Potential short-term effects of yak and Tibetan sheep dung on greenhouse gas emissions in two alpine grassland soils under laboratory conditions

Yak and Tibetan sheep graze extensively on natural grasslands in the Qinghai-Tibetan Plateau, and large amounts of excrement are directly deposited onto alpine grasslands. However, information on greenhouse gas (GHG) emissions from this excrement is limited. This study evaluated the short-term effects of yak and Tibetan sheep dung on nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) emissions from alpine steppe soil at a water holding capacity (WHC) of 40 or 60 % and from alpine meadow soil at a WHC of 60 or 80 % under laboratory conditions. Cumulative N₂O emissions over a 15-day incubation period at low soil moisture conditions ranged from 111 to 232 μg N₂O–N kg soil^?1 in the yak dung treatments, significantly (P?<?0.01) higher than that of sheep dung treatments (28.7 to 33.7 μg N₂O–N kg soil^?1) and untreated soils (1.04–6.94 μg N₂O–N kg soil^?1). At high soil moisture conditions, N₂O emissions were higher from sheep dung than yak dung and non-treated soils. No significant difference was found between the yak dung and non-treated alpine meadow soil at 80 % WHC. Low N₂O emission in the yak dung treatment from relatively wet soil was probably due to complete denitrification to N₂. Yak dung markedly (P?<?0.001) increased CH₄ and CO₂ emissions, likely being the main source of these two gases. The addition of sheep dung markedly (P?<?0.001) elevated CO₂ emissions. Dung application significantly (P?<?0.01) increased global warming potential, particularly for alpine steppe soil. In conclusion, our findings suggest that yak and Tibetan sheep dung deposited on alpine grassland soils may increase GHG emissions.     

Strong pH influence on N2O and CH4 fluxes from forested organic soils

Greenhouse gas (GHG) emissions from farmed organic soils can have a major impact on national emission budgets. This investigation was conducted to evaluate whether afforestation of such soils could mitigate this problem. Over the period 1994–1997, emissions of methane (CH₄) and nitrous oxide (N₂O) were recorded from an organic soil site in Sweden, forested with silver birch (Betula pendula Roth), using static field chambers. The site was used for grazing prior to forestation. Soil pH and soil carbon content varied greatly across the site. The soil pH ranged from 3.6 to 5.9 and soil carbon from 34 to 42%. The mean annual N₂O emission was 19.4 (± 6.7) kg N₂O‐N ha^?1 and was strongly correlated with soil pH (r = ?0.93, P < 0.01) and soil carbon content (r = 0.97, P < 0.001). The N₂O emissions showed large spatial and temporal variability with greatest emissions during the summer periods. The site was a sink for CH₄ (i.e. ?0.8 (± 0.5) kg CH₄ ha^?1 year^?1) and the flux correlated well with the C/N ratio (r = 0.93, P < 0.01), N₂O emission (r = 0.92, P < 0.01), soil pH (r = ?0.95, P < 0.01) and soil carbon (r = 0.97, P < 0.001). CH₄ flux followed a seasonal pattern, with uptake dominating during the summer, and emission during winter. This study indicates that, because of the large N₂O emissions, afforestation may not mitigate the GHG emissions from fertile peat soils with acidic pH, although it can reduce the net GHG because of greater CO₂ assimilation by the trees compared with agricultural crops.     

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.     

Effects of biochar addition on greenhouse gas emissions during freeze–thaw cycles in a black soil region,Northeast China

As global warming intensifies, the soil environment in middle to high latitudes will undergo more extensive and frequent freeze–thaw cycles (FTCs), which will significantly affect the carbon and nitrogen cycles of soil ecosystems and aggravate greenhouse gas (GHG) emissions. Biochar can increase soil organic carbon storage and mitigate climate change. To effectively control GHG emissions, soil supplemented with biochar at different application rates (0%, 2%, 4% and 6% [w/w]) under different numbers of FTCs (0, 3, 6, 9, and 12) was selected as the research object. The soil GHG emission characteristics in different experimental treatments and their relationships with soil physical and chemical properties were determined. Our results showed that N₂O and CO₂ emissions were promoted during FTCs, with values of 3.13–50.37 and 16.22–135.50 μg m⁻² h⁻¹, respectively. The order of N₂O and CO₂ emissions with respect to biochar application rate was as follows: 2% > 0% > 4% > 6%. CH₄ emissions were negative during FTCs, varying from −1.62 to −10.59 μg m⁻² h⁻¹, and negative CH₄ emissions were promoted by biochar. Correlation analysis showed that N₂O, CO₂ and CH₄ emissions were significantly correlated with pH, soil moisture and soil organic matter (SOM), total nitrogen (TN) and ${\mathrm{NH}}_4^{+}$–N contents (p < .01). The conceptual path model demonstrated that GHG emissions were significantly influenced by FTCs, moisture, SOM and biochar application rate. Our results indicate that the effects of FTCs on GHG emissions were greater than those of biochar application. Biochar application rates of 4% or 6% should be considered in the future to reduce soil GHG emissions in the black soil region of Northeast China. Our results can help provide a theoretical basis and effective strategy to reduce soil GHG emissions during FTCs in seasonally frozen regions.     

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.     

Dissolved organic matter and inorganic N jointly regulate greenhouse gases fluxes from forest soils with different moistures during a freeze-thaw period

ABSTRACT

Antecedent soil moisture before freezing can affect greenhouse gases (GHG) fluxes from soils during thaw, but their critical threshold values for GHG fluxes and the underlying mechanisms are still not clear. By using packed soil-core incubation experiments, we have studied nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) fluxes from a mature broadleaf and Korean pine-mixed forest soil and an adjacent white birch forest soil with nine levels of soil moisture ranging from 10 to 90% water-filled pore space (WFPS) during a 2-month freezing at ?8°C and the following 10-day thaw at 10°C. The threshold values of soil moisture ranged from 50 to 70% WFPS for CH₄ uptake and from 70 to 90% WFPS for N₂O and CO₂ emissions from the two soils during the freeze-thaw period. Under the optimum soil moisture condition, fulvic-like compounds with high bioavailability contributed more than 60% of dissolved organic matter (DOM) in the soil. Cumulative N₂O emissions from forest soils during the freeze-thaw period were greatest when the concentration ratio of nitrate-N to dissolved organic carbon (DOC) was 0.04 g N g^?1 C. Cumulative soil CO₂ emissions and CH₄ uptake during the freeze-thaw period were both regulated by the interaction between soil DOC and net N mineralization. The activities of β-1,4-glucosidase and β-1,4-N-acetyl-glucosaminidase, microbial biomass C and N, and the microbial biomass C-to-N ratios, were all significantly correlated to the soil N₂O, CO₂, and CH₄ fluxes. Overall, upon a freeze-thaw period with different soil moistures, GHG fluxes from forest soils were jointly regulated by inorganic N and DOC concentrations, and related to the labile components of DOM released into the soil, which could be strictly controlled by the related microbial properties.     

施氮水平对太行山前平原冬小麦-夏玉米轮作体系土壤温室气体通量的影响

应用静态明箱-气相色谱法对4 个施氮肥水平N0 [0 kg(N)·hm^-2]、N200 [200 kg(N)·hm^-2]、N400 [400kg(N)·hm^-2]、N600 [600 kg(N)·hm^-2]的夏玉米-冬小麦季轮作体系2008~2010 年的土壤温室气体(CH₄、CO₂ 和N₂O)排放通量进行研究, 同时观测5 cm 土层土壤温度并记录降水量。结果表明: 太行山前平原冬小麦-夏玉米轮作农田生态系统为CH₄ 吸收汇, CO₂ 和N₂O 排放源。随着氮肥施入量的增加土壤对CH₄ 的吸收速率降低, 而CO₂ 和N₂O 的排放速率增加。冬小麦季施氮处理土壤对CH₄ 的吸收速率显著低于无氮肥的N0 处理, 而N600处理土壤CO₂ 和N₂O 排放速率显著高于N0 处理(P<0.05)。施肥和灌溉会直接导致土壤CO₂ 和N₂O 的排放通量增加, 同时土壤对CH₄ 的吸收峰值减小。土壤温度升高和降水量增加以及干湿交替加剧均会造成N₂O 和CO₂排放速率增加。同时在持续干燥和低温条件的冬季不施氮处理观测到土壤对N₂O 的吸收现象。N0、N200、N400 和N600 处理土壤CH₄ 年排放总量(kg·hm^-2·a^-1)分别为-1.42、-0.75、-0.82、-0.92(2008~2009 年)和-2.60、-1.47、-1.35、-1.76(2009~2010 年), N0、N200、N400 和N600 处理土壤CO₂ 年排放总量(kg·hm^-2·a^-1)分别为15 597.6、19 345.6、21 455.9、29 012.5(2008~2009 年)和10 317.7、11 474.0、13 983.5、20 639.3(2009~2010年), N0、N200、N400 和N600 处理土壤N₂O 年排放总量(kg·hm^-2·a^-1)分别为1.05、2.16、5.27、6.98(2008~2009年)和1.49、2.31、4.42、5.81(2009~2010 年)。     

Effect of nitrogen fertilization on methane flux in a structured clay soil cultivated with onion in Central Hokkaido,Japan

Abstract

This study was conducted to investigate the effect of N fertilization on the soil CH₄ flux during the growing season of onion in a structured clay soil with stagnant water at depths of 70–80 cm and with a peat-mixed subsoil. The following 4 treatments were analyzed over a period of two years: T1) fertilized, onion growing, T2) fertilized, bare field, T3) unfertilized, onion growing, and T4) unfertilized, bare field. In the fertilized T1 and T2 treatments, fertilizers (mixture of 3 : 1 NH₄NO₃ : (NH₄)₂SO₄) at rates of 322 kg N ha^?1 in 1999 and 242 kg N ha^?1 in 2000 were applied as basal fertilizers before onion was transplanted. CH₄ fluxes among the treatments ranged from ?0.06 to 0.12 mg CH₄-C m^?2 h^?1 in 1999, and from ?0.03 to 0.01 mg CH₄-C m^?2 h^?1 in 2000, which were high after heavy rain in summer. Cumulative CH₄ flux from May to November in the fertilized T1 and T2 treatments was 59 mg CH₄-C m^?2 for both treatments in 1999, and 3.2 and ?0.9 mg CH₄-C m^?2 in 2000, respectively. On the other hand, in the unfertilized T3 and T4 treatments, the cumulative CH₄ flux was 0.2 and ?9.2 mg CH₄-C m^?2 in 1999, and ?26 and ?20 mg CH₄-C m^?2 in 2000, respectively. Although the cumulative CH₄ flux in each treatment was higher in 1999 than in 2000, the fertilized treatments in both years showed a significantly higher cumulative CH₄ flux than the unfertilized treatments. This might be ascribed to the higher level of nitrification in the fertilized treatments, because a high nitrate concentration was observed in the fertilized treatments in the onion growing season. The results also revealed that onion growing did not exert a significant influence on the CH₄ flux. The precipitation from May to November was 642 mm in 1999 and 1,008 mm in 2000, and the CH₄ emission increased when the precipitation was low. In addition, the CH₄ concentration in the soil profile increased with the increase of the depth in summer as the soil was dry. These findings indicated that CH₄ diffusion from the soil to the atmosphere was inhibited by rainwater.     

Temperature response of ammonia and greenhouse gas emission from manure amended silty clay soil

Soil temperature plays an important role in organic matter decomposition, thus likely to affect ammonia and gaseous emission from land application of manure. An incubation experiment was conducted to quantify ammonia and greenhouse gas (GHG) (N₂O, CO₂ and CH₄) emissions from manure and urea applied at 215?kg N ha^?1 to Fargo-Ryan silty clay soil. Soil (250?g) amended with solid beef manure (SM), straw-bedded solid beef manure (BM), urea only (UO), and control (CT) were incubated at 5, 10, 15, and 25 °C for 31 days at constant 60% water holding capacity (WHC). The cumulative GHGs and NH₃ emission generally increased with temperature and highest emission observed at 25 °C. Across temperature levels, 0.11–1.3% and 0.1–0.7% of the total N was lost as N₂O and NH₃, respectively. Cumulative CO₂ emission from manure was higher than UO and CT at all temperatures (P?<?0.05). Methane accounted for <0.1% of the total C (CO₂?+?CH₄) emission across temperatures. The Q₁₀ values (temperature sensitivity coefficient) derived from Arrhenius and exponential models ranged 1.5–3.7 for N₂O, 1.4–6.4 for CO₂, 1.6–5.8 for CH₄, and 1.4–5.0 for NH_3. Our results demonstrated that temperature significantly influences NH₃ and GHG emissions irrespective of soil amendment but the magnitude of emission varied with soil nutrient availability and substrate quality. Overall, the highest temperature resulted in the highest emission of NH₃ and GHGs.     

Soil–atmosphere greenhouse gas exchange in a cool,temperate Eucalyptus delegatensis forest in south-eastern Australia

Forests are the largest C sink (vegetation and soil) in the terrestrial biosphere and may additionally provide an important soil methane (CH₄) sink, whilst producing little nitrous oxide (N₂O) when nutrients are tightly cycled. In this study, we determine the magnitude and spatial variation of soil–atmosphere N₂O, CH₄ and CO₂ exchange in a Eucalyptus delegatensis forest in New South Wales, Australia, and investigate how the magnitude of the fluxes depends on the presence of N₂-fixing tree species (Acacia dealbata), the proximity of creeks, and changing environmental conditions. Soil trace gas exchange was measured along replicated transects and in forest plots with and without presence of A. dealbata using static manual chambers and an automated trace gas measurement system for 2 weeks next to an eddy covariance tower measuring net ecosystem CO₂ exchange. CH₄ was taken up by the forest soil (?51.8 μg CH₄-C m^?2 h^?1) and was significantly correlated with relative saturation (S_r) of the soil. The soil within creek lines was a net CH₄ source (up to 33.5 μg CH₄-C m^?2 h^?1), whereas the wider forest soil was a CH₄ sink regardless of distance from the creek line. Soil N₂O emissions were small (<3.3 μg N₂O-N m^?2 h^?1) throughout the 2-week period, despite major rain and snowfall. Soil N₂O emissions only correlated with soil and air temperature. The presence of A. dealbata in the understorey had no influence on the magnitude of CH₄ uptake, N₂O emission or soil N parameters. N₂O production increased with increasing soil moisture (up to 50% S_r) in laboratory incubations and gross nitrification was negative or negligible as measured through ¹⁵N isotope pool dilution.The small N₂O emissions are probably due to the limited capacity for nitrification in this late successional forest soil with C:N ratios >20. Soil–atmosphere exchange of CO₂ was several orders of magnitude greater (88.8 mg CO₂-C m^?2 h^?1) than CH₄ and N₂O, and represented 43% of total ecosystem respiration. The forest was a net greenhouse gas sink (126.22 kg CO₂-equivalents ha^?1 d^?1) during the 2-week measurement period, of which soil CH₄ uptake contributed only 0.3% and N₂O emissions offset only 0.3%.     

The effects of catena positions on greenhouse gas emissions along a seasonal wetland (dambo) transect in tropical Zimbabwe

Wetlands are major natural sources of greenhouse gases (GHGs). In central and southern Africa, one of the most extensive wetlands are dambos (seasonal wetlands) which occupy 20–25% of land area. However, there are very little data on GHG methane (CH₄), carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions from dambos, and this study presents the first estimates from dambos in Zimbabwe. The objective was to evaluate the effects of catena positions; upland, dambo mid-slope and dambo bottom, on GHG emissions along an undisturbed dambo transect. Methane emissions were ?0.3, 29.5 and ?1.3 mg m^?2 hr^?1, N₂O emission were 40.1, 3.9 and 5.5 µg m² hr^?1, while CO₂ emissions were 2648.9, 896.2 and 590.1 mg m^?2 hr^?1 for upland, mid-slope and bottom catena, respectively. Our results showed that uplands were important sources of N₂O and CO₂, and a sink for CH₄, while the dambo mid-slope position was a major source of CH₄, but a weak source of CO₂ and N₂O. Dambo bottom catena was weak source GHGs. Overall, dambos were major sources of CH₄ and weak sources of N₂O and CO₂.We concluded that, depending on catenal position, dambos can be major or minor sources of GHGs.     

Impact of Shrub Willow (<Emphasis Type="Italic">Salix</Emphasis> spp.) as a Potential Bioenergy Feedstock on Water Quality and Greenhouse Gas Emissions

The development of shrub willow as a bioenergy feedstock contributes to renewable energy portfolios in many countries with temperate climates and marginal croplands. As willow is developed commercially in the US Northeast, there is a need to better understand its impact on water quality and greenhouse gas (GHG) emissions compared to alternative land uses (e.g., corn, hay). We measured the impact of cultivated willow of various ages (2 and 5 years) and management strategies (fertilized vs. unfertilized) compared to corn and hay on water table depth, soil water NO₃ ^? and PO₄ ^3? concentrations, and N₂O, CH₄, and CO₂ fluxes at the soil-atmosphere interface during a drier than normal year in heavy clay soils with marginal agricultural value in upstate New York, USA. Soil water concentrations resulted in higher PO₄ ^3? in willow and higher NO₃ ^? in corn and hay, although willow is unlikely to negatively impact water quality with respect to phosphorus due to shorter periods of hydrologic connectivity in willow and hay than in corn. Gas fluxes varied spatially and temporally with hot moments of CH₄ and N₂O in corn and hay and seasonally variable CO₂ in willow. While CH₄ did not vary between fields, N₂O was higher in corn and hay, and CO₂ in willow, resulting in no net difference between CO₂ equivalent (CH₄, CO₂, and N₂O) emissions between fields. Converting marginal cropland on clay soils from corn or hay to willow left overall GHG emissions unaffected, slightly increased PO₄ ^3?, and decreased NO₃ ^? concentrations in soil water.     

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

Abstract

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.     

Nitrous oxide and methane emissions from grassland treated with bark- or sawdust-containing manure at different rates

On the main Japanese island of Honshu, bark or sawdust is often added to cattle excreta as part of the composting process. Dairy farmers sometimes need to dispose of manure that is excess to their requirements by spreading it on their grasslands. We assessed the effect of application of bark- or sawdust-containing manure at different rates on annual nitrous oxide (N₂O) and methane (CH₄) emissions from a grassland soil. Nitrous oxide and CH₄ fluxes from an orchardgrass (Dactylis glomerata L.) grassland that received this manure at 0, 50, 100, 200, or 300?Mg?ha^?1?yr^?1 were measured over a two-year period by using closed chambers. Two-way analysis of variance (ANOVA) was employed to examine the effect of annual manure application rates and years on annual N₂O and CH₄ emissions. Annual N₂O emissions ranged from 0.47 to 3.03?kg?N?ha^?1?yr^?1 and increased with increasing manure application rate. Nitrous oxide emissions during the 140-day period following manure application increased with increasing manure application rate, with the total nitrogen concentration in the manure, and with cumulative precipitation during the 140-day period. However, manure application rate did not affect the N₂O emission factors of the manure. The overall average N₂O emission factor was 0.068%. Annual CH₄ emissions ranged from ?1.12 to 0.01?kg?C?ha^?1?yr^?1. The annual manure application rate did not affect annual CH₄ emissions.     

Acid Mine Drainage Treatment Assisted by Lignite-Derived Humic Substances

Rewetting of agriculturally used peatlands has been proposed as a measure to stop soil subsidence, conserve peat and rehabilitate ecosystem functioning. Unintended consequences might involve nutrient release and changes in the greenhouse gas (GHG) balance towards CH₄-dominated emission. To investigate the risks and benefits of rewetting, we subjected soil columns from drained peat- and clay-covered peatlands to different water level treatments: permanently low, permanently inundated and fluctuating (first inundated, then drained). Surface water and soil pore water chemistry, soil-extractable nutrients and greenhouse gas fluxes were measured throughout the experiment. Permanent inundation released large amounts of nutrients into pore water, especially phosphorus (up to 11.7 mg P-PO₄ l^?1) and ammonium (4.8 mg N-NH₄ l^?1). Phosphorus release was larger in peat than in clay soil, presumably due to the larger pool of iron-bound phosphorus in peat. Furthermore, substantial amounts of phosphorus and potassium were exported from the soil matrix to the surface water, risking the pollution of local species-rich (semi-)aquatic ecosystems. Rewetting of both clay and peat soil reduced CO₂ emissions. CH₄ emissions increased, but, in contrast to the expectations, the fluxes were relatively low. Calculations showed that rewetting reduced net cumulative GHG emissions expressed as CO₂ equivalents.     

Validation of the DNDC-Rice model by using CH4 and N2O flux data from rice cultivated in pots under alternate wetting and drying irrigation management

The DNDC (DeNitrification-DeComposition)-Rice model, one of the most advanced process-based models for the estimation of greenhouse gas emissions from paddy fields, has been discussed mostly in terms of the reproducibility of observed methane (CH₄) emissions from Japanese rice paddies, but the model has not yet been validated for tropical rice paddies under alternate wetting and drying (AWD) irrigation management, a water-saving technique. We validated the model by using CH₄ and nitrous oxide (N₂O) flux data from rice in pots cultivated under AWD irrigation management in a screen-house at the International Rice Research Institute (Los Baños, the Philippines). After minor modification and adjustment of the model to the experimental irrigation conditions, we calculated grain yield and straw production. The observed mean daily CH₄ fluxes from the continuous flooding (CF) and AWD pots were 4.49 and 1.22?kg?C?ha^?1?day^?1, respectively, and the observed mean daily N₂O fluxes from the pots were 0.105 and 34.1?g?N?ha^?1?day^?1, respectively. The root-mean-square errors, indicators of simulation error, of daily CH₄ fluxes from CF and AWD pots were calculated as 1.76 and 1.86?kg?C?ha^?1?day^?1, respectively, and those of daily N₂O fluxes were 2.23 and 124?g?N?ha^?1?day^?1, respectively. The simulated gross CH₄ emissions for CF and AWD from the puddling stage (2 days before transplanting) to harvest (97 days after transplanting) were 417 and 126?kg?C?ha^?1, respectively; these values were 9.8% lower and 0.76% higher, respectively, than the observed values. The simulated gross N₂O emissions during the same period were 0.0279 and 1.45?kg?N?ha^?1 for CF and AWD, respectively; these values were respectively 87% and 29% lower than the observed values. The observed total global warming potential (GWP) of AWD resulting from the CH₄ and N₂O emissions was approximately one-third of that in the CF treatment. The simulated GWPs of both CF and AWD were close to the observed values despite the discrepancy in N₂O emissions, because N₂O emissions contributed much less than CH₄ emissions to the total GWP. These results suggest that the DNDC-Rice model can be used to estimate CH₄ emission and total GWP from tropical paddy fields under both CF and AWD conditions.     

Water availability and abundance of microbial groups are key determinants of greenhouse gas fluxes in a dryland forest ecosystem

Forests are considered key biomes that could contribute to minimising global warming as they sequester carbon (C) and contribute to mitigate emissions of the potent greenhouse gases (GHG) including nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂). Management practices are prevalent in forestry, particularly in dryland ecosystems, known to be water and nitrogen (N) limited. Irrigation and fertilisation are thus routinely applied to increase the yield of forest products. However, the contribution of forest management practices to current GHG budgets and consequently to soil net global warming potential (GWP) is still largely unaccounted for, particularly in dryland ecosystems. We quantified the long-term effect (six years) of irrigation and fertilisation and the impact of land-use change, from grassland to a Eucalyptus plantation on N₂O, CH₄ and CO₂ emissions and soil net GWP, within a dryland ecosystem. To identify biotic and abiotic drivers of GHG emissions, we explored the relationship of N₂O, CH₄ and CO₂ fluxes with soil abiotic characteristics and abundance of ammonia-oxidizers, N₂O-reducing bacteria, methanotrophs and total soil bacteria. Our results show that GHG emissions, particularly N₂O and CO₂ are constrained by water availability and both N₂O and CH₄ are constrained by N availability in the soil. We also provide evidence of functional microbial groups being key players in driving GHG emissions. Our findings illustrate that GHG emission budgets can be affected by forest management practices and provide a better mechanistic understanding for future mitigation options.     

中国亚热带中部三峡库区不同土地利用方式下甲烷氧化潜力研究

To compare the CH4 oxidation potential among diferent land uses and seasons,and to observe its response to monsoon precipitation pattern and carbon and nitrogen parameters,a one-year study was conducted for diferent land uses (vegetable field,tilled and non-tilled orchard,upland crops and pine forest) in central subtropical China.Results showed significant diferences in CH4 oxidation potential among diferent land uses(ranging from 3.08 to 0.36 kg CH4 ha-1 year-1).Upland with corn-peanut-sweet potato rotation showed the highest CH4 emission,while pine forest showed the highest CH4 oxidation potential among all land uses.Non-tilled citrus orchard (0.72±0.08 kg CH4 ha-1 year-1)absorbed two times more CH4 than tilled citrus orchard(0.38±0.06kg CH4 ha-1 year-1).Irrespective of diferent vegetation,inorganic N fertilizer application significantly influenced CH4 fluxes across the sites (R2=0.86,P=0.002).Water-filled pore space,soil microbial biomass carbon,and dissolved nitrogen showed significant efects across diferent land uses (31% to 38% of variability)in one linear regression model.However,their cumulative interaction was significant for pine forest only,which might be attributed to undisturbed microbial communities legitimately responding to other variables,leading to net CH4 oxidation in the soil.These results suggested that i)natural soil condition tended to create win-win situation for CH4 oxidation,and agricultural activities could disrupt the oxidation potentials of the soils;and ii)specific management practices including but not limiting to efficient fertilizer application and utilization,water use efciency,and less soil disruption might be required to increase the CH4 uptake from the soil.     

土壤有机碳对沼渣或牛粪施用后温室气体排放潜力的影响—盆栽试验结果

A change in the European Union energy policy has markedly promoted the expansion of biogas production.Consequently,large amounts of nutrient-rich residues are being used as organic fertilizers.In this study,a pot experiment was conducted to simulate the high-risk situation of enhanced greenhouse gas (GHG) emissions following organic fertilizer application in energy maize cultivation.We hypothesized that cattle slurry application enhanced CO2 and N2O fluxes compared to biogas digestate because of the overall higher carbon (C) and nitrogen (N) input,and that higher levels of CO2 and N2O emissions could be expected by increasing soil organic C (SOC) and N contents.Biogas digestate and cattle slurry,at a rate of 150 kg NH4+-N ha-1,were incorporated into 3 soil types with low,medium,and high SOC contents (Cambisol,Mollic Gleysol,and Sapric Histosol,termed Clow,Cmedium,and Chigh,respectively).The GHG exchange (CO2,CH4,and N2O) was measured on 5 replicates over a period of 22 d using the closed chamber technique.The application of cattle slurry resulted in significantly higher CO2 and N2O fluxes compared to the application of biogas digestate.No differences were observed in CH4 exchange,which was close to zero for all treatments.Significantly higher CO2 emissions were observed in Chigh compared to the other two soil types,whereas the highest N2O emissions were observed in Cmedium.Thus,the results demonstrate the importance of soil type-adapted fertilization with respect to changing soil physical and environmental conditions.     

Fluxes of CO2, CH4, and N2O in an alpine meadow affected by yak excreta on the Qinghai-Tibetan plateau during summer grazing periods

To assess the impacts of yak excreta patches on greenhouse gas (GHG) fluxes in the alpine meadow of the Qinghai-Tibetan plateau, methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) fluxes were measured for the first time from experimental excreta patches placed on the meadow during the summer grazing seasons in 2005 and 2006. Dung patches were CH₄ sources (average 586 μg m⁻² h⁻¹ in 2005 and 199 μg m⁻² h⁻¹ in 2006) during the investigation period of two years, while urine patches (average −31 μg m⁻² h⁻¹ in 2005 and −33 μg m⁻² h⁻¹ in 2006) and control plots (average −28 μg m⁻² h⁻¹ in 2005 and −30 μg m⁻² h⁻¹ in 2006) consumed CH₄. The cumulative CO₂ emission for dung patches was about 36-50% higher than control plots during the experimental period in 2005 and 2006. The cumulative N₂O emissions for both urine and dung patches were 2.1-3.7 and 1.8-3.5 times greater than control plots in 2005 and 2006, respectively. Soil water-filled pore space (WFPS) explained 35% and 36% of CH₄ flux variation for urine patches and control plots, respectively. Soil temperature explained 40-75% of temporal variation of CO₂ emissions for all treatments. Temporal N₂O flux variation in urine patches (34%), dung patches (48%), and control (56%) plots was mainly driven by the simultaneous effect of soil temperature and WFPS. Although yak excreta patches significantly affected GHG fluxes, their contributions to the whole grazing alpine meadow in terms of CO₂ equivalents are limited under the moderate grazing intensity (1.45 yak ha⁻¹). However, the contributions of excreta patches to N₂O emissions are not negligible when estimating N₂O emissions in the grazing meadow. In this study, the N₂O emission factor of yak excreta patches varied with year (about 0.9-1.0%, and 0.1-0.2% in 2005 and 2006, respectively), which was lower than IPCC default value of 2%.