Modeling nitrous oxide emissions from tile-drained winter wheat fields in Central France

Modeling nitrous oxide (N₂O) 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 N₂O flux measurements at eight sites cropped with winter wheat across a tile-drained landscape (around 30-km²) 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 N₂O emitted through denitrification were added in NOE_V2. DNDC95 and NOE_V2 successfully predicted background N₂O 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.     

Field Validation of DNDC Model for Methane and Nitrous Oxide Emissions from Rice-based Production Systems of India

The DNDC (DeNitrification and DeComposition) model was tested against experimental data on CH₄ and N₂O emissions from rice fields at different geographical locations in India. There was a good agreement between the simulated and observed values of CH₄ and N₂O emissions. The difference between observed and simulated CH₄ 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 N₂O emissions ranged from −237.8 to 28.6%. However, some discrepancies existed between observed and simulated seasonal patterns of CH₄ and N₂O emissions. The model simulated zero N₂O emissions from continuously flooded rice fields and poorly simulated CH₄ 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. CO₂, NO, NO₂, N₂ and NH₃ emissions. Sensitivity tests for CH₄ indicate that soil texture and pH significantly influenced the CH₄ emission. Changes in organic C content had a moderate influence on CH₄ emission on these sites. Introducing the mid-season drainage reduced CH₄ 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.     

Modelling nitrous oxide emissions from dairy-grazed pastures

Soil N₂O 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 N₂O 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 N₂O coincided with rainfall events and high soil moisture content. Large inherent variations in N₂O fluxes were observed throughout the year in both the ungrazed (control) and grazed pastures. Fluxes averaged 4.3 and 5.0 g N₂O/ha/day for the two ungrazed sites. The N₂O fluxes from the grazed sites were much higher than for the ungrazed sites, averaging 26.4 g N₂O/ha/day for the fine sandy loam soil, and 32.0 g N₂O/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 N₂O 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 N₂O emission pulses and trends from both the ungrazed and grazed pastures. The modified model fairly reproduced the real variability in underlying processes regulating N₂O emissions and could be suitable for simulating N₂O emissions from a range of New Zealand grazed pastures. The NZ-DNDC estimates of total yearly emissions of N₂O 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.     

Diffusion analysis of N2O cycling in a fertilized soil

The behavior of nitrous oxide (N₂O) in fertilized soil was studied in terms of soil fluxes, the production rates at various depths and the turnover in soil. The diffusive losses of N₂O to the atmosphere calculated from soil N₂O profile compared favorably with the flux directly determined with a closed chamber technique. The estimate of N₂O production rates at several depths demonstrated that the sites of N₂O production was only near the soil surface. The calculated residence time of N₂O in the entire soil column studied was only 1.4 hour during active emission period and less than 1 day even in the later period having trace N₂O emission. The prolonged N₂O emission observed after the active phase was due likely to a lasting N₂O production rather than a supply from the soil N₂O reservoir. The results suggested that most N₂O in soil was emitted quite promptly to the atmosphere after its production. A minor role of soil as an N₂O reservoir is emphasized from the viewpoint of the origin of groundwater N₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

Carrot cropping on organic soil is a hotspot for nitrous oxide emissions

The emissions of the greenhouse gas nitrous oxide (N₂O) were measured from a non nitrogen fertilized carrot (Daucus carota ssp. sativa) field on an organic soil in Sweden during one cropping and post-harvest season. The cumulative emission during the measuring period of 149?days was 41 (±2.8) kg N₂O ha^?1. Dividing the measuring period into a cropping and a post-harvest period revealed that the presence of carrots strongly stimulated N₂O emissions, as the emission during the cropping period was one order of magnitude higher compared to the post-harvest period. The N₂O emission from the carrot field were higher than fluxes reported from cereal crop and grass production, but in the same order as reported fluxes from vegetable cropping on organic soils. In conclusion, our results indicate that the cultivation of root vegetable, such as carrots, on organic soil can be a high point source for N₂O emissions.     

N2O and NO emissions from grassland soils after the application of cattle and swine excreta

N₂O and NO fluxes from grassland soil after the application of cattle and swine excreta were measured by a closed chamber method in the autumn and winter of 1994 to 1995. Fresh excrement and urine were spread on the grassland experimental plots and these gas fluxes were measured one or two times a week. In the autumn experiment, N₂O and NO fluxes began to increase several days after the application, the NO flux reaching a maximum after 16 days. In the winter experiment, N₂O and NO fluxes began to increase 45 days after the application and reached a maximum after 80 days. Nitrous oxide flux was influenced by soil water content, high water content leading to high N₂O flux. The ratio of NO-N/N₂O-N in the flux was in the range of 1.1 to 13.7, and negatively correlated to the soil water content. In the winter experiment, the total emission rate of NO was 0.48% and 0.45% of total nitrogen in the applied cattle and swine excreta, respectively. The total emission rate of N₂O was 0.085% and 0.098% in the applied cattle and swine excreta, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparing a process-based agro-ecosystem model to the IPCC methodology for developing a national inventory of N2O emissions from arable lands in China

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 N₂O emissions from cropland soils, field studies have shown that there are important factors that influence N₂O 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 N₂O 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 km². 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 N₂O emissions from soils. National totals were the sum of results for all crop simulations across all counties. Baseline simulations estimated that total N₂O emission from arable land in China in 1990 was 0.31 Tg N₂O-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 N₂O emissions. The fertilizer-induced emission was 0.13 Tg N₂O-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.     

N2O and NO emission from agricultural fields and soils under natural vegetation: summarizing available measurement data and modeling of global annual emissions

The number of published N₂O 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 N₂O and 189 NO emission measurements for agricultural fields, and 207 N₂O and 210 NO measurements for soils under natural vegetation. The factors that significantly influence agricultural N₂O 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 N₂O 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. N₂O 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 N₂O-N and 1.4 Tg NO-N) and grassland (0.8 Tg N₂O-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.     

Increase of N2O Fluxes in Agricultural Peat and Sandy Soil under Elevated CO2 Concentration: Concomitant Changes in Soil Moisture, Groundwater Table and Biomass Production of Phleum pratense

The effects of elevated atmospheric CO₂ concentration on soil moisture, N₂O fluxes, and biomass production of Phleum pratense were studied in the laboratory. Farmed peat and sandy soil mesocosms sown with P. pratense were fertilized with a commercial fertilizer. In peat soil 10 g N m⁻² of commercial fertilizer were added and in sandy soil 15 g N m⁻². In both experiments, soil moisture was regulated with deionized water; 18 mesocosms were tended to keep equally moist, and the other 18 were watered with equal amounts of water. Nine mesocosms from both watering treatments were grown under ambient (360 μmol mol⁻¹) CO₂ concentration and the remaining nine under doubled (720 μmol mol⁻¹) CO₂. N₂O efflux was monitored using a closed chamber technique and a gas chromatograph. The elevated supply of CO₂ increased production of above- and belowground biomass, soil moisture and N₂O fluxes, but decreased the total N content in the aboveground biomass, especially for the sandy soil. In similar water levels, N₂O efflux from the sandy soil was the same magnitude as that from the peat soil. In addition to moisture, N availability was the main limiting factor for N₂O production, but C availability also seemed to regulate the denitrification activity. In addition to an increase in C availability the increase in the N₂O efflux under the raised CO₂ concentration also required a simultaneous increase in soil moisture.     

Effects of N management on N2O and CH4 fluxes and15N

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 CH₄ and N₂O 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 N₂O and CH₄ 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 with¹⁵N-fertilizer were established to trace the fate of the added N. Weekly fluxes of N₂O and CH₄ were measured during the snow-free periods of the year. Although CH₄ was consumed when soils were drying, flood irrigation converted the meadow into a net source of CH₄. Nitrogen fertilization did not affect CH₄ flux but increased N₂O emissions. About 5% of the applied N was lost as N₂O from spring applied NH₄NO₃, far greater than the amount lost as N₂O from urea or fall applied NH₄NO₃. Fertilizer N additions increased forage biomass to a maximum of 14.6 Mg ha^-1 with spring applied NH₄NO₃. Plant uptake of N-fertilizer was greater with spring applications (42%), than with fall applications (22%).     

A Review of the Movement and Fate of N<Subscript>2</Subscript>O in the Subsoil

Understanding the fate of N₂O in the subsoil is important in accurately assessing the direct and indirect fluxes of N₂O to the environment. The production, movement and ultimate fate of N₂O in the subsoil are all poorly understood. Movement of N₂O in the subsoil occurs predominantly via diffusion but convective fluxes can also occur. Diffusion gradients in the soil have been used to determine N₂O surface fluxes with varying success. Infiltration of water into the soil may lead to entrapment, and the temporary storage of N₂O, ebullition, or the transport of dissolved N₂O in soil leachates. The reduction of N₂O to N₂ is potentially enhanced when N₂O is entrapped. Few studies have examined the effect of infiltrating water on a previously known N₂O concentration in the soil. Future studies are required to better establish the consumption and movement of N₂O in the subsoil during water infiltration. This paper reviews past work on the movement and fate of N₂O in the subsoil and makes suggestions for future studies.     

Nitrous oxide emissions from agricultural fields during winter and spring thaw as affected by management practices

Highest rates of N₂O emissions from fertilized as well as natural ecosystems have often been measured at spring thaw. But, it is not clear if management practices have an effect on winter and spring thaw emissions, or if measurements conducted over several years would reveal different emission patterns depending on winter conditions. In this study, we present N₂O fluxes obtained using the flux-gradient approach over four winter and spring thaw periods, spanning from 1993 to 1996, at two locations in Ontario, Canada. Several agricultural fields (bare soil, barley, soybean, canola, grass, corn) subjected to various management practices (manure and nitrogen fertilizer addition, alfalfa ploughing, fallowing) were monitored. Nitrous oxide emissions from these fields from January to April over four years ranged between 0 and 4.8 kg N ha^-1. These thaw emissions are substantial and should be considered in the nitrous oxide budgets in regions where thaw periods occur. Our study indicates that agricultural management can play a role in mitigating these emissions. Our data show that fallowing, manure application and alfalfa incorporation in the fall lead to high spring emissions, while the presence of plants (as in the case of alfalfa or grass) can result in negligible emissions during thaw. This presents an opportunity for mitigation of N₂O emissions through the use of over-wintering cover crops.     

Temporal and Spatial Variations in N2O Emissions from a Chinese Cabbage Field as a Function of Type of Fertilizer and Application

We conducted a field experiment in an Andosol near Tsukuba (Japan) to study the effects of the type of nitrogen fertilizer on nitrous oxide (N₂O) emissions and on nitrogen uptake by Chinese cabbage (Brassica campestris L.). We used four treatments: fertilizer containing no nitrogen (CONT), broadcast application of urea (BR-U), band application of urea (B-U), and band application of controlled-release urea (B-CU). The application rate was 250 kg N ha⁻¹, a conventional rate in the region. We measured N₂O flux two or three times a week during the 82-day growth period, then divided the cumulative emissions into three stages: early (28 days), middle (27 days), and late (27 days). The temporal variation in N₂O emissions differed among the treatments. Broadcast urea application produced 70% of N₂O emissions during the early stage. N₂O emissions increased with increasing cabbage growth in the CONT treatment, indicating that plant growth accompanied by increasing root biomass could stimulate N₂O emissions from unfertilized soil. There were no differences in the patterns of temporal variation in N₂O flux between the two band applications (B-U and B-CU); N₂O emissions in the early and middle stages were 46 and 42%, respectively, for B-U, vs. 41 and 40% for B-CU. However, the overall N₂O emission was reduced by 40.5% in the B-CU treatment compared with the B-U treatment. N₂O emissions from the soils within fertilized bands were dramatically higher than those between the fertilized bands, and this trend continued until harvesting.     

The Effect of Future Climate Perturbations on N<Subscript>2</Subscript>O Emissions from a Fertilized Humid Grassland

N₂O emissions from a fertilized humid grassland near Cork, Ireland were continuously measured during 2003 using an eddy covariance system. For most of the year emissions were close to zero and 60% of the emissions occurred in eight major events of 2–20 days’ duration. Two hundred and seven kg ha⁻¹ of synthetic N and 130 kg ha⁻¹ organic N were applied over the year and the total measured annual N₂O emission was 11.6 kg N ha⁻¹. The flux data were used to test the prediction of N₂O emissions by the DNDC (DeNitrification – DeComposition) model. The model predicted total emissions of 15.4 kg N ha⁻¹, 32 % more than the observed emissions. On this basis the model was further used to simulate (a) background (non-anthropogenic) N₂O emissions and (b) the effect on N₂O emissions of future climate perturbations based on the Hadley Center model output of the IS92a scenario for Ireland. DNDC predicts 1.7 kg N ha⁻¹ year⁻¹ of background N₂O emissions, accounting for 15% of the observed emissions. Climate shifts will increase total annual modeled N₂O emissions from 15.4 kg N ha⁻¹ to 22.4 kg N ha⁻¹ if current levels of N applications are maintained, or to 21.2 kg N ha⁻¹ if synthetic N applications are reduced to 170 kg N ha⁻¹ to comply with recent EU water quality legislation. Thus the projected increase in N₂O emissions due to climate change is far larger than the decrease expected from reduced fertilizer applications.     

Effects of deep application of urea on NO and N2O emissions from an Andisol

A modeling study revealed that the depth of nitric oxide (NO) production in soil is crucial for its flux, while that of nitrous oxide (N₂O) is not. To verify this result, laboratory experiments with soil columns classified as Andisol (Hydric Hapludand) were conducted, with changing the depth of urea application, at 0–0.1 or 0.1–0.2 m. All the NO concentration profiles in soil exhibited a sharp peak at each fertilized layer within 5 days of fertilizer application. NO concentration in soil decreased abruptly as the distance from the fertilized layer increased. These findings imply that NO is produced mainly within the fertilized layer, but does not diffuse widely in the soil columns, because of rapid NO uptake within the soil. As a result, the NO flux from soil columns fertilized at 0.1–0.2 m depth over the 48-day study period was reduced to almost the same rate as that of the unfertilized one. The total NO emissions from soil columns unfertilized and fertilized at 0–0.1 and 0.1–0.2 m depth were 0.02, 1.39 (± 0.05) and 0.05 (± 0.03) kg N ha^–1, respectively, suggesting that NO emission derived from N fertilizer could be reduced to 2% by shifting the depth of fertilizer application by 0.1 m. On the other hand, soil N₂O concentration profiles exhibited a gentler peak, because of the lower uptake by soil. N₂O fluxes were affected more by the soil conditions, e.g. soil water content, than the distance between fertilized depth and soil surface. The total N₂O emissions from soil columns unfertilized and fertilized at 0–0.1 and 0.1–0.2 m were 0.02, 0.16 (± 0.03) and 0.25 (± 0.04) kg N ha^–1, respectively.     

Effects of the herbicides butachlor and bensulfuron-methyl on N2O emissions from a dry-seeded rice field

Independent field and laboratory incubation experiments were conducted to investigate the effects of two commonly used herbicides butachlor and bensulfuron-methyl on N₂O emissions from a dry-seeded rice field. Three treatments were applied in field experiments: a fertilized control without herbicide, fertilized plots amended with butachlor equivalent to 2.55 L ha^?1 of 60 % by weight active ingredient and fertilized plots amended with bensulfuron-methyl equivalent to 300 g ha^?1 of 10 % by weight active ingredient. Herbicides were applied twice in the rice growing season according to local farming practices. The same treatments were used in laboratory incubation experiments, i.e., a fertilized control without herbicide and fertilized soil amended with the herbicide butachlor or bensulfuron-methyl. The soil moisture was adjusted to 0.55 g g^?1 in the lab incubation experiments based on the average water content determined in the dry-seeded rice field. The field and laboratory simulation experiments all showed that the butachlor applications led to significantly increased N₂O emissions (p < 0.05), whereas bensulfuron-methyl had no effect on N₂O emissions (p > 0.05). Butachlor enhanced the N₂O emissions by up to 177.5 % over the entire rice growing season. Moreover, butachlor and bensulfuron-methyl treatment led to a marginal stimulation of the soil respiration rates. A further investigation in the field experiments suggested that the butachlor-enhanced N₂O emissions resulted from increased soil ammonium nitrogen and nitrate nitrogen contents and the more abundance of ammonia-oxidizing and denitrifying bacteria in the late stage after the herbicide application. The bensulfuron-methyl treatment had no influence on N₂O emissions during the rice growing season, which was attributed to the low soil nitrate nitrogen contents during this period.     

Emissions of nitrous oxide from boreal agricultural clay and loamy sand soils

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 (N₂O) emissions from agricultural mineral soils in the boreal region. N₂O 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. N₂O 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 N₂O 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.     

Fluxes of methane and nitrous oxide in water-saving rice production in north China

Lowland rice production is currently facing serious water shortages in numerous Asian countries. In the North China Plain water limitations are severe. Water-saving rice production techniques are therefore increasingly searched for. Here we present the first study of trace gas emissions from a water-saving rice production system where soils are mulched and are kept close to field capacity in order to compare their contribution to global warming with traditional paddy rice. In a two-year field experiment close to Beijing, CH₄ and N₂O fluxes were monitored in two forms of the Ground Cover Rice Production System (GCRPS) and in traditional paddy fields using closed chambers. With paddy rice the observed CH₄ emissions were very low, about 0.3 g CH₄ m⁻² a⁻¹ in 2001 and about 1 g CH₄ m⁻² a⁻¹ in 2002. In GCRPS, the CH₄ emissions were negligible. N₂O fluxes in GCRPS were similar, 0.5 to 0.6 g N₂O m⁻² a⁻¹ in 2001 and 2002, and emission peaks mainly followed fertilizer applications. In paddy rice, N₂O fluxes were unexpectedly low throughout the year 2001 (0.03 g N₂O m⁻² a⁻¹), and in 2002 larger emissions occurred during the drainage period. So with 0.4 g N₂O m⁻² a⁻¹ the cumulative flux was similar to emissions in GCRPS. Total CO₂ equivalent fluxes calculated according to IPCC methodology were tenfold higher in GCRPS compared to paddy in 2001. In 2002, fluxes from both systems were similar with 175 and 141 g CO₂ equivalents m⁻² a⁻¹ from GCRPS and paddy. Burkhard Sattelmacher deceased.     

Modeling Trace Gas Emissions from Agricultural Ecosystems

A computer simulation model was developed for predicting trace gas emissions from agricultural ecosystems. The denitrification-decomposition (DNDC) model consists of two components. The first component, consisting of the soil climate, crop growth, and decomposition submodels, predicts soil temperature, moisture, pH, Eh, and substrate concentration profiles based on ecological drivers (e.g., climate, soil, vegetation, and anthropogenic activity). The second component, consisting of the nitrification, denitrification, and fermentation submodels, predicts NH₃, NO, N₂O, and CH₄ fluxes based on the soil environmental variables. Classical laws of physics, chemistry, or biology or empirical equations generated from laboratory observations were used in the model to parameterize each specific reaction. The entire model links trace gas emissions to basic ecological drivers. Through validation against data sets of NO, N₂O, CH₄, and NH₃ emissions measured at four agricultural sites, the model showed its ability to capture patterns and magnitudes of trace gas emissions.     

Fungal and bacterial contributions to codenitrification emissions of N<Subscript>2</Subscript>O and N<Subscript>2</Subscript> following urea deposition to soil

Grazed pastures contribute significantly to anthropogenic emissions of N₂O but the respective contributions of archaea, bacteria and fungi to codenitrification in such systems is unresolved. This study examined the relative contributions of bacteria and fungi to rates of denitrification and codenitrification under a simulated ruminant urine event. It was hypothesised that fungi would be primarily responsible for both codenitrification and total N₂O and N₂ emissions. The effects of bacterial (streptomycin), fungal (cycloheximide), and combined inhibitor treatments were measured in a laboratory mesocosm experiment, on soil that had received ¹⁵N labelled urea. Soil inorganic-N concentrations, N₂O and N₂ gas fluxes were measured over 51 days. On Days 42 and 51, when nitrification was actively proceeding in the positive control, the inhibitor treatments inhibited nitrification as evidenced by increased soil NH ₄ ⁺ -N concentrations and decreased soil NO ₂ ^? -N and NO ₃ ^? -N concentrations. Codenitrification was observed to contribute to total fluxes of both N₂O (≥ 33%) and N₂ (≥ 3%) in urine-amended grassland soils. Cycloheximide inhibition decreased NH ₄ ⁺ –¹⁵N enrichment and reduced N₂O fluxes while reducing the contribution of codenitrification to total N₂O fluxes by ≥ 66 and ≥ 42%, respectively. Thus, given archaea do not respond to significant urea deposition, it is proposed that fungi, not bacteria, dominated total N₂O fluxes, and the codenitrification N₂O fluxes, from a simulated urine amended pasture soil.