Nitrous oxide emissions from boreal organic soil under different land-use

Nitrous oxide emissions were studied with a static chamber technique during 2 years from a drained organic soil in eastern Finland. After drainage, the soil was forested with birch (Betula pendula Roth) and 22 years later, part of the forest was felled and then used for cultivation of barley (Hordeum vulgare L.) and grass. The annual N₂O emissions from the cultivated soil (from 8.3 to 11.0 kg N₂O-N ha⁻¹ year⁻¹) were ca. twice the annual emission from the adjacent forest site (4.2 kg N₂O-N ha⁻¹ year⁻¹). The N₂O emissions from the soils without plants (kept bare by regular cutting or tilling) were also lower (from 6.5 to 7.1 kg N₂O-N ha⁻¹ year⁻¹) than those from the cultivated soil. There was a high seasonal variation in the fluxes with a maximum in spring and early summer. The N₂O fluxes during the winter period accounted for 15-60% of the total annual emissions. N₂O fluxes during the snow-free periods were related to the water table (WT) level, water-filled pore space, carbon mineralisation and the soil temperature. A linear regression model with CO₂ production, WT and soil temperature at the depth of 5 cm as independent variables explained 54% of the variation in the weekly mean N₂O fluxes during the snow-free periods. N₂O fluxes were associated with in situ net nitrification, which alone explained 58% of the variation in the mean N₂O fluxes during the snow-free period. The N₂O-N emissions were from 1.5 to 5% of net nitrification. The acetylene blockage technique indicated that most of the N₂O emitted in the snow-free period originated from denitrification.     

温度对旱田土壤N2O排放的影响研究

以南方亚热带代表性旱田土壤－贵州玉米－油菜轮作田、大豆－冬小麦轮作田和休耕地为研究对象，同步观测了整轮作期土壤N2O排放通量和温度的季节变化。同时，采用DNDC模型定量探讨了未来气温变化对土壤N2O排放的潜在影响。结果表明，温度是土壤N2O排放通量规律性日变化的最主要控制因素；除大豆地外，其他作物生长季节和休耕地的N2O排放通量季节变化与温度之间均存在一定程度的正相关性，其中冬季休耕地的N2O排放通量与温度间存在弱指数函数关系。模型检验结果表明，除大豆地外，其余试验地的N2O排放通量均随年均气温升高而升高，在冬春季，土壤N2O排放通量对气温变化的敏感性强于夏秋季，尤其以冬春季休耕地受体气温变化的影响最为显著。     

Diurnal, seasonal, and inter-annual variations of N2O fluxes from native semi-arid grassland soils of inner Mongolia

In order to investigate the diurnal, seasonal, and inter-annual variations of nitrous oxide (N₂O) flux and associated microbiological mechanisms, in situ measurements of N₂O Flux from unfertilized, ungrazed, and unirrigated semi-arid grassland soils in Inner Mongolia, northeast China were undertaken using a closed chamber technique from 1995 to 2003. In addition, laboratory experiments were carried out using the acetylene inhibition method (AIM) in 1998 and 2001. The results showed no significant linear relationship between soil moisture and diurnal N₂O flux, or between N₂O flux and temperature (i.e., temperature at 0-15 cm depth, temperature of surface soil, and temperature of inner chamber air). However, the results showed a significant influence of growing season on diurnal variations of N₂O flux. N₂O efflux was usually high in spring or summer, and low in winter. The mean total annual N₂O fluxes was 0.73±0.52 kg N₂O-N ha⁻¹ yr⁻¹, with a coefficient of variation of annual N₂O flux of 71.6%. Based on our estimates from 5 yr of data, the total N₂O emission from all of the temperate grassland soils of China was approximately 0.21 Tg N₂O-N yr⁻¹, which was about 21% of the total global flux from temperate grassland soils. It was the distribution of effective rainfall, rather than precipitation intensity, that influenced seasonal and inter-annual variations of N₂O flux. Our laboratory incubation study revealed that heterotrophic nitrification was the principal source of N₂O in the studied soils.     

Effect of urease and nitrification inhibitors on N transformation, gaseous emissions of ammonia and nitrous oxide, pasture yield and N uptake in grazed pasture system

Nitrogen (N) losses via nitrate (NO₃⁻) leaching, ammonia (NH₃) volatilization and nitrous oxide (N₂O) emissions from grazed pastures in New Zealand are one of the major contributors to environmental degradation. The use of N inhibitors (urease and nitrification inhibitors) may have a role in mitigating these N losses. A one-year field experiment was conducted on a permanent dairy-grazed pasture site at Massey University, Palmerston North, New Zealand to quantify these N losses and to assess the effect of N inhibitors in reducing such losses during May 2005-2006. Cow urine at 600 kg N ha⁻¹ rate with or without urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) or (trade name “Agrotain”) (3 L ha⁻¹), nitrification inhibitor dicyandiamide (DCD) (7 kg ha⁻¹) and the use of double inhibitor (DI) containing a combination of both Agrotain and DCD (3:7) were applied to field plots in autumn, spring and summer. Pasture production, NH₃ and N₂O fluxes, soil mineral N concentrations, microbial biomass C and N, and soil pH were measured following the application of treatments during each season. All measured parameters, except soil microbial biomass C and N, were influenced by the added inhibitors during the three seasons. Agrotain reduced NH₃ emissions over urine alone by 29%, 93% and 31% in autumn, spring and summer respectively but had little effect on N₂O emission. DCD reduced N₂O emission over urine alone by 52%, 39% and 16% in autumn, spring and summer respectively but increased NH₃ emission by 56%, 9% and 17% over urine alone during those three seasons. The double inhibitor reduced NH₃ by 14%, 78% and 9% and N₂O emissions by 37%, 67% and 28% over urine alone in autumn, spring and summer respectively. The double inhibitor also increased pasture dry matter by 10%, 11% and 8% and N uptake by the 17%, 28% and 10% over urine alone during autumn, spring and summer respectively. Changes in soil mineral N and pH suggested a delay in urine-N hydrolysis with Agrotain, and reduced nitrification with DCD. The combination of Agrotain and DCD was more effective in reducing both NH₃ and N₂O emissions, improving pasture production, controlling urea hydrolysis and retaining N in NH₄⁺ form. These results suggest that the combination of both urease and nitrification inhibitors may have the most potential to reduce N losses if losses are associated with urine and improve pasture production in intensively grazed systems.     

Nitrogen oxides emission from soils bearing a potato crop as influenced by fertilization with treated pig slurries and composts

Nitrous oxide, nitric oxide and denitrification losses from an irrigated soil amended with organic fertilizers with different soluble organic carbon fractions and ammonium contents were studied in a field study covering the growing season of potato (Solanum tuberosum). Untreated pig slurry (IPS) with and without the nitrification inhibitor dicyandiamide (DCD), digested thin fraction of pig slurry (DTP), composted solid fraction of pig slurry (CP) and composted municipal solid waste (MSW) mixed with urea were applied at a rate of 175 kg available N ha⁻¹, and emissions were compared with those from urea (U) and a control treatment without any added N fertilizer (Control). The cumulative denitrification losses correlated significantly with the soluble carbohydrates, dissolved N and total C added. Added dissolved organic C (DOC) and dissolved N affected the N₂O/N₂ ratio, and a lower ratio was observed for organic fertilizers than from urea or unfertilized controls. The proportion of N₂O produced from nitrification was higher from urea than from organic fertilizers. Accumulated N₂O losses during the crop season ranged from 3.69 to 7.31 kg N₂O-N ha⁻¹ for control and urea, respectively, whereas NO losses ranged from 0.005 to 0.24 kg NO-N ha⁻¹, respectively. Digested thin fraction of pig slurry compared to IPS mitigated the total N₂O emission by 48% and the denitrification rate by 33%, but did not influence NO emissions. Composted pig slurry compared to untreated pig slurry increased the N₂O emission by 40% and NO emission by 55%, but reduced the denitrification losses (34%). DCD partially inhibited nitrification rates and reduced N₂O and NO emissions from pig slurry by at least 83% and 77%, respectively. MSW+U, with a C:N ratio higher than that of the composted pig slurry, produced the largest denitrification losses (33.3 kg N ha⁻¹), although N₂O and NO emissions were lower than for the U and CP treatments.This work has shown that for an irrigated clay loam soil additions of treated organic fertilizers can mitigate the emissions of the atmospheric pollutants NO and N₂O in comparison with urea.     

Sources and rates of nitrous oxide emissions from grazed grassland after application of N-labelled mineral fertilizer and slurry

Nitrogen (N) fertilizer application and grazing are known to induce nitrous oxide (N₂O) emissions from grassland soils. In a field study, general information on rates of N₂O emission, the effect of cattle grazing and the type (mineral fertilizer, cattle slurry) and amount of N supply on the flux of N₂O from a sandy soil were investigated. N₂O emissions from permanent grassland managed as a mixed system (two cuts followed by two grazing cycles) were monitored over 11 months during 2001-2002 in northern Germany using the closed chamber method. The field experiment consisted of four regionally relevant fertilizer combinations, i.e. two mineral N application rates (0 and 100 kg N ha⁻¹ yr⁻¹) and two slurry levels (0 and 74 kg N ha⁻¹ yr⁻¹).Mean cumulative N₂O-N loss was 3.0 kg ha⁻¹ yr⁻¹, and the cumulative ¹⁵N-labelled N₂O emissions varied from 0.03% to 0.19% of the ¹⁵N applied. ¹⁵N labelling indicated that more N₂O was emitted from mineral N than from slurry treated plots, and in all treatments the soil N pool was always clearly the major source of N₂O. Regarding the total cumulative N₂O losses, differences among treatments were not significant, which was caused by: (i) a high variance in emissions during and after cattle grazing due to the random distribution of excrements and by (ii) high N₂ fixation of white clover in the 0 kg N ha⁻¹ treatments, which resulted in similar N status of all treatments. However before grazing started, treatments showed significant differences. After cattle grazing in summer, N₂O emission rates were higher than around the time of spring fertilizer application, or in winter. Grazing resulted in N₂O flux rates up to 489 μg N₂O-N m⁻² h⁻¹ and the grazing period contributed 31-57% to the cumulative N₂O emission. During freeze-thaw cycles in winter (December-February) N₂O emission rates of up to 147 μg N₂O-N m⁻² h⁻¹ were measured, which contributed up to 26% to the annual N₂O flux. The results suggest that N fertilizer application and grazing caused only short-term increases of N₂O flux rates whereas the major share of annual N₂O emission emitted from the soil N pool. The significantly increased N₂O fluxes during freeze-thaw cycles show the importance of emission events in winter which need to be covered by measurements for obtaining reliable estimates of annual N₂O emissions.     

Nitrous oxide flux from soil amino acid mineralization

Nitrous oxide (N₂O) is a greenhouse gas produced during microbial transformation of soil N that has been implicated in global climate warming. Nitrous oxide efflux from N fertilized soils has been modeled using NO₃⁻ content with a limited success, but predicting N₂O production in non-fertilized soils has proven to be much more complex. The present study investigates the contribution of soil amino acid (AA) mineralization to N₂O flux from semi-arid soils. In laboratory incubations (−34 kPa moisture potential), soil mineralization of eleven AAs (100 μg AA-N g⁻¹ soil) promoted a wide range in the production of N₂O (156.0±79.3 ng N₂O-N g⁻¹ soil) during 12 d incubations. Comparison of the δ¹³C content (‰) of the individual AAs and the δ¹³C signature of the respired AA-CO₂-C determined that, with the exception of TYR, all of the AAs were completely mineralized during incubations, allowing for the calculation of a N₂O-N conversion rate from each AA. Next, soils from three different semi-arid vegetation ecosystems with a wide range in total N content were incubated and monitored for CO₂ and N₂O efflux. A model utilizing CO₂ respired from the three soils as a measure of organic matter C mineralization, a preincubation soil AA composition of each soil, and the N₂O-N conversion rate from the AA incubations effectively predicted the range of N₂O production by all three soils. Nitrous oxide flux did not correspond to factors shown to influence anaerobic denitrification, including soil NO₃⁻ contents, soil moisture, oxygen consumption, and CO₂ respiration, suggesting that nitrification and aerobic nitrifier denitrification could be contributing to N₂O production in these soils. Results indicate that quantification of AA mineralization may be useful for predicting N₂O production in soils.     

The influence of winter soil cover on spring nitrous oxide emissions from an agricultural soil

In temperate regions, a majority of N₂O is emitted during spring soil thawing. We examined the influence of two winter field covers, snow and winter rye, on soil temperature and subsequent spring N₂O emissions from a New York corn field over two years. The first season (2006-07) was a cold winter (2309 h below 0 °C at 8 cm soil depth), historically typical for the region. The snow removal treatment resulted in colder soils and higher N₂O fluxes (73.3 vs. 57.9 ng N₂O-N cm⁻² h⁻¹). The rye cover had no effect on N₂O emissions. The second season (2007-08) was a much milder winter (1271 h below freezing at 8 cm soil depth), with lower N₂O fluxes overall. The winter rye cover resulted in lower N₂O fluxes (5.9 vs. 33.7 ng N₂O-N cm⁻² h⁻¹), but snow removal had no effect. Climate scenarios predict warmer temperature and less snow cover in the region. Under these conditions, spring N₂O emissions can be expected to decrease and could be further reduced by winter rye crops.     

Tillage effects on N2O emissions as influenced by a winter cover crop

Conservation tillage practices are widely used to protect against soil erosion and soil C losses, whereas winter cover crops are used mainly to protect against N losses during autumn and winter. For the greenhouse gas balance of a cropping system the effect of reduced tillage and cover crops on N₂O emissions may be more important than the effect on soil C. This study monitored emissions of N₂O between September 2008 and May 2009 in three tillage treatments, i.e., conventional tillage (CT), reduced tillage (RT) and direct drilling (DD), all with (+CC) or without (−CC) fodder radish as a winter cover crop. Cover crop growth, soil mineral N dynamics, and other soil characteristics were recorded. Furthermore, soil concentrations of N₂O were determined eight times during the monitoring period using permanently installed needles. There was little evidence for effects of the cover crop on soil mineral N. Following spring tillage and slurry application soil mineral N was dominated by the input from slurry. Nitrous oxide emissions during autumn, winter and early spring remained low, although higher emissions from +CC treatments were indicated after freezing events. Following spring tillage and slurry application by direct injection N₂O emissions were stimulated in all tillage treatments, reaching 250-400 μg N m⁻² h⁻¹ except in the CT + CC treatment, where emissions peaked at 900 μg N m⁻² h⁻¹. Accumulated emissions ranged from 1.6 to 3.9 kg N₂O ha⁻¹. A strong positive interaction between cover crop and tillage was observed. Soil concentration profiles of N₂O showed a significant accumulation of N₂O in CT relative to RT and DD treatments after spring tillage and slurry application, and a positive interaction between slurry and cover crop residues. A comparison in early May of N₂O emissions with flux estimates based on soil concentration profiles indicated that much of the N₂O emitted was produced near the soil surface.     

How Effective is Reduced Tillage–Cover Crop Management in Reducing N2O Fluxes from Arable Crop Soils?

Field management is expected to influence nitrous oxide (N₂O) production from arable cropping systems through effects on soil physics and biology. Measurements of N₂O flux were carried out on a weekly basis from April 2008 to August 2009 for a spring sown barley crop at Oak Park Research Centre, Carlow, Ireland. The soil was a free draining sandy loam typical of the majority of cereal growing land in Ireland. The aims of this study were to investigate the suitability of combining reduced tillage and a mustard cover crop (RT?CCC) to mitigate nitrous oxide emissions from arable soils and to validate the DeNitrification?CDeComposition (DNDC) model version (v. 9.2) for estimating N₂O emissions. In addition, the model was used to simulate N₂O emissions for two sets of future climate scenarios (period 2021?C2060). Field results showed that although the daily emissions were significantly higher for RT?CCC on two occasions (p?<?0.05), no significant effect (p?>?0.05) on the cumulative N₂O flux, compared with the CT treatment, was found. DNDC was validated using N₂O data collected from this study in combination with previously collected data and shown to be suitable for estimating N₂O emissions (r ²?=?0.70), water-filled pore space (WFPS) (r ²?=?0.58) and soil temperature (r ²?=?0.87) from this field. The relative deviations of the simulated to the measured N₂O values with the 140?kg N ha^?1 fertiliser application rate were ?36?% for RT?CCC and ?19?% for CT. Root mean square error values were 0.014 and 0.007?kg N₂O?CN ha^?1 day^?1, respectively, indicating a reasonable fit. Future cumulative N₂O fluxes and total denitrification were predicted to increase under the RT?CCC management for all future climate projections, whilst predictions were inconsistent under the CT. Our study suggests that the use of RT?CCC as an alternative farm management system for spring barley, if the sole objective is to reduce N₂O emissions, may not be successful.     

Contribution of nitrification and denitrification to N2O emissions from urine patches

Urine deposition by grazing livestock causes an immediate increase in nitrous oxide (N₂O) emissions, but the responsible mechanisms are not well understood. A nitrogen-15 (¹⁵N) labelling study was conducted in an organic grass-clover sward to examine the initial effect of urine on the rates and N₂O loss ratio of nitrification (i.e. moles of N₂O-N produced per moles of nitrate produced) and denitrification (i.e. moles of N₂O produced per moles of N₂O+N₂ produced). The effect of artificial urine (52.9 g N m⁻²) and ammonium solution (52.9 g N m⁻²) was examined in separate experiments at 45% and 35% water-filled pore space (WFPS), respectively, and in each experiment a water control was included. The N₂O loss derived from nitrification or denitrification was determined in the field immediately after application of ¹⁵N-labelled solutions. During the next 24 h, gross nitrification rates were measured in the field, whereas the denitrification rates were measured in soil cores in the laboratory. Compared with the water control, urine application increased the N₂O emission from 3.9 to 42.3 μg N₂O-N m⁻² h⁻¹, whereas application of ammonium increased the emission from 0.9 to 6.1 μg N₂O-N m⁻² h⁻¹. In the urine-affected soil, nitrification and denitrification contributed equally to the N₂O emission, and the increased N₂O loss resulted from a combination of higher rates and higher N₂O loss ratios of the processes. In the present study, an enhanced nitrification rate seemed to be the most important factor explaining the high initial N₂O emission from urine patches deposited on well-aerated soils.     

Earthworm activity as a determinant for N2O emission from crop residue

Earthworm activity may have an effect on nitrous oxide (N₂O) emissions from crop residue. However, the importance of this effect and its main controlling variables are largely unknown. The main objective of this study was to determine under which conditions and to what extent earthworm activity impacts N₂O emissions from grass residue. For this purpose we initiated a 90-day (experiment I) and a 50-day (experiment II) laboratory mesocosm experiment using a Typic Fluvaquent pasture soil with silt loam texture. In all treatments, residue was applied, and emissions of N₂O and carbon dioxide (CO₂) were measured. In experiment I the residue was applied on top of the soil surface and we tested (a) the effects of the anecic earthworm species Aporrectodea longa (Ude) vs. the epigeic species Lumbricus rubellus (Hoffmeister) and (b) interactions between earthworm activity and bulk density (1.06 vs. 1.61 g cm⁻³). In experiment II we tested the effect of L. rubellus after residue was artificially incorporated in the soil. In experiment I, N₂O emissions in the presence of earthworms significantly increased from 55.7 to 789.1 μg N₂O-N kg⁻¹ soil (L. rubellus; p<0.001) or to 227.2 μg N₂O-N kg⁻¹ soil (A. longa; p<0.05). This effect was not dependent on bulk density. However, if the residue was incorporated into the soil (experiment II) the earthworm effect disappeared and emissions were higher (1064.2 μg N₂O-N kg⁻¹ soil). At the end of the experiment and after removal of earthworms, a drying/wetting and freezing/thawing cycle resulted in significantly higher emissions of N₂O and CO₂ from soil with prior presence of L. rubellus. Soil with prior presence of L. rubellus also had higher potential denitrification. We conclude that the main effect of earthworm activity on N₂O emissions is through mixing residue into the soil, switching residue decomposition from an aerobic and low denitrification pathway to one with significant denitrification and N₂O production. Furthermore, A. longa activity resulted in more stable soil organic matter than L. rubellus.     

Spatial variability of nitrous oxide emissions in an unmanaged old‐growth beech forest

Nitrous oxide (N₂O) is a high‐impact greenhouse gas. Due to the scarcity of unmanaged forests in Central Europe, its long‐term natural background emission level is not entirely clear. We measured soil N₂O emissions in an unmanaged, old‐growth beech forest in the Hainich National Park, Germany, at 15 plots over a 1‐year period. The average annual measured N₂O flux rate was (0.49 ± 0.44) kg N ha^–1 y^–1. The N₂O emissions showed background‐emission patterns with two N₂O peaks. A correlation analysis shows that the distance between plots (up to 380 m) does not control flux correlations. Comparison of measured data with annual N₂O flux rates obtained from a standard model (Forest‐DNDC) without site‐specific recalibration reveals that the model overestimates the actual measured N₂O flux rates mainly in spring. Temporal variability of measured N₂O flux was better depicted by the model at plots with high soil organic C (SOC) content. Modeled N₂O flux rates were increased during freezing only when SOC was > 0.06 kg C kg^–1. The results indicate that the natural background of N₂O emissions may be lower than assumed by most approaches.     

Simulation of N<Subscript>2</Subscript>O fluxes from Irish arable soils: effect of climate change and management

Emissions of nitrous oxide (N₂O) from an Irish arable soil were simulated using the DeNitrification–DeComposition (DNDC) model. The soil chosen was a free-draining sandy loam typical of the majority of cereal growing land in Ireland, and one that has been previously used to test and validate DNDC-model. DeNitrification–DeComposition model was considered suitable to estimate N₂O fluxes from Irish arable soils however, underestimated the flux by 24%. The objectives of this study were to estimate future N₂O fluxes from a spring barley field under conventional (moulboard plowing) and reduced (chisel plowing) tillage and different N-fertilzer application rates. Three climate scenarios, a baseline of measured climatic data from the weather station at Kilkenny and a high- and low-temperature-sensitive scenarios predicted by the Hadley Global Climate Model (HadCM₄) based on the AB1 emission scenario of the Intergovernment Panel on Climate Change (IPCC) were investigated. For conventional tillage under all scenarios, three peaks of N₂O emissions were predicted; an early spring peak coinciding mostly with soil plowing, a mid/late spring peak coinciding with fertilizer application and an early autumn peak coinciding with residue incorporation and onset of autumn rainfall. Under reduced tillage, due to the less amount of soil disturbance, the early spring peak was not predicted. In all cases, the total amount of N₂O emitted in the late spring peak due to fertilizer application was less than the sum of the other peaks. Under climate change, using the high-temperature-increase scenario, DNDC predicted an increase in N₂O emissions from both conventional and reduced tillage, ranging from 58% to 88% depending upon N application rate. In contrast, annual fluxes of N₂O either decreased or increased slightly in the low temperature increase scenario relative to N application (−26 to +16%). Outputs from the model indicate that elevated temperature and precipitation increase N mineralization and total denitrification leading to greater fluxes of N₂O. Annual uncertainties due to the use of two different future climate scenarios were significantly high, ranging from 74% to 95% and from 71% to 90% for the conventional and reduced tillage.     

N2O and NO emissions from an Andisol field as influenced by pelleted poultry manure

Animal manures from intensive livestock operations can be pelleted to improve handlings and recyclings of embodied nutrients. The aim of this study was to evaluate the influence of pelleted poultry manure on N₂O and NO fluxes from an Andisol field. In autumn 2006 and summer 2007, poultry manure (PM), pelleted poultry manure (PP), and chemical fertilizer (CF) were applied at a rate of 120 kg N ha⁻¹ in each cultivation period to Komatsuna (Brassica rapa var. peruviridis). Nitrous oxide and NO fluxes were measured using an automated monitoring system. A soil incubation experiment was also conducted to determine the influence of intact and ground pelleted manure on N₂O, NO, and CO₂ production with a water-filled pore space (WFPS) of 30 or 50%. In the field measurements, N₂O emission rates from the organic fertilizer treatments were larger than that from the CF treatment, possibly because organic C stimulated denitrification. The highest N₂O flux was observed from the PP treatment after a rainfall following fertilization, and the cumulative emission rate (2.72 ± 0.22 kg N ha⁻¹ y⁻¹) was 3.9 and 7.1 times that from the PM and CF treatments, respectively. In contrast, NO emission rates were highest from the CF treatment. The NO/N₂O flux ratio indicated that nitrification was the dominant process for NO and N₂O production from the CF treatment. Cumulative N₂O emission rates from all treatments were generally higher during the wetter cultivation period (autumn 2006) than during the drier cultivation period (summer 2007). In contrast, NO emission rates were higher in the drier than in the wetter cultivation period. The incubation experiment results showed a synergistic effect of soil moisture and the pelleted manure form on N₂O emission rates. The intact pelleted manure with the 50% WFPS treatment produced the highest N₂O and CO₂ fluxes and resulted in the lowest soil NO₃⁻ content after the incubation. These results indicate that anaerobic conditions inside the pellets, caused by rainfall and heterotrophic microbial activities, led to denitrification, resulting in high N₂O fluxes. Controlling the timing of N application by avoiding wet conditions might be one mitigation option to reduce N₂O emission rates from the PP treatment in this study field.     

Nitrous oxide emissions from a bermudagrass pasture: Interseeded winter rye and poultry litter

Adequate use of manure in grasslands may constitute an economical means of manure disposal and an abundant source of nutrients for plants; however, excessive nitrogen (N) additions to these soils could create new environmental risks such as increasing nitrous oxide (N₂O) emissions. These potentially adverse effects in grasslands may be mitigated by improved management practices. In pasture systems, the combined effects of poultry litter applications and interseeded rye (Secale cereale L.) on N₂O emissions are still not well established. This study was conducted to estimate the magnitude of soil surface N₂O fluxes as affected by interseeded winter rye forage, annually spring-applied composted turkey litter as well as by weather and soil parameters. Fluxes were measured by vented chambers during 2 yr in a bermudagrass (Cynodon dactylon [L.] Pers.) pasture in moderately well-drained Tonti gravelly silt loam (fine-loamy, active, mesic Typic Fragiudault) located in northwestern Arkansas, USA. During the 60 d following turkey litter applications, N₂O fluxes were frequently well correlated with soil nitrate (NO₃⁻; r: up to 0.82, P's < 0.05) implying substrate stimulation on soil N₂O production. Likewise, rainfall patterns strongly influenced N₂O fluxes. Large rainfalls of 91 and 32 mm occurred within 6 d prior to the maximum N₂O flux means (263 and 290 μg N m⁻² h⁻¹, respectively). Treatment effects on N₂O emissions were significant only in spring periods following manure addition, particularly in the second year of our study. In the spring of 2000, additions of composted turkey litter resulted in 1.5-fold increase in seasonal cumulative N₂O emissions (P = 0.04) which was directly associated to a numerically greater soil NO₃⁻. In the spring of 2001, soils planted to rye exhibited a pronounced significant effect on mitigating N₂O emissions (30 vs. 112 mg N m⁻²; P = 0.04). During the winter and early spring, rye growth also decreased quantities of both soil NO₃⁻ and water-filled pore space (WFPS) partly accounting for the lower N₂O emissions in these fields. These results suggest that because poultry litter additions increased and interseeded rye diminished N₂O emissions, the combined implementation of both management practices can produce environmental benefits while sustaining productivity in temperate pasture systems.     

Effect of management, climate and soil conditions on N2O and NO emissions from an arable crop rotation using high temporal resolution measurements

Quantifying the nitrous oxide (N₂O) and nitric oxide (NO) fluxes emitted from croplands remains a major challenge. Field measurements in different climates, soil and agricultural conditions are still scarce and emissions are generally assessed from a small number of measurements. In this study, we report continuously measured N₂O and NO fluxes with a high temporal resolution over a 2-year crop sequence of barley and maize in northern France. Measurements were carried out using 6 automatic chambers at a rate of 16 mean flux measurements per day. Additional laboratory measurements on soil cores were conducted to study the response of NO and N₂O emissions to environmental conditions.The detection limit of the chamber setup was found to be 3 ng N m⁻² s⁻¹ for N₂O and 0.1 ng N m⁻² s⁻¹ for NO. Nitrous oxide fluxes were higher than the threshold 37% of the time, while they were 72% of the time for NO fluxes.The cumulated annual NO and N₂O emissions were 1.7 kg N₂O-N ha⁻¹ and 0.5 kg NO-N ha⁻¹ in 2007, but 2.9 kg N₂O-N ha⁻¹ and 0.7 kg NO-N ha⁻¹ in 2008. These inter-annual differences were largely related to crop types and to their respective management practices. The forms, amounts and timing of nitrogen applications and the mineralization of organic matter by incorporation of crop residues were found to be the main factor controlling the emissions peaks. The inter-annual variability was also due to different weather conditions encountered in 2007 and 2008. In 2007, the fractioned N inputs applied on barley (54 kg ha⁻¹ in March and in April) did not generate N₂O emissions peaks because of the low rainfall during the spring. However, the significant rainfall observed in the summer and fall of 2007, promoted rapid decomposition of barley residues which caused high levels of N₂O emissions. In 2008, the application of dairy cattle slurry and mineral fertilizer before the emergence of maize (107 kg N_min ha⁻¹ or 130 kg N_tot ha⁻¹ in all) coincided with large rainfalls promoting both NO and N₂O emissions, which remained high until early summer.Laboratory measurements corroborated the field observations: NO fluxes were maximum at a water-filled pore space (WFPS) of around 27% while N₂O fluxes were optimal at 68% WFPS, with a maximum potentially 14 times larger than for NO.     

Responses of soil organic matter and greenhouse gas fluxes to soil management and land use changes in a humid temperate region of southern Europe

We studied the effects of soil management and changes of land use on soils of three adjacent plots of cropland, pasture and oak (Quercus robur) forest. The pasture and the forest were established in part of the cropland, respectively, 20 and 40 yr before the study began. Soil organic matter (SOM) dynamics, water-filled pore space (WFPS), soil temperature, inorganic N and microbial C, as well as fluxes of CO₂, CH₄ and N₂O were measured in the plots over 25 months. The transformation of the cropland to mowed pasture slightly increased the soil organic and microbial C contents, whereas afforestation significantly increased these variables. The cropland and pasture soils showed low CH₄ uptake rates (<1 kg C ha⁻¹ yr⁻¹) and, coinciding with WFPS values >70%, episodes of CH₄ emission, which could be favoured by soil compaction. In the forest site, possibly because of the changes in soil structure and microbial activity, the soil always acted as a sink for CH₄ (4.7 kg C ha⁻¹ yr⁻¹). The N₂O releases at the cropland and pasture sites (2.7 and 4.8 kg N₂O-N ha⁻¹ yr⁻¹) were, respectively, 3 and 6 times higher than at the forest site (0.8 kg N₂O-N ha⁻¹ yr⁻¹). The highest N₂O emissions in the cultivated soils were related to fertilisation and slurry application, and always occurred when the WFPS >60%. These results show that the changes in soil properties as a consequence of the transformation of cropfield to intensive grassland do not imply substantial changes in SOM or in the dynamics of CH₄ and N₂O. On the contrary, afforestation resulted in increases in SOM content and CH₄ uptake, as well as decreases in N₂O emissions.     

N<Subscript>2</Subscript>O emission from conventional and minimum-tilled soils

In this study, we investigated N₂O emissions from two fields under minimum tillage, cropped with maize (MT maize) and summer oats (MT oats), and a conventionally tilled field cropped with maize (CT maize). Nitrous oxide losses from the MT maize and MT oats fields (5.27 and 3.64 kg N₂O-N ha⁻¹, respectively) were significantly higher than those from the CT maize field (0.27 kg N₂O-N ha⁻¹) over a period of 1 year. The lower moisture content in CT maize (43% water-filled pore space [WFPS] compared to 60–65%) probably caused the difference in total N₂O emissions. Denitrification was found to be the major source of N₂O loss. Emission factors calculated from the MT field data were high (0.04) compared to the CT field (0.001). All data were simulated with the denitrification decomposition model (DNDC). For the CT field, N₂O and N₂O + N₂ emissions were largely overestimated. For the MT fields, there was a better agreement with the total N₂O and N₂O + N₂ emissions, although the N₂O emissions from the MT maize field were underestimated. The simulated N₂O emissions were particularly influenced by fertilization, but several other measured N₂O emission peaks associated with other management practices at higher WFPS were not captured by the model. Several mismatches between simulated and measured \textNH₄⁺ {\text{NH}}_4^ + , \textNO₃^- {\text{NO}}_3^ - and WFPS for all fields were observed. These mismatches together with the insensitivity of the DNDC model for increased N₂O emissions at the management practices different from fertilizer application explain the limited similarity between the simulated and measured N₂O emissions pattern from the MT fields.     

Long-term application of organic manure and nitrogen fertilizer on N2O emissions, soil quality and crop production in a sandy loam soil

A long-term field experiment was established to determine the influence of mineral fertilizer (NPK) or organic manure (composed of wheat straw, oil cake and cottonseed cake) on soil fertility. A tract of calcareous fluvo-aquic soil (aquic inceptisol) in the Fengqiu State Key Experimental Station for Ecological Agriculture (Fengqiu county, Henan province, China) was fertilized beginning in September 1989 and N₂O emissions were examined during the maize and wheat growth seasons of 2002-2003. The study involved seven treatments: organic manure (OM), half-organic manure plus half-fertilizer N (1/2 OMN), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK) and control (CK). Manured soils had higher organic C and N contents, but lower pH and bulk densities than soils receiving the various mineralized fertilizers especially those lacking P, indicating that long-term application of manures could efficiently prevent the leaching of applied N from and increase N content in the plowed layer. The application of manures and fertilizers at a rate of 300 kg N ha⁻¹ year⁻¹ significantly increased N₂O emissions from 150 g N₂O-N ha⁻¹ year⁻¹ in the CK treatment soil to 856 g N₂O-N ha⁻¹ year⁻¹ in the OM treatment soil; however, there was no significant difference between the effect of fertilizer and manure on N₂O emission. More N₂O was released during the 102-day maize growth season than during the 236-day wheat growth season in the N-fertilized soils but not in N-unfertilized soils. N₂O emission was significantly affected by soil moisture during the maize growth season and by soil temperature during the wheat growth season. In sum, this study showed that manure added to a soil tested did not result in greater N₂O emission than treatment with a N-containing fertilizer, but did confer greater benefits for soil fertility and the environment.