Nitrogen fixation is an ecologically important microbial process that can contribute bioavailable combined N to habitats low in N. Shipworms, or wood-boring bivalves, host N2-fixing and cellulolytic symbiotic bacteria in gill bacteriocytes, which have been implicated as a necessary adaptation to an N-poor C-rich (wooden) diet. Shipworm symbionts are known to fix N within the gill habitat and newly fixed N is subsequently incorporated into non-symbiont containing host tissue. The presence of N2-fixation in gill bacteriocytes presents a conundrum because N2-fixation is tightly regulated by oxygen in most other diazotrophic microbes. Also, the direct evidence of new N being incorporated into the host tissue indicates that there are potentially complex nutrient cycles in this symbiosis, which have not been investigated. We used the cultivated symbiont Teredinibacter turnerae, which has been isolated from many shipworm species, as a model organism to elucidate controls on N2-fixation and N release in the shipworm symbiosis. Our results indicate that headspace oxygen concentration does not control biomass specific N2-fixation and respiration activity in T. turnerae, but it does influence the magnitude of the growth rate and timing of culture growth. Also, we examined the controls of oxygen on inorganic nutrient uptake rates, and documented a small amount of dissolved inorganic nitrogen release. While the N budget is only partially balanced, we provide indirect evidence for the allocation of fixed N to the excretion of exopolymeric substances and dissolved organic nitrogen; future studies that measure these additional N sinks are necessary to close the N budget. Although there are limitations of using pure cultures to investigate a complex symbiotic system, this study provides direct experimental evidence that T. turnerae has adaptations that are conducive to N2-fixation in gill bacteriocytes.

The production of rape and other leaf vegetables for local and export markets by smallholder farmers in sub-Saharan Africa has been constrained by soil fertility depletion associated with continuous cropping with inadequate addition of major nutrients like Nitrogen (N), Phosphorus (P) and Potassium (K). Biomass transfer of multipurpose tree prunings (usually legumes) to croplands has been shown to significantly increase the availability of soil N. Nitrogen mineralization of the leguminous biomass provides a major pathway through which the fixed N becomes available for use by other plants. The extent to which a specific type of plant residue influences soil fertility, crop growth and N recovery is in part determined by its biochemical qualities, decomposition patterns and the concurrent timing of nutrient release and crop nutrient demand. Consequently, the main challenge with the use of biomass from leguminous trees is to ensure that the release of N from mineralization is synchronised with the crop‟s demand. The utilization of multipurpose tree prunings as a source of nitrogen for the production of rape (Brassica napus L.) and spinach (Spinacea olearacea L.) was studied in a series of experiments. Prunings of four leguminous tree prunings commonly found in agroforestry systems namely Leucaena leucocephala, Calliandra calothyrsus, Acacia angustissima and Acacia karoo were used. The objectives of the study were: i) To determine the effect of chemical composition of the various leguminous tree prunings and their decomposition and N release patterns and ii) To evaluate the short term nutrient supply of the various leguminous tree prunings with or without supplemental inorganic nitrogen on the growth and yield responses of rape and spinach, respectively. Results indicated that rates of decomposition and N release decreased in the order: L. leucocephala > A. angustissima > C. calothyrsus > A. karoo. The ratios of lignin-to-N (r = 0.85) and soluble condensed tannins-to-N (r = 0.89) were negatively correlated with N release. The rates of decomposition and nitrogen mineralization of the prunings used as soil ameliorants were best predicted by their (lignin+soluble condensed tannin)-to-N ratios (r = 0.91). Soil amelioration with the various leguminous prunings significantly increased yields (P < 0.05) relative to the yields of plots that did not receive any amelioration. Total biomass, leaf number, area and size as well as saleable leaf yields increased linearly for all treatments. The quality of the prunings used as soil ameliorants significantly affected (P < 0.05) the efficiency of N recovery. Prunings of L. leucocephala which were the most labile had higher nutrient recovery rates and increased yields compared to the other leguminous amendments. Soil amendment with prunings of A. karoo on the other hand, which were the most recalcitrant, resulted in relatively lower N recovery rates. Supplementation of pruning-N with inorganic fertilizer further increased yields over the 0N treatment, indicating improved N recovery by the leafy vegetables. Crop growth and rates of nitrogen recovery of the leafy vegetables were corroborated by the short term nutrient supply capabilities of the leguminous prunings. Leguminous tree prunings can be used as a source of N for vegetable production as evidenced by the higher yields realized from amending the soil with the various prunings relative to the unfertilized plants. However, the rate and amount of N mineralized from the prunings and hence the net benefit obtained by the crop determines their suitability for vegetable production. / Dissertation (MSc Agric)--University of Pretoria, 2013. / gm2014 / Plant Production and Soil Science / Unrestricted

Pollution is one of the greatest concerns with pulverized coal combustion. With tightening standards on pollution emissions, more information is needed to create better design models. Burner modifications are the most efficient changes that can be made to assure sufficient carbon burnout and low NOx emissions. Experiments were performed in the BYU Flat Flame Burner (FFB) lab, operating under fuel rich conditions for pyrolysis experiments and fuel lean conditions for char oxidation experiments. Effects of temperature, coal rank, residence time, and post flame oxygen content on mass release, nitrogen release, and reactivity were examined. Elemental and Inductively coupled plasma (ICP) analyses were used to determine the mass and nitrogen release of coals and chars. FT-IR was used to determine gas phase nitrogen compositions on selected experiments. Results of char oxidation experiments were fit to a first-order model to obtain an Arrhenius pre-exponential factor, while activation energies were approximated using a published correlation. CPD model calculations were used to find experimental residence times and particle diameters that obtained full pyrolysis yields. Oxy-fuel experiments were performed by switching the burner diluent gas from N2 to CO2. Oxy-fuel experiments exhibited a rank effect in nitrogen release. Bituminous coal tests showed no statistically significant difference in mass or nitrogen release between the two conditions. A sub-bituminous coal exhibited a greater mass and nitrogen release for the same residence time under the CO2 environment, which could be due to early gasification of the char. Two samples of a chemically treated coal with different additive concentrations were tested against an untreated sample for combustion enhancement. The treated samples showed an increase on the order of 15% absolute in pyrolysis yield compared to the untreated sample. An increase in reactivity on the order of 35% was observed for the higher concentrated sample, but not for the lower treatment concentration. Gas phase nitrogen measurements showed both HCN and NH3 at the 1300 K gas temperature condition. HCN and NH3 release during pyrolysis was largely rank dependent, with more HCN formed initially than NH3 for 5 of the 6 samples. However, a Polish bituminous coal was found to have more NH3 than HCN. These nitrogen species data can be used to evaluate or refine nitrogen transformation mechanisms.

<p>Cereal rye (<i>Secale cereale</i>, L., CR) is the most commonly utilized cover crop species within the United States. Yet, the total land area planted to CR on an annual basis remains relatively low despite its numerous proven environmental benefits. The relatively low rates of CR adoption could be due to a dearth of knowledge surrounding certain agronomic and economic components of CR adoption. Currently, there exists knowledge gaps within the scientific literature regarding CR performance, N cycling, and associated economic risk. <a>Thus, to address the above-mentioned knowledge gaps, three individual studies were developed to: i) investigate the fate of scavenged CR nitrogen (N) amongst soil N pools, ii) assess the suitability of visible-spectrum vegetation indices (VIs) to predict CR biomass and nutrient accumulation (BiNA), and iii) characterize the economic risk of CR adoption at a regional scale over time.</a></p> <p>In the first study, ¹⁵N, a stable isotope of N, was used in an aerobic incubation to track the fate of CR root and shoot N among the soil microbial biomass, inorganic, and organic N pools, as well as explore CR N bioavailability over a simulated corn growing season. In this study, the C:N ratio of the shoot residues was 16:1 and the roots was 31:1 and differences in residue quality affected the dynamics of CR N release from each residue type. On average, 14% of whole plant CR N was recovered in the soil inorganic N pool at the final sample date. Correspondingly, at the final sampling date 53%, 33%, and less than 1% of whole plant CR N was recovered as soil organic N, undecomposed residue, and as microbial biomass N, respectively. Most CR N remained unavailable to plants during the first cash crop growing season subsequent to termination. This knowledge could support the advancement of N fertilizer management strategies for cropping systems containing cereal rye.</p> <p>In the second study, a commercially available unmanned aerial vehicle (UAV) outfitted with a standard RGB sensor was used to collect aerial imagery of growing CR from which visible-spectrum VIs were computed. Computed VIs were then coupled with weather and geographic data using linear multiple regression to produce prediction models for CR biomass, carbon (C), N, phosphorus (P), potassium (K), and sulfur (S). Five visible-spectrum VIs (Visible Atmospherically Resistant Index (VARI), Green Leaf Index (GLI), Modified Green Red Vegetation Index (MGRVI), Red Green Blue Vegetation Index (RGBVI), and Excess of Green (ExG)) were evaluated and the results determined that MGRVI was the best predictor for CR biomass, C, K, and S and that RGBVI was the best predictor for CR N and P. Furthermore, the final prediction models for the VIs selected as the best predictors developed in this study performed satisfactorily in the prediction of CR biomass, C, N, P, K, and S producing adjusted R² values of 0.79, 0.79, 0.75, 0.81, 0.81, and 0.78, respectively. The results of this study have the potential to aid producers in making informed decisions regarding CR and fertility management. </p> <p>In the final study, agronomic data for corn and soybean cropping systems with and without CR was collected from six states (Illinois, Indiana, Iowa, Minnesota, Missouri, and Wisconsin) and used within a Monte-Carlo stochastic simulation to characterize the economic risk of adopting CR at a regional scale over time. The results of this study indicate that average net returns to CR are always negative regardless of CR tenure primarily due to added costs and increased variability in cash crop grain yields associated with CR adoption. Further, the results demonstrate that the additional risk assumed by adopting CR is not adequately compensated for with current CR adoption incentive programs and that the risk premium necessary can be 1.7 to 15 times greater than existing incentive payments. Knowledge gained from this study could be used to reimagine current incentive programs to further promote adoption of CR.</p>