Theses & Dissertations
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This collection is exclusively made up of theses, dissertations, and project reports submitted as a requirement for completing a graduate degree at UPR-Mayagüez.
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PublicationManejo de fertilizante nitrogenado para la optimización del rendimiento de una línea pura de maíz (𝘡𝘦𝘢 𝘮𝘢𝘺𝘴 𝘓.)( 2015)Nitrogen (N) is one of the most important nutrients needed to maximize inbred maize (𝘡𝘦𝘢 𝘮𝘢𝘺𝘴 𝘓.) yield. An integrated management of the different contributing N sources to the agroecosystem can help improve N use efficiency. This study evaluated the effect of six fertilizer N levels (0, 34, 68, 102, 135 and 203 kg N ha⁻¹) and of a maize-fallow and maize-cowpea (𝘝𝘪𝘨𝘯𝘢 𝘶𝘯𝘨𝘶𝘪𝘤𝘶𝘭𝘢𝘵𝘢) rotation on inbred maize seed yield. The experiment was performed in a Jacaguas soil series (𝘓𝘰𝘢𝘮𝘺-𝘴𝘬𝘦𝘭𝘦𝘵𝘢𝘭, 𝘮𝘪𝘹𝘦𝘥, 𝘴𝘶𝘱𝘦𝘳𝘢𝘤𝘵𝘪𝘷𝘦, 𝘪𝘴𝘰𝘩𝘺𝘱𝘦𝘳𝘵𝘩𝘦𝘳𝘮𝘪𝘤 𝘍𝘭𝘶𝘷𝘦𝘯𝘵𝘪𝘤 𝘏𝘢𝘱𝘭𝘶𝘴𝘵𝘰𝘭𝘭𝘴) in the DowAgrosciences® experimental farm in Santa Isabel, Puerto Rico during the 2013-2014 winter season. Crop development was evaluated using plant height and flag leaf area as indicators. The parameters GreenSeeker®, SPAD-502® and N concentration in the indicator leaf were evaluated as indicators of N sufficiency. The cropping rotation maize-fallow and maize-cowpea did not affect seed yield performance (p>0.05). The fertilizer N level influenced seed yield (p<0.05) with an optimum fertilizer N level of 68 kg N ha⁻¹ for a seed yield of 2,918 kg ha⁻¹. The agronomic measurements of plant height, SPAD-502®, GreenSeeker® and N concentration in leaf tissue were adequate indicators of crop N sufficiency during the vegetative stages V6 to V12. In this study, the inbred maize line D065125VH requires 68 kg N ha⁻¹ to produce an optimum seed yield of 2,918 kg ha⁻¹ either with a rotation with cowpea or a fallow-maize cropping system.
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PublicationPresence, quantification and analysis of ironstone in a Guanajibo soil profile( 2012)Plinthite is defined as a weakly cemented material rich in iron, poor in humus –a mixture of clay and other diluents, such as quartz. It commonly occurs as dark red redox concentrations that can change irreversibly to ironstone hardpans or irregular aggregates on exposure to repeated wetting and drying. The presence of this material may affect plant root growth, soil fertility as well as soil drainage, acidity, and management. The studied soil belongs to the Guanajibo series and is located in the municipality of Cabo Rojo, Puerto Rico. The objectives of this study were: (i) determine soil layers color and ground ironstone colors and relate these to mineral components; (ii) quantify on volume and mass bases the presence of ironstone in each soil profile; (iii) determine mineral components in ironstone and soil by x-ray diffraction (XRD) and determine the content of iron and aluminum from each horizon by extracting the soil and grounded ironstone by two distinct methods: citrate-bicarbonate dithionite (CBD) and ammonium oxalate (OX). The CBD method extracts the crystalline fraction of the iron while the OX method removes the iron complexes with organic matter and amorphous iron. We suggest that reddish 10R and 5YR are associated to the presence of hematite and reddish yellow (2.5YR to 7.5YR) are associated with the presence of goethite. The highest content of ironstone was found in the upper horizon Ap, with a reduction in the next two lower horizons Bt and Btv1. An increase was observed in horizon Btv2 indicating that the soil was formed by alluvial deposits. The content of iron oxides and the effective cation exchange capacity (ECEC) were related to the clay content of each horizon. Higher clay content coincided with higher iron oxides content and higher ECEC. The opposite was observed for aluminum oxides content. The ECEC was low in all horizons, indicative of the presence of highly weathered minerals. This finding was confirmed by XRD analysis, showing minerals such as kaolinite, goethite, quartz, hematite and gibbsite. The main component of ironstone was goethite and the main component of the soil was kaolinite. Each horizon was classified as plinthic or not plinthic following the requirements established by the USDA- Natural Resources Conservation Service: the soil fine-fraction must have more than 2.5% of iron in the CBD extraction, and a ratio between OX and CBD extractable iron (OX/CBD) of less than 0.10. Of the five horizons only Btv1 was classified as plinthic, showing 2.8% CBD extractable iron and a ratio less than 0.10. The other horizons met with the requirement of a OX/CBD ratio less than 0.10, but all had less than 2.5% of iron extracted by the CBD method.
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PublicationEvaluación agronómica y morfológica de variedades de arroz (𝘖𝘳𝘺𝘻𝘢 𝘴𝘢𝘵𝘪𝘷𝘢 𝘓.) en secano bajo condiciones climáticas de Puerto Rico( 2013)Rice (Oryza sativa L.) is one of the most important food crops in the world, and specifically in Puerto Rico. However, water availability is a limiting factor for rice production that can be overcome through the development of drought resistant genotypes. In order to determine their adaptability to the climatic conditions of Puerto Rico, 30 upland rice varieties were grown at the Lajas Substation of the Agricultural Experiment Station of the University of Puerto Rico. The experiment was conducted under two planting systems, rainfed and flood irrigation, using a randomized complete block with a split plot arrangement and four replications. The planting systems constituted the main plots and the 30 rice varieties the subplots. The variables evaluated were flowering date, days to maturity, growth habit, plant height, grain yield and its components, biomass, incidence of Helminthosporium oryzae, resistance to shattering, lodging, drought index and harvest index. The results showed variability among genotypes under both planting systems. Cultivars ‘Chenire’ (4948 and 1875 kg/ha, flood irrigation and dryland, respectively) and ‘Pirogue’ (4074 and 1863 kg/ha) had higher grain yield under both conditions and were identified as the most drought resistant cultivars (STI>1.4), with high mean relative performance (MRP>3.6), higher harvest index and higher geometric mean productivity (GMP>2700). The cultivar ‘PR-358’ (13,830 and 6,510 kg/ha) produced the greatest amount of biomass among all cultivars. Under irrigated conditions, 1000 seed weight was 21.5 to 32.2 g, panicle length varied from 13.3 to 30.0 cm. The average height of the plants ranged from 0.80 to 1.77 m, the mean values of days to flowering and days to maturity were respectively 57-106 and 74-123 days, and the density of the panicle varied from compact to open. Under rainfed conditions, 1000 seeds weight ranged from 18.6 to 34.4 g, panicle length varied from 13.3 to 28.1 cm, the average height of the plants ranged from 0.55 to 1.14 m. The mean values of days to flowering and days to maturity were, respectively, 61-109 and 81-129 days, and the density of the panicle varied from compact to intermediate. Under rainfed conditions, the variables days to flowering, growth habit and maturity were not correlated with any of the other variables. Furthermore, the results of this research suggest that cultivars ‘Chenire’, ‘Pirogue’, ‘IR-64’ can be planted under both systems and can be used for the development of rice with greater drought tolerance.
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PublicationMolecular simulations of model Langmuir monolayers( 2005)The study of Langmuir monolayers has generated the attention of researchers because of their unique properties and their not well understood phase equilibrium. These monolayers exhibit interesting phase diagrams where the unusual liquid-liquid equilibrium can be observed for a single component monolayer submitted to an external applied pressure. In this study, the thermodynamic properties of a model Langmuir monolayer were determined using two types of computer simulations. First, Monte Carlo simulations in the Isothermal-Isobaric ensemble were used to obtain adsorption isotherms of Langmuir monolayers. The results clearly show coexistence of two liquid phases, denominated as liquid expanded state (LES) and liquid condensed state (LCS). Radial distribution function and distribution functions of enthalpies for the monolayer were also computed to clearly identify each liquid phase and the coexistence region. A second model was used to obtain the critical properties for this model system. The phase equilibrium between the liquid phases and the LES-Vapor (V) phases has been considered using Monte Carlo computer simulations in the Standard Virtual Gibbs Ensemble. The Caillete- Mathias phase diagrams were constructed and two models were implemented in order to determine the critical parameters of the system. Specifically, the Ising Model and the rectilinear approximation were used to identify the critical temperature (Tc*) and the critical density (ρc*), respectively. These critical parameters were identified by varying the interaction between the surfactant molecules and the aqueous phase. Finally, we have identified the coexistence between the LES and LCS states, in agreement with experimental and theoretical evidence in the literature. Furthermore, we have successfully identified the critical parameters Tc* and ρc* for the LES-LCS and the LES-V equilibrium of the monolayer.
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PublicationThe role of ultrafast events of hemoglobin I and hemoglobin II ligand complexes from Lucina pectinata( 2005)In hemeproteins, the nature of the distal iron ligand, the distal heme environment and the heme iron electronic structure are essential factors in ligand binding dynamics. Ultrafast time resolved absorption studies were performed in HbI(Fe III)CN, HbII(Fe III)CN, HbI(Fe II)CN and HbII(Fe II)CN to evaluate the effect of distal heme environment and the iron electronic structure. The time constants for the cyanide (CN) relaxation of each compound were 3.12 ps, 3.57 ps, 5.78 ps and 5.68 ps respectively. According the results, HbI and HbII ferric CN derivatives did not photodissociate and were dominated by the relaxation of an unphotolyzed derivative through vibrational cooling. In contrast, the HbI and HbII ferrous CN complexes suggested photodissociation of the ligand with no geminate recombination and the ultrafast spectra of both species were dominated by the relaxation of the deoxy species. The results suggested also that the Phe/B10/Tyr substitution did not affect CN dynamics. However, difference in the relaxation time constants was observed between HbICN and HbIICN iron oxidation state. This was interpreted in terms of differences in the relaxation pathway of both species due to their iron electronic nature. Time resolved ultrafast absorption studies were also performed in HbICO, HbIICO and HbI mutants; HbI(Phe/B10/Tyr)CO, HbI(Phe/B10/Val)CO and HbI(Gln/E7/Val)CO. The relaxation time constants of CO derivatives were 9.19 ps, 2.87 ps, 6.23 ps, 4.29 ps and 5.80 ps for HbI, HbII, HbI(Phe/B10/Tyr), HbI(Phe/B10/Val) and HbI(Gln/E7/Val), respectively. Ultrafast results indicated that the dynamics of the HbI mutants resembled that of HbI, suggesting that they both have the similar structural conformational arrangement. The differences between HbII and the HbI(Phe/B10/Tyr) in signal relaxation support the suggestion that the orientation of these distal environment may vary in both adopting two different conformation (open and closed). Similarly, in HbI the docking site process may help to establish a barrier to the reverse rebinding process and thereby inhibits ultrafast geminate ligand rebinding in the closed conformation.