Thesis (Ph. D.)--Biology, Georgia Institute of Technology, 2006. / Klausmeier, Christopher, Committee Member ; Montoya, Joseph, Committee Member ; Snell, Terry, Committee Member ; Sarnelle, Orlando, Committee Member ; Hay, Mark, Committee Chair.

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Thesis (M. Sc.)--University of Canterbury, 2003. / Typescript (photocopy). Includes bibliographical references (leaves 104-110). Also available via the World Wide Web

No description available.

Thesis (M.S.)--Baylor University, 2009. / Includes bibliographical references (p. 65-72).

The popularity of growers using only postemergence (POST) herbicides for weed management in soybean was enabled by the commercialization of glyphosate-resistant soybean. The efficacy and flexibility provided by this technology diminished the use of soil residual herbicides and arguably, increased soybean yield loss from early-season weed competition. While, the rapid evolution and biogeographical spread of herbicide-resistant weeds, especially glyphosate-resistant biotypes, has renewed interest into the use of soil residual products, herbicide-resistant soybean technologies continue to be developed that may once again entice growers into POST-only weed management systems. The commercial interest in soybean yield advancements justifies further characterizing the benefits provided by early-season weed control beyond those of herbicide-resistance management. Furthermore, as awareness heightens regarding techniques that will enhance the sustainability of agro-ecosystems, specific focus on resource utilization will help to evaluate the viability of this weed management strategy. Field experiments were conducted across four sites throughout southern Illinois in 2012 and 2013 to study the influence of early-season weed management strategies on soybean nutrient accumulation, grain yield parameters, and the acquisition of nutrients by broadleaved and grass weeds. Increasing periods of weed competition duration were established by removing weeds at heights of 10, 20, 30 or 45 cm with glyphosate. A weed-free treatment utilizing a comprehensive soil residual and POST herbicide program was included to implement a weed-free comparison. Two standard herbicide management strategies that simulate common grower practices were also evaluated for comparison: flumioxazin PRE followed by glyphosate POST and two sequential POST glyphosate applications. Averaged across all 11 mineral nutrients analyzed in this experiment, broadleaved weeds accumulated 149 and 108% more nutrients than grasses in 2012 and 2013, respectively. Competition from 20-cm weeds reduced the acquisition of N, P, Ca, Mg, S, Fe, B, Cu, and Zn by soybean in 2012; these nutrients in addition to K and Mn were reduced by the same level of competition in 2013. N and Fe were the nutrients in soybean most notably impacted by weed interference. Reductions in soybean grain yield were the result of competition with 30-cm weeds in 2012, and 10-cm weeds in 2013; while, both standard herbicide regimens yielded less than the weed-free treatment in 2013 only. Additionally in 2013, average soybean seed weight and grain oil content was reduced when weeds were not removed before a height of 10 and 20 cm, respectively. The rate of decomposition and nutrient release was measured for waterhemp and giant foxtail desiccated by glyphosate at heights of 10, 20, 30, and 45 cm in two southern Illinois soybean fields. Weed biomass was grown under greenhouse conditions to ensure homogeneity and litterbag methodology was utilized to track in situ mass and nutrient losses, expressed as a decay constant (k) regressed over time according to the single exponential decay model. The effect of specie and height both had a strong influence on the intrinsic properties of the weed biomass and the associated rate of decay. Concentrations of the recalcitrant cell wall components (cellulose, hemicellulose, and lignin) were generally greatest as weed height (plant age and development) increased and with giant foxtail compared with waterhemp. Ca, Mg, and S concentrations were greater in waterhemp, while N was greater in giant foxtail. N and K concentrations decreased with increasing weed height. After 16 weeks, 10-cm waterhemp and giant foxtail detritus had lost 10 and 12% more mass compared to the 45-cm height. Decomposition rates revealed mass loss was highest for 10-cm waterhemp (kD = 0.022) and lowest for 45-cm giant foxtail (kD = 0.011) and this process was negatively correlated to the overall amount of cell wall constituents (r = -0.73). Nutrient release rates followed a similar trend in that shorter (younger) weeds and waterhemp liberated nutrients more readily. Across all tested plant material, K was the nutrient most rapidly released, whereas, Ca was the most strongly retained nutrient. Although the pressing challenge of managing herbicide-resistant weeds justifies the implementation of early-season weed control tactics, this research suggests there are ancillary benefits that are provided by this strategy. The use of a robust, broad-spectrum soil residual herbicide program in conjunction with timely POST applications provides the foundation for early-season weed management, thereby minimizing non-crop nutrient use and enhancing the nutrient acquisition capacity in soybean. This strategy facilitates more sustainable crop production by requiring fewer supplemental nutritional inputs while also protecting grain yield.

As an alternative to testing nutrient components separately, four common media formulations were used: Murashige and Skoog (MS), Driver and Kuniyuki (DKW), woody plant medium (WPM) and Anderson's revised medium (AND). Each medium was tested separately. Then high salts formulation (MS and DKW) were mixed with low salts formulation (WPM and AND) at a half and half concentration. In total, eight different media were tested spanning high, intermediate and low nutrient salts concentrations. To test the media two different plant species were chosen, a woody species Hydrangea quercifolia (oakleaf hydrangea) and an herbaceous species Tagetes erecta (African marigold). Nodal explants were harvested from H. quercifolia `Dayspring' stock plants grown in raised beds in a greenhouse. After being disinfested, explants were placed on the eight treatment media, along with 1.0 µM benzyladenine (BA) and 1.0 µM indolebutryic acid (IBA). In addition to the plant growth regulators (PGR's), 10 ppm Orthene insecticide and 150 ppm Benlate fungicide were included in the tested media to prevent contamination from a spider mite infestation. Explants placed on WPM were significantly different than explants on other media. WPM explants initiated growth the most, but elongation was sluggish and leaves showed signs of deficiencies after 8 to 10 weeks in vitro. Intermediate salts media DKW/WPM and DKW/AND had fewer explants initiate growth then explants on WPM, but the few that did elongated. These explants had the maximum lengths of any other explant on all other treatments. Tagetes erecta `Marvel Orange' seeds were sown in polyethylene flats in a lab under cool white fluorescent lamps. After about a month apical shoot tips were harvested, surface disinfested, and placed in vitro on the eight treatment media, with the same PGR's and additives as the hydrangea experiment. Tagetes explants responded substantially faster than the Hydrangea explants, with growth initiating on all treatments within a week. Initially there were significant differences between treatments, but after 3 months in vitro there were no differences between treatments. Although no data was taken, there was observed differences between the treatment media. Explants on low salts media of WPM and AND show signs of nutrient deficiencies, with high salt media showed no deficiencies. Overall the best growth of axillary shoots was seen on high salt media of MS and DKW.

Made available in DSpace on 2014-06-11T19:23:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-28Bitstream added on 2014-06-13T18:09:32Z : No. of bitstreams: 1 peixoto_fc_me_jabo.pdf: 395583 bytes, checksum: 5301166e57d35ee4c63acfab04548a15 (MD5) / Sekita Agropecuaria / Com o objetivo de avaliar o crescimento e o acúmulo de macronutrientes em cenoura „Forto‟ e obter equações que melhores os representem, conduziu-se um experimento em São Gotardo (MG), de maio a setembro de 2004. As amostragens de plantas foram realizadas aos 40, 50, 60, 70, 80, 90, 100, 110 e 120 dias após a semeadura (DAS), para determinação da matéria seca e do acúmulo de macronutrientes em folhas e raiz da cenoura. Aos 40 DAS, cinco dias após ter sido realizado o desbaste, a planta de cenoura „Forto‟ apresentava 0,18 g e 0,04 g em matéria seca de folhas (MSF) e de raiz (MSR), respectivamente. A partir de então, até 88 DAS, a partição de matéria seca mostrou-se favorável na parte aérea. A MSR de cenoura foi pequena até dois terços do cultivo, ou seja, 80 DAS. A partir de então, verificou-se que a quantidade de matéria alocada nesta parte da planta teve forte incremento, ultrapassando, aos 88 DAS, a quantidade de MSF. O acúmulo de nutrientes foi pequeno até 60 DAS, coincidindo com o período de menor acúmulo de matéria seca. A ordem decrescente de macronutrientes acumulados pela cultura foi K, N, Ca, P, S e Mg, nas quantidades de 906,7; 438,0; 155,5; 87,4; 58 e 37,6 mg planta-1, respectivamente. A raiz participou com 60,5% do acúmulo de N, 86,1% de P, 58,0% de K, 25,5% de Ca, 55,6% de Mg e 65,5% de S. / In order to quantify the growth and accumulation of macronutrients of carrot 'Forto', and obtain equations that best represent them, it was carried out experiment in the São Gotardo (MG), from May to September of 2004. Samples of plants were taken at 40, 50, 60, 70, 80, 90, 100, 110 and 120 days after sowing (DAS) to determine dry matter and accumulation of macronutrients in leaves and roots of carrot. At 40 DAS, five days after thinning, the plants had 0.18 g and 0.04 g of leaves dry mass (LDM) and root dry mass (RDM), respectively. From then, until 88 DAS, the partitioning of dry matter in the aerial part were more pronounced. The RDM was low until 80 DAS, which corresponded to two thirds of the crop cycle, from when the amount of material allocated in this part of the plant had strong growth surpassing at 88 DAS the amount of LDM. The nutrient accumulation was small until 60 DAS, coinciding with the period of lower dry matter accumulation in the plant. The order of decreasing macronutrient accumulation by the plant was K, N, Ca, P, S e Mg, in the amounts of 906.7, 438.0, 155.5, 87.4, 58.0 and 37.6 mg plant-1, respectively. The commercial root participated with 60.5% of the accumulation of N, 86.1% of P, 58.0% of K, 25.5% of Ca, 55.6% of Mg and 65.5% of S.

abstract: Nitrate contamination to groundwater and surface water is a serious problem in areas with high agricultural production due to over application of fertilizers. There is a need for alternative technologies to reduce nutrient runoff without compromising yield. Carbon nanoparticles have adsorptive properties and have shown to improve germination and yield of a variety of crops. Graphite nanoparticles (CNP) were studied under a variety of different fertilizer conditions to grow lettuce for the three seasons of summer, fall, and winter. The aim of this thesis was to quantify the effect of CNPs on nitrate leaching and lettuce growth. This was accomplished by measuring the lettuce leaf yield, formulating a nutrient balance using the leachate, plant tissue, and soil data, and changing the hydraulic conductivity of the soil to assess the effect on nutrient mobility. summer and fall experiments used Arizona soil with different amounts of nitrogen, phosphorus, and potassium (NPK) fertilizer being applied to the soil with and without CNPs. The winter experiments used three different soil blends of Arizona soil, Arizona soil blended with 30% sand, and Arizona soil blended with 70% sand with a constant fertilizer treatment of 30% NPK with and without CNPs. The results showed that the 70% NPK with CNP treatment was best at reducing the amount of nitrate leached while having little to no compromise in yield. The winter experiments showed that the effectiveness of CNPs in reducing nitrate leaching and enhancing yield, improved with the higher the hydraulic conductivity of the soil. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2018

Abstract Plants have evolved various adaptive strategies for balancing the benefits and costs of having a high affinity for resources, plasticity of growth allocation and mycorrhizal symbiosis. The relative growth rates of mycorrhizal and non-mycorrhizal plants were modelled for stable and variable nutrient availability. Mycorrhizal plants had higher growth rates at low and non-mycorrhizal plants at high nutrient availability. Variation in nutrient availability reduced the growth rate of mycorrhizal plants due to a high affinity for nutrients. However, mycorrhizal plants may be able to buffer against external fluctuations and therefore experience less environmental variation than non-mycorrhizal plants. Non-mycorrhizal plants may even benefit from variation. The optimal allocation of growth between shoot and roots depends on the availability of energy and nutrients. The optimisation model predicted that the requirement for phenotypic plasticity of shoot/root allocation is greatest in environments with low resource availability. Plants with a high affinity for resources required more plasticity in order to tolerate variation than plants with a low affinity. The model predicted a trade-off between the ability to deplete resources and the ability to tolerate resource fluctuations. Changes in the availability and ratio of resources lead to changes in the structure and composition of vegetation during primary succession. The field study of the forested phases of the land uplift island Hailuoto showed a successional change in the vegetation from the dominance of bryophytes and deciduous dwarf shrubs to dominance by lichens and evergreen dwarf shrubs. The humus layer became thinner and the availability of nutrients declined, while the C/N ratio of soil organic matter increased during succession indicating a decline in the quality of organic matter. The increased soil respiration rate indicates a successional increase in the energetic costs of decomposing organic matter. Nutrients mediate both direct and indirect trophic interactions. Indirect interactions of nutrient cycling are not explicit in continuous time models. A transformation to a discrete time model was shown to make the indirect interactions explicit as transition probabilities and allowed their dynamic contribution to be evaluated with an elasticity analysis. The importance of indirect interactions was greater in tundra than temperate forest and increased with the rate of nutrient cycling.