Nitrogen turnover and leaching in cropping systems with ryegrass catch crops

This thesis deals with perennial ryegrass (Lolium perenne L.) catch crops and their short- and long-term effects on nitrogen leaching and nitrogen turnover in soils. Results are presented from three field experiments on a sandy soil in south-west Sweden, where undersown catch crops were used in cropping systems with and without applications of liquid manure. The effects of different tillage practices on soil mineral nitrogen and leaching were also studied. Two coupled simulation models, which describe water flow and nitrogen transformations and transport in soil, were used for calculations of nitrogen mineralization and soil nitrogen balances. A more detailed study of the residual effects of ryegrass on the nitrogen supyly to the subsequent crops and nitrogen leaching was performed in lysimeters, using 'N-labelled ryegrass. Undersown catch crops efficiently reduced nitrogen losses when mineral fertilizer or manure was applied at normal rates (90-1 10 kg Nha). Over five years, undersown catch crops reduced nitrogen leaching by 60%, on average, compared with soil which was conventionally tilled in August-September. Incorporation of catch crops affected nitrogen mineralization mainly during the first growing season following incorporation, when approximately 20-30% of catch crop nitrogen was released. The results emphasize the importance of an early onset of nitrogen mineralization in spring after incorporation of catch crops. This is necessary in order to overcome the soil-depletion effect of nitrogen uptake induced by the catch crop. Simulations showed that incorporation of catch crop material in late autumn instead of spring can result in a time distribution of nitrogen mineralization more suitable for a subsequent cereal crop, but this was not verified by the results of the lysimeter experiment. It seems important to obtain further knowledge of how to improve the degree of synchronization between nitrogen mineralization after incorporation of catch crops and nitrogen demand of the subsequent crops. According to simulations, the main part of the catch crop nitrogen contributed to a long-term accumulation of soil organic nitrogen (+I0 kg N per hectare and year), while it slowly declined in autumn-tilled soil given mineral fertilizer (-30 kg N per hectare and year). However, the accumulation of soil organic nitrogen due to the catch crops was very modest compared with the total amount of organic nitrogen in the soil

Effect of nitrogen fertilizer placement on nitrogen uptake and yield of sweet corn (Zea mays L. saccharata) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University, New Zealand

Five placements of nitrogen fertilizer applied to sweet corn (Zea mays L. saccharata) at the four fully expanded leaf stage, that is control (no nitrogen), a band of nitrogen placed on the soil surface near the row, on the soil surface between the rows, at 3 cm depth between the rows and at 10 cm depth between the rows were studied following three sowing times. Total plant nitrogen and sap nitrate were determined along with total plant dry weight at six growth stages. Leaf extension and leaf appearance were also followed in order to monitor the response of plants to nitrogen fertilizer applied. Nitrogen fertilizer application resulted in significantly higher nitrogen uptake, plant dry weight and marketable ears under both dry and wet conditions. Nitrogen fertilizer applied at 10 cm depth between rows resulted in significantly higher nitrogen uptake, plant dry weight and marketable ears than that applied on the soil surface between rows under dry condition. Nitrogen fertilizer applied on the soil surface near the plants performed well under both dry and wet conditions. The sap nitrate test was more sensitive than total nitrogen measurement in indicating the timing of nitrogen uptake. Sap nitrate levels were influenced by nitrogen fertilizer application and soil water content. The general critical value of sap nitrate over the vegetative growing period was about 1000 ppm. The sap nitrate test appeared to be a very useful monitoring tool for plant nitrogen status. Further studies in the uses of sap nitrate test, especially the critical value, are needed. Use of leaf extension to detect the response of plants to nitrogen fertilizer applied was not successful. Nitrogen fertilizer application tended to accelerate leaf appearance under the low soil nitrogen status

Effect of ammonium concentration on alcoholic fermentation kinetics by wine yeasts for high sugar content

Kinetics of alcoholic fermentation by Saccharomyces cerevisiae wine strains in a synthetic medium with high sugar content were established for different nitrogen initial content and are presented for 4 strains. The composition of the medium was close to grape must except that the nitrogen source consisted mainly in ammonium and was varied from 120 to 290 mg N/L assimilable nitrogen. The overall nitrogen consumed was also estimated in order to determine nitrogen requirement variability. The effect of assimilable nitrogen was in general greater on sugar consumption rates than on growth and 3 kinds of effect on sugar consumption rates were observed: i) existence of an optimal initial nitrogen level for a maximal sugar consumption rate (inhibition if excess), ii) no effect of nitrogen beyond the intermediary level (saturation), iii) sugar consumption rate proportional to the initial nitrogen level (activation). In all cases, the amount of consumed nitrogen increased with its initial concentration and so did the fructophilic capacity of the strains. The optimal requirement varied from 0.62 to 0.91 mg N per g of sugars according to the different strains. There was no general correlation between the sugar assimilation rates and the nitrogen requirement

Structures, enthalpies of formation, and ionization energies for the parent and binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives: A G4MP2 theoretical study

Gas phase standard state (298.15 K, 1 atm) structures, enthalpies of formation, and ionization energies (IEs) were calculated at the G4MP2 composite method level of theory for the parent and binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives. Increasing nitrogen content increases the enthalpies of formation for the carbon-nitrogen, nitrogen-phosphorus, and silicon-nitrogen binary cubanes, with the opposite enthalpies of formation trend for increasing phosphorus content within the carbon-phosphorus, nitrogen-phosphorus, and silicon-phosphorus derivatives. Varying carbon/silicon content in the carbon-silicon cubanes results in no general trends for enthalpies of formation. Isomerization enthalpies within the homolog groups having more than one isomer vary widely with atomic composition and substitution patterns. Increasing nitrogen content of the carbon-nitrogen and nitrogen-phosphorus derivatives increases the IE, increasing silicon content in the carbon-silicon cubanes and phosphorus content of the carbon-phosphorus cubanes decreases the IE, while no IE clear trends are evident based on relative atomic content for the silicon-nitrogen and silicon-phosphorus compounds. The binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives are predicted to display potentially tunable thermodynamic stability and redox behavior depending on the atom identities and relative positions

EarthN: A new Earth System Nitrogen Model

The amount of nitrogen in the atmosphere, oceans, crust, and mantle have important ramifications for Earth's biologic and geologic history. Despite this importance, the history and cycling of nitrogen in the Earth system is poorly constrained over time. For example, various models and proxies contrastingly support atmospheric mass stasis, net outgassing, or net ingassing over time. In addition, the amount available to and processing of nitrogen by organisms is intricately linked with and provides feedbacks on oxygen and nutrient cycles. To investigate the Earth system nitrogen cycle over geologic history, we have constructed a new nitrogen cycle model: EarthN. This model is driven by mantle cooling, links biologic nitrogen cycling to phosphate and oxygen, and incorporates geologic and biologic fluxes. Model output is consistent with large (2-4x) changes in atmospheric mass over time, typically indicating atmospheric drawdown and nitrogen sequestration into the mantle and continental crust. Critical controls on nitrogen distribution include mantle cooling history, weathering, and the total Bulk Silicate Earth+atmosphere nitrogen budget. Linking the nitrogen cycle to phosphorous and oxygen levels, instead of carbon as has been previously done, provides new and more dynamic insight into the history of nitrogen on the planet.Comment: 36 pages, 12 figure

Oxygen molecule dissociation on carbon nanostructures with different types of nitrogen doping

Energy barrier of oxygen molecule dissociation on carbon nanotube or graphene with different types of nitrogen doping is investigated using density functional theory. The results show that the energy barriers can be reduced efficiently by all types of nitrogen doping in both carbon nanotubes and graphene. Graphite-like nitrogen and Stone-Wales defect nitrogen decrease the energy barrier more efficiently than pyridine-like nitrogen, and a dissociation barrier lower than 0.2 eV can be obtained. Higher nitrogen concentration reduces the energy barrier much more efficiently for graphite-like nitrogen. These observations are closely related to partial occupation of {\pi}* orbitals and change of work functions. Our results thus provide useful insights into the oxygen reduction reactions.Comment: Accepted by Nanoscal

Polarization and readout of coupled single spins in diamond

We study the coupling of a single nitrogen-vacancy center in diamond to a nearby single nitrogen defect at room temperature. The magnetic dipolar coupling leads to a splitting in the electron spin resonance frequency of the nitrogen-vacancy center, allowing readout of the state of a single nitrogen electron spin. At magnetic fields where the spin splitting of the two centers is the same we observe a strong polarization of the nitrogen electron spin. The amount of polarization can be controlled by the optical excitation power. We combine the polarization and the readout in time-resolved pump-probe measurements to determine the spin relaxation time of a single nitrogen electron spin. Finally, we discuss indications for hyperfine-induced polarization of the nitrogen nuclear spin

Ionized Nitrogen Mono-hydride Bands are Identified in the Pre-solar and Carbonado Diamond Spectra

None of the well established Nitrogen related IR absorption bands, common in synthetic and terrestrial diamonds, have been identified in the pre-solar diamond spectra. In the carbonado diamond spectra only the single nitrogen impurity (C centre) is identified and the assignments of the rest of the nitrogen-related bands are still debated. It is speculated that the unidentified bands in the Nitrogen absorption region are not induced by Nitrogen but rather by Nitrogen-hydrides because in the interstellar environment Nitrogen reacts with Hydrogen and forms NH+; NH; NH2; NH3. Among these Hydrides the electronic configuration of NH+ is the closest to Carbon. Thus this ionized Nitrogen-mono-hydride is the best candidate to substitute Carbon in the diamond structure. The bands of the substitutional NH+ defect are deduced by red shifting the irradiation induced N+ bands due to the mass of the additional Hydrogen. The six bands of the NH+ defects are identified in both the pre-solar and the carbonado diamond spectra. The new assignments identify all of the nitrogen-related bands in the spectra, indicating that pre-solar and carbonado diamonds contain only single nitrogen impurities

Effect of Nitrogen Fertilizer Dose and Application Timing on Yield and Nitrogen Use Efficiency of Irrigated Hybrid Rice under Semi-Arid Conditions

Nitrogen fertilizer is the major input in rice production and the optimum rate and application timing management assure profitability and sustainability of the production system. This study aims to investigate hybrid rice response to different nitrogen fertilizer levels and the timing of application and quantify hybrid rice nitrogen use efficiency. Field experiments were conducted during the dry and the wet seasons 2016 at the research station of Africa Rice at Ndiaye in Senegal. Six nitrogen rates (0, 60, 90, 120, 150 and 180 kg N/ha) and three hybrid rice varieties (AR031H, AR032H, AR033H) and one inbred variety (Sahel108) and two nitrogen fertilizer application timings (three split and four split) were combined within a split-split plot design. The results showed significant effect of nitrogen rate and timing on rice grain yield that varied from 4.10 to 11.58 tons/ha and most the yield components. Rice grain yield exhibited curvilinear relationship with the applied nitrogen rates during the dry season under both nitrogen application timings and a linear relationship during the wet season under three splits. Nitrogen rate of 150 kg/ha was revealed optimum with best performance achieved by the Hybrid rice AR033H. Hybrid rice genotypes achieved greater nitrogen use efficiency compared to the inbred rice Sahel108. Hence, hybrid rice genotypes, and nitrogen rate of 150 kg/ha applied in four splits could be recommended to improve rice production and food security for achieving self-sufficiency in rice as targeted by Senegal and the neighboring countries