The influence of nitrate and ammonium fertilization on N2O release and CH4 uptake of a well-drained topsoil demonstrated by a soil microcosm experiment

The effects of the application of KNO₃ and NH₄Cl (100 kg N ha^?1) on N₂O release and CH₄ uptake by a well-aerated topsoil (porosity: 55%, water-filled pore space: 67% of the total pore space) were studied in a laboratory incubation experiment over 50 days using a soil microcosm system with an automated registration of N₂O and CH₄ fluxes. The total N₂O-N losses over 50 days were low for all treatments and amounted to 0.9 mg m^?2 for the control, 1.2 mg m^?2 for the soil columns fertilized with KNO3, and 7.3 mg m^?2 for the soil columns fertilized with NH₄Cl. The slightly elevated N₂O release after the application Of NH₄Cl was associated with the nitrification of NH₄⁺ added. Only ?0.06% of the fertilized NH₄?N was lost as N₂O. This nitrogen fertilization reduced the CH₄ uptake of the soil columns by 43% (NH₄Cl) and 21% (KNO₃), respectively.     

Methane and N2O emissions, nitrate concentrations of drainage water, and zinc and copper uptake by rice fertilized with anaerobically digested cattle or pig slurry

We have examined the effects of different types of slurry on CH₄ and N₂O emissions, Zn and Cu contents of rice, and nitrate content of the drainage water. The experiment included four treatments: (1) anaerobically digested cattle slurry (ADCS), (2) ADCS filtered to remove the coarse organic matter fraction, (3) anaerobically digested pig slurry (ADPS), and (4) chemical fertilizer (CF). The application rate was 30?g?NH₄?CN?m^?2. Different amounts of C were incorporated with fertilization: 725?g?C?m^?2 in ADCS, 352?g?m^?2 in filtered ADCS, and 75?g?m^?2 in ADPS. The average CH₄ emissions during a growing period were 304, 359, 452, and 579?mg?m^?2?day^?1 in the CF, ADPS, filtered ADCS, and ADCS treatments, respectively. The CH₄ emission was significantly higher in ADCS than in CF and ADPS. Negligible N₂O emissions were observed during the growing period. Comparable concentrations of Zn and Cu were observed in the rice grain among the treatments. In contrast, their concentrations in the stems and leaves were significantly higher in ADPS than in CF treated rice, although the values were lower than the upper limit of feed additives. Nitrate concentrations in the drainage water were consistently low (0.5?mg?N?L^?1). The present study suggested that ADPS, containing a lower amount of C than ADCS, might be an organic fertilizer in paddy field with comparable environmental impacts to chemical fertilizers (CF), but long-term field studies are needed to better understand the effects of these organic fertilizers.     

Nitrous oxide and methane fluxes during the growing season from cultivated peat soils,peaty marl and gyttja clay under different cropping systems

Drainage of peatlands affects the fluxes of greenhouse gases (GHGs). Organic soils used for agriculture contribute a large proportion of anthropogenic GHG emissions, and on-farm mitigation options are important. This field study investigated whether choice of a cropping system can be used to mitigate emissions of N₂O and influence CH₄ fluxes from cultivated organic and carbon-rich soils during the growing season. Ten different sites in southern Sweden representing peat soils, peaty marl and gyttja clay, with a range of different soil properties, were used for on-site measurements of N₂O and CH₄ fluxes. The fluxes during the growing season from soils under two different crops grown in the same field and same environmental conditions were monitored. Crop intensities varied from grasslands to intensive potato cultivation. The results showed no difference in median seasonal N₂O emissions between the two crops compared. Median seasonal emissions ranged from 0 to 919?µg?N₂O?m^?2?h^?1, with peaks on individual sampling occasions of up to 3317?µg?N₂O?m^?2?h^?1. Nitrous oxide emissions differed widely between sites, indicating that soil properties are a regulating factor. However, pH was the only soil factor that correlated with N₂O emissions (negative exponential correlation). The type of crop grown on the soil did not influence CH₄ fluxes. Median seasonal CH₄ flux from the different sites ranged from uptake of 36?µg CH₄?m^?2?h^?1 to release of 4.5?µg?CH₄?m^?2?h^?1. From our results, it was concluded that farmers cannot mitigate N₂O emissions during the growing season or influence CH₄ fluxes by changing the cropping system in the field.     

Influence of increasing temperature and nitrogen input on greenhouse gas emissions from a desert steppe soil in Inner Mongolia

We investigated the effect of increasing soil temperature and nitrogen on greenhouse gas (GHG) emissions [carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O)] from a desert steppe soil in Inner Mongolia, China. Two temperature levels (heating versus no heating) and two nitrogen (N) fertilizer application levels (0 and 100?kg?N?ha^?1?year^?1) were examined in a complete randomized design with six replications. The GHG surface fluxes and their concentrations in soil (0 to 50?cm) were collected bi-weekly from June 2006 to November 2007. Carbon dioxide and N₂O emissions were not affected by heating or N treatment, but compared with other seasons, CO₂ was higher in summer [average of 29.6 versus 8.6?mg carbon (C) m^?2?h^?1 over all other seasons] and N₂O was lower in winter (average of 2.6 versus 4.0?mg?N?m^?2?h^?1 over all other seasons). Desert steppe soil is a CH₄ sink with the highest rate of consumption occurring in summer. Heating decreased CH₄ consumption only in the summer. Increasing surface soil temperature by 1.3°C or applying 100?kg?ha^?1?year^?1 N fertilizer had no effect on the overall GHG emissions. Seasonal variability in GHG emission reflected changes in temperature and soil moisture content. At an average CH₄ consumption rate of 31.65?µg?C?m^?2?h^?1, the 30.73 million ha of desert steppe soil in Inner Mongolia can consume (sequestrate) about 85?×?10^6?kg CH₄-C, an offset equivalent to 711?×?10^6?kg CO₂-C emissions annually. Thus, desert steppe soil should be considered an important CH₄ sink and its potential in reducing GHG emission and mitigating climate change warrants further investigation.     

Nitrous oxide and methane fluxes from organic soils under agriculture

Trace gas fluxes of N₂O and CH₄ were measured weekly over 12 months on cultivated peaty soils in southern Germany using a closed chamber technique. The aim was to quantify the effects of management intensity and of soil and climatic factors on the seasonal variation and the total annual exchange rates of these gases between the soil and the atmosphere. The four experimental sites had been drained for many decades and used as meadows (fertilized and unfertilized) and arable land (fertilized and unfertilized), respectively. Total annual N₂O-N losses amounted to 4.2, 15.6, 19.8 and 56.4 kg ha^–1 year^–1 for the fertilized meadow, the fertilized field, the unfertilized meadow and the unfertilized field, respectively. Emission of N₂O occurred mainly in the winter when the groundwater level was high. At all sites maximum emission rates were induced by frost. The largest annual N₂O emission by far occurred from the unfertilized field where the soil pH was low (4.0). At this site 71% of the seasonal variation of N₂O emission rates could be explained by changes in the groundwater level and soil nitrate content. A significant relationship between N₂O emission rates and these factors was also obtained for the other sites, which had a soil pH between 5.1 and 5.8, though the relation was weak (R² = 15–27%). All sites were net sinks for atmospheric methane. Up to 78% of the seasonal variation in CH₄ flux rates could be explained by changes in the groundwater level. The total annual CH₄-C uptake was significantly affected by agricultural land use with greater CH₄ consumption occurring on the meadows (1043 and 833 g ha^–1) and less on the cultivated fields (209 and 213 g ha^–1).     

Methane emissions from paddy fields in Bali Island,Indonesia

Abstract

Methane emission rates from plots with and without fertilizer and rice straw application, and growth of two rice varieties (an improved variety, IR74 or IR64, and a local variety, Krueng Aceh) in two Indonesian paddy fields (Inceptisol and Alfisol soils of volcanic ash origin) were measured every week throughout the growth period in the first and the second cropping seasons, 1994. The CH₄ emission rates from the fields were similar between the two varieties. The effect of chemical fertilizer on the increase of the emissions was observed only in the Tabanan paddy field for the plots treated with rice straw. Application of rice straw increased the CH₄ emission rates. The mean rates of CH₄ emission were 1.37-2.13 mg CH₄?C m^?2 h^?1 for the plots without rice straw and 2.14–3.62 mg CH₄?C m^?2 h^?1 for the plots with rice straw application in the Alfisol plots, and 2.32–3.32 mg CH₄ -C m-2 h-1 for the plots without rice straw and 4.18–6.35 mg CH₄?C m^?2 h^?1 for the plots with rice straw application in the Inceptisol plots, respectively. Total amounts of CH₄ emitted during the growth period were 3.9–6.8 and 2.6–3.3 g CH₄?C m^?2 for the Alfisol plots and 6.9–10.7 and 4.2–5.8 g CH₄?C m^?2 for the Inceptisol plots with and without rice straw application, respectively. These findings suggested that CH₄ emission from tropical paddy fields with soils of volcanic ash origin is low.     

CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Abstract

Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO₂ flux was highest at PB (128 ± 85 mg CO₂-C m^?2 h^?1) and lowest at SB1 (47 ± 19 mg CO₂-C m^?2 h^?1) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH₄ uptake rate was highest at SB1 [–91 ± 21 μg CH₄-C m^?2 h^?1] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N₂O flux was highest [3.6 ± 4.7 μg N₂O-N m^?2 h^?1] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.     

Nitrogen fertilization of wheat residue affecting nitrous oxide and methane emission from a central Ohio Luvisol

Fertilization of wheat (Triticum aestivum, L.) residue applied to degraded soils has shown promise as an option to restoring soil organic C (SOC) stocks, but the impact of the practice on N2O and CH4 emissions is not clear. It was hypothesized that, in addition to the mulch-induced soil wetness conditions favorable for N2O and CH4 formation, emission of these gases will be stimulated due to increased availability of mineral N and interference of NH4⁺ with CH4 oxidation in soils. During the period February–November 2000, fluxes of N2O and CH4 were monitored in a plant-free central Ohio Crosby soil (fine, mixed, mesic Aeric Ochraqualf) amended for 4 years with wheat straw (bare, 0; low, 8 Mg ha^–1 year^–1; and high, 16 Mg ha^–1 year^–1) without and with N fertilization (244 kg N ha^–1). The average annual N2O fluxes were 1.1 kg N2O-N ha^–1 in the unfertilized and 4.1 kg N2O-N ha^–1 in the fertilized treatments. Annual N2O emission (Y, mg N2O-N m^–2) was strongly correlated to the maximum daily flux (X, mg N2O-N m^–2 day^–1; Y=48.3X−58.1, R²=0.85, P<0.001) recorded on experimental plots. These flux maxima occurred at spring thaw in the unfertilized, and 6–30 days after fertilization in the fertilized treatments. Net CH4 uptakes were measured on some occasions; overall, however, all the treatments were net CH4 emitters with annual rates of 3.6, 4.9 and 5.1 kg CH4-C ha^–1 in the bare, low and high residue treatments, respectively. No significant effect of fertilization and mulch rate on CH4 fluxes was found, but temperature and landscape position appeared as strong controllers. Regardless of treatments, the highest CH4-emitting plots were located in a minor depressional area at the experimental site. A comparison of SOC gain and N2O and CH4 emission expressed as CO2-equivalents indicates that the residue treatments have a net CO2-mitigating effect, but since C sequestration rates are expected to decrease with time, that positive effect will likely vanish after 7 and 12 more years in the fertilized and unfertilized residue treatments, respectively.     

Effect of plant-mediated oxygen supply and drainage on greenhouse gas emission from a tropical peatland in Central Kalimantan,Indonesia

Abstract

To evaluate the hypothesis that plant-mediated oxygen supplies decrease methane (CH₄) production and total global warming potential (GWP) in a tropical peatland, the authors compared the fluxes and dissolved concentrations of greenhouse gases [GHGs; CH₄, carbon dioxide (CO₂) and nitrous oxide (N₂O)] and dissolved oxygen (DO) at multiple peatland ecosystems in Central Kalimantan, Indonesia. Study ecosystems included tropical peat swamp forest and degraded peatland areas that were burned and/or drained during the rainy season. CH₄ fluxes were significantly influenced by land use and drainage, which were highest in the flooded burnt sites (5.75 ± 6.66 mg C m^?2 h^?1) followed by the flooded forest sites (1.37 ± 2.03 mg C m^?2 h^?1), the drained burnt site (0.220 ± 0.143 mg C m^?2 h^?1), and the drained forest site (0.0084 ± 0.0321 mg C m^?2 h^?1). Dissolved CH₄ concentrations were also significantly affected by land use and drainage, which were highest in the flooded burnt sites (124 ± 84 μmol L^?1) followed by the drained burnt site (45.2 ± 29.8 μmol L^?1), the flooded forest sites (1.15 ± 1.38 μmol L^?1) and the drained forest site (0.860 ± 0.819 μmol L^?1). DO concentrations were influenced by land use only, which were significantly higher in the forest sites (6.9 ± 5.6 μmol L^?1) compared to the burnt sites (4.0 ± 2.9 μmol L^?1). These results suggest that CH₄ produced in the peat might be oxidized by plant-mediated oxygen supply in the forest sites. CO₂ fluxes were significantly higher in the drained forest site (340 ± 250 mg C m^?2 h^?1 with a water table level of ?20 to ?60 cm) than in the drained burnt site (108 ± 115 mg C m^?2 h^?1 with a water table level of ?15 to +10 cm). Dissolved CO₂ concentrations were 0.6–3.5 mmol L^?1, also highest in the drained forest site. These results suggested enhanced CO₂ emission by aerobic peat decomposition and plant respiration in the drained forest site. N₂O fluxes ranged from ?2.4 to ?8.7 μg N m^?2 h^?1 in the flooded sites and from 3.4 to 8.1 μg N m^?2 h^?1 in the drained sites. The negative N₂O fluxes might be caused by N₂O consumption by denitrification under flooded conditions. Dissolved N₂O concentrations were 0.005–0.22 μmol L^?1 but occurred at < 0.01 μmol L^?1 in most cases. GWP was mainly determined by CO₂ flux, with the highest levels in the drained forest site. Despite having almost the same CO₂ flux, GWP in the flooded burnt sites was 20% higher than that in the flooded forest sites due to the large CH₄ emission (not significant). N₂O fluxes made little contribution to GWP.     

Methane and nitrous oxide fluxes, and carbon dioxide production in boreal forest soil fertilized with wood ash and nitrogen

Wood ash has been used to alleviate nutrient deficiencies and acidification in boreal forest soils. However, ash and nitrogen (N) fertilization may affect microbial processes producing or consuming greenhouse gases: methane (CH₄), nitrous oxide (N₂O) and carbon dioxide (CO₂). Ash and N fertilization can stimulate nitrification and denitrification and, therefore, increase N₂O emission and suppress CH₄ uptake rate. Ash may also stimulate microbial respiration thereby enhancing CO₂ emission. The fluxes of CH₄, N₂O and CO₂ were measured in a boreal spruce forest soil treated with wood ash and/or N (ammonium nitrate) during three growing seasons. In addition to in situ measurements, CH₄ oxidation potential, CO₂ production, net nitrification and N₂O production were studied in laboratory incubations. The mean in situ N₂O emissions and in situ CO₂ production from the untreated, N, ash and ash + N treatments were not significantly different, ranging from 11 to 17 μg N₂O m^?2 h^?1 and from 533 to 611 mg CO₂ m^?2 h^?1. However, ash increased the CH₄ oxidation in a forest soil profile which could be seen both in the laboratory experiments and in the CH₄ uptake rates in situ. The mean in situ CH₄ uptake rate in the untreated, N, ash and ash + N plots were 153 ± 5, 123 ± 8, 188 ± 10 and 178 ± 18 μg m^?2 h^?1, respectively.     

Influence of mineral and organic fertilizers on soil organic carbon pools

Abstract

The influence of farmyard manure (FYM) and equivalent mineral NPK application on organic matter content, hot water extractable carbon (HWC), microbial biomass C (C_mic), and grain yields in a long-term field experiment was assessed after 40 years in Hungary. The unfertilized plot, FYM fertilized plots and plots fertilized with equivalent NPK fertilizer contained 0.99%, 1.13% and 1.05% total organic carbon (TOC) respectively. Compared to the unfertilized plot, FYM application resulted in 8.2% higher TOC than equivalent NPK fertilization. The highest TOC was only 1.21%, much lower than expected for a soil containing 21.3% of clay. The quantity of HWC varied depending on the type of fertilization: Compared to control, FYM treatments lead to 29% more HWC than mineral fertilization (FYM: 328 mg kg^?1; NPK: 264 mg kg^?1). The impact of FYM and equivalent NPK fertilizer on C_mic was contrary. FYM and NPK resulted in 304 and 423 mg kg^?1 C_mic, respectively. The difference was 119 mg kg^?1; 42% as compared to the unfertilized plot. Despite the higher HWC content, FYM treatments lead to significantly less (35%) grain yields than equivalent NPK doses; C_mic content showed closer correlation to grain yields.     

Effect of nitrogen fertilization on methane and carbon dioxide production potential in relation to labile carbon pools in tropical flooded rice soils in eastern India

In an incubation experiment with flooded rice soil fertilized with different N amounts and sampled at different rice stages, the methane (CH₄) and carbon dioxide (CO₂) production in relation to soil labile carbon (C) pools under two temperature (35°C and 45°C) and moisture (aerobic and submerged) regimes were investigated. The field treatments imposed in the wet season included unfertilized control and 40, 80 and 120 kg ha^?1 N fertilization. The production of CH₄ was significantly higher (27%) under submerged compared to aerobic conditions, whereas CO₂ production was significantly increased under aerobic by 21% compared to submerged conditions. The average labile C pools were significantly increased by 21% at the highest dose of N (120 kg ha^?1) compared to control and was found highest at rice panicle initiation stage. But the grain yield had significantly responded only up to 80 kg ha^?1 N, although soil labile C as well as gaseous C emission was noticed to be highest at 120 kg ha^?1 N. Hence, 80 kg N ha^?1 is a better option in the wet season at low land tropical flooded rice in eastern India for sustaining grain yield and minimizing potential emission of CO₂ and CH₄.     

Effect of Application of Rice Straw and Cellulose on Methane Emission and Biological Nitrogen Fixation in a Subtropical Paddy Field

A field experiment was conducted to evaluate the effect of the incorporation of rice straw and cellulose on methane flux, soil-acetylene reduction activity (ARA) and rice plant growth under a subtropical climate. Rice straw and cellulose (as paper) were applied at the rates of 4 and 10 t ha^-1. Emission rates of CH₄ from the paddy field without and with straw and cellulose amendments were measured by using the closed chamber method. Stimulation of N₂-fixation by the amendments was measured as soil-ARA under anaerobic conditions. The measurements indicated that the application of 10 t ha^-1 cellulose resulted in a relatively high emission of CH₄, with an average flux of 106.7 mg CH₄ m^-2 h^-1, followed by 10 t ha^-1 straw, 51.7 mg m^-2 h^-1, compared with the control, 5.3 mg m^-2 h^-1. Application of straw and cellulose at the rate of 10 t ha^-1 to the paddy field increased the CH₄ emission 10 and 21 fold over the values of the control, respectively as estimated seasonal emissions. The soil-ARA levels in the treatments during the cultivation period were positive. The stimulation of ARA by the amendment with 10 t ha^-1 cellulose occurred at the early stage of rice growth, while the maximum ARA-peak occurred in the 10 t ha^-1 straw-amended soil at around the heading stage. Amendment with straw at 10 t ha^-1 significantly increased the total dry matter weight of rice, whereas growth inhibition was induced by cellulose incorporation. The differences in CH₄ flux, and soil-ARA among the treatments were most evident at the heading stage.     

Controlled irrigation and drainage of a rice paddy field reduced global warming potential of its gas emissions

The effect of controlled drainage on methane (CH₄) and nitrous oxide (N₂O) emissions from a paddy field under controlled irrigation (CI) was investigated by controlling the sub-surface drainage percolation rate with a lysimeter. CI technology is one of the major water-saving irrigation methods for rice growing in China. Water percolation rates were adjusted to three values (2, 5, and 8 mm d^?1) in the study. On the one hand, the CH₄ emission flux and total CH₄ emission from paddy fields under CI decreased with the increase of percolation rates. Total CH₄ emissions during the growth stage of rice were 1.83, 1.16, and 1.05 g m^?2 in the 2, 5, and 8 mm d^?1 plots, respectively. On the other hand, the N₂O emission flux and total N₂O emissions from paddy fields under CI increased with the increase of percolation rates. Total N₂O emissions during the growth stage of rice were 0.304, 0.367, and 0.480 g m^?2 in the 2, 5, and 8 mm d^?1 plots, respectively. The seasonal carbon dioxide (CO₂) equivalent of CH₄ and N₂O emissions from paddy fields under CI was lowest in the 2 mm d^?1 plot (1364 kg CO₂ ha^?1). This value was 1.4% and 19.4% lower compared with that in the 5 and 8 mm d^?1 plots, respectively. The joint application of CI and controlled drainage may be an effective mitigation strategy for reducing the carbon dioxide equivalents of CH₄ and N₂O emissions from paddy fields.     

Nitrous oxide emission derived from soil organic matter decomposition from tropical agricultural peat soil in central Kalimantan,Indonesia

Our previous research showed large amounts of nitrous oxide (N₂O) emission (>200?kg?N?ha^?1?year^?1) from agricultural peat soil. In this study, we investigated the factors influencing relatively large N₂O fluxes and the source of nitrogen (N) substrate for N₂O in a tropical peatland in central Kalimantan, Indonesia. Using a static chamber method, N₂O and carbon dioxide (CO₂) fluxes were measured in three conventionally cultivated croplands (conventional), an unplanted and unfertilized bare treatment (bare) in each cropland, and unfertilized grassland over a three-year period. Based on the difference in N₂O emission from two treatments, contribution of the N source for N₂O was calculated. Nitrous oxide concentrations at five depths (5–80?cm) were also measured for calculating net N₂O production in soil. Annual N fertilizer application rates in the croplands ranged from 472 to 1607?kg?N?ha^?1?year^?1. There were no significant differences in between N₂O fluxes in the two treatments at each site. Annual N₂O emission in conventional and bare treatments varied from 10.9 to 698 and 6.55 to 858?kg?N?ha^?1?year^?1, respectively. However, there was also no significant difference between annual N₂O emissions in the two treatments at each site. This suggests most of the emitted N₂O was derived from the decomposition of peat. There were significant positive correlations between N₂O and CO₂ fluxes in bare treatment in two croplands where N₂O flux was higher than at another cropland. Nitrous oxide concentration distribution in soil measured in the conventional treatment showed that N₂O was mainly produced in the surface soil down to 15?cm in the soil. The logarithmic value of the ratio of N₂O flux and nitrate concentration was positively correlated with water filled pore space (WEPS). These results suggest that large N₂O emission in agricultural tropical peatland was caused by denitrification with high decomposition of peat. In addition, N₂O was mainly produced by denitrification at high range of WFPS in surface soil.     

Effect of potassium phosphate fertilization on production and emission of methane and its C-stable isotope composition in rice microcosms

Rice fields are an important source for atmospheric CH₄, but the effects of fertilization are not well known. We studied the turnover of CH₄ in rice soil microcosms without and with addition of potassium phosphate. Height and tiller number of rice plants were higher in the fertilized than in the unfertilized microcosms. Emission rates of CH₄ were also higher, but porewater concentrations of CH₄ were lower. The δ¹³C values of the emitted CH₄ and of the CH₄ in the porewater were both 2-6% higher in the fertilized microcosms than in the control. Potassium phosphate did not affect rate and isotopic signature of CH₄ production in anoxic soil slurries. On the other hand, roots retrieved from fertilized microcosms at the end of incubation exhibited slightly higher CH₄ production rates and slightly higher CH₄-δ¹³C values compared to roots from unfertilized plants. Addition of potassium phosphate to excised rice roots generally inhibited CH₄ production and resulted in increasingly lower δ¹³C values of the produced CH₄. Fractionation of ¹³C during plant ventilation (i.e. δ¹³C in pore water CH₄ versus CH₄ emitted) was larger in the fertilized microcosms than in the control. Besides plant ventilation, this difference may also have been caused by CH₄ oxidation in the rhizosphere. However, calculation from the isotopic data showed that less than 27% of the produced CH₄ was oxidized. Collectively, our results indicate that potassium phosphate fertilization stimulated CH₄ emission by enhancing root methanogenesis, plant ventilation and/or CH₄ oxidation, resulting in residence times of CH₄ in the porewater in the order of hours.     

Application of wood ash accelerates soil respiration and tree growth on drained peatland

Forested peatlands contain large pools of terrestrial carbon. As well as drainage, forest management such as fertilizer application can affect these pools. We studied the effect of wood ash (application rates 0, 5 and 15 t ha^?1) on the heterotrophic soil respiration (CO₂ efflux), cellulose decomposition, soil nutrients, biomass production and amount of C accumulated in a tree stand on a pine‐dominated drained mire in central Finland. The ash was spread 13 years before the respiration measurements. The annual CO₂ efflux was statistically modelled using soil temperature as the driving variable. Wood ash application increased the amounts of mineral nutrients of peat substantially and increased soil pH in the uppermost 10 cm layer by 1.5–2 pH units. In the surface peat, the decomposition rate of cellulose in the ash plots was roughly double that in control plots. Annual CO₂ efflux was least on the unfertilized site, 238 g CO₂‐C m^?2 year^?1. The use of wood ash nearly doubled CO₂ efflux to 420–475 g CO₂‐Cm^?2 year^?1 on plots fertilized with 5–15 t ha^?1 of ash, respectively. Furthermore, ash treatments resulted also in increased stand growth, and during the measurement year, the growing stand on ash plots accumulated carbon 11–12 times faster than the control plot. The difference between peat C emission and amount of C sequestered by trees on the ash plots was 43–58 g C m^?2, while on the control plot it was 204 g C m^?2. Our conclusion is that adding wood ash as a fertilizer increases more C sequestration in the tree stand than C efflux from the peat.     

Carbon exchange in a freshwater marsh in the Sanjiang Plain, northeastern China

Northern wetlands are critically important to global change because of their role in modulating atmospheric concentrations of greenhouse gases, especially CO₂ and CH₄. At present, continuous observations for CO₂ and CH₄ fluxes from northern wetlands in Asia are still very limited. In this paper, two growing season measurements for CO₂ flux by eddy covariance technique and CH₄ flux by static chamber technique were conducted in 2004 and 2005, at a permanently inundated marsh in the Sanjiang Plain, northeastern China. The seasonal variations of CO₂ exchange and CH₄ flux and the environmental controls on them were investigated. During the growing seasons, large variations in net ecosystem CO₂ exchange (NEE) and gross ecosystem productivity (GEP) were observed with the range of −4.0 to 2.2 (where negative exchange is a gain of carbon from the atmosphere) and 0-7.6 g C m⁻² d⁻¹, respectively. Ecosystem respiration (RE) displayed relatively smooth seasonal pattern with the range of 0.8-4.2 g C m⁻² d⁻¹. More than 70% of the total GEP was consumed by respiration, which resulted in a net CO₂ uptake of 143 ± 9.8 and 100 ± 9.2 g C m⁻² for the marsh over the growing seasons of 2004 and 2005, respectively. A significant portion of the accumulated NEE-C was lost by CH₄ emission during the growing seasons, indicating the great potential of CH₄ emission from the inundated marsh. Air temperature and leaf area index jointly affected the seasonal variation of GEP and the seasonal dynamic of RE was mainly controlled by soil temperature and leaf area index. Soil temperature also exerted the dominant influence over variation of CH₄ flux while no significant relationship was found between CH₄ emission and water table level. The close relationships between carbon fluxes and temperature can provide insights into the response of marsh carbon exchange to a changing climate. Future long term flux measurements over the freshwater marsh ecosystems are undoubtedly necessary.     

Nitrous oxide emissions from artificial urine patches applied to different N-fertilized swards and estimated annual N2O emissions for differently fertilized pastures in an upland location in Germany

Abstract. Artificial urine containing 20.2 g N per patch of 0.2 m² was applied in May and September to permanent grassland swards of a long‐term experiment in the western uplands of Germany (location Rengen/Eifel), which were fertilized with 0, 120, 240, 360 kg N ha^?1 yr^?1 given as calcium ammonium nitrate. The effect on N₂O fluxes measured regularly during a 357‐day period with the closed‐chamber technique were as follows. (1) N₂O emission varied widely among the fertilized control areas without urine, and when a threshold water‐filled pore space >60% was exceeded, the greater the topsoil nitrate content the greater the flux from the individual urine patches on the fertilized swards. (2) After urine application in May, 1.4–4.2% of the applied urine‐N was lost as N₂O from the fertilized swards; and after urine application in September, 0.3–0.9% of the applied urine‐N was lost. The primary influence on N₂O flux from urine patches was the date of simulated grazing, N‐fertilization rate being a secondary influence. (3) The large differences in N₂O emissions between unfertilized and fertilized swards after May‐applied urine contrasted with only small differences after urine applied in September, indicating an interaction between time of urine application and N‐fertilizer rate. (4) The estimated annual N₂O emissions were in the range 0.6–1.6 kg N₂O‐N per livestock unit, or 1.4, 3.6, 4.1 and 5.1 kg N₂O‐N ha^?1 from the 0–360 kg ha^?1 of fertilizer‐N. The study demonstrated that date of grazing and N‐fertilizer application could influence the N₂O emission from urine patches to such an extent that both factors should be considered in detailed large‐scale estimations of N₂O fluxes from grazed grassland.     

No significant difference in N2O emission,fertilizer-induced N2O emission factor and CH4 absorption between anaerobically digested cattle slurry and chemical fertilizer applied timothy (Phleum pratense L.) sward in central Hokkaido,Japan

Abstract

Nitrous oxide (N₂O) and methane (CH₄) fluxes from a fertilized timothy (Phleum pratense L.) sward on the northern island of Japan were measured over 2?years using a randomized block design in the field. The objectives of the present study were to obtain annual N₂O and CH₄ emission rates and to elucidate the effect of the applied material (control [no nitrogen], anaerobically digested cattle slurry [ADCS] or chemical fertilizer [CF]) and the application season (autumn or spring) on the annual N₂O emission, fertilizer-induced N₂O emission factor (EF) and the annual CH₄ absorption. Ammonium sulfate was applied to the CF plots at the same application rate of NH₄-N to the ADCS plots. A three-way ANOVA was used to examine the significance of the factors (the applied material, the application season and the year). The ANOVA for the annual N₂O emission rates showed a significant effect with regard to the applied material (P?=?0.042). The annual N₂O emission rate from the control plots (0.398?kg N₂O-N ha^?1?year^?1) was significantly lower than that from the ADCS plots (0.708?kg N₂O-N ha^?1?year^?1) and the CF plots (0.636?kg N₂O-N ha^?1?year^?1). There was no significant difference in the annual N₂O emission rate between the ADCS and CF plots. The ANOVA for the EFs showed insignificance of all factors (P?>?0.05). The total mean?±?standard error of the EFs (fertilizer-induced N₂O-N emission/total applied N) was 0.0024?±?0.0007 (kg N₂O-N [kg N]^?1), which is similar to the reported EF (0.0032?±?0.0013) for well-drained uplands in Japan. The CH₄ absorption rates differed significantly between years (P?=?0.014). The CH₄ absorption rate in the first year (3.28?kg CH₄?ha^?1?year^?1) was higher than that in the second year (2.31?kg CH₄?ha^?1?year^?1), probably as a result of lower precipitation in the first year. In conclusion, under the same application rate of NH₄-N, differences in the applied materials (ADCS or CF) and the application season (autumn or spring) led to no significant differences in N₂O emission, fertilizer-induced N₂O EF and CH₄ absorption.