Effect of land use on methane flux from soil

Effects of Biofuel Crop Switchgrass (Panicum virgatum) Cultivation on Soil Carbon Sequestration and Greenhouse Gas Emissions: A Review

Under the macroenvironmental background of global warming, all countries are working to limit climate change. Internationally, biofuel plants are considered to have great potential in carbon neutralization. Several countries have begun using biofuel crops as energy sources to neutralize carbon emissions. Switchgrass (Panicum virgatum) is considered a resource-efficient low-input crop that produces bioenergy. In this paper, we reviewed the effects of switchgrass cultivation on carbon sequestration and greenhouse gas (GHG) emissions. Moreover, the future application and research of switchgrass are discussed and prospected. Switchgrass has huge aboveground and underground biomass, manifesting its huge carbon sequestration potential. The net change of soil surface 30 cm soil organic carbon in 15 years is predicted to be 6.49 Mg ha^-1, significantly higher than that of other crops. In addition, its net ecosystem CO₂ exchange is about -485 to -118 g C m^-2 yr^-1, which greatly affects the annual CO₂ flux of the cultivation environment. Nitrogen (N) fertilizer is the main source of N₂O emission in the switchgrass field. Nitrogen addition increases the yield of switchgrass and also increases the N₂O flux of switchgrass soil. It is necessary to formulate the most appropriate N fertilizer application strategy. CH₄ emissions are also an important indicator of carbon debt. The effects of switchgrass cultivation on CH₄ emissions may be significant but are often ignored. Future studies on GHG emissions by switchgrass should also focus on CH₄. In conclusion, as a biofuel crop, switchgrass can well balance the effects of climate change. It is necessary to conduct studies of switchgrass globally with the long-term dimension of climate change effects.

In situ measurements and meta-analysis reveal that land-use changes combined with low nitrogen application promote methane uptake by temperate grasslands in China

Methane (CH₄) oxidation in well-aerated grassland soils is an important sink for atmospheric CH₄, which can be largely modified by land-use changes. However, the impacts of land-use changes (i.e., from native grasslands to artificial grasslands (AG) and croplands (CL)) on soil CH₄ uptake in China remain uncertain. Therefore, the 2-year CH₄ flux was measured from 3 land-use types, including heavily grazed steppe (HG, control), AG, and CL, in the agro-pastoral ecotone of Northern China to elucidate this impact. Moreover, a meta-analysis was conducted to elucidate this effect across Chinese grasslands. The results showed that the land-use types could not change the seasonal patterns but significantly (p < 0.05) influenced the strength of soil CH₄ uptake. The mean annual CH₄ uptake followed the decreasing order of 14.7 ± 0.48 (mean ± 1 standard error) (CL), 3.28 ± 0.09 (AG), and 1.24 ± 0.07 kg CH₄-C ha^-1 yr^-1 (HG) in 2012-2014. This spatial variation pattern was linear and negatively (n = 6, r_adj.²= 0.73, p < 0.05) associated with the annual mean soil water-filled pore space. Non-growing season CH₄ uptake contributed 22-46% to the annual CH₄ uptake across land-use types. The meta-analysis also confirmed that the land-use changes significantly (p < 0.05) promoted the annual soil CH₄ uptake in temperate grasslands in China. This increased uptake is primarily related to the significant (p < 0.05) decrease in the soil water contents and the increase in the sand contents due to the land-use changes. Furthermore, nitrogen application not exceeding 100 kg N ha^-1 yr^-1 in these N-limited ecosystems significantly (p < 0.05) promoted soil CH₄ uptake. Collectively, our study demonstrated that land-use changes combined with low N application promoted soil CH₄ uptake in the temperate grasslands of China.

Effects of afforestation on soil CH4 and N2O fluxes in a nsubtropical karst landscape

Afforestation is of importance for terrestrial carbon sequestration as well as soil and water conservation in karst landscapes. However, few studies have evaluated the effects of afforestation on soil CH₄ and N₂O emissions in subtropical karst areas. Thus, a year-round field experiment was conducted to quantify the effects of afforestation on soil CH₄ and N₂O fluxes from a subtropical karst landscape in South China. In this study, soil CH₄ and N₂O fluxes were simultaneously monitored using static chamber-gas chromatography from three paired sites, including a cropland site (SC) and adjacent sites at two stages of afforestation, a shrubland (SD) and a woodland (AF). The results showed that annual soil CH₄ uptake for SC, SD, and AF sites were 1.53 ± 0.20 kg C ha^-1 yr^-1, 2.90 ± 0.20 kg C ha^-1 yr^-1, and 5.68 ± 0.18 kg C ha^-1 yr^-1, respectively. Afforestation (i.e., SD and AF sites) significantly increased soil CH₄ uptake compared with the adjacent cropland. Annual soil N₂O fluxes for SC, SD, and AF sites were 2.38 ± 0.17 kg N ha^-1 yr^-1, 0.94 ± 0.14 kg N ha^-1 yr^-1, and 0.47 ± 0.01 kg N ha^-1 yr^-1, respectively. Afforestation significantly decreased soil N₂O fluxes compared with the adjacent cropland. The effects of afforestation on soil CH₄ and N₂O fluxes in the present study were mainly attributed to changes in soil characteristics, such as temperature and moisture, as these were significantly correlated with soil CH₄ and N₂O fluxes across different experimental sites. The present study highlights that afforestation is an effective land use management practice to mitigate non-CO₂ greenhouse gas emissions from subtropical karst landscapes in South China.

Effects of mild alternate wetting and drying irrigation and mid-season drainage on CH4 and N2O emissions in rice cultivation

Rice, one of the major sources of CH₄ and N₂O emissions, is also the largest consumer of water resources. Mild alternate wetting and drying (AWD) irrigation is widely adopted to save irrigation water resources and maintain rice production, but its effects on CH₄ and N₂O emissions are unclear. In addition, previous studies have revealed different effects of mid-season drainage on global warming potential (GWP), owing to the different criteria used. In this study, a pot experiment was conducted to investigate the effects of mild AWD irrigation and mid-season drainage (a specific soil moisture) on CH₄ and N₂O emissions during rice cultivation. Four water management systems were applied: AWD + D0 (mild AWD irrigation without mid-season drainage), AWD + D1 (mild AWD irrigation with mid-season drainage), CF + D0 (continuous flooding without mid-season drainage) and CF + D1 (continuous flooding with mid-season drainage); nitrogen was applied at two levels (N90 and N180) along with each treatment. The results showed that mild AWD irrigation reduced CH₄ cumulative emissions by an average of 87.1% but increased N₂O cumulative emissions by an average of 280% compared to the values observed with CF irrigation. Mid-season drainage did not affect N₂O emissions but interrupted CH₄ fluxes and significantly reduced CH₄ cumulative emissions. CH₄ and N₂O cumulative emissions were reduced by an average of 25.0% and 54.2%, respectively, with N90 application compared to values observed with N180 application. Unexpectedly, mild AWD irrigation did not reduce GWP and yield-scaled GWP unlike CF irrigation because a high N₂O emission peak occurred during mild AWD irrigation. Furthermore, we observed an obvious trade-off between CH₄ and N₂O. We suggest that maintaining flooding during nitrogen application but applying mild AWD irrigation for the remaining period may be helpful in reducing CH₄ and N₂O emissions and GWP.

Variations in Greenhouse Gas Fluxes in Response to Short-Term Changes in Weather Variables at Three Elevation Ranges, Wakiso District, Uganda

Weather conditions are among the major factors leading to the increasing greenhouse gas (GHG) fluxes from the agricultural soils. In this study, variations in the soil GHG fluxes with precipitation and soil temperatures at different elevation ranges in banana–coffee farms, in the Wakiso District, Uganda, were evaluated. The soil GHG fluxes were collected weekly, using the chamber method, and analyzed by using gas chromatography. Parallel soil temperature samples were collected by using a REOTEMP soil thermometer. Daily precipitation was measured with an automated weather station instrument installed on-site. The results showed that CO2, N2O, and CH4 fluxes were significantly different between the sites at different elevation ranges. Daily precipitation and soil temperatures significantly (p < 0.05) affected the soil GHG fluxes. Along an elevation gradient, daily precipitation and soil temperatures positively associated with the soil GHG fluxes. The combined factors of daily precipitation and soil temperatures also influence the soil GHG fluxes, but their effect was less than that of the single effects. Overall, daily precipitation and soil temperatures are key weather factors driving the soil GHG fluxes in time and space. This particular study suggests that agriculture at lower elevation levels would help reduce the magnitudes of the soil GHG fluxes. However, this study did not measure the soil GHG fluxes from the non-cultivated ecosystems. Therefore, future studies should focus on assessing the variations in the soil GHG fluxes from non-cultivated ecosystems relative to agriculture systems, at varying elevation ranges.

How do methane rates vary with soil moisture and compaction, N compound and rate, and dung addition in a tropical soil?

Soil moisture and compaction, and source of N and bovine urine can reduce methane (CH₄) rates from agricultural soils. However, the magnitude of the effect is unknown in tropical soil under different conditions, as well as the potential of different urine-N concentration, volume, and sources of N in such an effect. This study aimed to investigate the effects of different soil conditions (moist, dry, compacted, moist-dung, moist-dung-compacted), N concentration in urine (2.5, 5.0, 10.0, and 15.0 g N L^-1), volume of urine (25, 50, 100, and 200 ml kg^-1 dry soil), and source of N (ammonium, nitrate, and urea) on CH₄ emissions. A tropical Ferralsol soil from marandu-grass pasture was incubated during 106 days and the CH₄ concentration determined by gas chromatography. The CH₄ rates varied significantly according to the soil conditions when manipulated the urine-N (p < 0.01) and averaged 0.75, - 0.50, 1.14, 6.23, and 8.17 μg C-CH₄ m^-2 h^-1for the moist, dry, compacted, moist-dung, and moist-dung-compacted soil, respectively, and, not responded to the level of N (p = 0.73) averaging 2.57 μg C-CH₄ m^-2 h^-1. When evaluated, the volumes of urine cumulative CH₄ averages were - 0.52, - 1.24, - 0.88, 14.48, and 18.56 μg C-CH₄ m^-2 h^-1 for the moist, dry, compacted, moist-dung, and moist-dung-compacted, respectively. Soils were affected by soil treatments (p < 0.001) but not by urine volumes (p = 0.30). The source of N did not influence the CH₄ rates (p = 0.1) averaging 0.88, - 1.26, and - 1.19 μg C-CH₄ m^-2 h^-1 respectively, for urea, nitrate, and ammonium. The CH₄ fluxes in tropical Ferralsols are controlled by the soil characteristics and dung addition.

Nitrous oxide and methane production from denitrifying woodchip bioreactors at three hydraulic residence times

Denitrifying bioreactors remove nitrate (NO₃^-) from agricultural drainage and are slated to be an integral part of nitrogen reduction strategies in the Mississippi River Basin. However, incomplete denitrification can result in nitrous oxide (N₂O) production and anaerobic conditions within bioreactors may be conducive to methane (CH₄) production via methanogenesis. Greenhouse gas production has the potential to trade excess NO₃^- in surface water with excess greenhouses gases in the atmosphere. Our study examined N₂O and CH₄ production from pilot scale (6.38 m³) bioreactors across three hydraulic residence times (HRTs), 2, 8, and 16 h. Production was measured from both the surface of the bioreactors and dissolved in the bioreactor effluent. Nitrous oxide and CH₄ was produced across all HRTs, with the majority dissolved in the effluent. Nitrous oxide production was significantly greater (P < 0.05) from 2 h HRTs (478.43 mg N₂O m^-3 day^-1) than from 8 (29.95 mg N₂O m^-3 day^-1) and 16 (36.61 mg N₂O m^-3 day^-1) hour HRTs. Methane production was significantly less (P < 0.05) from 2 h HRTs (0.51 g C m³ day^-1) compared to 8 (1.50 g C m³ day^-1) and 16 (1.69 g C m³ day^-1) hour HRTs. The 2 h HRTs had significantly greater (P = 0.05) impacts to climate change compared to 8 and 16 h HRTs. Results from this study suggest managing HRTs between 6 and 8 h in field bioreactors could minimize total greenhouse gas production and maximize NO₃^- removal.

Greenhouse gas flux with reflooding of a drained salt marsh soil

Salt marshes are highly effective carbon (C) sinks and bury more C per square meter annually than any other ecosystem. Reclamation and anthropogenic impacts, however, have resulted in extensive losses of salt marshes. Carbon credits can be generated and sold by restoring marshes, but only if C sequestration and net reductions in greenhouse gases (GHG) are reliably quantified. Restored marshes, however, may exhibit different patterns of GHG emissions than natural marshes and it is possible that they could temporarily become sources of N₂O even in the usually N-limited estuarine environment. Research on short-term GHG flux following salt marsh restoration is limited to studies of two restored marshes which examined GHG flux more than six months after the return of tidal flooding. Here we report on a laboratory experiment in which soil cores collected from a drained agricultural marsh on the St. Lawrence Estuary were flooded with estuary water. Gas flux measurements immediately after flooding revealed small increases in N₂O and CH₄, but a large decline in CO₂ yielding, from a climatic perspective, a net cooling effect over the observation period. In addition to restoring the land’s capacity to sequester C once a marsh develops, returning tidal flooding thus appears to have the added benefit of stemming large ongoing C losses. With more than 400 km² of undeveloped dykeland, Eastern Canada is well positioned to restore large sections of marsh and contribute to reducing atmospheric CO₂ concentrations.

No tillage and liming reduce greenhouse gas emissions from poorly drained agricultural soils in Mediterranean regions

No tillage (NT) has been associated to increased N2O emission from poorly drained agricultural soils. This is the case for soils with a low permeable Bt horizon, which generates a perched water layer after water addition (via rainfall or irrigation) over a long period of time. Moreover, these soils often have problems of acidity and require liming application to sustain crop productivity; changes in soil pH have large implications for the production and consumption of soil greenhouse gas (GHG) emissions. Here, we assessed in a split-plot design the individual and interactive effects of tillage practices (conventional tillage (CT) vs. NT) and liming (Ca-amendment vs. not-amendment) on N2O and CH4 emissions from poorly drained acidic soils, over a field experiment with a rainfed triticale crop. Soil mineral N concentrations, pH, temperature, moisture, water soluble organic carbon, GHG fluxes and denitrification capacity were measured during the experiment. Tillage increased N2O emissions by 68% compared to NT and generally led to higher CH4 emissions; both effects were due to the higher soil moisture content under CT plots. Under CT, liming reduced N2O emissions by 61% whereas no effect was observed under NT. Under both CT and NT, CH4 oxidation was enhanced after liming application due to decreased Al(3+) toxicity. Based on our results, NT should be promoted as a means to improve soil physical properties and concurrently reduce N2O and CH4 emissions. Raising the soil pH via liming has positive effects on crop yield; here we show that it may also serve to mitigate CH4 emissions and, under CT, abate N2O emissions.

Summary of performance data for technologies to control gaseous, odor, and particulate emissions from livestock operations: Air management practices assessment tool (AMPAT)

The livestock and poultry production industry, regulatory agencies, and researchers lack a current, science-based guide and data base for evaluation of air quality mitigation technologies. Data collected from science-based review of mitigation technologies using practical, stakeholders-oriented evaluation criteria to identify knowledge gaps/needs and focuses for future research efforts on technologies and areas with the greatest impact potential is presented in the Literature Database tab on the air management practices tool (AMPAT). The AMPAT is web-based (available at www.agronext.iastate.edu/ampat) and provides an objective overview of mitigation practices best suited to address odor, gaseous, and particulate matter (PM) emissions at livestock operations. The data was compiled into Excel spreadsheets from a literature review of 265 papers was performed to (1) evaluate mitigation technologies performance for emissions of odor, volatile organic compounds (VOCs), ammonia (NH₃), hydrogen sulfide (H₂S), particulate matter (PM), and greenhouse gases (GHGs) and to (2) inform future research needs.

Impacts of Enhanced-Efficiency Nitrogen Fertilizers on Greenhouse Gas Emissions in a Coastal Plain Soil under Cotton

Enhanced-efficiency N fertilizers (EENFs) have the potential to increase crop yield while decreasing soil N loss. However, the effect of EENFs on greenhouse gas (GHG) emissions from different agricultural systems is not well understood. Thus, studies from a variety of locations and cropping systems are needed to evaluate their impact. An experiment was initiated on a Coastal Plain soil under cotton ( L.) production for comparing EENFs to traditional sources. Nitrogen sources included urea, ammonia sulfate (AS), urea-ammonia sulfate (UAS), controlled-release, polymer-coated urea (Environmental Smart Nitrogen [ESN]), stabilized granular urea (SuperU), poultry litter (PL), poultry litter plus AgrotainPlus (PLA), and an unfertilized control. Carbon dioxide (CO), nitrous oxide (NO), and methane (CH) fluxes were monitored regularly after fertilization through harvest from 2009 to 2011 using a closed-chamber method. Poultry litter and PLA had higher CO flux than other N treatments, while ESN and SU were generally lowest following fertilization. Nitrous oxide fluxes were highly variable and rarely affected by N treatments; PL and PLA were higher but only during the few samplings in 2010 and 2011. Methane fluxes were higher in 2009 (wet year) than 2010 or 2011, and N treatments had minimal impact. Global warming potential (GWP), calculated from cumulative GHG fluxes, was highest with PL and PLA and lowest for control, UAS, ESN, and SU. Results suggest that PL application to cotton increases GHG flux, but GHG flux reductions from EENFs were infrequently different from standard inorganic fertilizers, suggesting their higher cost may render them presently impractical.

Soil Methane Sink Capacity Response to a Long-Term Wildfire Chronosequence in Northern Sweden

Boreal forests occupy nearly one fifth of the terrestrial land surface and are recognised as globally important regulators of carbon (C) cycling and greenhouse gas emissions. Carbon sequestration processes in these forests include assimilation of CO2 into biomass and subsequently into soil organic matter, and soil microbial oxidation of methane (CH4). In this study we explored how ecosystem retrogression, which drives vegetation change, regulates the important process of soil CH4 oxidation in boreal forests. We measured soil CH4 oxidation processes on a group of 30 forested islands in northern Sweden differing greatly in fire history, and collectively representing a retrogressive chronosequence, spanning 5000 years. Across these islands the build-up of soil organic matter was observed to increase with time since fire disturbance, with a significant correlation between greater humus depth and increased net soil CH4 oxidation rates. We suggest that this increase in net CH4 oxidation rates, in the absence of disturbance, results as deeper humus stores accumulate and provide niches for methanotrophs to thrive. By using this gradient we have discovered important regulatory controls on the stability of soil CH4 oxidation processes that could not have not been explored through shorter-term experiments. Our findings indicate that in the absence of human interventions such as fire suppression, and with increased wildfire frequency, the globally important boreal CH4 sink could be diminished.

Soil Methane and Carbon Dioxide Fluxes from Cropland and Riparian Buffers in Different Hydrogeomorphic Settings

Riparian buffers contribute to the mitigation of nutrient pollution in agricultural landscapes, but there is concern regarding their potential to be hot spots of greenhouse gas production. This study compared soil CO and CH fluxes in adjacent crop fields and riparian buffers (a flood-prone forest and a flood-protected grassland along an incised channel) and examined the impact of water table depth (WTD) and flood events on the variability of gas fluxes in riparian zones. Results showed significantly ( < 0.001) higher CO emission in riparian areas than in adjoining croplands (6.8 ± 0.6 vs. 3.6 ± 0.5 Mg CO-C ha yr; mean ± SE). Daily flux of CO and soil temperature were significantly related ( < 0.002), with Q values ranging between 1.75 and 2.53. Significant relationships ( < 0.05) were found between CH daily flux and WTD. Flood events resulted in enhanced CH emission (up to +44.5 mg CH-C m d in a swale) under warm soil conditions (>22°C), but the effect of flooding was less pronounced in early spring (emission <1.06 mg CH-C m d), probably due to low soil temperature. Although CH flux direction alternated at all sites, overall the croplands and the flood-affected riparian forest were CH sources, with annual emission averaging +0.04 ± 0.17 and +0.92 ± 1.6 kg CH-C ha, respectively. In the riparian forest, a topographic depression (<8% of the total area) accounted for 78% of the annual CH emission, underscoring the significance of landscape heterogeneity on CH dynamics in riparian buffers. The nonflooded riparian grassland, however, was a net CH sink (-1.08 ± 0.22 kg CH-C ha yr), probably due to the presence of subsurface tile drains and a dredged/incised channel at that study site. Although these hydrological alterations may have contributed to improvement in the CH sink strength of the riparian grassland, this must be weighed against the water quality maintenance functions and other ecological services provided by riparian buffers.

Ranking factors affecting emissions of GHG from incubated agricultural soils

Agriculture significantly contributes to global greenhouse gas (GHG) emissions and there is a need to develop effective mitigation strategies. The efficacy of methods to reduce GHG fluxes from agricultural soils can be affected by a range of interacting management and environmental factors. Uniquely, we used the Taguchi experimental design methodology to rank the relative importance of six factors known to affect the emission of GHG from soil: nitrate (NO₃^-) addition, carbon quality (labile and non-labile C), soil temperature, water-filled pore space (WFPS) and extent of soil compaction. Grassland soil was incubated in jars where selected factors, considered at two or three amounts within the experimental range, were combined in an orthogonal array to determine the importance and interactions between factors with a L₁₆ design, comprising 16 experimental units. Within this L₁₆ design, 216 combinations of the full factorial experimental design were represented. Headspace nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂) concentrations were measured and used to calculate fluxes. Results found for the relative influence of factors (WFPS and NO₃^- addition were the main factors affecting N₂O fluxes, whilst glucose, NO₃^- and soil temperature were the main factors affecting CO₂ and CH₄ fluxes) were consistent with those already well documented. Interactions between factors were also studied and results showed that factors with little individual influence became more influential in combination. The proposed methodology offers new possibilities for GHG researchers to study interactions between influential factors and address the optimized sets of conditions to reduce GHG emissions in agro-ecosystems, while reducing the number of experimental units required compared with conventional experimental procedures that adjust one variable at a time.

Measuring and modeling the effects of drainage water management on soil greenhouse gas fluxes from corn and soybean fields

Controlled tile drainage can boost crop yields and improve water quality, but it also has the potential to increase GHG emissions. This study compared in-situ chamber-based measures of soil CH4, N2O, and CO2 fluxes for silt loam soil under corn and soybean cropping with conventional tile drainage (UTD) and controlled tile drainage (CTD). A semi-empirical model (NEMIS-NOE) was also used to predict soil N2O fluxes from soils using observed soil data. Observed N2O and CH4 fluxes between UTD and CTD fields during the farming season were not significantly different at 0.05 level. Soils were primarily a sink for CH4 but in some cases a source (sources were associated exclusively with CTD). The average N2O fluxes measured ranged between 0.003 and 0.028 kg N ha(-1) day(-1). There were some significantly higher (p ≤ 0.05) CO2 fluxes associated with CTD relative to UTD during some years of study. Correlation analyses indicated that the shallower the water table, the greater the CO2 fluxes. Higher corn plant C for CTD tended to offset estimated higher CTD CO2 C losses via soil respiration by ∼100-300 kg C ha(-1). There were good fits between observed and predicted (NEMIS-NOE) N2O fluxes for corn (R(2) = 0.70) and soybean (R(2) = 0.53). Predicted N2O fluxes were higher for CTD for approximately 70% of the paired-field study periods suggesting that soil physical factors, such as water-filled pore space, imposed by CTD have potentially strong impacts on net N fluxes. Model predictions of daily cumulative N2O fluxes for the agronomically-active study period for corn-CTD and corn-UTD, as a percentage of total N fertilizer applied, were 3.1% and 2.6%, respectively. For predicted N2O fluxes on basis of yield units, indices were 0.0005 and 0.0004 (kg N kg(-1) crop grain yield) for CTD and UTD corn fields, respectively, and 0.0011 and 0.0005 for CTD and UTD soybean fields, respectively.

Methane production and consumption in loess soil at different slope position

Methane (CH(4)) production and consumption and soil respiration in loess soils collected from summit (Top), back slope (Middle), and slope bottom (Bottom) positions were assessed in laboratory incubations. The CH(4) production potential was determined under conditions which can occur in the field (relatively short-term flooding periods with initially ambient O(2) concentrations), and the CH(4) oxidation potential was estimated in wet soils enriched with CH(4). None of the soils tested in this study emitted a significant amount of CH(4). In fact, the Middle and Bottom soils, especially at the depth of 20-40 cm, were a consistent sink of methane. Soils collected at different slope positions significantly differed in their methanogenic, methanotrophic, and respiration activities. In comparison with the Top position (as reference soil), methane production and both CO(2) production and O(2) consumption under flooding were significantly stimulated in the soil from the Middle slope position (P < 0.001), while they were reduced in the Bottom soil (not significantly, by 6 to 57%). All upper soils (0-20 cm) completely oxidized the added methane (5 kPa) during 9-11 days of incubation. Soils collected from the 20-40 cm at the Middle and Bottom slope positions, however, consumed significantly more CH(4) than the Top soil (P < 0.001).

Ecosystem-scale biosphere-atmosphere interactions of a hemiboreal mixed forest stand at Järvselja, Estonia

During two measurement campaigns, from August to September 2008 and 2009, we quantified the major ecosystem fluxes in a hemiboreal forest ecosystem in Järvselja, Estonia. The main aim of this study was to separate the ecosystem flux components and gain insight into the performance of a multi-species multi-layered tree stand. Carbon dioxide and water vapor fluxes were measured using the eddy covariance method above and below the canopy in conjunction with the microclimate. Leaf and soil contributions were quantified separately by cuvette and chamber measurements, including fluxes of carbon dioxide, water vapor, nitrogen oxides, nitrous oxide, methane, ozone, sulfur dioxide, and biogenic volatile organic compounds (isoprene and monoterpenes). The latter have been as well characterized for monoterpenes in detail. Based on measured atmospheric trace gas concentrations, the flux tower site can be characterized as remote and rural with low anthropogenic disturbances. Our results presented here encourage future experimental efforts to be directed towards year round integrated biosphere-atmosphere measurements and development of process-oriented models of forest-atmosphere exchange taking the special case of a multi-layered and multi-species tree stand into account. As climate change likely leads to spatial extension of hemiboreal forest ecosystems a deep understanding of the processes and interactions therein is needed to foster management and mitigation strategies.

Methane flux in cropland and adjacent riparian buffers with different vegetation covers

While water quality functions of conservation buffers established adjacent to cropped fields have been widely documented, the relative contribution of these re-established perennial plant systems to greenhouse gases has not been completely documented. In the case of methane (CH(4)), these systems have the potential to serve as sinks of CH(4) or may provide favorable conditions for CH(4) production. This study quantifies CH(4) flux from soils of riparian buffer systems comprised of three vegetation types and compares these fluxes with those of adjacent crop fields. We measured soil properties and diel and seasonal variations of CH(4) flux in 7 to 17 yr-old re-established riparian forest buffers, warm-season and cool-season grass filters, and an adjacent crop field located in the Bear Creek watershed in central Iowa. Forest buffer and grass filter soils had significantly lower bulk density (P < 0.01); and higher pH (P < 0.01), total carbon (TC) (P < 0.01), and total nitrogen (TN) (P < 0.01) than crop field soils. There was no significant relationship between CH(4) flux and soil moisture or soil temperature among sites within the range of conditions observed. Cumulative CH(4) flux was -0.80 kg CH(4)-C ha(-1) yr(-1) in the cropped field, -0.46 kg CH(4)-C ha(-1) yr(-1) within the forest buffers, and 0.04 kg CH(4)-C ha(-1) yr(-1) within grass filters, but difference among vegetation covers was not significant. Results suggest that CH(4) flux was not changed after establishment of perennial vegetation on cropped soils, despite significant changes in soil properties.

Nitrogen, tillage, and crop rotation effects on carbon dioxide and methane fluxes from irrigated cropping systems

Long-term effects of tillage intensity, N fertilization, and crop rotation on carbon dioxide (CO(2)) and methane (CH(4)) flux from semiarid irrigated soils are poorly understood. We evaluated effects of: (i) tillage intensity [no-till (NT) and conventional moldboard plow tillage (CT)] in a continuous corn rotation; (ii) N fertilization levels [0-246 kg N ha(-1) for corn (Zea mays L.); 0 and 56 kg N ha(-1) for dry bean (Phaseolus vulgaris L.); 0 and 112 kg N ha(-1) for barley (Hordeum distichon L.)]; and (iii) crop rotation under NT soil management [corn-barley (NT-CB); continuous corn (NT-CC); corn-dry bean (NT-CDb)] on CO(2) and CH(4) flux from a clay loam soil. Carbon dioxide and CH(4) fluxes were monitored one to three times per week using vented nonsteady state closed chambers. No-till reduced (14%) growing season (154 d) cumulative CO(2) emissions relative to CT (NT: 2.08 Mg CO(2)-C ha(-1); CT: 2.41 Mg CO(2)-C ha(-1)), while N fertilization had no effect. Significantly lower (18%) growing season CO(2) fluxes were found in NT-CDb than NT-CC and NT-CB (11.4, 13.2 and 13.9 kg CO(2)-C ha(-1)d(-1) respectively). Growing season CH(4) emissions were higher in NT (20.2 g CH(4) ha(-1)) than in CT (1.2 g CH(4) ha(-1)). Nitrogen fertilization and cropping rotation did not affect CH(4) flux. Implementation of NT for 7 yr with no N fertilization was not adequate for restoring the CH(4) oxidation capacity of this clay loam soil relative to CT plowed and fertilized soil.

Greenhouse gas fluxes in an eastern Corn Belt soil: weather, nitrogen source, and rotation

Relative contributions of diverse, managed ecosystems to greenhouse gases are not completely documented. This study was conducted to estimate soil surface fluxes of carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O) as affected by management practices and weather. Gas fluxes were measured by vented, static chambers in Drummer and Raub soil series during two growing seasons. Treatments evaluated were corn cropped continuously (CC) or in rotation with soybean (CS) and fertilized with in-season urea-ammonium nitrate (UAN) or liquid swine manure applied in the spring (SM) or fall (FM). Soybean (SC) rotated with CS and restored prairie grass (PG) were also included. The CO(2) fluxes correlated (P <or= 0.001) with soil temperature (rho: 0.74) and accumulated rainfall 120 h before sampling (rho: 0.53); N(2)O fluxes correlated with soil temperature (rho: 0.34). Seasonal CO(2)-C emissions were not different across treatments (4.4 Mg ha(-1) yr(-1)) but differed between years. Manured soils were net seasonal CH(4)-C emitters (0.159-0.329 kg ha(-1) yr(-1)), whereas CSUAN and CCUAN exhibited CH(4)-C uptake (-0.128 and -0.177 kg ha(-1) yr(-1), respectively). Treatments significantly influenced seasonal N(2)O-N emissions (P < 0.001) and ranged from <1.0 kg ha(-)(1) yr(-1) in PG and SC to between 3 and 5 kg ha(-1) yr(-1) in CCFM and CSUAN and >8 kg ha(-1) yr(-1) in CCSM; differences were driven by pulse emissions after N fertilization in concurrence with major rainfall events. These results suggest fall manure application, corn-soybean rotation, and restoration of prairies may diminish N(2)O emissions and hence contribute to global warming mitigation.

Greenhouse gas emissions and global warming potential of reclaimed forest and grassland soils

Although greenhouse gas (GHG) emissions from soils are important, reclaimed mine soil (RMS) ecosystems are not widely assessed. Postreclamation land uses (forest, hay, and pasture) were investigated to: (i) monitor the magnitude of GHG fluxes, (ii) estimate their global warming potential (GWP), (iii) identify the relationship between GHG fluxes and soil properties, and (iv) develop a soil quality index by principal component analysis (PCA). The GHG fluxes were measured for 1 yr cycle and simultaneous measurements were also made for soil moisture and temperature. The RMS-forest, -hay, and -pasture land uses had weighted average fluxes of 1.16, 1.66, and 3.06 g CO(2)-C m(-2) d(-1); 0.33, 0.48 and 1.1 mg CH(4)-C m(-2) d(-1); and 0.33, 0.70, and 1.06 mg N(2)O-N m(-2) d(-1), respectively. The CO(2), CH(4), and N(2)O fluxes were consistently high in the RMS-pasture and low in the RMS-forest. The GWP (CO(2)-C equivalent) of the postreclamation land uses was in the order of RMS-forest (4.5 Mg ha(-1) yr(-1)) = RMS-hay (6.8 Mg ha(-1) yr(-1)) < RMS-pasture (12.3 Mg ha(-1) yr(-1)). The PCA showed that four PCs with eigenvalues > 1 explained 88.8% of the total variance in the soil properties. The first PC is mostly characterized by soil physical properties and the second by chemical properties. Soil and air temperatures were positively correlated with CO(2), CH(4), and N(2)O fluxes. The results suggest that GWP from RMS can be minimized by establishing forest land use.

Greenhouse gas emissions from two soils receiving nitrogen fertilizer and swine manure slurry

The interactive effects of soil texture and type of N fertility (i.e., manure vs. commercial N fertilizer) on N(2)O and CH(4) emissions have not been well established. This study was conducted to assess the impact of soil type and N fertility on greenhouse gas fluxes (N(2)O, CH(4), and CO(2)) from the soil surface. The soils used were a sandy loam (789 g kg(-1) sand and 138 g kg(-1) clay) and a clay soil (216 g kg(-1) sand, and 415 g kg(-1) clay). Chamber experiments were conducted using plastic buckets as the experimental units. The treatments applied to each soil type were: (i) control (no added N), (ii) urea-ammonium nitrate (UAN), and (iii) liquid swine manure slurry. Greenhouse gas fluxes were measured over 8 weeks. Within the UAN and swine manure treatments both N(2)O and CH(4) emissions were greater in the sandy loam than in the clay soil. In the sandy loam soil N(2)O emissions were significantly different among all N treatments, but in the clay soil only the manure treatment had significantly higher N(2)O emissions. It is thought that the major differences between the two soils controlling both N(2)O and CH(4) emissions were cation exchange capacity (CEC) and percent water-filled pore space (%WFPS). We speculate that the higher CEC in the clay soil reduced N availability through increased adsorption of NH(4)(+) compared to the sandy loam soil. In addition the higher average %WFPS in the sandy loam may have favored higher denitrification and CH(4) production than in the clay soil.

Agricultural opportunities to mitigate greenhouse gas emissions

Agriculture is a source for three primary greenhouse gases (GHGs): CO(2), CH(4), and N(2)O. It can also be a sink for CO(2) through C sequestration into biomass products and soil organic matter. We summarized the literature on GHG emissions and C sequestration, providing a perspective on how agriculture can reduce its GHG burden and how it can help to mitigate GHG emissions through conservation measures. Impacts of agricultural practices and systems on GHG emission are reviewed and potential trade-offs among potential mitigation options are discussed. Conservation practices that help prevent soil erosion, may also sequester soil C and enhance CH(4) consumption. Managing N to match crop needs can reduce N(2)O emission and avoid adverse impacts on water quality. Manipulating animal diet and manure management can reduce CH(4) and N(2)O emission from animal agriculture. All segments of agriculture have management options that can reduce agriculture's environmental footprint.

Methane oxidation and production activity in soils from natural and agricultural ecosystems

Methane (CH4) flux from soil to the atmosphere is the result of two microbial processes, methanogenesis and CH4 oxidation. Land use may have a profound impact on the relative activities of these groups of organisms. In this study, the CH4 production and consumption potentials of soils from agricultural and nonagricultural ecosystems were assessed in laboratory incubations. Methane production potentials of most soils were low and in the range of 0.02 to 0.35 nmol CH4 g soil(-1) h(-1); however, soils from two of the agricultural sites that experience periodic water saturation had CH4 production potentials from 100 to 300 nmol CH4 g soil(-1) h(-1). The high methanogenic potential suggests that CH4 consumers may not be wholly dependent on atmospheric CH4 for their survival and maintenance. The prairie soils exhibited the highest CH4 oxidation under ambient atmospheric CH4 concentrations, and CH4 oxidation activity was markedly enhanced in incubations with an atmosphere enriched in CH4. This stimulated CH4 oxidation activity was generally greater in the agricultural soils as compared with the forest and prairie soils. Methane oxidation appeared to be related to soil nitrogen status. Under ambient atmospheric CH4 concentrations, CH4 oxidation was negatively related to soil mineral N (NO2- + NO3- + NH4+) concentration. However, a positive relationship between soil mineral N status and CH4 oxidation activity was observed in incubations with atmospheres enriched in CH4. This pattern suggests that the agricultural lands contain different populations of CH4 oxidizers than the natural systems.