• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 111
  • 59
  • 17
  • 10
  • 10
  • 10
  • 10
  • 10
  • 10
  • 6
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 243
  • 243
  • 66
  • 57
  • 44
  • 39
  • 38
  • 29
  • 26
  • 25
  • 24
  • 23
  • 19
  • 19
  • 18
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
151

Conservação dos solos e preços de terras agrícolas no Brasil / Soil conservation and farmland prices in Brazil

Telles, Tiago Santos, 1984- 27 August 2018 (has links)
Orientador: Bastiaan Philip Reydon / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Economia / Made available in DSpace on 2018-08-27T05:27:00Z (GMT). No. of bitstreams: 1 Telles_TiagoSantos_D.pdf: 2532419 bytes, checksum: 074d49e9f68a6dcd4d343ff801020e43 (MD5) Previous issue date: 2015 / Resumo: Os preços de terras agrícolas podem ser determinados tanto pelos fatores produtivos quanto pelos fatores especulativos. Entre os fatores produtivos, é reconhecido que investimentos na conservação dos solos em áreas destinadas às atividades agropecuárias podem valorizar as terras agrícolas. O plantio direto na palha é uma tecnologia que integra diretrizes da agricultura conservacionista e que garante uma série de vantagens à produção agropecuária, com possíveis impactos no preço das terras, o que contribui para que a adoção desse tipo de preparo do solo esteja crescendo no Brasil. Essa expansão foi de tal grandeza que no Censo Agropecuário 2006, realizado pelo Instituto Brasileiro de Geografia e Estatística (IBGE), foi dedicada uma seção específica para o levantamento de informações sobre os tipos de preparo do solo. Esse levantamento possibilitou o cruzamento de informações sobre os tipos de preparo do solo com o preço das terras agrícolas, oferecendo a possibilidade de verificar se as terras utilizadas com o plantio direto na palha são mais valorizadas do que aquelas utilizadas com outros tipos de preparo, ou seja, cultivo convencional ou cultivo mínimo. Os resultados indicaram que no Estado do Paraná as terras agrícolas em áreas de lavouras temporárias com plantio direto na palha, quando comparadas aos demais tipos de preparo, são mais valorizadas. Essa valorização das terras associada ao plantio direto na palha também pode ser observada em outras Unidades da Federação, tais como Bahia, São Paulo, Rio Grande do Sul, Mato Grosso do Sul, Mato Grosso e Goiás. Mas o fenômeno da expansão do plantio direto na palha e aumento do valor das terras que utilizam a tecnologia pode estar relacionado a outros aspectos técnicos e econômicos inerentes a esta tecnologia, dentre os quais: a redução de risco de perdas de produção associados às questões climáticas e de custos, redução no número de operações agrícolas em comparação aos outros tipos de preparo e simplificação na gestão da propriedade agrícola. Adicionalmente, outro fator que pode ter influenciado essa relação entre plantio direto e valorização das terras agrícolas foram ações governamentais, por meio de programas e políticas públicas com foco na conservação e recuperação dos solos. Isso suscita a questão de que é válido investigar com mais profundidade a repercussão do programas dessa natureza na valorização do ativo terra enquanto fator para a tomada de decisão dos agricultores na adoção de práticas propostas pela agricultura conservacionista / Abstract: The cost of farm lands is determined by both productive and speculative factors. Soil conservation is one such factor that might result in the appreciation of areas dedicated to agriculture. The no-tillage (NT) is a technology integrating the guidelines of conservation agriculture and ensures several advantages to agricultural productions. It also impacts land prices and, in turn, favors the adoption of this type of soil preparation in Brazil. The expansion of the use of the NT was so significant that the 2006 Agricultural Census, carried out by the Brazilian Institute of Geography and Statistics (IBGE), dedicated one specific section for the acquisition of information about the types of soil preparation. The collected data allowed the study of the correlation between the type of soil preparation and the cost of farm lands. In particular, it enabled the comparison between the direct prices of lands using NT or other soil preparation, that are conventional tillage and minimum tillage. The results indicate that, in Parana State, farm lands in large areas of annual crops using NT are negotiated at higher prices comparison with land using other forms of soil preparation. This Brazilian farm land appreciation in association with the NT was also observed in other Federation units, such as Bahia, São Paulo, Rio Grande do Sul, Mato Grosso do Sul, Mato Grosso and Goias. The observed higher prices might also be associated with other technical and economical aspects, inherent to the NT, such as the reduction of risk of yield loss due to climate issues and decreased costs, diminished number of agriculture operations, in comparison with the other types of soil preparation and simplified management of the property. Additionally, another factor that might have influence on this relationship between the NT and the appreciation of the farm lands were governmental actions, represented by public programs and policies focusing on the conservation and restoration of soils. It raises the question that it is important to investigate more deeply the repercussion of such policies in the appreciation of land as an asset in the farmer's decision to adopt practices of the tillage conservation agriculture / Doutorado / Desenvolvimento Economico, Espaço e Meio Ambiente / Doutor em Desenvolvimento Economico
152

Manejo químico e físico do solo em área de pastagem para o cultivo de soja em diferentes sistemas de produção / Management chemical and physical soil in pastures area for soybean crop in different production systems

Zanfolin, Priscila Roberta Leme 16 December 2015 (has links)
Submitted by Michele Mologni (mologni@unoeste.br) on 2017-06-13T13:04:14Z No. of bitstreams: 1 Priscila Roberta Leme Zanfolin.pdf: 1468658 bytes, checksum: b1d544f8a48ffa0d526a03a58e7676fc (MD5) / Made available in DSpace on 2017-06-13T13:04:14Z (GMT). No. of bitstreams: 1 Priscila Roberta Leme Zanfolin.pdf: 1468658 bytes, checksum: b1d544f8a48ffa0d526a03a58e7676fc (MD5) Previous issue date: 2015-12-16 / The growing demand for food ally to the country's need to ensure positive results in the trade balance, direct, increasingly, studies to agriculture with high yields. In order to achieve these results with low-impact activities, was aimed with this work, to verify the effect of no tillage with scarifier and the use of fertilizers and corrective performed in the culture of brachiaria preceding soybean cultivation, as a low fertility soil and degraded structure, to improve soy production environment and forage conducted in no tillage system with integrated Crop-Livestock. The experiment was conducted in extensive grazing area at the Experimental Farm of the University of Western São Paulo - UNOESTE in Presidente Bernardes-SP, in a soil classified as Acrisol dystrophic. The treatments consist of plots submitted or not to mechanical handling with scarifier type matabroto, each plot gets five chemical treatments, as follows: 1. Without fertilization and liming (control); 2- Application of lime; 3 Application of lime + gypsum; 4- Application of lime + gypsum + NPK; 5- Application of lime + gypsum + NPK + micronutrients. Both the management with ripper as chemical treatments were made 30 days prior to desiccation of pasture (45 days before soybean sowing) in 2013 and were repeated in the year 2014. The experimental design was in bands, in factorial scheme 2 x 5, with four replications. To evaluate the effect of the treatments was determined straw contribution by brachiaria and soil samples were collected in the layers 0-10, 10-20, 20-40 and 40-60 cm, which were physically analyzed for density soil, porosity, water retention curve in the soil and aggregate stability. The soil was also analyzed for particulate C and N fractions and associated minerals. Soybean yield was determined in the season 2013/2014 and 2014/2015. During the cultivation of soy in the 2014/2015 crop was evaluated soil moisture profile. Data were subjected to analysis of variance and t test comparison of means at 5% error probability. The benefits brought by scarifying the soil physical properties are not lasting, since the chemical quality contributes to the structuring of the soil medium and long term. / A crescente demanda por alimento aliada a necessidade do país em garantir resultados positivos na balança comercial, direcionam, cada vez mais, estudos visando agricultura com altas produtividades. A fim de alcançar esses resultados com atividades de baixo impacto ambiental, objetivou-se, com esse trabalho,verificar o efeito do preparo mínimo do solo com escarificador e do uso de adubos e corretivos realizados na cultura da braquiária, antecedendo o cultivo da soja, na qualidade de um solo de baixa fertilidade e com estrutura degradada, visando melhorar o ambiente de produção de soja e forragem conduzidas em Sistema Semeadura Direta com integração Lavoura-Pecuária. O experimento foi conduzido em área de pastagem extensiva na Fazenda Experimental da Universidade do Oeste Paulista - UNOESTE, em Presidente Bernardes-SP, em um solo classificado como Argissolo Vermelho distroférrico. Os tratamentos experimentais são constituídos por talhões submetidos ou não ao manejo mecânico com escarificador tipo matabroto, sendo que cada talhão recebe cinco tratamentos químicos, sendo eles: 1- Sem adubação e sem calagem (testemunha); 2- Com aplicação de calcário; 3- Com aplicação de calcário+gesso; 4- Com aplicação de calcário+gesso+NPK; 5- Com aplicação de calcário+gesso+NPK+micronutrientes. Tanto o manejo com escarificador como os tratamentos químicos foram efetuados 30 dias antes da dessecação da pastagem (45 dias antes da semeadura da soja) no ano de 2013 e foram repetidos no ano de 2014. O delineamento experimental foi em faixas, em esquema fatorial 2 x 5, com quatro repetições. Para avaliação do efeito dos tratamentos, foi determinado o aporte de palha pela braquiária e foram coletadas amostras de solo nas camadas de 0-10, 10-20, 20-40 e 40-60 cm, as quais foram analisadas fisicamente quanto à densidade do solo, porosidade, curva de retenção de água no solo e estabilidade de agregados. O solo também foi analisado quanto às frações de C e N particulados e associados a minerais. A produtividade da soja foi determinada na safra 2013/2014 e 2014/2015. Durante o cultivo da soja na safra 2014/2015 foi avaliada a umidade do solo no perfil. Os dados foram submetidos à análise de variância e ao teste t de comparação de médias ao nível de 5% de probabilidade de erro. Os benefícios trazidos pela escarificação às características físicas do solo não são duradouras, já a qualidade química colabora para a estruturação do solo a médio e longo prazo.
153

Streambank erosion: mechanisms and mitigation techniques

Cnossen, Peter D. January 1987 (has links)
This report presents a study of the various mechanisms that may cause erosion of streambanks and the corresponding mitigation techniques used to combat them. The determination of each may depend upon a number of considerations. The source of the information comes from a variety of reports and papers, which are referenced in the text. Of all the mitigation techniques available to prevent streambank erosion, fabrics will generally offer the most cost effective method. Fabrics have had a good service record since their inception approximately 20 years ago. Further, as the technology continues to advance, it seems likely that fabric applications in this area will only increase. However, there are some concerns that need to be addressed. These include, assessment of geotextile performance in long term use under the different forces it will be subjected to, clogging potential of fabrics for various soil distributions, and the type of fabrics, woven or nonwoven, used in these applications. These factors should become more clearly defined as long term case study data becomes available. / M. Eng.
154

Soil genesis on relatively young surface mined lands in southern West Virginia

Sweeney, Larry Ross January 1979 (has links)
In this study I observed, described and measured differences in morphological, physical and chemical properties as a function of age on mine soils formed from overburden from the New River formation of the Pennsylvanian system in southern West Virginia. Within each group, we sampled nine separate sites and further categorized each to one of three predominant overburden types as observed in the exposed highwall (either predominantly sandstone or shale or an approximately even mixture of the two). Three “topsoiled” sites were sampled for comparative purposes, along with three contiguous soil series commonly found in the region. The most striking differences attributable to age were depth of profile development and horizonation. Aggregate stability, hydraulic conductivity and soil color also showed significant variance with age. The mine soils were generally more fertile in those elements analyzed than the natural soils, and the A horizons of mine soils and the natural soils contained approximately the same amounts of coarse fragments. Among the mine soils, the 5 year old soils were more fertile than the 2 or 10 year old soils. Ten years was not enough time to cause significant differences in textural classification of these soils. Texture was reflective of the parent material. / Master of Science
155

The Economics of Smallholder Households in Central Haiti

Kennedy, Nathan S. 14 May 2015 (has links)
Smallholder households in Haiti face many natural resource management challenges. Agricultural production occurs on deforested hillsides prone to erosion. Charcoal is in an important source of income, and woodfuel stocks are often over-exploited. Donor-funded projects and non- governmental organizations have made large investments in programs that promote soil conservation practices and reforestation. Despite the magnitude of the problems and the amount invested, there are relatively few economic analyses of the long-term adoption of soil conservation practices and woodfuel management. This dissertation uses an economics approach to examine the adoption of conservation practices and the management of woodfuel resources in Central Haiti using cross-sectional data covering 600 households. The results show that plot and household characteristics have different effects on adoption across different classes of soil practices, particularly with regard to perceived soil quality, market access, and household health status. The results also provide evidence of the management of charcoal woodfuel stocks on private land. These findings inform the design and targeting of new programs related to soil conservation and reforestation in Haiti and other developing countries. / Ph. D.
156

Sustainable use of soil resource base in the Dominican Republic:a farm level economic analysis of soil conservation practices

Hwang, Sang Won 12 January 2010 (has links)
Income effects associated with specific levels of erosion reduction for a representative farm in the Bao watershed area in the Dominican Republic are examined in a linear programming framework. Estimation of costs expected in response to specific levels of erosion reduction and the income effects of changes in agricultural policies on the farmer's ability to conserve soil are examined. Results indicate that income losses will be substantial when complying with soil loss standards without introducing soil conservation practices. Net income reduction of 36% can be expected with a reduction in soil loss by 50%. With the introduction of soil conservation practices, substantial reductions in erosion can be obtained with only a minor reduction in net income. For example, with grass strips, 50% reduction in soil loss can be expected with only a 7% reduction in income. Analysis of the effects of changes in agricultural policies indicates that restricting access to credit and changes in tenure from secure land holdings to lack of land titles does not affect the incentive to conserve soil in the short run. Furthermore, analysis of effects of changes in agricultural pricing policies indicates that the promotions of coffee, sweet potatoes, and beans represent the least-costly means of meeting the twin goals of erosion reduction and income maintenance. / Master of Science
157

Cross-compliance as a soil conservation strategy: a case study of the North Fork of the Forked Deer River basin in western Tennessee

Grumbach, Alyson Renee January 1983 (has links)
The purpose of this study was to determine whether cross-compliance strategies, administered in the North Fork of the Forked Deer River Basin in Western Tennessee, would be likely to provide farmers with benefits great enough to offset costs of compliance, thereby providing an incentive for increased conservation efforts. The cross-compliance strategies examined in this study included Agricultural Stabilization and Conservation Service commodity programs, Commodity Credit Corporation loans, Small Business Administration loans, and Federal Crop Insurance. Cross-compliance strategies were then designed such that program benefits would be contingent upon a farmer's compliance with maximu;n erosion rate limits of 5, 10, 15, or 20 tons per acre per year. No consideration was given to water quality impacts of the various selected erosion rates. A random sample of farmers in the watershed were surveyed, and information from these surveys, combined with information from government agency offices, provided estimates of average benefits which farmers in the area have received from government programs. Survey information was then used to estimate present erosion rates, with the Universal Soil Loss Equation. Costs which farmers could expect to incur in order to achieve each of the four soil loss limits were then determined using standard budgetary techniques. These discounted costs were then compared with discounted expected program benefits, over a ten-year period. Results indicated that cross-compliance strategies with the higher soil loss limits of 15 or 20 tons could provide benefits which may outweigh compliance costs. However, lower soil loss limits may be too costly, discouraging participation in the program. / M.S.
158

Cultivation practices, maize and soybean productivity and soil properties on fragile slopes in Yunnan Province, China

Wang, ShuHui January 2003 (has links)
Sustainable agriculture in China is highly threatened by rapid urbanization, land degradation and high population pressure. Yunnan Province, south-west China, is 94% mountainous and lacks flat land. Food shortages and inappropriate cultivation have led to intensive cultivation of steep, marginal and fragile land and have increased soil erosion. To curb this situation and assist with poverty alleviation, it is crucial to develop more productive and sustainable cropping systems. An experiment was conducted on sloping areas from 1999 to 2001 in Wang Jia Catchment, Yunnan Province. The project aim was to evaluate the effects of five selected cultivation practices on maize productivity and soil properties. The treatments were: (1) downslope cultivation without mulch, (2) contour cultivation without mulch, (3) contour cultivation with polythene mulch, (4) contour cultivation with polythene and wheat straw mulch (Integrated Contour with Plastic and Straw Mulch Treatment, INCOPLAST) and (5) contour cultivation with polythene mulch and intercropping, wide and narrow row spacing, with soybean in wide row spacing. Crop growth parameters and soil physical properties were measured throughout the cropping seasons. Considering three years data, contour cultivation with polythene mulch generally increased soil temperature by a mean of 1-2°C. The polythene retained considerably more soil moisture during dry weather. However, during wet weather, polythene prevented rainfall directly falling on the soil, which led to less soil moisture content. The soil temperature and moisture regimes under polythene mulch made plants grow faster and canopies develop well, leading to higher final yields. The benefit of polythene was 33-54% more yield than downslope cultivation without mulch treatment, over three seasons. Contour cultivation plus polythene and straw mulch retained significantly higher soil moisture levels. The yield of this treatment in 1999 was ranked second, but in 2000 it had the highest yield and in 2001 it was also more effective than contour cultivation with polythene mulch treatment. Contour cultivation with polythene mulch and intercropping improved maize yield. The soybean harvest also contributed to net income, the crop had a similar function to straw mulch and increased N availability. Contour cultivation increased yields over the range 7.2-11.2% over three seasons compared with downslope cultivation, equivalent to ~500-1000 kg per hectare more grain produced. There were few clear trends in soil properties over the 1999-2001 period. However, N concentrations increased in the contour cultivation with polythene mulch and intercropping treatment. Both contour cultivation with polythene and straw mulch and contour cultivation with polythene mulch and intercropping gave apparent increases in total K, probably resulting from both decayed straw and decomposed soybean leaves. In terms of simple cost-benefit evaluation, downslope cultivation had the lowest input and output, while contour cultivation had a similar input, but a higher output. Contour cultivation with polythene had the highest net return. Contour cultivation with polythene and straw had a high output but did not give a higher net return than contour cultivation with polythene. Contour cultivation with polythene mulch and intercropping generally had the highest input and output and could give a higher net return than contour cultivation with polythene when the soybean harvest was successful, but over three years this treatment had the greatest risk from crop failure. It is recommended that replacing downslope cultivation with contour cultivation can increase crop yields and this simple action could contribute to the development of more sustainable cropping systems in Yunnan. Polythene mulch achieved higher maize yields but its environmental impact requires further study. It is considered that contour cultivation with polythene and straw mulch or soybean intercropping could contribute towards more productive and sustainable cropping systems where soil conservation is high priority. The technique could assist with long-term soil, water and nutrient conservation and improved crop productivity.
159

Soil micromorphology and image analysis : a study of Bronze Age to recently improved soils at Lairg, Sutherland, Scotland

Acott, Timothy G. January 1993 (has links)
The applications of multispectral and morphometric image analysis to soil thin section descriptions is examined. It is shown that unsupervised classification and contrast stretching can be used to enhance and label features of interest. Morphometric measurements, allow the shape and abundance of features in thin sections to be compared and statistical relationships established. This method of analysis offers a precision beyond that which is possible using a qualitative approach. Using soil micromorphology as the main analytical technique a case study was carried out to evaluate the applicability of image analysis to an investigation of an archaeological site at Lairg in northern Scotland. The interactions of anthropogenic activity and pedogenesis since the Bronze Age is examined. The condition of the soils prior to the Bronze Age is not known because no buried soils predated this period. Evidence suggests that in freely draining situations complete podzols might have formed by this time. During the Bronze and Iron Age intensive cultivation of soils occurred with associated erosion. In areas of the site, where human activity is dated to the Post Medieval period, deepening of A horizons is apparent and the soils are maintained as Brown Podzols. In many areas where human activity stops stagnopodzols are the dominant soil type. The potential of image analysis to aid soil micromorphological descriptions is demonstrated. Contrast stretching aided a qualitative subdivision of thin section slides during the case study. Morphometric analysis confirmed a relationship between shape of voids and c/f ratios in an Iron Age buried A horizon, A PM buried A horizon and an undated deep topsoil. It is concluded that the full benefits of image analysis, when used as a routine tool to aid thin section descriptions, will only be realised when procedures become more interactive and processes can be speeded up.
160

Estimativa de erosão pela Equação Universal de Perda de Solo (USLE) e transferência de sedimentos para todo território Brasileiro / Estimation of erosion by the Universal soil loss Equation (USLE) and sediment transfer for Brazilian territory

Gomez, Javier Dario Pulido 28 August 2012 (has links)
O presente trabalho é uma tentativa de validar uma metodologia para estimar a produção de sedimentos para todo território Brasileiro. Foram utilizadas ferramentas de sistemas de informação geográfi ca (GIS), estatística espacial, modelagem e gerenciamento de bancos de dados aplicados a conservação de solos, permitindo combinar a equação Universal de Perda do Solo (USLE) com diferentes modelos de taxa de transferência de sedimentos (SDR). A metodologia utilizou como base de teste dados da rede sedimentométrica brasileira composta de 201 bacias. As estimativas foram analisadas por regressão linear múltipla obtendo valores de R2 de até de 46% entre dados observados e modelados. Observou-se a pouca sensibilidade do modelo USLE em relação ao fator de erosividade (fator R) quando duas observações por métodos diferentes diferem espacialmente em seus valores máximos entre 18000 MJ.mm.ha-1.h-1.ano-1 e 28000 MJ.mm.ha-1.h-1.ano-1 . Por outro lado o modelo mostrou-se sensível ao fator de cobertura do solo (Fator C da USLE) afetando as taxas máximas estimadas de erosão entre 160 Mg.ha-1.ano-1 ate 460 Mg.ha-1.ano-1. Nesse sentido a metodologia sugerida pode ser utilizada para dar indicativos sobre mudanças de uso da terra em escalas regionais e subsidiar tomadas de decisões quanto ao planejamento e gestão territorial. / This work is an attempt to validate a methodology for estimating sediment production for the whole Brazilian territory. Tools were used geographic information systems (GIS), spatial statistics, modeling and database management applied to soil conservation, allowing combine the Universal Soil Loss Equation (USLE) with different models of sediment transfer rate (SDR). The methodology used as test data of Brazilian sedimentometric network composed of 201 basins. The estimates were analysed by multiple linear regression getting values of R2 to 46% between observed and modelled data. Noted the low sensitivity of USLE model in relation to the erosivity factor (R factor) when two observations by different methods differ in their maximum values and spatial distribution of 18000 MJ.mm.ha-1.h-1.year-1 and 28000 MJ.mm.ha-1.h-1.year-1. the other aspects the model proved to be sensitive to soil coverage factor (factor C of USLE) affecting the estimated maximum rates of erosion between 160 Mg.ha-1.year-1 up to 460 Mg.ha-1.year-1.

Page generated in 0.0917 seconds