Nitrous oxide emissions from three rice paddy fields in China

Nitrous oxide (N₂O) fluxes from rice paddy fields were measured in Nanjing, Yingtan and Fengqiu, using closed chamber method in 1994. The results showed that N₂O fluxes varied temporally, spatially and geographic regionally, with the total amounts of N₂O emissions during the period of rice growth ranged from 13.66 to 98.11mg/m² in Nanjing, 1.73 to 3.65mg/m² in Yingtan and 178.04 to 472.26mg/m² in Fengqiu, respectively. Soil water regime and soil texture had significant effects on N₂O production and emission from rice paddy fields. The mean N₂O fluxes from sandy, loamy and clayey rice paddy fields were 182.2,82.8 and 68.7 μg N₂O-N/m²/h, respectively. High N₂O fluxes occurred when rice paddy fields were imposed by alternation of irrigation and drainage and almost no N₂O emitted when the fields were submerged continuously. The rice paddy field applied with ammonium sulphate emitted more N₂O than with urea and N₂O-N losses of applied ammonium sulphate and urea ranged from 0.038 to 0.28% and 0.033 to 0.16%, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Quantification of N-losses as NH3, NO, and N2O and N2 from fertilized maize fields in southwestern France

Emissions of nitrogen compounds (NO, NH₃, N₂O and N₂) from heavily fertilized (280 kg(N) ha^-1) and irrigated maize fields were studied over an annual cultivation cycle in southwestern France. NO and N₂O emissions were measured by chamber techniques throughout the year. During fertilization and maize growth periods, chamber measurements were intensified and complemented by flux-gradient micrometeorological measurements of NO_x and NH₃. The two methods used, Bowen ratio and a simplified aerodynamical techniques, agree quite well and quantify NO_x and NH₃ flux variations during the period of intense emission which followed fertilizer application. Over a yearly cycle, nitrogen loss in the form of NH₃, NO and N₂O were calculated using micrometeorological flux measurements and emission algorithms calibrated with field data (chambers). The soil denitrification potential represented by the ratio N₂O/(N₂O+N₂) was measured in the laboratory to calculate potential total gaseous nitrogen loss. Taking into account all uncertainties, the total N loss into the atmosphere represents 30 to 110 kg(N) ha^-1 with about less than 1% as NH₃, 40% as NO, 14% as N₂O and 46% as N₂. This is in agreement with the agronomic nitrogen budget based on the N fertilizer input and soil furniture and, on the N-output by crops and crop residues, which displays a net imbalance of 50 to 100 kg(N) ha^-1.     

Effect of nitrapyrin on nitrous oxide emission from fallow soils fertilized with anhydrous ammonia

Nitrous oxide emission from three soils was measured using a chamber technique. Treatments sampled were unfertilized soil, and soil fertilized with 60 or 80 kg N ha^–1 of band-applied anhydrous ammonia ± nitrapyrin. The flux of nitrous oxide from unfertilized soil was very low (1.1 to 1.6 g N ha^–1 day^–1).Application of anhydrous ammonia caused a significant increase in the cumulative emission of nitrous oxide in two soils over 27 or 29 days compared with unfertilized soil. Fertilizer-induced loss of nitrous oxide was highest in a calcareous clay soil which had the highest nitrification rate and accumulated the highest concentration of nitrite within the fertilizer bands. Fertilizer-induced losses of nitrous oxide were < 0.05% of the applied fertilizer.Addition of nitrapyrin inhibited nitrification in all soils and reduced nitrite accumulation in the fertilizer bands. Nitrapyrin addition significantly reduced fertilizer-induced loss of nitrous oxide only in the calcareous clay soil. In the other soil, nitrapyrin had a lower bioactivity (relative inhibition of nitrification) which may have been due to its higher organic matter content.

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Resumo Este trabalho constitui de uma avaliação da quantidade de óxido nitroso emitido por três solos. A emissão de óxido nitroso foi determinada em solos não fertilizados e onde a amônia-anidra (60 e 80 kg de N ha^–1) foi aplicada, em bandas, com e sem nitrapyrin. O fluxo diário de óxido nitroso nos solos onde não se aplicou o fertilizante variou entre 1.1 e 1.6 g N ha^–1. A aplicação da amônia-anidra causou um significativo aumento na emissão de óxido nitroso em dois solos. A emissão de óxido nitroso induzida pela aplicação do fertilizante foi mais alta em um solo calcáreo-argiloso. Foi neste solo onde a nitrificação ocorreu mais intensamente e um maior acúmulo de nitrito foi observado. As perdas de óxido nitroso induzidas pela aplicação da amônia-anidra foram menores do que 0.05% do fertilizante aplicado. A aplicação conjunta de nitrapyrin com o fertilizante inibiu parcialmente a nitrificação nos três solos e reduziu o acúmulo de nitrito nas bandas do fertilizante. A adição de nitrapyrin reduziu significativamente a emissão de óxido nitroso somente no solo calcáreo-argiloso. No outro solo, a inibição relativa da nitrificação (bio-atividade) foi a mais baixa observada. A baixa bio-atividade do nitrapyrin sugere um efeito causado pelo mais alto teor de matéria orgânica verificado neste solo.

     

Nitrous oxide emission from a rice paddy field in Japan

The flux of nitrous oxide (N₂O) from a rice paddy field to the atmosphere was measured at Ryuhgasaki experiment station in Ibaraki Prefecture of Japan by closed chamber method, from the summer of 1992 to the summer of 1993. During the rice-cultivated and flooding periods when methane (CH₄) was emitted, no emission or uptake of N₂O was measured because the flux values were below the detection limits. After the final water drainage for harvest in August or September, N₂O began to emit from the soil surface while the emission of CH₄ was stopped, and N₂O was emitted continually until the re-flooding day in the following spring. In the first few months after the final water drainage, the N₂O flux was in the range of 10–20 μgN/m²/hour, then in the latter several months during the cold season, the N₂O flux was less than 10 μgN/m²/hour. The vertical profiles of N₂O, CO₂ and CH₄ concentrations in the plowed layer of the soil down to a depth of 20 cm, were also measured six times in the fallow season. The maximum concentrations of N₂O and CO₂ were found in the plowed layer in the early period, and which demonstrates that most of the N₂O was produced in the plowed layer through nitrification, due to the decomposition of organic matter accumulated in the plowed layer during the rice-growing and water-flooding period. On the contrary, the vertical profiles in the cold season showed a gradual increase in the concentrations of N₂O and CO₂ in the plowed layer. It clearly indicates that a small amount of N₂O was emitted to the atmosphere by diffusion through the plowed layer from the sub-soil layer where a large source of N₂O was expected to exist. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Emissions of N2O from Scottish agricultural soils, as a function of fertilizer N

Potato fields and cut (ungrazed) grassland in SE Scotland gave greater annual N₂O emissions per ha (1.0–3.2 kg N₂O–N ha^-1) than spring barley or winter wheat fields (0.3–0.8 kg N₂O–N ha^-1), but in terms of emission per unit of N applied the order was potatoes > barley > grass > wheat. On the arable land, especially the potato fields, a large part of the emissions occurred after harvest.When the grassland data were combined with those for 2 years' earlier work at the same site, the mean emission over 3 years, for fertilization with ammonium nitrate, was 2.24 kg N₂O–N ha^-1 (0.62% of the N applied). Also, a very strong relationship between N₂O emission and soil nitrate content was found for the grassland, provided the water-filled pore space was > 70%. Significant relationships were also found between the emissions from potato fields and the soil mineral N content, with the added feature that the emission per unit of soil mineral N was an order of magnitude larger after harvest than before, possibly due to the effect of labile organic residues on denitrification.Generally the emissions measured were lower, as a function of the N applied, than those used as the basis for the current value adopted by IPCC, possibly because spring/early summer temperatures in SE Scotland are lower than those where the other data were obtained. The role of other factors contributing to emissions, e.g. winter freeze–thaw events and green manure inputs, are discussed, together with the possible implications of future increases in nitrogen fertilizer use in the tropics.     

Nitrous oxide emissions from agricultural soils

This paper addresses three topics related to N₂O emissions from agricultural soils. First, an assessment of the current knowledge of N₂O emissions from agricultural soils and the role of agricultural systems in the global N₂O are discussed. Secondly, a critique on the methodology presented in the OECD/OCDE (1991) program on national inventories of N₂O is presented. Finally, technical options for controlling N₂O emissions from agricultural fields are discussed.The amount of N₂O derived from nitrogen applied to agricultural soils from atmospheric deposition, mineral N fertilizer, animal wastes or biologically fixed N, is not accurately known. It is estimated that the world-wide N₂O emitteddirectly from agricultural fields as a result of the deposition of all the above nitrogen sources is 2–3 Tg N annually. This amounts to 20–30% of the total N₂O emitted annually from the earth's surface. An unknown, but probably significant, amount of N₂O is generated indirectly in on and off farm activities associated with food production and consumption.Management options to limitdirect N₂O emissions from N-fertilized soils should emphasize improving N-use efficiency. Such management options include managing irrigation frequency, timing and quantity; applying N only to meet crop demand through multiple applications during the growing season or by using controlled release fertilizers; applying sufficient N only to meet crop needs; or using nitrification inhibitors. Most of these options have not been field tested. Agricultural management practices may not appreciably affect indirect N₂O emissions.     

Nitrous oxide emissions for 6 years from a gray lowland soil cultivated with onions in Hokkaido, Japan

We studied nitrous oxide (N₂O) emissions every growing season (April to October) for 6 years (19952000), in a Gray Lowland soil cultivated with onions in central Hokkaido, Japan. Emission of N₂O from the onion field ranged from 0.00 to 1.86 mgN m^–2 h^–1. The seasonal pattern of N₂O emission was the same for 6 years. The largest N₂O emissions appeared near harvesting in August to October, and not, as might be expected, just after fertilization in May. The seasonal patterns of soil nitrate (NO₃ ^–) and, ammonium (NH₄ ⁺) levels and the ratio of N₂O to NO emission indicated that the main process of N₂O production after fertilization was nitrification, and the main process of N₂O production around harvest time was denitrification. N₂O emission was strongly influenced by the drying–wetting process of the soil, as well as by the high soil water content. The annual N₂O emission during the growing season ranged from 3.5 to 15.6 kgN ha^–1. The annual nitrogen loss by N₂O emission as a percentage of fertilizer-N ranged from 1.1 to 6.4%. About 70% of the annual N₂O emission occurred near harvesting in August to October, and less than 20% occurred just after fertilization in May to July. High N₂O fluxes around the harvesting stage and a high proportion of N₂O emission to total fertilizer-N appeared to be probably a characteristic of the study area located in central Hokkaido, Japan.     

Fertilizer-induced nitric oxide emissions from agricultural soils

We summarize and evaluate 23 studies of the effect of fertilizer use on nitric oxide (NO) emission from agricultural soils. To quantify this effect we selected only field-scale studies with duration of at least one complete growing season and excluded studies with a legume as the principle crop. Only 6 studies met the established criteria, resulting in a total of 12 observations of soil/crop/fertilizer combinations, all in temperate areas. For these studies, the amount of NO emitted was linearly related to the amount of fertilizer applied (R² = 0.64) and about 0.5% of applied nitrogen was emitted as NO during the crop growing season. The available data are too limited to separate the effects of fertilizer type, soil type, or crop management.     

Nitrous oxide (N2O) emissions from soils in warm climates

N₂O emission rates seem to be higher from soils in warm climates than from soils in temperate climates. Warm and moist conditions promote microbial processes that generate N₂O. Clearance of tropical forests enhances N₂O formation, but emission measurements from other agricultural operations in the tropics are few. Limiting fertilizer application to recommended rates applied at appropriate times and avoiding fallow land wherever practical serves to limit N₂O emissions. More specific advice for agriculture in warm climates requires further studies.     

Direct emission of nitrous oxide from agricultural soils

This analysis is based on published measurements of nitrous oxide (N₂O) emission from fertilized and unfertilized fields. Data was selected in order to evaluate the importance of factors that regulate N₂O production, including soil conditions, type of crop, nitrogen (N) fertilizer type and soil and crop management. Reported N₂O losses from anhydrous ammonia and organic N fertilizers or combinations of organic and synthetic N fertilizers are higher than those for other types of N fertilizer. However, the range of management and environmental conditions represented by the data set is inadequate for use in estimating emission factors for each fertilizer type. The data are appropriate for estimating the order of magnitude of emissions. The longer the period over which measurements are made, the higher the fertilizer-induced emission. Therefore, a simple equation to relate the total annual direct N₂O–N emission (E) from fertilized fields to the N fertilizer applied (F), was based on the measurements covering periods of one year: E=1+1.25×F, with E and F in kg N ha^-1 yr^-1. This relationship is independent of the type of fertilizer. Although the above regression equation includes considerable uncertainty, it may be appropriate for global estimates.     

Process-based modelling of nitrous oxide emissions from different nitrogen sources in mown grassland

The process-based Pasture Simulation Model (PaSim 2.5) has been extended to simulate N₂O production and emission from grassland caused by nitrogen inputs from different sources. The model was used to assess the influence of management on N₂O emissions, such as the effect of shifts in the amount and timing of fertilizer application. Model performance has been tested against season-long field measurements at two different field sites. Simulation results agreed favourably with measured N₂O emission and soil air concentrations, except during an extremely wet period at one site when grass growth was very poor. The results of short-term and long-term simulation runs demonstrated the potential of the model to estimate N₂O emission factors under various conditions. During the first growing season, simulated emissions from organic fertilizers were lower than from synthetic fertilizers because more of the nitrogen was used to build up soil organic matter. The relative difference between the fertilizer types became larger with increasing application rate. The difference between fertilizer types was smaller at steady-state when higher soil organic matter content from repeated application of organic fertilizer over time led to enhanced mineralization and N₂O emissions. The dependence of simulated N₂O emissions on N input was close to linear at low, but non-linear at high fertilization rates. Emission factors calculated from the linear part of the curve suggested that the factors used in the current IPCC method underestimate the long-term effects of changes in fertilizer management. Furthermore the simulations show that N₂O emissions caused by nitrogen inputs from the decomposition of harvest losses and from biological fixation in grassland can be considerable and should not be neglected in national emission inventories. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of chemical fertilizer form on N2O, NO and NO2 fluxes from Andisol field

N₂O, NO and NO₂ fluxes from an Andosol soil in Japan after fertilization were measured 6 times per day for 10 months from June 1997 to April 1998 with a fully automated flux monitoring system in lysimeters. Three nitrogen chemical fertilizers were applied to the soil–calcium nitrate (NI), controlled-release urea (CU), and controlled-release calcium nitrate (CN), and also no nitrogen fertilizer (NN). The total amount of nitrogen applied was 15 g N m^–2 in the first and the second cultivation period of Chinese vegetable. In the first measuremnt period of 89 days, the total N₂O emissions from NI, CN, CU, and NN were 18.4, 16.3, 48.7, and 9.60 mgN m^–2, respectively. The total NO emissions from NI, CN, CU, and NN were 48.4, 33.7, 149, and 13.7 mgN m^–2, respectively. In the second measurement period of 53 days, the total N₂O emissions from NI, CN, and CU were 9.66, 7.23, and 20.6 mgN m^–2, respectively. The total NO emissions from NI, CN, and CU were 24.7, 2.60 and 34.2 mgN m^–2, respectively. The total N₂O emission from CU was significantly higher than CN. In the third cultivation period, all plots were applied with 10 g N m^–2 of ammonium phosphate (AP) and winter barley was cultivated. In the third measurement period of 155 days, the total N₂O and NO emissions were 9.02 mgN m^–2 and 10.2 mgN m^–2, respectively. N₂O and NO peaks were observed just after the fertilization for 30 days and 15 days, respectively. N₂O, NO and NO₂ fluxes for the year were estimated to be 38.6 81.5, 48.2 181, and –24.8 to –39.3 mgN m^–2, respectively. NO₂ was absorbed in all the plots, and a negative correlation was found between NO₂ flux and the NO₂ concentration just after the chamber closed. NO was absorbed in the winter period, and a negative correlation was found between NO flux and the NO concentration just after the chamber closed. A diurnal pattern was observed in N₂O and NO fluxes in the summer, similar to air and soil temperature. We could find a negative relationship between flux ratio of NO-N to N₂O-N and water-filled pore space (WFPS), and a positive relationship between NO-N and N₂O-N fluxes and temperature. Q₁₀ values were 3.1 for N₂O and 8.7 for NO between 530 °C.     

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.     

Nitrous oxide production in riparian zones and groundwater

This paper addresses the question of whether riparian zones and groundwater are hotspots of nitrous oxide (N₂O) flux in the landscape. First, we describe how riparian zones and groundwater function as transformers of N, with a particular emphasis on mechanisms of N₂O production in these ecosystems. We then present specific data on N₂O flux in these ecosystems and attempt to reconcile these data with existing regional scale estimates of N flux for Norway and with estimates of N₂O flux for Norway produced using the OECD/IPCC/IEA Phase II methodology for calculation of regional and global N₂O budgets. While the OECD/IPCC/IEA approach produces estimates of riparian and groundwater N₂O flux that are reasonable, given what we know about regional scale N balances and actual data on N₂O flux, it does not allow us to determine if riparian zones and groundwater are hotspots of N₂O production in the landscape. The approach fails to answer this question because it is unable to account for spatially explicit phenomena such as riparian and groundwater processing of excess agricultural N. Research needs that would allow us to address this question are discussed.     

Measurement of nitrous oxide and di-nitrogen emissions from agricultural soils

Nitrous oxide can be produced during nitrification, denitrification, dissimilatory reduction of NO ₃ ^- to NH ₄ ⁺ and chemo-denitrification. Since soils are a mosaic of aerobic and anaerobic zones, it is likely that multiple processes are contributing simultaneously to N₂O production in a soil profile. The N₂O produced by all processes may mix to form one pool before being reduced to N₂ by denitrification. Reliable methods are needed for measuring the fluxes of N₂O and N₂ simultaneously from agricultural soils. The C₂H₂ inhibition and ¹⁵N gas-flux methods are suitable for use in undisturbed soils in the field. The main disadvantage of C₂H₂ is that as well as blocking N₂O reductase, it also blocks nitrification and dissimilatory reduction of NO ₃ ^- to NH ₄ ⁺ . Potentially the ¹⁵ N gas-flux method can give reliable measurements of the fluxes of N₂O and N₂ when all N transformation processes proceed naturally. The analysis of ¹⁵N in N₂ and N₂O is now fully automated by continuous-flow isotope-ratio mass spectrometry for 12-ml gas samples contained in septum-capped vials. Depending on the methodology, the limit of detection ranges from 4 to 11 g N ha^-1day^-1 for N₂ and 4 to 15 g N ha^-1day^-1 for N₂O. By measuring the ¹⁵N content and distribution of ¹⁵N atoms in the N₂O molecules, information can also be obtained to help diagnose the sources of N₂O and the processes producing it. Only a limited number of field studies have been done using the ¹⁵N gas-flux method on agricultural soils. The measured flux rates and mole fractions of N₂O have been highly variable. In rain-fed agricultural soils, soil temperature and water-filled pore space change with the weather and so are difficult to modify. Soil organic C, NO ₃ ^- and pH should be amenable to more control. The effect of organic C depends on the degree of anaerobiosis generated as a result of its metabolism. If conditions for denitrification are not limiting, split applications of organic C will produce more N₂O than a single application because of the time lag in the synthesis of N₂O reductase. Increasing the NO ₃ ^- concentration above the K _m value for NO ₃ ^- reductase, or decreasing soil pH from 7 to 5, will have little effect on denitrification rate but will increase the mole fraction of N₂O. The effect of NO ₃ ^- concentration on the mole fraction of N₂O is enhanced at low pH. Manipulating the interaction between NO ₃ ^- supply and soil pH offers the best hope for minimising N₂O and N₂ fluxes.     

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.     

The effect of agricultural practices on methane and nitrous oxide emissions from rice field and pot experiments

The authors of this paper measured the methane and nitrous oxide fluxes emissions from rice field with different rice varieties and the two fluxes from pot experiments with different soil water regime and fertilizer treatment. The experiment results showed that: (1) The CH₄ emission rates were different among different varieties; (2) There was a trade-off between CH₄ and N₂O emissions from rice field with some agricultural practices; (3) We must consider the mitigation options comprehensively to mitigate CH₄ and N₂O emissions from rice fields. This revised version was published online in August 2006 with corrections to the Cover Date.     

Controlling nitrous oxide emissions from grassland livestock production systems

There is growing awareness that grassland livestock production systems are major sources of nitrous oxide (N₂O). Controlling these emissions requires a thorough understanding of all sources and controlling factors at the farm level. This paper examines the various controlling factors and proposes farm management measures to decrease N₂O emissions from intensively managed grassland livestock farming systems. Two types of regulating mechanisms of N₂O emissions can be distinguished, i.e. environmental regulators and farm management regulators. Both types of regulators may influence the number and size of N₂O sources, and the timing of the emissions. At the field and farm scales, two clusters of environmental regulating factors have been identified, i.e. soil and climate, and three levels of management regulators, i.e. strategic, tactical and operational. Though the understanding of these controls is still incomplete, the available information suggests that there is large scope for diminishing N₂O emissions at the farm scale, using strategies that have been identified already. For example, model calculations indicate that it may be possible to decrease total N₂O emissions from intensively managed dairy farms in The Netherlands in the short term from a mean of about 19 to about 13 kg N per ha per year by more effective nutrient management, whilst maintaining productivity. There is scope for a further reduction to a level of about 6 kg N per ha per year. Advisory tools for controlling N₂O emissions have to be developed for all three management levels, i.e. strategic, tactical and operational, to be able to effectively implement emission reduction options and strategies in practice. Some strategies and best management practices to decrease N₂O emissions from grassland livestock farming systems are suggested.     

Soil-land-use-system approach to estimate nitrous oxide emissions from agricultural soils

Emissions of nitrous oxide (N₂O) from agricultural soils contribute significantly to the anthropogenic greenhouse effect. Numerous studies have been conducted during the last three decades to improve the understanding of the processes involved in the release of N₂O from agricultural soils. This enabled the creation of process based models on site and field scale. In addition, a growing number of N₂O emission data are available for different soil-land-use-systems from various climates. The integration of these data in global and national N₂O budgets leads to more improved estimations. Surprisingly, N₂O-emission calculations are rare on regional meso and macro scales. The spatial identification of areas with a high efflux of N₂O on regional meso and macro scales is essential for the implementation of N₂O emission mitigation strategies, thus leading to an increased sustainability of land use. On the basis of the ecosystem approach of Matson and Vitousek (1990), we introduce a new method to estimate regional N₂O emissions from agricultural soils on meso and macro scales. This method considers spatial environmental information from available spatial and statistical data as well as quantitative and qualitative expertise by using the tools of a geographic information system (GIS). An environmental information system (EIS) was built up for a dairy farm region in Southern Germany which includes soil, land use, topography, N₂O emission and farm management data. Using all information in the EIS, it was possible (i) to identify different spatial soil-land-use-systems, (ii) to link emission data and process knowledge to these soil-land-use-systems and (iii) to visualize spatial emission potentials. On this basis, N₂O emission potentials for each of the communities in the study region and the whole region were estimated. The estimated annual N₂O emission potential from agricultural soils for the examined dairy farm region in Southern Germany covering around 775 km² is about 3.0 kg N₂O-N ha⁻¹. This revised version was published online in August 2006 with corrections to the Cover Date.