Seiichi Nishimura

Ammonia volatilization from the surface of a Japanese paddy field during rice cultivation

Abstract Ammonia (NH3) volatilization from the surface of a Japanese paddy field during rice cultivation was measured using the dynamic chamber method with a dry NH3 collector. A preliminary investigation showed that a dry NH3 collector with phosphoric-acid-impregnated filters could collect volatilized NH3 with sufficient efficiency. The experimental field included six lysimeter plots of Gray Lowland soil with a soil pH (H2O) of 5.7. Urea was applied as nitrogen fertilizer at a rate of 50 kg N ha−1 by incorporation with puddling into the plowed layer as the basal fertilization (BF) and at rates of 30 and 10 kg N ha−1 by top-dressing as the first (AF1) and second (AF2) additional fertilizations, respectively. Relatively strong NH3 volatilization occurred immediately after AF1 with a maximum flux of 45 g N ha−1 h−1. In contrast, the NH3 volatilization fluxes following BF or AF2 were weaker. The ammonium (NH+ 4) concentration and the flooded water table were found to be major factors influencing NH3 volatilization; higher NH3 volatilization fluxes were often observed with a higher NH+ 4 concentration in floodwater and a lower water table. Incorporation of urea with puddling resulted in lower NH+ 4 concentrations in floodwater than in the case of top-dressing application, which likely resulted in fewer NH3 volatilization fluxes after BF than after AF1 and AF2. In contrast, relatively strong NH3 volatilization occurred in the plots immediately drained after AF1, which suggested that a top-dressing application under nearly drained conditions enhanced NH3 volatilization. The ratio of NH3 volatilization loss to applied nitrogen for each application of fertilization was 0.2 ± 0.1, 3.8 ± 2.2 and 0.7 ± 0.5% for BF, AF1 and AF2, respectively. In addition, the total ratio of NH3 volatilization loss to total applied nitrogen throughout rice cultivation was estimated to be 1.4 ± 0.8%. These values were smaller than those reported from other Asian paddy fields, with the exception of the maximum NH3 loss after AF1, 9.0%, which was comparable to the minimum NH3 loss reported in Asian paddy fields. The application rates of nitrogen fertilizer in the present study were smaller than those in Asian paddy fields, although they are conventional for Japan. In conclusion, the very small values of NH3 volatilization recorded in the present were ascribed to the small rates of urea application per fertilization, which restrained increases in NH+ 4 concentrations in floodwater, and to the relatively low soil pH, which resulted in prevention of NH+ 4 dissociation in floodwater.

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.

Nitrous oxide evolved from soil covered with plastic mulch film in horticultural field

Soil solarization practice, in which soil is covered with plastic mulch film and exposed to high temperature prior to crop cultivation, is expected to be an effective method for reducing weeds and pathogenic microorganisms without using agricultural chemicals. Although the production of nitrous oxide (N2O), a major greenhouse gas, is enhanced in fertilized soil covered with plastic mulch films, its transport route to the atmosphere has not been sufficiently elucidated to date. In this study, we investigated the N2O evolution from plastic-mulch-film-covered agricultural soil. In a horticultural field where ridge soil was covered with a plastic mulch film after fertilization, we observed significant N2O flux from the soil surface of the unfertilized furrow between the ridges, indicating the horizontal diffusion of N2O from the ridge soil covered with the mulch film to the adjacent furrow soil surface. On the other hand, the measurement of the permeance (permeation coefficient) of the plastic mulch film for gaseous N2O by laboratory experiment revealed that N2O gradually permeated the mulch film; the permeance increased exponentially with an increase in ambient temperature, indicating possible N2O emission by permeation through the mulch film under field conditions. In winter, the amount of N2O emission by permeation through the mulch film was estimated to be lower than that emitted from the furrow soil surface, and it was lower than that in summer. On the other hand, it was estimated to be much higher in summer owing to the higher permeance of the film at high temperatures.

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.

Upward diffusion of nitrous oxide produced by denitrification near shallow groundwater table in the summer: a lysimeter experiment

Movement of nitrous oxide (N2O) produced in subsoil and shallow groundwater is important in determining the direct and indirect N2O emissions from agricultural soils. From the results of our previous study in a lysimeter-contained Gray lowland soil in the summer, we hypothesized that if a large amount of N2O is produced near shallow groundwater table in the summer, it will diffuse upward to the atmosphere. To examine this hypothesis, we conducted a one-year experiment in the same lysimeters for the cultivation of soybean–wheat double cropping (SW) or upland rice (UR). Dissolved N2O concentration in the drainage water in the UR plots exceeded 0.4 mg N L−1 in the summer, whereas that in the SW plots remained <0.1 mg N L−1. Analyses of the concentrations of nitrate and dissolved N2O in the drainage water and their nitrogen and oxygen isotopic compositions (δ15N and δ18O) during the summer revealed that denitrification was the main process for the N2O production near the groundwater table. There was a significant positive correlation between the dissolved N2O concentration and soil-surface N2O flux in the summer. Calculated upward diffusive N2O fluxes at three soil depths by Ficks law also supported our hypothesis. The δ15N values of N2O in the soil-surface flux were similar to those in the shallow groundwater in the UR plots during the summer. Such similarity was not found in the SW plots. We conclude that our hypothesis was confirmed by the above results. Comparison of the monitored data with other seasons indicates that low soil water content was a driving force for the upward N2O diffusion as well as the high dissolved N2O concentration.

Groundwater-induced emissions of nitrous oxide through the soil surface and from subsurface drainage in an Andosol upland field: A monolith lysimeter study

Nitrous oxide (N2O) produced in shallow groundwater has two emission pathways to the atmosphere: dissolution in subsurface drainage and groundwater and later degassing from water surfaces open to the atmosphere, and upward gas diffusion. N2O undergoing upward diffusion through the soil surface cannot usually be distinguished from N2O produced in the topsoil. To evaluate the emission pathway and rate of groundwater-induced N2O, we conducted a one-year experiment using monolith lysimeters containing 1 m-long undisturbed Andosol. We measured emission of N2O via the soil surface and dissolved N2O emitted via subsurface drainage from the non-planted lysimeters under two conditions without fertilizer-nitrogen (N) addition: (1) with the groundwater table at 0.9 m depth (GW), and (2) without any groundwater table (nonGW). Total soil surface N2O emissions in the GW and nonGW treatments were 21.0 ± 6.3 and 17.0 ± 1.1 mg N m–2 yr–1, respectively (mean ± standard error, n = 3), and the difference between the two treatments was not significant. Total dissolved N2O emissions via drainage in the GW and nonGW treatments were 11.40 ± 5.68 and 0.42 ± 0.03 mg N m–2 yr–1, respectively. The presence of groundwater significantly increased dissolved N2O emission under zero fertilizer-N addition. This is due to the one to three orders of magnitude higher concentration of dissolved N2O in the GW treatment. Our results indicate that the presence of groundwater increases total N2O emissions from an Andosol upland field via these two pathways.

Seasonal and diurnal variations in net carbon dioxide flux throughout the year from soil in paddy field

In contrast to upland croplands, carbon dioxide (CO2) emission from soils has rarely been investigated previously in fields with paddy rice cultivation. In this study, we hypothesized that CO2 emission from paddy soils is suppressed to be a low level due the soil submergence for months for paddy rice cultivation and conducted a continuous measurement of net CO2 flux from the soil/water surface of a paddy field throughout the year, including both the submerged and drained periods. The net CO2 flux was generally near zero during the submerged period with paddy rice cultivation and showed a slight CO2 influx in the daytime and efflux at nighttime, indicating dominance of photosynthetic CO2 uptake and respiratory CO2 release by aquatic weeds and algae in paddy water. The diurnal variations in net CO2 flux and dissolved CO2 concentration had negative correlations with the pH of paddy water. A remarkably high CO2 efflux was observed during the period with intermittent drainage in summer. Unexpectedly, the cumulative CO2 emissions throughout the year were not considerably lower than those reported in upland croplands ranging from 1309 to 2160 g CO2 m−2 yr−1, of which 41–48% was emitted from the first drainage in summer to the rice harvest in autumn. In summary, in this study, we revealed that CO2 emission from soil in paddy fields is strictly suppressed during the submerged period, but considerably enhanced by the succeeding drainage, which may negate the suppressed CO2 emission during the submerged period.

Time-lagged induction of N2O emission and its trade-off with NO emission from a nitrogen fertilized Andisol

Abstract To understand the influence of basal application of N fertilizer on nitrification potential and N2O and NO emissions, four soil samples were collected from an upland Andisol field just before (sample 1) and 4 (sample 2), 36 (sample 3) and 72 (sample 4) days after the basal application of N fertilizer during the Chinese cabbage growing season from 12 September to 30 November 2005. The potentials of N2O production and nitrification of the soils were determined using a 15N tracer technique and the soils were incubated for 25 days at 25°C and 60% water-filled pore space (WFPS). The results revealed that as much as 84–97% N2O and almost all NO were produced by nitrification. The 15N2O emission peak occurred approximately 350 h after the beginning of incubation for samples 1 and 2, but just 48 h later in samples 3 and 4. Total 15N2O emission during the 25-day incubation of samples 3 and 4 ranged from 190 to 198 µg N kg−1 soil, which was significantly higher than the 99–108 µg N kg−1 soil recorded in samples 1 and 2. Basal application of N fertilizer did not immediately increase the nitrification potential and the ratio of N2O to N added, but did dramatically increase the nitrification potential and the ratio of N2O to N added as (15NH4)2SO4 36–72 days after the basal N fertilizer was added. In contrast, NO emission was negatively correlated with nitrification potential and total N2O emission. As a result, a trade-off relationship between total NO and N2O emissions was identified. The results indicated that there was a time-lagged induction of the change of N turnover in the soil, which was possibly caused by slow population growth of the nitrifiers and/or a slow shift in the microbial community in the soil.

Trends of lettuce and carrot yields and soil enzyme activities during transition from conventional to organic farming in an Andosol

Abstract It has been reported that crop yields drop and then increase during the first few years of organic farming, and these yield recoveries have been attributed to gradual improvements in soil properties, such as soil microbial activities to mineralize nitrogen (N) or to suppress plant disease. To clarify whether yield increase during organic transition is caused by improvement of soil microbial activities, we compared identically managed organic and conventional plots of 1-year lettuce (Lactuca sativa L.)–carrot (Daucus carota L.) rotation for 3 years (organic plots: first 3 years after switching from conventional to organic management; conventional plots: managed in the same way as organic plots for 3 years but receiving chemical fertilizer, fungicide, insecticide and herbicide) in an Andosol field. During organic transition, yields of organic lettuce and carrots were lower than those of conventional lettuce and carrots for only the first year. Yield drop and recovery of lettuce were thought to be caused by changes in the amount of N uptake, though yield fluctuation of carrots was mainly caused by damage from insects. Although soil enzyme activities may be responsible for N mineralization, various soil enzyme activities promptly responded to organic amendment to become higher under organic management than under conventional management even after the first lettuce cropping (6 months after switching to organic management; much shorter than the period of organic transition). However, discriminant analysis using activities of six soil enzymes (dehydrogenase, β-glucosidase, β-galactosidase, α-glucosidase, cellulase and protease) indicated that 18–24 months (a period close to that of the organic transition) were needed for the pattern of various soil enzyme activities to be in a steady state after switching to organic management. The pattern of soil enzyme activities fluctuating to a plateau during the second lettuce cropping seemed to show a tendency similar to that of N uptake and yield of lettuce during organic transition. Soil available N in organic plots also became higher than that in conventional plots in the third year. These results suggested that improved N uptake and yield of lettuce during organic transition in an Andosol might be caused by either improvement in various soil enzyme activities or accumulation of soil available N. Yield response of carrots demanding less N was attributed not to N mineralization but to damage from insects.