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[pt] O presente trabalho trata da influência do cobrimento da armadura longitudinal sobre a resistência de aderência em regiões de emenda por traspasse de elementos de concreto armado comprimidos. Neste estudo foram ensaiados dezoito pilares de concreto armado com seção transversal de 200 mm x 150 mm e comprimento de 1100 mm, com armadura longitudinal composta de barras de aço CA-50 com diâmetro nominal de 12,5 mm e estribos de 5 mm. O arranjo da armadura longitudinal definiu três séries de pilares, sendo a Série 1 composta por seis pilares com a armadura longitudinal contínua, e as Séries 2 e 3 cada uma composta por seis pilares com a armadura longitudinal, tendo uma emenda por traspasse localizada na região da metade da altura do pilar de 470 cm e 235 mm de comprimento, respectivamente. Os ensaios consistiram na aplicação de uma força de compressão com uma excentricidade de 20 mm, sendo tal excentricidade aplicada apenas na direção da menor dimensão da seção transversal. Para os seis pilares de cada série o cobrimento da armadura longitudinal variou de 25 mm até que a metade do diâmetro da barra longitudinal ficasse exposta. Os resultados obtidos indicam que a influência do cobrimento sobre a capacidade do pilar resistir às solicitações torna-se visível quando a relação da espessura do cobrimento c e do diâmetro da barra fi é inferior a 0,4. Para pilares com barras emendadas por traspasse e com armadura exposta até a metade de seu diâmetro, a aderência na zona da emenda foi substancialmente afetada, provocando a ruptura do pilar sob forças inferiores às alcançadas em pilares com cobrimento adequado. / [en] The present work describes the influence of the concrete cover of the longitudinal reinforcement on the bond strength along the overlapping splice zones of compressed elements. Tests have been carried out on eighteen reinforced concrete columns, with cross section of 200 mm x 150 mm and 1100 mm of length. The longitudinal reinforcement consisted of CA-50 steel bars with nominal diameter of 12,5 mm and stirrups of 5 mm. Three series of columns (Serie 1, Serie 2 and Serie 3) were defined according to the arrangements of the longitudinal reinforcement: Series 1 composed by six columns with continuous longitudinal reinforcement; Series 2 and 3 composed by six columns each, presenting an overlapping splice of 470 mm and 235 mm of lenght, respectively. The columns were submited to a load apllied with an eccentricity of 20 mm in the direction of the smallest dimension of the cross section. In each series, the concrete cover varied from 25 mm to a value corresponding to the situation in which half of the diameter of the longitudinal bar was exposed. The results showed that the influence of the concrete cover on the column strength becomes relevant when the ratio c/ Ø of the cover thickness c to the bar diameter Ø is less than 0,4. For columns with overlapping splice and reinforcement exposed up to the half of diameter, the bond along the overlapping zone has been substancially affected, resulting in the column failure at lower loads when compared to columns with proper value of concrete cover.

Construction of land use and land cover (LULC) maps was accomplished through the use of remote sensing and GIS. Remote sensing and GIS were used to classify 1990 Landsat 5 and 2000 Landsat 7 Mississippi Gulf Coast imagery into six LULC classes: urban, barren, forested vegetation, non-forested vegetation, marsh, and water. An accuracy assessment was performed on the 2000 LULC map to determine the reliability of the map. Finally, GIS software was used to quantify and illustrate the various LULC conversions that took place over the ten year span of time. The paper concludes that remote sensing and GIS can be used to create LULC maps. It also notes that the maps generated can be used to delineate the changes that take place over time.

Cotton (Gossypium hirsutum L.), is cultivated in the United States, primarily in regions characterized by long, hot summers to optimize plant growth. Virginia is the northernmost state where cotton is grown, with approximately 84,000 acres annually. The unique challenges of cultivating cotton in Virginia stems from its relatively short season due to its geographical location, lack of large contiguous acreage, and distinctive issues with pests. A significant pest of this region is the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), which emerged as a major threat to mid-Atlantic cotton during the late 2010s. L. lineolaris utilize a variety of wild and cultivated hosts to survive the winter months. The overwintering success and distribution of diapause survival L. lineolaris was measured on cover crops and weeds common in the Mid-Atlantic. Densities varied between weed and cultivated hosts, with L. lineolaris exhibiting increased survival in legumes compared to grains. Carbohydrate, lipid and protein levels were measured within diapausing and non-diapausing L. lineolaris specimens. Overwintering specimens usually had elevated level of carbohydrates and lipids, while containing decreased concentrations of protein. Nutrient quantification provided an effective tool in selecting for diapause status in L. lineolaris. Through the results from this study, an alternative method to dissection for determining diapause status in L. lineolaris has been identified. In the spring, movement of L. lineolaris throughout the landscape is highly dependent on host senesce. Flight analysis, behavioral assays and nutritional quantification assays on L. lineolaris populations from different weed hosts were performed to assess the flight capacity of specimens fed from different hosts. While weed hosts type provided populations with differing internal nutrient levels, sustained flight was not different between populations. When dispersal of L. lineolaris into cotton occurs, insecticide treatments following scouting are often necessary to prevent economic damage to the plant. Insecticide experiments were conducted aiming to assess the impact of different active ingredients on L. lineolaris, secondary pests, and natural enemy populations. Findings indicated that insecticides used to control L. lineolaris were successful at lowering pest populations and acephate was found to impact natural enemy populations. Plots applied with acephate experienced secondary pest outbreaks, highlighting the crucial role of natural enemies. / Doctor of Philosophy / Cotton is cultivated throughout the southern United States, extending up the east coast and into North Carolina and Virginia. Virginia poses unique challenges for cotton growers due to specific pest issues and need for region-specific research. The tarnished plant bug is a key pest of mid-summer cotton across this region. Overwintering studies were conducted to investigate host preferences on cover crop and weed hosts, as well as diapause survival and termination timing on cover crops. These studies revealed that hairy vetch and deadnettle species may harbor larger populations compared to other weed hosts, and that cover crops such as hairy vetch and crimson clove led to greater overwintering survival compared to grains. During diapause, metabolic changes occur that can lead to increased fat body to aid in overwintering survival. Diapausing and non-diapausing tarnished plant bugs were used in assays to quantify differences in the nutrients commonly found in this fat body. This study successfully found differences in carbohydrates, lipids and proteins levels between the diapausing and non-diapausing populations. This may allow for the identification of reproductive status of tarnished plant bugs based on nutrient levels. Flight capacity, activity levels and nutrient levels in tarnished plant bug populations taken from spring and summer weed hosts were investigated, with the objective to understand the ability of these populations to transition to cotton in the mid-summer. There were some indicators that flight initiation may be influenced by weed host, while all populations had similar flight potentials. Once in cotton, tarnished plant bugs are primarily treated with chemical insecticides which may produce unknown consequences to the system as a whole. Experiments were conducted to assess the impact of insecticides on non-target species within cotton were conducted in the field. Certain insecticides were identified to be harmful to non-target and potentially beneficial insect species, which contributed to outbreaks of other secondary pest species.

Anaerobic soil disinfestation (ASD) is a promising alternative to chemical fumigation to control soil-borne plant pathogens and weeds. This research focused on evaluating several locally available carbon sources for ASD on weed control, evaluating the performance of brewers' spent grain (a promising carbon source) under field conditions, and evaluating whether yeast addition enhanced the effectiveness of ASD treatments. A series of greenhouse trials were conducted at the Southern Piedmont AREC (Agricultural Research and Extension Center). The greenhouse trials were conducted in PVC tubes, 20 cm tall and 15 cm in diameter. The first set of trials evaluated ASD conducted over 21-day periods of ASD using locally available carbon sources. The carbon sources included brewer`s spent grain, buckwheat (Fagopyrum esculentum), cowpea (Vigna unguiculata), paper mulch, peanut (Arachis hypogaea) shells, rice bran, sorghum-sudangrass (Sorghum drummondii), and waste coffee grounds applied at 4 mg of C/g of soil. The targeted weed species included common chickweed (Stellaria media (L.) Vill.), redroot pigweed (Amaranthus retroflexus L.), white clover (Trifolium repens L.), and yellow nutsedge (Cyperus esculentus L.). All ASD treatments significantly reduced weed viability compared to the non-treated control. The yeast amendments enhanced weed control over ASD without yeast. The second set of greenhouse trials was focused on ASD using brewer`s spent grain, and on evaluating ASD at the half and one-third carbon dose rates. The target pests were the same weed species in the first set of trials, and Pythium irregulare was added as an additional target pest. This set of trials indicated yeast enhanced addition the effect of BSG in ASD on both weeds and P. irregulare, indicating the potential to reduce carbon input necessary for effective ASD. A follow-up, two seasons, open-field trial conducted over two growing seasons at the Hampton Roads AREC focused on understanding the effects of ASD on weed density and strawberry fruit yield and fruit quality in annual hill strawberry production. The treatments included ASD at standard or half carbon dose rates, with or without yeast. Fumigation (80% chloropicrin + 20% 1,3-dichloropropene) and non-treated plots were used as control groups. Weed suppression with ASD was consistent for most of the broadleaf weed species, and total weed counts were significantly reduced compared to non-treated controls. Yield from ASD with yeast was higher than ASD without yeast and non-treated control in one growing season, while the increase in yield did not occur in another growing season. Yeast may have potentially enhanced the yield effects of ASD but lacked consistency. Yeast may have the potential to enhance ASD effectiveness. / Doctor of Philosophy / Strawberry is a high-value crop known for its brightly colored, sweet tasting, juicy and fleshy fruit that possesses a unique aroma. The southern region is the second large region of strawberry production in the United States. Strawberry is susceptible to soil-borne pests, including weeds and diseases. Preplant control of soil-borne diseases and weeds is important for strawberry production. Early season weeds can compete with newly transplanted strawberry plugs for nutrients, light, and other resources. However, currently, the limited options of pre-plant chemical fumigants and herbicides available in strawberry plasticulture make weed control a challenge in strawberry production. Anaerobic soil disinfestation (ASD) may be an effective alternative to preplant chemical fumigation. Anaerobic soil disinfestation involves three steps- applying carbon sources to the soil, covering the bed with black tarp, and watering the soil to maintain certain soil moisture to field capacity generally for 21 days. However, there are only a few studies on weed control using ASD in the southern region; locally available carbon sources also need to be evaluated. Thus, this study focused on evaluating several locally available carbon sources (cover crops, brewer`s spent grain, used coffee ground, paper mulch, peanut shell) for ASD to control troublesome weeds (common chickweed, redroot pigweed, white clover, yellow nutsedge). This study also explored a new method that involves mixing distiller's yeast with solid carbon sources in order to enhance the ASD weed control effect. Additionally, this study evaluated the effect of ASD using reduced carbon inputs, potentially reducing the total cost of ASD by reducing the carbon input. A series of greenhouse studies were conducted at the Southern Piedmont Agricultural Research and Extension Center (AREC), Blackstone, VA, with a follow-up field study done at the Hampton Roads AREC. The greenhouse trials evaluated carbon sources including brewer`s spent grain, buckwheat, cowpea, paper mulch, peanut shells, rice bran, sorghum-sudangrass, and waste coffee grounds. These greenhouse experiments were conducted in containers made from PVC tubes, and strawberry plants were not involved. The main objective of the greenhouse trial was to test the suppression of four troublesome weeds, including common chickweed, redroot pigweed, yellow nutsedge, and white clover. The most effective treatments in the greenhouse studies were further investigated in the field trial. The brewer`s spent grain was again used in the field trial, and treatments included ASD using a full or half dose of brewer's spent grain, with or without yeast. We evaluated the effects of these treatments on weed control, plant crop growth, and crop yields. Fruit quality factors, including fruit firmness, sweetness, and size, were also evaluated. In summary, all of the carbon sources evaluated provide similar weed control. Adding yeast showed potential to enhance the effect of ASD using brewer`s spent grain. Adding yeast also increased the effectiveness of the half-rate of the carbon source, showing the potential for effective pre-plant pest control for strawberry using ASD treatments with significantly reduced C dose rates.

The land surface and atmosphere interact through complex feedback loops that link energy and water cycles. Effectively characterizing these linkages is critical to modeling weather and climate extremes accurately. Seasonal variability in vegetation growth and human-driven land cover changes (LCC) can alter the biophysical properties of the land surface, which can in turn influence the water cycle. We quantified the impacts of seasonal variability in vegetation growth on land surface energy and water balances using ecosystem-scale eddy covariance and large aperture scintillometer observations. Our results indicated that the monthly precipitation and seasonal vegetation characteristics such as leaf area index, root length, and stomatal resistance are the main factors influencing ecosystem land surface energy and water balances when soil moisture and available energy are not limited. Using a regional-scale climate model, we examined the effect of LCC and irrigation on summer water cycle characteristics. Changes in biophysical properties due to LCC reducing the evapotranspiration, atmospheric moisture, and summer precipitation over the contiguous United States (CONUS). The combined effects of LCC and irrigation indicated a significant drying over the CONUS, with increased duration and decreased intensity of dry spells, and reduced duration, frequency, and intensity of wet spells. Irrigated cropland areas will become drier due to the added effect of low-precipitation wet spells and long periods (3-4% increase) of dry days, whereas rainfed croplands are characterized by intense (1-5% increase), short-duration wet spells and long periods of dry days. An analysis based on future climate change projections indicated that 3–4 °C of warming and an intensified water cycle will occur over the CONUS by the end of the 21st century. The results of this study highlighted the importance of the accurate representation of seasonal vegetation changes and LCC while forecasting present and future climate. / Doctor of Philosophy / The land surface and atmosphere interact through complex feedback loops that link energy and water cycles. Effectively characterizing these linkages is critical to accurately model weather and climate extremes. We quantified the influence of human-driven land cover change (LCC), in this case, LCC associated with irrigated agriculture, and seasonal vegetation growth on the water cycle using a regional climate model and ecosystem-level observations. Our results indicated that monthly precipitation and seasonal vegetation growth are the main factors influencing land surface energy and water balances when soil moisture and solar energy are not limited. Our results showed that irrigation-related LCC reduced summer precipitation over the contiguous United States (CONUS), with an increased number of dry days (days with less than 1 mm precipitation) and reduced hourly, daily, and summer precipitation totals. Irrigated cropland areas are becoming drier due to the combined effects of low precipitation and long dry days, whereas rainfed croplands are characterized by intense short-duration precipitation and long dry days. Climate change analyses indicate that 3–4 °C of warming and an intensified water cycle will occur over the CONUS by the end of the 21st century. The results of this study highlight the importance of the accurate representation of LCC while forecasting future climate.

It is known that subsidence cracking may cause premature deterioration of concrete slab structures in salt laden environments. Chlorides from either deicing salts or marine environments may cause chloride-induced corrosion of the reinforcing steel resulting in spalling of the cover concrete. Concrete specimens with 16 mm (# 5) diameter bars were cast with various cover depths, bar spacing and two concrete mixture types to determine the influence that epoxy coated reinforcement, cement type and bar spacing may have on the probability of subsidence cracking in bridge deck slabs. It was determined that there is not a significant difference in the probability of cracking of concrete between concrete cast with epoxy coated reinforcing steel and bare reinforcing steel. Concrete subsidence cracking was found to be dependent upon the clear cover depth and cement type. / Master of Science

The objectives of this research were: 1) to quantify the amount of supplemental nitrogen (N) to maximize organic broccoli (Brassica olearcea var. italica) on transition soils, 2) to evaluate the ability of leguminous cover crops lablab (Dolichos lablab L.), soybean (Glycine max L.), sunn hemp (Crotalria juncea L.) and a sunn hemp and cowpea mixture (Vigna sinensis Endl.) to supply N and suppress weeds and, 3) to compare the effect on N availability and broccoli yield potential of incorporating cover crops with conventional tillage (CT) or mulching cover crops with no-tillage (NT) practices. Broccoli was grown during the third year of organic transition in the spring and fall of 2006 at the Kentland Agricultural Research Farm in Blacksburg, VA. Supplemental N significantly increased broccoli yield up until 112 kg ha-1 with a quadratic correlation with leaf N. The NT treatment yielded no difference during the spring, but in the fall CT surpassed NT. On the other hand, N uptake, measured by leaf N, under NT conditions increased with supplemental N, which suggests NT has equivalent yield potential as CT when N is not limiting. Yields from leguminous residues did not differ, even though quality and quantity of cover crop biomass did. This suggests that N availability from cover crop legumes may be impacted other ecological process such as soil microbial activity. Also, cover crop residues differed in their ability to suppress weeds. The results from this study give organic growers in transition tools to maximize productivity and sustainability. / Master of Science

M.S.

Strawberry is an economically important crop in California, with an estimated value of $2.68 billion in 2023. In California strawberry production, mitigation of low plant health and yield often focuses on major soilborne pathogens, while the contribution of minor pathogens and abiotic disorders to production shortcomings are often overlooked. The objectives of the first project in this thesis are to determine the pathogenicity of multiple minor pathogens and quantify other biotic and abiotic factors that can reduce plant health such as viruses and soil salinity. Two pathogens of the black root rot complex, Pythium spp. and Rhizoctonia spp. as well as Neopestalotiopsis rosae are included in this study. The pathogens were identified using ITS DNA sequencing and evaluated for optimal colony growth temperatures. Over the course of two trials, Koch's postulates of P. ultimum and P. irregulare isolates were confirmed for pathogenicity of strawberry roots and crowns, Rhizoctonia spp. isolates were confirmed over 2 trials for pathogenicity of strawberry roots and crowns, and Neopestalotiopsis rosae isolates were confirmed for pathogenicity of strawberry crowns, leaves, and fruit. In 2022 and 2023, 60 root zone soil samples of symptomatic plants that tested negative for major soilborne pathogens were evaluated for electrical conductivity (ECe). Average soil ECe was 1.17 dS/m ranging between 0.18 and 2.45 dS/m, categorizing all samples as non- or slightly-saline except for two which were moderately-saline. Virus testing between 2022 and 2024 diagnosed eight positive samples out of 38 total samples: three in 2022 for Beet pseudo-yellows, two samples in 2023 for Strawberry mild yellow edge and Strawberry polerovirus 1 and one for Strawberry polerovirus 1, and two samples in 2024 for Beet pseudo-yellows. The results from this study suggest that while the tested minor pathogens can infect and reduce strawberry plant health, it is unlikely they are the sole cause of the observed plant mortality from recent diagnostic samples. Additionally, the low to moderate soil salinity levels and infrequent positive virus diagnostics are also not likely the sole cause of observed plant mortality. Future research into these topics could focus on the combination of major and minor pathogens as well as abiotic disorders to decipher how each factor affects plant health. Additionally, Macrophomina phaseolina (MP), an important soilborne pathogen in California strawberry production, was observed to cause 29.7%-52.0% of late-season strawberry mortality in major strawberry growing districts in recent surveys. The objective of the study of this thesis is to assess the efficacy of crop termination and cover cropping on MP suppression to reduce disease incidence of Macrophomina root rot and improve strawberry yield and soil health. Studies were conducted using conventional field soil as a pot trial and a field trial, as well as an organic field trial. The greenhouse pot trial utilized strawberry cultivars Albion and Royal Royce planted in soil collected from a conventional grower field in the Santa Maria district in a randomized complete block design. Treatments included untreated control soil (C), untreated control soil planted with wheat (W) 'Summit 515’ (C+W), soil fumigated with metam potassium (crop termination) planted with wheat (CT+W), and soil fumigated with metam potassium (crop termination) and chloropicrin (flat fumigation) (CT+FF). Plant infection and soil pathogen levels were assessed via plating on semi-selective media and using a pour plate method, respectively. Two repetitions of the trial were conducted. There was no significant soil treatment × cultivar interaction or cultivar effects in trial 1 and 2 for the MP CFU/g soil, but there was a significant soil treatment effect in the MP CFU/g soil of both trials (P = 0.0001). The trial 1 CT+W treatment had the highest-level MP CFU/g soil, which descended in significance to C+W, then C, and then finally CT+FF. In trial 2 CT+W had a significantly higher MP CFU/g soil value than the other treatments, while C and C+W were comparable to each other and both higher than CT+FF. Chemical soil evaluations for mineralizable carbon (MinC) and permanganate oxidizable carbon (POXC) were also performed. Trial 1 C+W had a significantly higher MinC value than CT+FF, while C and CT+W were comparable with both treatments. In the trial 2 MinC soil test the soil treatment × cultivar interaction and the main effects were not statistically significant. In trial 1 and trial 2 POXC soil tests the soil treatment × cultivar interaction and the main effects were not statistically significant. The second year of this study took place in the field and soil samples were collected pre- and post-soil treatments of CT, CT+W, CT+Triticale ‘Pacheco’ (T), CT+W+FF, and CT+T+FF to be evaluated for MP CFU/g soil. T was added as a cover crop treatment to compare a triticale variety to wheat as well as its prevalence as a cover crop in California. There was a significant soil treatment effect (P = 0.02) with post-cover crop wheat treatment having a significantly higher MP CFU/g soil than post-cover crop triticale. The strawberry cultivar Portola was planted after fumigation across all cover crop blocks. Additionally, an organic strawberry field trial compared wheat and triticale cover crops for MP suppression with strawberry cultivars Valiant and Monterey. Soil and plants were tested in the same manner as the pot trial. MP CFU/g soil, MinC, and POXC were not significantly different between soil treatments. Preliminary results suggest single season cover cropping cannot manage high pathogen levels, while crop termination can reduce the pathogen inoculum if the application is timed correctly. The completion of this project will include plant mortality evaluations and microbiome analyses from the field trials. This research aims to help the California strawberry industry by enhancing disease management and reducing fumigant use.