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1.
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
2.
Nations are now obligated to assess their greenhouse gas emissions under the protocols of Article 4 of the United Nations
Framework Convention on Climate Change. The IPCC has developed `spreadsheet-format' methodologies for countries to estimate
national greenhouse gas emissions by economic sector. Each activity has a magnitude and emission rate and their product is
summed over all included activities to generate a national total (IPCC, 1997). For N 2O emissions from cropland soils, field studies have shown that there are important factors that influence N 2O emissions at specific field sites that are not considered in the IPCC methodology. We used DNDC, a process-oriented agroecosystem
model, to develop an unofficial national inventory of direct N 2O emissions from cropland in China. We assembled county-scale data on soil properties, daily weather, crop areas, N-fertilizer
use, livestock populations (for manure inputs to cropland), and agricultural management for the 2500 counties in mainland
China. Total 1990 cropland area was 0.95 million km 2. Total N-fertilizer use in China in 1990 was 16.6 Tg N. The average fertilization rate was 175 kg N ha −1 cropland. One-year simulations with DNDC were run for each crop type in each county to generate estimates of direct N 2O emissions from soils. National totals were the sum of results for all crop simulations across all counties. Baseline simulations
estimated that total N 2O emission from arable land in China in 1990 was 0.31 Tg N 2O-N yr −1. We also ran simulations with zero N-fertilizer input; the difference between the zero-fertilizer and the baseline run is
an estimate of fertilizer-induced N 2O emissions. The fertilizer-induced emission was 0.13 Tg N 2O-N yr −1, about 0.8% of total N-fertilizer use (lower than the mean but within the IPCC range of 1.25±1.0%). We compared these results
to our estimates of county-scale IPCC methodology emissions. Total emissions were similar but geographical patterns were quite
different.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
The global warming potential of nitrous oxide (N 2O) and its long atmospheric lifetime mean its presence in the atmosphere is of major concern, and that methods are required
to measure and reduce emissions. Large spatial and temporal variations means, however, that simple extrapolation of measured
data is inappropriate, and that other methods of quantification are required. Although process-based models have been developed
to simulate these emissions, they often require a large amount of input data that is not available at a regional scale, making
regional and global emission estimates difficult to achieve. The spatial extent of organic soils means that quantification
of emissions from these soil types is also required, but will not be achievable using a process-based model that has not been
developed to simulate soil water contents above field capacity or organic soils. The ECOSSE model was developed to overcome
these limitations, and with a requirement for only input data that is readily available at a regional scale, it can be used
to quantify regional emissions and directly inform land-use change decisions. ECOSSE includes the major processes of nitrogen
(N) turnover, with material being exchanged between pools of SOM at rates modified by temperature, soil moisture, soil pH
and crop cover. Evaluation of its performance at site-scale is presented to demonstrate its ability to adequately simulate
soil N contents and N 2O emissions from cropland soils in Europe. Mitigation scenarios and sensitivity analyses are also presented to demonstrate
how ECOSSE can be used to estimate the impact of future climate and land-use change on N 2O emissions. 相似文献
4.
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
6.
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
7.
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
8.
The incorporation of legume cover crops into annual grain rotations remains limited, despite extensive evidence that they
can reduce negative environmental impacts of agroecosystems while maintaining crop yields. Diversified grain rotations that
include a winter cereal have a unique niche for interseeding cover crops. To understand how management-driven soil fertility
differences and inter-seeding with grains influenced red clover ( Trifolium pratense) N 2 fixation, we estimated biological N 2 fixation (BNF) in 2006 and 2007, using the 15N natural abundance method across 15 farm fields characterized based on the reliance on BNF derived N inputs as a fraction
of total N inputs. Plant treatments included winter grain with and without interseeded red clover, monoculture clover, monoculture
orchardgrass ( Dactylis glomerata), and clover-orchardgrass mixtures. Fields with a history of legume-based management had larger labile soil nitrogen pools
and lower soil P levels. Orchardgrass biomass was positively correlated with the management-induced N fertility gradient,
but we did not detect any relationship between soil N availability and clover N 2 fixation. Interseeding clover with a winter cereal did not alter winter grain yield, however, clover production was lower
during the establishment year when interseeded with taller winter grain varieties, most likely due to competition for light.
Interseeding clover increased the % N from fixation relative to the monoculture clover (72% vs. 63%, respectively) and the
average total N 2 fixed at the end of the first growing season (57 vs. 47 kg N ha −1, respectively). Similar principles could be applied to develop more cash crop-cover crop complementary pairings that provide
both an annual grain harvest and legume cover crop benefits. 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.
Nitrous oxide (N 2O) is a powerful greenhouse gas. As the UK government is committed to reducing greenhouse gas emissions, it is important to know not only how much of these gases are released but also where and when. Targeted measurements of emissions in relation to crop growth cycles, soil wetness and fertiliser applications were used to derive annual emission rates for specific combinations of soil type, land management and fertiliser practices. These annual emission rates were then spatially scaled to derive regional figures through the development of a Geographic Information System (GIS) based model framework. Digital soil and land use maps at a scale of 1:25000 for two test areas of approximately 200000 ha each (Lothians and the Ayrshire Basin) were overlain with a climate map within the GIS, deriving unique combinations of soil wetness and land use. The calculated annual emission rates (kg N ha –1 yr –1) were then applied to these and multiplied by the total area of each soil/land use type to derive annual emission losses for each area. The annual emission of nitrous oxide from the Lothians was determined as approximately 381000 kg N yr –1, while the emissions from the Ayrshire Basin were predicted to be 794000 kg N yr –1. This indicates the increased emissions associated with both the wetter soils of Ayrshire and the greater extent of grazed pasture systems in this area. Due to the detailed scale of the input data, localised areas with large emissions were identified. Abatement strategies would be concentrated on areas of high emissions that include a change to crops with lower emission potential, reducing fertiliser and manure inputs, reducing grazing intensity and improving soil drainage.Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1024422604493 相似文献
11.
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
12.
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
13.
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
14.
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
15.
Excessive nitrogen fertiliser application and irrigation in the North China Plain leads to nitrate accumulation in sub-soil and water pollution. HERMES, a dynamic, process-oriented soil-crop model was used to evaluate the effects of improved nitrate and water management on nitrate leaching losses. The model was validated against field studies with a winter wheat ( Triticum aestivum L.)–summer maize ( Zea mays L.) double-cropping system. A real-time model-based nitrogen fertiliser recommendation (NFR) was carried out for one wheat crop within the rotation and compared to farmers’ practice and soil mineral nitrogen (N min) content-based fertilisation treatments. Consequences of varying irrigation and annual weather variability on model-based NFR and further model outputs were assessed via simulation scenarios. A best-practice simulation scenario with model-based NFR and adapted irrigation was compared to reduced N and farmers’ practice treatments and to a dry and a wet scenario. Results of the real-time model-based NFR and the other treatments showed no differences in grain yield. Different fertiliser inputs led to higher nitrogen use efficiency (not significant) of the model-based NFR. Increasing amounts of irrigation resulted in significantly higher N leaching, higher N requirements and reduced yields. The impact of weather variation on model-based NFR was smaller. In the best-practice scenario simulation, nitrogen input could be reduced to 17.1 % of conventional farmers’ practice, irrigation water to 72.3 % and nitrogen leaching below 0.9 m to 1.8 % and below 2.0 m soil depth to 0.9 % within 2 years. The model-based NFR in combination with adapted irrigation had the highest potential to reduce nitrate leaching. 相似文献
16.
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
17.
Soil N 2O emissions were measured during four seasons from two highly productive grass-clover dairy pastures to assess the influences of soil moisture, temperature, availability of N (NH
4
+
and NO
3
–
) and soluble C on N 2O emissions, and to use the emission data to validate and refine a simulation model (DNDC). The soils at these pasture sites (Karapoti fine sandy loam, and Tokomaru silt loam) differed in texture and drainage characteristics. Emission peaks for N 2O coincided with rainfall events and high soil moisture content. Large inherent variations in N 2O fluxes were observed throughout the year in both the ungrazed (control) and grazed pastures. Fluxes averaged 4.3 and 5.0 g N 2O/ha/day for the two ungrazed sites. The N 2O fluxes from the grazed sites were much higher than for the ungrazed sites, averaging 26.4 g N 2O/ha/day for the fine sandy loam soil, and 32.0 g N 2O/ha/day for the silt loam soil. Our results showed that excretal and fertiliser-N input, and water-filled pore space (WFPS) were the variables that most strongly regulated N 2O fluxes. The DNDC model was modified to include the effects of day length on pasture growth, and of excretal-N inputs from grazing animals; the value of the WFPS threshold was also modified. The modified model NZ-DNDC simulated effectively most of the WFPS and N 2O emission pulses and trends from both the ungrazed and grazed pastures. The modified model fairly reproduced the real variability in underlying processes regulating N 2O emissions and could be suitable for simulating N 2O emissions from a range of New Zealand grazed pastures. The NZ-DNDC estimates of total yearly emissions of N 2O from the grazed and ungrazed sites of both farms were within the uncertainty range of the measured emissions. The measured emissions changed with changes in soil moisture resulting from rainfall and were about 20% higher in the poorly drained silt loam soil than in the well-drained sandy loam soil. The model accounts for these climatic variations in rainfall, and was also able to pick up differences in emissions resulting from differences in soil texture. 相似文献
18.
Agricultural soils are a major source of the greenhouse gas nitrous oxide (N 2O). Nitrous oxide emission models can be used to predict the effectiveness of N 2O mitigation strategies; however, these models require rigorous testing before they can be used with confidence. Expert-N, a modular process based N 2O emission model, was tested to determine its ability at predicting nitrogen (N) cycling in the soil–plant–atmosphere system under Canadian agroclimatic conditions. Ancillary data and N 2O emissions were collected/measured from a corn cultivated clay-loam soil that was under different tillage and red clover treatments. The treatments were conventional till (CT) with and without red clover (rc) underseeded in the previous year's wheat crop (CT-Crc and CT-C, respectively), and no till (NT) with and without red clover underseeded in the previous year's wheat crop (NT-Crc and NT-C, respectively). Expert-N provided good estimates of N 2O emissions, and predictions correlated well (positive) with the measured emissions ( r
2 0.55–0.83). There was no statistically significant difference between measured and predicted daily emissions. The predicted emissions, integrated over the growing season (25 May–4 October, 1995), were 0.56, 0.57, 0.62, and 0.62 kg N 2O-N ha –1 for CT-C, CT-Crc, NT-C, and NT-Crc, respectively. The measured emissions over the same period were 1.29, 1.07, 0.96, and 1.04 kg N 2O-N ha –1 for CT-C, CT-Crc, NT-C, and NT-Crc, respectively. The modelled emissions underestimated the integrated measured emissions by 35–55%; however, the integrated measured emissions had an estimated uncertainty of ±35%. The model provided good predictions of the soil temperatures, moisture contents, and soil nitrate levels with no significant difference from the measured data. Correlations between modelled and measured values for these soil properties in the first 30 cm soil layer were positive and high with r
2 0.71–0.93. 相似文献
19.
Modeling nitrous oxide (N 2O) emissions from agricultural soils is still a challenge due to influences of artificial management practices on the complex interactions between soil factors and microbial activities. The aims of this study were to evaluate the process-based DeNitrification-DeComposition (DNDC, version 9.5) model and modified non-linear empirical Nitrous Oxide Emission (NOE V2) model with weekly N 2O flux measurements at eight sites cropped with winter wheat across a tile-drained landscape (around 30-km 2) in Central France. Adjustments of the model default field capacity and wilting point and the optimum crop production were necessary for DNDC95 to better match soil water content and crop biomass yields, respectively. Multiple effects of varying soil water and nitrate contents on the fraction of N 2O emitted through denitrification were added in NOE V2. DNDC95 and NOE V2 successfully predicted background N 2O emissions and fertilizer-induced emission peaks at all sites during the experimental period but overestimated the daily fluxes on the sampling dates by 54 and 25 % on average, respectively. Cumulative emissions were slightly overestimated by DNDC95 (4 %) and underestimated by NOE V2 (15 %). The differences between evaluations of both models for daily and cumulative emissions indicate that low frequency measurements induced uncertainty in model validation. Nonetheless, our validations for soil water content with daily resolution suggest that DNDC95 well represented the effect of tile drainage on soil hydrology. The model overestimated soil ammonium and nitrate contents mostly due to incorrect nitrogen partitioning when urea ammonium nitrate solution was applied. The performance of the model would be improved if DNDC included the canopy interception and foliar nitrogen uptake when liquid fertilizer was sprayed over the crops. 相似文献
20.
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
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