Cumulative CH4 Emissions Research Articles

Phosphorus availability as a primary constraint on methane emission from a freshwater wetland

Human activities have increased phosphorus (P) loading in wetland ecosystems worldwide. However, little is known about the effect of P enrichment on CH4 emissions from these ecosystems. In this study, a 4-year P addition experiment was conducted to examine the effects of increased P availability on CH4 emission in a Deyeuxia angustifolia-dominated freshwater marsh in the Sanjiang Plain in northeastern China. Phosphorus was added at four rates (0, 1.2, 4.8 and 9.6 g P m−2 year−1). We investigated CH4 emission during the growing season (early May to late September) using opaque chamber and gas chromatography method. Our results indicated that the effect of P enrichment on CH4 emission was time-dependent. Increased P availability did not affect CH4 emission in 2007 and 2008, but decreased in 2009 and 2010. Notably, four years of P addition decreased cumulative CH4 emission during the growing season in the freshwater marsh, and the effect did not change with fertilization rates. From 2007 to 2010, P additions of 1.2, 4.8 and 9.6 g P m−2 year−1 caused a decline in growing-season CH4 emissions by averages of 23%, 38% and 26%, respectively. Our results suggest that long-term P enrichment driven by agricultural activities would reduce CH4 emission from temperate freshwater wetlands. This study also highlights the impact of experimental duration on accurate assessments of the effect of P addition on wetland CH4 budget.

Seasonal variations of CH4 and N2O emissions in response to water management of paddy fields located in Southeast China

Water management is one of the most important practices that affect methane (CH4) and nitrous oxide (N2O) emissions from paddy fields. A field experiment was designed to study the effects of controlled irrigation (CI) on CH4 and N2O emissions from paddy fields, with traditional irrigation (TI) as the control. The effects of CI on CH4 and N2O emissions from paddy fields were very clear. The peaks of CH4 emissions from the CI paddies were observed 1–2d after the water layer disappeared. Afterward, the emissions reduced rapidly and remained low until the soil was re-flooded. A slight increase of CH4 emission was observed in a short period after re-flooding. N2O emissions peaks from CI paddies were all observed 8–10d after the fertilization at the WFPS ranging from 78.1% to 85.3%. Soil drying caused substantial N2O emissions, whereas no substantial N2O emissions were observed when the soil was re-wetted after the dry phase. Compared with TI, the cumulative CH4 emissions from the CI fields were reduced by 81.8% on the average, whereas the cumulative N2O emissions were increased by 135.4% on the average. The integrative global warming potential of CH4 and N2O on a 100-year horizon decreased by 27.3% in the CI paddy fields, whereas no significant difference in the rice yield was observed between the CI and TI fields. These results suggest that CI can effectively mitigate the integrative greenhouse effect caused by CH4 and N2O emissions from paddy fields while ensuring the rice yield.

Pattern of methane emission and water productivity under different methods of rice crop establishment

Methane (CH4) emission and water productivity were estimated in an experiment conducted during wet (rainy) season of 2010 at the research farm of Indian Agricultural Research Institute, New Delhi, India. Treatments comprising three methods of crop establishment viz., conventional transplanting (CT), system of rice intensification (SRI) and double transplanting (DT) were laid out in randomized block design with four replications. Scented rice (Oryza sativa L) variety ‘Pusa Basmati 1401’ was transplanted in puddle field. In CT and SRI 21 and 12-day-old seedlings, respectively, were transplanted while in DT overall 45-day-old seedlings were transplanted. In CT and DT flooded conditions while in SRI saturated conditions were maintained. Results indicated that among the methods of crop establishment, CT had maximum cumulative CH4 emission (32.33 kg ha−1) followed by DT (29.30 kg ha−1) and SRI (19.93 kg ha−1). Temporal CH4 flux fluctuated between 79.7 and 482.0 mg m−2 day−1 under CT; 46.0 and 315.0 mg m−2 day−1 in SRI and 86.7 and 467.3 mg m−2 day−1 in DT. Considerable temporal variations in the individual CH4 fluxes were observed. Flux of CH4 was generally higher in early stage of crop and peaked about 21 days after transplanting coinciding with tillering stage of crop. CH4 flux declined gradually from 75 days after transplanting and stabilized at the harvest stage of rice in all the three methods of transplanting. Global warming potential was highest in CT (807.4 kg CO2 ha−1) and lowest in SRI (498.25 kg CO2 ha−1). However, a reverse trend was observed with carbon efficiency ratio. The water savings to the extent of six irrigations was recorded in SRI over CT. A saving of 27.4 % irrigation water and 18.5 % total water was recorded in SRI over CT while the corresponding values of DT over CT were 14.5 and 9.8 %. Water productivity of SRI (3.56 kg/ha mm) was significantly higher as compared to DT (2.87 kg/ha mm) and CT (2.61 kg/ha mm).

Annual N2O and CH4 emissions from intensively managed vegetable fields in Nanjing, China

Nitrous oxide (N2O) and methane (CH4) emissions were monitored from an intensive vegetable production region with four typical consecutive rotations and a bare fallow in Nanjing, China, from 2009 to 2010. The four consecutive rotations were established as follows: Celery (Apium graveolens dulce L.)–Tung choy (Ipomoea aquatica Forsk L.)–Baby bok choy (Brassica rapa Chinensis L.)–Amaranth (Amaranthus mangostanus L.) (C-T-Bb-A), Choy sum (Brassica rapa Chinensis L.)–Celery–Tung choy–Bok choy (Brassica rapa Chinensis L.) (Cs-C-T-Bc), Garland chrysanthemum (Chrysanthemum coronarium L.)–Tung choy–Bok choy (G-T-Bc), and Celery–Choy sum–Lettuce (Lactuca sativa L.)–Bok choy (C-Cs-L-Bc). Annual cumulative N2O emissions were 237.7 ± 18.3, 137.2 ± 8.5, 100.9 ± 7.5, 56.4 ± 10.6 and 29.2 ± 3.7 kg N ha−1 from the G-T-Bc, C-T-Bb-A, Cs-C-T-Bc, C-Cs-L-Bc rotation fields and the bare fallow, respectively. Cumulative N2O emissions from the rotation fields, except the C-Cs-L-Bc rotation, were significantly higher than that from the bare fallow. Annual cumulative CH4 emissions were 9.0 ± 3.5, 13.9 ± 1.5, 18.8 ± 1.2, 12.1 ± 3.8 and 16.1 ± 3.5 kg C ha−1 from the bare fallow, C-T-Bb-A, Cs-C-T-Bc, G-T-Bc and C-Cs-L-Bc, respectively, and they did not show significant differences among systems. The annual N2O emission factor averaged 2.6%, ranging from 1.2% to 5.0%, and was higher than the current IPCC default value (1.0%). Total N fertilizer application rate explained 35.5% of annual N2O emissions. N2O emissions from intensively managed vegetable fields were characterized by high fluxes and emission factors that varied with cropping systems. Frequent year-round monitoring of N2O fluxes from intensively managed vegetable fields is essential for better constraint of the national N2O budget.

Greenhouse gas emissions during the seedling stage of rice agriculture as affected by cultivar type and crop density

Methane (CH4) and nitrous oxide (N2O) emissions from a paddy nursery at the rice seedling stage were measured on a daily basis by using the conventional rice cultivar Nangeng 56 under both conventional (NG-C) and reduced (NG-R) sowing density, and the hybrid rice Changyou 3 under both conventional (CY-C) and reduced (CY-R) sowing density. High N2O and CH4 emissions were observed during the first and last 2 weeks, respectively. Cumulative CH4 emissions were significantly (P < 0.001) affected by sowing density rather than by the rice cultivar. Cumulative CH4 emissions reached 68.2 kg C ha−1 in the CY-C treatment and 121.6 kg C ha−1 in the NG-C treatment, which were significantly (P < 0.001) higher than the emissions at reduced sowing densities (15.9 kg C ha−1 in the CY-R treatment and 20.9 kg C ha−1 in the NG-R treatment). Under the conventional sowing density, cumulative CH4 emissions during the seedling stage were comparable to data of rice-growing season. Both the rice cultivar and the sowing density significantly (P < 0.05–0.01) affected cumulative N2O emissions. Relative to the CY cultivar, the NG cultivar increased global warming potential (GWP) over a 100-year horizon by 62.1% and 70.7% under the reduced and conventional sowing densities, respectively. The GWP of N2O and CH4 during the seedling stage was equivalent to the GWP of the entire rice-growing season in this region, indicating that the seedling stage is an important greenhouse gas emission source of rice agriculture.

Contribution of urine and dung patches from grazing sheep to methane and carbon dioxide fluxes in an inner mongolian desert grassland.

The effects of sheep urine and dung patches on methane (CH4) and carbon dioxide (CO2) fluxes were investigated during the summer-autumn in 2010, to evaluate their contribution to climate change in a desert grassland in Inner Mongolia, China. Results indicate that the cumulative CH4 emissions for dung patches, urine patches and control plots were − −0.076, −0.084, and −0.114 g/m2 and these were net CH4 sinks during the measured period. The level of CH4 intake from urine and dung plots decreased 25.7%, and 33.3%, respectively, compared with a control plot. CO2 fluxes differed (p<0.01) in urine plots, with an average of 569.20 mg/m2/h compared with control plots (357.62 mg/m2/h) across all sampling days. Dung patches have cumulative CO2 emissions that were 15.9% higher compared with the control during the 55-d period. Overall, sheep excrement weakened CH4 intake and increased CO2 emissions.

Nitrous oxide and methane emission from a flooded rice field as influenced by separate and combined application of herbicides bensulfuron methyl and pretilachlor

Combination of divergent active principles to achieve broad-spectrum control is gaining popularity to manage the weed menace in intensive agriculture. However, such application could have non-target impacts on the soil processes affecting soil ecology and environmental interactions. A field experiment was conducted to investigate the impact of separate and combined applications of herbicides bensulfuron methyl and pretilachlor on the emission of N2O and CH4, and related soil and microbial parameters in a flooded alluvial field planted to rice cv Lalat. Single application of the herbicide bensulfuron methyl or pretilachlor resulted in a significant reduction of N2O and CH4 emissions while the combination of these two herbicides distinctly increased N2O and CH4 emissions. Cumulative N2O emissions (kg N2O–N) followed the order of bensulfuron methyl (0.35kgha−1)<pretilachlor (0.36kgha−1)<control (0.45kgha−1)<bensulfuron methyl 0.6%+pretilachlor 6.0% single dose (0.49kgha−1)<bensulfuron methyl 0.6%+pretilachlor 6.0% double dose (0.54kgha−1). Cumulative CH4 emissions (kg CH4), on the other hand, followed the order of bensulfuron methyl (47.89kgha−1)<pretilachlor (73.17kgha−1)<bensulfuron methyl 0.6%+pretilachlor 6.0% single dose (93.50kgha−1)<control (106.54kgha−1)<bensulfuron methyl 0.6%+pretilachlor 6.0% double dose (124.67kgha−1). The inhibitory effect of separate application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% on N2O emission was linked to lower mineral N, lower denitrifying and nitrifying activity and low denitrifier and nitrifier populations. Inhibitory effect on CH4 emission, on the contrary, was linked to prevention in the drop of redox potential, lower readily mineralizable carbon (RMC) and microbial biomass carbon (MBC) contents as well as lower methanogenic and higher methanotrophic bacterial population. Admittedly, stimulatory effect of combined application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% at double dose on N2O and CH4 emission was related to reversal of the identified indicators of inhibition. Results indicate that while individual application of herbicides bensulfuron methyl 0.6% or pretilachlor 6.0% can reduce N2O and CH4 emission from flooded soil planted to rice, their combined application at normal dose can keep the emission at a comparatively lower level with significantly higher grain yield as compared to the herbicides applied alone.

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.

Effect of ammonium-based, non-sulfate fertilizers on CH4 emissions from a paddy field with a typical Chinese water management regime

Abstract The effects of ammonium-based, non-sulfate fertilizers, such as urea and/or ammonium phosphate (NH4H2PO4), on methane (CH4) emissions from paddy rice fields deserve attention, as they are being used increasingly for rice cultivation. A four-year field campaign was conducted in the Yangtze River Delta from 2004 to 2007 to assess the effects of different application rates of urea plus NH4H2PO4 on the CH4 emissions from a paddy rice field. The experimental field was under a typical Chinese water regime that follows a flooding-midseason drainage-reflooding-moist irrigation mode. Over the course of four years, the mean cumulative CH4 emissions during the rice seasons were 221, 136 and 112 kg C ha−1 for nitrogen addition rates of 0, 150 and 250 kg N ha−1, respectively. Compared to the treatment without nitrogen amendments, the 150 kg N ha−1 decreased the CH4 emissions by 6–59% (P

Mitigating methane emissions from irrigated paddy fields by application of aerobically composted livestock manures in eastern China

AbstractLivestock manure heaps and wetland rice fields are major sources of CH4 emissions. A field experiment with an associated composting study were undertaken to investigate CH4 emissions during manure composting and subsequent land application on paddy. Over a 24‐day period in the composting experiment, CH4 emissions from stored manure was 17 times higher than that from composting manure, indicating that composting as an aerobic process was effective in mitigating CH4 emissions compared with manure storage, which is normally under an anaerobic environment. Stored and composted manures were subsequently applied as organic fertilizers in the field experiment. Compared with the non‐fertilized control treatment, stored and composted manures increased grain yields by 30% and 21%, respectively. During the full rice‐growing season, the cumulative CH4 emission was 15.8 g CH4/m2 with the application of composted manure, only one‐third of that from stored manure. CH4 emission per unit of grain yield was significantly decreased by composted manure, with a reduction of 56% from the control and 73% from stored manure. The results indicate that composted livestock manure in rice cultivation is a triple‐win option through sustaining rice yield, mitigating CH4 emissions and re‐utilizing livestock waste.

Greenhouse Gas Emission from Contrasting Management Scenarios in the Northern Corn Belt

The agricultural sector is a small but significant contributor to the overall anthropogenic greenhouse gas (GHG) emission and a major contributor of N2O emission in the United States. Land management practices or systems that reduce GHG emission would aid in slowing climate change. We measured the emission of CO2, CH4, and N2O from three management scenarios: business as usual (BAU), maximum C sequestration (MAXC), and optimum greenhouse gas benefits (OGGB). The BAU scenario was chisel or moldboard plowed, fertilized, in a 2‐yr rotation (corn [Zea mays L.]–soybean [Glycine max (L.) Merr.]). The MAXC and OGGB scenarios were strip tilled in a 4‐yr rotation (corn–soybean–wheat [Triticum aestivum L.]/alfalfa [Medicago sativa L.]–alfalfa). The MAXC received fertilizer inputs but the OGGB scenario was not fertilized. Nitrous oxide, CO2, and CH4 emissions were collected using vented static chambers. Carbon dioxide flux increased briefly following tillage, but the impact of tillage was negligible when CO2 flux was integrated across an entire year. The soil tended to be neutral to a slight CH4 sink under these managements scenarios. The N2O flux during spring thaw accounted for up to 65% of its annual emission, compared with 6% or less due to application of N fertilizer. Annual cumulative emissions of CO2, CH4, and N2O did not vary significantly among these three management scenarios. Reducing tillage and increasing the length of the crop rotation did not appreciably change GHG emissions. Strategies that reduce N2O flux during spring thaw could reduce annual N2O emission.

Greenhouse gas emission from direct seeding paddy field under different rice tillage systems in central China

Agricultural tillage practices play an important role in the production and/or consumption of green house gas (GHG) that contributes substantially to the observed global warming. Central China is one of the world's major rice producing areas but a few studies have tried to characterize the mechanisms of GHG release from rice paddy field and quantify global warming (GWPs) based on GHGs emission on this region. In this study four tillage systems consisting of no-tillage with no fertilizer (NT0), conventional tillage with no fertilizer (CT0), no-tillage with compound fertilizer (NTC) and conventional tillage with compound fertilizer (CTC) applications in rice (Oryza sativa L.) cultivation were compared in terms of the carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions from different tillage systems of the subtropical region of China during the rice growing season in 2008. GWPs based on CO2, CH4 and N2O's cumulative emissions were also compared. Tillage and fertilization had no influence on CO2 emissions. No-tillage had no effect on N2O emissions but significantly affected CH4 emissions. Application of fertilizer significantly affected CH4 and N2O emissions. Higher CH4 emissions and lower N2O emissions were observed in CTC than in NTC. Cumulative CH4 emission flux in NTC was 51.68 g CH4 m−2 while it was 65.96 g CH4 m−2 in CTC, 28% (p < 0.05) higher than that in NTC. Cumulative N2O emission flux in CTC was 561.00 mg N2O m−2, and was 741.71 mg N2O m−2 in NTC, 33% (p < 0.05) higher than that in CTC. There was no significant difference in N2O emissions between NT0 and CT0 systems, but significant in CH4 emissions. GWP of CTC was 26011.58 kg CO2 ha−1, which was 12% higher than that in NTC (23361.3 kg CO2 ha−1), therefore our findings show that no-tillage system was an effective strategy to reduce GWP from rice paddies in central China and thus can serve as a good agricultural system for environmental conservation.

N2O and CH4 fluxes from a volcanic grassland soil in Nasu, Japan: Comparison between manure plus fertilizer plot and fertilizer-only plot

We examined the effects of manure + fertilizer application and fertilizer-only application on nitrous oxide (N2O) and methane (CH4) fluxes from a volcanic grassland soil in Nasu, Japan. In the manure + fertilizer applied plot (manure plot), the sum of N mineralized from the manure and N applied as ammonium sulfate was adjusted to 210 kg N ha−1 year−1. In the fertilizer-only applied plot (fertilizer plot), 210 kg N ha−1 year−1 was applied as ammonium sulfate. The manure was applied to the manure plot in November and the fertilizer was applied to both plots in March, May, July and September. From November 2004 to November 2006, we regularly measured N2O and CH4 fluxes using closed chambers. Annual N2O emissions from the manure and fertilizer plots ranged from 7.0 to 11.0 and from 4.7 to 9.1 kg N ha−1, respectively. Annual N2O emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). This difference could be attributed to N2O emissions following manure application. N2O fluxes were correlated with soil temperature (R = 0.70, P < 0.001), NH+ 4 concentration in the soil (R = 0.67, P < 0.001), soil pH (R = –0.46, P < 0.001) and NO− 3 concentration in the soil (R = 0.40, P < 0.001). When included in the multiple regression model (R = 0.72, P < 0.001), however, the following variables were significant: NH+ 4 concentration in the soil (β = 0.52, P < 0.001), soil temperature (β = 0.36, P < 0.001) and soil moisture content (β = 0.26, P < 0.001). Annual CH4 emissions from the manure and fertilizer plots ranged from –0.74 to –0.16 and from –0.84 to –0.52 kg C ha−1, respectively. No significant difference was observed in annual CH4 emissions between the plots. During the third grass-growing period from July to September, however, cumulative CH4 emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). CH4 fluxes were correlated with NH+ 4 concentration in the soil (R = 0.21, P < 0.05) and soil moisture content (R = 0.20, P < 0.05). When included in the multiple regression model (R = 0.29, P < 0.05), both NH+ 4 concentration in the soil (β = 0.20, P < 0.05) and soil moisture content (β = 0.20, P < 0.05) were significant.

Reduction in greenhouse gas emissions by no-tilling rice cultivation in Hachirogata polder, northern Japan: Life-cycle inventory analysis

The scenarios for conventional puddling and no-tilling rice (Oryza sativa L.) cultivation were compared in terms of greenhouse gas (GHG) emissions from paddy fields, fuel consumption and manufacturing of invested materials using a life cycle inventory (LCI) based analysis. Only the differences between the scenarios were examined. The no-tilling scenario omitted both tilling and puddling, but included spraying of a non-selective herbicide and used a transplanter equipped with a rotor. Fertilization was a basal single application of controlled release fertilizer in nursery boxes for all scenarios. After transplanting, there were no differences in machine work, invested materials or rice yields between the scenarios. The no-tilling scenario saved on fuel consumption, totaling carbon dioxide (CO2) output of 42 kg ha−1, which was equal to the 6% reported GHG emissions from fuel consumption by operating machines during rice production in Japan. Methane (CH4) and nitrous oxide (N2O) emissions from the paddy fields were also monitored and compared for the scenarios. Methane has a major effect on global warming as part of the GHG emitted from paddy fields. The cumulative CH4 emissions from the no-tilling cultivation were 43% lower than those from conventional puddling cultivation because the plow layer was more oxidative in no-tilling cultivation. The N2O emissions were not significantly different between the cultivation scenarios. There were no significant differences in soil respiration, soil carbon contents or straw yields between the cultivation scenarios. The effect of tillage on CO2 flux in the paddy fields did not seem to be significant in this study. Consequently, the GHG emissions from the no-tilling field counted as CO2 using global warming potentials were 1,741 kg CO2 ha−1 lower than those from the conventional puddling field. In conclusion, no-tilling rice cultivation has the potential to save 1,783 kg CO2 ha−1 calculated using the sum of fuel consumption and GHG emissions from paddy fields. No-tilling rice cultivation is considered to be environmentally friendly agriculture with respect to reducing GHG emissions.

Greenhouse gas emissions during co-composting of cattle mortalities with manure

Following outbreaks of bovine spongiform encephalopathy (BSE), fewer cattle mortalities are being rendered. Composting may be a viable on-farm alternative for disposal of cattle carcasses. A study was conducted to assess feasibility and greenhouse gas (GHG) emissions during co-composting of cattle mortalities and manure. Using a tractor-mounted front-end loader, windrows were constructed containing manure + straw (control; CK) or manure + straw + cattle mortalities (cattle mortality; CM). The composting process lasted 310 d. The windrows were turned twice, at days 93 and 211, using either a tractor-mounted front-end loader or a specialized shredder bucket. Maximum windrow temperatures were >50 °C for 36 out of 92 d (before first turning) and 142 out of 208 d (after first turning) for the CM treatment and cattle mortalities were completely decomposed except for a few large bones. The cumulative CO2 and CH4 emissions were significantly affected by the mortality treatment, but not by the turning technology or their interactions. Significantly higher CO2 (53.6 g d−1 m−2) and CH4 (2.204 g d−1m−2) emissions were observed during the co-composting of cattle mortalities than manure composted with straw (23.0 and 0.742 g d−1m−2 for CO2 and CH4, respectively). Similarly, N2O emissions were higher with mortalities than without and, for the CM treatment only, higher with shredder bucket than front-end loader turning. In the final compost, CM had higher TN and NH 4 + -N contents than CK while TC and the C/N ratio were higher with compost turned with the front-end loader than with the shredder bucket. In conclusion, composting was an effective means of disposing of cattle mortalities, but did increase GHG emissions and the N content in the final compost. It is not known if GHG emissions are different than those that would be released from natural decomposition of carcasses. The higher N content in compost containing mortalities would increase its agronomic value.

Fully coupled dual-porosity model for anisotropic formations

A two-dimensional dual-porosity model for coupled rainwater and landfill gas transport through capillary barrier covers (CBCs) was established. The proposed model was partially verified using published data from a laboratory loess column test. By fitting the field-measured data using the proposed model, the optimal dual-porosity parameters of the in-situ loess of a loess/gravel CBC in Northwest China were determined to be wf = 0.1 (volume fraction of macropore system), Kf/Km = 150 (intrinsic permeability ratio of macropore to micropore system) and Re = 1 (reduction factor of mass exchange at the interface between macropore and micropore systems). This model was used to predict the performance of the CBC experiencing a 15-day rainfall period followed by a 30-day no-rainfall period. Results showed that the presence of macropores induced an earlier occurrence of percolation accompanied with a higher percolation rate. The cumulative percolation and CH4 emission rate derived from the dual-porosity model were about 50 % and one order of magnitude higher than those predicted by the single-porosity model, respectively. In addition, the existence of gravel layer had remarkable influence on minimizing water percolation and CH4 emission, but these were practically independent of its thickness. The results of this study can provide an effective method, crucial parameters and guidelines for the design of CBCs.

Methane emission from a flooded field of Eastern India as influenced by planting date and age of rice (Oryza sativa L.) seedlings

Abstract Flooded paddy is considered to be one of the major anthropogenic sources of atmospheric methane (CH4), a potent greenhouse gas. Emission of CH4 from flooded rice soils is affected by a multitude of factors including crop management practices. In a field study, CH4 fluxes from a sub-humid tropical flooded field of Cuttack, eastern India, as affected by planting with 20 and 35-day old rice (Oryza sativa L.) seedlings on two sets of planting dates were measured with the closed chamber method in 2002–2003 encompassing wet (kharif) season, 2002 and dry (rabi) season, 2003. In the wet season of 2002, CH4 emission from staggered planting was measured with two varieties viz. Lalat and Gayatri, while during the dry season of 2003, the experiment was conducted with cv. Lalat. CH4 emission was low from plots planted to aged seedlings (35-day) as well as seedlings transplanted late in both sets of experiments that were transplanted to the main field with an interval of 15 days during the two growing seasons. Cumulative CH4 emission from early- and late-transplanted plots during wet season, 2002 was 408.77 and 308.58 kg ha−1 and during the dry season, 2003 was 431.35 and 328.66 kg ha−1, respectively. Early transplanted seedlings had higher number of tillers and exhibited low soil redox (Eh) potential thereby favouring higher CH4 emission. There was no statistically significant yield reduction due to transplanting of aged seedlings or planting late over that of young seedlings planted early. Our results suggest that in rainfed rice cultivation, as practiced in greater part of Asia and Africa, transplanting late with comparatively aged seedlings could lead to a considerable reduction in CH4 emission without being detrimental to the yield.

Temporal variations in soil–atmosphere methane exchange after fire in a peat swamp forest in West Siberia

Temporal variations in methane (CH4) exchange between the soil and the atmosphere during a period of 3 years after a forest fire were estimated by combining field measurements of CH4 flux with an analysis of satellite images. The study area was located in a boreal peat swamp forest in the West Siberian plain that experienced a severe fire in the summer of 1998. The surface of the burned area was classified into bare soil, open water and recovered vegetation. In the summers of 1999 and 2000, CH4 fluxes, using a closed-chamber method, and environmental variables, such as soil temperature and soil water content, for each of the three surface types in the burned area and in the unburned area were measured. In general, CH4 fluxes were controlled by the surface moisture in the burned area and by the temperature in the unburned forest. Temporal changes in the areal coverage of soil, water and vegetation in the burned area were investigated using NOAA AVHRR (Advanced Very High Resolution Radiometer) data with subpixel land-cover characterization. Based on the satellite information, temporal changes in the moisture conditions of the burned surface were estimated and temporal variations in the CH4 fluxes for the entire burned area were calculated. The cumulative CH4 emission rates from the entire burned area during the summer (from June to August) were estimated to range from 0.39 to 0.48 g C m−2 during the period from 1999 to 2001. In contrast, unburned forest soils were consistently net CH4 consumers. The cumulative consumption rate during the summer was calculated to be approximately 0.4 g C m−2 based on a reanalysis air temperature dataset. As the surface soil had become extremely wet since the fire, the soil had become a net emitter of CH4 after the fire disturbance, although CH4 oxidation predominated in the unburned forest.

Methane and nitrous oxide emissions from a paddy field with Japanese conventional water management and fertilizer application

The seasonal courses of methane (CH4) and nitrous oxide (N2O) fluxes were simultaneously monitored in a paddy field using a closed chamber system with automated gas sampling and analyzing equipment. Water management and fertilizer application practices followed Japanese conventional ones. CH4 flux gradually increased after the first flood irrigation of the field and reached ∼150 mg CH4 m−2 d−1 at the beginning of July. After the first summer drainage, however, CH4 flux dropped rapidly to almost zero within a few days. CH4 flux then gradually increased again according to intermittent flood irrigations, but was much less than that before the first drainage. Immediately after the first flood irrigation, N2O flux rapidly increased, although its temporal peak lasted only within a few days. During the subsequent continuously and intermittently flooded periods, N2O flux remained at almost zero until the final drainage, except for slight and temporal peaks just after the top‐dress application of supplemental fertilizer. About 1 week after the final drainage in autumn, N2O flux gradually increased, and the most significant high peak of N2O flux was observed after the harvest of rice plants, which lasted for about 2 weeks. The amounts of cumulative CH4 and N2O emissions throughout the whole year of 2002 were 3128 mg CH4 m−2 and 60.2 mg N m−2, respectively. Both the amounts of cumulative CH4 and N2O emissions during the rice cultivation period were low compared with those reported in previous studies. These results suggest the advantage of Japanese conventional water management and fertilizer application for reducing the combined effect for global warming by CH4 and N2O emissions from paddy fields, since the practices of drainage and intermittent flood irrigation in summer markedly lessen CH4 emission in the latter half of the rice cultivation period with little enhancement of N2O emission.

Methane (CH4) release from littoral wetlands of Boreal lakes during an extended flooding period

AbstractLake littoral zones have a transitional nature and dynamic conditions, which are reflected in their CH4 emissions. Thus, detailed studies are needed to assess the littoral CH4 emissions in a regional scale. In this study, CH4 fluxes were followed during the ice‐free seasons in 1998 and 1999 by using the static chamber method in the littoral zone of two lakes in Finland. An exceptionally high water level in 1998 caused an unusually long inundation in otherwise ephemerally flooded zone. The flooding was normal in year 1999. The factors controlling CH4 emissions were examined and statistical response functions were constructed. Further, the effect of extended flooding on the littoral CH4 budged was estimated. The methane flux was primarily regulated by the water level in grass and sedge dominated eulittoral zone, but not in infralittoral reed and water lily stands. Methane emissions in the sedge dominated zone decreased significantly, when the flood was high enough to submerge the venting structures of the plants. Besides water level, sediment temperature determined CH4 emission. The cumulative CH4 emissions from the whole littoral wetlands in wet year were 1.1 times (L. Kevätön), or 0.61 and 0.79 times (L. Mekrijärvi) those in dry year. The crucial factor was the discrepancy between the exceptional and the average water level. The extension of inundated area does not necessarily increase CH4 emissions if the flood reaches infrequently inundated areas, which apparently have low CH4 production potential. This is the case especially, if the emissions in lower zones simultaneously decrease due to high water level. Our study analyses these complex responses between CH4 emissions and water level.