Browsing by Subject "Nitrifikationshemmer"

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Gaseous N emissions from a loamy soil as affected by N fertilization strategies, and by the use of nitrification and urease inhibitors - Results from field and incubation experiments
(2023) Guzman Bustamante, Ivan; Müller, Torsten
Agricultural activities are responsible for a substantial share of anthropogenic greenhouse gases. At the same time, agricultural production must feed a growing world population under a changing climate. In the case of wheat, the use of nitrogen (N) fertilizers is needed in order to insure grain yield and quality. Nevertheless, its use is associated with reactive N losses, which are detrimental for the environment and human health. Among the gaseous N species emitted after N fertilization we find nitrous oxide (N2O), a potent greenhouse gas, and ammonia (NH3) that after its deposition can be oxidized to N2O. Chemical compounds such as nitrification and urease inhibitors (NIs and UIs, respectively) are a useful tool, able to raise the fertilizer nitrogen use efficiency, by retarding the nitrification of ammonium based fertilizer in the case of NIs and by retarding the hydrolysis of urea in the case of UIs. A side benefit of the use of NIs is the reduction of N2O emissions. The use of UIs reduces the NH3 volatilization. One of the most used NIs in Europe is 3,4-dimethylpyrazol phosphate (DMPP) which can be applied with ammonium sulfate nitrate (ASN). The relatively new NI, 3,4-dimethylpyrazol succinic acid (DMPSA), acts similarly to DMPP but has a different time of action and can be applied to several fertilizers, unlike DMPP. N-(n-butyl) thiophosphoric triamide (NBPT) is an effective UI that provenly reduces NH3 volatilization by inhibiting the urease enzyme. In a two-year field experiment with winter wheat several fertilizer strategies were tested, including splitting strategies, use of NIs and reduction of N amount. Reducing N amount reduces the amount of soil mineral N, which is the substrate for N2O producing microbiological processes, nitrification and denitrification. Splitting of N fertilizer might reduce soil mineral N as well because N fertilizer applications are better suited to the physiological needs of the wheat plants. Applying NIs in splitting schemes may further mitigate emissions. The relationship between N amount and N2O losses in a wheat production system was investigated by applying lower and higher N amounts than the recommended N application rate. Use of DMPP was able to reduce N2O emissions in both years, not only on an annual basis (by 21 %: 3.1 vs 2.5 kg N2O-N ha-1 a-1 average for both years) but also during winter, when up to 18 % of total annual emissions occurred. A change of the soil microbial community due to DMPP could be the reason for the reduction of winter emissions 8 to 12 months after DMPP application. An economic assessment of N fertilizer amount showed that DMPP applied with suboptimal N fertilizer amounts can maintain yield and at the same time decrease yield scaled N2O emissions compared to an optimal N fertilizer rate without NI. Using CAN together with the NI DMPSA reduced N2O emissions only during the vegetation period. On an annual basis, DMPSA did not significantly reduce N2O emissions. Because DMPSA and DMPP were applied with different N fertilizers with different ammonium and nitrate shares, a direct comparison between these two NIs cannot be made. A traditional threefold split fertilization did not reduce annual emissions compared to a single application of ASN or CAN. Nevertheless, the use of DMPP in twofold split applications reduced annual emissions significantly by 33 % and increased protein content by 1.6 %. Because N2O flux peaks were not as high as expected after N fertilization during the first year, a short experiment investigating the effect of soil moisture, N and C application on N2O fluxes was conducted. A C limitation of the field was found, which explained high N2O emission events when C was available, e.g. after rewetting of dry soil and incorporation of straw after harvest. In this context we tested the removal of wheat straw – which should reduce the organic substrate supply for denitrifiers – as a possible mitigation strategy. Nevertheless, the removal of straw had no effect on N2O emissions. Furthermore, the effect of DMPP on microorganisms was studied in an incubation experiment: the copy number of bacterial amoA genes (nitrifiers) was lowered by the use of DMPP, while the number of archaeal amoA genes was increased by DMPP. Gene copy number of denitrifiers was unaffected by DMPP, nevertheless, soil respiration was reduced when DMPP was applied. It seems as DMPP has an inhibiting effect on heterotrophic organisms, nevertheless, the investigated variables did not support this hypothesis, so that further investigation is needed. The effect of NBPT and straw residues on NH3 and N2O emissions was studied in a two-week incubation experiment with a slightly alkaline soil. NBPT reduced NH3 volatilization and N2O fluxes from urea fertilization almost completely. Incorporation of straw residues significantly increased N2O emissions. In a further four-week incubation experiment, the effect of NBPT in two concentrations and DMPP was studied. A higher NBPT concentration as the recommended rate, reduced NH3 emissions by 53 %; DMPP on the other hand increased NH3 volatilization by 70 %. Regarding N2O, DMPP reduced emissions to the same level as the unfertilized control; NBPT only shifted the emission peak so that by the end of the experiment no difference in the cumulative N2O emission was found between urea and NBPT treatments. These results show that UI can lead to a reduction of N2O emissions, but the ammonium formed by the urea hydrolysis should be used by crops, otherwise it serves as a substrate for N2O production in soils. In the final incubation experiment, the combined application of a NI (DMPSA) and a UI (NBPT) was studied. Lower concentrations than the recommended doses were applied in order to assess synergistic effects. The combined application of DMPSA and NBPT did not lead to synergistic effects in the analyzed variables (soil urea amount, soil mineral N, ammonia volatilization, soil respiration and N2O emission). The higher the NBPT concentration, the slower urea was hydrolyzed and the higher the reduction in NH3 volatilization. A third of DMPSA application rate was enough to reduce N2O emissions; however, the use of NI increased NH3 losses. Our results highlight the importance of annual datasets when assessing mitigation strategies for N2O. For wheat production, a reduction of the N fertilizer amount when a NI is used should be taken into consideration. When elite wheat cultivars are grown split application with NI fertilizers could ensure high protein content and simultaneously reduce N2O emission. Urea fertilizer should be applied with NI and UI so that NH3 volatilization and N2O emission is reduced. Nevertheless, long-term effects of these compounds on soil microbiology must be monitored to avoid unseen ecotoxicological effects. Since some of these compounds or their metabolites might be absorbed by plants and end up in food and feed more research is needed to protect consumers.
Nitrous oxide emissions and mitigation strategies in winter oilseed rape cultivation
(2019) Kesenheimer, Katharina Anne; Müller, Torsten
After carbon dioxide and methane, nitrous oxide, is the third most important greenhouse gas in the atmosphere. Nitrous oxide contributes to the greenhouse gas effect as well as to ozone depletion. The major portion of anthropogenic N2O emissions are stimulated by the use of nitrogen fertilizers in agriculture. The main processes for N2O production in soils are nitrification and denitrification. Various environmental and management factors such as precipitation, soil type, tillage, and crop residues affect these processes. N2O emissions can occur substantially in the post-harvest period. In Germany, approximately 50 % of the annual N2O emissions can occur during winter. This exhibits the importance and necessity of annual data sets which prevent misinterpretations instigated by investigations limited to the vegetation period. Winter oilseed rape is the most important raw material for biodiesel in Germany. As of 2018, the framework of the European Renewable Energy Directive requires that the use of biofuels achieve GHG savings of at least 50 % compared to fossil fuels. Feedstock production for biodiesel contributes more than half of the total GHG emissions. To close the nutrient cycle with renewable energy, digestate from biogas plants can be used as a substitute for mineral N fertilizer permitting the reduction of GHG emissions in the production process of synthetic fertilizers. When compared to other crops, OSR has a high N demand. The low N removal by the seeds results in inefficient use of nitrogen and therefore a high N surplus in the soil which is susceptible to gaseous or leaching losses to the environment. Another potential risk for N2O losses are crop residues after harvest. The type of soil cultivation can have both positive and negative implications on N2O emissions which depend, among other things, on tillage depth, soil type and moisture. Results from studies measuring N2O emissions from different tillage systems are contradicting and site dependent. This study aims to investigate the effect of (a) N fertilization (mineral and organic), (b) nitrification inhibitors, (c) crop residues and (d) tillage on direct N2O emissions and, inter alia, yield and soil nitrogen dynamics in OSR production. N2O emissions were monitored for three years over a range of N fertilization levels at five study sites chosen so as to best represent typical winter oilseed rape production in Germany. Furthermore, the effect of the nitrification inhibitor (NI) TZ+MP (1H-1,2,4-triazole and 3- methylpyrazole) with digestate is investigated. Additional experiments for 15N labelled crop residues, nitrification inhibitor DMPP (3,4-dimethylepyrazole phosphate) with mineral fertilizer and soil tillage were implemented. A high spatial and temporal variability in N2O fluxes over all sites was observed. At each site, increased N2O fluxes were often detected after N fertilization in conjunction with rainfall events. During the first six weeks after harvest we frequently observed increased N2O fluxes following rainfall. In this postharvest period of winter oilseed rape, nitrate contents in the top soil were generally elevated. There were no considerable N2O pulses observed during thawing of frozen soil. Winters were mild without any severe frost periods in all three surveyed years which could be a reason for the generally low N2O winter fluxes observed in this study. On all examined sites, increasing N fertilization significantly enhanced N2O flux rates. Data obtained during the study were used to augment an existing model, wherefrom a new emission factor for OSR can be calculated. Assuming a quantity of 200 kg N ha-1 the global fertilizer-related emission factor derived from the exponential model was 0.6 %. This factor is within the uncertainty range of the EF1 IPCC emission factor (0.3 % – 3.0 %), but about 40 % lower than the 1 % IPCC default. The nitrification inhibitor (NI) TZ+MP combined with digestate mitigated the N2O fluxes significantly across all study sites and experimental years. As already noted in the fertilizer experiment, a high spatial and temporal variability in N2O fluxes over all sites was observed. The magnitudes of the N2O fluxes also showed similar trends. Over the entire investigation, the application of the NI significantly reduced annual N2O emission by a factor of three. During the fertilization period this mitigation effect was six times significant. This clearly emphasizes the importance of annual data sets to avoid overestimating NI effects.