Researcher Database

Researcher Profile and Settings


Affiliation (Master)

  • Research Faculty of Agriculture Research Innovation and Cooperation Cooperative Promotion

Affiliation (Master)

  • Research Faculty of Agriculture Research Innovation and Cooperation Cooperative Promotion


Profile and Settings


  • PhD in Environmental Biogeochemistry(Lincoln University, New Zealand)
  • B. Agricultural Science 1st class Hon.(Lincoln University, New Zealand)

Profile and Settings

  • Profile

    I research greenhouse gas emissions from soils, particularly N2O and CO2 emissions. I am a Japanese but I did my degree (undergraduate and PhD) at Lincoln University, New Zealand. When I was a student, I did most of my research in pastoral ecosystems, but in my postdoctorial position, my research field was extended to upland farming. I was based at NIAES, Japan, looking at the use of coated fertilizer on N2O mitigation, the use of microbial inoculant to reduce N2O emissions from legume systems etc. Now I am an assosiate professor at Hokkaido University, Research Faculty of Agriculture.
  • Name (Japanese)

  • Name (Kana)

  • Name


Alternate Names


Research Interests

  • 牧草   安定同位体   温度依存性   亜酸化窒素   土壌呼吸   

Research Areas

  • Life sciences / Plant nutrition, soil science

Research Experience

  • 2017/04 - Today Hokkaido University, Japan Research Faculty of Agriculture Associate Professor
  • 2013/01 - 2017/03 Hokkaido University, Japan Research Faculty of Agriculture Tenure-Track Assistant Professor
  • 2010/01 - 2012/12 NIAES, Japan Postdoctorial scientist


  • 2007 - 2010  Lincoln University, New Zealand  Soil and Physical Sciences Department  PhD (Environmental Biogeochemistry)
  • 2002/07 - 2006/06  Lincoln University, New Zealand  B.Agr.Sci. (1st Hon.)


  • 2022/09 2022年度(第21回)日本農学進歩賞
  • 2022/09 第40回(2022年度)日本土壌肥料学会奨励賞
  • 2017/04 2016年度笹川科学研究奨励賞
  • 2012/12 National Institute for Agro-Environmental Sciences, Japan Young Scientist Award
    受賞者: Yoshitaka Uchida

Published Papers

  • Shinsaku Nakamura, Toshifumi Igarashi, Yoshitaka Uchida, Mayumi Ito, Kazuyo Hirose, Tsutomu Sato, Walubita Mufalo, Meki Chirwa, Imasiku Nyambe, Hokuto Nakata, Shouta Nakayama, Mayumi Ishizuka
    Minerals 12 (5) 2022/05 
    Effects of the water content of ground surface on windborne lead (Pb) dispersion from the zinc (Zn) leach residue site at the Kabwe mine, Zambia, were simulated. The Pb-bearing Zn plant leach residue site was selected as the source of the dispersion, and water conditions of the surface of the source were evaluated by the modified normalized difference water index (MNDWI) under the actual weather conditions in the year 2019. The MNDWI was calculated based on Sentinel-2 datasets, which were acquired in the year 2019. The index was used for monitoring the surface condition of the source necessary for simulating Pb dispersion, because the higher surface water content reduces the intensity of windborne source. The results showed that the wind speeds and directions had huge impacts on Pb dispersion when the MNDWI had negative values, and that the dispersion was inhibited when the MNDWI had positive values. These indicate that the water content of the surface is sensitive to dispersion, and that MNDWI is an effective parameter that expresses the source strength.
  • Toru Hamamoto, Nhamo Nhamo, David Chikoye, Ikabongo Mukumbuta, Yoshitaka Uchida
    SCIENTIFIC REPORTS 12 (1) 6368 - 6368 2045-2322 2022/04 
    In sub-Saharan Africa, efforts have been made to increase soil carbon (C) content in agricultural ecosystems due to severe soil degradation. The use of organic materials is a feasible method for recovering soil organic C; however, the effects of organic amendments on soil microbial communities and C cycles under C-limited soil conditions are still unknown. In this study, we conducted field experiments in Zambia using organic amendments at two sites with contrasting C content. At both sites, temporal changes in soil carbon dioxide (CO2) emissions and prokaryotic community structures were monitored during the crop growing season (126 days). The organic amendments increased CO2 emissions and prokaryotic abundance at the Kabwe site, whereas no direct impacts were observed at the Lusaka site. We also observed a larger temporal variability in the soil microbial community structure at Kabwe than that at Lusaka. These contrasting results between the two soils may be due to the microbial community stability differences between each site. However, as organic amendments have considerable potential to enhance microbial abundance and consequently sequester C at the Kabwe site, site-specific strategies are required to address the issues of soil C depletion in drylands.
  • Chidozie J. Oraegbunam, Sunday E. Obalum, Toshihiro Watanabe, Yvonne M. Madegwa, Yoshitaka Uchida
    APPLIED SOIL ECOLOGY 170 0929-1393 2022/02 
    The use of charred organic materials (biochar) as soil amendment can alter soil nutrient, microbial abundance, and their diversities. These alterations can be influenced by the biochar source, application method and amount, but the details are still unknown. Thus, this study aimed to compare two methods of biochar application (surface or mixed) on carbon (C) and nitrogen (N) losses with their related effect on microbial community under C-depleted sandy soil. Chicken manure (CM), rice husk (RH) and rice straw (RS), pyrolyzed at 350 degrees C to produce biochar, were tested in a pot trial. The biochar was applied singly, and in combined forms (CM + RH and CM + RS) under dent corn, as mixed (incorporated) or surface application, at different rates of 0, 15, and 30 g kg(-1) soil (equivalent to 0, 7.5 and 15.0 Mg ha(-1)). The soil respiration (S-R), leaching loss of organic-C and inorganic-N (as nitrate-N), microbial biomass C at top 10 cm soils, bacterial relative abundance and community structure were measured. The application methods' effect on S-R was unclear but the surface application reduced the C leaching loss and increased nitrate-N loss compared to the mixed application, in general. The microbial biomass C was found to be significantly higher (P < 0.001) under the surface applied (459 +/- 252 mg C kg(-1) soil) compared to the mixed applied (76.1 +/- 18.5 mg C kg(-1) soil). Surface application of biochar also increased microbial diversity on soil surface. The increase in diversity was characterized by an increase in OTU numbers within the phylum Actinobacteria and Proteobacteria. We concluded that surface application of biochar increased the microbial di-versities in the soil and thus, can retain C in low C soils through higher immobilization of C, but might be un-suitable when biochar is applied with the aim being to reduce nitrate-N loss in soils.
  • Yufita Dwi Chinta, Yoshitaka Uchida, Hajime Araki
    APPLIED SOIL ECOLOGY 168 0929-1393 2021/12 [Refereed]
    Nitrogen (N) mineralization, the conversion of organic N into inorganic N, plant available N, is a microbemediated processes. However, the roles that specific microbial taxa play in the release of N from cover crop residues during the residual decomposition have been understudied. Pot-based experiments were established in soils incorporated with rye, hairy vetch (HV), and rye+HV cover crop residues. We used DNA-based molecular approaches to quantify and identify bacteria and fungi under each cover crop. Correlation analysis was used to evaluate the roles of specific microbial taxa (i.e., the dominant, influenced, and keystone taxa). Fungal DNA in all cover crop-treated soils peaked within 5-25 days following residue incorporation, which was also the critical period for N mineralization. Additionally, positive links occupied the correlation networks within and between bacteria and fungi in all treatments, suggesting that the microbes synergistically cooperated to degrade the residues and mineralize N. The abundance of decomposers (e.g., Cytophagaceae and Sinobacteraceae) was promoted by HV and rye+HV inputs due to residue lability. The dominant (e.g., Mortierellaceae, Hypomicrobiaceae, and Aspergillaceae), influenced (i.e., Actinosynnemataceae, unidentified SAR202, and Parachlamydiaceae), and keystone (e.g., Clostridiaceae, Cystofilobasidiaceae, and Dolo 23) taxa were positively or negatively correlated with N availability indicators (i.e., soil inorganic N, beta-glucosidase enzyme activity, and soil microbial biomass) in each cover crop-treated soil. The results indicate that the taxa were principally responsible for N mineralization from each cover crop input during the residual decomposition period.
  • Yvonne Musavi Madegwa, Yoshitaka Uchida
    JOURNAL OF ENVIRONMENTAL MANAGEMENT 297 113356 - 113356 0301-4797 2021/11 [Refereed]
    Lime is used to reduce soil acidification in agricultural soils. However, its effects on the soil microbial community are not well understood. Additionally, the soil microbial community is known to be influenced by fertilizers. However, the question remains whether liming influences the magnitude of fertilizers' impact on soil microbial communities. Therefore, an incubation experiment was performed to understand the effect of lime application (pH = 6.5 and 5.5 for the soils with and without lime, respectively) and fertilizer (digestate, urea and control) on the soil microbial community structures, stability and gene functions. Soils were sampled weekly after the application of fertilizers for a month. For microbial community analysis, DNA was extracted and sequenced targeting 16 S rRNA region. For gene abundances i.e 16 S rRNA, ammonia oxidizing archaea (AOA), ammonia oxidizing bacteria (AOB), nitrous oxide reductase (nosZ) and nitrite reductase (nirS) quantitative PCR was conducted. In results, the relative abundance of Actinobacteria was influenced more strongly by digestate in lime soils, while Alphaproteobacteria was influenced more strongly by digestate in the no lime soil. In NL treatments, digestate had a significant effect on more operational taxonomic units (146) compared to lime (127), indicating that lime application increased soil microbial community's stability. Liming and fertilizer had a significant effect on 16 S rRNA gene copy numbers with the highest values observed in lime plus digestate treatments. Soil pH had a significant effect on AOA, nosZ and nirS gene copy numbers with the highest values observed in lime treatments. In the lime treatments digestate application had a positive impact on AOB gene copy numbers but this was not the case for soils without liming treatments. These results indicate that soil pH and fertilizer type should be taken into consideration for the management of functional gene abundance in agricultural soils.
  • Shinsaku Nakamura, Toshifumi Igarashi, Yoshitaka Uchida, Mayumi Ito, Kazuyo Hirose, Tsutomu Sato, Walubita Mufalo, Meki Chirwa, Imasiku Nyambe, Hokuto Nakata, Shouta Nakayama, Mayumi Ishizuka
    MINERALS 11 (8) 2021/08 [Refereed]
    Dispersion of lead (Pb) in mine wastes was simulated for reproducing Pb contamination of soil in Kabwe District, Zambia. Local weather data of year 2019 were monitored in situ and used for the simulations. The plume model, weak puff model, and no puff model were adopted for calculation of Pb dispersion under different wind conditions. The results showed that Pb dispersion from the Kabwe mine was directly affected by wind directions and speeds in the dry season, although it was not appreciably affected in the rainy season. This may be because the source strength is lower in the rainy season due to higher water content of the surface. This indicates that Pb dispersion patterns depend on the season. In addition, the distribution of the amount of deposited Pb-bearing soils around the mine corresponded to the distribution of Pb contents in soils. These results suggest that Pb contamination in soils primarily results from dispersion of fine mine wastes.
  • Akane Chiba, Yoshitaka Uchida, Susanne Kublik, Gisle Vestergaard, Franz Buegger, Michael Schloter, Stefanie Schulz
    MICROORGANISMS 9 (2) 2021/02 [Refereed]
    This study aimed to investigate the effects of different levels of soil- and plant-associated bacterial diversity on the rates of litter decomposition, and bacterial community dynamics during its early phases. We performed an incubation experiment where soil bacterial diversity (but not abundance) was manipulated by autoclaving and reinoculation. Natural or autoclaved maize leaves were applied to the soils and incubated for 6 weeks. Bacterial diversity was assessed before and during litter decomposition using 16S rRNA gene metabarcoding. We found a positive correlation between litter decomposition rates and soil bacterial diversity. The soil with the highest bacterial diversity was dominated by oligotrophic bacteria including Acidobacteria, Nitrospiraceae, and Gaiellaceae, and its community composition did not change during the incubation. In the less diverse soils, those taxa were absent but were replaced by copiotrophic bacteria, such as Caulobacteraceae and Beijerinckiaceae, until the end of the incubation period. SourceTracker analysis revealed that litter-associated bacteria, such as Beijerinckiaceae, only became part of the bacterial communities in the less diverse soils. This suggests a pivotal role of oligotrophic bacteria during the early phases of litter decomposition and the predominance of copiotrophic bacteria at low diversity.
  • Jin-Feng Lin, Eva-Maria Minarsch, Munehide Ishiguro, Yoshitaka Uchida
    APPLIED AND ENVIRONMENTAL SOIL SCIENCE 2021 1687-7667 2021/02 [Refereed]
    In natural farming rice paddies, intertillage (tillage between rows, during rice growth period) is often performed mainly to remove weeds without the use of chemicals. Also, the intertillage disturbs soil surfaces, potentially impacting the characteristics of soil microbial communities, such as their diversity and abundance. Natural farming systems aim to maintain biodiversity, but it remains unclear whether the intertillage impacts soil microbes in rice paddies. Thus, this study aimed to understand to what extent "five times intertillage" treatment (5T) influences soil bacterial abundance and community structures compared with no tillage (NT), under a natural farming rice paddy system. Soils were sampled at rice proximity, soil surface, and 10 cm depth in a natural farming rice paddy, during the early to late vegetative phase (June to July), in Hokkaido, Japan. The 16S rRNA community structures and abundance were analyzed by next generation sequencing (NGS) and quantitative PCR, respectively. We observed that NT had significantly higher bacterial abundances at the soil surface than 5T. However, there were no clear differences between 5T and NT, regarding the bacterial community structures, including their diversity indices. Instead, the sampling timings markedly impacted the bacterial community structures for the rice proximity and soil surface, showing increasing diversity indices at the late vegetative stage, compared to the early vegetative stage, suggesting the interaction between the crop growth and bacterial communities. In this study, we did not observe the significant difference between the rice yield from NT (2.3 +/- 0.7 t.ha(-1)) and 5T plots (2.7 +/- 0.9 t.ha(-1)); however, the 5T might have negatively impacted soil bacterial abundances but not the community structure of the bacteria.
  • Maiko Akari, Yoshitaka Uchida
    APPLIED AND ENVIRONMENTAL SOIL SCIENCE 2021 1687-7667 2021/01 [Refereed]
    Livestock waste-based products, such as composted manure, are often used in crop production systems. The products' microbial characteristics differ depending on animal waste treatment methods used (e.g., biogas production/composting). The question remains whether different livestock waste-based products differently impact soil microbiota. A pot experiment with five treatments (control, chemical fertilizer, digestate + chemical fertilizer, wheat straw compost + chemical fertilizer, and woodchip compost + chemical fertilizer) was conducted to compare the survival rates of microbial communities from digestate and composted manure, after their application to agricultural soil. Potatoes were planted in each pot. The changes in soil pH, the concentration of ammonium and nitrate, and the microbial community properties were monitored after 1, 6, 10, and 14 weeks of the application of livestock waste-based products. The application of composted manure, especially woodchip compost, showed a relatively more extensive impact on the soil microbial community structure than the other treatments. Woodchip compost contained a relatively more abundant and diverse bacterial community than digestate, and its family-level bacterial community structure was similar to that of the soil. These characteristics might determine the extent of the impact of livestock waste-based products on soil microbial communities. Digestate markedly influenced the inorganic nitrogen concentrations in soils but did not affect the soil microbial community. In conclusion, the survival rate of microbes of livestock waste-based products varies depending on the product type. Further investigation is needed to fully understand their impact on soils' microbial functions.
  • Misato Toda, Juni Motoki, Yoshitaka Uchida
    In recent decades, the rate of milk production per unit land area and per cow has increased with the intensification of the dairy system. The possible environmental risks arising from nutrients surpluses, such as nitrogen (N), are often evaluated using the N balance approach. In Hokkaido, the biggest dairy farming area in Japan, many dairy farms have started introducing a new dairy farming system called the total mixed ration (TMR) and biogas system. Feed and manure are managed at a community scale in these systems while each farm focuses primarily on milking cows. Thus, calculating the N balance for this system is complicated. Therefore, this study aimed to evaluate the N surplus and use efficiency (NUE), focusing mainly on the community-based dairy farming system, as described above. We investigated twenty dairy farms comprising a TMR centre (TMR-based farms) and nineteen conventional dairy farms (conventional farms). The Hokkaido dairy farms had a smaller N surplus and higher NUE than farms in other countries. The whole farm N surplus and NUE ranged from -163 to 701 kg N ha(-1) and from 20% to 171% with median values of 40.5 kg N ha(-1) and 69.5%, respectively. One of the possible reasons for the smaller N surplus and higher NUE is a lower stocking rate (averaged 1.3 cows ha(-1)) on Hokkaido dairy farms. There were strong relationships between feed N and N surplus because the studied dairy farms depended on purchased feed. In the comparison between the TMR centre and conventional dairy farms, the milk production level per cow and stocking rate tended to increase, and variations between farms decreased on the TMR-based farms. Increasing the amount of home-grown feed with pasture management is essential to decreasing N surplus for the new dairy farming systems.
  • Patricia N. Mwilola, Ikabongo Mukumbuta, Victor Shitumbanuma, Benson H. Chishala, Yoshitaka Uchida, Hokuto Nakata, Shouta Nakayama, Mayumi Ishizuka
    Health risks due to heavy metal (HM) contamination is of global concern. Despite concerns of high levels of HMs in soils near Kabwe mine in Zambia, edible crop production is common, posing potential health risks. This study assessed the potential of chicken manure (CM), triple superphosphate (TSP) and a blended fertilizer (BF; consisting of Nitrogen, Phosphorous and Potassium (NPK) fertilizer and composted chicken manure) to reduce lead (Pb), zinc (Zn) and cadmium (Cd) in soils and their accumulation in maize grown near the Kabwe mine. Maize was grown to maturity and its HM concentrations and associated health risk indices were calculated. All soil amendments decreased bioavailable soil Pb concentrations by 29-36%, but only CM decreased Zn, while the amendments increased or had no effect on Cd concentrations compared to the control. The amendments reduced Pb (>25%) and Zn concentrations (>18%) in the maize stover and grain. However, Cd concentrations in maize grain increased in the BF and TSP treatments. Bioaccumulation factors showed that Cd had the highest mobility from the soil into maize stover and grain, indicating the need for greater attention on Cd in Kabwe despite its apparently lower soil concentration compared to Pb and Zn. The hazard quotients for Pb and Cd were much greater than one, indicating a high risk of possible exposure to toxic levels by people consuming maize grain grown in this area. This study demonstrated the significant potential of manure and phosphate-based amendments to reduce Pb and Zn, and to some extent Cd, uptake in maize grain and consequently reduce associated health risks.
  • Rio Doya, Shouta M. M. Nakayama, Hokuto Nakata, Haruya Toyomaki, John Yabe, Kaampwe Muzandu, Yared B. Yohannes, Andrew Kataba, Golden Zyambo, Takahiro Ogawa, Yoshitaka Uchida, Yoshinori Ikenaka, Mayumi Ishizuka
    ENVIRONMENTAL SCIENCE & TECHNOLOGY 54 (22) 14474 - 14481 0013-936X 2020/11 [Refereed]
    We investigated the potential effects of different land use and other environmental factors on animals living in a contaminated environment. The study site in Kabwe, Zambia, is currently undergoing urban expansion, while lead contamination from former mining activities is still prevalent. We focused on a habitat generalist lizards (Trachylepis wahlbergii). The livers, lungs, blood, and stomach contents of 224 lizards were analyzed for their lead, zinc, cadmium, copper, nickel, and arsenic concentrations. Habitat types were categorized based on vegetation data obtained from satellite images. Multiple regression analysis revealed that land use categories of habitats and three other factors significantly affected lead concentrations in the lizards. Further investigation suggested that the lead concentrations in lizards living in bare fields were higher than expected based on the distance from the contaminant source, while those in lizards living in green fields were lower than expected. In addition, the lead concentration of lungs was higher than that of the liver in 19% of the lizards, implying direct exposure to lead via dust inhalation besides digestive exposure. Since vegetation reduces the production of dust from surface soil, it is plausible that dust from the mine is one of the contamination sources and that vegetation can reduce exposure to this.
  • Yui Yoshii, Isabell von Rein, Kabenuka Munthali, Mukuka Mwansa, Hokuto Nakata, Shota Nakayama, Mayumi Ishizuka, Yoshitaka Uchida
    SOUTH AFRICAN JOURNAL OF PLANT AND SOIL 37 (5) 351 - 360 0257-1862 2020/11 [Refereed]
    High levels of lead (Pb) in the soil is a serious issue in the city of Kabwe, Zambia. Phytoremediation is an effective approach to revive the life-supporting functions of the soils. Locally available soil amendments, such as chicken manure, can strengthen phytoremediation. This study aims to find an appropriate combination of a locally available Pb hyperaccumulator, lemongrass (Cymbopogon citratus (DC.) Stapf.), and soil amendments, to minimize the Pb pollution. After a short-term (78 day) pot experiment with lemongrass and three soil amendments (chicken manure, biochar of chicken manure, and urea) on a Pb-contaminated soil in Kabwe, an edible crop, dent corn (Zea mays var. indentata (Sturtev.) L.H.Bailey), was grown for two weeks. Chicken manure combined with lemongrass had the most beneficial impact, reducing the Pb level in dent corn by 19%, compared to the Pb in dent corn grown on the control soil. By growing lemongrass in the Kabwe soil with chicken manure, the exchangeable soil Pb was reduced by 70%. The growth of lemongrass without chicken manure reduced the exchangeable soil Pb by 20%. In conclusion, lemongrass successfully reduced Pb levels, in combination with chicken manure. Soil amendments must be chosen carefully by considering the soil properties and environmental conditions for an optimized Pb reduction.
  • Toru Hamamoto, Yoshitaka Uchida, Isabell von Rein, Ikabongo Mukumbuta
    Science of The Total Environment 740 140006 - 140006 0048-9697 2020/10 [Refereed][Not invited]
    Nitrous oxide (N2O) emissions from soils applied with livestock excreta have been widely reported previously. The highest N2O emissions from soils are also often reported during thawing periods in cold regions where soil freezing is common. However, the combined effects of cow urine application and freeze-thaw events on N2O emissions and the related enzyme activities are still not clear. Thus, we simulated a freeze-thaw event at -3 °C for 7 days, and then increased to 3 °C for 46 days using intact soil cores with cow urine (392 kg N ha-1). We compared the factors influencing the magnitudes of N2O emissions through soil microbial processes with and without the freeze-thaw event. Dicyandiamide (DCD), an inhibitor of nitrification, was added to investigate the significance of nitrification on N2O emissions. The N2O emission rates from the urine-applied soils peaked to approximately 1000 μg N2O-N m-2 h-1 immediately after the soils thawed. Soil freezing with urine application was significantly higher cumulative N2O emissions (537 mg N2O-N m-2), compared to non-frozen soils with urine (247 mg N2O-N m-2) during the incubation period (54 days). The effect of DCD application on N2O emissions was not clear during the freeze-thaw event, although nitrate production rates were reduced. After the freezing event, soil moisture (water-filled pore space) was significantly higher in the non-frozen soils compared to the frozen soils, due to a 9% decline in bulk density of frozen soils. Additionally, the impact of thawing on urease and denitrification enzyme activities was influenced by the urine application. Urine application increased the urease activity, while the freezing event decreased the magnitudes. The physical changes in the soils were also important controlling factors of the N2O emissions from cow urine-applied soils in cold regions.
  • 濱本 亨, 龍見 史恵, 内田 義崇
    日本土壌肥料学会講演要旨集 一般社団法人 日本土壌肥料学会 66 95 - 95 0288-5840 2020/09/01
  • Rafael A. Muchanga, Toshiyuki Hirata, Yoshitaka Uchida, Ryusuke Hatano, Hajime Araki
    AGRONOMY JOURNAL 112 (3) 1636 - 1648 0002-1962 2020/05 [Refereed]
    Depending on management, cover crops may improve soil and environmental quality and tomato (Solanum lycopersicum L.) yield. We evaluated the effects of hairy vetch (HV; Vicia villosa R.) residue management and the biculture of HV and rye (Secale cereale L.) on soil organic carbon (SOC) and total nitrogen (STN), microbial biomass nitrogen (MBN), soil inorganic nitrogen, and tomato yield for 2 yr in a plastic high tunnel. The SOC in the surface 10-cm depth was 2.87-17.5% significantly greater in HV incorporation (HVI), HV mulch (HVM), and the biculture of HV and rye treatments (HV+RYE), than in a no cover crop treatment (bare fallow). However, cover crop management effects on STN varied with soil depths (0- to 10- and 10- to 30-cm depths) and years, and HVI tended to be more effective than other treatments in increasing STN. Residual soil nitrate-N was increased by cover crops, more so by HV monoculture than HV+RYE. The MBN and inorganic N (NO3--N + NH4+-N) were greater in HVI than either HVM or HV+RYE. Tomato total yield was 11.1-43.8% significantly greater in HVI and HVM than in bare fallow. However, the effects of HV+RYE on MBN, inorganic N, and tomato yield varied with C/N ratio of residues and best results were obtained with a C/N ratio of 17.6 than with 23.7. Therefore, if an adequate seeding HV/rye ratio (2:1) is used, HV+RYE is a better management practice to increase SOC and STN at topsoil and tomato yield with least residual N.
  • Hiroko Akiyama, Akinori Yamamoto, Yoshitaka Uchida, Yuko Takada Hoshino, Kanako Tago, Yong Wang, Masahito Hayatsu
    The Science of the total environment 713 136677 - 136677 2020/01/15 [Refereed][Not invited]
    Crop residues are produced from agriculture in large amounts globally. Crop residues are known to be a source of nitrous oxide (N2O); however, contrasting results have been reported. Furthermore, the effect of crop residues on nitric oxide (NO) and methane (CH4) fluxes has not been well studied. We investigated N2O, NO, and CH4 fluxes after low C/N crop residue (cabbages and potatoes) inputs to lysimeter fields for two years using with automated flux monitoring system. Lysimeters were filled with two contrasting soil types, Andosol (total C: 33.1 g kg-1; clay: 18%) and Fluvisol (17.7 g kg-1; 36%). Nitrogen application rates were 250 kg N ha-1 of synthetic fertilizer and 272 kg N ha-1 of cow manure compost for cabbage, and 120 kg N ha-1 of synthetic fertilizer and 136 kg N ha-1 of cow manure compost for potato, respectively. Large N2O peaks were observed after crop residues were left on the surface of the soil for 1 to 2 weeks in summer, but not in winter. The annual N2O emission factors (EFs) for cabbage residues were 3.02% and 5.37% for Andosol and Fluvisol, respectively. Those for potatoes were 7.51% and 5.10% for Andosol and Fluvisol, respectively. The EFs were much higher than the mean EFs of synthetic fertilizers from Japan's agricultural fields (0.62%). Moreover, the EFs were much higher than the Intergovernmental Panel on Climate Change (IPCC) default N2O EFs for synthetic fertilizers and crop residues (1%). The annual NO EFs for potatoes were 1.35% and 2.44% for Andosol and Fluvisol, respectively, while no emission was observed after cabbage residue input. Crop residues did not affect CH4 uptake by soil. Our results suggest that low C/N crop residue input to soils can create a hotspot of N2O emission, when temperature and water conditions are not limiting factors for microbial activity.
  • Rafael A. Muchanga, Yoshitaka Uchida, Toshiyuki Hirata, Ryusuke Hatano, Hajime Araki
    HORTICULTURE JOURNAL 89 (4) 394 - 402 2189-0102 2020 
    The nitrogen (N) contribution of rye (Secale cereale L.) to tomato production may increase when grown and applied with hairy vetch (Vicia villosa R.) to the soil. To examine the uptake and recovery efficiency by tomatoes and retention in the soil of N derived from N-15-labeled rye applied as a monoculture and biculture with hairy vetch, a Wagner pot examination was conducted under plastic high tunnel conditions in Sapporo, Japan. Irrespective of cover crop residue management, the peak of rye-derived N uptake occurred between 4 and 8 weeks after transplanting (WAT) and ceased between 8 and 12 WAT. Rye-derived N uptake by tomatoes (shoot + fruit) was 58.3% greater in rye monoculture treatment than in the biculture of hairy vetch and rye treatment because of higher rye-derived N input, whereas rye-derived N recovery was greater in the biculture treatment (34.0%) than in monoculture treatment (26.9%). The soil retained 47.0% and 52.5% of the rye-derived N input in the biculture (972 mg N/pot) and rye monoculture (1943 mg N/pot) treatments, respectively. Rye-derived N stored in the roots and possibly lost was estimated at 19.0% and 20.6% of the rye-derived N input in the biculture and monoculture treatments, respectively. Hairy vetch in the biculture treatment contributed 46.2% more N to tomato production than rye, and the hairy vetch N contribution was more significant during the late period (4-8 WAT) than the early period (0-4 WAT) of tomato cultivation. Therefore, the biculture may change the N release pattern from both hairy vetch and rye, with the cover crops releasing high amounts of N in both the early and late periods of tomato cultivation. These results may help improve N management in vegetable production systems by maximizing the use of plant-derived N by crops, thereby reducing N fertilizer inputs.
  • Toru Hamamoto, Yoshitaka Uchida
    SUSTAINABILITY 11 (23) 2019/12 
    Earthworms are commonly known as essential modifiers of soil carbon (C) and nitrogen (N) cycles, but the effects of their species on nutrient cycles and interaction with soil microbial activities during the decomposition of organic materials remain unclear. We conducted an incubation experiment to investigate the effect of two different epigeic earthworms (M. hilgendorfi and E. fetida) on C and N concentrations and related enzyme activities in agricultural soils with added barley residues (ground barley powder). To achieve this, four treatments were included; (1) M. hilgendorfi and barley, (2) E. fetida and barley, (3) barley without earthworms, and (4) without earthworms and without barley. After 32 days incubation, we measured soil pH, inorganic N, microbial biomass C (MBC), water or hot-water soluble C, and soil enzyme activities. We also measured CO2 emissions during the incubation. Our results indicated the earthworm activity in soils had no effect on the cumulative CO2 emissions. However, M. hilgendorfi had a potential to accumulate MBC (2.9 g kg(-1) soil) and nitrate-N (39 mg kg(-1) soil), compared to E. fetida (2.5 g kg(-1) soil and 14 mg kg(-1) soil, respectively). In conclusion, the interaction between soil microbes and earthworm is influenced by earthworm species, consequently influencing the soil C and N dynamics.
  • 濱本 亨, 内田 義崇
    日本土壌肥料学会講演要旨集 一般社団法人 日本土壌肥料学会 65 96 - 96 0288-5840 2019/09/03
  • Yoshitaka Uchida, Mihoko Moriizumi, Moe Shimotsuma
    SOIL SCIENCE AND PLANT NUTRITION 65 (4) 409 - 418 0038-0768 2019/07 
    Hairy vetch (Vicia villosa Roth ssp. dasycarpa) mulch is widely used as green manure. This mulch decomposes in the soil and produces nitrous oxide (N2O) emissions. Although rice husk charcoal can be used as a soil conditioner to reduce N2O emissions, the effects of charcoal on the decomposition of vetch mulch and consequent N2O emissions have not been well studied. We conducted an incubation experiment to examine how the decomposition of vetch mulch, charcoal amendments and two soil moisture regimes (field capacity and at a slightly drier moisture regime) affect the mineralisation of N during decomposition. We applied high-performance size-exclusion chromatography and chemiluminescent N detection to quantify soluble organic-N compounds of various molecular sizes. Changes over time in inorganic-N, soluble organic-N fractions and N2O fluxes were measured in soils . We found that vetch mulch induced the accumulation of small-molecular-size soluble organic-N compounds in the early phase during decomposition; however, in wet soils with charcoal, the small-molecular-weight N fraction was depleted earlier than in wet soils without charcoal, suggesting more rapid mineralisation in wet soils. Charcoal in wet soils resulted in earlier and sharper N2O peak emissions and did not reduce cumulative N2O emissions in vetch mulch treatments, suggesting that previously reported N2O emission reductions due to charcoal do not occur in the soils . The rates of N2O emission did not correlate with the concentrations of soluble organic N and inorganic N, indicating that other factors control the N2O emission rates during the decomposition of vetch mulch. Our results indicated that the incorporation of charcoal does not reduce N2O emissions in soils where vetch mulch is applied. The depletion of nitrate-N in wet soils with charcoal demonstrates that adding charcoal can reduce nitrate-N leaching from soils.
  • Nagane Miwako, Shibata Hideaki, Uchida Yoshitaka, Tateno Ryunosuke
    The Japanese Forest Society Congress 日本森林学会 130 (0) 358 - 358 2019 [Refereed][Not invited]

    [in Japanese]

  • Oka M, Uchida Y
    Environmental pollution (Barking, Essex : 1987) 243 (Pt A) 713 - 722 0269-7491 2018/12 [Refereed][Not invited]
    Heavy metal contamination of soil in the vicinity of mining sites is a serious environmental problem around the world when mining residue (slag) is dispersed as dust. We conducted an incubation experiment to investigate the effect of a slag containing high levels of Pb and Zn (62.2 and 33.6 g kg(-1) slag as PbO and ZnO, respectively, sampled from a site formerly used as a lead and zinc mine) on the nitrogen cycle when mixed with soil (0-0.048 g slag g(-1), soil). The nitrogen cycle provides many life supporting-functions. To assess the quality of the soil in terms of the nitrogen cycle we focused on the dynamics of nitrate and ammonium, and bacterial community structure and functions within the soil. After two weeks of pre-incubation, N-15-labeled urea (500 mg N kg(-1)) was added to the soil. Changes in soil pH, the concentration and N-15 ratio of nitrate (NO(3) over bar-N) and ammonium, and bacterial relative abundance and community structure were measured. Results indicated that increasing the ratio of slag to soil had a stronger negative effect on nitrification than ammonification, as suggested by slower nitrate accumulation rates as the slag:soil ratio increased. In the treatment with the highest amount of slag, the concentration of NO(3) over bar-N was 50% of that in the controls at the end of the incubation. Regarding the bacterial community, Firmicutes had a positive and Planctomycetes a negative correlation with increasing slag concentration. Bacterial community functional analysis showed the proportion of bacterial DNA sequences related to nitrogen metabolism was depressed with increasing slag, from 0.68 to 0.65. We concluded that the slag impacted the soil bacterial community structure, and consequently influenced nitrogen dynamics. This study could form the basis of further investigation into the resistance of the nitrogen cycle to contamination in relation to soil bacterial community. (C) 2018 Elsevier Ltd. All rights reserved.
  • Yoshitaka Uchida, Hirosato Mogi, Toru Hamamoto, Miwako Nagane, Misato Toda, Moe Shimotsuma, Yui Yoshii, Yuto Maeda, Miyuki Oka
    Applied and Environmental Soil Science 2018/06/26 [Refereed][Not invited]
  • Toru Hamamoto, Meki Chirwa, Imasiku Nyambe, Yoshitaka Uchida
    Applied and Environmental Soil Science 2018 Article ID 7939123  1687-7675 2018 [Refereed][Not invited]
    The conversion of natural lands into agricultural lands can lead to changes in the soil microbial community structure which, in turn, can affect soil functions. However, few studies have examined the effect of land use changes on the soil microbial community structure in sub-Saharan Africa. Therefore, the aim of this research was to investigate the relationships among soil characteristics and microbial communities in natural and agricultural ecosystems in a semideveloped lowland farm in the central region of Zambia, within which small-scale wetlands had been partly developed as watermelon (Citrullus lanatus) and/or maize (Zea mays) farms. We sampled soils from four different land use types within this farm: "native forest," "grassland," "watermelon farm," and "maize farm." We found that the land use type had a significant effect on the soil bacterial community structure at the class level, with the class Bacilli having significantly higher relative abundances in the forest sites and Gammaproteobacteria having significantly higher relative abundances in the maize sites than in the other land use types. These findings indicate that these bacterial classes may be sensitive to changes in soil ecosystems, and so further studies are required to investigate microbial indicators for the sustainable development of wetlands in sub-Saharan Africa.
  • Ikabongo Mukumbuta, Yoshitaka Uchida, Ryusuke Hatano
    Biology and Fertility of Soils 54 (1) 71 - 81 0178-2762 2018/01/01 [Refereed][Not invited]
    We assessed the effect of liming on (1) N2O production by denitrification under aerobic conditions using the 15N tracer method (experiment 1) and (2) the reduction of N2O to N2 under anaerobic conditions using the acetylene inhibition method (experiment 2). A Mollic Andosol with three lime treatments (unlimed soil, 4 and 20 mg CaCO3 kg−1) was incubated at 15 and 25 °C for 22 days at 50% and then 80% WFPS with or without 200 mg N kg−1 added as 15N enriched KNO3 in experiment 1. In experiment 2, the limed and unlimed soils were incubated under completely anaerobic conditions for 44 h (with or without 100 mg N kg−1 as KNO3). In experiment 1, limed treatments increased N2O fluxes at 50% WFPS but decreased these fluxes at 80% WFPS. At 25 °C, cumulative N2O and 15N2O emissions in the high lime treatment were the lowest (with at least 30% less 15N2O and total N2O than the unlimed soil). Under anaerobic conditions, the high lime treatment showed at least 50% less N2O than the unlimed treatment at both temperatures with or without KNO3 addition but showed enhanced N2 production. Our results suggest that the positive effect of liming on the mitigation of N2O evolution from soil was influenced by soil temperature and moisture conditions.
  • Yong Wang, Yoshitaka Uchida, Yumi Shimomura, Hiroko Akiyama, Masahito Hayatsu
    SCIENTIFIC REPORTS 7 (1) 803 - 803 2045-2322 2017/04 [Refereed][Not invited]
    Agricultural soil is often subjected to waterlogging after heavy rainfalls, resulting in sharp and explosive increases in the emission of nitrous oxide (N2O), an important greenhouse gas primarily released from agricultural soil ecosystems. Previous studies on waterlogged soil examined the abundance of denitrifiers but not the composition of denitrifier communities in soil. Also, the PCR primers used in those studies could only detect partial groups of denitrifiers. Here, we performed pyrosequencing analyses with the aid of recently developed PCR primers exhibiting high coverage for three denitrification genes, nirK, nirS, and nosZ to examine the effect of short-term waterlogging on denitrifier communities in soil. We found that microbial communities harboring denitrification genes in the top 5 cm of soil distributed according to soil depth, water-soluble carbon, and nitrate nitrogen. Short-term waterlogging scarcely affected abundance, richness, or the alpha-diversities of microbial communities harboring nirK, nirS, and nosZ genes, but significantly affected their composition, particularly in microbial communities at soil depths of 0 to 1 cm. Our results indicated that the composition of denitrifying microbial communities but not the abundance of denitrifiers in soil was responsive to short-term waterlogging of an agricultural soil ecosystem.
  • Hirosato Mogi, Miyuki Anzai, Yoshitaka Uchida
    GRASSLAND SCIENCE 63 (2) 132 - 138 1744-6961 2017/04 [Refereed][Not invited]
    Nitrification and denitrification are important processes of the nitrogen (N) cycle in soils because of their relations to N availability for plants and to environmental risks. However, paddock scale heterogeneity of these processes is not well understood in pasture ecosystems. Thus, we focused on the variability of nitrification and denitrification potentials within one pasture paddock. Twelve soil samples were taken from various places within a 2.3 ha paddock in September and were analyzed for nitrification and denitrification potentials, inorganic-N, total carbon (C) and N, C/N ratio, soil pH and moisture contents. The variability of the denitrification potentials was smaller than that of the nitrification potentials. We found that inorganic-N, total C and N, and soil pH were positively correlated to the nitrification potential. We also identified a "hot-area" with 3.3-fold higher nitrification potentials than other areas. A better understanding of this paddock scale nitrification variability may help to decrease environmental risks, such as nitrate leaching and/or nitrous oxide emissions, and to improve N use efficiencies.
  • Moe Shimotsuma, Yoshitaka Uchida, Yasuhiro Nakajima, Hiroko Akiyama
    SOIL SCIENCE AND PLANT NUTRITION 63 (2) 178 - 184 0038-0768 2017 [Refereed][Not invited]
    Legumes, including hairy vetch (Vicia villosa Roth), are widely used as green manures. They fix nitrogen (N) and provide the N to other crops when they decompose, and thus are considered alternatives for chemical N fertilizers. However, N-rich plant residues, including hairy vetch, are also sources of soil nitrous oxide (N2O) emissions, a greenhouse gas. On one hand, rice (Oryza sativa L. ssp. japonica) husk biochar is widely used as a soil conditioner in Japan and has been reported as a tool to mitigate soil N2O emissions. We conducted a soil core incubation experiment (1.5months) to compare the N2O emissions during the decomposition of surface-applied hairy vetch (0.8kg dried hairy vetch m(-2) soil) under semi-saturated soil moisture conditions (similar to 100% water-filled pore space (WFPS)), using two soil types, namely Andosol and Fluvisol. Throughout the incubation period, the use of biochar suppressed soil NH4+-N concentrations in Andosol, whereas the effect of biochar on NH4+-N was not clear in Fluvisol. Biochar increased the nitrate (NO3--N) levels both in Andosol and Fluvisol, suggesting a negative influence on denitrification and/or a positive influence on nitrification. Biochar application did not influence the cumulative N2O emissions. Our study suggests that rice husk biochar is not a good option to mitigate N2O emissions during the decomposition of surface-applied hairy vetch, although this study was performed under laboratory conditions without plants. However, the trends of the inorganic-N concentration changes followed by the addition of hairy vetch and biochar were markedly different between the two soil types. Thus, factors behind the differences need to be further studied.
  • Yoshitaka Uchida, Kawawa Banda, Toru Hamamoto, Yui Yoshii, Kabenuka Munthali, Mukuka Mwansa, Moses Mukuka, Mubanga Mutale, Nobuyasu Naruse, Yukihiro Takahashi
    bioRxiv 2017/01 [Not refereed][Not invited]
  • Misato Toda, Yoshitaka Uchida
    SOIL RESEARCH 55 (5-6) 524 - 533 1838-675X 2017 
    Legumes add not only nitrogen (N), but also carbon (C) to soils, so their effects on the soil microbial community may be different from those of chemical fertiliser. Soil microbes often compete with plants for N when excess C is applied due to their increased N immobilisation potentials and denitrification. In the present study we evaluated the effects of the 9-year use of a green manure legume (hairy vetch; Vicia villosa) in a greenhouse tomato system on soil microbial community structures as well as on the decrease of nitrate when rice straw was incorporated into the soil. Soil microbial community structures and their diversity were altered by the long-term use of legumes. The ratios of Acidobacteria, Gemmatimonadetes and Proteobacteria increased in the hairy vetch soils. The rates of decrease in nitrate were similar in soils with a history of chemical fertiliser and hairy vetch, following the addition of rice straw. In addition, during incubation with added rice straw, the difference between the two soil microbial community structures became less clear within 2 weeks. Thus, we conclude that even though growing a green manure legume changed soil bacterial community structures, this did not result in relatively faster loss of available N for plants when rice straw was added to the soils.
  • Shimotsuma Moe, Moriizumi Mihoko, Uchida Yoshitaka
    日本土壌肥料学会講演要旨集 一般社団法人 日本土壌肥料学会 62 10 - 10 2016
    日本土壌肥料学会講演要旨集 一般社団法人 日本土壌肥料学会 62 167 - 167 2016
  • Xi Li, Jagadeesh Yeluripati, Edward O. Jones, Yoshitaka Uchida, Ryusuke Hatano
    ECOLOGICAL MODELLING 316 14 - 27 0304-3800 2015/11 [Refereed][Not invited]
    With the position of nitrous oxide (N2O) being the greenhouse gas with the highest global warming potential and its long atmospheric lifetime, the anthropogenic production of N2O is of major concern. The process-based model, ECOSSE, was partly developed to quantify emissions of greenhouse gases with an input data requirement that is readily available at regional scale. Hierarchical Bayesian (HB) methods are potentially used to reduce the uncertainty and to explain the spatial variability of estimated parameters. Here, we used a Hierarchical Bayesian method to calibrate the parameters of the N2O and nitrogen monoxide (NO) sub-model of ECOSSE and to quantify the uncertainty of model simulations and to investigate the model extrapolation using soil information. The sub model simulated N2O emission from nitrification and denitrification, while the simulated NO from nitrification. The HB calibration reduced the uncertainty in the N2O and NO simulations. The model's root mean square error (RMSE) was decreased by 18% and 29% for N2O and NO across field sites compared to an uncalibrated model. Parameters for nitrification could be considered universal, while parameters for denitrification challenged the assumption that these parameters may be considered universal constant values across sites. Parameters of the NO module could be considered constant for model extrapolation to regional scale. The calibrated parameters derived from soil-specific calibration could be served as default values for the N2O module extrapolation for similar soil types. Otherwise, the mean value of posterior distribution of calibration parameters in multi-dataset could be served as the parameter for model up scaling at regional scale. (C) 2015 Elsevier B.V. All rights reserved.
  • Yoshitaka Uchida, Timothy J. Clough
    GRASSLAND SCIENCE 61 (2) 61 - 74 1744-6961 2015/06 [Refereed][Not invited]
    Grazed pastures contribute significantly to the global nitrous oxide (N2O) budget. In grazed pastures, the highest N2O emission rates are often reported during winter when soils are wet. This review discusses the current knowledge about factors controlling winter N2O emissions in grazed pastures. High N2O emissions from pastures during winter are also observed from winter-housed animal feeding systems. At near-zero temperature, N2O producing microbial activity is limited but some soil microbial communities adjust to low temperature better than others. Soil microbiological studies focusing on the identification of cold-tolerant denitrifiers and/or changes in microbial community structures under cold conditions are required. In winter-grazed pastures, the availability of substrates, such as nitrate (NO3-) and labile organic carbon (C), for soil microbes producing N2O is influenced by factors such as animal wintering system, effluent management systems and plant activity. When animals are housed, N2O emissions during the winter storage of manures and the emissions after their application are important contributors to N2O inventories. The activity of pasture during winter and its relationship to N2O emissions requires further study in order to understand the competition between plants and N2O producing microbes for nitrogen, and the role of root exudation. Additionally, the effect of low temperatures on nutrient availability under urine patches is still not well known. The reduction of N2O to dinitrogen is regulated by an enzyme N2O reductase and its encoding gene (nosZ) expression needs to be studied in more detail to investigate the mechanisms behind winter N2O emissions. To mitigate N2O emissions during winter, restricted grazing regimes and the use of nitrification inhibitors have been studied; however, little is known about the effectiveness of these methods in mitigating N2O emissions during freeze/thaw cycles and during periods of snow-cover.
  • Hiroko Akiyama, Yoshitaka Uchida, Kanako Tago, Yuko Takada Hoshino, Yumi Shimomura, Yong Wang, Masahito Hayatsu
    SOIL SCIENCE AND PLANT NUTRITION 61 (3) 541 - 551 0038-0768 2015/05 [Refereed][Not invited]
    Soil type influences the effectiveness of enhanced-efficiency fertilizers in reducing nitrous oxide (N2O) and nitric oxide (NO) emissions, although the effect has not been well studied. We measured N2O, NO and methane (CH4) fluxes after the application of enhanced-efficiency fertilizers and conventional fertilizer (urea) in two contrasting soils, an Andosol and a Fluvisol, in lysimeter fields. Brassica rapa var. perviridis L.H.Bailey (komatsuna) was cultivated for 1.5months in spring and in autumn. A nitrification inhibitor, dicyandiamide (DCD), and polymer coated urea (CU) were tested in the spring and autumn experiments, respectively. In spring, DCD was effective in reducing N2O and NO emissions in the Andosol but not in the Fluvisol, compared with urea. Nitrification was likely to be a more important production process for N2O and NO in the Andosol than in the Fluvisol. This difference in N2O and NO production processes was inferred to be the main reason why DCD effectively reduced N2O and NO emissions only in the Andosol. Yield-scaled N2O emission for DCD was lower by 63% than for urea in the Andosol, but no difference was observed in the Fluvisol. In autumn in the Andosol, CU increased N2O emission compared with urea, but no difference was observed for NO emissions. In the Fluvisol, CU was not effective in reducing N2O and NO emissions. CH4 uptake from the Andosol was significantly higher than that from the Fluvisol. Fertilizer type had no effect on cumulative CH4 uptake in either soil. Our results showed that the effectiveness of DCD and CU in reducing N2O and NO emissions varied with soil because the main production processes of these gases varied with soil.
  • Toru Hamamoto, Yoshitaka Uchida
    Applied and Environmental Soil Science 2015 1687-7675 2015 [Refereed][Not invited]
    Cow urine deposition on pasture soils is a major source of N-related environmental impacts in the dairy farming systems. The urine-N can potentially be lost to the ground water as nitrate (NO3-) and to the atmosphere as nitrous oxide (N). These N-related environmental impacts are possibly related to the sodium (Na+) concentrations in urine. We sampled a pasture soil and separated it into three aggregate size groups (0-3, 3-5, and 5-7 mm). Then, cow urine with variable Na+ concentrations (4.3-6.1 g Na+ L-1) was added to the soil cores. We treated the cores with simulated heavy rains and measured the amounts of calcium (Ca2+), Na+, potassium (K+), and inorganic-N leached from the soils. N emission rates were also determined throughout the experimental period. Increasing Na+ concentration in urine decreased the loss of NO3- (-20%), after repeatedly applied simulated rain treatments (30 mm × 3), whereas it increased the loss of ammonium (31%) and K+ (19%). For the loss of Ca2+ and the emissions of N, the effect of the Na+ concentrations was unclear. Field level studies and studies focusing on the mechanisms behind the changes in nutrient losses are needed.
  • Akinori Yamamoto, Yoshitaka Uchida, Hiroko Akiyama, Yasuhiro Nakajima
    RAPID COMMUNICATIONS IN MASS SPECTROMETRY 28 (13) 1444 - 1452 0951-4198 2014/07 [Refereed][Not invited]
    RATIONALEThe difference between the 15N natural abundance of 14N-15N-O and 15N-14N-O (site preference; SP) is used to understand the mechanisms underlying N2O emissions from soils. We investigated the use of quantum cascade laser (QCL) absorption spectrometry for continuous and precise analysis of the SP of N2O emitted from a field soil at atmospheric mixing ratios. METHODSA QCL-based spectrometer was used to determine the SP of soil-emitted N2O accumulated in a closed chamber system without preconcentration. N2O standards (<2500 ppbv) were used to evaluate the precision of the QCL spectrometry (QCLS) system. CO2 and H2O were removed from the gas samples. Intercomparison measurements of QCLS and isotope ratio mass spectrometry (IRMS) were performed on N2O calibration gases at different mixing ratios. The observed dependency of the QCLS result on the N2O mixing ratio was corrected. RESULTSMeasurement of SP of N2O emitted from the field suggested that the SP of N2O varied from 0 to 40 parts per thousand over a period of 1month. The precisions of the SP measurements (300-2500 ppbv) were <1.9 parts per thousand for 15N values, <2.6 parts per thousand for 15N values, <2.1 parts per thousand for 15Nbulk values, and <2.1 parts per thousand for the SP (1min averaging time) obtained on a once-an-hour calibrated QCLS system, with a cell temperature control precision of +/- 0.01K. CONCLUSIONSContinuous and unattended measurements of the SP of N2O emitted from soils were achieved at low N2O mixing ratios. The accuracy of the QCLS measurements for the SP of N2O was significantly improved by precisely controlling the temperature of the system and by correcting for the concentration dependency of the raw data through an intercomparison with IRMS measurements. Copyright (c) 2014 John Wiley & Sons, Ltd.
  • Yoshitaka Uchida, Yong Wang, Hiroko Akiyama, Yasuhiro Nakajima, Masahito Hayatsu
    FEMS MICROBIOLOGY ECOLOGY 88 (2) 407 - 423 0168-6496 2014/05 [Refereed][Not invited]
    The contributions of large N2O pulses following waterlogging to the annual cumulative N2O productions were significant in a Fluvisol. To uncover the mechanisms underlying these large N2O pulses, a Fluvisol sampled from an agricultural field in Japan was subjected to waterlogging during incubation. Larger N2O emissions were observed in intact soil cores when compared to emissions from sieved soils, indicating the importance of soil properties. The most important factor controlling the magnitude of the N2O pulses after waterlogging was the soil moisture prior to waterlogging. The major pathway for N2O production was denitrification. Quantitative PCR and quantitative RT-PCR analyses showed that the denitrification genes (nirS, nirK, and nosZ) correlated with N2O emissions at the mRNA level but not at the DNA level. The change in denitrification gene mRNA levels was more prominent in the 0- to 1-cm soil compared with the 1- to 3-cm soil. Water-soluble and hot-water-soluble carbon contents also showed the highest amount in the 0- to 1-cm soil. These indicate that there was a strong variation in soil microbial properties over very small changes in soil depth, and this variation is important in determining the magnitude of N2O emissions.
  • Manabu Itakura, Yoshitaka Uchida, Hiroko Akiyama, Yuko Takada Hoshino, Yumi Shimomura, Sho Morimoto, Kanako Tago, Yong Wang, Chihiro Hayakawa, Yusuke Uetake, Cristina Sánchez, Shima Eda, Masahito Hayatsu, Kiwamu Minamisawa
    Nature Climate Change 3 (3) 208 - 212 1758-678X 2013/03 [Refereed][Not invited]
    Nitrous oxide (N2O) is a greenhouse gas that is also capable of destroying the ozone layer1. Agricultural soil is the largest source of N2O (ref.). Soybean is a globally important leguminous crop, and hosts symbiotic nitrogen-fixing soil bacteria (rhizobia) that can also produce N2O (ref.). In agricultural soil, N2O is emitted from fertilizer and soil nitrogen. In soybean ecosystems, N2O is also emitted from the degradation of the root nodules4. Organic nitrogen inside the nodules is mineralized to NH4+, followed by nitrification and denitrification that produce N2O. N2O is then emitted into the atmosphere or is further reduced to N2 by N2O reductase (N2OR), which is encoded by the nosZ gene. Pure culture and vermiculite pot experiments showed lower N2O emission by nosZ+ strains5 and nosZ++ strains (mutants with increased N2OR activity)6 of Bradyrhizobium japonicum than by nosZ-strains. A pot experiment using soil confirmed these results7. Although enhancing N2OR activity has been suggested as a N 2O mitigation option8,9, this has never been tested in the field. Here, we show that post-harvest N2O emission from soybean ecosystems due to degradation of nodules can be mitigated by inoculation of nosZ+ and non-genetically modified organism nosZ++ strains of B. japonicum at a field scale. Copyright © 2013 Macmillan Publishers Limited.
  • Manabu Itakura, Yoshitaka Uchida, Hiroko Akiyama, Yuko Takada Hoshino, Yumi Shimomura, Sho Morimoto, Kanako Tago, Yong Wang, Chihiro Hayakawa, Yusuke Uetake, Cristina Sánchez, Shima Eda, Masahito Hayatsu, Kiwamu Minamisawa
    Nature Climate Change 3 (3) 208 - 212 1758-678X 2013/03 [Refereed][Not invited]
    Nitrous oxide (N2O) is a greenhouse gas that is also capable of destroying the ozone layer1. Agricultural soil is the largest source of N2O (ref.). Soybean is a globally important leguminous crop, and hosts symbiotic nitrogen-fixing soil bacteria (rhizobia) that can also produce N2O (ref.). In agricultural soil, N2O is emitted from fertilizer and soil nitrogen. In soybean ecosystems, N2O is also emitted from the degradation of the root nodules4. Organic nitrogen inside the nodules is mineralized to NH4+, followed by nitrification and denitrification that produce N2O. N2O is then emitted into the atmosphere or is further reduced to N2 by N2O reductase (N2OR), which is encoded by the nosZ gene. Pure culture and vermiculite pot experiments showed lower N2O emission by nosZ+ strains5 and nosZ++ strains (mutants with increased N2OR activity)6 of Bradyrhizobium japonicum than by nosZ-strains. A pot experiment using soil confirmed these results7. Although enhancing N2OR activity has been suggested as a N 2O mitigation option8,9, this has never been tested in the field. Here, we show that post-harvest N2O emission from soybean ecosystems due to degradation of nodules can be mitigated by inoculation of nosZ+ and non-genetically modified organism nosZ++ strains of B. japonicum at a field scale. Copyright © 2013 Macmillan Publishers Limited.
  • Yoshitaka Uchida, Isabell von Rein, Hiroko Akiyama, Kazuyuki Yagi
    SOIL SCIENCE AND PLANT NUTRITION 59 (1) 46 - 55 0038-0768 2013/02 [Refereed][Not invited]
    Nitrogen (N) fertilizers applied on agricultural fields are an important source of nitrous oxide (N2O). The use of coated fertilizer is known to mitigate fertilizer derived N2O emissions; however, according to previous studies, the effectiveness of coated fertilizer as a mitigation option varies depending on the soil types. We hypothesized that this variability was due to the contribution of nitrification and denitrification to N2O emissions depending on the soil and fertilizer types. Two contrasting Japanese soils, Andosol and Fluvisol, were repacked in columns and treated with either urea or coated urea, and soil N2O emissions were monitored for 30 days at 55% water-filled pore space under laboratory conditions. Contribution of nitrification and denitrification to N2O emissions were determined for soils without fertilizer application and for soils at 7 and 28 days after urea or coated urea application, using a 15N tracer technique. The results imply that >60% and >80% of N2O emissions in Andosol were derived from nitrification at 7 and 28 days after application, respectively, regardless of the fertilizer types used. In Fluvisol, nitrification-derived N2O contributed 59 +/- 55% and 82 +/- 8% of soil N2O emissions at 7 and 28 days after application, respectively, when coated urea was applied, whereas the domination of nitrification-derived N2O to soil N2O emissions was not observed when urea was applied to Fluvisol. Soil ammonium () was depleted at 4 weeks after fertilizer application in Andosol, but was still available in Fluvisol at the same period, regardless of fertilizer types used. In Andosol, nitrification-derived N2O emissions increased when the availability was high but this was not the case for Fluvisol, when urea was applied, and we believe that the response of nitrifying microbes to the amount of available controls the differing trend of N2O emissions after the application of urea or of coated urea.
  • Yoshitaka Uchida, Hiroko Akiyama
    Soil Science and Plant Nutrition 59 (4) 477 - 487 0038-0768 2013 [Refereed][Not invited]
    In this review, the current knowledge of nitrous oxide (N2O) emissions from soybean (Glycine max (L.) Merr.) ecosystems, particularly on postharvest N2O emissions, is summarized and controlling factors of postharvest N2O emissions from soybean ecosystems are discussed. A new biological method to mitigate N2O emission is also presented. The latest (2006) guidelines of the Intergovernmental Panel on ClimateChange (IPCC) concluded that N2O emissions derived directly from biological nitrogen (N) fixation were not significant in legume crop ecosystems. The default N2O emission factor from biological N fixation was revised to zero, whereas the default N2Oemission factor for the decomposition of legume crop residues (postharvestN2Oemissions) was the same as that for nonlegume crop residues (1%). From previously measured field data, the percentage of N in soybean residue emitted as N2O after harvest was calculated to determine emission factors. Values ranged from 0.0- 10.0%(average 1.3%± 2.7%, median: 0.2%), indicating relatively low emission factors. The average emission factor calculated for N2O emissions from N in soybean residues was slightly higher than the default emission factor for N in crop residue specified in the guidelines. However, the volume of field-measured postharvest N2O emissions in soybean ecosystems is low compared with data for N2O emissions during the crop growing season. Previous field-measured data demonstrated that N2O emissions often peaked sharply immediately after the harvest. However, values for N2O fluxes in the currently available field data were determined on a weekly or monthly basis. This large time gap between samplings may have resulted in underestimation of postharvest N2O emissions in soybean ecosystems. More detailed field studies on postharvest N2O emissions from soybean ecosystems are needed. Nodule decomposition is the major source of postharvest N2O emissions in soybean ecosystems. A new microbiological method was recently developed to mitigate postharvest N2O emissions from soybean ecosystems utilizing N-fixing bacteria with increased N2O-reducing activity (increased expression of nosZ). This approach may potentially be applied to other leguminous crops and non-legume ecosystems. Ongoing research on the relationships between soil N2O emissions and nosZ may reveal a new method for N2O mitigation in the future. © 2013 Japanese Society of Soil Science and Plant Nutrition.
  • Yoshitaka Uchida, Seiichi Nishimura, Hiroko Akiyama
    AGRICULTURE ECOSYSTEMS & ENVIRONMENT 156 116 - 122 0167-8809 2012/08 [Refereed][Not invited]
    Factors controlling soil respiration (R-S) are of great interest because R-S plays a Critical role in determining global atmospheric carbon dioxide (CO2) concentrations. Substrate availability is one of the most important factors controlling R-S. Soil microorganisms consume various substrates ranging from simple sugars supplied by aboveground photosynthesis to complex humic acids in soil organic matter; however, substrate decomposition rates depend on substrate availability. Thus, R-S is partly determined by the amount and quality of available substrate. However, accurate quantification of the amount of available substrate is difficult because soil microorganisms utilize carbon (C) substrates of varying quality for R-S. Watersoluble C (WSC), hot-water-soluble C (HWSC), and microbial biomass C are known as indicators of the amount of available soil C substrate. We continuously measured R-S in two contrasting soils, Andosol and Fluvisol, during the cultivation of soybean and brassica crops with a 6-month fallow period between them. The total annual R-S in Andosol and Fluvisol were 376 +/- 23 and 408 +/- 49 g CO2-C m(-2), respectively, with no significant difference between them. WSC and HWSC were measured every month during R-S measurement. During the soybean growth period, R-S and WSC were correlated, and soil type did not affect R-S. During the fallow period, R-S, HWSC and microbial biomass C in Fluvisol were higher than those in Andosol, despite the total soil C in Andosol being higher than that in Fluvisol. R-S during brassica crop growth was not correlated with any of the measured substrate indicators. We therefore concluded that the relationships among the measures of available substrates and R-S at the field level could provide vital information on seasonal changes in the interaction between the effects of soil type and plants on R-S, thereby leading to a better understanding of belowground C dynamics. (C) 2012 Elsevier B.V. All rights reserved.
  • Yumi Shimomura, Sho Morimoto, Yuko Takada Hoshino, Yoshitaka Uchida, Hiroko Akiyama, Masahito Hayatsu
    MICROBES AND ENVIRONMENTS 27 (1) 94 - 98 1342-6311 2012/03 [Refereed][Not invited]
    Ammonia monooxygenase subunit A gene (amoA) is frequently used as a functional gene marker for diversity analysis of ammonia-oxidizing bacteria (AOB). To select a suitable amoA primer for real-time PCR and PCR-denaturing gradient gel electrophoresis (DGGE), three reverse primers (degenerate primer amoA-2R; non-degenerate primers amoA-2R-GG and amoA-2IR) were examined. No significant differences were observed among the three primers in terms of quantitative values of amoA from environmental samples using real-time PCR. We found that PCR-DGGE analysis with the amoA-2IR primer gave the best results in this studied soil. These results indicate that amoA-2IR is a suitable primer for community analysis of AOB in the environment.
  • Yoshitaka Uchida, Timothy J. Clough, Francis M. Kelliher, John E. Hunt, Robert R. Sherlock
    PLANT AND SOIL 345 (1-2) 171 - 186 0032-079X 2011/08 [Refereed][Not invited]
    Grazing ruminants urinate and deposit N onto pastoral soils at rates up to 1,000 kg ha(-1), with most of this deposited N present as urea. In urine patches, nitrous oxide (N2O) emissions can increase markedly. Soil derived CO2 fluxes can also increase due to priming effects.While N2O fluxes are affected by temperature, no studies have examined the interaction of pasture plants, urine and temperature on N2O fluxes and the associated CO2 fluxes. We postulated the response of N2O emissions to bovine urine application would be affected by plants and temperature. Dairy cattle urine was collected, labelled with N-15, and applied at 590 kg N ha(-1) to a sub-tropical soil,with and without pasture plants at 11A degrees, 19A degrees, and 23A degrees C. Over the experimental period (28 days), 0.2% (11A degrees C with plants) to 2.2% (23A degrees C with plants) of the applied N was emitted as N2O. At 11A degrees C, plants had no effect on cumulative N2O-N fluxes, whereas at 23A degrees C, the presence of plants significantly increased the flux, suggesting plant-derived C supply affected the N2O producing microbes. In contrast, a significant urine application effect on the cumulative CO2 flux was not affected by varying temperature from 11-23A degrees C or by growing plants in the soil. This study has shown that plants and their responses to temperature affect N2O emissions from ruminant urine deposition. The results have significant implications for forecasting and understanding the effect of elevated soil temperatures on N2O emissions and CO2 fluxes from grazed pasture systems.
  • Hiroko Akiyama, Yoshitaka Uchida, Akinori Yamamoto
    ACS Symposium Series 1072 165 - 178 1947-5918 2011 [Refereed][Not invited]
    This chapter describes field measurement techniques and mitigation options for methane (CH4) and nitrous oxide (N2O). Of the currently available technologies, the most potent and feasible options for mitigating CH4 from paddy rice fields are mid-season drainage and off-season rice straw application (i.e., rice straw from a previous season is incorporated into the soil long before cultivation) and the use of nitrification inhibitors to mitigate N2O emission from agricultural fields. Mid-season drainage and rice straw management were estimated to reduce global CH4 emission by 16% each. If both of these mitigation options were adopted, the global CH4 emission from rice paddies would be reduced by 30%. According to meta-analysis of field data, nitrification inhibitors significantly reduced N2O emission from agricultural fields (mean effect: -38%) compared with that of conventional fertilizers. © 2011 American Chemical Society.
  • N. Brueggemann, A. Gessler, Z. Kayler, S. G. Keel, F. Badeck, M. Barthel, P. Boeckx, N. Buchmann, E. Brugnoli, J. Esperschuetz, O. Gavrichkova, J. Ghashghaie, N. Gomez-Casanovas, C. Keitel, A. Knohl, D. Kuptz, S. Palacio, Y. Salmon, Y. Uchida, M. Bahn
    BIOGEOSCIENCES 8 (11) 3457 - 3489 1726-4170 2011 [Refereed][Not invited]
    The terrestrial carbon (C) cycle has received increasing interest over the past few decades, however, there is still a lack of understanding of the fate of newly assimilated C allocated within plants and to the soil, stored within ecosystems and lost to the atmosphere. Stable carbon isotope studies can give novel insights into these issues. In this review we provide an overview of an emerging picture of plant-soil-atmosphere C fluxes, as based on C isotope studies, and identify processes determining related C isotope signatures. The first part of the review focuses on isotopic fractionation processes within plants during and after photosynthesis. The second major part elaborates on plant-internal and plant-rhizosphere C allocation patterns at different time scales (diel, seasonal, interannual), including the speed of C transfer and time lags in the coupling of assimilation and respiration, as well as the magnitude and controls of plant-soil C allocation and respiratory fluxes. Plant responses to changing environmental conditions, the functional relationship between the physiological and phenological status of plants and C transfer, and interactions between C, water and nutrient dynamics are discussed. The role of the C counterflow from the rhizosphere to the aboveground parts of the plants, e. g. via CO2 dissolved in the xylem water or as xylem-transported sugars, is highlighted. The third part is centered around belowground C turnover, focusing especially on above-and belowground litter inputs, soil organic matter formation and turnover, production and loss of dissolved organic C, soil respiration and CO2 fixation by soil microbes. Furthermore, plant controls on microbial communities and activity via exudates and litter production as well as microbial community effects on C mineralization are reviewed. A further part of the paper is dedicated to physical interactions between soil CO2 and the soil matrix, such as CO2 diffusion and dissolution processes within the soil profile. Finally, we highlight state-of-the-art stable isotope methodologies and their latest developments. From the presented evidence we conclude that there exists a tight coupling of physical, chemical and biological processes involved in C cycling and C isotope fluxes in the plant-soil-atmosphere system. Generally, research using information from C isotopes allows an integrated view of the different processes involved. However, complex interactions among the range of processes complicate or currently impede the interpretation of isotopic signals in CO2 or organic compounds at the plant and ecosystem level. This review tries to identify present knowledge gaps in correctly interpreting carbon stable isotope signals in the plant-soil-atmosphere system and how future research approaches could contribute to closing these gaps.
  • Yoshitaka Uchida, John E. Hunt, Margaret M. Barbour, Timothy J. Clough, Francis M. Kelliher, Robert R. Sherlock
    PLANT AND SOIL 337 (1-2) 375 - 387 0032-079X 2010/12 [Refereed][Not invited]
    Despite abundant literature, the predicted response of soil respiration (R (S)) to soil temperature (T (S)) remains uncertain. We aimed to quantify the temperature dependency of soil respired CO(2) derived from organic matter (R (OM)), and investigated the relationship between the R (OM) responses to temperature, soil properties, and vegetation, using a natural (13)C abundance technique. Using pastoral soils of contrasting properties (termed low and high fertility) and by growing C(4) or C(3) grass species in soils with a different isotope signature, we measured the temperature sensitivity of R (OM) and R (S). In the low fertility soil, with plants, R (OM) rate was constant at T (S) ranging 13-27A degrees C but root-derived respiration (R (RD)) rate increased similar to 4 times when T (S) increased from 13 to 27A degrees C. In the high fertility soil, with plants, both R (RD) and R (OM) rates doubled as T (S) increased from 17-27A degrees C. When T (S) was increased, without plants present, from 13 to 27A degrees C, R (OM) rates increased similar to 3 times in both the high and low fertility soils, hence soil properties did not affect the temperature sensitivity of R (OM) when plants were absent. Our results did not support the idea of a universal nor simple relation between temperature and CO(2) production in soils.
  • Yoshitaka Uchida, Timothy J. Clough, Francis M. Kelliher, Robert R. Sherlock
    AUSTRALIAN JOURNAL OF SOIL RESEARCH 48 (5) 395 - 403 0004-9573 2010 [Refereed][Not invited]
    A relationship between soil respiration rate (R(s)) and temperature (T(s)), has been understood to be predicated on carbon (C) substrate availability. However, unlike T(s), C availability in soils is not a state variable that can be readily measured. The C in soils has come from plants, so the C supply rate can be affected by the weather and nutrient supply. We studied a fertile soil beneath pasture, measuring R(s) across a temperate - climate range of T(s). Our objectives were to: (1) quantify the synchrony of diurnal changes in T(s) and R(s) beneath pasture under conditions favourable for plants, (2) quantify responses of microbial respiration (R(m)) to the removal of plants and depletion of C supply over time at various T(s), and (3) determine if R(m) was related to water-soluble (WSC, 20 degrees C) and hot-water-soluble C (HWSC, 80 degrees C) contents. At a grassland site, R(s) increased with T(s) as predicted by an Arrhenius type relationship. Sampled soil was incubated at 3 degrees, 9 degrees, and 24 degrees C and R(m) was measured over 14 days. In addition soil samples were pre-incubated at 3 degrees or 9 degrees C for both 5 and 14 days, then incubated at 24 degrees C for 1 day and R(m) was measured. On day 2, R(m) was less than predicted at 24 degrees and 9 degrees C, respectively, suggesting a C availability limitation. The time courses of R(m), revealed that at 24 degrees C, R(m) utilised C that was not utilised at lower T(s), indicating that evidently recalcitrant C was available to microbes at a warmer temperature. The responses of R(m) at 24 degrees C after the pre-incubation treatments were identical for the 3 degrees C and 9 degrees C pre-incubation treatments, although significantly more C was respired during pre-incubation at 9 degrees C. The WSC and HWSC contents were unaffected by T(s), so did not provide useful measures of the C substrate available for R(m).
  • Yoshitaka Uchida, Tim J. Clough, Francis M. Kelliher, Robert R. Sherlock
    SOIL BIOLOGY & BIOCHEMISTRY 40 (4) 924 - 931 0038-0717 2008/04 [Refereed][Not invited]
    The dominant N2O emission source in New Zealand, calculated using the Intergovernmental Panel on Climate Change methodology, is agricultural soils. The largest source of N2O emissions in New Zealand occurs as a result of excreta deposition onto pasture during grazing. There is a dearth of studies examining the effect of soil compaction and soil aggregate size on N2O emissions from urine patches in grazed pastures. In this study, we repacked soil cores with four different soil aggregate sizes (< 1.0-5.6 mm diameter), applied bovine urine, and then subjected the soil cores to four levels of soil compaction. Fluxes of N2O were monitored for 37 days after which soil cores were allowed to dry out prior to a rewetting event. There was an interaction between aggregate size and soil compaction with the cumulative loss of N2O over the first 37 days ranging from 0.3% to 9.6% of the urine-N applied. The highest N2O emissions occurred from the smallest and most compacted aggregates. Even under the highest levels of compaction the NO loss front the large aggregates (4.0-5.6 mm diameter) was < 1% of the urine-N applied. Reasons for the observed differences in the N2O flux from the different-sized aggregates included varying gas diffusivities and higher rates of denitrification in the smallest aggregates, as evidenced by the disappearance of nitrate. (C) 2007 Elsevier Ltd. All rights reserved.


Research Projects

  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2022/04 -2025/03 
    Author : 山本 昭範, 常田 岳志, 内田 義崇
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2021/04 -2024/03 
    Author : 内田 義崇, 龍見 史恵
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2018/10 -2023/03 
    Author : 内田 義崇, 多胡 香奈子, 山本 昭範
    申請者らは、サブサハラアフリカにおける農地開発が土壌微生物コミュニティーの構造および機能にどのように影響を与えるかを調べてきた。これまでの研究では、硝化ポテンシャルはサイトの影響を大きく受けるが、同一サイト内では農地開発によって高くなる傾向が明らかになってきており、鍵となる硝化菌の種に着目して今年度は硝化機能遺伝子amoAの種レベルでのコミュニティー解析を進めた。その結果、硝化ポテンシャルが低いサイトでは、農地開発によってNitrosospira multiformisの相対存在量が増加しNitrosospira sp. Wyke8の相対的存在量が減少した。現在、これらの変動が土壌の硝化ポテンシャルとどのように関連しているのかについて解析を行っている。さらに、複数のザンビア産土壌を用いて、炭素投入(堆肥等)が土壌炭素動態や微生物多様性の変化にどのような影響を与えるかについても精緻に調査した。その結果、炭素投入の微生物多様性変化への影響は土壌によって大きく異なることがわかった。具体的には、炭素量が1%を上回り、水分保持力の大きい土壌においては、炭素投入の微生物への影響が小さくなり、炭素投入よりも水分量によって微生物多様性が変動することが定量された。また、炭素量が1%を下回るような極めて貧栄養な土壌においては、炭素投入による微生物量の増加、およびそれに伴う有機物分解速度の増加がより顕著であることも評価できた。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2018/04 -2023/03 
    Author : 石黒 宗秀, 波多野 隆介, 柏木 淳一, 内田 義崇, 荒木 肇
    本研究の目的は,肥料成分や放射性物質・界面活性剤・温室効果ガスなどの汚染物質の土壌中における動態を,土壌の表面特性と微生物活動に着目して明らかにし,その知見を用いて,土壌・水・大気保全技術を確立することである.本年度は,昨年度に引き続き次の研究を行った. 無肥料無農薬水田における窒素の動態に及ぼす中耕除草の影響を明らかにするために,無肥料無農薬水田において,中耕除草0回区,2回区,5回区を設定すると共に,化学肥料と農薬を使用する慣行区を設定し,比較検討した.3年目の本年度は,中耕除草回数が増加するに従い,稲の生育と収量が増加した.昨年までは相違が無かったため,土壌環境が徐々に良くなってきたものと思われる.しかし,窒素量に関しては,明瞭な相違は認められなかった.土壌が更に良好な状態になるにはあと数年必要と考えられた. 界面活性剤の吸着実験を行う際,土壌中の腐植物質が土壌水中に溶解し,それが吸光度測定による界面活性剤濃度の結果に影響する.その影響を取り除くために,可視光領域400nm波長の吸光度を利用することで,正確な測定が可能なことを明らかにした. 水田から排出されるCH4の温室効果ガス発生量を調べたところ,無肥料無農薬中耕除草区は,慣行区と比較して発生量が少なくなり,温室効果ガス削減に寄与する傾向を示した.中耕除草回数が最も多い5回区で,CH4の放出が多く,有機物分解が進むことが示唆された. 窒素固定能を持つ二つの微生物科が自然農法水田で相対的存在比が高いことを実証した.これらは,RhizobialesとRhodospirillalesである.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/04 -2022/03 
    Author : Koba Keisuke
    We developed the analytical setting of multi-isotope labelling of nitrogen compounds (MILNC) for N2O to elucidate the complex features of N2O productions and consumptions. We proposed the platform to measure 15N, 17O and 18O-labelled N2O by GC/MS, which allowed us to measure the production and consumption of N2O simultaneously. In addition, the process model we develop can facilitate the interpretation of the MILNC data to discuss the relative strength of production and consumption processes.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/04 -2021/03 
    Author : Araki Hajime
    The function of cover crop, which is a biological tool for sustainable agricultural production, was investigated from the biological properties of soil. Cover crops release nitrogen after incorporation into soil and contribute to the growth of subsequent crops. Surveys of kind and population soil nematodes have revealed that cover crop has created a bacterial-dominated environment and improved soil fertility. In nitrogen mineralization, β-glycosidase activity and soil microbial biomass, which became indicators of microbial activity, increased in bulk soil. The farming practice with cover crop and no-tillage also induced microbial variation, and aggregate size affected microbial species and organic matter degradation. In long-term practice, Rye (cover crop) and no-tillage system reduced the global warming potential. The soil properties and productivity were improved by increasing of soil carbon amount in soil.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2018/04 -2019/03 
    Author : 内田 義崇
    荒廃地土壌の生産性を回復させるためには、窒素が効率よく微生物により土壌へ固定されることが重要である。この研究では、サブサヘルアフリカで採取した荒廃地土壌において、先駆植物の根圏で窒素固定を行うコミュニティを明らかにする。本年度は、①ザンビアの荒廃地でAfrican fountain grass (Pennisetum setaceum)の根圏から採取した土壌や、②日本の荒廃地(都市部の建築現場跡地)における先駆作物の根圏土壌を用いた実験を行った。①に関しては、異なるDNA抽出法を試し、抽出法によって定量PCRや次世代シーケンサによる微生物群衆構造解析にバイアスが出ることが無いかを調査した。結果として、高額であり現地で手に入りにくい土壌DNA抽出キットを用いればより多くのDNAを抽出できるものの、群衆構造解析へのバイアスは少ないことがわかった。しかし、このことは定量PCRの結果が抽出法に強く影響を受けることを示唆しており、今後さらにサブサヘルアフリカで精緻な土壌微生物DNA研究を行っていく上で障壁となる。②に関しては、窒素固定微生物のDNA量を、定量PCRを用いて検証するための条件検討を行った。プライマはPo1FとPo1Rを用い、DNAの精製や希釈の条件などを検討した。結果として、AMPureを用いた精製を行うこと、プライマ濃度を高めることなどで、定量PCRによる土壌中窒素固定遺伝子の定量が成功することを明らかにした。また、ポプラ(Populus)、スギナ(Equisetum arvense)、白クローバー(Trifolium repens)などの先駆植物の根圏土壌において、窒素固定遺伝子量に差が見られる可能性があることが示唆された。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2016/04 -2018/03 
    Author : Yoshitaka Uchida
    To evaluate soil fertility, changes in soil microbial communities before and after the application of organic matter were evaluated. First, the comparison between organically farmed and conventionally farmed soil was performed. We used rice straw as an organic matter. In the next experiment, we evaluated using one soil but with different organic matter sources. We showed that the timing and application rates of soil organic matter were critically important in controlling soil microbial communities. To evaluate nitrogen cycle, we also investigated the flow of ammonium-nitrogen and nitrate-nitrogen. Interestingly, the flow and soil microbial community structures were correlated in one experiment but not for the other. Further studies are needed to research the mechanisms behind the different results.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2014/04 -2018/03 
    Author : Hashidoko Yasuyuki
    Active N2O emitting microorganisms were searched for, at the soils from reclaimed tropical peatland in Malaysia, Andisol corn farmland in Hokkaido, and palsa mire-degrading boreal peat in Finland Lapland, all of which are known as active N2O emission hotspots. Resulting active N2O emitting bacteria were compared their physiological and biological traits. Burkholderia spp. isolated as a hyper-active N2O emitter from tropical peat soils s were missing nosZ genes, while 4 strains out of 10 active N2O emitting Pseudomonas spp. rather harbored weakly functional nosZ gene. In boreal peatland, particularly degrading palsa bogs, Rhizobium sp. and Serratia sp. mixed colonies had abilities to release N2O from NO2-. In investigation of N2O production-repressing chemicals, Paraquat and allylisothiocyanate showed relatively strong N2O-emission inhibitory effect. For further screening, several differentiation-inducing factors toward bacteria were isolated and identified.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2014/07 -2017/03 
    Author : Uchida Yoshitaka
    We used hairy vetch as an example of plant residue. Andosol and Fluvisol were used because they were common in Japan. Also, rice husk charcoal was evaluated. In Fluvisol, N2O emissions were higher when compared to those from Andosol. There was a possibility of nitrogen adsorption by rice husk charcoal. The amount of nitrate, links to water pollution, was higher in Andosol when compared to Fluvisol. In Fluvisol, denitrification rates could be larger. The molecular size distribution of organic-nitrogen, during the decomposition of hairy vetch was variable.

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