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1.
The impact of development of land for agriculture and agricultural production practices on emissions of greenhouse gases is reviewed and evaluated within the context of anthropogenic radiative forcing of climate. Combined, these activities are estimated to contribute about 25%, 65%, and 90% of total anthropogenic emissions of CO 2, CH 4, and N 2O, respectively. Agriculture is also a significant contributor to global emissions of NH 3, CO, and NO. Over the last 150 y, cumulative emissions of CO 2 associated with land clearing for agriculture are comparable to those from combustion of fossil fuel, but the latter is the major source of CO 2 at present and is projected to become more dominant in the future. Ruminant animals, rice paddies, and biomass burning are principal agricultural sources of CH 4, and oxidation of CH 4 by aerobic soils has been reduced by perturbations to natural N cycles. Agricultural sources of N 2O have probably been substantially underestimated due to incomplete analysis of increased N flows in the environment, especially via NH 3 volatilization from animal manures, leaching of NO
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, and increased use of biological N fixation.The contribution of agriculture to radiative forcing of climate is analyzed using data from the Intergovernmental Panel on Climate Change (IPCC)(base case) and cases where the global warming potential of CH 4, and agricultural emissions of N 2O are doubled. With these scenarios, agriculture, including land clearing, is estimated to contribute between 28–33% of the radiative forcing created over the next 100yr by 1990 anthropogenic emissions of CO 2, CH 4, and N 2O. Analyses of the sources of agriculturally generated radiative climate forcing show that 80% is associated with tropical agriculture and that two-thirds comes from non-soil sources of greenhouse gases. The importance of agriculture to radiative forcing created by different countries varies widely and is illustrated by comparisons between the USA, India, and Brazil. Some caveats to these analyses include inadequate evaluations of the net greenhouse effects of agroecosystems, uncertainties in global fluxes of greenhouse gases, and incomplete understanding of tropospheric chemical processes.Extension of the analytical approach to projected future emissions of greenhouse gases (IPCC moderate growth scenario) indicates that agriculture will become a less important source of radiative forcing in the future. Technological approaches to mitigation of agricultural sources of greenhouse gases will probably focus on CH 4 and N 2O because emissions of CO 2 are essentially associated with the socio-political issue of tropical deforestation. Available technologies include dietary supplements to reduce CH 4 production by ruminant animals and various means of improving fertilizer N management to reduce N 2O emissions. Increased storage of C in soil organic matter is not considered to be viable because of slow accretion rates and misconceptions about losses of soil organic matter from agricultural soils. 相似文献
2.
In Japan, upland soils are an important source of nitrous oxide (N 2O) and nitric oxide (NO) gas emissions. This paper reports on an investigation of the effect of soil moisture near saturation on N 2O and NO emission rates from four upland soils in Japan of contrasting texture. The aim was to relate these effects to soil physical properties. Intact cores of each soil type were incubated in the laboratory at different moisture tensions after fertilisation with NH 4-N, NO 3-N or zero N. Emissions of N 2O and NO were measured regularly over a 16–20 day period. At the end of the incubation, soil cores were analysed for physical properties. Moisture and N fertiliser significantly affected rates of emissions of both N 2O and NO with large differences between the soil types. Nitrous oxide emissions were greatest in the finer-textured soils, whereas NO emissions were greater in the coarser-textured soils. Emissions of N 2O increased at higher moisture contents in all soils, but the magnitude of increase was much greater in finer-textured soils. Nitric oxide emissions were only significant in soils fertilised with NH 4-N and were negatively correlated with soil moisture. Analysis of soil properties showed that there was a strong relationship between the magnitude of emissions and soil physical properties. The importance of soil wetness to gas emissions was mainly through its influence on soil air-filled porosity, which itself was related to gas diffusivity. From the results of this research, we can now estimate likely effects of soil texture on emissions through the influence of soil type on soil aeration and soil drainage. This is of particular value in modelling N 2O and NO emissions from soil moisture status and land use inputs. 相似文献
3.
The number of published N 2O and NO emissions measurements is increasing steadily, providing additional information about driving factors of these emissions and allowing an improvement of statistical N-emission models. We summarized information from 1008 N 2O and 189 NO emission measurements for agricultural fields, and 207 N 2O and 210 NO measurements for soils under natural vegetation. The factors that significantly influence agricultural N 2O emissions were N application rate, crop type, fertilizer type, soil organic C content, soil pH and texture, and those for NO emissions include N application rate, soil N content and climate. Compared to an earlier analysis the 20% increase in the number of N 2O measurements for agriculture did not yield more insight or reduced uncertainty, because the representation of environmental and management conditions in agro-ecosystems did not improve, while for NO emissions the additional measurements in agricultural systems did yield a considerable improvement. N 2O emissions from soils under natural vegetation are significantly influenced by vegetation type, soil organic C content, soil pH, bulk density and drainage, while vegetation type and soil C content are major factors for NO emissions. Statistical models of these factors were used to calculate global annual emissions from fertilized cropland (3.3 Tg N 2O-N and 1.4 Tg NO-N) and grassland (0.8 Tg N 2O-N and 0.4 Tg NO-N). Global emissions were not calculated for soils under natural vegetation due to lack of data for many vegetation types. 相似文献
4.
The DNDC (DeNitrification and DeComposition) model was tested against experimental data on CH 4 and N 2O emissions from rice fields at different geographical locations in India. There was a good agreement between the simulated
and observed values of CH 4 and N 2O emissions. The difference between observed and simulated CH 4 emissions in all sites ranged from −11.6 to 62.5 kg C ha −1 season −1. Most discrepancies between simulated and observed seasonal fluxes were less than 20% of the field estimate of the seasonal
flux. The relative deviation between observed and simulated cumulative N 2O emissions ranged from −237.8 to 28.6%. However, some discrepancies existed between observed and simulated seasonal patterns
of CH 4 and N 2O emissions. The model simulated zero N 2O emissions from continuously flooded rice fields and poorly simulated CH 4 emissions from Allahabad site. For all other simulated cases, the model satisfactorily simulated the seasonal variations
in greenhouse gas emission from paddy fields with different land management. The model also simulated the C and N balances
in all the sites, including other gas fluxes, viz. CO 2, NO, NO 2, N 2 and NH 3 emissions. Sensitivity tests for CH 4 indicate that soil texture and pH significantly influenced the CH 4 emission. Changes in organic C content had a moderate influence on CH 4 emission on these sites. Introducing the mid-season drainage reduced CH 4 emissions significantly. Process-based biogeochemical modeling, as with DNDC, can help in identifying strategies for optimizing
resource use, increasing productivity, closing yield gaps and reducing adverse environmental impacts. 相似文献
5.
Increasing concentrations of methane (CH 4) in the atmosphere are projected to account for about 25% of the net radiative forcing. Biospheric emissions of CH 4 to the atmosphere total approximately 400 Tg C y -1. An estimated 300 Tg of CH 4-C y -1 is oxidized in the atmosphere by hydroxyl radicals while about 40 Tg y -1 remains in the atmosphere. Approximately 40 Tg y -1 of the atmospheric burden is oxidized in aerobic soils. Research efforts during the past several years have focused on quantifying
CH 4 sources while relatively less effort has been directed toward quantifying and understanding the soil sink for atmospheric
CH 4.
Recent research has demonstrated that land use change, including agricultural use of native forest and grassland systems has
decreased the soil sink for atmospheric methane. Some agricultural systems consume atmospheric CH 4 at rates less than 10% of those found in comparable undisturbed soils.
While it has been necessary to change land use practices over the past centuries to meet the required production of food and
fiber, we need to recognize and account for impacts of land use change on the biogeochemical nutrient cycles in the biosphere.
Changes that have ensued in these cycles have and will impact the atmospheric concentrations of CH 4 and N 2O. Since CH 4 and N 2O production and consumption are accomplished by a variety of soil microorganisms, the influence of changing agricultural,
forest, and, demographic patterns has been large. Existing management and technological practices may already exist to limit
the effect of land use change and agriculture on trace gas fluxes. It is therefore important to understand how management
and land use affect trace gas fluxes and to observe the effect of new technology on them.
This paper describes the role of aerobic soils in the global CH 4 budget and the impact of agriculture on this soil CH 4 sink. Examples from field studies made across subarctic, temperate and tropical climate gradients in grasslands are used
to demonstrate the influence of nutrient cycle perturbations on the soil consumption of atmospheric CH 4 and in increased N 2O emissions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Nitrous oxide (N 2O) flux simulations by four models were compared with year-round field measurements from five temperate agricultural sites in three countries. The field sites included an unfertilized, semi-arid rangeland with low N 2O fluxes in eastern Colorado, USA; two fertilizer treatments (urea and nitrate) on a fertilized grass ley cut for silage in Scotland; and two fertilized, cultivated crop fields in Germany where N 2O loss during the winter was quite high. The models used were daily trace gas versions of the CENTURY model, DNDC, ExpertN, and the NASA-Ames version of the CASA model. These models included similar components (soil physics, decomposition, plant growth, and nitrogen transformations), but in some cases used very different algorithms for these processes. All models generated similar results for the general cycling of nitrogen through the agro-ecosystems, but simulated nitrogen trace gas fluxes were quite different. In most cases the simulated N 2O fluxes were within a factor of about 2 of the observed annual fluxes, but even when models produced similar N 2O fluxes they often produced very different estimates of gaseous N loss as nitric oxide (NO), dinitrogen (N 2), and ammonia (NH 3). Accurate simulation of soil moisture appears to be a key requirement for reliable simulation of N 2O emissions. All models simulated the general pattern of low background fluxes with high fluxes following fertilization at the Scottish sites, but they could not (or were not designed to) accurately capture the observed effects of different fertilizer types on N 2O flux. None of the models were able to reliably generate large pulses of N 2O during brief winter thaws that were observed at the two German sites. All models except DNDC simulated very low N 2O fluxes for the dry site in Colorado. The US Trace Gas Network (TRAGNET) has provided a mechanism for this model and site intercomparison. Additional intercomparisons are needed with these and other models and additional data sets; these should include both tropical agro-ecosystems and new agricultural management techniques designed for sustainability. 相似文献
7.
Fluxes of CH 4 and N 2O were measured regularly in an agricultural field treated with 280 g m −2 of sewage sludge. In a nearby beech forest N 2O and CH 4 fluxes were measured in a well-drained (dry) area and in a wet area adjacent to a drainage canal. We observed brief increases
of both CH 4 and N 2O emissions immediately following soil applications of digested sewage sludge. Cumulated values for CH 4 emissions over the course of 328 days after sludge applications indicated a small net source in sludge treated plots (7.6
mg C m −2) whereas sludge-free soil constituted a small sink (-0.9 mg C m −2). The CH 4 emission amounted 0.01% of the sludge-C. Extrapolated to current rates of sludge applications in Danish agriculture this
amounts to 0.1% of the total agricultural derived CH 4. Sludge applications did not affect cumulated fluxes of N 2O showing 312 mg N 2O–N m −2 and 304 mg N m −2 with and without sludge, respectively. Four months after the sludge applications a significant effect on CO 2 and NO emissions was still obvious in the field, the latter perhaps due to elevated nitrification. Nitrous oxide emission
in the beech forest was about six times smaller (45 mg N m −2) than in the field and independent of drainage status. Methane oxidation was observed all-year round in the forest cumulating
to -225 mg C m −2 and -84 mg C m −2 in dry and wet areas. In a model experiment with incubated soil cores, nitrogen amendment (NH 4Cl) and perturbation significantly reduced CH 4 oxidation in the forest soil, presumably as a result of increased nitrification activity. Sludge also induced net CH 4 production in the otherwise strong CH 4 oxidising forest soil. This emphasises the potential for CH 4 emissions from sewage sludge applications onto land. The study shows, however, that emissions of N 2O and CH 4 induced by sewage sludge in the field is of minor importance and that factors such as land use (agriculture versus forest)
is a much stronger controller on the source/sink strengths of CH 4 and N 2O.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Forage production in irrigated mountain meadows plays a vital role in the livestock industry in Colorado and Wyoming. Mountain meadows are areas of intensive fertilization and irrigation which may impact regional CH 4 and N 2O fluxes. Nitrogen fertilization typically increases yields, but N-use efficiency is generally low. Neither the amount of fertilizer-N recovered by the forage nor the effect on N 2O and CH 4 emissions were known. These trace gases are long-lived in the atmosphere and contribute to global warming potential and stratospheric ozone depletion. From 1991 through 1993 studies were conducted to determine the effect of N source, and timing of N-fertilization on forage yield, N-uptake, and trace gas fluxes at the CSU Beef Improvement Center near Saratoga, Wyoming. Plots were fertilized with 168 kg N ha -1. Microplots labeled with 15N-fertilizer were established to trace the fate of the added N. Weekly fluxes of N 2O and CH 4 were measured during the snow-free periods of the year. Although CH 4 was consumed when soils were drying, flood irrigation converted the meadow into a net source of CH 4. Nitrogen fertilization did not affect CH 4 flux but increased N 2O emissions. About 5% of the applied N was lost as N 2O from spring applied NH 4NO 3, far greater than the amount lost as N 2O from urea or fall applied NH 4NO 3. Fertilizer N additions increased forage biomass to a maximum of 14.6 Mg ha -1 with spring applied NH 4NO 3. Plant uptake of N-fertilizer was greater with spring applications (42%), than with fall applications (22%). 相似文献
9.
N 2O is emitted from agricultural soils due to microbial transformation of N from fertilizers, manures and soil N reserves. N 2O also derives from N lost from agriculture to other ecosystems: as NH 3 or through NO
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leaching. Increased efficiency in crop N uptake and reduction of N losses should in principle diminish the amount of N 2O from agricultural sources. Precision in crop nutrient management is developing rapidly and should increase this efficiency. It should be possible to design guidelines on good agricultural practices for low N 2O emissions in special situations, e.g. irrigated agriculture, and for special operations, e.g. deep placement of fertilizers and manures. However, current information is insufficient for such guidelines. Slow-release fertilizers and fertilizers with inhibitors of soil enzymatic processes show promise as products which give reduced N 2O emissions, but they are expensive and have had little market penetration. Benefits and possible problems with their use needs further clarification. 相似文献
10.
In 1991, on farm management practices contributed 57.6 Tg CO 2 equivalent in greenhouse gas emissions, that is, about 10% of the anthropogenic GHG emissions in Canada. Approximately 11%
of these emissions were in the form of CO 2, 36% in the form of CH 4 and 53% in the form of N 2O. The CO 2 emissions were from soils; CH 4 emissions were from enteric fermentation and manure, and N 2O emissions were primarily a function of cropping practices and manure management. With the emissions from all other agricultural
practices included, such as the emissions from fossil fuels used for transportation, manufacturing, food processing etc.,
the agricultural sector's contributions were about 15% of Canada's emissions. In this publication, several options are examined
as to their potential for reducing greenhouse gas emissions. These involve soil and crop management, soil nutrient management,
improved feeding strategies, and carbon storage in industrial by-products. The Canadian Economic Emissions Model for Agriculture
(CEEMA) was used to predict the greenhouse gas emissions for the year 2010, as well as the impact of mitigation options on
greenhouse gas emissions from the agricultural sector. This model incorporates the Canadian Regional Agricultural sub-Model
(CRAM), which predicts the activities related to agriculture in Canada up to 2010, as well as a Greenhouse Gas Emissions sub-Model
(GGEM), which estimates the greenhouse gas emissions associated with the various agricultural activities. The greenhouse gas
emissions from all agricultural sources were 90.5 Tg CO 2 equivalent in 1991. Estimates based on CEEMA for the year 2010 indicate emissions are expected to be 98.0 Tg CO 2 equivalent under a business as usual scenario, which assumes that the present trends in management practices will continue.
The agricultural sector will then need to reduce its emissions by about 12.9 Tg CO 2 equivalent below 2010 forecasted emissions, if it is to attain its part of the Canadian government commitment made in Kyoto.
Technologies focusing on increasing the soil carbon sink, reducing greenhouse gas emissions and improving the overall farming
efficiency, need to be refined and developed as best management practices. The soils carbon sink can be increased through
reduced tillage, reduced summer fallowing, increased use of grasslands and forage crops, etc. Key areas for the possible reduction
of greenhouse gas emissions are improved soil nutrient management, improved manure storage and handling, better livestock
grazing and feeding strategies, etc. The overall impact of these options is dependent on the adoption rate. Agriculture's
greenhouse gas reduction commitment could probably be met if soils are recognized as a carbon sink under the Kyoto Accord
and if a wide range of management practices are adopted on a large scale. None of these options can currently be recommended
as measures because their socio-economic aspects have not been fully evaluated and there are still too many uncertainties
in the emission estimates.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
When manure slurry is removed from storages for land application, there is often ‘aged’ manure that remains because the storages are not completely emptied. Aged manure may act as an inoculum and alter subsequent methane (CH 4), nitrous oxide (N 2O) and ammonia (NH 3) emissions when fresh manure is added to the system, compared to an empty storage that is filled with fresh manure. Completely emptying manure storages may be a practice to decrease gas emissions, however, little pilot-scale research has been conducted to directly quantify the inoculum effect. Therefore, we compared CH 4, N 2O, and NH 3 emissions from three pilot-scale slurry tanks (~10.5 m 3 each) filled with a mixture of fresh manure and an inoculum of previously stored manure (i.e., partial emptying) to three tanks that contained only fresh manure (i.e., complete emptying). Gas fluxes were continuously measured over 155 d of warm season storage using flow-through steady-state chambers. The absence of an inoculum significantly reduced CH 4 emissions by 56 % compared to partially emptied (inoculated) tanks, while there was no difference in N 2O emissions. There was a significant 49 % reduction in greenhouse gas (GHG) emissions because the overall budget (as CO 2-eq) was dominated by CH 4. Complete manure storage emptying could be an effective GHG mitigation strategy; however, NH 3 emissions were significantly higher from un-inoculated tanks due to slower crust formation. Therefore additional NH 3 abatement should be considered. 相似文献
12.
Trace-gas emissions from animal feeding operations (AFOs) can contribute to air quality and global change gases. Previous and current estimated gas emissions from AFOs vary widely and many do not consider all forms of carbon (C) and nitrogen (N) emissions. Studies have found that as methanogenesis in the lagoons increased, conversion of ammonium (NH 4 +) to dinitrogen (N 2) also increased. The purpose of this research was to measure N 2 and CH 4 emissions from swine AFOs in three locations of the U.S. and to evaluate the possible universal relationship between lagoon methanogenesis and the conversion of NH 4 + to N 2 gas. This relationship was tested by measuring N 2 and CH 4 emissions in two climates at 22 different farms. Methanogenesis was correlated with NH 4 +-to-N 2 conversion by a near-constant N 2 to CH 4 emissions ratio of 0.20, regardless of C loading and climatic effects. The process is shown to be thermodynamically favored when there is competition between NH 4 + oxidizing reactions. Under methanogenic conditions (redox potentials of methanogenesis) N 2 production is favorable and nitrification/denitrification is not. Thus, N 2 production is stimulated in methanogenic conditions. Evaluation of NH 3 gas emissions from AFOs must consider other N emissions than NH 3. Finally, a statistical model was developed to estimate methane and N 2 emissions (kg gas ha ?1) given feed input per lagoon surface area (kg feed ha ?1) and local air temperature. Further studies are needed to investigate the mechanisms involved in manure processing and isolate the favorable mechanisms into engineering improved manure processing. 相似文献
13.
Nitrous oxide (N 2O) and nitric oxide (NO) fluxes resulting from long-term tomato cultivation in a glasshouse were continuously determined using the flow-through chamber method over the course of three cultivation periods. Gas concentrations were measured using an nondispersive infrared (gas filter correlation/infra-red) analyzer and a chemiluminescence-based analyzer, respectively. Following a basal application of fertilizer, daily N 2O and NO emission rates increased, with peaks lasting from 40 to 140 days. Short-term fluctuations in daily N 2O and NO emissions were affected by differences in nitrogen application, soil water, and soil temperature. Diurnal changes in N 2O and NO fluxes during the period of peak emissions depended primarily on soil temperature. Following the application of a top dressing (N as urea or calcium nitrate) in the irrigation water, the N 2O and NO fluxes increased immediately, with a very short period of peak emissions (1–5 h) after urea application. The duration of the peak period in daily accumulated N 2O and NO emissions following application of the top dressing ranged from 3 to 10 days. 相似文献
14.
Biogenic emissions of methane (CH 4) and nitrous oxide (N 2O) from animal manure are stimulated by the degradation of volatile solids ( VS) which serves as an energy source and a sink for atmospheric oxygen. Algorithms are presented which link carbon and nitrogen turnover in a dynamic prediction of CH 4 and N 2O emissions during handling and use of liquid manure (slurry). A sub-model for CH 4 emissions during storage relates CH 4 emissions to VS, temperature and storage time, and estimates the reduction in VS. A second sub-model estimates N 2O emissions from field-applied slurry as a function of VS, slurry N and soil water potential, but emissions are estimated using emission factors. The model indicated that daily flushing of slurry from cattle houses would reduce total annual CH 4 + N 2O emissions by 35% (CO 2 eq.), and that cooling of pig slurry in-house would reduce total annual CH 4 + N 2O emissions by 21% (CO 2 eq.). Anaerobic digestion of slurry and organic waste produces CH 4 at the expense of VS. Accordingly, the model predicted a 90% reduction of CH 4 emissions from outside stores with digested slurry, and a >50% reduction of N 2O emissions after spring application of digested as opposed to untreated slurry. The sensitivity of the model towards storage temperature and soil water potential was examined. This study indicates that simple algorithms to account for ambient climatic conditions may significantly improve the prediction of CH 4 and N 2O emissions from animal manure. 相似文献
15.
Tea fields represent an important source of nitrous oxide (N 2O) and nitric oxide (NO) emissions due to high nitrogen (N) fertilizer applications and very low soil pH. To investigate the temporal characteristics of N 2O and NO emissions, daily emissions were measured over 2½ years period using static closed-chamber/gas chromatograph and chemiluminescent measurement system in a tea field of subtropical central China. Our results revealed that N 2O and NO fluxes showed similar temporal trends, which were generally driven by temporal variations in soil temperature and soil moisture content and were also affected by fertilization events. The measured average annual N 2O and NO emissions were 10.9 and 3.3 kg N ha ?1 year ?1, respectively, highlighting the high N 2O and NO emissions from tea fields. To improve our understanding of N-cycling processes in tea ecosystems, we developed a new nitrogenous gas emission module for the water and nitrogen management model (WNMM, V2) that simulated daily N 2O and NO fluxes, in which the NO was simulated as being emitted from both nitrification and nitrite chemical decomposition. The results demonstrated that the WNMM captured the general temporal dynamics of N 2O (NSE = 0.40; R 2 = 0.52, RMSE = 0.03 kg N ha ?1 day ?1, P < 0.001) and NO (NSE = 0.41; R 2 = 0.44, RMSE = 0.01 kg N ha ?1 day ?1, P < 0.001) emissions. According to the simulation, denitrification was identified as the dominant process contributing 76.5% of the total N 2O emissions, while nitrification and nitrite chemical decomposition accounted for 52.3 and 47.7% of the total NO emissions, respectively. 相似文献
16.
Accurate estimates of nitrous oxide (N2O) emissions from agricultural soils and management factors that influence emissions are necessary to capture the impact of mitigation measures and carry out life cycle analyses aimed at identifying best practices to reduce greenhouse gas emissions. We propose improvements to a country specific method for estimating N2O emissions from agricultural soils in Canada based on a compilation of soil N2O flux data from recent published literature. We provide a framework for the development of empirical models that could be applied in regions where similar data and information on N2O emissions are available. The method considers spatial elements such as soil texture, topography and climate based on a quantitative empirical relationship between synthetic N-induced soil N2O emission factor (EF) and growing season precipitation (P) {N2OEF?=?e(0.00558P?7.7)}. Emission factors vary from less than 0.0025 kg N2O-N kg N?1 in semi-arid regions of Canada to greater than 0.025 kg N2O-N kg N?1 in humid regions. This approach differentiates soil N2O EFs based on management factors. Specifically, empirical ratio factors are applied for sources of N of 1.0, 0.84, and 0.28 for synthetic N, animal manure N and crop residue N, respectively. Crop type ratio factors where soil N2O EFs from applied manure- and synthetic-N on perennial crops are approximately 19% of those on annual crops. This proposed approach improves the accuracy of the dominant factors that modulate N2O emissions from N application to soils. 相似文献
17.
Emission measurements from dairy cows housed in a tying stall were carried out with the aim of finding factors that influence
the amount of emissions and means to reduce emissions. All sectors of animal husbandry were investigated. This enabled calculations
of emissions for the whole management system including housing, storage and spreading of manure. Emissions during aerobic
composting and anaerobic stacking of farmyard manure were compared. NH 3 and N 2O emissions from tying stalls for dairy cows are low (5.8 g NH 3 LU −1 d −1, 619.2 mg N 2O LU −1 d −1). Methane emissions from the animal housing are mainly caused by enteric fermentation. During storage and after spreading
of farmyard manure substantial differences concerning NH 3, N 2O and CH 4 emissions were observed with composted and anaerobically stacked farmyard manure. The compost emitted more NH 3 than the anaerobically stacked farmyard manure. About one third of the NH 3 emissions from the anaerobically stacked farmyard manure occurred after spreading. Total N losses were at a low level with
both storage systems. Greenhouse gas emissions (N 2O and CH 4) were much higher from the anaerobically stacked farmyard manure than from the composted one. As these are ecologically harmful
gases, they have to be considered when judging the form of manure treatment.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
Long-term studies of greenhouse gas fluxes from agricultural soils in different climate regions are needed to improve the existing calculation models used in greenhouse gas inventories. The aim of this study was to obtain more information on nitrous oxide (N 2O) emissions from agricultural mineral soils in the boreal region. N 2O emissions were studied during 2000–2002 on two soil types in Finland, a loamy sand and a clay with plots of grass, barley and fallow. N 2O fluxes were measured with static chambers throughout the year. Other parameters measured were water filled pore space (WFPS), soil mineral nitrogen concentration, soil porosity, soil temperature and depth of soil frost. The annual fluxes from the clay soil ranged from 3.7 to 7.8 kg N ha –1 and those from sandy loam from 1.5 to 7.5 kg N ha –1. On average 60% of the annual fluxes occurred outside the growing season, from October to April. Increasing the number of freeze-thaw events was found to increase the fluxes during winter and during the thawing period in spring. The results suggest that N 2O fluxes from these boreal mineral soils do not vary much as a function of applied fertiliser N and could probably be better estimated from soil physical properties, including soil porosity. 相似文献
19.
Vegetation loss and plant diversity decline in wetlands affect carbon and nitrogen cycling and consequently influence gas fluxes. Although extensive grazing by livestock and climate change have caused significant physical degradation of wetlands on the Qinghai-Tibet Plateau (QTP), and created a clear drainage gradient, the impact on greenhouse gas (GHG) emissions associated with this change has rarely been reported. A 3-year study (2013–2015) was conducted to examine the effect of vegetation change and seasonality on ecosystem respiration, methane (CH 4) and nitrous oxide (N 2O) fluxes in four classes of wetlands with distinct magnitudes of vegetation degradation: healthy vegetation (HV), slightly degraded (SD), moderately degraded, and heavily degraded (HD). We used the dark static chamber-chromatography method to measure the gas fluxes. Highly degraded wetlands were larger C and GHG sources than HV, despite lower methane emissions, due to the loss of gross primary production. SD and HD exhibited the highest cumulative mean annual ecosystem respiration and N 2O emissions, respectively. Ecosystem respiration and CH 4 fluxes were much higher during the growing seasons than in the non-growing seasons. Ecosystem respiration and N 2O fluxes were positively correlated with soil and air temperatures. This points at a potential effect of global warming on GHG emissions from the QTP wetlands. Top soil (0–20 cm) moisture content significantly correlated positively with CH 4 fluxes. Vegetation loss led to a reduced C uptake and increased global warming potential. Therefore, we recommend soil conservation measures and reduced livestock grazing in the wetlands in order to conserve their role as carbon sinks. 相似文献
20.
The authors of this paper measured the methane and nitrous oxide fluxes emissions from rice field with different rice varieties
and the two fluxes from pot experiments with different soil water regime and fertilizer treatment. The experiment results
showed that: (1) The CH 4 emission rates were different among different varieties; (2) There was a trade-off between CH 4 and N 2O emissions from rice field with some agricultural practices; (3) We must consider the mitigation options comprehensively
to mitigate CH 4 and N 2O emissions from rice fields.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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