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Ammonia (NH(3)) emissions from animal systems have become a primary concern for all of livestock production. The purpose of this research was to establish the relationship of nitrogen (N) emissions to specific components of swine production systems and to determine accurate NH(3) emission factors appropriate for the regional climate, geography, and production systems. Micrometeorological instrumentation and gas sensors were placed over two lagoons in North Carolina during 1997-1999 to obtain information for determining ammonia emissions over extended periods and without interfering with the surrounding climate. Ammonia emissions varied diurnally and seasonally and were related to lagoon ammonium concentration, acidity, temperature, and wind turbulence. Conversion of significant quantities of ammonium NH(4)(+) to dinitrogen gas (N(2)) were measured in all lagoons with the emission rate largely dependent on NH(4)(+) concentration. Lagoon NH(4)(+) conversion to N(2) accounted for the largest loss component of the N entering the farm (43% as N(2)); however, small amounts of N(2)O were emitted from the lagoon (0.1%) and from field applications (0.05%) when effluent was applied nearby. In disagreement with previous and current estimates of NH(3) emissions from confined animal feeding operation (CAFO) systems, and invalidating current assumptions that most or all emissions are in the form of NH(3), we found much smaller NH(3) emissions from animal housing (7%), lagoons (8%), and fields (2%) using independent measurements of N transformation and transport. Nitrogen input and output in the production system were evaluated, and 95% of input N was accounted for as output N from the system.

Approximately 60% of Mexico (1.973 × 106 km2) is arid or semi-arid with vegetation dominated by N2 fixing shrubs, such as mesquite (Prosopis juliflora). Little is known, however, how these ecosystems contribute to production of nitrous oxide (N2O), a known greenhouse gas. We investigated this by adding inorganic fertilizer (20 mg ammonium (NH4+) N kg-1 soil) to soil at different water contents (40%, 60%, 80%, and 100% of water-holding capacity (WHC)) sampled under the canopy of mesquite and outside its canopy, while production of carbon dioxide (CO2) and nitrous oxide (N2O), and dynamics NH4+, nitrite (NO2-), and nitrate (NO3-)) were monitored. The CO2 production rate was 1.5 times larger for soil sampled under the canopy of mesquite compared to soil sampled outside the canopy of shrubs and lower in soil incubated at 100% WHC compared to the other treatments. Production of N2O increased with increased water content within the first day, but decreased in soil at 80% and 100% WHC thereafter. The production of N2O was 1.9 times larger for soil sampled under the canopy of mesquite compared to soil sampled outside its canopy. The addition of 20 mg NH4+-N increased production of N2O 1.8-fold. It was found that the cumulative production of N2O was larger from soil sampled under the canopy of mesquite than outside it when amended with inorganic fertilizer and increased with increased water content of the soil within a day. The relationship between the emission of CO2 and N2O, water-holding capacity are discussed. [ABSTRACT FROM AUTHOR]

Since the early 1990s, we have been carrying out experiments on N2O production, emission and sorption from a variety of soils and ecosystems. These laboratory studies revealed insights on the complex process of N2O formation in soils under contrasting conditions. Within Belgium, we also carried out numerous field experiments to measure in situ N2O emissions, using the closed chamber technique. The latter allowed us to suggest a region-specific N2O-N emission factor (2.66% of the applied N) for direct soil emissions and to assess the spatial and temporal variability of N2O emissions. Recently, we have been using these N2O field emission data to validate an adapted version of the DNDC process-based model to predict direct N2O emissions from agricultural soils of the Flemish region. Ultimately, it is our aim to develop, based on this validated DNDC model, scenario analyses of future direct N2O emissions from agricultural soils. [ABSTRACT FROM AUTHOR]

Strategies used to reduce emissions of N2O and CH4 in rice production normally include irrigation management and fertilization. To date, little information has been published on the measures that can simultaneously reduce both emissions. Effects of application of a urease inhibitor, hydroquinone (HQ), and a nitrification inhibitor, dicyandiamide (DCD) together with urea (U) on N2O and CH4 emission from rice growing were studied in pot experiments. These fertilization treatments were carried out in the presence and absence of wheat straw, applied to the soil surface. Without wheat straw addition, in all treatments with inhibitor(s) the emission of N2O and CH4 was significantly reduced, as compared with the treatment whereby only urea was applied (control). Especially for the U+HQ+DCD treatment, the total emission of N2O and CH4 was about 1/3 and 1/2 of that in the control, respectively. In the presence of wheat straw, the total N2O emission from the U+HQ+DCD treatment was about 1/2 of that from the control. The total CH4 emission was less influenced. Wheat straw addition, however, induced a substantial increase in emissions of N2O and CH4. Hence, simultaneous application of organic materials with a high C/N ratio and N-fertilizer (e.g. urea) is not a suitable method to reduce the N2O and CH4 emission. Application of HQ+DCD together with urea seemed to improve the rice growth and to reduce both emissions. The NO3 −-N content of the rice plants and denitrification of (NO3 −+NO2 −)-N might contribute to the N2O emission from flooded rice fields. [ABSTRACT FROM AUTHOR]

Agricultural practices, soil characteristics and meteorological conditions are responsible for eventual nitrate accumulation in the subsoil. There is a lot of evidence that denitrification occurs in the subsoil and rates up to 60–70 kg ha-1 yr-1 might be possible. It has also been shown that in the presence of Fe2+ (formed through weathering of minerals) and an alkaline pH, nitrate can be chemically reduced. Another possible pathway of disappearance is through the formation of nitrite, which is unstable in acid conditions. With regard to the emission of N2O and N2, it can be stated that all conditions whereby the denitrification process becomes marginal are favourable for N2O formation rather than for N2. Because of its high solubility, however, an important amount of N2O might be transported with drainage water. [ABSTRACT FROM AUTHOR]

In 1995 a working group was assembled at the request of OECD/IPCC/IEA to revise the methodology for N2O from agriculture for the National Greenhouse Gas Inventories Methodology. The basics of the methodology developed to calculate annual country level nitrous oxide (N2O) emissions from agricultural soils is presented herein. Three sources of N2O are distinguished in the new methodology: (i) direct emissions from agricultural soils, (ii) emissions from animal production, and (iii) N2O emissions indirectly induced by agricultural activities. The methodology is a simple approach which requires only input data that are available from FAO databases. The methodology attempts to relate N2O emissions to the agricultural nitrogen (N) cycle and to systems into which N is transported once it leaves agricultural systems. These estimates are made with the realization that increased utilization of crop nutrients, including N, will be required to meet rapidly growing needs for food and fiber production in our immediate future. Anthropogenic N input into agricultural systems include N from synthetic fertilizer, animal wastes, increased biological N-fixation, cultivation of mineral and organic soils through enhanced organic matter mineralization, and mineralization of crop residue returned to the field. Nitrous oxide may be emitted directly to the atmosphere in agricultural fields, animal confinements or pastoral systems or be transported from agricultural systems into ground and surface waters through surface runoff. Nitrate leaching and runoff and food consumption by humans and introduction into sewage systems transport the N ultimately into surface water (rivers and oceans) where additional N2O is produced. Ammonia and oxides of N (NOx) are also emitted from agricultural systems and may be transported off-site and serve to fertilize other systems which leads to enhanced production of N2O. Eventually, all N that moves through the soil system will be either terminally sequestered in buried sediments or denitrified in aquatic systems. We estimated global N2O–N emissions for the year 1989, using midpoint emission factors from our methodology and the FAO data for 1989. Direct emissions from agricultural soils totaled 2.1 Tg N, direct emissions from animal production totaled 2.1 Tg N and indirect emissions resulting from agricultural N input into the atmosphere and aquatic systems totaled 2.1 Tg N2O–N for an annual total of 6.3 Tg N2O–N. The N2O input to the atmosphere from agricultural production as a whole has apparently been previously underestimated. These new estimates suggest that the missing N2O sources discussed in earlier IPCC reports is likely a biogenic (agricultural) one. [ABSTRACT FROM AUTHOR]

Abstract: Inhibitors are applied to improve the efficiency of N fertilizer use and to reduce N losses from the soil. However, little information is available on the effects of a urease inhibitor, hydroquinone (HQ), and a nitrification inhibitor, dicyandiamide (DCD), on urea-derived mineral N in the rhizosphere of rice plants and in the standing water. Furthermore, this is important to understand the contribution of rice plants to gaseous N losses in the presence of inhibitor(s). A rhizobox was used to simultaneously study urea-derived mineral N in the soil at increasing distances from rice roots, and the effect of growing plants on the behavior of fertilizer-N in soil. The combined application of urea (U) with DCD showed a significantly positive effect on rice growth. The redox potentials in the rhizosphere soil were higher in the presence than in the absence of DCD, especially when rice plants entered their vigorous growth stage. During the entire experimental period, NH4 +–N concentrations in the rhizosphere of rice plants were smaller in the U+DCD and U+HQ+DCD treatments than in the U and U+HQ treatments. On days 20 and 60 after fertilization, the U+DCD and U+HQ+DCD treatments showed a smaller concentration of (NO3 − +NO2 −)–N in soil less than 0.5cm from the rhizobox, compared to the U treatment. During the early period of rice growth, the NH4 +–N concentration of the standing water was higher in the presence than in the absence of DCD. However, there were no significant differences in NH4 +–N among all treatments after 20 days. In the absence of rice plants, also, the application of DCD and especially DCD and HQ, always increased the level of NH4 +–N and pH in the standing water. Thus, rice plants might reduce potential gaseous N losses from a urea-fertilized, flooded soil, due to the stimulating effect on rice growth in the presence of DCD or DCD+HQ. The N2O emissions from the urea-fertilized, rice-planted soil significantly decreased when DCD or DCD+HQ was used. From the results obtained, we conclude that DCD and DCD+HQ together with U can be an effective tool to improving crop growth and reducing N loss as N2O in rice cultivation, and that the use of a rhizobox is useful to study the interaction between plant uptake and the behavior of fertilizer-N in soil. [Copyright &y& Elsevier]

Abstract: Soils in Mexico are often contaminated with hydrocarbons and addition of waste water sludge and earthworms accelerates their removal. However, little is known how contamination and subsequent bioremediation affects emissions of N2O and CO2. A laboratory study was done to investigate the effect of waste water sludge and the earthworm Eisenia fetida on emission of N2O and CO2 in a sandy loam soil contaminated with the polycyclic aromatic hydrocarbons (PAHs): phenanthrene, anthracene and benzo(a)pyrene. Emissions of N2O and CO2, and concentrations of inorganic N (ammonium (NH4 +), nitrite (NO2 −) nitrate (NO3 −)) were monitored after 0, 5, 24, 72 and 168h. Adding E. fetida to the PAHs contaminated soil increased CO2 production rate significantly 2.0 times independent of the addition of sludge. The N2O emission rate from unamended soil expressed on a daily base was 5μgNkg−1 d−1 for the first 2h and increased to a maximum of 325μgNkg−1 d−1 after 48h and then decreased to 10μgNkg−1 d−1 after 168h. Addition of PAHs, E. fetida or PAHs+ E. fetida had no significant effect on the N2O emission rate. Adding sludge to the soil sharply increased the N2O emission rate to >400μgNkg−1 d−1 for the entire incubation with a maximum of 1134μgNkg−1 d−1 after 48h. Addition of E. fetida, PAHs or PAHs+ E. fetida to the sludge-amended soil reduced the N2O emission rate significantly compared to soil amended with sludge after 24h. It was found that contaminating soil with PAHs and adding earthworms had no effect on emissions of N2O. Emission of N2O, however, increased in sludge-amended soil, but addition of earthworms to this soil and contamination reduced it. [Copyright &y& Elsevier]