Browsing by Subject "nitrogen"
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Item A conceptual model to estimate the nitrogen requirement of corn (Zea mays L.)(Texas A&M University, 2007-04-25) Lopez Collado, Catalino JorgeThe objectives of this work were to evaluate the vegetative parameters used to estimate crop N demand and to estimate the accuracy and precision of the conceptual model of fertilization using an error propagation method. Corn plants were collected throughout the entire crop life cycle to determine the fresh and dry weight of the aboveground biomass and roots, root index, plant height, and corn grain yield. Three experiments were conducted, two under field conditions and one under greenhouse conditions. In the first field experiment in 2002, three sites were selected. The first site was the Texas A&M University (TAMU) Agricultural Experiment Station Research Farm in which a Ships clay soil was used. The second site was a cooperative farmer's land on a Weswood silt loam soil in Burleson County. These first two sites used Pioneer 32R25 as the corn hybrid. The third site was also a Ships soil in the TAMU Farm, but Dekalb 687 was the corn variety. In 2003, the second experiment was on a Ships soil in the field of TAMU Farm, and the third experiment was conducted in a greenhouse using Ships and Weswood soil. No differences in the root index and harvest index were observed, even when the Dekalb 687 hybrid was included. Variations in plant N concentration, moisture content, and yield were noted, but followed predictable patterns with time over the season. These parameters were consistent throughout the entire life cycle of the crop. The linear relationship between the fresh weight of aboveground biomass and fresh weight of roots was R2 = 0.92, the moisture content of corn plants over time was fit to a second grade polynomial with R2 = 0.98, and plant N content had a close linear relationship (R2=0.90) with the total plant dry weight, including roots, at harvest. The accuracy of the conceptual model was low under field conditions (55%), but high under greenhouse conditions (90%). Precision of the conceptual model was low both in the field (194%) and the greenhouse (115%) conditions.Item Continuous multi-phase feeding of broiler chickens(Texas A&M University, 2005-02-17) NasrilContinuous multi-phase feeding of broiler chickens was evaluated to optimize broiler nutrition and minimize environmental impact related to excess nitrogen in poultry manure. Four experiments were conducted. Experiments 1 and 2 studied effects of continuous multi-phase feeding during a 3-week starting period using battery brooders while experiments 3 and 4 evaluated multi-phase feeding during a traditional 7-week growing period using both battery brooders and floor pens. In the first and second experiments, the nutrient content of the multi-phase diets was changed every 24 hours in comparison to single-phase feeding. Results indicated that during the starter period, continuous multi-phase feeding had no significant influence on feed consumption, daily gain, feed to gain ratio or fecal nitrogen. In the third and fourth experiments, a four phase industry type broiler feeding program was compared to intensive multi-phase feeding programs created by linearly blending three different diets based on typical industry nutrient values and a commercial nutrient modeling computer program (EFG Natal?). In both intensive multi-phase feeding programs, the diets were changed every three days over a 7-week growth period. Broilers in experiment 3 were raised in Petersime battery brooders to primarily access nitrogen balance while birds in experiment 4 were raised in a floor pen on pine shaving litter to resemble commercial broiler production. The results indicated that intensive multi-phase feeding improved body weight gain and feed to gain ratio only in weeks 5 and 6 but not during the overall 7-week period. Nitrogen excretion and nitrogen retention were unaffected by the intensive multi-phase feeding systems. Economic analysis indicated that intensive multi-phase feeding programs could potentially lower feed costs per kilogram of gain. However, the high cost of implementing a continuous multi-phase feeding system may not justify the relatively small gain in lower feed cost per kilogram of gain. In conclusion, continuous multi-phase feeding of broiler chickens using corn-soy diets does not appear to be justified by either increased performance or reduced nitrogen excretion.Item The effect of nutrient limitations on the production of extracellular polymeric substances by drinking-water bacteria(2013-05) Evans, Ashley Nichole; Kirisits, Mary JoBiological filtration (biofiltration) of drinking-water is gaining popularity due the potential for biodegradation of an array of contaminants not removed by traditional drinking-water processes. However, previous research has suggested that biomass growth on biofilter media may lead to increased headloss, and thus, greater energy and water requirements for backwashing. Research has suggested that the main cause of headloss might be due to extracellular polymeric substances (EPS) rather than the bacterial cells themselves. As EPS production has been shown to increase under nitrogen- and phosphorus-limited or -depleted conditions, the goal of this research was to add to the body of knowledge regarding biofiltration by studying the relationship between EPS production and nutrient limitations in drinking-water. Batch experiments with a synthetic groundwater were run with a mixed community of drinking-water bacteria under nutrient-balanced (a molar carbon to nitrogen to phosphorus ratio [C:N:P] of 100:10:1), nutrient-limited (e.g., C:N:P of 100:10:0.1), and nutrient-depleted conditions (C:N:P of 100:0:1 or 100:10:0). After 5 days, growth was measured as the optical density at 600 nanometers (OD600), and the concentrations of free and bound carbohydrates and proteins, the main components of EPS, were measured. In batch experiments with 2.0 and 0.2 g/L as carbon (mixture of acetic acid, mannitol and sucrose) increases in EPS production per OD600 and decreases in growth were noted under nutrient-depleted conditions. When the same experiments were conducted with a pure culture of Bacillus cereus, bound polysaccharides normalized to OD600 increased under nitrogen- and phosphorus-depleted conditions. Since previous research suggested that Bradyrhizobium would be an important player in EPS production in drinking-water biofilters, similar batch experiments were conducted with Bradyrhizobium. However, due to experimental challenges with Bradyrhizobium japonicum USDA 110, differences in EPS production under nutrient limitations could not be reliably assessed. Additional work is required with Bradyrhizobium. Recommendations for future work include the replication of these batch conditions in steady-state chemostats containing biofilm attachment media and in bench-scale columns. Additionally, future work should include experiments at carbon concentrations as low as 2 mg/L to match typical carbon concentrations in drinking-water biofilters.Item Grassland carbon and nitrogen dynamics: effects of seasonal fire and clipping in a mixed-grass prairie of the southern great plains(Texas A&M University, 2006-08-16) Harris, Wylie NealPlant production and soil microbial biomass (SMB) in grassland ecosystems are linked by flows of carbon (C) and nitrogen (N) between the two groups of organisms. In native mixed grasslands of the southern Great Plains, these cycles are strongly influenced by climate. They may also be modulated by the timing and intensity of disturbances such as fire and clipping. We assessed the relative influence of climate and disturbance on plant community and soil C and N dynamics. Combined effects of fire and clipping were assessed in a 2x3 factorial design including spring fire and light clipping or continuous clipping. Seasonal fire effects were evaluated in a one-way analysis incorporating spring and fall fire in unclipped plots. Plant cover and biomass (by functional type), litter mass, SMB C and N, soil density fraction concentration and composition, soil organic C, total N, and inorganic N, soil temperature and moisture, soil respiration, and net N mineralization were measured at monthly intervals. C4 grasses were unaffected by fire or clipping, probably as a result of summer drought in both studyyears. Clipping reduced cover of C3 annual grasses but increased that of C3 perennials, resulting in no net change in C3 grass biomass. Fire did not affect C3 grass cover or biomass. Both fire and clipping reduced litter mass. This was reflected in seasonal declines in SMB C in fire treatments, suggesting that the primary input of microbial C in this ecosystem occurs by decomposition of current-season plant litter. Litter removal offers a single mechanism by which fire-induced increases in soil temperature and reductions in light soil density fraction concentration, soil moisture, and net N mineralization rates may be explained. Lack of treatment effects on soil respiration rates suggest that plant roots represent an important component of the plant-soil C cycle, not quantified in this research. Overall, treatment effects were relatively minor compared to seasonal climate-related changes in response variables, particularly in light of repeated summer drought.Item Modern Calibrations of Temperature and Nutrient Proxies for Paleoenvironmental Reconstructions in Tropical Mollusks(2014-12-15) Graniero, Lauren EMolluscan shell O- and C-isotope values have been shown to be useful indicators of upwelling and freshwater input (and thus nutrient status) in nearshore marine environments, but few studies have had the accompanying long term measurements of water ?^18O (?w) and dissolved inorganic carbon (DIC) ?^13C needed to best test the fidelity of shell isotope values as environmental indicators. Previously measured seawater ?w and ?^13CDIC values collected biweekly from 2011-2012 allow us to determine if shell ?^18O and ?^13C values record temperature, ?w, ?^13CDIC, and ultimately nutrient status in tropical waters. Conus, Vasum, and Strombus shell ?^18O values reflect predicted seasonal upwelling and freshening signals in the Pacific and seasonal freshening with minimal upwelling in the Caribbean. Both Pacific and Caribbean shell ?^13C profiles show cyclicity, but only Conus samples from Veracruz Beach (Pacific) record seasonal changes in ?13CDIC. This observation likely results from: (1) more distinct seasonal ?^13CDIC variation in Pacific waters compared with Caribbean waters and (2) greater availability of metabolic CO2 for shell growth in Strombus, which we hypothesize is related to greater activity associated with an herbivorous feeding habit. To examine N-isotope ratios (^15N/^14N) in tissues and shell organic matrix of bivalves as a proxy for natural and anthropogenic nutrient fluxes in coastal environments, Pinctada imbricata, Isognomon alatus, and Brachidontes exustus bivalves were live-collected and analyzed from eight sites in Bocas del Toro, Panama. Sites include a variety of coastal environments, including more urbanized, uninhabited, riverine, and oceanic sites. At all sites there is no single dominant source of organic matter contributing to bivalve ?^15N and ?^13C values. Bivalve ?^15N and ?^13C values likely represent a mixture of mangrove and seagrass N and C, although terrestrial sources cannot be ruled out. Despite hydrographic differences between end-members, we see minimal ?^15N and ?^13C difference between bivalves from the river-influenced Rio Guarumo site and those from the oceanic Escudo de Veraguas site, with no evidence for N from open-ocean phytoplankton in the latter. Lastly, ?^15N values of tissue and shell organic matrix correlate significantly for pterioideans P. imbricata and I. alatus. Thus for these species, N isotope studies of historical and fossil shells may provide records of ecology of past environments.Item Nitrogen nutrition of Alexandrium tamarense : using δ¹⁵N to track nitrogen source used for growth(2009-05) Smith, Christa Belle; Erdner, Deana L.; Pease, Tamara Kaye; McClelland, James W.Alexandrium tamarense is a harmful algal species that can produce saxitoxins, a suite of powerful neurotoxins that bioaccumulate up the food chain and can have severe economic and health impacts. With harmful algal blooms increasing temporally and spatially, it is important for us to understand the relationship between harmful algal blooms and nutrients, particularly nitrogen from anthropogenic sources. To this end, the stable nitrogen isotopic composition (δ¹⁵N) of medium nitrate, algal cells and toxin in both nitrogen-replete and nitrogen-limited batch cultures of A. tamarense were measured in order to assess the potential for using the δ¹⁵N of the toxin as a tracer of the nitrogen source used for growth. A. tamarense cells grown under nitrate-replete conditions were depleted by 1.5‰ relative to the growth medium, and saxitoxin was depleted by 1.5‰ relative to the whole cells. Under nitrate-limiting conditions, the isotopic difference between cells and saxitoxin changed as nitrate in the growth medium was depleted, indicating uncoupling of toxin synthesis and cell growth rates under changing external nutrient conditions. Determination of the absolute magnitude of the isotopic differences between the medium nitrate and either the cells or the saxitoxin was confounded by 1) using two different nitrate sources – one nitrate source was used to grow the inoculum and a different nitrate source was used for the experimental medium - with different ‰ values and 2) the presence of an unidentified, isotopically-light, nitrogen blank in the low-nitrate medium samples. I conclude that STX nitrogen isotope values have the potential to be used as nitrogen source indicators. However, overall fractionation between whole cells and STX is unknown due to the uncoupling between cell growth and STX synthesis observed during my nitrogen-limited experiment. Based on previous research on cell growth and toxin production dynamics under different nutrient regimes, it is also reasonable to assume that the observed results here may differ if a different nitrogen source was utilized by the cells for STX production. Further research could include isotope analysis of cultures grown on different nitrogen sources, such as ammonium and urea; isotopic analysis of additional compounds, such as amino acids; or use of additional stable isotopes, such as C or O.Item Optimization of row spacing and nitrogen fertilization for cotton(Texas A&M University, 2004-09-30) Clawson, Ernest LeslieUltra-narrow row (UNR) cotton (Gossypium hirsutum L.) is a production system using high plant populations in reduced row spacings. The responses of this production system to nitrogen fertilizer have not been fully investigated. Evaluations of yield and earliness of harvest are also important. A three-year study was conducted at the Texas Agricultural Experiment Station farm, Burleson County, TX, on a Ships clay (very-fine, mixed, active, thermic Chromic Hapluderts) and a Weswood silty clay loam (fine-silty, mixed, superactive, thermic Udifluventic Haplustepts). A split plot design was used. Nitrogen fertilizer rates of 0, 50, 101, and 151 kg N ha-1 were applied as the whole plots and row spacings of 19, 38, and 76 cm were established as the split plots. Data included lint yield and yield components, as well as earliness of crop maturity and earliness-related parameters such as boll distribution. Lint yield was increased by higher nitrogen rate. There was no nitrogen rate by row spacing interaction on lint yield, implying fertilizer rates do not need to be changed for UNR systems. Reductions in row spacing did not significantly affect lint yield in any year. Responses such as reduced bolls per plant, increased plant populations, increased ginout, and decreased boll size were often significant and combined to allow the crop to maintain equivalent yields as row spacings were reduced. The slight UNR earliness advantages were probably due to changes in boll distribution. Based on these results, increases in lint yield and earliness may not reliably contribute to the profitability of UNR cotton.Item Pilot-Scale Fermentation and Laboratory Nutrient Studies on Mixed-Acid Fermentation(2011-08-08) Smith, Aaron DouglasVia mixed-culture fermentation, the MixAlcoTM produces carboxylic acids, which are chemically converted into industrial chemicals and hydrocarbon fuels. Using pilot fermentation data, The Continuum Particle Distribution Model (CPDM) overestimated acid concentration (30?90% error) but more closely estimated conversion (<15% error). Incorporating the effect of air into the model reduced the absolute error of all predictions by >50%. To analyze fermentation data with semi-continuous streams, the Slope method calculates the average flowrate of material from the slope of the moving cumulative sum with respect to time. Although the Slope method does not significantly improve accuracy, it dramatically reduces error compared to traditional techniques (>40% vs. <2%). Nutrients are essential for microbial growth and metabolism. For a four-bottle fermentation train, five nutrient contacting patterns (single-point nutrient addition to Fermentors F1, F2, F3, F4, and multi-point parallel addition) were investigated. Compared to the traditional nutrient contacting method (all nutrients fed to F1), the near-optimal feeding strategies improved exit yield, culture yield, process yield, exit acetate-equivalent yield, conversion, and total acid productivity by approximately 31%, 39%, 46%, 31%, 100%, and 19%, respectively. To estimate nitrogen concentration profiles, a segregated-nitrogen model uses separate mass balances for solid- and liquid-phase nitrogen; the nitrogen reaction flux between phases is assumed to be zero. Using five fermentation trains, each with a different nutrient contacting pattern, the model predictions capture basic behavior; therefore, it is a reasonable tool for estimating and controlling nitrogen profiles. To determine the optimal scenario for mixed-acid fermentations, an array of batch fermentations was performed that independently varied the C/N ratio and the blend of carbohydrate (office paper) and nutrient (wet chicken manure (CM)). Reactant was defined as non-acid volatile solids (NAVS). C/N ratios were based on non-acid carbon (CNA). A blend of 93% paper and 7% wet CM (dry basis) with a C/N ratio of 37 g CNA/g N had the highest culture yield (0.21 g acidproduced/g NAVSinitial), total acid productivity (0.84 g acidproduced/(Lliq?d)), and conversion (0.43 g NAVSconsumed/g NAVSinitial).Item Soil and Plant Responses to Lipid-Extracted Algae(2014-08-25) Lewis, KatieAlthough algae is much more productive per area of cultivation compared to first-generation biofuel feedstocks, algae production may not be economically sustainable without high value coproducts. One of many possible coproducts may be algae residue following lipid extraction that might be used as a soil amendment for agricultural production. The overall objective of this series of experiments was to determine the feasibility and management strategies required to best utilize lipid-extracted algae (LEA) as an organic fertilizer and soil conditioner. Effects of LEA on nutrient availability, soil C storage, aggregate stability, soil acidity and salinity, greenhouse gas (GHG) loss, changes in soil microbial activity and community composition, and forage growth were assessed. Soil organic C (SOC) measured 392-d after amending soil with 1.5 and 3.0% LEA for a microcosm incubation was increased by approximately 0.2 and 0.3% OC, respectively, compared to the control. Approximately 10% of added LEA-C was mineralized and lost as CO2 compared with 15% of added wheat straw-C. Lipid-extracted algae enhanced aggregate formation and soil SOC storage in microaggregates at 0-15 cm depth over a 12-month field incubation with greater mean weight diameter by 12 months and approximately 42 and 66% of total SOC from 1.5 and 3.0% LEA treatments, respectively. With glass house and field studies, nutrient availability was enhanced with LEA amendments; however, LEA applied at a 30% rate decreased seedling emergence of foxtail millet (Setariaitalica) and salt-tolerant ryegrass (Lolium multiflorum), and thus, herbage mass (HM) and nutrient uptake were also decreased. Soil amended with 1.5% a LEA, however, increased HM of peal millet (Pennisetum glaucum), salt-tolerant ryegrass, and a sorghum-sudangrass hydrid [(Sorghum bicolor (L.) Moench ? Sorghum Sudanese (P.)]. Soil LEA-application should be a significant source of organic nutrients for microbial transformation and usage and plant uptake, and thus, may reduce inputs of inorganic fertilizer. The potential for LEA amendments enhancing aggregate formation, and consequently soil C storage, was indicated by mean weight diameter and SOC within macro- and microaggregates increasing over time. Lipid-extracted algae application may be a means of mitigating SOC losses due to agricultural production, and also, maintaining or improving soil structure and quality. However, problems with excess soil salinity, sodicity, and nutrients may occur at high LEA addition rates.Item Thermal signature reduction through liquid nitrogen and water injection(Texas A&M University, 2005-02-17) Guarnieri, Jason AntonioThe protection of aircraft against shoulder fired heat seeking missiles is of growing concern in the aviation community. This thesis presents a simple method for shielding the infrared signature of a jet engine from heat seeking missiles. The research efforts investigated two approaches to shield the thermal signature of the Noel Penny Type 401 turbojet at the Texas A&M University Propulsion Lab Test Cell. First, liquid nitrogen was injected through a manifold at a flow rate equivalent to the flow rate of exhaust gases, producing a small temperature reduction in the exhaust but no infrared shielding. Second, water was injected at a flow rate of 13% of the flow of exhaust gases, producing a greater temperature reduction and some shielding. Water was then injected through a manifold at a ?ow rate of 118% of the flow rate of exhaust gases, producing a substantial reduction in temperature and complete shielding of the infrared signature. Additionally, numerical simulations were performed using FLUENT to support these experiments. Results are presented in the form of thermocouple data and thermal images from the experiments, and in the form of temperature contours and streamtraces from the simulations.Item Urban Sodicity in a Humid Subtropical Climate: Impact on Biogeochemical Cycling(2012-10-19) Steele, Meredith KateUnderstanding the mechanisms of non-point source carbon and nutrients in urban watersheds will help to develop policies to maintain surface water quality and prevention of eutrophication. The purpose of this dissertation is to investigate the impact of sodium on carbon and nutrient leaching from the two main contributors; soil and leaf litter, and calculate the sodium exports in a humid subtropical urban river basin. The first chapter reviews the current literature on urbanization in watersheds. Chapter II quantifies the carbon and nutrient in intact soil core leachates and in water extractable solution from urban soils collected from 33 towns and cities across the state of Texas. Chapter III investigates the impact of sodicity and salinity on water extractable organic carbon and nitrogen from vegetation. Chapter IV investigates the export of sodium and chloride from the upper Trinity River basin. The results derived from this study indicate that sodium exports are elevated in urban watersheds and further that sodium in irrigation water elevates the loss of carbon and nutrients from both watershed soil and senesced vegetation and that this may contribute to high concentrations in urban freshwaters.