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1.
Understanding how agricultural management practices impact nitrous oxide (N 2O) emissions is prerequisite for developing mitigation protocols. We conducted a meta-analysis on 597 pairwise comparisons (129 papers) to assess how management affects N 2O emissions. Pairwise comparisons of practices aimed at improving fertilizer use efficiency (39%) and tillage (30%) dominated the dataset, while ecologically-based nutrient management (ENM) practices constituted 15% of the pairs. In general, across management practices, the quantity of N added was a more significant driver of N 2O fluxes than was the form of N (fertilizer, legume biomass or animal manures). Manure interacted with soil texture so that in coarse soils, N 2O emissions from manures tended to be higher compared to inorganic N fertilizers. The studies of ENM strategies frequently involved over-application of N inputs in the ENM treatments. Cover crops reduced N 2O emissions compared to bare fallows. However, during the cash crop growing season, when differences in N added and N source were confounded, the extra N inputs from cover crops were significantly correlated with the differences in N 2O emissions between treatments with and without cover crops. Overall, in 38% of the data pairs, N 2O emissions were reduced with limited impacts on yields; in half of these pairs, yields were maintained or increased while in the other half they were reduced by only ≤10%. Knowledge gaps on mitigation of agricultural N 2O emissions could be addressed by applying an ecosystem-based, cross-scale perspective in conjunction with the N saturation conceptual framework to guide research priorities and experimental designs. 相似文献
2.
This paper addresses three topics related to N 2O emissions from agricultural soils. First, an assessment of the current knowledge of N 2O emissions from agricultural soils and the role of agricultural systems in the global N 2O are discussed. Secondly, a critique on the methodology presented in the OECD/OCDE (1991) program on national inventories of N 2O is presented. Finally, technical options for controlling N 2O emissions from agricultural fields are discussed.The amount of N 2O derived from nitrogen applied to agricultural soils from atmospheric deposition, mineral N fertilizer, animal wastes or biologically fixed N, is not accurately known. It is estimated that the world-wide N 2O emitted directly from agricultural fields as a result of the deposition of all the above nitrogen sources is 2–3 Tg N annually. This amounts to 20–30% of the total N 2O emitted annually from the earth's surface. An unknown, but probably significant, amount of N 2O is generated indirectly in on and off farm activities associated with food production and consumption.Management options to limit direct N 2O emissions from N-fertilized soils should emphasize improving N-use efficiency. Such management options include managing irrigation frequency, timing and quantity; applying N only to meet crop demand through multiple applications during the growing season or by using controlled release fertilizers; applying sufficient N only to meet crop needs; or using nitrification inhibitors. Most of these options have not been field tested. Agricultural management practices may not appreciably affect indirect N 2O emissions. 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.
In 1995 a working group was assembled at the request of OECD/IPCC/IEA to revise the methodology for N 2O from agriculture for the National Greenhouse Gas Inventories Methodology. The basics of the methodology developed to calculate annual country level nitrous oxide (N 2O) emissions from agricultural soils is presented herein. Three sources of N 2O are distinguished in the new methodology: (i) direct emissions from agricultural soils, (ii) emissions from animal production, and (iii) N 2O emissions indirectly induced by agricultural activities. The methodology is a simple approach which requires only input data that are available from FAO databases. The methodology attempts to relate N 2O emissions to the agricultural nitrogen (N) cycle and to systems into which N is transported once it leaves agricultural systems. These estimates are made with the realization that increased utilization of crop nutrients, including N, will be required to meet rapidly growing needs for food and fiber production in our immediate future. Anthropogenic N input into agricultural systems include N from synthetic fertilizer, animal wastes, increased biological N-fixation, cultivation of mineral and organic soils through enhanced organic matter mineralization, and mineralization of crop residue returned to the field. Nitrous oxide may be emitted directly to the atmosphere in agricultural fields, animal confinements or pastoral systems or be transported from agricultural systems into ground and surface waters through surface runoff. Nitrate leaching and runoff and food consumption by humans and introduction into sewage systems transport the N ultimately into surface water (rivers and oceans) where additional N 2O is produced. Ammonia and oxides of N (NO x) are also emitted from agricultural systems and may be transported off-site and serve to fertilize other systems which leads to enhanced production of N 2O. Eventually, all N that moves through the soil system will be either terminally sequestered in buried sediments or denitrified in aquatic systems. We estimated global N 2O–N emissions for the year 1989, using midpoint emission factors from our methodology and the FAO data for 1989. Direct emissions from agricultural soils totaled 2.1 Tg N, direct emissions from animal production totaled 2.1 Tg N and indirect emissions resulting from agricultural N input into the atmosphere and aquatic systems totaled 2.1 Tg N 2O–N for an annual total of 6.3 Tg N 2O–N. The N 2O input to the atmosphere from agricultural production as a whole has apparently been previously underestimated. These new estimates suggest that the missing N 2O sources discussed in earlier IPCC reports is likely a biogenic (agricultural) one. 相似文献
5.
In most soils, formation and emissions of N 2O to the atmosphere are enhanced by an increase in available mineral nitrogen (N) through increased rates of nitrification and denitrification. Therefore, addition of N, whether in the form of organic or inorganic compounds eventually leads to enhanced N 2O emissions. Global N 2O emissions from agricultural systems have previously been related primarily to fertilizer N input from synthetic sources. Little attention has been paid to N input from other N sources or to the N 2O produced from N that has moved through agricultural systems. In a new methodology used to estimate N 2O emissions on the country or regional scale, that is briefly described in this paper, the anthropogenic N input data used include synthetic fertilizer, animal waste (feces and urine) used as fertilizer, N derived from enhanced biological N-fixation through N 2 fixing crops and crop residue returned to the field. Using FAO database information which includes data on synthetic fertilizer consumption, live animal production and crop production and estimates of N input from recycling of animal and crop N, estimates of total N into Asian agricultural systems and resulting N 2O emissions are described over the time period 1961 through 1994.During this time the quantity and relative amounts of different types of materials applied to agricultural soils in Asia as nitrogen (N) fertilizer have changed dramatically. In 1961, using the earliest entry from the FAO database, of the approximately 15.7 Tg of fertilizer N applied to agricultural fields 2.1 Tg N (13.5% of total N applied) was from synthetic sources, approximately 6.9 Tg N from animal wastes, 1.7 Tg N from biological N-fixation, and another 5 Tg N from reutilization of crop residue. In 1994, 40.2 Tg from synthetic fertilizer N (57.8% of total), 14.2 Tg from animal wastes, 2.5 Tg from biological N-fixation and 12.6 Tg from crop residue totalling 69.5 Tg N were utilized within agricultural soils in all Asian countries.The increases in N utilization have increased the emission of nitrous oxide from agricultural systems. Estimated N 2O from agricultural systems in Asia increased from about 0.8 Tg N 2O-N in 1961 to about 2.1 in 1994. The period of time when increases in N input and resulting N 2O emissions were greatest was during 1970–1990.This evaluation of N input into Asian agricultural systems and the resulting N 2O emissions demonstrates the large change in global agriculture that has occurred in recent decades. Because of the increased need for food production increases in N input are likely. Although the rate of increase of N input and N 2O emissions during the 1990s appears to have declined, we ask if this slowed rate of increase is a general long term trend or if global food production pressures will tend to accelerate N input demand and resulting N 2O emissions as we move into the 21st century. 相似文献
6.
Direct nitrous oxide (N 2O) emissions from agricultural soils contribute considerably to anthropogenic GHG emissions. Albeit a key source of emissions
in many countries, direct N 2O emissions are still calculated and reported to the United Nations Convention on Climate Change using default emission factors
defined in the IPCC guidelines (IPCC 1996, 2006). It is known that processes controlling production and transport of N 2O are highly sensitive to environmental conditions defined by weather, soil and management. The accuracy of N 2O emission budgets and the efficiency of mitigation can be improved if those dependencies are considered with regionalized
emission factors. In this study an empirical method originating from soft computing techniques based on measured data is developed
and applied to quantify direct N 2O emissions from agricultural soils at field and national level in Germany between 1990 and 2005. The method is used to derive
maps of emission factor distribution of direct N 2O emissions of agricultural land in Germany. Model results are compared with alternative empirical approaches from literature.
Results from developing empirical models show that grassland and cropland have to be differentiated according to the key controls
driving N 2O emissions. N 2O emissions of German croplands are highly influenced by climatic conditions and soil properties. The variability of N 2O fluxes on grasslands is mainly driven by the fertilizer N applied. The model comparison using measured European N 2O emissions exhibits profound discrepancies between the models used on a regional scale. The nationwide budgets derived span
a narrow range of −8 to 28% relative to direct N 2O emissions quantified by the German national inventory report. The emission factor of German agriculture estimated by the
developed model is 0.91% of fertilizer N applied. 相似文献
7.
In most countries, nitrous oxide (N 2O) emissions typically contribute less than 10% of the CO 2 equivalent greenhouse gas (GHG) emissions. In New Zealand, however, this gas contributes 17% of the nation’s total GHG emissions
due to the dominance of the agricultural sector. New Zealand’s target under the Kyoto Protocol is to reduce GHG emissions
to 1990 levels. Currently total GHG emissions are 17% above 1990 levels. The single largest source of N 2O emission in New Zealand is animal excreta deposited during grazing (80% of agricultural N 2O emissions), while N fertilizer use currently contributes only 14% of agricultural emissions. Nitrogen fertilizer use has,
however, increased 4-fold since 1990. Mitigation strategies for reducing N 2O emissions in New Zealand focus on (i) reducing the amount of N excreted to pasture, e.g. through diet manipulation; (ii)
increasing the N use efficiency of excreta or fertilizer, e.g. through grazing management or use of nitrification inhibitors;
or (iii) avoiding soil conditions that favour denitrification e.g. improving drainage and reducing soil compaction. Current
estimates suggest that, if fully implemented, these individual measures can reduce agricultural N 2O emissions by 7–20%. The highest reduction potentials are obtained from measures that reduce the amount of excreta N, or
increase the N use efficiency of excreta or fertilizer. However, New Zealand’s currently used N 2O inventory methodology will require refinement to ensure that a reduction in N 2O emissions achieved through implementation of any of these mitigation strategies can be fully accounted for. Furthermore,
as many of these mitigation strategies also affect other greenhouse gas emissions or other environmental losses, it is crucial
that both the economic and total environmental impacts of N 2O mitigation strategies are evaluated at a farm system’s level. 相似文献
8.
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
3
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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
9.
The Intergovernmental Panel on Climate Change (IPCC) standard methodology to conduct national inventories of soil N 2O emissions is based on default (or Tier I) emission factors for various sources. The objective of our study was to summarize
recent N 2O flux data from agricultural legume crops to assess the emission factor associated with rhizobial nitrogen fixation. Average
N 2O emissions from legumes are 1.0 kg N ha −1 for annual crops, 1.8 kg N ha −1 for pure forage crops and 0.4 kg N ha −1 for grass legume mixes. These values are only slightly greater than background emissions from agricultural crops and are
much lower that those predicted using 1996 IPCC methodology. These field flux measurements and other process-level studies
offer little support for the use of an emission factor for biological N fixation (BNF) by legume crops equal to that for fertiliser
N. We conclude that much of the increase in soil N 2O emissions in legume crops may be attributable to the N release from root exudates during the growing season and from decomposition
of crop residues after harvest, rather than from BNF per se. Consequently, we propose that the biological fixation process itself be removed from the IPCC N 2O inventory methodology, and that N 2O emissions induced by the growth of legume crops be estimated solely as a function of crop residue decomposition using an
estimate of above- and below-ground residue inputs, modified as necessary to reflect recent findings on N allocation. 相似文献
10.
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
11.
The DNDC model was used to estimate direct N 2O emissions from agricultural soils in Canada from 1970 to 1999. Simulations were carried out for three soil textures in seven soil groups, with two to four crop rotations within each soil group. Over the 30-year period, the average annual N 2O emission from agricultural soils in Canada was found to be 39.9 Gg N 2O–N, with a range from 20.0 to 77.0 Gg N 2O–N, and a general trend towards increasing N 2O emissions over time. The larger emissions are attributed to an increase in N-fertilizer application and perhaps to a trend in higher daily minimum temperatures. Annual estimates of N 2O emissions were variable, depending on timing of rainfall events and timing and duration of spring thaw events. We estimate, using DNDC, that emissions of N 2O in eastern Canada (Atlantic Provinces, Quebec, Ontario) were approximately 36% of the total emissions in Canada, though the area cropped represents 19% of the total. Over the 30-year period, the eastern Gleysolic soils had the largest average annual emissions of 2.47 kg N 2O–N ha –1 y –1 and soils of the dryer western Brown Chernozem had the smallest average emission of 0.54 kg N 2O–N ha –1 y –1. On average, for the seven soil groups, N 2O emissions during spring thaw were approximately 30% of total annual emissions. The average N 2O emissions estimates from 1990 to 1999 compared well with estimates for 1996 using the IPCC methodology, but unlike the IPCC methodology our modeling approach provides annual variations in N 2O emissions based on climatic differences. 相似文献
12.
Nitrogen retention and release following the incorporation of cover crops and green manures were examined in field trials in NE Scotland. These treatments reduced the amounts of nitrate-N by between 10–20 kg ha -1 thereby lowering the potential for leaching and gaseous N losses. However, uptake of N by overwintering crops was low, reflecting the short day-lengths and low soil temperatures associated with this part of Britain. Vegetation that had regenerated naturally was as effective as sown cover crops at taking up N over winter and in returning N to the soil for the following crop. Incorporation of residues generally resulted in lower mineralisation rates and reduced N 2O emissions than the cultivation of bare ground, indicating a temporary immobilisation of soil N following incorporation. Emissions from incorporated cover crops ranged from 23–44 g N 2O-N ha -1 over 19 days, compared with 61 g N 2O-N ha -1 emitted from bare ground. Emissions from incorporated green manures ranged from 409–580 g N 2O-N ha -1 over 53 days with 462 g N 2O-N ha -1 emitted from bare ground. Significant positive correlations between N 2O and soil NO 3
- after incorporation ( r=0.8–0.9; P<0.001 and r=0.1–0.4; P<0.05 for cover crops and green manures, respectively) suggest that this N 2O was mainly produced during nitrification. There was no significant effect of either cover cropping or green manuring on the N content or yield of the subsequent oats crop, suggesting that N was not sufficiently limiting in this soil for any benefits to become apparent immediately. However, benefits of increased sustainability as a result of increased organic matter concentrations may be seen in long-term organic rotations, and such systems warrant investigation. 相似文献
13.
This analysis is based on published measurements of nitrous oxide (N 2O) emission from fertilized and unfertilized fields. Data was selected in order to evaluate the importance of factors that regulate N 2O production, including soil conditions, type of crop, nitrogen (N) fertilizer type and soil and crop management. Reported N 2O losses from anhydrous ammonia and organic N fertilizers or combinations of organic and synthetic N fertilizers are higher than those for other types of N fertilizer. However, the range of management and environmental conditions represented by the data set is inadequate for use in estimating emission factors for each fertilizer type. The data are appropriate for estimating the order of magnitude of emissions. The longer the period over which measurements are made, the higher the fertilizer-induced emission. Therefore, a simple equation to relate the total annual direct N 2O–N emission (E) from fertilized fields to the N fertilizer applied (F), was based on the measurements covering periods of one year: E=1+1.25×F, with E and F in kg N ha -1 yr -1. This relationship is independent of the type of fertilizer. Although the above regression equation includes considerable uncertainty, it may be appropriate for global estimates. 相似文献
14.
According to the revised 1996 IPCC guidelines, several emission factors are needed to calculate national inventories of N 2O emissions from agriculture. To estimate the direct N 2O emissions from mineral soils, an emission factor of 0.0125 kg N 2O-N per kg N applied is currently being used. From recent literature data it was clearly shown that real N 2O emissions could differ substantially from this value. Based on the IPCC methodology an inventory of N 2O emission from agriculture in Europe (EU-15) has been made. In 1996, the N 2O emission was estimated at 672 Gg N 2O-N. The N 2O emission per country varied between 10 and 177 Gg N 2O-N. The N 2O emission per ha agricultural land in the various countries varied between 1.7 and 14.2 kg N 2O-N ha −1. Highest N 2O emissions per ha were found in countries with a high agricultural intensity, such as the Netherlands, Belgium-Luxembourg,
Denmark and Germany. Agricultural soils are a sink for atmospheric methane. An oxidation capacity of 2.5 and 1.5 kg CH 4 ha −1 yr −1 was put forward for grasslands and arable land, respectively. Based on land use data of 1993, the CH 4 sink of agricultural lands in EU-15 was estimated at 303.5 Gg CH 4. In general, it could be concluded that N 2O emissions from soils (327 Tg CO 2 equivalents) are far more important than its sink function for CH 4 (6.3 Tg CO 2 equivalents).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
Nitrous oxide (N 2O) emission from farmland is a concern for both environmental quality and agricultural productivity. Field experiments were
conducted in 1996–1997 to assess soil N 2O emissions as affected by timing of N fertilizer application and straw/tillage practices for crop production under irrigation
in southern Alberta. The crops were soft wheat ( Triticum aestivumL.) in 1996 and canola ( Brassica napusL.) in 1997. Nitrous oxide flux from soil was measured using a vented chamber technique and calculated from the increase in
concentration with time. Nitrous oxide fluxes for all treatments varied greatly during the year, with the greatest fluxes
occurring in association with freeze-thaw events during March and April. Emissions were greater when N fertilizer (100 kg
N ha −1) was applied in the fall compared to spring application. Straw removal at harvest in the fall increased N 2O emissions when N fertilizer was applied in the fall, but decreased emissions when no fertilizer was applied. Fall plowing
also increased N 2O emissions compared to spring plowing or direct seeding. The study showed that N 2O emissions may be minimized by applying N fertilizer in spring, retaining straw, and incorporating it in spring. The estimates
of regional N 2O emissions based on a fixed proportion of applied N may be tenuous since N 2O emission varied widely depending on straw and fertilizer management practices.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
Direct nitrous oxide emissions from a light-textured arable soil typical of North-Western Russia and subject to different
management systems were measured during three growing seasons (May–September) in 2003–2005. Cumulative fluxes varied between
0.26 ± 0.06 and 2.98 ± 1.56 kg N 2O–N ha −1, with the lowest flux produced where no N was added as mineral fertilizers/manures or where green manure/low inputs of mineral
fertilizer were used as a source of N. Highest cumulative fluxes were measured from the plots where high inputs of farmyard
manure were used. Of the crops studied, potatoes produced the highest N 2O fluxes; this was attributed to the use of furrows, in which the soil tended to be more compact with higher water-filled
pore space, making the soil more prone to denitrification than that in fields without furrows. The available N content of
the soil at the start of each growing season was quite low and cumulative N 2O fluxes were significantly affected by N-fertilizer application within one growing season. However, for different growing
seasons with highly changeable rainfall patterns and with different soil management for different crops, the quite high yearly
correlation between N application and N 2O fluxes was much reduced. 相似文献
17.
In Italy, managed soils account for about 50% of annual national emissions of nitrous oxide (N 2O), thus the effect of agricultural practices on N 2O emissions must be studied in order to develop mitigation strategies. Soil N 2O emissions were measured in two field campaigns (2013–2014 and 2014–2015) on durum wheat in a Mediterranean environment to test the mitigation potential of reduced tillage and nitrogen (N) fertilization rate. N 2O emissions were measured with a fully-transportable instrument developed during the project LIFE?+?IPNOA “Improved flux Prototypes for N 2O emission reduction from Agriculture” and equipped with an infrared laser detector. Reducing tillage from ploughing to minimum tillage had no effect on average daily N 2O flux, while decreasing the N rate from 170 to 110 kg N ha ?1 reduced the average daily N 2O flux, without negatively affecting the grain yield. Furthermore, N 2O daily flux were positively correlated with soil water filled pore space, NO 3-N, and NH 4-N concentrations, and they were largely variable between the two field campaigns as a result of different environmental and management conditions (i.e.: rainfall, different amount of crop residues incorporated in soil). Overall, the innovative fully-transportable instrument performed well in the field and allowed us to conclude that decreasing the N fertilizer rate was a valuable option to mitigate N 2O emissions without negative effects on wheat productivity. 相似文献
18.
In this study N 2O emissions from agriculture in Belgium have been split up per agro-pedological region and calculated per farm type. The N 2O emissions were calculated according to the `Revised 1996 IPCC guidelines for national greenhouse gas inventories'. Input
data were weighed averages of the N balance of a large number of farms per agro-pedological region and per farm type. As such,
the input data represent a theoretical farm in each agro-pedological region and for each distinguished farm type. In a first
part, N 2O emissions were calculated for 10 agro-pedological regions in Belgium. The yearly N 2O emissions varied between 225 and 462 kg N 2O-N. The highest N 2O emissions (around 400 kg N 2O-N yr −1) were found in regions with fertile soils, dominated by crop production or a combination of crop production and cattle breeding.
The lowest emissions (around 250 kg N 2O-N yr −1) were found in regions with extensive cattle breeding. N 2O emissions of 300 ± 15 kg N 2O-N yr −1 were found in regions with less extensive cattle breeding or in regions with combinations of cattle, pig and poultry breeding.
The N 2O emission per ha varied between 6 and 14 kg N 2O-N yr −1. In a second part, N 2O emissions were calculated for 12 different farm types. The yearly N 2O emissions varied between 273 and 512 kg N 2O-N. The highest emissions were found on farms with crop production or a combination of crop production and cattle breeding.
The lowest emissions were found on farms specialised in only one activity of animal breeding. Specialised pig farms and farms
with combinations of cattle caused the greatest threat with respect to N 2O releases from agriculture. Their N 2O emission per ha was 18–40 kg N 2O-N yr −1, which was significantly higher than the average N 2O release (10 kg N 2O-N yr −1 ha −1) for the other farm types.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
The process-based Pasture Simulation Model (PaSim 2.5) has been extended to simulate N 2O production and emission from grassland caused by nitrogen inputs from different sources. The model was used to assess the
influence of management on N 2O emissions, such as the effect of shifts in the amount and timing of fertilizer application. Model performance has been tested
against season-long field measurements at two different field sites. Simulation results agreed favourably with measured N 2O emission and soil air concentrations, except during an extremely wet period at one site when grass growth was very poor.
The results of short-term and long-term simulation runs demonstrated the potential of the model to estimate N 2O emission factors under various conditions. During the first growing season, simulated emissions from organic fertilizers
were lower than from synthetic fertilizers because more of the nitrogen was used to build up soil organic matter. The relative
difference between the fertilizer types became larger with increasing application rate. The difference between fertilizer
types was smaller at steady-state when higher soil organic matter content from repeated application of organic fertilizer
over time led to enhanced mineralization and N 2O emissions. The dependence of simulated N 2O emissions on N input was close to linear at low, but non-linear at high fertilization rates. Emission factors calculated
from the linear part of the curve suggested that the factors used in the current IPCC method underestimate the long-term effects
of changes in fertilizer management. Furthermore the simulations show that N 2O emissions caused by nitrogen inputs from the decomposition of harvest losses and from biological fixation in grassland can
be considerable and should not be neglected in national emission inventories.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
The zero tillage (ZT) system is used in a large area (>24 Mha) of crop production in Brazil. This management system can contribute
to soil C sequestration, but many studies in other countries have registered greater nitrous oxide emissions under ZT compared
to conventional tillage (CT), which may reduce greenhouse gas mitigation benefits. The aim of this study was to estimate the
emission of N 2O from cropping systems under conventional and zero tillage in an 18-year-old experiment conducted on a Rhodic Ferralsol in
the South of Brazil. Fluxes of N 2O were measured over two years using static-closed chambers in the two tillage systems with three crop rotations. Soil water
filled pore space (%WFPS) and soil mineral N were monitored along with rainfall and air temperature. Estimates of N 2O emissions were obtained by integrating the fluxes with time and also by applying the IPCC direct emission factor (EF1 = 1%)
to the amounts of N added as fertilisers and returned as crop residues. Fluxes of N 2O were relatively low, apart from a short period at the beginning of measurements. No relationship between N 2O fluxes and %WFPS or mineral N were observed. Nitrous oxide emissions were not influenced either by tillage system or crop
rotation. For the crop rotation receiving high rates of N fertiliser in the second year, field-measured N 2O emissions were significantly underestimated by the IPCC emission factor 1 (EF1). For the other treatments measured N 2O emissions fell within the EF1 uncertainty range, but always considerably lower than the EF1 estimate, which suggests IPCC
EF1 overestimates true N 2O emissions for the Ferralsol under evaluation. 相似文献
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