Hiroko Akiyama

Global estimations of the inventory and mitigation potential of methane emissions from rice cultivation conducted using the 2006 Intergovernmental Panel on Climate Change Guidelines

[1] The Intergovernmental Panel on Climate Change (IPCC) regularly publishes guidelines for national greenhouse gas inventories and methane emission (CH 4 ) from rice paddies has been an important component of these guidelines. While there have been many estimates of global CH 4 emissions from rice fields, none of them have been obtained using the IPCC guidelines. Therefore, we used the Tier 1 method described in the 2006 IPCC guidelines to estimate the global CH 4 emissions from rice fields. To accomplish this, we used country-specific statistical data regarding rice harvest areas and expert estimates of relevant agricultural activities. The estimated global emission for 2000 was 25.6 Tg a -1 , which is at the lower end of earlier estimates and close to the total emission summarized by individual national communications. Monte Carlo simulation revealed a 95% uncertainty range of 14.8-41.7 Tg a -1 ; however, the estimation uncertainty was found to depend on the reliability of the information available regarding the amount of organic amendments and the area of rice fields that were under continuous flooding. We estimated that if all of the continuously flooded rice fields were drained at least once during the growing season, the CH 4 emissions would be reduced by 4.1 Tg a -1 . Furthermore, we estimated that applying rice straw off season wherever and whenever possible would result in a further reduction in emissions of 4.1 Tg a -1 globally. Finally, if both of these mitigation options were adopted, the global CH 4 emission from rice paddies could be reduced by 7.6 Tg a -1 . Although draining continuously flooded rice fields may lead to an increase in nitrous oxide (N 2 O) emission, the global warming potential resulting from this increase is negligible when compared to the reduction in global warming potential that would result from the CH 4 reduction associated with draining the fields.

Estimations of emission factors for fertilizer-induced direct N2O emissions from agricultural soils in Japan: Summary of available data

Abstract Agricultural fields are significant sources of anthropogenic atmospheric nitrous oxide (N2O). We compiled and analyzed data on N2O emissions from Japanese agricultural fields (246 measurements from 36 sites) reported in peer-reviewed journals and research reports. Agricultural fields were classified into three categories: upland fields, tea fields and rice paddy fields. In this analysis, data measured over a period of more than 90 days for upland fields and 209 days for tea fields were used to estimate annual fertilizer-induced emission factors (EF) because of limitations in the available data. The EF is defined as the emission from fertilized plots minus the background emission (emission from a zero-N control plot), and is expressed as a percentage of the N applied. The mean of N2O emissions from upland fields with well-drained soils was significantly lower than that from poorly drained soils. Mean (± standard deviation) N2O emissions measured over a period of more than 90 days from fertilized upland fields were 1.03 ± 1.14 kg N ha−1 and 4.78 ± 5.36 kg N ha−1 for well-drained and poorly drained soils, respectively. Because the ratio of the total areas of well-drained soils and poorly drained soils was different from the ratio of the number of available EF data for each soil category, we used a weighted mean to estimate EF for all upland fields. The EF was estimated to be 0.62 ± 0.48% for all fertilized upland fields. Mean N2O emissions and the estimated EF for fertilized tea fields measured over a period of more than 209 days were 24.3 ± 16.3 kg N ha−1 and 2.82 ± 1.80%, respectively. The mean N2O emission and estimated EF from Japanese rice paddy fields were 0.36 kg N ha−1 and 0.31 ± 0.31% for the cropping season, respectively. Significant uncertainties remain in these results because of limitations in the available data.

Combined emission of CH4 and N2O from a paddy field was reduced by preceding upland crop cultivation

Since crop rotation between paddy rice and upland crops is widely conducted in Japan and other Asian countries, the effect of crop rotation on greenhouse gas emission should be clarified. In this study, methane (CH4) and nitrous oxide (N2O) fluxes were simultaneously measured for two years from 2004 to 2005 in a paddy rice field with three different cultivation histories, i.e. consecutive paddy rice cultivation (PR), single cropping of upland rice (UR), and double cropping of soybean and wheat (SW) in the preceding two years from 2002 to 2003. In 2004, the cumulative CH4 emissions in the UR and SW plots were 511 and 2817 g CH4 m−2 y−1, which were 8 and 46%, respectively, of that in the PR plots (6092 g CH4 m−2 y−1). In 2005, the cumulative CH4 emissions in the UR and SW plots were 5123 and 1331 g CH4 m−2 y−1, which were 87 and 23%, respectively, of that in the PR plots (5893 g CH4 m−2 y−1), although the differences were not statistically significant. The soil reduction/oxidation potential (Eh) in the UR plots was higher than that in the PR plots in 2004. However, no distinctive differences in soil Eh among the three cropping systems were found in 2005. In the spring of 2004, the soil iron (Fe) content determined by extraction with dithionite-ethylenediaminetetraacetic acid (EDTA) solution was higher in the UR plots than in the PR and SW plots. However, no significant differences in Fe content among the three cropping systems were found in the spring of 2002 and 2005. The application of a relatively small amount of residue from the upland rice (c. 30% of that from the paddy rice) and the removal of all aboveground crop residues of soybean and wheat before paddy rice cultivation in 2004 could have contributed significantly to the low CH4 emissions in the UR and SW plots. In addition, change in the form of soil Fe during the preceding periods with upland crop cultivation may also have been related to the decreases in CH4 emission. The cumulative N2O emissions ranged from 39 to 99 mg N m−2 y−1, and showed no significant difference among the three cropping systems in 2004 and 2005. These results indicate that the combined CH4 and N2O emission from paddy soil is reduced by the introduction of the preceding upland crop cultivation when crop residue from the previous upland crop is small or removed before paddy rice cultivation, although this effect was expected only for one year just after the land use change from upland crop cultivation to paddy rice cultivation.

Development of a System for Simultaneous and Continuous Measurement of Carbon Dioxide, Methane and Nitrous Oxide Fluxes from Croplands Based on the Automated Closed Chamber Method

A system for simultaneous and continuous measurement of fluxes of three major greenhouse gases, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), from croplands was developed based on the closed chamber method. Controlled by a computer, top-lids of the chambers placed in the field closed periodically, remained closed for about 30 min, and then opened again. During the closure of the chambers, the air in the chambers was circulated by air pumps, and part of the circulated air was injected to gas analyzers. CO2 concentration was monitored with an infra-red gas analyzer, and its increasing/decreasing rate during the 1-3-min period after the chamber closure was used for the flux calculation. Concentrations of CH4 and N2O were measured with two gas chromatographs 4 times at intervals of 8.5 min. The system was tested in lysimeter fields with Gray lowland soil under various conditions, including paddy rice cultivation, upland crop cultivation and also fallow condition. Both CH4 and N2O concentrations in the chambers increased linearly or remained almost constant during the 30-min period after the chamber closure. CO2 concentration in the chambers also increased (which indicates the predominance of respiratory CO2 emission by the crops and/or soil microorganisms) or decreased (which indicates the predominance of photosynthetic CO2 uptake by the crops) linearly during the 1-3-min period after the chamber closure. These results indicated that appropriate fluxes could be estimated for all the three gases based on the gas concentration measurements with adequate time intervals, and on the linear regression analyses. The system is expected to be effective for clarifying the comprehensive dynamics of greenhouse gases in, and for estimating the total net global warming potential of croplands. Furthermore, simultaneous measurement of the fluxes of multiple gases is also effective for analyzing the mutual relationships and mechanisms of the gas fluxes. Changes in environmental factors such as increase in air temperature or decrease in light intensity during the chamber closure (generally referred to as “chamber effect”) should be taken into account as a cause of error in the flux data.

Comparison of indirect nitrous oxide emission through lysimeter drainage between an Andosol upland field and a Fluvisol paddy field

Indirect emission of nitrous oxide (N2O) due to nitrogen (N) leaching and runoff from agricultural soils is a major source of atmospheric N2O. To evaluate the effect of agricultural land use in combination with soil type on indirect N2O emission through groundwater, we compared the indirect N2O emission between an upland field of Andosol and a paddy field of Fluvisol in a 1-year lysimeter experiment. We established a shallow groundwater table during the non-flooded fallow period in the Fluvisol paddy field to simulate moisture conditions in a lowland soil. Drainage was 795 mm yr−1 (median, n = 6) in the Andosol upland field, versus 1583 mm yr−1 in the Fluvisol paddy field due to flooding during part of the year. The total leached nitrate in the Andosol upland field (4.24 g N m−2 yr−1) was comparable to that in the Fluvisol paddy field (5.57 g N m−2 yr−1). The total indirect N2O emission in the Fluvisol paddy field (88.6 mg N m−2 yr−1) was 55 times that in the Andosol upland field (1.62 mg N m−2 yr−1). The daily indirect N2O emission during the flooded period (0.239 mg N m−2 d−1) was comparable to that in the non-flooded period (0.156 mg N m−2 d−1) in the Fluvisol paddy field. The decrease in dissolved N2O concentration due to the flooding was offset by the increase in the drainage volume. The groundwater emission factors (EF5g) were 0.0003 in the Andosol upland field and 0.0160 in the Fluvisol paddy field versus the IPCC default value of 0.0025. Although the lysimeters had some limitations to simulate actual field conditions, the results indicate that agricultural land use in combination with soil type can strongly affect indirect N2O emission through groundwater.

Effects of Riparian Denitrification on Stream Nitrate-Evidence from Isotope Analysis and Extreme Nitrate Leaching during Rainfall-

The effects of riparian denitrification on stream nitrate were investigated by detailed soil water observations and isotope analysis at a small headwater catchment in an urban area near Tokyo, central Japan. In the base flow period, stream nitrate concentration (<100 µM) was comparable with that of riparian ground water which had less nitrate than unsaturated soil water. Nitrogen isotope analysis showed that the consumption of nitrate by denitrification took place in riparian ground water, suggesting that denitrification is an important process to control nitrate leaching to streams. During rainfall, the concentration of stream nitrate increased up to 400 µM, which was comparable with that of pre-event soil water. The fact that soil water nitrate directly leached to streams indicated that the riparian denitrification process did not work during rainfall because of the rapid discharge of water. A decrease of denitrification effects is a possible reason for high stream nitrate concentration during rainfall.

Automated sampling system for long-term monitoring of nitrous oxide and methane fluxes from soils.

Abstract We describe an automated gas sampling system for monitoring trace gas fluxes from soils. The sampling system allows automated collection of gas samples in glass vials using a syringe pump connected to an automated static chamber installed in the field. The gas samples are transferred to a laboratory and then analyzed using a gas chromatography system. Comparisons between manual and automated sampling of standard gases showed good agreement (r 2 = 0.99996 for N2O, r 2 = 0.999 for CH4 and r 2 = 0.998 for CO2). In a field test, replicated flux measurements using two chambers generally showed good agreement. The sampling system allows frequent and long-term monitoring of fluxes under a wide range of weather conditions (tested temperatures ranged from –6.5 to 40°C; 127 mm day−1 max precipitation). The major advantages of the system are its increased portability, ease of operation and cost effectiveness compared with on-line automated sampling/analytical systems.

Comparison among amoA Primers Suited for Quantification and Diversity Analyses of Ammonia-Oxidizing Bacteria in Soil

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.

An acid-tolerant ammonia-oxidizing γ-proteobacterium from soil

Nitrification, the microbial oxidation of ammonia to nitrate via nitrite, occurs in a wide range of acidic soils. However, the ammonia-oxidizing bacteria (AOB) that have been isolated from soil to date are acid-sensitive. Here we report the isolation and characterization of an acid-adapted AOB from an acidic agricultural soil. The isolated AOB, strain TAO100, is classified within the Gammaproteobacteria based on phylogenetic characteristics. TAO100 can grow in the pH range of 5–7.5 and survive in highly acidic conditions until pH 2 by forming cell aggregates. Whereas all known gammaproteobacterial AOB (γ-AOB) species, which have been isolated from marine and saline aquatic environments, are halophiles, TAO100 is not phenotypically halophilic. Thus, TAO100 represents the first soil-originated and non-halophilic γ-AOB. The TAO100 genome is considerably smaller than those of other γ-AOB and lacks several genes associated with salt tolerance which are unnecessary for survival in soil. The ammonia monooxygenase subunit A gene of TAO100 and its transcript are higher in abundance than those of ammonia-oxidizing archaea and betaproteobacterial AOB in the strongly acidic soil. These results indicate that TAO100 plays an important role in the nitrification of acidic soils. Based on these results, we propose TAO100 as a novel species of a new genus, Candidatus Nitrosoglobus terrae.

Effect of lime-nitrogen application on N2O emission from an Andosol vegetable field

Lime-nitrogen (calcium cyanamide, CaCN2) is used as a nitrogenous fertilizer, pesticide, and herbicide. During the process of decomposition of lime-nitrogen in the soil, dicyandiamide (DCD), a nitrification inhibitor, is formed. Therefore, lime-nitrogen application may mitigate nitrous oxide (N2O) emission from the soil. We conducted a field experiment to investigate the effect of lime-nitrogen on nitrification and N2O emission in fertilized soils, and a soil incubation experiment for further analysis of the effect of the lime-nitrogen. In a field experiment we compared four nitrogen (N) fertilizer treatments: CF (chemical fertilizer), LN100 (application of all N fertilizer as lime-nitrogen), LN50 (application of 50% of N as lime nitrogen and the remainder as chemical fertilizer), and CFD (chemical fertilizer with DCD). In a soil incubation experiment, we also studied two nitrogen treatments: CF and lime-nitrogen. Soil nitrification activity was lower in the LN100, LN50, and CFD plots than in the CF plot. The duration of this reduction in soil nitrification activity was longer in the LN100 plot than in the other plots. We found an apparent decrease in the N2O emission rate between 7 and 14 days after fertilization in the LN100, LN50, and CFD plots compared with that in the CF plot. This period of decreased N2O emission paralleled that when DCD was detected in the topsoil layers of the former three plots. Moreover, in the soil incubation experiment, cumulative N2O emission was significantly lower in the lime-nitrogen treatment than in the CF treatment, although the difference in cumulative N2O emission among the plots was not significant in the field experiment. Correlation analysis suggested that application of lime-nitrogen affects N2O emission by controlling both the first (ammonium to nitrite) and the second (nitrite to nitrate) soil nitrification reactions, whereas DCD blocks only the first nitrification reaction.