Increased emissions of nitric oxide and nitrous oxide following tillage of a perennial pasture

About 40% of the agricultural land in the European Union (EU) is grassland used for animal production. When grassland is tilled, organically bound carbon and nitrogen are released, providing substrates for nitrifying and denitrifying microorganisms. The aim of this study was to examine the immediate effects of tillage of a perennial grassland carried out on different dates, on the emissions of nitric oxide (NO) and nitrous oxide (N₂O), monitored intensively over a 5-day period, in a humid, dairy farming area of northern Spain. Soil was tilled 12 days and 2 days prior to fertiliser application. Tillage, time of tillage, and N fertiliser application affected NO and N₂O emissions. Tillage 12 days before the start of the flux measurements resulted in higher emissions than tillage one day before, the difference being related to differences in soil mineral N and water-filled pore space (WFPS). Emissions of NO peaked at a WFPS of 50–60%, while N₂O fluxes peaked at 70–90% WFPS. Loss of N was greater as N₂O than as NO. The total loss of N as N₂O plus NO ranged from 0.027 kg N ha^–1 in unfertilised plots to 0.56 kg N ha^–1 in the tilled and N fertilised plot. Thereafter emissions decreased rapidly to low values. The results of this study indicate that tillage of perennial grassland may release large amounts of NO and N₂O, the amounts also depending on moisture conditions and addition of N fertiliser. We suggest that in order to reduce such emissions, application of N fertiliser should not immediately follow tillage of perennial grassland, as there is an extra supply of N from mineralisation of organic matter at this time.     

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.     

Spatial and temporal scaling of nitrous oxide emissions from the field to the regional scale in Scotland

Nitrous oxide (N₂O) 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     

N2O and CH4 emissions from fertilized agricultural soils in southwest France

Emissions of nitrogen compounds from heavily fertilized and irrigated maize fields have been studied in the Southwest of France, over an annual cultivation cycle. Strong nitrous oxide emissions from denitrification were observed after application of nitrogen fertilizer. Flux intensity appears to be stimulated by rain or irrigation. Emission algorithms, taking into account both nitrogen input and soil water content were established on the basis of the experimental data set. They allowed us to estimate annual nitrogen loss in the form of nitrous oxide modulated by rainfall. Production of methane is observed at the level of the water table under anoxic conditions. Nevertheless, the net flux between soil and atmosphere is negative for most of the time. When methane is produced, fluxes were very low due to methane oxidation in the soil surface layer.     

Influence of soil physical properties, fertiliser type and moisture tension on N2O and NO emissions from nearly saturated Japanese upland soils

In Japan, upland soils are an important source of nitrous oxide (N₂O) and nitric oxide (NO) gas emissions. This paper reports on an investigation of the effect of soil moisture near saturation on N₂O and NO emission rates from four upland soils in Japan of contrasting texture. The aim was to relate these effects to soil physical properties. Intact cores of each soil type were incubated in the laboratory at different moisture tensions after fertilisation with NH₄-N, NO₃-N or zero N. Emissions of N₂O and NO were measured regularly over a 16–20 day period. At the end of the incubation, soil cores were analysed for physical properties. Moisture and N fertiliser significantly affected rates of emissions of both N₂O and NO with large differences between the soil types. Nitrous oxide emissions were greatest in the finer-textured soils, whereas NO emissions were greater in the coarser-textured soils. Emissions of N₂O increased at higher moisture contents in all soils, but the magnitude of increase was much greater in finer-textured soils. Nitric oxide emissions were only significant in soils fertilised with NH₄-N and were negatively correlated with soil moisture. Analysis of soil properties showed that there was a strong relationship between the magnitude of emissions and soil physical properties. The importance of soil wetness to gas emissions was mainly through its influence on soil air-filled porosity, which itself was related to gas diffusivity. From the results of this research, we can now estimate likely effects of soil texture on emissions through the influence of soil type on soil aeration and soil drainage. This is of particular value in modelling N₂O and NO emissions from soil moisture status and land use inputs.     

The influence of controlled release fertilisers and the form of applied fertiliser nitrogen on nitrous oxide emissions from an andosol

A laboratory experiment was conducted to determine whether applying controlled release nitrogen fertilisers could reduce nitrous oxide emissions from an andosol maintained at different water contents, compared with applying standard nitrogen fertiliser. The effect of the form of N applied (NH₄-N or NO₃-N) was also investigated. Soil was collected from an arable field and sub-samples were treated with controlled release or standard fertiliser, applied at a rate of 200 g N g^–1 dry soil either as NH₄ ⁺ or NO₃ ^–. The soils were maintained at 40%, 55%, 70% or 85% water filled pore space (WFPS) and incubated at 25 °C for 50 days. Gas samples were collected and analysed every 3–4 days and soil samples were analysed on five occasions during the incubation. Emissions of N₂O were much greater from ammonium sulphate than from calcium nitrate fertiliser, indicating that nitrification was the main source of the N₂O. Emissions at 85% WFPS were greater than at the lower water contents in all treatments. The use of controlled release NH₄-N fertilisers reduced and delayed the maximum peak of emissions, but at 55% and 70% WFPS this did not always result in lower total emissions. Emissions from the controlled release NO₃-N fertiliser were very low, but only significantly lower than from standard NO₃-N fertiliser at water contents below 85% WFPS. The results demonstrate that choosing the appropriate form of fertiliser in relation to expected soil moisture could significantly reduce N₂O emissions. Applying the fertiliser in a controlled-release form could further reduce emissions by reducing the length of time that fertiliser nitrogen is present in the soil and available for nitrification or denitrification.     

Algorithms for calculating methane and nitrous oxide emissions from manure management

Biogenic emissions of methane (CH₄) and nitrous oxide (N₂O) from animal manure are stimulated by the degradation of volatile solids (VS) which serves as an energy source and a sink for atmospheric oxygen. Algorithms are presented which link carbon and nitrogen turnover in a dynamic prediction of CH₄ and N₂O emissions during handling and use of liquid manure (slurry). A sub-model for CH₄ emissions during storage relates CH₄ emissions to VS, temperature and storage time, and estimates the reduction in VS. A second sub-model estimates N₂O emissions from field-applied slurry as a function of VS, slurry N and soil water potential, but emissions are estimated using emission factors. The model indicated that daily flushing of slurry from cattle houses would reduce total annual CH₄ + N₂O emissions by 35% (CO₂ eq.), and that cooling of pig slurry in-house would reduce total annual CH₄ + N₂O emissions by 21% (CO₂ eq.). Anaerobic digestion of slurry and organic waste produces CH₄ at the expense of VS. Accordingly, the model predicted a 90% reduction of CH₄ emissions from outside stores with digested slurry, and a >50% reduction of N₂O emissions after spring application of digested as opposed to untreated slurry. The sensitivity of the model towards storage temperature and soil water potential was examined. This study indicates that simple algorithms to account for ambient climatic conditions may significantly improve the prediction of CH₄ and N₂O emissions from animal manure.     

Developing a country specific method for estimating nitrous oxide emissions from agricultural soils in Canada

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.

     

Emission of nitrous oxide from soils used for agriculture

Nitrous oxide is emitted into the atmosphere as a result of biomass burning, and biological processes in soils. Biomass burning is not only an instantaneous source of nitrous oxide, but it results in a longer term enhancement of the biogenic production of this gas. Measurements of nitrous oxide emissions from soils before and after a controlled burn showed that significantly more nitrous oxide was exhaled after the burn. The current belief is that 90% of the emissions come from soils. Nitrous oxide is formed in soils during the microbiological processes nitrification and denitrification. Because nitrous oxide is a gas it can escape from soil during these transformations. Nitrous oxide production is controlled by temperature, pH, water holding capacity of the soil, irrigation practices, fertilizer rate, tillage practice, soil type, oxygen concentration, availability of carbon, vegetation, land use practices and use of chemicals. Nitrous oxide emissions from agricultural soils are increased by the addition of fertilizer nitrogen and by the growth of legumes to fix atmospheric nitrogen. A recent analysis suggests that emissions of nitrous oxide from fertilized soils are not related to the type of fertilizer nitrogen applied and emissions can be calculated from the amount of nitrogen applied. Legumes also contribute to nitrous oxide emission in a number of ways, viz. atmospheric nitrogen fixed by legumes can be nitrified and denitrified in the same way as fertilizer nitrogen, thus providing a source of nitrous oxide, and symbiotically living Rhizobia in root nodules are able to denitrify and produce nitrous oxide. Conversion of tropical forests to crop production and pasture has a significant effect on the emission of nitrous oxide. Emissions of nitrous oxide increased by about a factor of two when a forest in central Brazil was clear cut, and pasture soils in the same area produced three times as much nitrous oxide as adjacent forest soils. Studies on temperate and tropical rice fields show that less than 0.1% of the applied nitrogen is emitted as nitrous oxide if the soils are flooded for a number of days before fertilizer application. However, if mineral nitrogen is present in the soil before flooding it will serve as a source of nitrous oxide during wetting and drying cycles before permanent flooding. Thus dry seeded rice can be a source of considerable nitrous oxide. There are also indirect contributions to nitrous oxide emission through volatilization of ammonia and emission of nitric oxides into the atmosphere, and their redistribution over the landscape through wet and dry deposition. In general nitrous oxide emissions can be decreased by management practices which optimize the crop's natural ability to compete with processes whereby plant available nitrogen is lost from the soil-plant system. If these options were implemented they would also result in increased productivity and reduced inputs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fertiliser timing and use of inhibitors to reduce N<Subscript>2</Subscript>O emissions of rainfed wheat in a semi-arid environment

Nitrogen (N) management is critical to the profitability of grain production systems, however careful management of fertiliser is needed to minimise environmental impacts. We investigated the effect of five N fertilisation strategies on nitrous oxide (N₂O) emissions and nitrogen use efficiency (NUE) of rainfed wheat grown on a clay soil in a temperate, semi-arid environment of south eastern Australia during 2013 and 2014. Treatments included urea application (50 kg N/ha) at sowing with and without nitrification inhibitor (3,4–dimethylpyrazole phosphate) and surface broadcasting of urea with and without urease inhibitor (n-butyl thiophosphoric triamide) at the end of tillering plus an unfertilised control. Daily N₂O emissions were low and responsive to in-season rainfall and fertiliser addition at sowing. Cumulative emissions from sowing until harvest were highest where N was applied at sowing in 2013; 160 g N₂O-N/ha, while the 0 N control emitted 28 g N₂O-N/ha (over 201 days). Emissions during 2014 were 77% lower than 2013 due to dry seasonal conditions; cumulative emissions were 49 g N₂O-N/ha where N was applied at sowing, with background emissions of around 0 g N₂O-N/ha (over 177 days). Inhibitors showed limited scope for reducing N₂O emissions in this environment, however deferring N application until the end of tillering reduced N₂O emissions. Grain yield responses to fertiliser were significant; increasing grain yield by 11–31% and NUE was generally high (recovery efficiency?>?68%). However, deferring N application until the end of tillering in 2014 reduced yield (??19%) and recovery of applied N (??74%).     

Methane and nitrous oxide emissions: an introduction

Methane and nitrous oxide are important greenhouse gases. They contribute to global warming. To a large extent, emissions of methane and nitrous oxide are connected with the intensification of food production. Therefore, feeding a growing world population and at the same time controlling these emissions is a great challenge. Important anthropogenic sources of biogenic methane are wet rice fields, cattle, animal waste, landfills and biomass burning. Important anthropogenic sources of biogenic nitrous oxide are land-use change, fertilizer production and use and manure application. The ultimate objective of the Framework Convention on Climate Change implies a stabilization of greenhouse gas concentrations in the atmosphere. As a small first step towards achieving this objective, the Convention requires the industrialized countries to bring their anthropogenic emissions of greenhouse gases by 2000 back to 1990 levels. It was also agreed that all parties would make national inventories of anthropogenic greenhouse gas emissions and programmes for control (UN, 1992).In this context, in February 1993 an international workshop was held in Amersfoort in the Netherlands to discuss methods in national emission inventories for methane and nitrous oxide, and options for control (Van Amstel, 1993). A selection of the papers presented in Amersfoort that focus on agricultural sources is published in this volume. This introductory chapter gives background information on biogenic sources and sinks of methane and nitrous oxide and options for their control. The goal of the Climate Convention is described as well as the IPCC effort to develop an internationally accepted methodology for the monitoring of greenhouse gas emissions and sinks. Finally, some preliminary results from country inventories are given. It is concluded that a common reporting framework and transparency of the inventories are important to obtain comparable results that can be used for complying with the requirements of the Climate Convention and for facilitating the international debate about appropriate response strategies.     

Soil carbon,soil nitrate,and soil emissions of nitrous oxide during cultivation of energy crops

Carbon (C) sequestration and soil emissions of nitrous oxide (N₂O) affect the carbon dioxide (CO₂) advantage of energy crops. A long-term study has been performed to evaluate the environmental effects of energy crop cultivation on the loamy sand soil of the drier northeast region of Germany. The experimental field, established in 1994, consisted of columns (0.25 ha each) cultivated with short rotation coppice (SRC: Salix and Populus) and columns cultivated with annual crops. The columns were subdivided into four blocks, with each receiving different fertilization treatments. The soil C content was measured annually from 1994 until 1997, and then in 2006. Soil N₂O levels were measured several times per week from 1999 to 2007. Water-filled pore space (WFPS) and soil nitrate measurements have been performed weekly since 2003. Increased C stocks were found in SRC columns, and C loss was observed in blocks with annual crops. The soil from fertilized blocks had higher levels of C than the soil from non-fertilized blocks. SRC cropping systems on dry, loamy sand soils are advantageous relative to annual cropping systems because of higher C sequestration, lower fertilized-induced N₂O emissions, and reduced background N₂O emissions in these soils. SRC cropping systems on dry, loamy sand soils have a CO₂ advantage (approximately 4 Mg CO₂ ha⁻¹ year⁻¹) relative to annual cropping systems.     

Assessing the sensitivity of modelled estimates of N2O emissions and yield to input uncertainty at a UK cropland experimental site using the DailyDayCent model

Biogeochemical models such as DailyDayCent (DDC) are increasingly used to help quantify the emissions of green-house gasses across different ecosystems and climates. For this use they require parameterisation to represent a heterogeneous region or are site specific and scaled upwards. This requires information on inputs such as climate, soil, land-use and land management. However, each input has an associated uncertainty, which propagates through the model to create an uncertainty in the modelled outputs. To have confidence in model projections, an assessment of how the uncertainty in inputs propagated through the model and its impact on modelled outputs is required. To achieve this, we used a pre-defined uncertainty range of key inputs; temperature, precipitation, clay content, bulk density and soil pH, and performed a sensitivity and uncertainty analysis, using Monte Carlo simulations. This allowed the effect of measurement uncertainty on the modelled annual N₂O emissions and crop yields at the Grange field experimental site to be quantified. Overall the range of model estimates simulated was relatively high and while the model was sensitive to each input parameter, uncertainty was driven by the sensitivity to soil pH. This decreased as the N fertiliser application rate increased, as at lower N application rates the model becomes more sensitive to other drivers of N mineralisation such as soil and climate inputs. Therefore, while our results indicate that DDC can provide a good estimate of annual N₂O emissions and crop yields under UK conditions, reducing the uncertainty in the input parameters will lead to more accurate simulations.     

Estimates of the interannual variations of N2O emissions from agricultural soils in Canada

The DNDC model was used to estimate direct N₂O 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 N₂O emission from agricultural soils in Canada was found to be 39.9 Gg N₂O–N, with a range from 20.0 to 77.0 Gg N₂O–N, and a general trend towards increasing N₂O 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 N₂O emissions were variable, depending on timing of rainfall events and timing and duration of spring thaw events. We estimate, using DNDC, that emissions of N₂O 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 N₂O–N ha^–1 y^–1 and soils of the dryer western Brown Chernozem had the smallest average emission of 0.54 kg N₂O–N ha^–1 y^–1. On average, for the seven soil groups, N₂O emissions during spring thaw were approximately 30% of total annual emissions. The average N₂O 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 N₂O emissions based on climatic differences.     

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.     

Nitrous oxide emissions from an Uruguayan argiudoll under different tillage and rotation treatments

Lack of local data limits estimation of nitrous oxide (N₂O) emissions from different land uses of Uruguay. As a first step towards obtaining local information, we measured from August 2003 to September 2004 N₂O fluxes from a rotation-by-tillage experiment established in 1993 and from a nearby natural pasture (NP). Nitrous oxide emission rates were measured on an event-driven basis by using the closed chamber technique with six replicates per treatment. Fluxes varied considerably with time and the higher rates (more than 30 g N ha⁻¹ day⁻¹) were generally associated with periods of high soil water content, high temperature, and/or decreasing soil nitrate. We could not identify, however, any statistically significant correlation between flux and these variables. Throughout the evaluation period, fluxes from crops or cultivated pastures tended to be higher than those from NP, but the effects of tillage (no-till and conventional tillage) or rotation (continuous tillage and rotation with pasture) were not consistent. The application of 112 kg N ha⁻¹ to barley did not increase N₂O fluxes probably due to a high fertilizer use efficiency caused by the recommended three-split application and by the lack of rain during this period. The annual cumulative flows of different treatments compared well with those estimated using IPCC methodology, but the high spatial and temporal variability observed in this one-year study indicate that further research is needed to obtain reliable data on N₂O fluxes from agricultural soils of Uruguay.     

Nitrous oxide mitigation potential of reduced tillage and N input in durum wheat in the Mediterranean

In Italy, managed soils account for about 50% of annual national emissions of nitrous oxide (N₂O), thus the effect of agricultural practices on N₂O emissions must be studied in order to develop mitigation strategies. Soil N₂O 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. N₂O emissions were measured with a fully-transportable instrument developed during the project LIFE?+?IPNOA “Improved flux Prototypes for N₂O emission reduction from Agriculture” and equipped with an infrared laser detector. Reducing tillage from ploughing to minimum tillage had no effect on average daily N₂O flux, while decreasing the N rate from 170 to 110 kg N ha^?1 reduced the average daily N₂O flux, without negatively affecting the grain yield. Furthermore, N₂O daily flux were positively correlated with soil water filled pore space, NO₃-N, and NH₄-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 N₂O emissions without negative effects on wheat productivity.     

Measurements of N2O and NO emissions during tomato cultivation using a flow-through chamber system in a glasshouse

Nitrous oxide (N₂O) and nitric oxide (NO) fluxes resulting from long-term tomato cultivation in a glasshouse were continuously determined using the flow-through chamber method over the course of three cultivation periods. Gas concentrations were measured using an nondispersive infrared (gas filter correlation/infra-red) analyzer and a chemiluminescence-based analyzer, respectively. Following a basal application of fertilizer, daily N₂O and NO emission rates increased, with peaks lasting from 40 to 140 days. Short-term fluctuations in daily N₂O and NO emissions were affected by differences in nitrogen application, soil water, and soil temperature. Diurnal changes in N₂O and NO fluxes during the period of peak emissions depended primarily on soil temperature. Following the application of a top dressing (N as urea or calcium nitrate) in the irrigation water, the N₂O and NO fluxes increased immediately, with a very short period of peak emissions (1–5 h) after urea application. The duration of the peak period in daily accumulated N₂O and NO emissions following application of the top dressing ranged from 3 to 10 days.     

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.     

Fluxes of nitrous oxide from soil under different crop rotations and tillage systems in the South of Brazil

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 N₂O 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 N₂O 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 N₂O 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 N₂O were relatively low, apart from a short period at the beginning of measurements. No relationship between N₂O 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 N₂O emissions were significantly underestimated by the IPCC emission factor 1 (EF1). For the other treatments measured N₂O emissions fell within the EF1 uncertainty range, but always considerably lower than the EF1 estimate, which suggests IPCC EF1 overestimates true N₂O emissions for the Ferralsol under evaluation.