Methane production in a flooded soil in response to elevated atmospheric carbon dioxide concentrations

 CH₄ production in a flooded soil as affected by elevated atmospheric CO₂ was quantified in a laboratory incubation study. CH₄ production in the flooded soil increased by 19.6%, 28.2%, and 33.4% after a 2-week incubation and by 38.2%, 62.4%, and 43.0% after a 3-week incubation under atmospheres of 498, 820, and 1050 μl l^–1 CO₂, respectively, over that in soil under the ambient CO₂ concentration. CH₄ production in slurry under 690, 920, and 1150 μl l^–1 CO₂ increased by 2.7%, 5.5%, and 5.0%, respectively, after a 3-day incubation, and by 6.7%, 12.8%, and 5.4%, respectively, after a 6-day incubation over that in slurry under the ambient CO₂ concentration. The increase in CH₄ production in the soil slurry under elevated CO₂ concentrations in a N₂ atmosphere was more pronounced than that under elevated CO₂ concentrations in air. These data suggested that elevated atmospheric CO₂ concentrations could promote methanogenic activity in flooded soil. Received: 2 March 1998     

Influence of the insecticide carbofuran on the production and oxidation of methane in a flooded rice soil

Applications of a commercial formulation of carbofuran, a carbamate insecticide, at rates of 2kg and 12kg active ingredient ha^–1 to flooded fields planted to rice led to significant inhibition of methane emission. Likewise, laboratory incubation studies showed that carbofuran applied at low rates (5 and 10μgg^–1soil) inhibited the net methane production relative to that of the control, but stimulated it when applied at a rate of 100μgg^–1soil. Interestingly, carbofuran increased the oxidation of methane when applied at low rates and inhibited it when applied at a rate of 100μgg^–1soil. Received: 5 May 1997     

Methane oxidation in arable soil as inhibited by ammonium, nitrite, and organic manure with respect to soil pH

 The effects of inorganic N and organic manure, applied to a loamy arable soil, on CH₄ oxidation were investigated in laboratory incubation experiments. Applications (40 mg N kg^–1) of NH₄Cl, (NH₄)₂SO₄, and urea caused strong instantaneous inhibition of CH₄ oxidation by 96%, 80%, and 84%, respectively. After nitrification of the added N the inhibitory effect was not fully reversible, resulting in an residual inhibition of 21%, 16%, and 25% in the NH₄Cl, (NH₄)₂SO₄, and urea treatments, respectively. With large NH₄ ⁺ applications [240 mg N kg^–1 as (NH₄)₂SO₄] the residual inhibition was as high as 64%. Exogenous NO₂ ^– (40 mg NO₂ ^–-N kg^–1) initially inhibited CH₄ oxidation by 84%, decreasing to 41% after its oxidation. Therefore, applied NO₂ ^– was a more effective inhibitor of CH₄ consumption than NH₄ ⁺. Temporary accumulation of NO₂ ^– during nitrification of added N was small (maximum: 1.9 mg NO₂ ^–-N kg^–1) and thus of minor importance with respect to the persistent inhibition after NH₄ ⁺ or urea application. CH₄ oxidation after NaNO₃ (40 mg N kg^–1) and NaCl addition did not differ to that of the untreated soil. The effect of organic manures on CH₄ oxidation depended on their C/N ratio: fresh sugar beet leaves enhanced mineralization, which caused an instantaneous 20% inhibition, whereas after wheat straw application available soil N was rapidly immobilized and no effect on CH₄ oxidation was found. The 28% increase in CH₄ oxidation after biowaste compost application was not related to its C/N ratio and was probably the result of an inoculation with methanotrophic bacteria. Only with high NH₄ ⁺ application rates (240 mg N kg^–1) could the persistent inhibitory effect partly be attributed to a pH decrease during nitrification. The exact reason for the observed persistent inhibition after a single, moderate NH₄ ⁺ or urea application is still unknown and merits further study. Received: 31 October 1997     

Methane production potentials of twenty-eight rice soils in China

 Soil CH₄ production potentials were investigated by incubating air-dried soils under anaerobic conditions in the laboratory. Twenty-eight soils from different fields and locations were collected for this study. Soil CH₄ production during a 100-day incubation differed greatly and were significantly correlated with soil organic content (r=0.61, P<0.01). The statistical significance increased when soils were grouped according to soil reduction rates. A significant correlation was also found between CH₄ production and total N content (r=0.64, P<0.01) and between CH₄ production and soil particle sizes of 0.25–0.05 mm (r=0.48, P<0.05). A negative exponential correlation was found between CH₄ production and aerobic soil pH (r=–0.74, P<0.01). The 28 soils were stratified into four groups on the basis of variation in CH₄ production rates which were associated with the soil reduction rate and soil organic content. The faster the Eh of soil fell, the more CH₄ was formed. Adding rice straw to Hangzhou and Beijing soils increased CH₄ production. The increase in CH₄ production was more pronounced in the soil with the lowest organic matter content and slowest reduction rate than in the soil with highest organic matter and fastest reduction rate. Inorganic fertilizer had no significant influence on CH₄ production potentials of either type of soil. Received: 26 November 1997     

Nitrification of ammonium in different components of a flooded rice soil system

Nitrification associated with the various components [subsurface soil from unplanted and planted (rhizosphere) fields, standing water and surface soil from planted and unplanted fields and leaf sheath suspensions] of submerged rice paddies was examined in incubation experiments with solutions inoculated with soil or water samples. Substantial nitrification occurred in all samples, standing water and surface soil samples in particular, during their 40-day incubation with NH ₄ ⁺ –N. Almost all the NH ₄ ⁺ –N, disappeared during incubation with standing water, was recovered as NO _inf3 ^sup- –N. This, compared to 70–80% from all soil samples and only 29% from leaf sheath suspensions. Significant loss of nitrogen, especially from leaf sheath suspensions, is probably due to nitrification-denitrification as evidenced by its complete recovery in the presence of N-Serve. Nitrification potential of the soil and water samples varied with the crop growth stage and was more pronounced at tillering and panicle inititation stages than at other stages. Nitrification potential of samples from green-manure-amended plots was distinctly less than that of samples from control and urea-amended plots. Most probable number (MPN) estimates of ammonium-oxidizing bacteria were always higher in surface soil in both planted and unplanted plots at all stages of crop growth.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

Wetland rice soils as sources and sinks of methane: a review and prospects for research

 Rice paddies are an important human-made ecosystem for the global CH₄ budget. CH₄, which is produced in the predominantly anaerobic bulk soil layers, is oxidized significantly before it reaches the atmosphere. Roots of rice, in addition to supporting the consumption of CH₄, contribute to the total CH₄ production in the soil. The various controls of CH₄ emission from this ecosystem depend on the structure of plant and microbial communities and their interactions. Availability of organic substrates, electron acceptors and other soil- and plant-related factors influence the activities of microbial communities. Agronomic practices including fertilization and application of pesticides have effects on CH₄ emission. Recent studies using molecular retrieval approaches with small subunit rRNA-encoding gene (rDNA) sequences and functional genes, showed the richness of diversity of the microbial community in rice paddy soils, which includes members of the Archaea and methanotrophs. There is need for further research to know the consequences, at the ecosystem level, of changes in microbial diversity and microbial communities in paddy soils. This will aid in understanding the mechanisms involved in the mitigating effects of certain agricultural practices. Received: 13 July 1999     

The role of rice plants in regulating mechanisms of methane missions

 Rice plants play a pivotal role in different levels of the methane (CH₄) budget of rice fields. CH₄ production in rice fields largely depends on plant-borne material that can be either decaying tissue or root exudates. The quantity and quality of root exudates is affected by mechanical impedance, presence of toxic elements, nutrient deficiencies, water status of growing medium, and nitrogenase activity in the rhizosphere. CH₄ oxidation in rice fields is localized in the rhizosphere where the concentration gradients of CH₄ and oxygen overlap. CH₄ oxidation capacity is a function of the downward transport of oxygen through the aerenchyma, which, in turn, also acts as a conduit for CH₄ from the soil to the atmosphere. The decisive step in the passage of CH₄ through rice plant is the transition from root to stem. However, rice plants show an enormous variety of morphological and physiological properties, including differences in root exudation and gas transfer capacity. Comparative studies on different cultivars are deemed crucial for accomplishing a better understanding of the mechanisms of CH₄ consumption in the rhizosphere and CH₄ transport through the rice plant as well as the interaction of these processes. The results of such studies are considered tools for devising mitigation options. Received: 7 April 1999     

Effect of climate and soil type on the immobilization of nitrogen by decomposing straw in northern and southern Europe

 Wheat straw enclosed in mesh bags was buried for periods up to 1 year over two seasons in Scottish, Danish and Portuguese soils treated with ¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃. Scottish soils were: Terryvale, a poorly drained sandy loam; and Tipperty, an imperfectly drained brown forest soil with a higher clay content. The Danish soil (Foulum) was a freely drained sandy loam and the Portuguese soils were a sandy soil (Evora) and a clay soil (Beja). During the first month, ¹⁵N was being incorporated into the straw in the Tipperty, Terryvale and Foulum soils simultaneously as the total N content was decreasing. Subsequently, the straws began to show net immobilization and the total N content of the original straw was exceeded in Tipperty and Foulum soils after 4 months and 8 months, respectively. Net immobilization in Terryvale was detected only in the second season and did not occur in the first because of high soil moisture content. The rates of ¹⁵N incorporation were similar in the two Portuguese soils, and a loss of N was only detected after 8 months. After 1 month, in the two clay soils, Beja and Tipperty, ¹⁵NO₃ ^– was incorporated into straw to a greater extent than ¹⁵NH₄ ⁺ and this was attributed to ¹⁵NH₄ ⁺ fixation by clay minerals. In contrast, ¹⁵NH₄ ⁺ was more efficiently incorporated than ¹⁵NO₃ ^– under waterlogged conditions (Terryvale) and NO₃ ^– loss could be attributed to denitrification. The proportion of added ¹⁵N in the straw residue after 1 month varied between 6% and 18% for ¹⁵NH₄ ⁺ and 2% and 23% for ¹⁵NO₃ ^– and immobilization of N in the longer term tended to be greater in soils from northern Europe than from Portugal. Received: 19 January 1998     

Temporal and spatial fluctuations in moisture affect humus microfungal community structure in microcosms

 The effects of temporal and spatial fluctuations in moisture on the microfungal community were studied in birch litter plus pine humus microcosms over 6 months. Two treatments were used: a uniform treatment in which moisture was maintained at the original moisture content throughout the profile over the course of the experiment; and a fluctuating moisture treatment in which the moisture content of the whole microcosm fluctuated weekly around the original moisture content. At 6 months, fungal species richness was higher and diversity was lower under moisture fluctuations than under uniform moisture. The number of fungal isolates and proportional diversity was significantly higher in the bottom layer in the fluctuating moisture treatment. The fluctuating moisture treatment and the bottom layer correlated significantly with the first PCA axis, which accounted for 66% of the variation in the fungal species data. The experiment suggests that even without drying, fluctuations in moisture can affect fungal community structure. Received: 3 June 1999     

Nitrous oxide production at different soil moisture contents in an arable soil in China

Abstract

Laboratory incubations were conducted to investigate nitrous oxide (N₂O) production from a subtropical arable soil (Typic Plinthodults) incubated at different soil moisture contents (SMC) and with different nitrogen sources using a 10% (v/v) acetylene (C₂H₂) inhibitory technique at 25°C. The production of N₂O and CO₂ was monitored during the incubations and changes in the contents of KCl-extractable NO^? ₃-N and NH⁺ ₄-N were determined. The production of N₂O increased slightly with an increase in SMC from 40% water-holding capacity (WHC) to 70% WHC, but increased dramatically at 100% WHC. After incubation the NO^? ₃-N content increased even at a SMC of 100% WHC. At a SMC of 100% WHC, the addition of NH⁺ ₄-N promoted the production of N₂O and CO₂, whereas the addition of NO^? ₃-N decreased N₂O production. Compared with the incubation without C₂H₂, the presence of C₂H₂ increased NH⁺ ₄-N content, but decreased NO^? ₃-N content, and there was no significant difference in N₂O production. These results indicate that heterotrophic nitrification contributes to N₂O production in the soil.     

Methane fluxes and nitrogen dynamics from a drained fenland peat

 Rates of methane uptake were measured in incubation studies with intact cores from adjacent fenland peats that have been under arable management and woodland management for at least the past 30 years. On two separate occasions the woodland peat showed greater rates of uptake than the arable peat. These rates ranged from 23.1 to 223.3 μg CH₄ m^–2 day^–1 for the woodland peat and from 29.6 to 157.6 μg CH₄ m^–2 day^–1 for the arable peat. When the peats were artificially flooded there was a decrease in the rate of methane oxidation, but neither site showed any net efflux of methane. ¹⁵N isotopic dilution was used to characterise nitrogen cycling within the two peats. Both showed similar rates of gross nitrogen mineralisation (3.58 mg N kg^–1 day^–1, arable peat; 3.54 N kg^–1 day^–1, woodland peat) and ammonium consumption (4.19 arable peat and 4.70 mg N kg^–1 day^–1 woodland peat). There were significant differences in their inorganic ammonium and nitrate pool sizes, and the rate of gross nitrification was significantly higher in the woodland peat (4.90 mg N kg^–1 day^–1) compared to the arable peat (1.90 mg N kg^–1 day^–1). These results are discussed in the light of high atmospheric nitrogen deposition. Received: 1 December 1997     

Nitrous oxide emissions and methane oxidation by soil following cultivation of two different leguminous pastures

 Nitrous oxide (N₂O) emissions and methane (CH₄) consumption were quantified following cultivation of two contrasting 4-year-old pastures. A clover sward was ploughed (to 150–200 mm depth) while a mixed herb ley sward was either ploughed (to 150–200 mm depth) or rotovated (to 50 mm depth). Cumulative N₂O emissions were significantly greater following ploughing of the clover sward, with 4.01 kg N₂O-N ha^–1 being emitted in a 48-day period. Emissions following ploughing and rotovating of the ley sward were much less and were not statistically different from each other, with 0.26 and 0.17 kg N₂O-N ha^–1 being measured, respectively, over a 55-day period. The large difference in cumulative N₂O between the clover and ley sites is presumably due to the initially higher soil NO₃ ^– content, greater water filled pore space and lower soil pH at the clover site. Results from a denitrification enzyme assay conducted on soils from both sites showed a strong negative relationship (r=–0.82) between soil pH and the N₂O:(N₂O+N₂) ratio. It is suggested that further research is required to determine if control of soil pH may provide a relatively cheap mitigation option for N₂O emissions from these soils. There were no significant differences in CH₄ oxidation rates due to sward type or form of cultivation. Received: 1 November 1998     

Methane emission from two Indian soils planted with different rice cultivars

In a greenhouse study, methane emissions were measured from two diverse Indian rice-growing soils planted to five rice cultivars under similar water regimes, fertilizer applications and environmental conditions. Significant variations were observed in methane emitted from soils growing different cultivars. Total methane emission varied between 8.04 and 20.92gm^–2 from IARI soil (Inceptisol) and between 1.47 and 10.91gm^–2 from Raipur soil (Vertisol) planted to rice. In all the cultivars, emissions from IARI soil were higher than from Raipur soil. The first methane flux peak was noticed during the reproductive phase and the second peak coincided with the grain-ripening stage of the rice cultivars. Received: July 7, 1996     

Effects of algae and fertilizer-nitrogen on pH, Eh and depth of aerobic soil in laboratory columns of a flooded sandy loam

 A sandy loam was incubated under floodwater in the laboratory either in the dark or in the light (7 h day, 20  °C; 17 h night, 15  °C) and with four N sources [control, ammonium carbonate [(NH₄)₂CO₃], ammonium chloride (NH₄Cl), potassium nitrate (KNO₃)]. In the dark, floodwater pH rose steadily from 6.4 to about 7.5 over 60 days in the control, KNO₃ and (NH₄)₂CO₃ treatments, but with NH₄Cl pH decreased to 5.8. In the light, algal growth began to affect the floodwater pH after 9 days. At the end of the night, pH values were similar for all treatments to those kept in the dark. During the day, pH changes depended on the morning pH value: the daily increase was zero at pH 5.6 rising to a maximum of about 2 units at pH 6.3 and falling again at higher pH values. Changes in the carbonate equilibria in response to CO₂ removal by algal photosynthesis partly explain the results, but increasing inputs of acid are also implicated below pH 6.3 possibly due to reduced volatilization and increased nitrification. Redox potential (Eh) in the floodwater was little affected by N treatment until algal growth began. Eh then decreased each day as pH rose and recovered during the night. The daily decrease in Eh per unit increase in pH rose from about 10 to 90 mV pH^–1 over the incubation period. Initially, therefore, O₂ concentration must have been increased during the day by algal photosynthesis (values <59 mV pH^–1), but later O₂ concentration must have fallen, due possibly to the decomposition of algal cells. The presence of algae initially increased the depth of the aerobic soil layer, but eventually an algal mat settled on the soil surface acting as a zone of O₂ demand as the algae decomposed. Received: 7 July 1997     

Evaluation of different zinc sources for lowland rice production

 ZnSO₄, Zn-enriched farmyard manure (Zn-FYM), Zn-tetraammonia complex sorbed on FYM [Zn(NH₃)₄-FYM] and Zn-ethylenediaminetetraacetate (Zn-EDTA) were compared as Zn sources for rice production under lowland conditions. The amount of Zn supplied by Zn-EDTA was one-tenth of that supplied by the other Zn sources. Zn application to a Zn-deficient soil corrected the visual symptoms of Zn deficiency and significantly increased the total biomass, grain yields and the harvest index of rice, as well as the Zn concentration in the grain and the uptake of Zn by the straw and the grains. Even with lower rates of application (0.25 and 0.5 mg Zn kg^–1 soil), Zn-EDTA treatments gave comparable values for these parameters, and the highest "Zn-mobilization efficiency" compared to the other Zn sources. The content of diethylenetriaminepentaacetate (DTPA)-extractable Zn in the soil of the different treatments after the harvest of rice was in the order; ZnSO₄=Zn-FYM>Zn(NH₃)₄-FYM=Zn-EDTA. The application of Zn also significantly increased the number of panicles that emerged between 80 to 93 days after transplanting, though the total number of panicles at harvest remained unaffected. The calculated panicle-emergence index had a positive correlation with the grain yield of rice. The Z_n-EDTA treatment, inspite of supplying the lowest amount of Zn, as well as leading to the lowest rate of Zn uptake, produced the highest yields. Therefore, we concluded Zn-EDTA to be the most efficient source of Zn for lowland rice production. Received: 20 October 1998     

Methane oxidation in the soil surface layer of a flooded rice field and the effect of ammonium

Summary The CH₄ flux from intact soil cores of a flooded rice field in Italy was measured under aerobic and anaerobic incubation conditions. The difference between the anaerobic and aerobic CH₄ fluxes was apparently due to CH₄ oxidation in the oxic soil surface layer. This conclusion was supported by measurements of the vertical CH₄ profile in the upper 2-cm layer, and of the V _max of CH₄ oxidation in slurried samples of the soil surface layer. About 80% of the CH₄ was oxidized during its passage through the soil surface layer. CH₄ oxidation was apparently limited by the concentration of CH₄ and/or O₂ in the active surface layer. The addition of ammonium to the water layer on top of the soil core reversibly increased the aerobic CH₄ fluxes due to inhibition of CH₄ oxidation in the soil surface layer.     

Influence of soil properties on the turnover of nitric oxide and nitrous oxide by nitrification and denitrification at constant temperature and moisture

 Soils are a major source of atmospheric NO and N₂O. Since the soil properties that regulate the production and consumption of NO and N₂O are still largely unknown, we studied N trace gas turnover by nitrification and denitrification in 20 soils as a function of various soil variables. Since fertilizer treatment, temperature and moisture are already known to affect N trace gas turnover, we avoided the masking effect of these soil variables by conducting the experiments in non-fertilized soils at constant temperature and moisture. In all soils nitrification was the dominant process of NO production, and in 50% of the soils nitrification was also the dominant process of N₂O production. Factor analysis extracted three factors which together explained 71% of the variance and identified three different soil groups. Group I contained acidic soils, which showed only low rates of microbial respiration and low contents of total and inorganic nitrogen. Group II mainly contained acidic forest soils, which showed relatively high respiration rates and high contents of total N and NH₄ ⁺. Group III mainly contained neutral agricultural soils with high potential rates of nitrification. The soils of group I produced the lowest amounts of NO and N₂O. The results of linear multiple regression conducted separately for each soil group explained between 44–100% of the variance. The soil variables that regulated consumption of NO, total production of NO and N₂O, and production of NO and N₂O by either nitrification or denitrification differed among the different soil groups. The soil pH, the contents of NH₄ ⁺, NO₂ ^– and NO₃ ^–, the texture, and the rates of microbial respiration and nitrification were among the important variables. Received: 28 October 1999     

Ammonium fixation by clay minerals in different layers of two paddy soils after flooding

 The influence of flooding and cellulose addition on the fixation of NH₄ ⁺ in different soil layers of two paddy soils from China (an entisol and an ultisol) was investigated. In both soils the content of total reducing substances (TRS) sharply increased during the first days after flooding and was highest in the anoxic layers. This increase, which was more pronounced in the entisol with the higher total C content, was accompanied by an increase in the concentration of non-exchangeable NH₄ ⁺ in both soils. The increase in mineralization after flooding, resulting in higher concentrations of exchangeable NH₄ ⁺, favoured the fixation of NH₄ ⁺. Although the application of cellulose resulted in higher TRS contents, the fixation of NH₄ ⁺ ions decreased, which may have been the result of microbiological N immobilization. Received: 29 April 1998     

Microbial response of an acid forest soil to experimental soil warming

 Effects of increased soil temperature on soil microbial biomass and dehydrogenase activity were examined on organic (O) horizon material in a low-elevation spruce-fir ecosystem. Soil temperature was maintained at 5  °C above ambient during the growing season in the experimental plots, and soil temperature, moisture, microbial biomass, and dehydrogenase activity were measured during the experiment. An incubation study was also conducted under three temperature regimes, 5, 15, and 25  °C, and under four moisture regimes of 20, 120, 220, and 320% to further evaluate these environmental factors on dehydrogenase activity and microbial biomass. Soil moisture content and microbial biomass controls were significantly lower (30% and 2 μg g^–1 soil, respectively) in the heated plots during the treatment period, suggesting that moisture content was important in controlling microbial biomass. In the incubation study, temperature appeared more important than moisture in controlling microbial biomass and dehydrogenase activity. Increasing temperature between 5  °C and 25  °C resulted in significant decreases in microbial biomass and dehydrogenase activity. Received: 7 August 1998     

Methane release from millipedes and other soil invertebrates in Central Europe

The potential for methane production was investigated in 47 species of soil invertebrates. No detectable methane production was found in slugs, earthworms, potworms, oribatid mites, woodlices, springtails, centipedes, ants and soil diptera larvae. However, significant methane production was found in several temperate millipedes including some species from the order Julida (Leptoiulus trilobatus, Megaphyllum projectum, Megaphyllum unilineatum, Unciger transsilvanicus, Unciger foetidus, Leptoiulus proximus and Julus scandinavius). On the other hand, methane production was not confirmed in Cylindroiulus boleti which belongs to the same family. Members of the other orders (Glomerida and Polydesmida) did not release methane with the exception of one questionable recorded release in Polydesmus complanatus (Polydesmida, Polydesmidae). Methane producing species of millipedes showed significantly lower weight-specific rates of methane release than the cockroach Periplaneta americana and termite Prorhinotermes simplex. Methane release from millipedes was temperature-dependent; for the temperature range 5-25 °C, a Q₁₀ between 1.55 and 2.17 was calculated and the relationship between methane release and temperature was described by an exponential curve. Our results suggest that although overall methane fluxes from soil invertebrates under study cannot substantially influence a methane budget in most ecosystems, methane production is significant at least in some millipedes and therefore can impact mesoenvironments and microenvironments inhabited by these invertebrates. This work also confirms that methane production is not only supported by tropic soil invertebrates, but also by temperate species.