Browsing by Subject "Lachgas"

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Abgabe von bodenbürtigem Lachgas über Pflanzen
(2003) Ferch, Norbert-Jakob; Römheld, Volker
The aim of this work was to explore and to rank the different ways and forms of transition of N2O through plants (dissolved in water and transported with the transpiration or gaseous through aerenchyma). To achieve this goal an experimental set-up had to be realized that allowed the determination of possible N2O emissions by plants, the determination of different ways of transition of N2O through the plant and the determination of different influencing factors (e.g. N2O concentration) on the N2O emissions. In the beginning experiments with closed chambers and with ?controlled opened chambers? were conducted in comparison to each other. In the experiments with closed chambers samples were drawn by means of molecular sieves and vacutainers. N2O concentrations of the samples were measured with a GC (gas chromatograph type HP 5890) equipped with an ECD (electron capture detector). Besides the two methods mentioned above in order to determine the N2O concentrations within the experiments with the ?controlled opened chambers? a third method was used for N2O measurement by means of a photo acoustic online measuring machine. The accuracy of the photo acoustic measurement was evaluated with the GC. For the questions of interest the photo acoustic measurement showed to be the best to determine differences of N2O emissions between different experimental treatments. The experiments that were taken in consideration were conducted in a ?controlled opened system? because in closed chambers CO2 concentration decreased rapidly. Additionally, the air in the closed chambers became saturated in water vapour within a few minutes. These two factors lead to inhibited growth of the plants and to undesired influences on the N2O measurements. The ?controlled opened system? consisted of a root and a shoot compartment. Both compartments were separated airtight from each other and from the surroundings. The root compartments were enriched with a definite amount of N2O. The N2O concentrations measured in the shoot compartments of the systems with N2O enrichment in the root compartment were compared with measurements of systems without N2O enrichment and measurements of ambient air. The necessity to divide the root compartment from the shoot compartment airtight was realised with a material on the basis of silicone that is usually used to make prints of teeth (Optosil, from Haereus) and a sealing mass (Prestik AE hellgrau, from Bostik GmbH). To determine the different factors potentially influencing the N2O emission through plants a hydroponical culture system was established that allowed controlling the following factors: concentration of nutrients, pH-factor, concentration of different water soluble gases (e. g. N2O, CO2) and the ratio between water and gas filled space in the root compartment. As experimental plants sunflower (Helianthus annuus cv. Frankasol), barley (Hordeum vulgare cv. Scarlet), rice (Oryza sativa cv. 94D-22) and corn (Zea mays cv. Helix) were used. For the experiment with sunflower (no aerenchyma, N2O dissolved in water available only) a relationship between N2O concentration in the root compartment, the emitted amount of N2O by the shoots and the intensity of transpiration in a diurnal pattern was found. In systems with gaseous availability of N2O in the root compartment the observed emissions were higher than in systems with availability of N2O dissolved only in water. From this it could be concluded, that gaseous N2O is better available for plants than N2O dissolved in water. Similar results were obtained from experiments with barley. The only difference was that the highest N2O emissions were observed in systems with availability of N2O dissolved in water only. The possible N2O emission through aerenchyma was checked with rice plants. In these experiments a pronounced diurnal pattern of the N2O emissions was also found. This lead to the conclusion that aerenchyma only have a small influence on the N2O emissions out of the root compartment through rice plants. Because the N2O emission in the three experiments described above followed the diurnal pattern of the transpiration, it was concluded that N2O was transported with the transpiration water flow from the root (compartment) to the shoot (compartment). The experiments with corn showed for all treatments (control and availability of N2O in gaseous form or dissolved in water) a net N2O depletion in the shoot compartment for night (darkness) and day (light) respectively, thus leading to the conclusion that N2O can be metabolised and used as a nitrogen source. All in all the experiments showed that the main way of transition of N2O through plants is water dissolved with the transpiration water flow and not gaseous (through aerenchyma).
Emission von Ammoniak (NH₃) und Lachgas (N₂O) von landwirtschaftlich genutzten Böden in Abhängigkeit von produktionstechnischen Maßnahmen
(2003) Leick, Barbara Cornelia Elisabeth; Engels, Christof
The goal of this research was to quantify event-based NH₃ and N₂O emissions in various farming systems and to propose emission-avoidance strategies. Emission measurements were made on pasture land (Allgaeu, Hohenheim) and on cultivated fields (Hohenheim, Biberach). These measurements were made after applying organic and mineral fertilizers, after incorporating crop residues, and after freeze / thaw cycles; furthermore, experiments were conducted using container plants of different species (leguminous, and non-leguminous) and different fertilizers. NH3 emissions data was gathered under field conditions using the wind tunnel method and the IHF method (Integrated Horizontal Flux). In the container experiments, data was gathered by taking photo-acoustic measurements. N₂O emissions data was compiled using closed chambers (Hohenheim measuring chambers) and using an open-chamber system in which an exchange occurred between the air in the chambers and the ambient air. N₂O levels were determined using a gas chromatograph or by photo-acoustic measurements. The NH₃ emissions after applying liquid manure to pasture land varied between 11 and 40% of the total nitrogen applied. Emission levels of less than 20% occurred when it rained shortly after spreading liquid manure causing it to be washed into the soil. The application technique (splash plate, surface banding and liquid manure injection) had no apparent influence on NH₃ emissions under these conditions. The N₂O emissions after liquid manure fertilization on pasture land in Hohenheim were 0.16% of the total NH4+-N. In comparison, the emissions in the Allgäu were between 1.7 and 2.3% of the total NH4+-N applied. Liquid manure injection led to higher emissions as did application using a splash plate. In the Allgäu, the N₂O emissions after mineral-nitrogen fertilization were markedly lower (0.3 to 0.8% of applied N) than after liquid manure application. In Hohenheim, the nitrogen form had no distinct influence on the emissions (<0.16% of applied N). Definitive differences between the two locations were observed during the experiments. These differences were based on N₂O losses due to the respective soil and weather conditions (precipitation, temperature). The higher emissions after applying liquid manure compared to those after applying mineral nitrogen fertilizer are explainable in that aside from the nitrogen compounds found in liquid manure, carbon compounds which promote the microbial formation of N₂O were also entering the soil. The NH3 emissions after liquid manure fertilization on cultivated fields using a splash plate varied between 25 and 35% of the applied NH4+-N. By using a slurry cultivator which combines application with immediate incorporation, the NH3 emissions can be clearly reduced to 6% of the applied NH4+-N. Application with a drag hose, in comparison to using a splash plate, did not always result in an emission reduction; however, in taller plants, a readable emission reduction was measured. The N₂O emissions after liquid manure application on cultivated fields varied between 0.1 and 2.2% of the applied NH4+-N whereby the emissions after guided application with the drag hose were always higher than after using a splash plate. Mineral fertilizer had lower N2O emissions (<0.13% of applied N), especially when ammonium fertilizer was brought out in combination with a nitrification inhibitor. The incorporation of green manure crops notedly increased N₂O emissions. N₂O emission after the incorporation of legumes was especially high. In the container experiments, a diurnal rhythm of the N₂O and NH₃ flows in growing rape and vetch was observed. This indicated a stomatal flow of these gaseous nitrogen forms. N₂O emissions also occurred outside of the vegetation period at temperatures between 0 and 5°C, with the N₂O emissions from the nitrogen fertilized parcels being greater than the emissions from the unfertilized parcels. In container experiments, the N₂O emissions after freeze / thaw cycles were greater from white clover than from perennial rye grass. In fallow soil columns, the N₂O emissions after freeze / thaw cycles were especially high if the content of nitrate and water-soluble organic carbon in the soil was large. The results of this research show that the emission of nitrogen-containing compounds after organic and inorganic fertilization can be reduced through application methods (immediate incorporation), appropriate fertilization technology (addition of nitrification inhibitors), but also through fertilizer application under favourable weather conditions to include seasonal and volume adjustment of the fertilizer based on the growth requirements of the plants. Because high N₂O emissions can also occur at low temperatures, cultivation practices that influence the availability of mineral nitrogen and easily degradable organic substances in the soil during cold weather have a large impact on the N₂O emissions from agricultural land.
Nitrous oxide emissions and mitigation strategies : measurements on an intensively fertilized vegetable cropped loamy soil
(2011) Pfab, Helena; Müller, Torsten
Nitrous oxide (N2O) is a potent greenhouse gas which is also involved in stratospheric ozone depletion. There is consensus that a reduction in N2O emissions is ecologically worthwhile. Agricultural soils are the major source of N2O emissions in Germany. It is known that high N-fertilization stimulates N2O emissions by providing substrate for the microbial production of N2O by nitrification and denitrification in soils. However, outside the vegetation period, winter freeze/thaw events can also lead to high N2O emissions. Winter emissions constitute about 50% of total emissions in Germany. Therefore, annual datasets are a prerequisite for the development of N2O mitigation strategies in regions with winter frost. Many studies have investigated mitigation strategies for N2O emissions from agricultural soils. However, N2O release from vegetable production has seldom been studied. None of the existing trace gas measurements on intensive vegetable production is representative for the climatic conditions of Southern Germany. Due to the high fertilizer N-input (resulting in high levels of mineral N in the soil) and N-rich residues in late autumn, high annual N2O emissions are to be expected. N2O fluxes were measured from a soilcropped with lettuce and cauliflower in Southern Germany by means of the closed chamber method, at least weekly, for two years. An additional study was conducted using 15 N labeled ammonium sulfate nitrate (ASN) fertilizer and exchange of labeled and unlabeled residues to obtain information about the sources (fertilizer, residues, soil internal mineralization) of N2O emissions. Different mitigation strategies such as fertilizer reduction, addition of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) and banded fertilization were evaluated with respect to their reduction potential on an annual base. Fertilizer reduction is supposed to decrease the soil mineral N level, reducing the available substrate for N2O producing microorganisms. DMPP is a chemical compound which inhibits nitrification enzymatically. In banded fertilization, ammonium rich fertilizer is applied in a depot. This high concentration is also supposed to inhibit nitrification as it is toxic to microorganisms. N2O emissions should be firstly reduced directly by this inhibition of nitrification and secondly, by a lower nitrate content in soil resulting in less N2O release due to denitrification. A high temporal variability in N2O fluxes was observed with emission peaks after N-fertilization, after the incorporation of crop residues (especially in combination with N-fertilization), after rewetting of dry soil and after thawing of frozen soil in winter. Total cumulative annual emissions were 8.8 and 4.7 kg N2O-N ha-1 a-1 for the first and second experimental year in the conventionally (broadcast) fertilized treatment. This treatment was fertilized according to the German Target Value System. N2O emission factors were 1.6 and 0.8%. This is within the range of 0.3 - 3% which is cited in the Guidelines for the Calculation of National Greenhouse Gas Inventories proposed by the Intergovernmental Panel of Climate Change (IPCC). A positive correlation was found in both years between the mean nitrate content of the top soil and the cumulative N2O emissions of all treatments (r2=0.44 and 0.68) as well as between the N-surpluses and the cumulative N2O emissions of the different fertilizer levels during the first year (r2=0.95). Fertilizer reduction from fertilization according to good agricultural practice following the recommendations of the German Target Value System reduced annual N2O emissions by 17% in the first experimental year without yield reduction. For the second year, the reducing effect was 10%, but statistically not significant. Another fertilizer reduction of a further 20% reduced N2O emissions, but also resulted in lower lettuce yields in the first year. Therefore, an additional fertilizer reduction is not recommendable. This work provides, for the first time, annual datasets on the effect of DMPP-application on N2O emissions. Addition of DMPP significantly reduced annual N2O emissions by > 40% during both years, there was also a pronounced effect, both during the vegetation period and winter. The reason for the reducing effect in winter is not yet clear because the degradation of the active agent DMPP is temperature dependent and should take about 6 to 8 weeks under summer climatic conditions. However, we still observed significant reductions in N2O emissions in winter, about 3 months after the application. Furthermore, a reduction in CO2 release was observed indicating a possible influence on heterotrophic activities or at least on their C-turnover. Due to its high N2O mitigation potential, further investigations concerning the functional and structural changes in microbial biomass after DMPP application are needed. Banded fertilization with ASN did not result in the expected reduction in N2O emissions on an annual base. Even when exchanging the ASN fertilizer by nitrate-free ammonium sulfate, N2O emissions were not diminished. We assume that the high emissions were derived from the microbially intact surroundings of the depots, where nitrification was not inhibited and nitrate concentrations were probably very high, creating ideal conditions for denitrification. After one year, the major part of the fertilizer-15N was found in the soil. Only between 13 -15% of the fertilizer was taken up by the marketable plant parts. 1.4% of the 15N was lost as N2O-N. Total 15N recovery was 70% after one year. The losses of non-recovered N were probably caused by nitrate leaching or as gaseous compounds such as N2 or NOx. Compared to cereal production systems, the N use efficiency of this vegetable production system is much lower, even with an optimized fertilization strategy. The measurement of 15N abundances in the N2O revealed that the most significant part of the emissions (38%) was derived from the fertilizer-N which had been taken up by cauliflower residues. N2O emissions directly derived from lettuce and cauliflower fertilizer contributed 26% and 20% respectively while N2O emissions from soil internal N pools accounted for 15%. The contribution of lettuce residues was negligible due to their low amount of C and N. The reason for the high importance of the cauliflower residues was ascribed to the temporarily C-limitation of the system and the provision of electron donators by organic material. Furthermore, O2 is consumed during their degradation leading to the formation of anaerobic microsites when soil moisture is high. These sites offer ideal conditions for denitrification. Especially the combination of mineral N-fertilization and input of organic substance was found to increase N2O emissions. Therefore, the influence of a de-synchronization of the incorporation of crop residues and the mineral N-fertilization by waiting periods of up to 3 weeks was tested in an additional field trial during the cultivation of chard. The longer the waiting time between incorporation of crop residues and N-fertilizer application was, the lower were the N2O emissions. However, the effect was not statistically significant on an annual base. In an additional microcosm incubation model study, the effect of reduced and increased input as well as of different C/N-ratios of cauliflower residues was analyzed. It was shown that due to the high nitrate level in the microcosms only the amount of residue input has an effect on the N2O emissions. The N2O emissions increased with increased amount of cauliflower residues. Although the emission factors were within the range given by the IPCC, the absolute annual N2O emission was high in intensive vegetable production due to the high N-input. Further research is required in order to fully understand the effect of DMPP on the processes of N2O production in the field. Our study underlines the importance of avoiding N-surpluses and of strategies for residue management to reduce N2O emissions in intensive vegetable production.