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Cotton (Gossipium hiristum, L) is a warm season perennial with indeterminant growth habit. In 1995, 42,500 and 300,000 hectares were grown in Virginia and North Carolina, respectively. Soil physical and chemical properties may limit cotton yields. The objective of this study was to; 1) determine influences of soil physical and chemical properties on yield, 2) validate existing preharvest yield estimators, and 3) determine the effect of subsoiling and/or subsurface liming on cotton development and root growth. Two hundred sites were sampled across the Coastal Plain of Virginia and North Carolina to a depth of 92 cm representing 5 major soil series. Soil samples were analyzed for selected physical and chemical properties from each horizon. Boll and plant counts were obtained while harvesting a 3-meter length of row at each site to determine yield for the 1996 and 1997 growing season. Cotton was grown in the greenhouse on 30 cm diameter cores of a soil with low subsoil pH and a hard pan to determine the effects of subsoiling and/or subsurface liming. Ninety days after planting, the cotton plants were harvested and the above ground biomass and rootmass were analyzed. Physical and chemical properties explained 52% of yield variability in 1996 and 27% in 1997. Physical and chemical properties that were significant to yield were surface bulk density, available water holding capacity, depth of the water table and Bt horizon, Mg, K, Ca, and Al content. Soil analysis for nutrient status at depths up to 45 cm were better indicators of cotton yield. Subsoiling with or without subsurface liming increased rooting depth over the untreated check. The subsurface liming reached first flower 11 days prior to the other treatments. The additional period for flowering and boll set in Virginia and North Carolina could increase potential yield. / Ph. D.

The object of this investigation was to determine, if possible, whether or not the magnesium ion concentration in the backfill has a significant effect upon the current efficiency of a pure magnesium anode when used to protect a steel cathode. Accordinging to H.A. Robinson, there should normally be no effect, but he indicated that there is room for doubt in some cases. It may be concluded, from the results obtained in this experimental work, that the current efficiency of magnesium anodes, when used as cathodic protectors of steel, is generally unaffected by changes in the concentration of magnesium sulfate in the backfill. It may be further stated that the presence of manganese ion also has no effect upon the current efficiency. The results indicate the possibility that current efficiency is appreciably affected by changes in the current density at the anode. It is suggested that further work be done in the study of this effect. It is further suggested that a wide variety of backfill conditions, for example, soils of different pH, be used in conjunction with this study. / M.S.

In Europe the views on the demand of magnesium by agricultural plants as well as on the need for magnesium fertilization are different. In European countries uses different methods for determining the available magnesium content in soil. Different assessment of soil characteristics in different countries as well as very unequal magnesium fertilization rates for crops have encouraged us to review the methods of determining available magnesium in soil and the effect of magnesium fertilizer on plants. The appropriateness of applying the magnesium determination methods commonly used in different soils in Europe was established and scientifically based as well as their relationship, recalculation algorithms for the values of available magnesium obtained by applying different determination methods were prepared. The effect of the plant available magnesium content in predominant soils of Lithuania determined by different methods and that of magnesium fertilizer on the yield of Italian ryegrass and spring barley were investigated. Summarizing the research developed the most suitable determination of available magnesium in Lithuanian soil and crop fertilization magnesium fertilizer recommendations. Different solubility of magnesium in different soils and magnesium fertilizers on agricultural plants in Lithuania was studied for the first time. / Požiūris į magnio poreikį žemės ūkio augalams, o tuo pačiu tręšimą magnio trąšomis, įvairiose šalyse nėra vienodas. Europos šalyse judrusis magnis dirvožemyje nustatomas labai įvairiais metodais. Skirtingas dirvožemio savybių vertinimas įvairiose šalyse, o taip pat labai nevienodos magnio trąšų normos augalams mus paskatino naujai peržiūrėti judriojo magnio nustatymo metodus dirvožemyje ir magnio trąšų įtaką augalams. Nustatytas ir moksliškai įvertintas dažniausiai Europoje naudojamų judriojo magnio nustatymo metodų taikymo tinkamumas įvairiuose dirvožemiuose, jų tarpusavio priklausomumas, parengti perskaičiavimo algoritmai tarp įvairiais metodais nustatytų judriojo magnio reikšmių. Vyraujančiuose Lietuvos dirvožemiuose ištirta įvairiais metodais nustatyto judriojo magnio kiekio ir magnio trąšų įtaka gausiažiedžių svidrių bei vasarinių miežių derliui ir kokybei. Apibendrinus atliktus tyrimus parengtos tinkamiausių judriojo magnio nustatymo Lietuvos dirvožemiuose metodų ir žemės ūkio augalų tręšimo magnio trąšomis rekomendacijos. Lietuvoje įvairaus tirpumo magnio kiekiai įvairiuose dirvožemiuose ir magnio trąšų įtaka žemės ūkio augalams tirta pirmą kartą.

O presente trabalho estuda a conformação da liga de magnésio AZ61 pelos processos de extrusão direta e forjamento, ambos a quente. No processo de extrusão, são submetidos à conformação corpos-de-prova da liga de magnésio AZ61 nos estados fundido e recristalizado. As geometrias de ferramenta são variadas e a influência destas variações sobre a força de processamento e propriedades mecânicas e microestrutura do material são analisada. Demonstra-se que a liga no estado inicialmente recristalizado tem propriedades mecânicas finais superiores à liga inicialmente fundida, embora demande de maior força de processamento. Demonstra-se também que a geometria de ferramenta tem influência sobre as respostas mecânicas obtidas das peças após extrusão. Referente ao processo de forjamento, a liga de magnésio AZ61 é processada apenas no estado recristalizado, variando-se a temperatura e o número de tapas de forjamento. Foi avaliada a influência destas variações de processo nas propriedades mecânicas finais da peça. Ao fim, percebe-se que ao se forjar as peças com múltiplas etapas de forjamento e temperaturas decrescentes, impede-se a recristalização do material, alcançando alto encruamento dos grãos, o que gera, na peça final, propriedades mecânicas superiores ao processo convencional. / This thesis studies the deformation of a magnesium alloy AZ61 by forward extrusion and forging processes, at elevated temperatures. In the extrusion process, the samples were deformed in as cast and recrystallized conditions. The tools geometries were variated and the influences on processing force, mechanical properties and material microstructure were analyzed. Was found that the recrystallized samples have better mechanical properties than as cast samples, after extruded, although it requires more processing force. Also was found that the tool geometry influences on mechanical properties and microstructure of extruded magnesium alloy. Relatively to the forging process, magnesium alloy AZ61 was processed only in the recrystallized state, varying the process temperature and the number of forging steps. Aimed to evaluate the process variations influences on the mechanical properties and microstructure of the final parts. At the end, was observed that when forging parts with multi-step forging and decreasing temperatures, to prevent recrystallization of the material, achieving high strain hardening of the grains, which results in final part with superior mechanical properties to the conventional process.

O presente trabalho estuda a conformação da liga de magnésio AZ61 pelos processos de extrusão direta e forjamento, ambos a quente. No processo de extrusão, são submetidos à conformação corpos-de-prova da liga de magnésio AZ61 nos estados fundido e recristalizado. As geometrias de ferramenta são variadas e a influência destas variações sobre a força de processamento e propriedades mecânicas e microestrutura do material são analisada. Demonstra-se que a liga no estado inicialmente recristalizado tem propriedades mecânicas finais superiores à liga inicialmente fundida, embora demande de maior força de processamento. Demonstra-se também que a geometria de ferramenta tem influência sobre as respostas mecânicas obtidas das peças após extrusão. Referente ao processo de forjamento, a liga de magnésio AZ61 é processada apenas no estado recristalizado, variando-se a temperatura e o número de tapas de forjamento. Foi avaliada a influência destas variações de processo nas propriedades mecânicas finais da peça. Ao fim, percebe-se que ao se forjar as peças com múltiplas etapas de forjamento e temperaturas decrescentes, impede-se a recristalização do material, alcançando alto encruamento dos grãos, o que gera, na peça final, propriedades mecânicas superiores ao processo convencional. / This thesis studies the deformation of a magnesium alloy AZ61 by forward extrusion and forging processes, at elevated temperatures. In the extrusion process, the samples were deformed in as cast and recrystallized conditions. The tools geometries were variated and the influences on processing force, mechanical properties and material microstructure were analyzed. Was found that the recrystallized samples have better mechanical properties than as cast samples, after extruded, although it requires more processing force. Also was found that the tool geometry influences on mechanical properties and microstructure of extruded magnesium alloy. Relatively to the forging process, magnesium alloy AZ61 was processed only in the recrystallized state, varying the process temperature and the number of forging steps. Aimed to evaluate the process variations influences on the mechanical properties and microstructure of the final parts. At the end, was observed that when forging parts with multi-step forging and decreasing temperatures, to prevent recrystallization of the material, achieving high strain hardening of the grains, which results in final part with superior mechanical properties to the conventional process.

O presente trabalho estuda a conformação da liga de magnésio AZ61 pelos processos de extrusão direta e forjamento, ambos a quente. No processo de extrusão, são submetidos à conformação corpos-de-prova da liga de magnésio AZ61 nos estados fundido e recristalizado. As geometrias de ferramenta são variadas e a influência destas variações sobre a força de processamento e propriedades mecânicas e microestrutura do material são analisada. Demonstra-se que a liga no estado inicialmente recristalizado tem propriedades mecânicas finais superiores à liga inicialmente fundida, embora demande de maior força de processamento. Demonstra-se também que a geometria de ferramenta tem influência sobre as respostas mecânicas obtidas das peças após extrusão. Referente ao processo de forjamento, a liga de magnésio AZ61 é processada apenas no estado recristalizado, variando-se a temperatura e o número de tapas de forjamento. Foi avaliada a influência destas variações de processo nas propriedades mecânicas finais da peça. Ao fim, percebe-se que ao se forjar as peças com múltiplas etapas de forjamento e temperaturas decrescentes, impede-se a recristalização do material, alcançando alto encruamento dos grãos, o que gera, na peça final, propriedades mecânicas superiores ao processo convencional. / This thesis studies the deformation of a magnesium alloy AZ61 by forward extrusion and forging processes, at elevated temperatures. In the extrusion process, the samples were deformed in as cast and recrystallized conditions. The tools geometries were variated and the influences on processing force, mechanical properties and material microstructure were analyzed. Was found that the recrystallized samples have better mechanical properties than as cast samples, after extruded, although it requires more processing force. Also was found that the tool geometry influences on mechanical properties and microstructure of extruded magnesium alloy. Relatively to the forging process, magnesium alloy AZ61 was processed only in the recrystallized state, varying the process temperature and the number of forging steps. Aimed to evaluate the process variations influences on the mechanical properties and microstructure of the final parts. At the end, was observed that when forging parts with multi-step forging and decreasing temperatures, to prevent recrystallization of the material, achieving high strain hardening of the grains, which results in final part with superior mechanical properties to the conventional process.