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Azolla microphyllaKaulf. (Azolla) biomass was composted to create a high nitrogen (N) organic matter amendment (Azolla compost). We examined the effect of this Azolla compost on carbon (C) and N mineralization and the production of biogenic gases, nitrous oxide (N2O) and carbon dioxide (CO2), in a soil incubation experiment. A pot experiment with upland kangkong (Ipomoea aquaticaForsk.) examined plant growth in silt loam soil treated with three levels of Azolla compost. The results showed that N2O production from soil increased with urea amendment, but not with Azolla compost treatments. The Azolla-amended soil showed enhanced CO2production throughout the 4-week incubation. The Azolla-treated soils showed a 98% lower global warming potential compared to urea treatment over the 4-week incubation. However, Azolla-amended soil had higher nitrate (NO3–) levels compared to urea-fertilized soil at 1 week of incubation, and these were maintained until the fourth week. Soils amended with Azolla compost showed lower ammonium nitrogen (NH4-N) levels than those in the urea-fertilized soils. The height and dry weight of upland kangkong fertilized with Azolla compost were similar to plants receiving urea fertilization. Therefore, the use of Azolla compost as a substitute for urea fertilizer would be beneficial for reducing the production of N2O while maintaining plant growth. [ABSTRACT FROM PUBLISHER]

In Japan, the total area covered by bamboo species has been increasing in recent years. A limited number of studies have been conducted to elucidate the changes in nutrient dynamics in forests invaded by bamboo species. Bamboo species are silica accumulators, taking up silica actively from the soil and accumulating most of the absorbed silica in the leaves. Therefore, it could be assumed that bamboo forests will absorb and return substantial amounts of silica to the soil especially when compared with forests in which non-silica accumulators are dominant (other types of forests). In addition, abundant silica uptake and return in bamboo forests might also change the available silica in the surface soil between bamboo forests and other types of forests. In this context, the silica content in litterfall and the available silica concentration in the surface soil from April 2004 to April 2005 were compared in forests invaded by bamboo species (Phyllostachys pubescensandP. bambusoides) and adjacent evergreen broad-leaved forest or coniferous forest in western Japan. The results showed that bamboo forests had a significantly higher silica content in litterfall through a year than the other two forest types and had a significantly higher available silica concentration in the surface soil from June to November in 2004 than the other two forest types. These findings suggest that when non-bamboo forests are invaded and dominated by bamboo species, the silica content in litterfall and the available silica concentration in the surface soil changes. [ABSTRACT FROM PUBLISHER]

The production/consumption of greenhouse gases (GHG) in soils are of great importance in global warming, but the involved soil physico-chemical and biological characteristics affecting GHG production and consumption potentials are poorly understood in different land-use types. Carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) production/consumption potentials from four land-use types and 10 soil types in central Japan and eastern Hungary, and their relationships with soil characteristics, were investigated. The average of CO2production in Japanese soils was significantly higher than that of Hungarian soils due to the relatively higher microbial biomass carbon (MBC) content. N2O production from both countries' soils did not exhibit a significant difference. Most soils except Japanese paddy and soybean soils showed the potentials for CH4consumption. Forest and grassland soils had relatively higher CO2and N2O production than orchard and cropland soils for both countries. From regression analyses, it could be concluded that soil total nitrogen (TN) and ammonium-nitrogen (NH4+-N) account for 40.8% and 25.5% variations of the soils' CO2and N2O productions, respectively. The CH4consumption was positively correlated with soil carbon/nitrogen (C/N) ratio, while soil MBC availability could account for 15% variation of CH4consumption under aerobic conditions. [ABSTRACT FROM AUTHOR]

To evaluate annual CO2 exchange rates in a wetland ecosystem, ecosystem respiration rate ( Re), net ecosystem productivity (NEP), and gross primary productivity (GPP) were investigated using the Closed Geosphere Experiment Facility (CGEF) located in northeastern Japan. The CGEF is highly airtight and equipped with a Geosphere Module (GM). The GM has a ground area of 5.8 × 8.7 m2 and an average height of 11.9 m, including a soil depth of 3.1 m. A wetland ecosystem dominated by Phragmites australis was introduced into the CGEF. Air temperature and CO2 concentration in the GM were controlled automatically. The hourly nighttime Re increased exponentially with the hourly average air temperature. Both hourly NEP and GPP depended on hourly photosynthetic photon flux density (PPFD). In addition, daily ecosystem CO2 exchange rates ( Re, NEP, and GPP) were influenced by above-ground plant biomass. The annual NEP was found to be 64.2 ± 19.2 g C m−2 yr−1 and it resulted from the annual GPP of 555.8 ± 17.0 g C m−2 yr−1 and annual Re of −491.6 ± 15.6 g C m−2 yr−1. Therefore, the wetland ecosystem behaved as a CO2 sink for the entire year. The annual CO2 exchange rates obtained were reasonable values compared to the findings of published studies in P. australis-dominated wild wetlands using the eddy covariance technique and the combined method of internal gas pressures and flow measurements and harvesting. [ABSTRACT FROM AUTHOR]

Upland blueberry (Vaccinium ashei Read.) requires acidic and organic matter rich soils for its cultivation. Recently, the raised bed cultivation system has widely been used for blueberry cultivation, but it has a potential to cause nitrogen (N) losses via leaching and nitrous oxide (N2O) emission especially with high rate of N application. We investigated the effects of organic amendments on N losses; via leaching ammonium ( ) and nitrate ( ) and N2O emission under acid soil conditions. The treatments were (i) ammonium sulfate application (AS), (ii) AS with peat moss (AS + PM), and (iii) AS with sawdust compost (AS + SD). A container (surface area: 47 cm × 40 cm = 0.188 m2) experiment to simulate raised bed cultivation system using an ochric Cambisol was conducted at Chiba University, Japan, during 2008 and 2009. A blueberry plant in each container received N fertilizer three times: 14.8, 23.8, and 14.8 g N m−2 in July 2008, March, and July 2009, respectively. Incorporation of peat moss and sawdust compost with ferrous sulfate effectively decreased soil pH to its optimal ranges (4.0–5.2) and resulted in increased growth and yield of blueberry (berry yield of 2009: 93, 285, and 348 g plant−1 in AS, AS + PM, and AS + SD treatment, respectively) due to increased soil porosity and consequently enhanced plant root biomass. Concurrently, the AS + SD treatment resulted in the least N losses, followed by AS + PM and AS treatment both through leaching and N2O emission. The emitted N2O amount over about two-year blueberry cultivation were 1.28, 0.80, and 0.58 g N m−2 for AS, AS + PM, and AS + SD treatments, respectively. These results indicated that application of organic amendments decreased N losses to the environment most likely due to increased plant N uptake, microbial N immobilization, and consequent reduction in nitrification, denitrification, and leaching. [ABSTRACT FROM PUBLISHER]

Fusarium wilt is caused by soil-borne pathogen Fusarium oxysporum. Tomato (Lycopersicon esculentum Mill.) is susceptible to Fusarium oxysporum f. sp. lycopersici race 1 and was infected with wilt disease. A pot experiment was conducted to investigate effects of inoculating arbuscular mycorrhizal (AM) fungus (Glomus etunicatium) on the microbial community in the rhizosphere soil and Fusarium wilt in tomato (cv. Oogatafukuju). The results indicated that AM fungal inoculation suppressed the Fusarium number in the rhizosphere soil of tomato and decreased the Fusarium wilt disease index. Compared to the control, AM fungal inoculation increased the actinomycete number but increased bacterial number. Bacterial and fungal numbers were high but actinomycetes number was low when tomato basal stems became discolored brown. Fusarium inoculation significantly suppressed development of AM colonization and decreased polyphenol oxidase (PPO) activity in leaves and roots of tomato. Inoculation with AM fungi and Fusarium maintained high PPO activity in leaves and roots. The AM colonization increased root growth of tomato, whereas Fusarium inoculation had no significant effect on tomato growth. These findings suggest that because AM fungal inoculation changes microbial communities and enhances PPO activity, it should suppress occurrence of Fusarium wilt in tomato. [ABSTRACT FROM AUTHOR]

To reduce nitrogen (N) loss from vegetable fields with minimum labor, the effects of a single application of different types of controlled mineralizing acetaldehyde condensation urea (CM-CDU) fertilizer on crop yield and N uptake, nitrate leaching from the surface soil (0–20 cm) and N2O emission from the soil after two continuous croppings of a leafy vegetable (komatsuna, Brassica napa L.) were examined. The following four treatments were established in plastic containers filled with an Andisol: urea, CM-CDU-4, CM-CDU-10 at a rate of 30 g N m−2 and a control (no N fertilizer). The CM-CDU-4 and CM-CDU-10 treatments released 80% of N at 25°C in 30–60 and 90–140 days after fertilizer application, respectively. The yields for the two crops were 1.55, 1.55, 1.26 and 0.34 kg fresh weight m−2 in urea, CM-CDU-4, CM-CDU-10 and the control, respectively. The amount of total nitrate leaching was 3.4, 2.3, 1.2 and 0.3 g N m−2 from urea, CM-CDU-4, CM-CDU-10 and the control, respectively. The total amount of N2O emission from urea, CM-CDU-4, CM-CDU-10 and the control over two crops was 0.12, 0.06, 0.04 and 0.01 g N m−2, respectively. The emission factors were 0.7, 0.3 and 0.2 from the urea, CM-CDU-4 and CM-CDU-10 treatments, respectively. The N use efficiency of urea, CM-CDU-4 and CM-CDU-10 was 87, 85 and 59%, respectively. Among the examined fertilizers, we recommend CM-CDU-4 as best for komatsuna production after examining two continuous croppings with a single application. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to investigate CH4 emissions from a sandy paddy soil as influenced by rice cultivars and atmospheric CO2 elevation. The experiment with two CO2 levels, 370 μL L−1 (ambient) and 570 μL L−1 (elevated), was performed in a climatron, located at the National Institute for Agro-Environmental Sciences, Tsukuba, Japan. Four rice cultivars were tested in this experiment, including IR65598, IR72, Dular and Koshihikari. Tiller number, root length and grain yield were clearly larger under elevated CO2 than under ambient CO2. IR72 and Dular showed significantly higher tiller number, root length and grain yield than Koshihikari and IR65598. Average daily CH4 fluxes under elevated CO2 were significantly larger by 10.9–23.8% than those under ambient CO2, and varied with the cultivars in the sequence Dular ≧ IR72>IR65598 ≧ Koshihikari. Dissolved organic C (DOC) content in the soil was obviously higher under elevated CO2 than under ambient CO2 and differed among the cultivars, in the sequence IR72>Dular>Koshihikari>IR65598. The differences in average daily CH4 fluxes between CO2 levels and among the cultivars were related to different root exudation as DOC content, root length and tiller number. This study indicated that Koshihikari should be a potential cultivar for mitigating CH4 emission and simultaneously keeping stable grain yield, because this cultivar emitted lowest CH4 emission and produced medium grain yield. [ABSTRACT FROM AUTHOR]

A 13C pulse-labeling experiment was conducted under ambient CO2 and free-air CO2 enrichment (FACE) conditions to understand how elevated CO2 affects the CH4 in soil bubbles and CH4 emissions from rice paddies. Two hills of rice plants enclosed by frames in ambient CO2 and FACE plots were labeled with 13CO2 at the panicle formation stage, and plants and soil bubbles were collected 2 and 51 days after the pulse labeling. CH4 and 13CH4 emissions were also measured by the closed-chamber method between the 2 bubble samplings. Conversion of photosynthate carbon to CH4 entrapped in soil bubbles and CH4 emission to the atmosphere occurred quickly, suggesting that recent photosynthates can be an important source of carbon for methanogenesis. About 1% of the 13C-labeled C taken up through photosynthesis was emitted as 13CH4 during the 7 weeks of measurement, most during the first 3 weeks after labeling. Total CH4 and 13CH4 emissions did not differ between the ambient CO2 and FACE treatments, because the entrapped CH4 in the soil and the root biomass were not affected by elevated CO2 levels in this study. [ABSTRACT FROM AUTHOR]

Field experiments were designed to quantify N2O emissions from corn fields after the application of different types of nitrogen fertilizers. Plots were established in South Kalimantan, Indonesia, and given either urea (200 kg ha−1), urea (170 kg ha−1) + dicyandiamide ([DCD] 20 kg ha−1) or controlled-release fertilizer LP-30 (214 kg ha−1) prior to the plantation of corn seeds (variety BISI 2). Each fertilizer treatment was equivalent to 90 kg N ha−1. Plots without chemical N fertilizer were also prepared as a control. The field was designed to have three replicates for each treatment with a randomized block design. Nitrous oxide fluxes were measured at 4, 8, 12, 21, 31, 41, 51, 72 and 92 days after fertilizer application (DAFA). Total N2O emission was the highest from the urea plots, followed by the LP-30 plots. The emissions from the urea + DCD plots did not differ from those from the control plots. The N2O emission from the urea + DCD plots was approximately one thirtieth of that from the urea treatment. However, fertilizer type had no effect on grain yield. Thus, the use of urea + DCD is considered to be the best mitigation option among the tested fertilizer applications for N2O emission from corn fields in Kalimantan, Indonesia. [ABSTRACT FROM AUTHOR]

There is limited knowledge about the differences in carbon availability and metabolic quotients in temperate volcanic and tropical forest soils, and associated key influencing factors. Forest soils at various depths were sampled under a tropical rainforest and adjacent tea garden after clear-cutting, and under three temperate forests developed on a volcanic soil (e.g. Betula ermanii and Picea jezoensis, and Pinus koraiensis mainly mixed with Tilia amurensis, Fraxinus mandshurica and Quercus mongolica), to study soil microbial biomass carbon (MBC) concentration and metabolic quotients ( qCO2, CO2-C/biomass-C). Soil MBC concentration and CO2 evolution were measured over 7-day and 21-day incubation periods, respectively, along with the main properties of the soils. On the basis of soil total C, both CO2 evolution and MBC concentrations appeared to decrease with increasing soil depth. There was a maximal qCO2 in the 0–2.5 cm soil under each forest stand. Neither incubation period affected the CO2 evolution rates, but incubation period did induce a significant difference in MBC concentration and qCO2 in tea soil and Picea jezoensis forest soil. The conversion of a tropical rainforest to a tea garden reduced the CO2 evolution and increased the qCO2 in soil. Comparing temperate and tropical forests, the results show that both Pinus koraiensis mixed with hardwoods and rainforest soil at less than 20 cm depth had a larger MBC concentration relative to soil total C and a lower qCO2 during both incubation periods, suggesting that microbial communities in both soils were more efficient in carbon use than communities in the other soils. Factor and regression analysis indicated that the 85% variation of the qCO2 in forest soils could be explained by soil properties such as the C:N ratio and the concentration of water soluble organic C and exchangeable Al ( P < 0.001). The qCO2 values in forest soils, particularly in temperate volcanic forest soils, decreased with an increasing Al/C ratio in water-soluble organic matter. Soil properties, such as exchangeable Ca, Mg and Al and water-soluble organic C:N ratio, were associated with the variation of MBC. Thus, MBC concentrations and qCO2 of the soils are useful soil parameters for studying soil C availability and microbial utilization efficiency under temperate and tropical forests. [ABSTRACT FROM AUTHOR]

A pot incubation experiment with rice residues (straw and root) was conducted under aerobic condition (60% of WHC, water holding capacity) for a period of 55 days in a greenhouse. The emissions of carbon dioxide (CO2) and nitrous oxide (N2O) were determined by the closed chamber method in a paddy soil. The soil was derived from quaternary red clay, and collected from the Ecological Station of Red Soil, the Chinese Academy of Sciences, located in Jiangxi Province, a subtropical region of China. The emissions of CO2 and N2O were increased by the amendment of rice residues. Significantly positive correlation was found between N2O and CO2 fluxes ( R = 0. 650*−0. 870*, P ≤ 0. 05). The cumulative emissions during the early stage of the incubation (<25 days after residue addition) accounted for about 67%–86% and 67%–80% of the total amount of CO2 and N2O emissions, respectively. Cumulative emissions and emission factors of the two gases were higher in the soils amended with rice straw than those with rice root. The two gas fluxes were positively correlated with microbial biomass C and N, as well as soluble organic C. N2O flux was positively correlated with NH4 +–N content at the early stage (<25 days), and negatively with NO3 −–N content at the later stage of this incubation (25–55 days), implying that both nitrification and denitrification may have contributed to N2O production. [ABSTRACT FROM AUTHOR]

Abstract: The response of soil carbon availability and microbial utilization efficiency to varying vegetations and to increasing temperature emphasizes the need for further research in volcanic forest soils. We have studied responses of soil microbial biomass C (MBC) concentrations and metabolic quotients (qCO2, CO2-C/biomass-C) to vegetations and temperature in temperate volcanic forest soils. Soils were sampled in April and October 2003 beneath four forest stands in close proximity (200 m apart) in central Japan: a Japanese cedar coniferous forest (CI), a pine coniferous forest (CII), and an oak-dominated hardwood on a grading and steep slope (DI and DII). The soil MBC concentrations and qCO2 values beneath each forest stand were measured under oxic conditions, along with the effect of temperature and the long-term storage at low temperature on both variables. Comparing different forest stands, it was indicated that the pine forest soil always showed the lowest MBC concentration relative to soil total C, and the largest qCO2 (P <0.05), suggesting that microbial communities in the soil were less efficient in C use than communities in the other forest soils. Under a same oak-dominated hardwood, a steep terrain induced a lower soil respiration and MBC concentration, but qCO2 values of both soils had no significant differences at 25 °C. The MBC concentration in the soils beneath each forest stand mostly had no differences during two sampling periods. The low-temperature storage induced an increase in soil MBC and a reduction of CO2 production, reducing the qCO2. There was a smaller MBC concentration in the CII soil than in the CI and DII soil within the range of 5 to 35 °C; the MBC concentration and qCO2 in the DI and CII soil appeared more sensitive at increasing temperature than those in the DII and CI soil. From the results obtained, it can be concluded that under similar climatic conditions and soil types, the MBC concentrations and qCO2 values of temperate volcanic forest soils vary with tree species and temperature, and that the high soil C-to-N ratios and low acidity can contribute to decreased soil MBC concentration and to increased qCO2. [Copyright &y& Elsevier]

An anaerobic incubation experiment was conducted to investigate methane (CH4) production potential in soil samples collected from a paddy field after exposure to free-air CO2 enrichment (FACE). The FACE experiment with two CO2 levels, ambient and ambient + 200 p.p.m.v CO2 during the rice growing season, was conducted at Shizukuishi, Iwate Prefecture, Japan. The soil was a wet Andosol. Soil samples were taken from the surface (0–1 cm) and the sub-surface (1–10 cm) soil layers 2 months after rice harvest. Sub-samples of the fresh soils were put into glass bottles and submerged under N2 gas headspace during the incubation. The results showed that, prior to incubation, the contents of total C and dissolved organic C (DOC) were significantly greater in FACE soil than ambient soil. During the incubation, CH4 production potential was approximately 2–4-fold higher in FACE soil than ambient soil and approximately 500–1,000-fold greater in surface soil than sub-surface soil. In general, the FACE soil contained more DOC than ambient soil, particularly in the surface soil layer. These findings suggest that FACE treatment exerted long-term positive effects on CH4 production and increased organic C content in this paddy soil, particularly in the surface soil layer. [ABSTRACT FROM AUTHOR]

Using the free-air CO2 enrichment (FACE) techniques, we carried out a 3-year mono-factorial experiment in temperate paddy rice fields of Japan (1998–2000) and a 3-year multifactorial experiment in subtropical paddy rice fields in the Yangtze River delta in China (2001–2003), to investigate the methane (CH4) emissions in response to an elevated atmospheric CO2 concentration (200±40 mmol mol−1 higher than that in the ambient atmosphere). No significant effect of the elevated CO2 upon seasonal accumulative CH4 emissions was observed in the first rice season, but significant stimulatory effects (CH4 increase ranging from 38% to 188%, with a mean of 88%) were observed in the second and third rice seasons in the fields with or without organic matter addition. The stimulatory effects of the elevated CO2 upon seasonal accumulative CH4 emissions were negatively correlated with the addition rates of decomposable organic carbon ( P<0.05), but positively with the rates of nitrogen fertilizers applied in either the current rice season ( P<0.05) or the whole year ( P<0.01). Six mechanisms were proposed to explain collectively the observations. Soil nitrogen availability was identified as an important regulator. The effect of soil nitrogen availability on the observed relation between elevated CO2 and CH4 emission can be explained by (a) modifying the C/N ratio of the plant residues formed in the previous growing season(s); (b) changing the inhibitory effect of high C/N ratio on plant residue decomposition in the current growing season; and (c) altering the stimulatory effects of CO2 enrichment upon plant growth, as well as nitrogen uptake in the current growing season. This study implies that the concurrent enrichment of reactive nitrogen in the global ecosystems may accelerate the increase of atmospheric methane by initiating a stimulatory effect of the ongoing dramatic atmospheric CO2 enrichment upon methane emissions from nitrogen-poor paddy rice ecosystems and further amplifying the existing stimulatory effect in nitrogen-rich paddy rice ecosystems. [ABSTRACT FROM AUTHOR]

CO2 efflux from tropical peat swamp substrates was measured under three different land uses (selectively logged forest, recently burned and cleared forest, and agriculture) in Jambi Province, eastern Sumatra over a six-month period that incorporated parts of both the major wet and dry seasons. Clearance of peat swamp forest and cultivation led to increased emissions: mean CO2 effluxes ranged from 2.59 ± 0.22 μmolCO2 m-2 sec-1 for peat beneath selectively logged forest to 4.44 ± 1.16 μmolCO2 m-2 sec-1 beneath recently burned and cleared forest to 5.58 ± 1.34 μmolCO2 m-2 sec-1 beneath settled agriculture. Mean CO2 effluxes were significantly correlated with soil temperature at 20 cm depth (Q10 = 2.5) and water-table position. We combined SPOT satellite and CO2 efflux data to establish that the conversion of selectively logged forest to agricultural land has led to a substantial increase in annual emissions of CO2-C in the study area. [ABSTRACT FROM AUTHOR]

Methane (CH4) is a particularly potent greenhouse gas with a radiative forcing 23 times that of CO2 on a per mass basis. Flooded rice paddies are a major source of CH4 emissions to the Earth's atmosphere. A free-air CO2 enrichment (FACE) experiment was conducted to evaluate changes in crop productivity and the crop ecosystem under enriched CO2 conditions during three rice growth seasons from 1998 to 2000 in a rice paddy at Shizukuishi, Iwate, Japan. To understand the influence of elevated atmospheric CO2 concentrations on CH4 emission, we measured methane flux from FACE rice fields and rice fields with ambient levels of CO2 during the 1999 and 2000 growing seasons. Methane production and oxidation potentials of soil samples collected when the rice was at the tillering and flowering stages in 2000 were measured in the laboratory by the anaerobic incubation and alternative propylene substrates methods, respectively. The average tiller number and root dry biomass were clearly larger in the plots with elevated CO2 during all rice growth stages. No difference in methane oxidation potential between FACE and ambient treatments was found, but the methane production potential of soils during the flowering stage was significantly greater under FACE than under ambient conditions. When free-air CO2 was enriched to 550 ppmv, the CH4 emissions from the rice paddy field increased significantly, by 38% in 1999 and 51% in 2000. The increased CH4 emissions were attributed to accelerated CH4 production potential as a result of more root exudates and root autolysis products and to increased plant-mediated CH4 emissions because of the larger rice tiller numbers under FACE conditions. [ABSTRACT FROM AUTHOR]

Mechanisms of methane oxidation in the plant-soil system of rice were studied in a pot experiment using two cultivars (PSBRc-30 and IR72) at two growth stages (flowering and heading). Methane emission was measured by chambers, while methane oxidation was determined through propylene amendment as an alternative substrate to be propylene oxide (PPO) and acetylene as an inhibitor for methane oxidizing (methanotrophic) bacteria. Cell numbers (methanotrophic and methanogenic bacteria) were determined by the most probable number method. The cultivar PSBRc-30 consistently showed higher methane emission rates than IR72. Methane flux clearly decreased from flowering to heading stages in both cultivars. This observation was largely reflected by trends in the mechanisms involved: either methanogenic cell numbers or activities decreased with plant age while methanotrophic cell numbers or activities generally showed an increasing trend. The methanogenic population was in the order of 105 g−1 dry soil, while the population of methanotrophs ranged from 104 to nearly 106 g−1 dry soil. Methanotrophic activity followed the order; root (1.7–2.8 nL PPO g−1 DM h−1) > shoot (0.7–2.0) > soil (0–0.4) when the consumption of alternative substrate was related to dry matter. Derived from the estimated amounts of soil and plant biomass in the pot experiment, however, the soil generally accounted for more than 90% of the total methane oxidation. Within the plant segments, methane oxidation activities in the root exceeded those of the shoot by factor of approximately 10. [ABSTRACT FROM AUTHOR]

A revolving furnace slag (RFS), which is a by-product of the steel industry, and a spent disposable portable body warmer (PBW), which harnessed the heat of iron oxidation reaction, were used as iron materials. Portions of 4 kg of Coarse and Medium Textured Gley soil were placed into plastic pots (3 L). RFS was added to the pots at the rate of 0 (control), 10, 20, 40, 100 ton ha−1, while PBW was added at 10 ton ha−1 only. Methane flux from the potted soil with rice plants and Eh were measured during cropping seasons in 1999 and 2000. In the 1999 experiment, the RFS treatments showed lower Eh values compared with the control, especially at the early period of cultivation, although the RFS was applied to maintain the soil oxidative. The rapid decrease in Eh under high application of RFS may be due to the high pH of the RFS (pH (RFS:H2O = 1:2.5) was 12.2). However, total methane emission during the cultivation period significantly decreased, about 10%, when 10–40 ton ha−1 of RFS and 10 ton ha−1 of PBW were applied. The grain yield was significantly increased, about 30%, when 40 or 100 ton ha−1 of RFS was applied. This was also partly due to the release of inorganic nutrients from RFS and also from soil. The latter, due to effect of the alkaline RFS on soil. In the 2000 experiment, the pots with soils from 1999 were used without further application of iron materials. The influence of high application of RFS on soil Eh disappeared, compared with 1999. Total methane emission significantly decreased, about 35%, at 20 ton ha−1 of RFS. However, the increase of grain yield caused by RFS in 1999 was diminished, compared with 1999. Production activity of both methane and carbon dioxide at the RFS treatments were decreased, while methane oxidizing activity was increased. The decrease in total methane emission may be attributed to not only inhibition of methane production but also enhanced methane oxidation. In conclusion, methane emission from paddy soil could be suppressed, over two cropping seasons by single application of RFS without loosing grain yield. [ABSTRACT FROM AUTHOR]

As part of a FACE (free-air CO2 enrichment) experiment in a rice paddy field in Shizukuishi (Iwate Prefecture, Japan), studies were conducted to determine the effects of elevated CO2 on N dynamics at three levels of N application. Rice plants were grown under ambient CO2 or ambient + 200 ppmV CO2 conditions throughout the growing season in an Andosol soil with each treatment having 4 replicated plots. Three levels of N fertilizer (high, standard and low; 15, 9 and 4 gN m−2, respectively) were applied to examine different N availability under both CO2 conditions. Soil samples were collected at 4 different times from upper and lower soil layers (0–1 cm and 1–10 cm soil depths, respectively) and analyzed for microbial biomass N (BN), mineralizable N (Min. N) and NH4 +-N in soil. Plant sampling was also done at 3 different times during the growing season to determine the N uptake by plant. Elevated CO2 significantly increased BN and Min. N in the upper soil layer at harvest by 25–42% and 18–24%, respectively, compared to ambient CO2, regardless of N application rate. In low N soil, these significant increases were also observed at the ripening stage. In addition, elevated CO2 only significantly increased the NH4 +-N in the upper soil layer at harvest in low N soil compared to ambient CO2. The N uptake was not significantly affected by CO2 treatment. These results indicate that elevated CO2 had significant positive influence on BN and Min. N in the upper soil layer in paddy soil at the later period of the cropping season at all levels of N application rates, but only at low levels of application rate on NH4 +-N. [ABSTRACT FROM AUTHOR]

Experiments were conducted in paddy fields at Shiga and Chiba Prefectures to study the effects of controlled-release coated urea (N-LP100) on soil microbial biomass and N uptake of rice plants by the 15N-tracer technique, during one cropping season. Three field fertilizer treatments (Zero N: 0 kgN ha−1, 15N-LP100: 64 kg N ha−1 and 15NH4Cl: 100 kg N ha−1) were set-up in the Shiga field experiment. After transplanting in the paddy fields at Shiga and Kashiwa (Chiba), a number of rice hills with standard growth were selected randomly and enclosed by polyacryl-plastic frames designated as microplots. 15N-LP100 (64 kg N ha−1) was applied in the Shiga and Kashiwa microplot experiments and the Shiga field experiment as deep-side placement (5 cm away from rice hill and 5 cm soil depth). Total N uptake of rice plants was analyzed in the course of plant growth. In addition, soils from the field fertilizer treatment plots and microplots (divided into 11 blocks) were taken and analyzed for microbial biomass N (BN) and biomass 15N (B15N). The results indicated that; (1) Plant N uptake from basal-applied fertilizers at the end of the study in the Shiga field experiment was 71.9 and 26.0% for 15N-LP100 and 15NH4Cl, respectively. In the Kashiwa microplot experiment, plant N uptake from applied 15N-LP100 was 51.2% at 67 days after transplanting (DAT) (2) Throughout the cropping season, BN was the highest, intermediate and the lowest for 15NH4Cl, 15N-LP100 and Zero N field experimental plots in the Shiga experiment, respectively. (3) In the micro-plot experiments, BN and B15N were generally higher in the soil block with deep-side application of 15N-LP100 compared with the other soil blocks. The deep-side placement of 15N-LP100 ensured a high efficiency of utilization of its N by rice plants. The method of 15N-LP100-placement also affected the spatial heterogeneity of microbial biomass N in the microplots. [ABSTRACT FROM AUTHOR]

An experiment was conducted in an Andosol paddy field in Shizukuishi (Iwate Prefecture, Japan) to determine the effects of free-air CO2 enrichment (FACE) on biological N2-fixation activity and soil microbial biomass C at three levels of N application. Rice ( Oryza sativa L. cv. Akitakomachi) plants were grown under ambient CO2 or FACE (ambient +200 µmol mol–1 CO2) conditions throughout the growing season with each treatment having four replicated plots. Three levels of N fertilizer (high, standard and low; 15, 9 and 4 g N m–2, respectively) were applied to examine the effect of different N availability under both CO2 conditions. Soil samples were collected at four different times from upper and lower soil layers (0–1-cm and 1–10-cm soil depths, respectively) and analysed for biological N2-fixation (BNF) activity and microbial biomass C (MBC) by the acetylene reduction and chloroform fumigation-extraction methods, respectively. The amounts of chlorophyll-type compounds (Chls), an index of algal growth, and soil available C were also determined. Compared to the ambient CO2 treatment, the FACE treatment had significantly higher BNF activity in both the upper and lower soil layers at ripening only in low-N soil and at harvest at all three levels of N fertilization rates. MBC was significantly increased by FACE in both the upper and lower soil layers from the middle to later period of the growing season compared to the ambient CO2 treatment. The FACE treatment increased the Chls in the upper soil layers at ripening only in low-N soil and at harvest at all three levels of N fertilization rates. The amount of soil available C was not significantly different between FACE and ambient CO2 treatments in both the upper and lower soil layers throughout the cropping season. From these results it can be concluded that the FACE treatment had a significantly positive influence on BNF activity, MBC and Chls at different levels of N fertilization rates in paddy field during the cropping season. [ABSTRACT FROM AUTHOR]

Controlled-environment chambers were used to study the effects of elevated CO2 concentrations on biological N fixation, N mineralization and C decomposition in rice soil. In three chambers, CO2 concentration was maintained at 353±15/396±23 µmol mol–1 (day/night; ambient CO2), while in another three, CO2 was maintained at 667±36/700±41 µmol mol–1 (day/night; elevated CO2) throughout the growing season. Rice (var. Nipponbare ) seedlings were grown under either ambient or elevated CO2 concentrations, and then transplanted into the soils in the corresponding chambers. At different growth stages, soil samples were taken from surface (0–1cm) and sub-surface (1–10cm) layers at the centre of four hills, then sieved (<1 mm) to remove root residues. Fresh soil was used to measure N fixation activity (using the acetylene reduction assay), NH4 + content and organic C. Separate sets of soil samples were transferred to serum bottles and anaerobically incubated at 30°C for 30 days to measure potential rates of N mineralization and C decomposition. Under an elevated atmospheric CO2 concentration, acetylene reduction activity significantly increased in the surface soil layer during the early cultivation stages and in the sub-surface soil layer during the latter part of cultivation. There was no difference in the amount of NH4 + in fresh soils between elevated and ambient CO2 chambers, while the rate of N mineralization was increased by elevated CO2 during the latter part of cultivation. Soils from the elevated CO2 chambers had obviously higher rate of C decomposition than that from the ambient CO2 chambers. CH4 production gradually increased with the growth of rice plants. These results suggest that elevated CO2 affected biological N fixation, N mineralization and C decomposition in submerged rice soil during the different growth stages of rice. [ABSTRACT FROM AUTHOR]

Presents information on a study which estimated the effect of aquatic weeds on methane flux from paddy soils throughout the period of rice growth. Materials and methods; Plant growth and peroxidase activity of rice roots; Methane oxidation activity of roots of three aquatic weeds; Discussion.