<p>Soil organic carbon (OC) is one of the most important terrestrial carbon pools and plays a major role in climate regulation, water quality, provisional services, and numerous other ecosystem functions. The conversion of natural vegetation and the supporting soil to intensively managed agricultural systems put soil at risk for loss due to erosion and enhanced microbial degradation with loss rates increased by orders of magnitude above the pre-managed system. The process has negatively impacted agricultural productivity on hillslopes by diminishing soil health, as well as the quality of stream water and coastal aquatic environments, and it is an important but as of yet poorly quantified factor in the region’s terrestrial C budgets. There have been substantial debates on the role of erosional and depositional processes on the landscape as a control on exchange of C between the land surface and the atmosphere. A central aspect of the debate stems from the limited data regarding the fate of soil erosion-induced transport of OC through stages of detachment and splash, transport and redistribution, deposition and burial. The overarching purpose of this thesis is to evaluate how dynamic patterns of soil OC erosion due to intensive agricultural management influences soil aggregate strength, the chemical nature of mobilized organic particles, and connectivity and sourcing between hillslope and streams. Using both simulated and natural, short-term, event-based erosive rainfall processes, with a multiproxy geochemical approach, we attempt to develop a comprehensive understanding of how upland watershed mechanistic controls soil movement and associated chemical alterations to the material exported through dissected segments from hillslope to the fluvial network. </p> <p>Our results demonstrate that erosive processes on hillslope connects between terrestrial sources to receiving potential deposition settings, actively ‘filter’ soil aggregates and particles and associated OC at each erosional stage (i.e., detachment and transport downhill/downstream), with distinct geochemistry in low relief and poorly drained agricultural systems, like the CCW. Complex interactions among tillage intensity, tillage practice-induced, oriented surface roughness, and storm-induced hydrological connectivity, that potentially impact the fate of these transported OC upon decomposition, deposition and burial, and have important implications for predicting landscape level heterogeneity in surface and buried soil chemistry upon mobilization and burial, as well as the dynamics of sourcing and transformation of material exported to inland water systems.</p>

As propriedades físicas do solo são preponderantes para a qualidade e produtividade da cultura da batata. Assim, o objetivo do presente trabalho foi avaliar algumas propriedades físicas do solo e a produtividade e qualidade dos tubérculos de batata. O experimento foi instalado em áreas de produção de batata na Chapada Diamantina (BA), de abril a agosto de 2005. O solo foi preparado pelo sistema convencional e pelo sistema alternativo MAFES, ambos associados ou não com a aplicação de Microrganismos Eficazes (EM). Foram avaliadas: a densidade do solo, a estabilidade de agregados, a resistência do solo à penetração, a taxa de infiltração de água e a retenção de água no solo. Também foi avaliada a alteração dessas propriedades do solo em relação à área antes do preparo, que estava sob pastagem de Brachiaria brizantha. A massa de torrões e touceiras colhidas juntamente com os tubérculos, bem como os danos mecânicos verificados durante a colheita mecanizada e a porcentagem de tubérculos com danos causados por larva alfinete, sarna e podridões foram quantificados. A produtividade nos diferentes tratamentos foi avaliada dentro da classificação comercial. Em relação ao pasto, os preparos convencional e MAFES alteraram a maioria das propriedades físicas avaliadas. Na área preparada pelo sistema MAFES foi observado, em relação ao preparo convencional, menor resistência à penetração em profundidades de 20 a 45 cm e entre os camalhões. A taxa de infiltração de água foi semelhante entre as áreas preparadas pelos dois sistemas, porém no sistema convencional a infiltração é mais superficial ocorrendo de forma lateral ao longo do perfil. No sistema MAFES a infiltração ocorreu verticalmente no perfil do solo. Menor porcentagem de tubérculos com danos mecânicos foi obtida na área preparada pelo sistema MAFES, devido, principalmente, a menor massa de torrões e touceiras colhidas juntamente com os tubérculos nessa área. A aplicação de EM teve pouca influência nas propriedades físicas do solo, mas propiciou condições que favoreceram o ataque de larva alfinete e sarna aos tubérculos. Apesar da utilização de EM ter reduzido a produção de tubérculos na área preparada pelo sistema MAFES, a produtividade e qualidade dos tubérculos nessa área foi superior a da área preparada pelo sistema convencional. / The physical soil properties have a relevant role on the yield and quality of potato crop. Thus, the purpose of the present research was to evaluate the effects on some soil physical properties on productivity and quality of potato tubers. The trial was set up in a commercial potato production field located in the Chapada Diamantina, BA, from April to August, 2000. Two distinct soil preparation systems (conventional and MAFES system), either associated or not with application of EM, have been trialed. The following soil properties were evaluated: bulk density, aggregate stability, soil penetration resistance, soil water retention and water infiltration rate. In addition, were evaluated the changes of such soil properties in comparison with the area cultivated with the grass Brachiaria brizantha, prior soil preparation. Other evaluations were performed such as the clod mass and clump of roots harvested together with potato tubers, the level of damage to the tubers caused by mechanical harvesting, and the amount of tubers affected by potato tuber moth, rots, and common scab. The yields of the different treatments were evaluated and tubers graded according to commercial patterns. Compared to the grass, both conventional and MAFES soil preparation systems have changed the physical soil properties studied. MAFES system outperformed the conventional preparation giving lesser resistance to penetration at 20 to 45 cm deep and between hills. The water infiltration rate was similar for both soil preparation systems; however for the conventional system the infiltration pattern is superficial occurring laterally in the soil profile. Regarding MAFES systems, the infiltration occurred vertically. The area prepared MAFES system also gave a fewer percentage of tubers exhibiting mechanical damage, due to smaller clod mass and clump of roots harvested together with potato tubers. EM application did not benefit physical soil properties, however influenced a higher attack of potato tuber moth and common scab. Although the yield decrease in the area prepared with MAFES system when the EM was applied, in this area the productivity and tuber quality outperformed the conventional system.

O estudo foi dividido em quatro partes. Na primeira parte analisou-se o impacto do clima na estocagem de carbono em solos de canaviais sem a queima da palhada. Foram escolhidos três regimes climáticos contrastantes do centro-sul do Brasil. O potencial de seqüestro de carbono orgânica no solo (COS) foi determinado, em cada regime climático, de acordo com a taxa anual de carbono remanescente no solo proveniente da palhada depositada. Para obter esta taxa, compararam-se os estoques de COS em canaviais com e sem queima da palhada. Esse ganho anual foi comparado com a entrada anual de carbono via palhada depositada. O ganho anual de COS (0-30 cm) em canaviais sem queima da palhada não resultou em diferenças significativas por clima: 1, 97 Mg ha-1 (clima norte), 2,00 Mg ha-1 (clima centro) e 1,70 Mg ha-1 (clima sul). Os regimes climáticos estudados também não revelaram diferenças significativas entre suas temperaturas e precipitações médias anuais. Porém, o aumento anual de COS um pouco menor no clima sul levou à conclusão que o potencial de seqüestro de carbono diminui ligeiramente em latitudes mais altas, devido à maior precipitação no centro-sul do Brasil. Na segunda parte avaliou-se o impacto da palhada sobre a estabilidade de agregados dos solos, que foi calculada pelo método de fracionamento proposto por Six et al. (2000a). A estabilidade de agregados no solo do canavial sem a queima da palhada aumentou, em média, 15,3% por ano na profundidade 0-30 cm. Na terceira parte, avaliou-se a diferença da estabilidade de agregados entre canaviais e mata nativa. O solo da mata nativa mostrou uma estabilidade de agregados significativamente maior (7,2 vezes). Supõe-se que a estabilidade de agregados seja maior na mata nativa como resultado da maior presença de matéria orgânica e biota no solo. Na quarta parte avaliou-se a origem do carbono nos agregados estáveis em água de fluxo contínuo para determinar que forma de agregação possui a melhor proteção contra a decomposição de carbono. Houve uma diferença significativa de \'delta\'13C entre os macroagregados e microagregados na camada superior, com 10% mais \'delta\'13C nos macroagregados. Isto indica mais carbono derivado da cobertura vegetal atual (C4), ou seja, mais incorporação da palhada nos macroagregados. O \'delta\'13C da fração de partículas livres ou agregados não estáveis em água de fluxo contínuo é menor em todas as profundidades, indicando que a matéria orgânica recente (C4) encontra-se no solo principalmente de forma agregada estável em água, evidenciando seu papel fundamental na estabilidade dos agregados. Constatou-se também, que quanto mais novo o macroagregado, maior o seu teor em carbono. Nos microagregados verificou-se o efeito contrário. Quanto mais velho o microagregado, maior o seu teor em carbono. Isso indica que o microagregado possui uma melhor proteção contra a decomposição de carbono, e também a capacidade de um aumento no teor de carbono, no decorrer do tempo, em virtude da assimilação de carbono mais novo. Conclui-se, que em termos de seqüestro de carbono de longa duração, é propício avaliar mecanismos de proteção do carbono recalcitrante dentro dos microagregados e estudar como técnicas agrícolas podem proteger melhor esta fração / The study was divided in four parts. The first part investigated climate impact on soil carbon stocks in sugar cane fields cultivated without green trash burning. For this purpose, three contrasting climates were chosen in Central and Southern Brazil. The sequestration potential of soil organic carbon (SOC) was determined for each climate, calculating how much of the carbon derived from deposited green trash remains in the soil every year. To obtain this rate, SOC stocks of sugar cane fields cultivated with and without green trash burning were compared. The annual difference (0-30 cm) did not differ significantly between climates: 1, 97 Mg ha-1 (Northern Climate), 2,00 Mg ha-1 (Central Climate) and 1,70 Mg ha-1 (Southern Climate). The climates did not show significant differences between their average annual temperatures and their annual precipitation. Nevertheless, a slightly smaller gain of SOC stocks in the Southern Climate leads to the conclusion that higher latitudes tend to stock slightly less COS due to higher annual precipitation. The second part evaluated the impact of green trash deposition on soil aggregate stability, which was calculated according to Six et al. (2000a). Soil aggregate stability under sugar cane fields cultivated with green trash burning had an average increase of 15,3% for soil depth 0-30 cm. The third part studied soil aggregate stability between sugar cane and natural forest vegetation. The forest soil revealed significantly higher (7,2 times) aggregate stability, supposedly due to higher organic matter content and more soil biota. The forth part examined the origin of carbon inside water-stable aggregates to determine which aggregation form provides better protection against carbon decomposition. The top soil layer showed a significant difference in \'delta\'13C between macro-aggregates (10% more \'delta\'13C) and microaggregates which means that more carbon derived from green trash (C4) was incorporated in macro-aggregates. \'delta\'13C of free soil particles or water-unstable aggregates is smaller for all soil layers indicating that fresh organic matter (green trash) is predominantly encountered in a water stable aggregated form in the soil. Furthermore, a correlation analysis revealed that more recent macro-aggregates had higher C content. The opposite was observed for micro-aggregates: the older the micro-aggregate, the higher its carbon content, leading to the conclusion that microaggregates protect carbon better against decomposition and are also capable to enrich their carbon pool through C assimilation. Given its long-term soil carbon sequestration potential, it is recommended to investigate carbon protection mechanisms for the recalcitrant C pool in micro-aggregates and also to study how agricultural techniques could improve the protection of the recalcitrant C pool

As propriedades físicas do solo são preponderantes para a qualidade e produtividade da cultura da batata. Assim, o objetivo do presente trabalho foi avaliar algumas propriedades físicas do solo e a produtividade e qualidade dos tubérculos de batata. O experimento foi instalado em áreas de produção de batata na Chapada Diamantina (BA), de abril a agosto de 2005. O solo foi preparado pelo sistema convencional e pelo sistema alternativo MAFES, ambos associados ou não com a aplicação de Microrganismos Eficazes (EM). Foram avaliadas: a densidade do solo, a estabilidade de agregados, a resistência do solo à penetração, a taxa de infiltração de água e a retenção de água no solo. Também foi avaliada a alteração dessas propriedades do solo em relação à área antes do preparo, que estava sob pastagem de Brachiaria brizantha. A massa de torrões e touceiras colhidas juntamente com os tubérculos, bem como os danos mecânicos verificados durante a colheita mecanizada e a porcentagem de tubérculos com danos causados por larva alfinete, sarna e podridões foram quantificados. A produtividade nos diferentes tratamentos foi avaliada dentro da classificação comercial. Em relação ao pasto, os preparos convencional e MAFES alteraram a maioria das propriedades físicas avaliadas. Na área preparada pelo sistema MAFES foi observado, em relação ao preparo convencional, menor resistência à penetração em profundidades de 20 a 45 cm e entre os camalhões. A taxa de infiltração de água foi semelhante entre as áreas preparadas pelos dois sistemas, porém no sistema convencional a infiltração é mais superficial ocorrendo de forma lateral ao longo do perfil. No sistema MAFES a infiltração ocorreu verticalmente no perfil do solo. Menor porcentagem de tubérculos com danos mecânicos foi obtida na área preparada pelo sistema MAFES, devido, principalmente, a menor massa de torrões e touceiras colhidas juntamente com os tubérculos nessa área. A aplicação de EM teve pouca influência nas propriedades físicas do solo, mas propiciou condições que favoreceram o ataque de larva alfinete e sarna aos tubérculos. Apesar da utilização de EM ter reduzido a produção de tubérculos na área preparada pelo sistema MAFES, a produtividade e qualidade dos tubérculos nessa área foi superior a da área preparada pelo sistema convencional. / The physical soil properties have a relevant role on the yield and quality of potato crop. Thus, the purpose of the present research was to evaluate the effects on some soil physical properties on productivity and quality of potato tubers. The trial was set up in a commercial potato production field located in the Chapada Diamantina, BA, from April to August, 2000. Two distinct soil preparation systems (conventional and MAFES system), either associated or not with application of EM, have been trialed. The following soil properties were evaluated: bulk density, aggregate stability, soil penetration resistance, soil water retention and water infiltration rate. In addition, were evaluated the changes of such soil properties in comparison with the area cultivated with the grass Brachiaria brizantha, prior soil preparation. Other evaluations were performed such as the clod mass and clump of roots harvested together with potato tubers, the level of damage to the tubers caused by mechanical harvesting, and the amount of tubers affected by potato tuber moth, rots, and common scab. The yields of the different treatments were evaluated and tubers graded according to commercial patterns. Compared to the grass, both conventional and MAFES soil preparation systems have changed the physical soil properties studied. MAFES system outperformed the conventional preparation giving lesser resistance to penetration at 20 to 45 cm deep and between hills. The water infiltration rate was similar for both soil preparation systems; however for the conventional system the infiltration pattern is superficial occurring laterally in the soil profile. Regarding MAFES systems, the infiltration occurred vertically. The area prepared MAFES system also gave a fewer percentage of tubers exhibiting mechanical damage, due to smaller clod mass and clump of roots harvested together with potato tubers. EM application did not benefit physical soil properties, however influenced a higher attack of potato tuber moth and common scab. Although the yield decrease in the area prepared with MAFES system when the EM was applied, in this area the productivity and tuber quality outperformed the conventional system.

nÃo hà / The aim of this study was to evaluate the effects in the Caatinga biome of the technique of thinning on the dynamics of herbaceous phytomass productivity; fine roots; the deposition, accumulation and rates of decomposition of litter; aggregate stability; respirometry of the soil; stocks of carbon and nitrogen; and characterisation of changes in the spectral behaviour of the canopy. The study was carried out in two stages: the first in watersheds in the town of Iguatu, in the south central region of the State of CearÃ, Brazil, and the second in the watershed of the Caxitorà River, in the northern region of the state. The Iguatu experimental area comprised two watersheds, one under thinning for 5 years (CR5) and the other preserved with natural vegetation for 35 years (CS35). The variables to be sampled were: productivity of herbaceous biomass; fine roots; gravimetric moisture; isotope &#948;13C (â); aggregate stability; deposition, accumulation and rates of decomposition of litter; and stocks of total organic carbon and total nitrogen in the 0-20, 20-40 and 40-60 cm layers, from April 2013 to March 2014. The data were submitted to the analysis of means test and compared by t-test (p&#8804; 0.05). The increase in the intensity of herbaceous plants resulting from thinning contributed to an increase in stocks of total organic carbon (249% and 139% in the 20-40 cm and 40-60 cm layers respectively) and of total nitrogen (142% and 137% respectively), in relation to the area under preservation. The 0-10 cm layer of CR5 stored double the amount of fine roots found in CS35. In the topsoil (0-20 cm) of CR5, aggregates with a size 2.15 times greater than those found in CS35 were obtained. The greater conservation of litter on the soil of CR5 is associated with the greater input of lignified woody biomass from thinning, and consequently with the lower rates of decomposition and respirometry, which are evidenced by the low CO2 emissions into the atmosphere. Thinning in a Vertisol of the Caatinga biome has an influence on soil structure and on the stocks of carbon and nitrogen, making possible lower rates of CO2 emission and improving conditions for the infiltration of water. In the second phase of the experiment, SRTM (Shuttle Radar Topography Mission) data were used to evaluate the effect of the illumination geometry on the spectral characterisation of the canopy, as well as images from the OLI/Landsat 8 sensor, representative of the rainy and dry seasons of 2013. The images were converted into physical values (surface reflectance factors), the NDVI was calculated, and with the technique of principal component analysis images PC1 and PC2 were generated. Dispersion for the values of PC1 and PC2 from the different canopies was evaluated in a two-dimensional space. It was found that the reflectance intensity of the incident electromagnetic radiation in canopies of the caatinga biome is not only influenced by seasonality, but also by the illumination geometry arising from the topographical characteristics of the terrain. The effect of shading was predominant during the dry season, especially under low lighting conditions, irrespective of the structure of the plant cover. The NDVI proved to be unsuitable for detecting changes in the spectral behaviour of the Caatinga biome during the rainy season. / Objetivou-se com este trabalho avaliar os efeitos da tÃcnica de raleamento do bioma caatinga sobre a dinÃmica da produtividade de fitomassa herbÃcea; raÃzes finas; deposiÃÃo, acumulaÃÃo e taxas de decomposiÃÃo da serapilheira; estabilidade de agregados; respirometria do solo; estoque de carbono, nitrogÃnio e caracterizaÃÃo das alteraÃÃes no comportamento espectral do dossel. O estudo foi conduzido em duas etapas: a primeira em microbacias hidrogrÃficas no municÃpio de Iguatu, regiÃo centro sul e a segunda na bacia hidrogrÃfica do rio CaxitorÃ, regiÃo norte, ambas no estado do CearÃ. A Ãrea experimental de Iguatu consistiu de duas microbacias adjacentes, sendo uma raleada por 5 anos (CR5) e a outra conservada com vegetaÃÃo natural hà 35 anos (CS35). As variÃveis amostradas foram: produtividade de fitomassa herbÃcea, raÃzes finas, umidade gravimÃtrica, isÃtopo &#948;13C (â), estabilidade de agregados, deposiÃÃo, acumulaÃÃo e taxas de decomposiÃÃo da serapilheira, estoque de carbono orgÃnico total e nitrogÃnio total nas camadas de 0-20, 20-40 e 40-60 cm entre abril/2013 e marÃo/2014. Os dados foram submetidos à anÃlise de teste de mÃdia e confrontados pelo Teste T (p&#8804;0,05). O aumento da intensidade de plantas herbÃceas decorrente da tÃcnica de raleamento contribuiu para o acrÃscimo nos estoques de carbono orgÃnico total (249% e 139% nas camadas 20-40 cm e 40-60 cm, respectivamente) e do nitrogÃnio total (142% e 137%, respectivamente) em relaÃÃo à Ãrea conservada. A camada de 0-10 cm da parcela CR5 armazenou o dobro do quantitativo de raÃzes finas encontradas em relaÃÃo a CS35. Na camada superficial do solo (0-20 cm) da CR5 foram obtidos agregados com tamanho de 2,15 vezes acima dos obtidos na CS35. A maior conservaÃÃo de serapilheira no solo da CR5 està associada aos maiores aportes de fitomassa lenhosa lignificada proveniente do raleamento, e consequentemente das menores taxas de decomposiÃÃo e respirometria, constatada pelas baixas emissÃes de CO2 à atmosfera. O raleamento em Vertissolo do bioma Caatinga exerce influÃncia na estruturaÃÃo do solo, no estoque de Carbono e NitrogÃnio, possibilitando as menores taxas de emissÃo de CO2 e melhorando as condiÃÃes para a infiltraÃÃo de Ãgua. Jà na segunda etapa do experimento, foram utilizados dados do SRTM (Shuttle Radar Topography Mission) para avaliaÃÃo do efeito da geometria de iluminaÃÃo na caracterizaÃÃo espectral do dossel, alÃm de imagens do sensor OLI/LANDSAT 8 representativas da estaÃÃo chuvosa e seca de 2013. As imagens foram convertidas em valores fÃsicos (fatores de reflectÃncia de superfÃcie), calculado o Ãndice NDVI e, a partir da tÃcnica de componentes principais, geradas imagens PC1 e PC2. Foram avaliadas as dispersÃes dos valores de PC1 e PC2, em um espaÃo bidimensional, provenientes dos diferentes dossÃis. Os resultados indicaram que a intensidade de reflectÃncia da radiaÃÃo eletromagnÃtica incidente em dossÃis do bioma caatinga à influenciada tanto pela sazonalidade climÃtica quanto pela geometria de iluminaÃÃo decorrentes das caracterÃsticas topogrÃficas do relevo. O efeito sombreamento foi predominante durante o perÃodo seco, principalmente para condiÃÃo de pouca iluminaÃÃo independentemente da estrutura de cobertura vegetal. O NDVI nÃo se mostrou adequado para detectar alteraÃÃes no comportamento espectral do bioma caatinga durante a estaÃÃo chuvosa.

O estudo foi dividido em quatro partes. Na primeira parte analisou-se o impacto do clima na estocagem de carbono em solos de canaviais sem a queima da palhada. Foram escolhidos três regimes climáticos contrastantes do centro-sul do Brasil. O potencial de seqüestro de carbono orgânica no solo (COS) foi determinado, em cada regime climático, de acordo com a taxa anual de carbono remanescente no solo proveniente da palhada depositada. Para obter esta taxa, compararam-se os estoques de COS em canaviais com e sem queima da palhada. Esse ganho anual foi comparado com a entrada anual de carbono via palhada depositada. O ganho anual de COS (0-30 cm) em canaviais sem queima da palhada não resultou em diferenças significativas por clima: 1, 97 Mg ha-1 (clima norte), 2,00 Mg ha-1 (clima centro) e 1,70 Mg ha-1 (clima sul). Os regimes climáticos estudados também não revelaram diferenças significativas entre suas temperaturas e precipitações médias anuais. Porém, o aumento anual de COS um pouco menor no clima sul levou à conclusão que o potencial de seqüestro de carbono diminui ligeiramente em latitudes mais altas, devido à maior precipitação no centro-sul do Brasil. Na segunda parte avaliou-se o impacto da palhada sobre a estabilidade de agregados dos solos, que foi calculada pelo método de fracionamento proposto por Six et al. (2000a). A estabilidade de agregados no solo do canavial sem a queima da palhada aumentou, em média, 15,3% por ano na profundidade 0-30 cm. Na terceira parte, avaliou-se a diferença da estabilidade de agregados entre canaviais e mata nativa. O solo da mata nativa mostrou uma estabilidade de agregados significativamente maior (7,2 vezes). Supõe-se que a estabilidade de agregados seja maior na mata nativa como resultado da maior presença de matéria orgânica e biota no solo. Na quarta parte avaliou-se a origem do carbono nos agregados estáveis em água de fluxo contínuo para determinar que forma de agregação possui a melhor proteção contra a decomposição de carbono. Houve uma diferença significativa de \'delta\'13C entre os macroagregados e microagregados na camada superior, com 10% mais \'delta\'13C nos macroagregados. Isto indica mais carbono derivado da cobertura vegetal atual (C4), ou seja, mais incorporação da palhada nos macroagregados. O \'delta\'13C da fração de partículas livres ou agregados não estáveis em água de fluxo contínuo é menor em todas as profundidades, indicando que a matéria orgânica recente (C4) encontra-se no solo principalmente de forma agregada estável em água, evidenciando seu papel fundamental na estabilidade dos agregados. Constatou-se também, que quanto mais novo o macroagregado, maior o seu teor em carbono. Nos microagregados verificou-se o efeito contrário. Quanto mais velho o microagregado, maior o seu teor em carbono. Isso indica que o microagregado possui uma melhor proteção contra a decomposição de carbono, e também a capacidade de um aumento no teor de carbono, no decorrer do tempo, em virtude da assimilação de carbono mais novo. Conclui-se, que em termos de seqüestro de carbono de longa duração, é propício avaliar mecanismos de proteção do carbono recalcitrante dentro dos microagregados e estudar como técnicas agrícolas podem proteger melhor esta fração / The study was divided in four parts. The first part investigated climate impact on soil carbon stocks in sugar cane fields cultivated without green trash burning. For this purpose, three contrasting climates were chosen in Central and Southern Brazil. The sequestration potential of soil organic carbon (SOC) was determined for each climate, calculating how much of the carbon derived from deposited green trash remains in the soil every year. To obtain this rate, SOC stocks of sugar cane fields cultivated with and without green trash burning were compared. The annual difference (0-30 cm) did not differ significantly between climates: 1, 97 Mg ha-1 (Northern Climate), 2,00 Mg ha-1 (Central Climate) and 1,70 Mg ha-1 (Southern Climate). The climates did not show significant differences between their average annual temperatures and their annual precipitation. Nevertheless, a slightly smaller gain of SOC stocks in the Southern Climate leads to the conclusion that higher latitudes tend to stock slightly less COS due to higher annual precipitation. The second part evaluated the impact of green trash deposition on soil aggregate stability, which was calculated according to Six et al. (2000a). Soil aggregate stability under sugar cane fields cultivated with green trash burning had an average increase of 15,3% for soil depth 0-30 cm. The third part studied soil aggregate stability between sugar cane and natural forest vegetation. The forest soil revealed significantly higher (7,2 times) aggregate stability, supposedly due to higher organic matter content and more soil biota. The forth part examined the origin of carbon inside water-stable aggregates to determine which aggregation form provides better protection against carbon decomposition. The top soil layer showed a significant difference in \'delta\'13C between macro-aggregates (10% more \'delta\'13C) and microaggregates which means that more carbon derived from green trash (C4) was incorporated in macro-aggregates. \'delta\'13C of free soil particles or water-unstable aggregates is smaller for all soil layers indicating that fresh organic matter (green trash) is predominantly encountered in a water stable aggregated form in the soil. Furthermore, a correlation analysis revealed that more recent macro-aggregates had higher C content. The opposite was observed for micro-aggregates: the older the micro-aggregate, the higher its carbon content, leading to the conclusion that microaggregates protect carbon better against decomposition and are also capable to enrich their carbon pool through C assimilation. Given its long-term soil carbon sequestration potential, it is recommended to investigate carbon protection mechanisms for the recalcitrant C pool in micro-aggregates and also to study how agricultural techniques could improve the protection of the recalcitrant C pool

No description available.

Efficient road network and connectivity play vital role in the development of any country. Majority of the rural roads are unpaved and connectivity of rural roads is always a major challenge. Unpaved roads are also used for temporary transportation facilities like access roads, haul roads for mines, forest roads and parking lots. Since these roads do not have asphalt surfacing, they are subjected to early failures due to distresses like rutting, pot holes and depressions . Stabilization of unpaved roads using geosynthetics has been proved to be promising in increasing the lifespan of these roads because they facilitate economical, aesthetic and effective design of the roads. Inclusion of geosynthetic layers at the interface of subgrade soil and granular sub-base, reduces the surface heave, ensures a better stress distribution and reduces the stresses transferred to the subgrade soil, as demonstrated by earlier researchers. Wide variety of geosynthetics like woven and nonwoven geotextiles, uniaxial and biaxial geogrids and geocells are used as reinforcement in road sections. Geotextiles improve the strength by interfacial friction, lateral restraint and membrane effect. Geogrids provide additional benefit of interlocking. Geocells are honeycomb shaped geosynthetic cellular confining systems filled with aggregates in which the reinforcement action is derived not only by friction and interlocking, but also by confinement. Load-deformation characteristics of reinforced soil-aggregate systems under static, repeated and cyclic loads is a potential topic of interest considering the fact that the design of geosynthetic reinforced unpaved roads is still under development and experimentation. The objective of the present study is to understand the beneficial use of geosynthetics in unpaved roads and to provide clear insight into the influence of geosynthetics on the cyclic loading characteristics of unpaved roads through laboratory experiments. California Bearing Ratio (CBR) tests were carried out on unreinforced and reinforced soil-aggregate systems to study the effect of various parameters such as type of reinforcement, form of reinforcement, quantity of reinforcement, and water content of the subgrade soil on the load-penetration response of the various systems. Modified CBR tests were also carried out to understand the influence of boundary of the mould and anchorage of reinforcement on the behavior of reinforced soil-aggregate systems. Behavior of unreinforced and reinforced soil-aggregate systems under repeated and cyclic loading is also studied to understand the resilience of the composite systems. From the measured stress-strain response, the elastic and plastic strains developed in various systems are compared. Different moduli such as secant modulus, cyclic modulus and resilient modulus are computed for different systems and compared. To investigate the effectiveness of geosynthetics in improving the load - bearing capacity, repeated load tests were carried out on model sections of unpaved road constructed in a steel test tank of size 750 mm × 750 mm × 620 mm. The effect of various parameters like the form of reinforcement, quantity of reinforcement, height of geocell layer and the position of geocell layer on the load-deformation behaviour of the unpaved model road sections was studied. Static and cyclic triaxial tests were carried out on unreinforced and reinforced granular sub-base materials to understand their stress strain behavior under static and cyclic loading conditions. The influence of quantity and form of reinforcement on the stress-strain behaviour of these materials was studied. From the studies it is observed that the use of reinforcement increases the CBR value of the soil-aggregate systems. Studies with two different sizes of CBR moulds indicated that the boundary effect in the standard CBR mould leads to the overestimation of the CBR value, resulting in unconservative design of road sections. Providing anchorage to the reinforcement in CBR tests did not produce an appreciable change in the load-penetration behavior. From the repeated load tests it was observed that the reinforced systems did not show any improvement in the load-deformation behaviour at low levels of rut depth. At higher rut depths, the reinforced systems developed less plastic settlements and more elastic settlements and low resilient modulus compared to unreinforced systems. From the model tests on unpaved road sections, it was observed that the improvement in the cyclic load resistance of the road due to the inclusion of geocell layer depends on the height of the geocell layer and its position. Increasing the height of geocell layer resulted in improved performance up to certain height of the geocell layer, beyond which, further increase in the height reduced the load resistance because of the inadequate granular overlay thickness and inadequate compaction of aggregate within the geocell pockets. Static and cyclic triaxial tests showed that the geogrid and geocell reinforced granular sub-base material sustained higher peak stresses and exhibited increase in modulus compared to the unreinforced specimens. Results of element and model tests carried out in this study gave important insight into the load-deformation characteristics of reinforced soil-aggregate systems under static, repeated and dynamic loads. The results provide guidelines regarding the selection of type, quantity and configuration of geosynthetic reinforcement while designing unpaved roads and the expected performance of these reinforced unpaved roads.

We investigated the effects of substrate (cellulose or starch) and different clay contents on the production of microbial extracellular polymeric substances (EPS) and concomitant development of stable soil aggregates. Soils were incubated with different amounts of montmorillonite (+ 0.1%, + 1%, + 10%) both with and without two substrates of contrasting quality (starch and cellulose). Microbial respiration (CO2), biomass carbon (C), EPS-protein, and EPS-polysaccharide were determined over the experimental period. The diversity and compositional shifts of microbial communities (bacteria/archaea) were analysed by sequencing 16S rRNA gene fragments amplified from soil DNA. Soil aggregate size distribution was determined and geometric mean diameter calculated for aggregate formation. Aggregate stabilities were compared among 1–2-mm size fraction. Starch amendment supported a faster increase than cellulose in both respiration and microbial biomass. Microbial community structure and composition differed depending on the C substrate added. However, clay addition had a more pronounced effect on alpha diversity compared to the addition of starch or cellulose. Substrate addition resulted in an increased EPS concentration only if combined with clay addition. At high clay addition, starch resulted in higher EPS concentrations than cellulose. Where additional substrate was not provided, EPS-protein was only weakly correlated with aggregate formation and stability. The relationship became stronger with addition of substrate. Labile organic C thus clearly plays a role in aggregate formation, but increasing clay content was found to enhance aggregate stability and additionally resulted in the development of distinct microbial communities and increased EPS production.