophic archaea.<br> Conclusion The use of biochar made from leftover rice straw has an interactive effect on SMFC operation and both methods can be used to reduce CH4 emission from straw-amended paddy soil. No potential conflict of interest relevant to this article was reported.

Japan Society on Water Environment Acta Medica Okayama 1348-2165 23 5 2025 Biochar-amended Sediment Microbial Fuel Cells for Water Quality Improvement in Intensive and Extensive Pond Drainages in Central Vietnam 234 249 EN Uyen Tu Nguyen Graduate School of Environmental and Life Science, Okayama University Morihiro Maeda Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Hiroaki Somura Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Nozomi Nakahara Department of Comprehensive Technical Solutions, Okayama University Gamamada Liyanage Erandi Priyangika Perera Graduate School of Environmental and Life Science, Okayama University Chiyu Nakano Graduate School of Environmental and Life Science, Okayama University Huu Tien Le Department of Education, Science and Technology Quang Tri Branch, Hue University Yuta Nishina Research Institute for Interdisciplinary Science, Okayama University The use of nutrient-rich feed in shrimp farming in Central Vietnam has led to high nitrogen (N) and phosphorus (P) contents in the pond sediment. The objectives of the study were to assess the effectiveness of biochar-sediment microbial fuel cells (BC-SMFCs) in suppressing P and N release from two types of sediment in intensive (Int) and extensive (Ext) pond drainages in Central Vietnam. Single chamber SMFCs were set up and operated under open or closed-circuit (no SMFC or SMFC) conditions. Coconut shell biochar (BC) was amended to sediments at 1%. For Int-sediment, total phosphorus (TP) release was reduced by no BC-SMFCs through co-precipitation with Fe. On the other hand, BC-SMFCs did not suppress TP release because P was released from BC and organic matter decomposition was enhanced in the sediment. Application of BC enhanced organic N mineralization in the sediment. Nitrification and denitrification occurred in the overlying water, reducing mineral N concentrations. For Ext-sediment, BC addition and SMFC conditions did not affect TP and total nitrogen (TN) release because of low initial organic matter content, and less reductive condition. Our study suggested that the effect of SMFCs was masked by BC which released more P from Int-sediment to the water. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 1438-4957 2025 From sewage sludge to agriculture: governmental initiatives, technologies, and sustainable practices in Japan EN Thu Huong Nguyen Graduate School of Engineering, Kyoto University Taku Fujiwara Graduate School of Engineering, Kyoto University Hiromasa Yamashita Water Supply and Sewerage Department, National Institute for Land and Infrastructure Management Hironori Togawa Water Supply and Sewerage Department, National Institute for Land and Infrastructure Management Haruo Miyake R & D Department, Japan Sewage Works Agency Masako Goto 1St Research Department, Japan Institute of Wastewater Engineering and Technology Hideaki Nagare Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Masato Nakamura Institute for Rural Engineering, NARO Fumiko Oritate Institute for Rural Engineering, NARO Hirotaka Ihara Institute for Agro-Environmental Sciences, NARO Morihiro Maeda Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Sewage sludge (SS), an underutilized but valuable resource for agriculture, contains essential nutrients, such as phosphorus. In Japan, where dependence on imported fertilizers is high and global price fluctuations persist, using SS as fertilizer presents a sustainable alternative aligned with circular economy goals. This review analyzes Japan’s current efforts to repurpose SS, focusing on technological developments and key policy initiatives that promote safe and effective application. Selective phosphorus recovery technologies mitigate resource depletion, while holistic approaches, such as composting and carbonization, maximize sludge utilization for agricultural applications. Government-led initiatives, including public awareness campaigns, quality assurance standards and research support, have facilitated the adoption of sludge-based fertilizers. To contextualize Japan’s position, international trends, particularly in the EU, are also examined. These comparisons reveal both common strategies and areas for policy and technological advancement, especially regarding regulation of emerging contaminants. By integrating national case studies with global perspectives, the study offers insights into the economic, environmental, and social benefits of SS reuse, contributing to Japan’s goals of resource self-sufficiency and carbon neutrality, while also informing broader sustainable agriculture transitions worldwide. No potential conflict of interest relevant to this article was reported.

Japan Society on Water Environment Acta Medica Okayama 1348-2165 22 6 2024 Effects of Sediment Microbial Fuel Cells on CH4 and CO2 Emissions from Straw Amended Paddy Soil 271 285 EN Adhena Tesfau Bekele Graduate School of Environmental and Life Science, Okayama University Morihiro Maeda Graduate School of Environmental and Life Science, Okayama University Satoshi Akao Faculty of Science and Engineering, Doshisha University Hiroaki Somura Graduate School of Environmental and Life Science, Okayama University Chiyu Nakano Organization for Research Strategy and Development, Okayama University Yuta Nishina Research Institute for Interdisciplinary Science, Okayama University Straw returning into paddy soil enhances soil organic matter which usually promotes the emission of greenhouse gases to the atmosphere. The application of sediment microbial fuel cells (SMFCs) to paddy soil activates power-generating microorganisms and enhances organic matter biodegradation. In the present study, rice straw addition in SMFCs was examined to determine its effect on CH4 and CO2 emissions. Columns (height, 25 cm; inner diameter, 9 cm) with four treatments: soil without and with rice straw under SMFC and without SMFC conditions were incubated at 25°C for 70 days. Anodic potential values at 7 cm depth sediment were kept higher by SMFCs than those without SMFCs. Cumulative CH4 emission was significantly reduced by SMFC with straw amendment (p < 0.05) with no significant effect on CO2 emission. 16S rRNA gene analysis results showed that Firmicutes at the phylum, Closteridiales and Acidobacteriales at order level were dominant on the anode of straw-added SMFC, whereas Methanomicrobiales were in the treatment without SMFC, indicating that a certain group of methanogens were suppressed by SMFC. Our results suggest that the anodic redox environment together with the enrichment of straw-degrading bacteria contributed to a competitive advantage of electrogenesis over methanogenesis in straw-added SMFC system. No potential conflict of interest relevant to this article was reported.

Japan Society of Hydrology and Water Resources Acta Medica Okayama 1882-3416 19 1 2025 Evaluation of the temporal behavior of fulvic acid iron in Asahi River, Okayama, Japan 36 43 EN Rohdof Lactem Yengeh Graduate School of Environmental and Life Science, Okayama University Hiroaki Somura Graduate School of Environmental and Life Science, Okayama University Toshitsugu Moroizumi Graduate School of Environmental and Life Science, Okayama University Yasushi Mori Graduate School of Environmental and Life Science, Okayama University Morihiro Maeda Graduate School of Environmental and Life Science, Okayama University Iron is essential for biogeochemical processes in aquatic ecosystems, but its riverine concentration can be affected by environmental conditions. This study assessed weekly fulvic acid iron (FAFe) concentration at a single sampling site in Asahi River from 2022–2023 to explore the differences in the temporal scales. The objectives of this study were to evaluate the effects of physicochemical properties of the river on the concentration of FAFe, analyze the concentration of FAFe in spring, summer, autumn and winter, and assess the relationship between FAFe concentration and land use types of the watershed. The results indicated that physicochemical parameters, such as pH and surface water temperature (SWT) seemed to influence FAFe concentration (p < 0.05). Hydrological dynamics influenced FAFe concentration and transport, revealing an increasing trend during spring (p < 0.001) and summer (p = 0.05), with non-significant trends during autumn and winter (p > 0.05). FAFe exhibited a strong positive correlation with total organic carbon (TOC) (p < 0.001). Upland fields significantly influenced FAFe concentration (p < 0.01) through runoff with abundant NO3– and PO43– into the river. Thus, FAFe concentration in Asahi River was influenced by pH, SWT, TOC, hydrological regime, and agricultural runoff. No potential conflict of interest relevant to this article was reported.

Informa UK Limited Acta Medica Okayama 0038-0768 71 2 2024 Effects of aged microplastics on paddy soil properties and greenhouse gas emissions under laboratory aerobic conditions 215 224 EN Tian Zhang Graduate School of Environmental and Life Science, Okayama University Hiroaki Somura Graduate School of Environmental and Life Science, Okayama University Satoshi Akao Faculty of Science and Engineering, Doshisha University Nozomi Nakahara Environmental Management Center, Okayama University Gamamada Liyanage Erandi Priyangika Perera Graduate School of Environmental and Life Science, Okayama University Chiyu Nakano Graduate School of Natural Science and Technology, Okayama University Morihiro Maeda Graduate School of Environmental and Life Science, Okayama University Microplastics (MPs) formed after changes in chemical or physical properties may alter soil properties, which in turn may affect microbial activities and greenhouse gas (GHG) emissions. However, few studies have focused on the effects of aged MPs changes on soil properties and greenhouse gas emissions. Therefore, we aimed to investigate the impact of MPs with different aging times on soil GHG emissions and dissolved organic carbon (DOC). Low-density polyethylene (PE) and polylactic acid (PLA) were treated with ultraviolet (UV) irradiation for 0–2 weeks. Soil was incubated with PE or PLA 1% (w/w) concentration at 60% water holding capacity (WHC) for 35 days. Emissions of nitrous oxide (N2O) and carbon dioxide (CO2) were measured on days 0, 1, 3, 5, 7, 14, 21, 28, and 35. Results showed that CO2 and N2O emissions were higher (p < 0.05) in MPs-amended treatments than those without MPs and increased with MPs age. The addition of virgin PE did not affect soil DOC content, whereas aged PE and all PLA additions significantly increased soil DOC content on day 0, probably because UV irradiation caused the degradation of MPs to smaller molecules. In addition, aged MPs addition altered DOC spectral characteristics on day 7, possibly because aged PE and PLA promote microbial decomposition of organic matter by altering soil properties. Changes in soil DOC content and specific ultraviolet absorbance (SUVA) by aged PE and PLA probably promoted the emissions of CO2 and N2O compared to virgin MPs or soil only. Our study revealed that aged PE and PLA promote GHG emissions from soil by changing DOC contents and qualities. No potential conflict of interest relevant to this article was reported.

Informa UK Limited Acta Medica Okayama 0038-0768 69 2 2023 Greenhouse gas emissions from agricultural soil amended with kitchen compost of varying ages 137 147 EN Tran Thi Minh Chau Graduate School of Environmental and Life Science, Okayama University Takashi Someya Faculty of Agriculture, Saga University Satoshi Akao Faculty of Science and Engineering, Doshisha University Masato Nakamura Institute for Rural Engineering, NARO Fumiko Oritate Institute for Rural Engineering, NARO Hiroaki Somura Graduate School of Environmental and Life Science, Okayama University Shinzo Yamane Faculty of Agriculture and Marine Science, Kochi University Morihiro Maeda Graduate School of Environmental and Life Science, Okayama University 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 degrees 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. No potential conflict of interest relevant to this article was reported.