Tree clearing is practised for greater beef production and hence monetary gains from grazing systems of central Queensland. The high rates of clearing in the past and even recently (577, 000 ha/yr during 1999-2001) were mainly to develop land for pastures. The sustainability of cleared pasture systems over the long-term is questioned. Three major types of tree communities i.e. Eucalyptus populnea F. Muell., E. melanophloia F. Muell. and Acacia harpophylla F. Muell. ex. Benth. were selected on one property in central Queensland to quantify the impacts of clearing on pasture production and composition, and soil properties. The impacts were measured over time-since-clearing (recent (&lt5 years), medium (11-13years) and old (&gt30 years)) in unreplicated cleared pastures in comparison to their replicated uncleared/intact woodland pastures of each tree community. Measures of pasture above-ground biomass production on a single property over time-sinceclearing in cleared systems showed that gains were not sustained over the long-term. The difference in response to clearing between tree communities was evident and important to support the future policy decisions. The impact of clearing on soil properties (physicochemical and biological) was confirmed, and explained the lesser availability of nutrients with time of clearing in cleared pastures. The changes in some soil properties underscored the associated risks and changes in ecosystem functions due to clearing. Less litter was produced at cleared than uncleared pastures, but nutrient release was faster at cleared compared to uncleared systems. The overall effect of clearing in terms of pasture and litter production, and major soil parameters were analysed using multivariate analyses.

Earthquakes are among the most destructive natural disasters affecting urban populations. Structural damage caused by the earthquakes varies depending not only on the seismic source and propagation properties but also on the soil properties. The amplitude and frequency content of seismic shear waves reaching the earth&rsquo / s surface is dependent on local soil conditions. It is well known that the soft sediments on top of hard bedrock can greatly amplify the ground motion and cause severe structural damage. When the fundamental period of the soil is close to the fundamental period of a structure, structural damage increases significantly. Estimation of the fundamental periods, amplification factors and types of soils is critical in terms of reduction of loss and casualties. For the reasons stated, estimation of dynamic behavior of soils has become one of the major topics of earthquake engineering. Studies for determining dynamic properties of soils depend fundamentally on the estimation of the S-wave velocity profiles, amplification factors and ground response. In this study first, the Multi-Mode Spatial Autocorrelation (MMSPAC) method is used to estimate the S-wave velocity profiles at the sites of interest. This method is different than the other ones in the sense that it works for the higher modes as well as the fundamental mode. In the second part, Horizontal to Vertical Spectral Ratio (HVSR) method will be used on both microtremor and ground motion data. Finally, the amplification factors from alternative methods are compared with each other. Consistent results are obtained in terms of both fundamental frequencies and amplification factors.

In this dissertation, the framework is being developed for a new method to predict the settlements of shallow foundations on granular soil based on field seismic and laboratory dynamic tests. The new method combines small-strain seismic measurements in the field with nonlinear measurements in the field and/or in the laboratory. The small-strain shear modulus (Gmax ) of granular soil and the stress dependency of Gmax is determined from the shear wave velocity measurements in the field. Normalized shear modulus (G/Gmax ) versus log shear strain(log [gamma]) curves are determined from field or laboratory measurements or from empirical relationships. The G/Gmax -- log [gamma] curves and Gmax values are combined to determine the shear stress-shear strain response of granular soil starting from strains of 0.0001% up to 0.2-0.5%. The shear stress-shear strain responses at strains beyond 1.0-2.0 % are evaluated by adjusting the normalized shear modulus curves to larger-strain triaxial test data. A user defined soil model (MoDaMP) combines these relationships and incorporates the effect of increasing confining pressure during foundation loading. The MoDaMP is implemented in a finite element program, PLAXIS, via a subroutine. Measured settlements from load-settlement tests at three different sites where field seismic and laboratory dynamic measurements are available, are compared with the predicted settlements using MoDaMP. Predictions with MoDaMP are also compared with predictions with two commonly used methods based on Standard Penetration and Cone Penetration tests. The comparison of the predicted settlements with the measured settlements show that the new method developed in this research works well in working stress ranges. The capability of the new method has significant benefits in hard-to-sample soils such as in large-grained soils with cobbles and cemented soils where conventional penetration test methods fail to capture the behavior of the soil. The new method is an effective-stress analysis which has applicability to slower-draining soils such as plastic silts and clays. / text

Žemės dirbimas yra vienas iš daugiausia darbo, energetinių bei laiko sąnaudų reikalaujančių technologinių darbų auginant augalus. Todėl įvairaus intensyvumo žemės dirbimo sistemų nustatymas, kurios nemažindamos žemės ūkio augalų derliaus neblogintų dirvožemio agrocheminių savybių, yra svarbus ir ekonomine, ir aplinkosaugine prasme. Pasikliaujama ribotu paviršiaus purenimu, ražienine sėja. Taip sutaupomos lėšos, mažiau gaištama laiko dirvai ruošti. Dėl gilaus ir pastovaus žemės dirbimo gali mažėti humuso kiekis, o tai sąlygoja mažesnį žemės ūkio augalų derlių. Tyrimų tikslas – įvertinti tiesioginės sėjos į neįdirbtą dirvą, supaprastinto žemės dirbimo ir šiaudų bei kitų augalinių liekanų įtaką dirvožemio agrocheminėms savybėms. Stacionarus bandymas įrengtas 1999 m. Aleksandro Stulginskio universiteto Bandymų stotyje. Lauko bandymas dviejų veiksnių: A veiksnys – šiaudų įterpimas: šiaudai pašalinti (-Š); šiaudai susmulkinti ir paskleisti (+Š). B veiksnys – žemės dirbimo sistemos: įprastinis gilus arimas 23–25 cm gyliu rudenį (GA); seklus arimas 10–12 cm gyliu rudenį (SA); seklus purenimas kultivatoriumi plokščiapjūviais noragėliais ir lėkštiniais padargais 8–10 cm gyliu rudenį (KL); seklus purenimas rotoriniu kultivatoriumi 5–6 cm gyliu prieš sėją (RK); seklus žaliosios trąšos įterpimas rotoriniu kultivatoriumi 5–6 cm gyliu prieš sėją (ŽTRK); neįdirbta dirva, tiesioginė sėja (ND). Pastovus šiaudų panaudojimas didina dirvožemio pH, humuso ir azoto kiekius. Humusą ir azotą... [toliau žr. visą tekstą] / Cultivation is one of energy and time-consuming activities of cropping. Establishment of various intensity tillage systems that does not influence the agrochemical soil properties and yield loss is important for both economical and environmental sense. Ploughing is being replaced by reduced topsoil loosening or cultication. It helps to save time and money for soil preparation. Deep and constant tillage can cause the decrease of humus substances that can lead to lower crop yield. Objective of the experiment – to assess how direct sowing into ploughless soil, reduced tillage and straw incorporation influence agrochemical soil properties. Stationary two factor field experiment was established in Experimental Station of Aleksandras Stulginskis University in 1999. Treatments: Factor A – straw incorporation: without straw (-Š); with straw (+Š). Factor B– soil tillage systems: deep ploughing at 23–25 cm depth in autumn (GA); shallow ploughing at 10–12 cm depth in autumn (SA); shallow loosening at 8–10 cm depth in autumn (KL); shallow loosening with rotary cultivator at 5–6 cm depth before sowing (RK); shallow incorporation of green manure with rotary cultivator at 5–6 cm depth before sowing (ŽTRK); no tillage, direct sowing (ND). Constant use of straw increases the amount of soil pH, humus and nitrogen. The amount of humus and nitrogen is mostly increased by shallow loosening with rotary cultivator (RK), shallow implementation of green manure by this cultivator in spring (ŽTRK) and... [to full text]

Submitted by Claudia Rocha (claudia.rocha@udesc.br) on 2017-12-01T12:56:57Z No. of bitstreams: 1 PGCS15MA129.pdf: 879531 bytes, checksum: e78ae25345fc9732cf6389f2d2af1fb2 (MD5) / Made available in DSpace on 2017-12-01T12:56:57Z (GMT). No. of bitstreams: 1 PGCS15MA129.pdf: 879531 bytes, checksum: e78ae25345fc9732cf6389f2d2af1fb2 (MD5) Previous issue date: 2015-04-28 / Capes / Cover crops can be grown in the vineyards to erosion control and also as an alternative to prevent over vegetative vigor, due to competition for water and nutrients. The objective of this study was to evaluate the effects of cultivation and management of cover crops in vineyard of Cabernet Sauvignon in the Southern Brasilian Higlands. They were determined soil chemical properties and its correlation with the leaf nutrient content and also the dry matter production (DM) of cover plants and vine branches. The evaluations were in the 2013/14 season, in an experiment started in 2009. The treatments were composed by a control, the succession of annual species, buckwheat (Fagopyrum esculentum) and ryegrass (Lolium multiflorum), the perennial specie fescue (Festuca arundinacea) and wild plants, in addition to managements with and without transfer the cultural residue from the line to the leading vine. The leaves sampling was performed at "veraison" stage, while the soil sampling was made at three layers (0 - 5, 5 - 10, 10 - 15 cm) in the stage of ripening berries. In general, cover crops and their management did not affect the pH, Al, Ca and Mg in the soil. But the annual increased available P in the layer 0 - 5 cm, while the perennial generally increased the exchangeable K in layers up to 15 cm relative to the control. The fescue reduced the P and K leaf content compared to other treatments, N compared to annual and native plants and Mg compared to annual plants. The exchangeable K and the K/Mg ratio in the soil correlated positively with the K content and with the K/Mg ratio and negatively with Ca and Mg content in the leaves. The soil Ca content correlated positively with K leaf content, as well as soil Mg, with the K and P leaf content. The K/Mg soil rate correlated negatively with Ca and Mg, and positively with the K/Mg ratio in the leaves. The succession of annual species produced higher DM than perennial, but this resulted in lower dry branches mass relative to the control. Overall, the management of cover crops was little influence in the evaluated variables / Plantas de cobertura do solo podem ser cultivadas nos vinhedos para controle da erosão e também como alternativa para evitar o excesso de vigor vegetativo, devido à competição por água e nutrientes. O objetivo deste trabalho foi avaliar os efeitos do cultivo e do manejo dos resíduos das plantas de cobertura em vinhedo da cultivar Cabernet Sauvignon na região do Planalto Sul Catarinense. Foram determinados os atributos químicos do solo e sua correlação com os teores foliares de nutrientes e também a produção de massa seca (MS) das plantas de cobertura e dos ramos da videira. As avaliações foram realizadas na safra 2013/14, em um experimento iniciado em 2009. Os tratamentos foram compostos por um testemunha, pela sucessão de espécies anuais, o trigo mourisco (Fagopyrum esculentum) e o azevém (Lolium multiflorum), pela espécie perene festuca (Festuca arundinacea) e por plantas espontâneas, além dos manejos com e sem a transferência do resíduo cultural da linha para a entrelinha da videira. A amostragem das folhas foi realizada na fase de “veraison”, enquanto a do solo foi feita em três camadas (0 - 5, 5 - 10 e 10 - 15 cm) na fase da maturação das bagas. Em geral, as plantas de cobertura e seu manejo não afetaram o pH, os teores de Al, Ca e Mg trocáveis no solo. Porém as anuais aumentaram o P extraível na camada 0 - 5 cm, enquanto a perene em geral aumentou o K extraível nas camadas até 15 cm, relativamente à testemunha. A festuca reduziu os teores foliares de P e K relativamente aos demais tratamentos, de N relativamente às plantas anuais e nativas e, de Mg relativamente às anuais. O K extraível e a relação K/Mg do solo correlacionaram-se positivamente com o teor de K e com a relação K/Mg e, negativamente com os teores de Ca e Mg nas folhas. O Ca do solo correlacionou-se positivamente com o teor de K foliar, assim como o Mg do solo, com os teores de K e P foliares. A relação K/Mg do solo correlacionou-se negativamente com os teores de Ca e Mg e, positivamente com a relação K/Mg foliares. A sucessão de anuais produziu maior MS do que a perene, porém essa resultou em menor MS de ramos relativamente à testemunha. Em geral, houve pouca influência do manejo das plantas de cobertura nas variáveis avaliadas

Submitted by Socorro Pontes (socorrop@ufersa.edu.br) on 2016-11-10T13:24:03Z No. of bitstreams: 1 RaimundoFOJ_DISSERT.pdf: 5109809 bytes, checksum: 17891bc19c02d08252058bf14be4b86e (MD5) / Approved for entry into archive by Vanessa Christiane (referencia@ufersa.edu.br) on 2016-11-14T13:41:17Z (GMT) No. of bitstreams: 1 RaimundoFOJ_DISSERT.pdf: 5109809 bytes, checksum: 17891bc19c02d08252058bf14be4b86e (MD5) / Approved for entry into archive by Vanessa Christiane (referencia@ufersa.edu.br) on 2017-01-24T14:33:17Z (GMT) No. of bitstreams: 1 RaimundoFOJ_DISSERT.pdf: 5109809 bytes, checksum: 17891bc19c02d08252058bf14be4b86e (MD5) / Made available in DSpace on 2017-03-21T14:48:38Z (GMT). No. of bitstreams: 1 RaimundoFOJ_DISSERT.pdf: 5109809 bytes, checksum: 17891bc19c02d08252058bf14be4b86e (MD5) Previous issue date: 2016-02-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Knowledge of the use and occupation of land and water management is extremely necessary for an integrated and sustainable management of its resources, particularly water and soil. Allied to this, the spatial distribution of soil properties play a fundamental role in the design and understanding of human impacts on watersheds. Then, describe and map the land use and occupation with the spatial variability of its attributes is very important to put into practice techniques of rational and appropriate management of exploitation of these resources. Geostatistics has contributed increasingly to space research soil attributes. Therefore, the objective of this work dissertation was to map the use and occupation of land along with their attributes, using GIS and geostatistics, a perennial watershed shed in semi-arid conditions. The watershed of pecks Creek belongs to the middle reaches of the river basin of Apodi-Mossoró River, located in the west of Rio Grande do Norte state. inderformadas and misshapen collected soil to carry out the laboratory of physical water and soil chemical attributes analyzes were performed. The study showed that the use of geostatistics was suitable for the measurement of the spatial dependence of soil properties in a watershed, with the theoretical models, exponential and spherical, who played better results. Among the attributes of the soil studied the chemicals suffered greater interference of human impacts in the area. With this work it was possible to conclude that the map of land use and occupation, along with maps of spatial variability of soil attributes, proved to be a powerful assessment tool of environmental impacts on watersheds and contribute to the planning rational use and land use in watersheds sustainably / O conhecimento do uso e ocupação do solo em bacias hidrográficas é extremamente necessário para um gerenciamento integrado e sustentável de seus recursos, em especial água e solo. Aliado a isso, a espacialização dos atributos do solo tem papel fundamental no dimensionamento e entendimento dos impactos antrópicos em bacias hidrográficas. Logo, descrever e mapear o uso e ocupação do solo juntamente com a variabilidade espacial de seus atributos é de suma importância para se colocar em prática técnicas de manejo racional e adequada de exploração desses recursos. A geoestatística tem contribuído cada vez mais para pesquisa espacial de atributos do solo. Portanto, o objetivo deste trabalho de dissertação foi mapear o uso e ocupação do solo juntamente com seus atributos, utilizando SIG e geoestatística, numa microbacia hidrográfica perene de vertente, em condições semiáridas. A microbacia hidrográfica do Riacho da bica pertence ao médio curso da bacia hidrográfica do rio Apodi-Mossoró, localizada no Oeste do estado do Rio Grande do Norte. Foram realizadas coletas inderformadas e deformadas do solo para realização das analises laboratoriais dos atributos físico-hídricos e químicos do solo. O estudo mostrou que o uso da geoestatística foi adequado para a mensuração da dependência espacial dos atributos do solo numa microbacia hidrográfica, sendo os modelos teóricos, exponencial e esférico, os que desempenharam melhores resultados. Dentre os atributos do solo estudados, os químicos sofreram maior interferência dos impactos antrópicos na área. Com esse trabalho foi possível concluir que, o mapa de uso e ocupação do solo, juntamente com os mapas de variabilidade espacial dos atributos do solo, mostrou-se uma poderosa ferramenta de avaliação de impactos ambientais em microbacias hidrográficas, além de contribuírem para o planejamento racional do uso e ocupação do solo em bacias hidrográficas de forma sustentável / 2016-10-20

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Starting from the assumption that changes in land use can provide changes in physical and chemical properties, influencing its quality, the study aimed to verify whether the introduction of Pinus taeda L., on soil under native grassland conditions, can degrade physical and chemical quality of Haplumbrept soil in different rotations. The study was conducted in the region of Campos de Cima da Serra - RS, Brazil, where there are large forested areas with pine trees. To this, were selected two study areas, one in the first (RT1) and another in the second rotation (RT2), with 13 years of age. For each stand, was assessed a combined area of grassland adjacent (control). In each area, five trenches were opened and collected soil samples at depths from 0.0 to 0.05, from 0.05 to 0.20, 0.20 to 0.40 and 0.40-0.60 m. Changes in physical properties were analyzed using the following parameters: particle size, particle density, bulk density, porosity, macro and micro porosity, hydraulic conductivity of saturated soil, soil air permeability and size distribution of water stable aggregates. The chemical determinations were: calcium, magnesium, phosphorus, potassium, pH, pHSMP, exchangeable aluminum, total nitrogen and total organic carbon. At RT1 was a change in the macro and microporosity, influencing the behavior of hydraulic conductivity and air permeability at 6 and 10 kPa. At RT2, the effect of pine in the macro, microporosity and hence hydraulic conductivity, occurred only in the surface layer (0.0 to 0.05 m) due to the management adopted in the area. Considering the two study areas, there was a reduction of the aggregate stability in the layer from 0.05 to 0.20 m. However, in the same layer, the RT2 presented an increase in stability of aggregates of smaller size classes, reflecting the management type. The chemical properties were altered mainly in the surface layers, with reductions of exchangeable bases (Ca and Mg) and elevation of P saturation. The pine has also promoted increased levels of Al and decrease in pH, increasing soil acidity and reducing thereby the quality of Haplumbrept soil. In RT1, the content of C and N were reduced in the surface layer, but in RT2, levels of C and N were similar to natural field, inferring in the long run, the ability to restore the levels of C in soil. / Partindo-se do pressuposto de que mudanças no uso do solo podem proporcionar alterações nas propriedades físicas e químicas, influenciando a sua qualidade, o objetivo do estudo foi verificar se a introdução da espécie Pinus taeda L., em solo sob campo natural, pode degradar física e quimicamente a qualidade do Cambissolo Húmico, em diferentes rotações. O estudo foi conduzido na região dos Campos de Cima da Serra RS, Brasil, onde ocorrem grandes áreas florestadas com pínus. Para isso, foram escolhidas duas áreas de estudo, uma em primeira (RT1) e a outra em segunda rotação (RT2), com 13 anos de idade. Para cada povoamento, foi avaliada conjuntamente uma área de campo natural adjacente (testemunha). Em cada área, foram abertas 5 trincheiras e coletadas amostras de solo nas profundidades 0,0-0,05; 0,05-0,20; 0,20-0,40 e 0,40-0,60 m. As alterações nas propriedades físicas foram analisadas através das seguintes determinações: granulometria, densidade de partículas, densidade do solo, porosidade total, macro e microporosidade, condutividade hidráulica do solo saturado, permeabilidade do solo ao ar, e distribuição do tamanho de agregados estáveis em água. As determinações químicas realizadas foram: cálcio, magnésio, fósforo, potássio, pH em água, pHSMP, alumínio trocável, nitrogênio total e carbono orgânico total. Na RT1 houve alteração na macro e microporosidade, influenciando o comportamento da condutividade hidráulica e permeabilidade ao ar a 6 e 10kPa. Na RT2, o efeito do pínus na macro, microporosidade e, consequentemente, na condutividade hidráulica, ocorreu somente na camada superficial (0,0 a 0,05 m), devido ao manejo adotado na área. Considerando as duas áreas de estudo, houve redução da estabilidade dos agregados na camada de 0,05 a 0,20 m. No entanto, na mesma camada, a RT2 apresentou elevação na estabilidade de agregados de classes de tamanho menores, refletindo o manejo adotado. As propriedades químicas foram alteradas principalmente nas camadas superficiais, apresentando reduções das bases trocáveis (Ca e Mg) e elevações dos teores de P trocável. O pínus também promoveu o aumento nos teores de Al e a diminuição do pH, elevando a acidez do solo e reduzindo, dessa forma, a qualidade do Cambissolo Húmico. Na RT1, os teores de C e N foram reduzidos na camada superficial, porém, na RT2, os níveis de C e N apresentaram-se similares ao campo natural, inferindo, em longo prazo, a capacidade de restauração dos níveis de C no solo.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Productivity of an area is characterized by a series of factors of soil, climate, genetic potential and attack of diseases and pests and competition. Among these various factors, in the soil, the physical quality is not taken into consideration in order to set the production potential of a crop. The resistance to penetration of the soil (RP) should receive attention when it seeks to improve the quality of the soil, because it is an attribute that has direct reflection on crop productivity. Spatial variability of soil physical properties may have a better evaluation by Geostatistics, which determines the spatial dependence of each attribute. In addition to the determination of resistance to penetration, it is recommended connecting additional information such as soil type, water content and particle size, as they may be indicative of the reliability of the results. Added to this, it is important to determine the number of subsamples which must be used, i.e. how many samples must be carried out at one point to provide greater precision. Thus, the objective of this study was to verify the spatial variability of the values of RP, particle size and soil moisture, as well as verify the influence of the particle size and soil moisture at the time of determination of the values and define what the minimum number of subsamples which must compose each sample. To this end, the work is in two studies. In the first one, analysis were performed in 12 equidistant points among themselves, where in each of the repetitions were made determinations of cross shaped RP, spaced 0.20 m between each other within a maximum radius of 2 m totaling 41 samples, where four collection methodologies were tested. In the second one, in an area of 4.58 ha, was generated a sample of 10 x 10 m, with a total of 425 points. RP determinations were performed, particle size and soil moisture in four depths. It was found that using a methodology to collect least number of subsamples shows no significant changes in the values of coefficient of variation and the determination of subsamples near the midpoint, in densely populated meshes, eliminates the possibility of embedding medium which may belong to the erroneous point neighbor. Furthermore, the sampling mesh was efficient to demonstrate the variability and attributes presented spatial differential behaviour. The degree of compression of the varied depending on the depth. The correlation analysis, only the attribute humidity presented negative correlation with the RP. / A produtividade de uma área é caracterizada por uma série de fatores de solo, clima, potencial genético e ataque de doenças e pragas e matocompetição. Dentre estes vários fatores, no solo, a qualidade física não é levada em consideração para se determinar o potencial produtivo de uma lavoura. A resistência à penetração do solo (RP) deve receber atenção quando se busca melhorar a qualidade do solo, pois é um atributo que tem reflexo direto na produtividade das culturas. A variabilidade espacial das propriedades físicas do solo pode ter uma melhor avaliação através da Geoestatística, onde se determina a dependência espacial de cada atributo. Além da determinação da resistência à penetração, é recomendável relacionar informações complementares ao tipo de solo tais como, teor de água e granulometria, pois podem ser indicativos da confiabilidade dos resultados. Somado a isto, é importante determinar o número de subamostras que devem ser utilizadas, ou seja, quantas amostras devem ser realizadas em um ponto para que se tenha a maior precisão. Desta forma, o objetivo deste estudo foi verificar a variabilidade espacial dos valores de RP, granulometria e umidade do solo, bem como verificar a influência da granulometria e da umidade do solo no momento da determinação dos valores e definir qual o número mínimo de subamostras que devem compor cada amostra. Para tanto, o trabalho constitui-se em dois estudos. No primeiro, foram realizadas análises em 12 pontos equidistantes entre si, onde em cada uma das repetições foram realizadas determinações de RP em forma de cruz, espaçadas 0,20 m entre si, dentro de um raio máximo de 2 metros totalizando 41 amostras, onde foram testadas quatro metodologias de coleta. No segundo, em uma área de 4,58 ha, foi gerada uma malha amostral de 10 x 10 m, totalizando 425 pontos. Foram realizadas determinações de RP, granulometria e umidade do solo em quatro profundidades. Verificou-se que o usode uma metodologia com coleta de menor número de subamostras não apresenta alterações significativas nos valores de coeficiente de variação, além de que a determinação de subamostras próximas ao ponto central, em malhas adensadas, elimina a possibilidade de embutir médias errôneas que possam pertencer ao ponto vizinho. Além disso, a malha amostral foi eficiente para demonstrar a variabilidade e os atributos apresentaram comportamento espacial diferenciado. O grau de compactação da área variou conforme a profundidade. Quanto à análise de correlação, somente o atributo umidade apresentou correlação negativa com a RP.

The submitted diploma thesis aims to extend the use of thermogravimetry for the analysis of organic C and total N contents in soils. The advantages of thermogravimetry in comparison to conventional analytical methods are that it is a versatile technique that provides fast analysis, does not require sample pretreatment and chemicals– and can be used for the analysis of various soil types. The research work performed so far showed correlations between thermogravimetric data and some soil properties. In the past, intact soils exposed to 76% relative humidity (RH) were analyzed by thermogravimetry for these purposes. However, this humidity is problematic to achieve and maintain for most thermogravimeters. Recent work has shown that correlations can be observed in agricultural land exposed to lower RH. Therefore, it can be assumed that a correlation between TG data exists in soils exposed to any RH. TG could then be used to analyze soil properties under any known RH conditions. The aim of this work was to verify this hypothesis and try to incorporate knowledge of RH into the relationships between TG and soil properties. For this reason, intact soils exposed to the relative humidity of 30, 55, and 76% were analyzed in this work. It was demonstrated the dependence between organic C content and mass loss between 320 and 330°C as well as total nitrogen content and mass loss between 410 and 420°C independently of relative humidity. Based on that knowledge, we have derived equations enabling determination of the content of organic C and total N for RH ranging 43% - 76% using mass losses and knowledge of RH. Nevertheless, due to the low number of tested RH, the equations are still only preliminary and need to be improved by analyzing soil samples at a larger number of RH.

Thesis (M.Sc. Agriculture (Pasture Science)) -- University of Limpopo, 2020 / Bush encroachment is a major problem in arid and semi-arid savannas characterized by a grass layer interspersed with a shrub stratum. Land cover change as a result of rapid proliferation of woody species in previously open rangelands alters herbaceous species and impacts soil properties. So far, little is known about the threshold at which woody plant density and cover affects herbaceous cover and the underlying mechanisms driving bush encroachment in arid and semi-arid rangelands are still debated. The objectives of this dissertation were to (1) to assess woody species composition and structure along an encroachment gradient and to explore the relationship between woody vegetation and herbaceous vegetation. (2) To determine the effect of increasing tree density and cover on grass species richness, diversity, evenness and selected soil nutrients in a bush encroached rangeland. In order to address these objectives, a semi-arid rangeland was demarcated into three encroachment gradients spanning from open to intermediate and intensive. Within each encroachment gradient six plots of 10 m x 10 m were randomly selected, whereby woody and herbaceous vegetation were assessed and soil properties determined. A discernible increase in woody species diversity and evenness was found along the transition from open to intensive bush encroached rangeland. Leguminous woody species Vachellia spp. and Dichrostachys cinerea were dominant along the bush encroachment gradient. Tree height was found to be positively correlated with long crown diameter (LCD) and short crown diameter (SCD). Furthermore, increasing tree density resulted in a 53% decline in grass species richness (GR). A decline in GR mirrored an increase in the composition of the decreaser species Panicum maximum (90%). Increasing woody plant density and cover also increased macro-nutrients; total carbon, nitrogen, phosphorus, exchangeable calcium and magnesium by 21%-159% in the shallow rangeland soils. Such quantitative information will assist rangeland managers to better understand the effects of varying bush encroachment intensities on herbaceous species composition, richness and soil properties in semi-arid savanna rangelands.