Rozprawy doktorskie na temat „Soil carbon”

Rapid anthropogenic climate change is one of the greatest challenges that human civilisation will face in the 21st century. A 25-180 % increase in atmospheric carbon dioxide content since the early 1800’s and a predicted increase of 2-3% each year will lead to a 2-6°C rise in tropospheric temperatures. The consequences of increased atmospheric temperatures are profound and would put unsustainable strain on human infrastructure, which was conservatively estimated in the Stern Review (2006) to cost approximately 20% of GDP. Given the political, technical, economic and social barriers preventing the transition to a low carbon economy, there is an unequivocal need to research ‘geoengineering’ technologies that can bridge the gap between carbon emission reduction targets and actual emissions. Soil mineral carbonation is one such technology. The atmosphere is one of the smallest carbon pools at the Earth’s Surface (depending on how each pool is demarcated). Soils turn over the quantity of carbon in the atmosphere in under a decade and collectively form one of the largest carbon pools (3-4 times the quantity of carbon in the atmosphere). Land use change since the agricultural revolution has released 256 GtC (40 % of anthropogenic emissions). Research investigating the potential for carbon accumulation in soils is primarily focused on restoring organic carbon concentration to pre-agricultural values through modification of farming practices. The research presented in this thesis is the first that explores the potential of increasing the inorganic carbon pool as an emissions mitigation technology. Inorganic carbon accumulation is promoted by introducing divalent cation rich (predominantly calcium and magnesium) silicate and hydroxide minerals into the soil, which weather and supersaturate the soil solution with respect to carbonate minerals (predominantly calcite, aragonite, magnesite and dolomite). The carbon in the resultant precipitate is derived from the atmosphere. This is analogous to mineral carbonation technologies which induce carbonate precipitation from silicate weathering in industrial scale reactors at elevated temperatures and pressures. However, carbonation in soil exploits natural weathering processes to the same effect with minimal energy and infrastructure input. The research presented in this thesis broadly investigates soil mineral carbonation by contributing work towards the fundamental issues associated with application of soil mineral carbonation technology. Research activity described herein covers a range of laboratory batch weathering experiments, field work, geochemical modelling, plant growth trials, soil microcosm experiments and literature reviews. While eclectic, all work packages contribute to the same goal of describing the efficacy, effectiveness and potential impacts of soil mineral carbonation. The efficacy of mineral carbonation technology is primarily limited by the availability of appropriate silicate bearing material. A literature search suggests that approximately 15-16 Gt a- 1 of silicate rich ‘waste’ materials are produced as a consequence of human activity. This has a carbon capture potential between 190 and 332 MtC a-1, which is equivalent to other emissions mitigation strategies. Quarrying silicate specifically for carbonation is a suggested strategy that may be able to store on the order of 102 GtC a-1 (based on two sites in the US). Therefore, mineral carbonation may form part of global mitigation strategies collectively equivalent to 14 GtC a-1 to stabilise the CO2 concentration of the atmosphere at 500 parts per million by volume. Considering that the potential capacity of soil mineral carbonation is sufficient to act as a substantial emissions mitigation strategy it was appropriate to investigate issues associated with the application of such a technology. In the first instance, sites known to contain silicates were investigated. These include soils developed on natural silicates (on the Whin Sill in Northumberland), construction and demolition waste (at a brownfield site and waste transfer stations) and slag (at a former steelworks). Interpretation of fieldwork results suggests that inorganic carbon accumulation is rapid (up to 38 gC kg-1(soil) a-1), and is orders of magnitude xxv greater than organic carbon accumulation in natural soils. The average concentration of inorganic carbon (20-30 Kg m-3) is equivalent to organic carbon in natural soils. The unusually light carbon and oxygen isotope ratios of the carbonate (-3.1 ‰ and -27.5 ‰ for δ13C and -3.9 ‰ and -20.9 ‰ for δ18O) were used to determine that up to 55% of the carbon was derived from the atmosphere. The rate of carbon capture, which is the same as the precipitation rate of carbonate, is a function of solution chemistry. The more supersaturated a solution is with respect to a carbonate mineral, the more rapid the precipitation rate. Saturation of a solution is a function of divalent cation and carbonate anion concentration. Therefore, the supply of each of these components was investigated in laboratory experiments. Batch weathering experiments were used to investigate the supply of calcium from artificial silicates (hydrated cement gel). Up to 70-80 % of the calcium contained in the mineral was removed, which is consistent with efficiencies reported for conventional mineral carbonation. The log rate of weathering was between -10.66 and -6.86 mol Ca cm-2 sec-1, which is several orders of magnitude greater than that usually reported for natural silicates. Microcosm experiments were conducted to investigate the rate of supply of carbonate from the organic carbon mineralisation in high pH solutions. The research clearly demonstrates that high pH solutions inhibit the breakdown of organic carbon as a function of nutrient supply. Where organic carbon was successfully mineralised the log rates (-3.4 mmol g-1(field moist soil) sec-1) were equivalent to that found in previous studies. While the influx of dissolved carbonate mineral components into the soil solution is the primary controlling step in the rate of carbon accumulation, there is a complex relationship between soil physical properties and geochemistry. This was highlighted in a numerical model that was constructed for this thesis, which suggests that soil pore volume and particle size distribution are important variables. An additional numerical model was constructed to investigate the transportation of silicate material to the application site. This model suggests that an economics of soil mineral carbonation is a function of transport costs, the value of the silicate material and the price of carbon. Field observations, growth trials, microcosm experiments and previous research suggest a complex interaction between biology, weathering and carbonate precipitation. Additional work is required to investigate carbonate precipitation mediated by plant and microorganism activity and the degree to which soil mixed with silicates impact on ecosystem functioning. This research has demonstrated that mineral carbonation in soils could form a substantial emissions mitigation strategy, but additional work is required in a number of areas to which this thesis provides a suitable foundation.

Soil organic matter (SOM) models simplify the complex turnover dynamics of organic matter in soils. Stabilization mechanisms are currently thought to play a dominant role in SOM turnover but they are not explicitly accounted for in most SOM models. One study addresses the implementation of an approach to account for the stabilization mechanism of physical protection in the SOC model RothC using 13C abundance measurements in conjunction with soil size fractionation data. SOM models are increasingly used to support policy decisions on carbon (C) mitigation and credibility of model predictions move into the focus of research. A site scale, Monte Carlo based model uncertainty analysis of a SOM model was carried out. One of the major results was that uncertainty and factor importance depend on the combination of external drivers. A different approach was used with the SOM ECOSSE model to estimate uncertainties in soil organic carbon (SOC) stock changes of mineral and organic soils in Scotland. The average statistical model error from site scale evaluation was transferred to regional scale uncertainty to give an indication of the uncertainty in national scale predictions. National scale simulations were carried out subsequently to quantify SOC stock changes differentiating between organic and mineral soils and land use change types. Organic soils turned out to be most vulnerable to SOC losses in the last decades. The final study of this thesis emplyed the RothC model to simulate possible futures of global SOC stock changes under land use change and ten different climate scenarios. Land use change turned out to be of minor importance. The regionally balance between soil C inputs and decomposition leads to a diverse map of regional C gains and losses with different degrees of certainty.

The interest in using sugarcane straw as a feedstock for bioenergy production has been increased considerably. However, indiscriminate straw removal may negatively affect soil functioning. Therefore, this work aimed to quantify and characterize soil solution translocating along the profile, under straw removal rates from the soil surface. Lysimeter systems were built with 1, 20, 50, and 100 cm soil columns, with a sandy clay loam texture, from a commercial sugarcane field in Piracicaba-SP, southeastern Brazil. The experiment was conducted in open area, where the lysimeters were subjected to rainfall and sun radiation. After the soil stabilization within the lysimeters, the treatments were added, consisting of four straw amounts (0, 3, 6, and 12 Mg ha-1), representing straw removal rates of 100 (bare soil), 75, 50, and 0%, respectively. After one year of the first straw addition, the same straw amounts were added again simulating the second harvest. Drained solution was collected and quantified by 17 months and soil moisture was determined over a period of two months using sensors. Dissolved organic carbon (DOC) concentration was measured in automatic analyzer. The soil solution and straw solution, made in water infusion, were characterized in High performance liquid chromatography (HPLC) to verify the presence of toxic compounds. After that, straw and soil solution were used in tests with soybean seed to evaluate the effects in plant germination and initial growth. At the end of the experiment, soil bulk density and soil organic carbon (SOC) analyses were performed. Remaining straw was weight before the new addition, and weight again at the end to determine the decomposition rates. The accumulated volume of solution drained was 30, 11 and 4% lower under 100, 75 and 50% removal rates compared to no removal. Bare soil stored less water, indicating susceptibility to lose water by evaporation. Simulation showed that 100% and 75% removal can induce longer periods of water restriction, which impair sugarcane growth. The DOC production on topsoil was higher in no straw removal; the retention was higher in 1 to 20 cm in no removal and higher in 20 to 50 cm in 50 and 75% removal rates. Bare soil released more DOC below 01 cm indicating a possible C loss. Below 100 cm DOC leachate was quite similar in all treatments, what shows a higher C retention and small C loss even in higher DOC production. Even with differences in DOC retention, increases in C stock below 5 cm were not noticed. We found many phenolic compounds in the straw solution, not found in the soil solution, indicating that in natural conditions straw does not release toxic compounds into soil solution. Plant growth was negatively affected by straw solution, but not by soil solution. Our findings suggest that the medium straw maintenance prevents variations and loss on soil water content. Higher straw amount increases DOC production, which likely alters its composition and subsequent retention in soil. Carbon stock did not increase in the soil subsurface, but probably will in the long-term. The higher straw removal, proportionally, the higher the C losses in the form of CO2 and DOC, consequently the lower soil C retention. More straw on soil surface release more C amounts to the soil, retained or translocated with soil water, may be stored in deeper soil layers. Higher water percolation in the soil profile does not mean higher C losses by leaching in deeper soil. This study has the practical objective of finding an amount of straw to be maintained in the field that ensures the C storage and the better soil functioning, and also supply feedstock for bioenergy production.
O interesse no uso da palha de cana-de-açúcar como matéria-prima para a produção de bioenergia vem crescendo consideravelmente. No entanto, a remoção excessiva da palha pode afetar negativamente o funcionamento do solo. Portanto, o objetivo deste trabalho foi quantificar e caracterizar a solução ao longo do perfil sob níveis de remoção de palha da superfície do solo. Para isso, foi construído um sistema de lisímetros com colunas de 1, 20, 50 e 100 cm de solo, de textura franco argilo arenosa, proveniente de área comercial de cana-de-açúcar em Piracicaba-SP, Brasil. O experimento foi conduzido em área aberta, sujeito a precipitação e luz natural. Depois da estabilização do solo dentro dos tubos, foram adicionados os seguintes tratamentos: 0, 3, 6 e 12 Mg ha-1 de massa seca, representando 100 (solo nu), 75, 50 e 0% de intensidade de remoção de palha, respectivamente, sendo adicionados novamente após um ano. A solução percolada foi coletada e quantificada por 17 meses, a umidade do solo foi determinada por dois meses usando sensores. A concentração de carbono orgânico dissolvido (COD) foi mensurada com analisador automático. A solução do solo e solução da palha, feita por infusão em água, foram caracterizadas em HPLC para verificar a presença de compostos tóxicos. Posteriormente, as soluções da palha e solo foram usadas em testes de sementes de soja para avaliar os efeitos na germinação e crescimento inicial. Ao final do experimento, foram realizadas análises de densidade do solo e carbono orgânica do solo (COS). A palha remanescente foi pesada após um ano, anterior a nova adição, e pesada novamente ao final do experimento, para determinar a taxa de decomposição. O volume de solução percolado foi 30, 11 e 4% menor em 100, 75 e 50% do que em 0% de remoção, respectivamente. O solo descoberto armazenou menos água, indicando susceptibilidade à perda de água por evaporação. A simulação mostrou que 100 e 75% de remoção induzem longos períodos de restrição hídrica, que pode prejudicar o crescimento da planta. A produção de COD na camada superficial foi maior no solo sem remoção; a retenção foi maior de 1 a 20 cm em solo sem remoção, e maior em 20 a 50 cm em 50 e 75% de remoção. O solo descoberto liberou mais COD em de 20 cm do que em superfície, indicando perda de C. Abaixo de 100 cm, o COD lixiviado foi similar nos tratamentos, indicando grande retenção de C e pequenas perdas por lixiviação, mesmo em alta produção de COD. Mesmo com diferenças na retenção de COD, não foi identificado aumento no estoque de C abaixo de 5 cm. Foram encontrados compostos fenólicos na solução da palha, não encontrados na solução do solo, indicando que em condições naturais a palha não libera quantidades significativas de compostos tóxicos na solução do solo. O crescimento de plantas foi negativamente afetado pela solução da palha, mas não pela solução do solo. Nossos resultados sugerem que a manutenção de quantidade média de palha previne perdas e variação no conteúdo de água do solo. Maior quantidade de palha aumenta a produção de COD, que provavelmente altera sua composição, alterando a retenção no solo. O estoque de C não aumentou consideravelmente em subsuperfície, mas muito provavelmente aumentará em escala de tempo maior. Quanto maior a remoção de palha, proporcionalmente maior as taxas de C liberadas na forma de CO2 e COD em subsuperfície, consequentemente, menor a retenção de C no solo. Maiores quantidades de palha na superfície liberam mais C para o solo, retido ou translocado com a água, podendo ser estocado em maiores profundidades do solo. Maior percolação de água no solo não significa maiores perdas de C por lixiviação em profundidade.

Carbon (C) as a driver of soil denitrification was investigated in a series of four laboratory incubation experiments employing stable nitrogen (N) and C isotope approaches. The research addressed the lack of knowledge on mechanisms through which the quantity and quality of organic‐C containing substrates interact with denitrification. The amount of organic matter added to soil was manipulated to relate C respiration with process rates of denitrification. Respiration derived from dissolved organic matter C was linearly related to denitrification but the direction of the relationship was variable in time. This may be most likely an effect of changing quality of the C available and possibly microbial community structure. Nitrous oxide (N2O) emission from denitrification at the later stages of residue decomposition was driven by nitrate (NO3‐) accumulation in the soil rather than C provided by the residue. Denitrification across a vertical shallow soil profile formed in a laboratory microcosm was investigated. A surface hotspot formed immediately as a response to residue‐C addition and increased rates of N2O production. N2O reduction occurred at depth. The hotspot at depth was related to an indirect effect of residue‐C, which was depletion of O2. Further, to address the complexity of low molecular weight C substrate available to denitrifiers in the soil solution, denitrification rates in response to glucose, citric acid and glutamic acid supplied individually versus in mixture were characterised. Carbon substrate quality regulated N2O production rates via interactions within the soil microbial community and with the soil solid phase. Overall, the experiments showed that C stimulates strong N2O emission peaks and increase cumulative N2O emissions from arable soil along a gradient of varying C substrate complexity and quantity. Interaction in space and time play an important role when C containing inputs affected other proximal drivers of denitrification such as NO3‐ and O2.

Global urbanization has resulted in rapidly increased urban land. Soils are the foundation that supports plant growth and human activities in urban areas. Furthermore, urban soils have potential to provide a carbon sink to mitigate greenhouse gas emission and climate change. However, typical urban land development practices including vegetation clearing, topsoil removal, stockpiling, compaction, grading and building result in degraded soils. In this work, we evaluated an urban soil rehabilitation technique that includes compost incorporation to a 60-cm depth via deep tillage followed by more typical topsoil replacement. Our objectives were to assess the change in soil physical characteristics, soil carbon sequestration, greenhouse gas emissions, and stormwater mitigation after both typical urban land development practices and post-development rehabilitation. We found typical urban land development practices altered soil properties dramatically including increasing bulk density, decreasing aggregation and decreasing soil permeability. In the surface soils, construction activities broke macroaggregates into smaller fractions leading to carbon loss, even in the most stable mineral-bound carbon pool. We evaluated the effects of the soil rehabilitation technique under study, profile rebuilding, on soils exposed to these typical land development practices. Profile rebuilding incorporates compost amendment and deep tillage to address subsoil compaction. In the subsurface soils, profile rebuilding increased carbon storage in available and aggregate-protected carbon pools and microbial biomass which could partially offset soil carbon loss resulting from land development. Yet, urban soil rehabilitation increased greenhouse gas emissions while typical land development resulted in similar greenhouse gas emissions compared to undisturbed soils. Additionally, rehabilitated soils had higher saturated soil hydraulic conductivity in subsurface soils compared to other practices which could help mitigate stormwater runoff in urban areas. In our study, we found urban soil management practices can have a significant impact on urban ecosystem service provision. However, broader study integrating urban soil management practices with other ecosystem elements, such as vegetation, will help further develop effective strategies for sustainable cities.
Ph. D.

Les sols sont la principale composantede l’écosystème terrestre et le plus grand réservoir de carbone organique sur Terre, étant très réactifs aux perturbations humaines et aux changements climatiques. Malgré leur importance dans les réservoirs de carbone, la dynamique du carbone des sols est une source importante d'incertitudes pour les prévisions climatiques futures. Le but de la thèse était d'explorer différents aspects d’études du carbone des sols (mesures expérimentales, modélisation et évaluation de bases de données) à différentes échelles spatiales (de l'échelle d'un profil à l'échelle globale). Nous avons souligné que l'estimation des stocks globaux de carbone du sol est encore assez incertaine.Par conséquent le rôle du carbone des sols dans la dynamique du climat devient l'une des principales incertitudes dans les modèles du système terrestre utilisés pour prédire les changements climatiques futurs. La deuxième partie de la thèse porte sur la présentation d'une nouvelle version du modèle IPSL-Land Surface appelé ORCHIDEE-SOM, intégrant la dynamique du 14C dans le sol. Plusieurs tests effectués supposent que les améliorations du modèle devraient se focaliser davantage sur une paramétrisation dépendante de la profondeur,principalement pour la diffusion, afin d'améliorer la représentation du cycle global du carbone dans les modèles de surface terrestre, contribuant ainsi à contraindre les prédictions futures du réchauffement climatique
Soils are the major components ofthe terrestrial ecosystems and the largest organiccarbon reservoir on Earth, being very reactive tohuman disturbance and climate change. Despiteits importance within the carbon reservoirs, soilcarbon dynamics is an important source ofuncertainties for future climate predictions. Theaim of the thesis was to explore different aspectsof soil carbon studies (Experimentalmeasurements, modeling, and databaseevaluation) at different spatial scales (from thescale of a profile to the global scale). Wehighlighted that the estimation of the global soilcarbon stocks is still quite uncertain.Consequently, the role of soil carbon in theclimate dynamics becomes one of the majoruncertainties in the Earth system models (ESMs)used to predict future climate change. Thesecond part of thesis deals with the presentationof a new version of the IPSL-Land SurfaceModel called ORCHIDEE-SOM, incorporatingthe 14C dynamics in the soil. Several tests doneassume that model improvements should focusmore on a depth dependent parameterization,mainly for the diffusion, in order to improve therepresentation of the global carbon cycle inLand Surface Models, thus helping to constrainthe predictions of the future soil organic carbonresponse to global warming

Thesis (M.S.)--West Virginia University, 2002.
Title from document title page. Document formatted into pages; contains x, 282 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

As we strive to find new technologies to dispose of our municipal solid waste, compost-like outputs (CLOs) are becoming more widely created. As a product of both aerobic and anaerobic digestion, they provide a potentially important carbon store and some have proven to enhance existing carbon stores when added to brownfield sites and agricultural land. However, the CO2 flux from this artificial soil is relatively high when compared to natural soils. The aerobic digestion process under which it is produced lasts only 9 days, producing a material which is still comparatively unstable and yet to mature. The CLO is laid in windrows where it is hoped that it will stabilise and mature; if the humification process at this stage can be optimised, would an even greater carbon store be achieved? This thesis seeks to answer this question, through the research into humification in both natural and artificial systems; through the measurement of CO2 flux to assess the stability of CLO over time; using adapted methodologies to gauge the maturity of this artificial soil by analysing the amount of humic acids present; by adding proposed catalysts to the material in fully factorial lysimeter studies; and by examining the affects of different physical environmental conditions under which CLO product humifies. The results of a series of experimental trials, undertaken over a three year period, are presented. Manganese-coated sand and char, both currently ‘waste’ products were both used as potential catalysts for the humification process of CLO. Temporal trends were seen in most samples using infra-red gas analysis, an alkali extraction technique, UV photospectrometry, fluorescence and a novel pseudo-thermogravimetric analysis. The waterlogging of the samples appeared to have an effect on the humification process and a great deal of concurrent data was seen upon the addition of Mn-coated sand and char to the CLO. Both appeared to have a stabilising effect on the CLO, reducing flux rate and increasing humification as compared to a control. An overriding theme present throughout this thesis is the heterogeneous and contaminated nature of the non-source-segregated CLO tested. It is therefore recommended that similar studies be undertaken on a purer, more homogenous CLO in order to assess whether promising results seen could be elucidated in order to gauge the efficacy of biochar and Mn in encouraging the production of humic substances. A field trial would allow the unified soil system to be considered, rather than the CLO alone.

Increased global industrialisation and deforestation have placed enormous burden on our atmosphere and environment. For no other reason than future proofing soils against major climate variability – a possible side effect of growing atmospheric CO2, diverting more of this carbon (C) from our air to where it can do considerably more good seems very worthwhile. This has made soil carbon storage and its measurement such an important and intense area of current research activity. To know and fully understand the impacts of various land management practices on soil carbon building processes requires before anything further is said or done the ability to measure carbon stocks reliably. The enormous challenges are to do this for huge land areas with a sensitivity to see the real changes occurring with an awareness of the spatial, seasonal or other variations that may be as significant. This research study had set out to advance our understanding of soil carbon and its measurement. It has investigated what has gone before and is currently being done but also considers ideas on the horizon. From this base, several novel approaches have been taken to develop innovative methods of dealing with these immediate questions with an aim to easing the soil carbon data crisis. One of the major problems is the natural variability of carbon in soils over relatively small distances leading to uncertainties in carbon analyses which easily amplify in terms of carbon stocks. To capture this variability using conventional methods available today make on-the-ground measurement prohibitively costly. Specifically to deal with this problem a system named the Soil Carbon Bench (SCB) was developed at the centre of this research to cope with large amounts of soil and in fact to enable carbon analysis of whole cores by trusted combustion. This newly developed apparatus formed the core of the work and in its test-bed form has been tested on carbonaceous calibration materials and was then demonstrated on soil cores recovered from a trial field under lucerne rotation. Its accuracy has been equivalent or better than standard analytical methods and when evaluated in terms of its cost efficiencies and determining carbon stocks on the work to date it has done so with a smaller margin of error and at much lower cost. The relative costs of determining soil C stocks were estimated to be about 1/5 of conventional methods along with improved precision. Soil C data obtained with the SCB had a lower variance and C stocks could be replicated so that total C values per 50cm core were typically within 0.2g or 0.0003 kg/kg of the site mean. The research has succeeded at addressing the benefits of analysing whole cores and paved a way to more efficient carbon surveys that easily respond to any changing protocol requirements as may be recommended by bodies such as the IPCC. There are iv numerous other possibilities to test in conjunction with sampling designs and the support of emerging proximal techniques under experimentation. Another but related area was to elucidate reliable ways to differentiate and determine soil carbon forms which are of great importance when considering carbon pools and storage. Thermal analytical studies were not only an ideal complement to the development of the SCB but provided many insights into the thermal behaviour of soil carbon components relevant to these pools. While it provided useful information related to loss on ignition methods (an important alternative method for large scale soil determination) it has opened up further possibilities for productive investigation that encompass characterising soil components and organic matter (OM) stabilisation. In particular it has shown real potential for the determination of black carbon and bushfire residues not easily detected by other instruments, but important for calibrating rapid soil spectral techniques.

The Podzols of the world are divided into intra-zonal and zonal according to then location. Zonal Podzols are typical for boreal and taiga zone associated to climate conditions. Intra-zonal podzols are not necessarily limited by climate and are typical for mineral poor substrates. The Intra-zonal Podzols of the Brazilian Amazon cover important surfaces of the upper Amazon basin. Their formation is attributed to perched groundwater associated to organic matter and metals accumulations in reducing/acidic environments. Podzols have a great capacity of storing important amounts of soil organic carbon in deep thick spodic horizons (Bh), in soil depths ranging from 1.5 to 5m. Previous research concerning the soil carbon stock in Amazon soils have not taken into account the deep carbon stock (below 1 m soil depth) of Podzols. Given this, the main goal of this research was to quantify and to map the soil organic carbon stock in the region of Rio Negro basin, considering the carbon stored in the first soil meter as well as the carbon stored in deep soil horizons up to 3m. The amount of soil organic carbon stored in soils of Rio Negro basin was evaluated in different map scales, from local surveys, to the scale of the basin. High spatial and spectral resolution remote sensing images were necessary in order to map the soil types of the studied areas and to estimate the soil carbon stock in local and regional scale. Therefore, a multi-sensor analysis was applied with the aim of generating a series of biophysical attributes that can be indirectly related to lateral variation of soil types. The soil organic carbon stock was also estimated for the area of the Brazilian portion of the Rio Negro basin, based on geostatistical analysis (multiple regression kriging), remote sensing images and legacy data. We observed that Podzols store an average carbon stock of 18 kg C m-2 on the first soil meter. Similar amount was observed in adjacent soils (mainly Ferralsols and Acrisols) with an average carbon stock of 15 kg C m-2. However if we take into account a 3 m soil depth, the amount of carbon stored in Podzols is significantly higher with values ranging from 55 kg C m-2 to 82 kg C m-2, which is higher than the one stored in adjacent soils (18 kg C m-2 to 25 kg C m-2). Given this, the amount of carbon stored in deep soil horizons of Podzols should be considered as an important carbon reservoir, face a scenario of global climate change
Os Espodossolos podem ser divididos em zonais e intrazonais de acordo com área onde ocorrem. Os Espodossolos zonais são típicos de áreas boreais e taiga, delimitados por condições climáticas. Já os intrazonais não são condicionados pelo clima. Os Espodossolo intrazonais brasileiros ocupam uma grande extensão da alta bacia amazônica, tendo sua formação atribuída à ocorrência de lençóis freáticos suspensos associados à acumulação de complexos organometálicos em ambientes ácidos redutores. Esses solos tem a capacidade de estocar grandes quantidades de carbono orgânico em horizontes espódicos profundos (Bh), em profundidades que podem variar de 1,5m a 5m. Pesquisas atuais relacionadas ao estoque de carbono em solos amazônicos, não levam em consideração os estoques encontrados no horizonte Bh (abaixo de 1m de profundidade). Sendo assim, o principal objetivo da presente pesquisa foi quantificar e mapear o estoque de carbono nos solos da bacia do Rio Negro, tendo-se em vista aquele estocado no primeiro metro de solo, bem como o carbono armazenado em até 3m de profundidade. A quantidade de carbono orgânico estocado nos solos da bacia do Rio Negro foi estimada em diferentes escalas de mapeamento, desde mapas locais até a escala da bacia do Rio Negro. Imagens de sensoriamento remoto de alta resolução espacial e espectral foram essenciais para viabilizar o mapeamento dos solos nas áreas estudadas e permitir a estimativa do estoque de carbono. Uma análise multisensor foi adotada buscando-se gerar informações biofísicas indiretamente associadas à variação lateral dos tipos de solo. Após o mapeamento do estoque de carbono em escala regional, partiu-se para a estimativa na escala da bacia do Rio Negro, com base em análise geoestatística (krigagem por regressão linear), imagens de sensoriamento remoto e base de dados de domínio público. Após o mapeamento do estoque de carbono na escala da bacia, constatou-se que os Espodossolos têm um estoque médio de 18 kg C m-2, para 1m de profundidade, valor similar ao observado em solos adjacentes (Latossolos e Argissolos) os quais tem um estoque de 15 kg C m-2. Quando são considerados os estoques profundos, até 3m, a quantidade de carbono dos Espodossolos é superior com valores variando de 55 kg C m-2 a 82 kg C m-2. Estoque relativamente maior que aquele observado em solos adjacentes para esta profundidade (18 kg C m-2 a 25 kg C m-2). Portanto, o estoque de carbono profundo dos Espodossolos, não deve ser negligenciado levando-se em conta cenários futuros de mudanças climáticas

Soils are the largest pool of carbon (C) in terrestrial ecosystems and store 1500 Gt of C in their soil organic matter (SOM). SOM is a dynamic, complex and heterogeneous mixture, which influences soil quality through a wide range of soil properties. Labile SOM comprises a small fraction of total SOM (approximately 5%), but due to its rapid turnover has been suggested to be most vulnerable to loss following soil disturbance. This research was undertaken to examine the consequences of soil disturbance on labile SOM, its availability and protection in soils using the isotopic analysis of soil-respired CO₂ (δ¹³CO₂). A range of soils were incubated in both the short- (minutes) and long-term (months) to assess changes in labile SOM. Shifts in soil-respired δ¹³CO₂ over the course of soil incubations were found to reflect changes in labile substrate utilisation. There was a rapid depletion of δ¹³CO₂ (from a starting range between -22.5 and -23.9‰, to between -25.8 and -27.5‰) immediately after soil sampling. These initial changes in δ¹³CO₂ indicated an increased availability of labile SOM following the disturbance of coring the soil and starting the incubations. Subsequently δ¹³CO₂ reverted back to the initial, relatively enriched starting values, but this took several months and was due to labile SOM pools becoming exhausted. A subsequent study was undertaken to test if soil-respired δ¹³CO₂ values are a direct function of the amount of labile SOM and soil physical conditions. A range of pasture soils were incubated in the short-term (300 minutes), and changes in soil-respired δ¹³CO₂ were measured along with physical and chemical soil properties. Equilibrium soil-respired δ¹³CO₂, observed after the initial rapid depletion and stabilisation, was a function of the amount of labile SOM (measured as hot water extractable C, HWEC), total soil C and soil protection capacity (measured as specific soil surface area, SSA). An independent experimental approach to assess the effect of SSA, where labile SOM was immobilised onto allophane – a clay mineral with large, active surface area – indicated limited availability of labile SOM through more enriched δ¹³CO₂ (in a range between -20.5 and -20.6 ‰) and a significant (up to three times) reduction in HWEC. In the third study, isotopic measurements were coupled with CO₂ evolution rates to directly test whether equilibrium soil-respired δ¹³CO₂ can reflect labile SOM vulnerability to loss. Soils were sampled from an experimental tillage trial with different management treatments (chemical fallow, arable cropping and permanent pasture) with a range of C inputs and soil disturbance regimes. Soils were incubated in the short- (300 minutes) and long-term (600 days) and changes in δ¹³CO₂ and respiration rates measured. Physical and chemical fractionation methods were used to quantify the amount of labile SOM. Pasture soils were characterised by higher labile SOM estimates (HWEC; sand-sized C; labile C respired during long-term incubations) than the other soils. Long-term absence of plant inputs in fallow soils resulted in a significant depletion of labile SOM (close to 50% based on sand-sized C and HWEC estimates) compared with pasture soils. The values of δ¹³CO₂ became more depleted in 13C from fallow to pasture soils (from -26.3 ‰ to -28.1 ‰) and, when standardised (against the isotopic composition of the solid soil material), Δ¹³CO₂ values also showed a decrease from fallow to pasture soils (from -0.3 ‰ to -1.1 ‰). Moreover, these patterns in isotopic measures were in strong agreement with the amount of labile SOM and its availability across the soils, and were best explained by the isotopic values of the labile HWEC fraction. Collectively, these results confirm that labile SOM availability and utilisation change immediately after soil disturbance. Moreover, isotopic analysis of soil-respired CO₂ is a powerful technique, which enables us to probe mechanisms and examine the consequences of soil disturbance on labile SOM by reflecting its availability and the degree of SOM protection.

El balanç entre l´entrada de C (dels residus vegetals) i sortides de C (principalment com CO2 de la descomposició del carboni orgànic del sòl -SOC-), determina el contingut de SOC, que és el depòsit de C més voluminós a la superfície terrestre. Als agroecosistemes semiàrids Mediterránis, l’aigua és el principal factor limitant del creixement del cultiu i de l´entrada de residus al sòl. Les pràctiques agronòmiques alternatives poden millorar el creixement vegetal i augmentar la quantitat de residus (entrada de C) en aquestos sistemes. No obstant això la resposta del contingut de SOC dependrà del balanç de les entrades amb les sortides de C. Aquest treball estudia els efectes de l’adopció a llarg termini de sistemes de conreu (NT, sembra directa; MT, mínim conreu CT, conreu convencional) i del nivell de fertilizació nitrogenada (zero; mitjà, 60 kg N ha-1; alt, 120 kg N ha-1) al balanç de C del sòl i el contingut de SOC. El contingut de SOC augmentà finalment 4.3 i 3.9 Mg C ha-1 sota NT repecte a MT i CT. Nivells mitjans i alts de fertilització nitrogenada augmentaren el contingut de SOC en 3.4 i 4.5 Mg C ha-1 respecte al contingut a les parcel•les no fertilitzades. L´adopció a llarg termini de pràctiques de conreu de conservació (sembra directa), juntament amb l’ús adequat de la fertilització nitrogenada van demostrar ser eines per a millorar la sostenibilitat dels nostres secans i emmagatzemar C al sòl.
El balance entre la entrada de C (de los residuos vegetales) y salidas de C (principalmente como CO2 de la descomposición del carbono orgánico del suelo -SOC-), determina el contenido de SOC, que es el mayor depósito terrestre de C. En agroecosistemas semiáridos Mediterráneos, el agua es el principal factor limitante del crecimiento del cultivo y de la entrada de residuos en el suelo. Las prácticas agronómicas alternativas pueden mejorar el crecimiento vegetal y aumentar la cantidad de residuos (entrada de C) en estos sistemas. Este trabajo estudió los efectos de la adopción a largo plazo de sistemas de laboreo (NT, no-laboreo; MT, laboreo minimo; CT, laboreo convencional) y del nivel de fertilización nitrogenada (cero; medio, 60 kg N ha-1; alto, 120 kg N ha-1) en el balance de C del suelo y el contenido de SOC. El contenido de SOC aumentó en 4.3 y 3.9 Mg C ha-1 bajo NT con respecto a MT y CT. Niveles medios y altos de fertilización nitrogenada aumentaron el contenido de SOC en 3.4 y 4.5 Mg C ha-1 con respecto al contenido en las parcelas no fertilizadas. La adopción a largo plazo de prácticas de laboreo de conservación (no-laboreo o siembra directa), junto con el uso adecuado de la fertilitzación nitrogenada demostraron ser herramientas para mejorar la sostenibilidad de los secanos semiáridos Mediterráneos y almacenar C en el suelo.
The balance between C inputs (from plant residues) and C outputs (mainly as CO2 from soil organic carbon -SOC- decomposition) determines the content of SOC which is is the largest terrestrial reservoir of carbon. Under semiarid Mediterranean agroecosystems, water limitation restrains plant growth and the return of crop residues to the soil. Alternative agronomical practices may improve crop growth and increase return of crop residue (C inputs) under these systems. This work studied the effects of long term adoption of tillage practices (NT, no-tillage; MT, minimum tillage; CT, conventional tillage) and nitrogen (N) fertilization level (zero; medium, 60 kg N ha-1; high, 120 kg N ha-1) on the SOC balance and the content of SOC. The stock of SOC was increased by 4.3 and 3.9 Mg C ha-1 under NT in comparison to MT and CT respectively. Long-term medium and high N fertilization increased the stock of SOC by 3.4 and 4.5 Mg C ha-1 in contrast to unfertilized plots. Long-term adoption of conservation tillage practices (no-tillage) together with adequate N fertilizer use, proved to be effective tools to improve sustainability of semiarid Mediterranean drylands and to store C in the soil.

In the face of ever increasing atmospheric CO₂ a better understanding of soil properties and processes and the effect of management practices, such as the application of nitrogen fertilizer is of importance and could potentially improve our ability to sustainably manage forestry systems. With that in mind this study was conducted in order to investigate the effects of tree species and fertilization on soil carbon and the soil microbial community. To this end, soil from fertilized and unfertilized plots at Berwick forest, under stands of Pinus radiata and Sequoia sempervirens at Hanmer and under six different tree species at Holt forest was sampled. Two glasshouse pot trials were established using soil collected from the Hanmer and Berwick forest sites and seedlings of Pinus radiata, Sequoia sempervirens, and Eucalyptus nitens were grown. Soil properties were determined from both the field sites and pot trials including soil organic matter, carbon, nitrogen, and microbial biomass by chloroform fumigation extraction. Biolog ecoplates were used to determine the relative differences in diversity based on substrate utilization patterns of the soil microbial communities in soil sampled from the glasshouse pot trials. Soil microbial biomass carbon, nitrogen and the ratio of microbial biomass carbon:nitrogen differed significantly between Pinus radiata and the other tree species sampled at Holt forest. Significant effects of fertilization and tree species on soil carbon and microbial biomass were observed in both pot trials. Soil carbon differed significantly between Eucalyptus nitens and both Pinus radiata and Sequoia sempervirens in the first pot trial and relative to both, E. nitens contributed significantly more carbon. No significant effect of either fertilization or tree species on the catabolic diversity of the soil microbial community in both glasshouse pot trials was observed. The results demonstrated the effects that fertilization and tree species can have. Particularly notable was the short-time period in which tree species effects became apparent coupled with the absence of any aboveground inputs to the soil.

At the global scale, soils are the primary terrestrial reservoir of carbon and therefore have a major influence on the concentration of carbon dioxide in the atmosphere. Soil organic carbon stocks are estimated to have decreased by an average of fifty two percent in temperate regions since 1850. Land use change and management practices are the primary drivers of this decrease. Temperate upland regions have been identified as important for climate regulation, both in terms of current stocks of soil carbon and future sequestration potential. Therefore, appropriate on-farm management of soil carbon stocks in these regions has the potential to contribute to climate change mitigation goals. This thesis is a contribution to ongoing efforts to improve on–farm soil carbon management. It does so through the development of mapping practices that incorporate both ecological and social data. The ecological aspect of the research identified a role for existing farm survey data in accurately predicting soil carbon distribution without the need for time and labour-intensive field work. The engagement with social science methods acknowledges a societal bias towards scientific ways of representing soil carbon and the marginalisation of alternative, often experiential, knowledge. The research demonstrated a way for different knowledges to be incorporated into soil carbon mapping practices and identified a role for under-utilised scientific and non-scientific knowledge of soil carbon for improving spatially-explicit management plans. The mapping methods were developed around three case study farms in the Lake District National Park in Cumbria. This region is an upland landscape which has been identified as an important space for carbon management in the UK. The research offers a distinct and timely approach to assessing the potential of interdisciplinary mapping to improve the management of soil carbon at the farm scale and has wider implications for the management of ecological systems.

This thesis presents novel techniques for spatial prediction of soil carbon. Chapter 1 introduces a method to incorporate the local scale spatial variability of soil organic carbon into regional scale mapping. Different to the conventional approach of using globally calibrated single model for the entire region, this method uses a combination of locally and globally calibrated models to predict soil organic carbon at regional scale, using a moving widow approach. Chapter 2 studies how diverse spatial modelling techniques perform under varying training sample sizes, in terms of soil carbon predictions. The study explores the behaviour of various algorithms ranging from simple linear models to complex machine learning techniques trained under numerous sample sizes. Chapter 3 investigates how to optimally use infrared spectroscopy inferred soil carbon data for mapping. Infrared soil spectroscopic data is considered as a timely, low-cost input for spatial modelling of soil carbon. However these data are associated higher measurement errors compared to the standard dry combustion technique. This study establishes a methodology in the model-based geostatistics to filter out the measurement error variability through the inclusion of the error information in the covariance structure of the spatial model. In disaggregating soil information, uncertainty of the disaggregation process is not often discussed. Underestimation of inferential or predictive uncertainty in statistical modelling leads to inaccurate statistical summaries and overconfident decisions. The use of Bayesian inference allows for quantifying the uncertainty associated with disaggregation process. Chapter 4 introduces Bayesian area-to-point regression kriging with a case study of downscaling regional scale soil organic carbon map to farm scale information.

The potential for using RMP (refiner mechanical process) pulp mill fibre waste as a soil amendment was investigated by determining levels of net carbon mineralization. Under optimum conditions (laboratory incubation study), the pulp fibre waste, being a relatively homogeneous substrate, was found to mineralize at one rate of -0.0078 d⁻¹. In field applications the rate of net mineralization was slower, with rates of -0.0034 d⁻¹ and -0.0037 d⁻¹, as determined by soil respiration and litter bag trials, respectively. A loading effect was noted for this amendment, where increasing the levels of application was found to cause decreases in the mineralization rate. Using pulp fibre waste in forest landing rehabilitation appears to increase the levels of microbial activity in the surface horizon. The higher levels of productivity should lead to improvements in soil structure, and would be a better alternative to only tilling and fertilizing the soil.
Land and Food Systems, Faculty of
Graduate

Thesis (Ph.D.) -- La Trobe University, 2006.
Research. "A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy, [to the] Centre for Applied Alpine Ecology, Department of Agricultural Sciences, School of Life Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora". Includes bibliographical references (leaves 172-186). Also available via the World Wide Web.

In order to predict how terrestrial ecosystems will respond to global change, there is growing recognition that we need to better understand linkages between plant and soil processes. Previously the factors and processes with potential to influence the terrestrial carbon (C) cycle have been investigated in isolation from each other. This study investigated the interactions of nutrient availability and warming in controlling the soil carbon dynamics, with regards to the fate of already sequestered carbon in soil, under conditions of increasing atmospheric temperatures. The project objectives were addressed by three independent experiments designed to explain specific components of the carbon-nutrient cycle interactions, and the findings brought together to describe the implications for future soil carbon storage. The main measurements collected throughout this project included soil carbon dioxide (CO2) fluxes, partitioned into autotrophic and heterotrophic components, net ecosystem exchange and respiration fluxes, and background soil moisture and temperature data, backed by gas, soil and biomass analyses. In the two field experiments, these measurements were taken from plots with or without any inorganic nutrient additions or in the presence or absence of legumes providing biological nitrogen addition to the ecosystem. In the laboratory, temperature and nutrient availability were manipulated within the ecosystem. The reduction in decomposition rates, without reduction of productivity as a result of inorganic nutrient additions, indicated the potential for increasing C storage. There was also evidence that nutrient availability controls the strength of the link between plant and soil processes in semi-natural grasslands. The yields, decomposition rates and soil C fluxes recorded in the presence and absence of legumes provided some evidence of N2 fixation, improving ecosystem productivity and soil properties while reducing soil C effluxes, in a managed grassland. In the laboratory, the warming of soils from lysimeters with and without plants, receiving or not receiving fertiliser, supported the findings from field experiments regarding the importance of the soil-plant link in controlling C fluxes. However, C stocks and δ13C analyses showed that over a year’s worth of warming and nutrient manipulations made little difference to the amount of C stored in the soil, indicating that edaphic factors have greater control over the response of C dynamics to increased temperatures.

Three studies were completed to investigate the influence of mineral assemblage on soil organic carbon (SOC) cycling and pedogenesis in forest soils. Two studies utilized a lithosequence of four parent materials (rhyolite, granite, basalt, limestone/volcanic cinders) under Pinus ponderosa, to explicitly quantify the contribution of parent material mineral assemblage to the character of the resulting soil. The first study explored variation in pedogenesis and elemental mass loss as a product of parent material through a combination of quantitative X-ray diffraction and elemental mass balance. Results indicated significant differences in degree of soil development, profile characteristics, and mass flux according to parent material.The second study utilized the same lithosequence of soils, but focused on organic C cycling. This study explored variation in SOC content among soils of differing mineralogy and correlations among soil physiochemical variables, SOC content, soil microbial community composition and respiration rates. Metal-humus complex and Fe-oxyhydroxide content emerged as important predictors of SOC dynamics across all parent materials, showing significant correlation with both SOC content and bacterial community composition. Results indicated that within a specific ecosystem, SOC dynamics and microbial community vary predictably with soil physicochemical variables directly related to mineralogical differences among soil parent materials.The third study focused specifically on the influence of goethite and gibbsite on dissolved organic matter characteristics and microbial communities which utilize DOM as a growth substrate. Iron and aluminum oxides were selected for this study due to their wide spread occurrence in soils and their abundance of reactive surface area, qualities which enable them to have a significant effect on SOC transported through forest soils. Results indicated that exposure to goethite and gibbsite surfaces induces significant differences in DOM quality, including changes in thermal properties, molecular structure, and concentrations of P and N. Investigation of the decomposer communities indicated that exposure to goethite and gibbsite surfaces caused significant differences in microbial community structure.These investigations emphasize the important role of mineral assemblage in shaping soil characteristics and regulating the cycling of C in soils, from the molecular scale to the pedon scale.

El canvi climàtic, produït per l’increment de la concentració de gasos d’efecte hivernacle a l’atmosfera, amenaça la integritat del nostre planeta. En aquestes circumstàncies el biochar, material obtingut a partir de biomassa pirolitzada, s’ha proposat com a una possible mesura per augmentar el segrest de carboni en sòls. L’aplicació de biochar en sòls pot servir com a magatzem de carboni a llarg termini compensant les emissions de CO2. No obstant, l’eficàcia del biochar depèn del tipus de biochar i sòl utilitzats. L’objectiu principal d’aquesta tesi és avaluar els efectes de l’aplicació de biochars de pi (PB) i de blat de moro (ZB) a una dosi de 6.5 g kg-1 en un sòl franco-arenós amb pH neutre i baix contingut de carboni orgànic (CO) en condicions de camp durant dos anys. Els objectius específics són els efectes de l’aplicació de biochar en : 1) la resistència termoquímica del CO del sòl (Capítol 1 i Capítol 2); 2) la disponibilitat del CO pels microorganismes (Capítol 3); 3) la protecció física del CO per oclusió en els agregats (Capítol 4). Els mètodes utilitzats per estudiar els efectes del biochar sobre la resistència del CO van ser: pèrdua de pes per ignició (LOI), combustió-seca (TOC), oxidació forta (sO) i feble (mO) amb dicromat-potàssic, hidròlisis-àcida (AH), oxidació amb peròxid d’hidrogen (PO) i anàlisis-isotòpic. A més, el CO-resistent del sòl i del biochar es va estimar mitjançant un balanç de masses. També, es van dur a terme dos mostrejos de sòl a curt i llarg termini (2 i 26 mesos), i es van incubar durant 250 dies. El dia 30 i 250 d’incubació va ser determinada la quantitat i la senyal isotòpica del CO2-C respirat. Addicionalment, es va mesurar el CO-dissolt en les mostres de sòl mitjançant el mètode d’extracció amb aigua-calenta. Les propietats físiques van ser avaluades quantificant el pes dels agregats estables amb aigua destil·lada i de la fracció en partícules amb hexametafosfat (per la disgregació dels agregats) utilitzant el wet-sieving apparatus. A més, el CO procedent del sòl natiu i del biochar dins i fora dels agregats es va estimar mitjançant un balanç de masses utilitzant el mO i el TOC. També es va estimar la contribució de CO del sòl i del biochar en els sòls esmenats amb ZB utilitzant el anàlisis-isotòpic. Es van trobar quantitats de ROC similars en els sòls controls estimats mitjançant mO i AH (5 g CO kg-1), mentre que més contingut de ROC es va observar en els sòls esmenats (6-12 g CO kg-1). La presencia de biochar es va detectar en els sòls esmenats mitjançant la comparació del δ13C en sòls esmenats i no-esmenats, independentment de l’origen del biochar. D’altra banda, el 35% del CO del biochar de ZB dels sòls esmenats es va perdre en dos anys com a resultat de la dissolució del biochar en el sòl. A curt termini, es va observar un priming-negatiu en sòls esmenats amb PB i el contrari en sòls esmenats amb ZB, en resposta al major contingut de CO-làbil del ZB. No obstant, un lleuger priming negatiu es va observar en els dos sòls esmenats a mig termini ja que augmenta la protecció física del CO. Mentre el PB tendeix a ser incorporat en els agregats, el ZB promou l’oclusió del CO natiu del sòl. Al esgotar-se el CO-làbil, el CO queda protegit dins dels agregats. Per tant, l’aplicació del biochar en sòls agrícoles mediterranis augmenta la persistència del CO en el sòl com a resultat de la resistència innata del CO del biochar i la protecció física augmentant el contingut de CO dins dels agregats.
El incremento de gases de efecto invernadero en la atmosfera puede tener consecuencias severas para nuestro planeta. El uso de biochar como enmienda, material obtenido a partir de biomasa pirolizada, se ha propuesto como estrategia para el secuestro de carbono en el suelo. Sin embargo, la efectividad del biochar varía mucho dependiendo del biochar y el tipo de suelo. El objetivo principal de esta tesis es evaluar los efectos de dos biochares, de restos de pino (PB) y mazorca de maíz (ZB), incorporados a una dosis de 6.5 g kg-1 en un suelo de viña franco-arenosa con pH neutro y bajo contenido de carbono orgánico (CO), en condiciones de campo durante dos años. Los objetivos específicos fueron la evaluación de: 1) la resistencia del CO en el suelo a los procesos termoquímicos (Capítulo 1 y Capítulo 2); 2) la disponibilidad de CO a ser mineralizada por microorganismos del suelo (Capítulo 3); y 3) protección física de CO por aumento de agregados (Capítulo 4). Los métodos analíticos utilizados para evaluar los efectos del biochar en el CO resistente del suelo fueron: pérdida de peso por ignición (LOI), combustión-seca (TOC), oxidación fuerte (sO) y suave (mO) con dicromato potásico, hidrólisis-ácida (AH), oxidación con peróxido de hidrogeno (PO) y análisis isotópico. Además, se estimó el CO-resistente del suelo y del biochar a través de un balance de masas. Por otro lado, el suelo se muestreó a corto y medio plazo (2 y 26 meses) y las muestras se incubaron en el laboratorio durante 250 días. Se determinó el CO2-C liberado durante la respiración del suelo y la señal isotópica del día 30 y 250 de incubación. Además, se cuantificó el CO disuelto mediante un extracto con agua caliente. Para evaluar las propiedades físicas, se determinaron los agregados estables en agua destilada y el peso de la fracción particulada con hexametafosfato para la disrupción de los agregados usando el wet-sieving apparatus. El CO oxidable del suelo nativo y del biochar dentro y fuera de los agregados se estimó a través de un balance de masas usando mO y TOC. Por otro lado, mediante el análisis isotópico se estimó la contribución de CO del suelo nativo y del biochar en suelos enmendados con ZB. Se cuantificaron valores similares de ROC en los suelos control mediante AH y mO (5 g C kg-1), mientras que se obtuvieron valores de ROC más altos en los suelos enmendados con biochar (6-12 g C kg-1). Además, la detección cualitativa de biochar se logró comparando δ13C en suelos enmendados y controles, independientemente del origen del biochar. Sin embargo, el 35% de ZB-CO se perdió durante los dos años de experimento por dilución del biochar en el suelo. A corto plazo se observó un priming-negativo en suelos enmendados con PB y al contrario en los suelos con ZB debido al mayor contenido de CO-lábil en ZB comparado con PB. Sin embargo, se encontró un priming ligeramente negativo a medio plazo en ambos suelos enmendados con biochar, como consecuencia de una mayor protección física del CO. Mayores cantidades de TOC y BOC se encontraron en los agregados de los suelos enmendados aunque tuvieron lugar dos procesos diferentes, mientras el PB tiende a incorporarse en agregados el ZB promueve la oclusión del CO del suelo nativo. Al agotarse el CO-lábil, el CO-ocluido queda protegido previniendo las pérdidas adicionales por degradación. Por lo tanto, la aplicación de biochar a un suelo agrícola mediterráneo aumenta la persistencia del CO del suelo debido a la resistencia innata al biochar-CO y la protección física del CO, que previene la degradación biótica o abiótica del CO.
The increment of global threats due to climate change, caused by an increase in atmospheric concentration of GHGs, is predicted to have a severe impact on our planet. The use of biochar, obtained from the thermochemical conversion of biomass in an oxygen-limited environment, as a soil amendment has been proposed as one strategy for C-sequestration. Many environmental benefits have been attributed to the application of biochar into soil, including long-term C-sequestration compensating for CO2 emissions. However, biochar effectiveness still remains under debate because effects can vary greatly depending on biochar and soil type. The main objective of this thesis was to assess the effects of two contrasting biochars, from pine wood (PB) and corn cob (ZB) remains, incorporated at a rate of 6.5 g kg-1 on a sandy loam vineyard soil with neutral pH and low organic carbon (OC) content, in field conditions over two years. Specifically, the aims were to evaluate the consequences of the addition of the different biochars on: 1) soil OC resistance to thermochemical processes (Chapter 1 and Chapter 2); 2) the potential OC availability to be mineralized by soil microorganisms (Chapter 3); and 3) physical OC protection by the promotion of aggregates (Chapter 4). The analytical methods used to evaluate the effects of biochar in soil OC-resistance were: weight loss-on-ignition (LOI), dry-combustion (TOC), strong (sO) and mild (mO) acid potassium dichromate oxidations, acid hydrolysis (AH), peroxide-oxidation (PO) and isotope analysis. Moreover, soil and biochar resistant-OC (ROC) was estimated through a mass balance. Also, soil field samples were collected at the short- and the medium-term (2 and 26 months after the application, respectively), and then incubated in the lab for 250 additional days. The CO2-C released as soil respiration and the CO2-C isotopic signature were assessed after 30 and 250 days of the incubation. Additionally, dissolved-OC was assessed in the field soil samples by hot-water extraction. Regarding physical properties, water-stable aggregates and particulate fraction weight were determined using a wet-sieving apparatus, using distilled water or hexametaphosphate for aggregates disruption. Oxidisable and resistant OC (attributed mainly to native soil and biochar, respectively) inside and outside of aggregates was estimated through a mass balance using mO and TOC. On the other hand, native soil and biochar-OC contribution in ZB biochar-amended soil was estimated by isotope analysis. The ROC estimated by AH and mO led to similar values in control soil (5 g C kg-1 soil), whereas higher ROC values were obtained in biochar-amended ones (6-12 g C kg-1 soil). Moreover, qualitative biochar detection was achieved by comparing δ13C in amended and non-amended soils regardless of the biochar feedstock origin. However, 35% of ZB biochar-OC was apparently lost over two years, which was attributed to biochar dilution into soil. In addition, in the short-term, negative-priming was observed in amended-soil with PB (made at high temperature) whereas positive-priming was seen in those amended with ZB (produced at lower temperatures) as a result of the highest labile-OC content in ZB biochar compared to PB. However, in the medium-term, slightly negative-priming effects in both biochar-amended soils were found. This could be explained by promotion of physical protection processes preventing priming. This fact was corroborated as higher TOC and BOC amount was observed inside of aggregates in biochar-amended soils compare to controls. It seems that PB tended to be incorporated into aggregates while ZB promoted native soil-OC occlusion. Then, after labile-OC has been exhausted, the promotion of OC occlusion prevented further losses. Therefore, the application of biochar to a Mediterranean agricultural soil increases soil-OC persistence due to innate biochar-OC resistance and OC physical protection, which decrease OC degradation by abiotic and biotic agents.

High latitude soils are estimated to store a considerable part of the global pool of soil organic carbon (SOC). Studies of global and regional SOC pools have estimated total inventories in northern Sweden’s subarctic region to fall within 10-50 kg m-2. However, correction factors for stone and boulder content of soils are often overlooked in SOC-studies and soil profiles are commonly normalized to a depth of 1 m, which can result in substantial overestimates of the SOC pool if a large part of the soil volume is occupied by stones/boulders or if the soil depth is shallower than 1 m. This study was performed to quantify SOC in soils of the Torneträsk catchment area using detailed measures of soil depth and stone/boulder contents. Two non-destructive sampling methods, ground penetrating radar (GPR) and rod penetration, were used to measure soil depth and stone and boulder content in the catchment area. Results show that average soil depth (n = 52344) varied between 0.95 – 2.14 m depending on elevation and the average mire depth was 0.63 m. Stone and boulder content of the soil was estimated to 49 – 68 % depending on elevation. The results were added to existing carbon and soil density data from the Torneträsk catchment area and total SOC inventories were calculated to 6.8 – 13.1 kg m-2. The results of this study indicate that previous studies on regional and global scale may have overestimated the SOC pools in the subarctic regions of northern Sweden.

The thinning of loblolly pine plantations has a great potential to influence the fluxes and storage of carbon within managed stands. This study looked at the effects of thinning on aboveground carbon and mineral soil carbon storage, 14-years after the thinning of an 8-year-old loblolly pine plantation on the piedmont of Virginia. The study also examined soil respiration for one year following the second thinning of the same stand at age twenty-two. The study was conducted using three replicate .222 hectare stands planted using 3.05 by 3.05 meter spacing in 1980 at the Reynolds Homestead in Critz, VA. Using two different sample collection methods it was determined that soil carbon was evenly dispersed throughout thinned plots, and that random sampling techniques were adequate for capturing spatial variability. Soil carbon showed a significant negative correlation with soil depth (p=0.0001), and by testing the difference between intercepts in this relationship, it was determined that thinning significantly increased soil carbon by 31.9% across all depths (p=0.0004). However, after accounting for losses in aboveground wood production, thinning resulted in an overall 10% loss in stand carbon storage. However, this analysis did not take into account the fate of wood products following removal. Soil respiration, soil temperature, and soil moisture were measured every month for one year near randomly selected stumps and trees. In order to account for spatial variation, split plots were measured at positions adjacent to stumps and 1.5 meters away from stumps. Soil temperature and moisture were both significantly affected by thinning. Regression analysis was performed to determine significant drivers in soil CO2 efflux. Temperature proved to be the most significant driver of soil respiration, with a positive correlation in thinned and unthinned stands. When modeled using regression, thinning was a significant variable for predicting soil respiration (p < 0.0009), but explained only 3.4% of the variation. The effects of thinning were responsible for decreased respiration, however, when coupled with increased temperatures, soil respiration was elevated in thinned stands.
Master of Science

本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである
Kyoto University (京都大学)
0048
新制・論文博士
農学博士
乙第7364号
論農博第1616号
新制||農||583(附属図書館)
学位論文||H2||N2249(農学部図書室)
UT51-91-A56
(主査)教授 久馬 一剛, 教授 千田 貢, 教授 髙橋 英一
学位規則第5条第2項該当

In recent times there is an increasing interest in the quantification of the variation in soil organic carbon (SOC) in space and time. Quantification of this variation is important since SOC is important for many soil physical, chemical and biological properties and soil processes which lead to sustainable crop production in agricultural soil. In addition, SOC also helps to reduce the impacts of climatic change if it can be stored in soil for the long term in what is called “soil carbon sequestration”. The focus of the work included in this thesis is to model the space and time variation using both statistical as well as process/mechanistic models of SOC. In process modelling of SOC, the Rothamsted carbon model (RothC model) was used to assess the spatial and temporal changes in SOC. The RothC model can be used to simulate the variation of SOC over the time using readily available spatial data. Therefore, this research has (a) tested the application of mid infra red / partial least-square regression models (MIR/PLSR models) in predicting SOC in archived soil data in combination with newly collected SOC data; (b) assessed changes in SOC using legacy soil data as the baseline survey; (c) mapped the measurable SOC fractions related to RothC model at the catchment scale; (d) simulated SOC across a catchment with the RothC model using readily available spatial data; (e) calibrated the rate constants of the RothC model at the catchment scale using Bayesian inverse modelling. The first research chapter (chapter 3) concentrates on the development of MIR/PLSR models to predict total SOC in archived soil datasets in relation to legacy soil datasets. The legacy soil information can be used to assess the temporal changes of SOC if they are considered to be the baseline survey. However, the use of legacy soil data directly for comparison will not be possible due to differences in the laboratory method used to measure SOC (analytical) and in the sampling support (see chapter 4 for more details). Therefore, an attempt was made to predict total SOC for archived soil data which corresponds to a legacy soil dataset collected in year 2000 in combination with newly collected data in year 2010. A total of eight (8) different MIR/PLSR calibration models were developed to predict SOC in archived soils. In development of these models an attempt was made to select samples (n = 24) from archived soil data using different sampling strategies which were used in combination (spiking) with the newly collected dataset for year 2010. It was found that all developed calibration models performed well based on internal cross validation. However, the independent validation results revealed sample selection through the Kernnard Stone algorithm performed best compared to other approaches, e.g. conditional latin hypercube sampling. In practical terms, it is not possible to analyse a large number of soil samples in archives with traditional lab based methods. Therefore, development of effective and practical oriented MIR/PLSR models will be cost effective and save laboratory processing time in relation to the determination of total SOC in archived soil properties. Chapter 4 is focused on the assessment of the change in SOC at the catchment scale using legacy soil data as the baseline survey. In this chapter two main approaches were used to assess the change in SOC namely; design-based inference methods and model-based inference methods. It also demonstrated “how to get design-based estimates when the sampling design is non-probabilistic” which is common for most legacy datasets. Design-based inference was carried out to see the change in SOC after calculating the 95 % confidence interval around the mean for the considered soil-land use complexes (SLU). If the 95 % confidence intervals for a considered SLU complex overlap each other, then it was concluded that the change is statistically not significant at the 0.05 probability level. In the model-based approach digital soil mapping (DSM) techniques were utilized where linear mixed models (LMM) were used to map the changes in SOC across the catchment. This chapter also reported issues with legacy soil data when they are used as the baseline survey and some of the ways to overcome those issues. Both statistical inference methods revealed that there is a drop in SOC between the two surveys (year 2000 and year 2010). However, that drop was not reported as statistically significant at the 0.05 probability level for both inference methods. Chapter 5 is focused on mapping measurable fractions of the RothC model at the catchment scale. The measurable fractions of the RothC model were predicted based on MIR spectra acquired for the 2010 dataset using newly developed MIR/PLSR models from the Australian carbon research programme (SCaRP) lead by CSIRO (2009 – 2012). Even though there are many papers related to mapping SOC there are only very few papers that are available related to mapping of SOC fractions. According to the reviewed literature this is the first time that measurable fractions of SOC related to the RothC model have been mapped. For the mapping purposes three separate LMMs were used and developed models were validated with leave-one-out-cross validation. In addition, conditional sequential Gaussian simulations were carried out to assess the uncertainties related to predicted maps. Throughout this chapter it is discussed how these DSM outputs can be used as inputs to the RothC model in order to run it spatially. Finally chapter 6 and 7 are focused on process modelling of SOC with RothC model. Chapter 6 highlights different ways of running RothC model spatially across a catchment. As the first step, the RothC model was initialized across the landscape using different initialization methods. A novel approach was tested where temporal C inputs were predicted from MODIS derived NPP data. Once data is prepared simulations across landscapes were carried out with 50 model combinations. These different model combinations consisting of different rate constants (2 levels), methods of initialization (5 levels) and sources of C inputs (5 levels) were compared (2 × 5 × 5 = 50 model combinations). It was found that different methods of initialization resulted in statistically significant initial SOC pools that are used as part of the RothC model. Further, it revealed that at the end of the simulations, (after 10 years) total SOC was statistically different at the 0.05 probability level based on different combinations. Results highlighted that there is great potential to use satellite derived products as drivers for future modelling of SOC. In chapter 7 Bayesian inverse modelling was utilized to estimate the uncertainty of the rate constants of the RothC model. The RothC model was re-programmed and calibrated in a Bayesian context using the “DREAM” algorithm. Once the posterior probability density functions (PDF) for the four (4) rate constants were obtained, they were used to carry out simulations using the entire PDF. Simulated results show the uncertainty created due to uncertainty about the model rate constants. This is an important step since process models such as RothC are widely applied to assess the impact of future climatic scenarios in relation to SOC without any calibration or assessment of uncertainties of the simulations. According to reviewed literature this is the first application of DREAM algorithm in calibration of RothC model rate constants for a catchment scale dataset.

The European renewable energy directive 2009/28/EC (E.C. 2009) provides a legislative framework for reducing GHG emissions by 20%, while achieving a 20% share of energy from renewable sources by 2020. Perennial energy crops could significantly contribute to limit GHG emissions through replacing equivalent fossil fuels and by sequestering a considerable amount of carbon into the soil through the large amounts of belowground biomass produced. The objective of this study is to evaluate the effects of land use change that perennial energy crops have on croplands (switchgrass) and marginal grasslands (miscanthus). For that purpose above and belowground biomass, SOC variation and Net Ecosystem Exchange were evaluated after five years of growth. At aboveground level both crops produced high biomass under cropland conditions as well as under marginal soils. At belowground level they also produced large amounts of biomass, but no significant influences on SOC in the upper layer (0-30 cm) were found. This is probably because of the "priming effect" that caused fast carbon substitution. In switchgrass only it was found a significant SOC increase in deeper layers (30-60 cm), while in the whole soil profile (0-60 cm) SOC increased from 42 to 51 ha-1. However, the short experimental periods (for both switchgrass and miscanthus), in which land use change was evaluated, do not permit to determine the real capacity of perennial energy crops to accumulate SOC. In conclusion the large amounts of belowground biomass enhanced the SOC dynamic through the priming effect resulting in increased SOC in cropland but not in marginal grassland.

The European renewable energy directive 2009/28/EC (E.C. 2009) provides a legislative framework for reducing GHG emissions by 20%, while achieving a 20% share of energy from renewable sources by 2020. Perennial energy crops could significantly contribute to limit GHG emissions through replacing equivalent fossil fuels and by sequestering a considerable amount of carbon into the soil through the large amounts of belowground biomass produced. The objective of this study is to evaluate the effects of land use change that perennial energy crops have on croplands (switchgrass) and marginal grasslands (miscanthus). For that purpose above and belowground biomass, SOC variation and Net Ecosystem Exchange were evaluated after five years of growth. At aboveground level both crops produced high biomass under cropland conditions as well as under marginal soils. At belowground level they also produced large amounts of biomass, but no significant influences on SOC in the upper layer (0-30 cm) were found. This is probably because of the "priming effect" that caused fast carbon substitution. In switchgrass only it was found a significant SOC increase in deeper layers (30-60 cm), while in the whole soil profile (0-60 cm) SOC increased from 42 to 51 ha-1. However, the short experimental periods (for both switchgrass and miscanthus), in which land use change was evaluated, do not permit to determine the real capacity of perennial energy crops to accumulate SOC. In conclusion the large amounts of belowground biomass enhanced the SOC dynamic through the priming effect resulting in increased SOC in cropland but not in marginal grassland.

Cycling of nutrients, such as Carbon (C) and Nitrogen (N), is one of the most important soil functions and is strongly related to the composition of the soil microbial community. However, soil is increasingly under environmental pressures that threaten its ecological functions and sustainability. To maintain soil functional sustainability, it is important to understand how soil withstands environmental stresses (subsequently referred to as resistance) and recovers from stresses (subsequently referred to as resilience). This study focused on the resistance and resilience of C and N processes and the underpinning microbial communities to a persistent Cu stress or a transient heat stress. The main advances and novel findings of this thesis are: (1) C mineralization is more resistant and resilient than ammonia oxidation and denitrification, and thus the combination of C and N processes are more informative than measuring a single process to interpret the overall resistance and resilience; (2) microbial composition and microbial physiological evolution play important roles in affecting resistance and resilience; (3) soil physico-chemical properties (e.g. organic matter, soil water and soil pH) are critically important in conferring resistance and resilience. The outcome of this study advances the understanding of the mechanisms of soil resistance and resilience of C and N cycling to environmental changes. The results generated here are an essential step for improving soil sustainability and promoting agricultural productivity under future environmental challenges.

This dissertation focusses on quantifying C stocks from forest ecosystems in the Eastern Himalayan. Total soil C and N stocks significantly increased with altitude and decreased with soil depth. Carbon and N stocks were significantly correlated with altitude which accounted for 73% and 47% of the variation in C and N stocks, respectively. To elucidate the driving processes of C and N stocks, inputs and stability, C and N isotopes in soil and biomass were measured. Overstorey vegetation contributes significantly to the soil C, as 13C of overstorey and soil showed similar trends. The slope of soil δ13C versus the C concentration, indicative of organic matter decomposition, was smallest at the highest altitude forest. This suggests slow turnover of C and N in the high altitude forest soils. Sequential density fractionation, DRIFT spectroscopy and IRMS were used to determine the different proportion and forms of C in forest soils. Lighter soil density fractions had a greater proportion of aliphatic C, while the heavier soil density fractions had a greater proportion of aromatic C. The larger proportion of aromatic C in the higher soil density fractions suggests that SOC in this fraction has been more processed, corroborated by the accompanied decreased C:N ratio and enrichment of δ13C with increasing soil density fractions. Aboveground biomass (AGB) allometric equations were developed to estimate forest AGB C stocks for the study area. Estimated AGB C stocks increased with altitude from 57 to 207 Mg C ha-1. The use of measured C concentration rather than an assumed 50% C for biomass reduced estimated AGB C stocks between 6.8 and 8.6%. The estimation of C stocks in the forest soils and biomass allometric equations for the different forest types in Bhutan will enable the region to better monitor its C stocks and emission to benefit from the United Nations REDD programs.

Thesis (MSc)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: The research was conducted in the Kwa-Zulu Natal midlands, South Africa. The vertical distribution of soil organic carbon (SOC) stocks were successfully predicted by stochastic exponential models developed for the three main land uses in the area, which are farmlands, forestry plantations and grasslands. These models, in combination with regular surface sampling, may be used for monitoring SOC dynamics in the area and mapping SOC stocks. Bulk density measurements are needed in combination with SOC content (%wt) to calculate such SOC stocks. Considering the disadvantages of bulk density sampling and measurement, an effort was made to determine if one of the commonly-used existing stochastic models could be used to successfully predict bulk densities for soils with known texture and SOC content to replace direct measurements, taking into account that different managements might affect final results. Statistica software was used to correlate the Saxton & Rawls model predictions and associated regressions with measured values for the study area. A clear distribution trend was achieved using Statistica and the correlations were fair with r2 values close to 0.5 for individual regressions and substantially higher for area averages. However, considering the depth-stratified averages and correcting for the effects of particle density changes for soils with high soil organic matter, high correlations for 2 of the 3 studied land uses were achieved (r2 values of 0.99 and 0.81 in forests and grasslands respectively). Therefore, although Saxton and Rawls (2006) predictions of bulk density may be used, it is preferable to conduct direct bulk density determinations. The proposed models to calculate the vertical distribution of SOC would substantially reduce the cost of soil carbon inventories to 1m soil depth in the study area by limiting observations to the soil surface. Triplicate 5cm-deep soil core samples would be collected at the soil surface per observation point for determination of ρb (bulk density) and Corg (organic carbon). On average, the accuracy of the normalized depth-distribution model is rather high for grasslands and forests/forest plantations (R2 = 0.98), but somewhat lower for cultivated lands (R2 = 0.96) due to mixing of the plough layer to cultivation depth. Carbon stocks to 1m depth were calculated as an integral of the normalized exponential distribution, multiplied by the value of Corg observed at the soil surface and expressed on volume basis as carbon density (Cv, kg∙m-3). The resulting stock assessment was compared to the observed values using piece-integration for sampled depth increments to give SOC stocks on an area basis (kg∙m-2). The estimated prediction error on average was 1.2 (9%) and 3.7 kg∙m-2 (21.6%) in grasslands and forests respectively, while for cultivated lands the error was 1.3 kg.m-2 (9.5%). Further improvement to reduce these errors may be achieved by introducing the soil type as variable and grouping the functions by soil type rather than land uses. The results of this work were presented at the seminar of the department of Soil Science, Stellenbosch University (Ros et al., 2014), the combined congress of the South African Soil Science, Horticulture and Agronomy societies (Rozanov et al., 2015), the First Global Soil Map conference, France (Wiese et al., 2013), the 20th International Congress of Soil Science, Korea (Wiese et al. 2014) and were submitted for publication in Geoderma special issue dedicated to digital soil mapping of soil organic carbon following the presentation at the 20th ICSS, Korea (Wiese et al., 2014).
AFRIKAANSE OPSOMMING: Hierdie navorsing is in die Kwa-Zulu Natalse middellande van Suid-Afrika gedoen. Die vertikale verspreiding van grondorganiese koolstof (GOK) is suksesvol voorspel deur middel van stogastiese eksponensiële modelle wat vir die drie hoof landsgebruike ontwikkel is. In kombinasie met roetine monsterneming by die grondoppervlak kan hierdie modelle suksesvol aangewend word vir die monitering van GOK dinamika in die studiegebied, sowel as kartering van GOK voorraad. Bulkdigtheidsmetings word tesame met GOK inhoud (%massa) benodig om die GOK voorraad te bereken. Weens die nadele van monsterneming vir bulkdigtheidsbepalings is ‘n poging aangewend om te bepaal of een van die mees algemeen gebruikte bestaande stogastiese modelle (Saxton & Rawls 2006) gebruik kan word om die bulkdigtheid van gronde suksesvol vanaf tekstuur en GOK inhoud te voorspel en sodoende direkte metings te vervang. Statistica sagteware is gebruik om die voorspellings met behulp van die Saxton & Rawls modelle en gevolglike regressies met gemete waardes vanuit die studiegebied te korreleer en ‘n duidelike verspreidingstendens is hierdeur opgelewer. Die korrelasies vir individuele regressies was redelik met r2 waardes naby 0.5 en merkwaardig hoër waardes vir area gemiddeldes. Hoë korrelasies is egter behaal vir 2 van die 3 bestudeerde landsgebruike (r2 waardes van 0.99 en 0.81 in bosbou en grasveld onderskeidelik) wanneer die gemiddelde dieptestratifikasies gebruik en gekorrigeer word vir die verandering in deeltjiedigtheid vir gronde met hoë grondorganiese material. Alhoewel die Saxton and Rawls (2006) voorspellings van bulkdigtheid gebruik kan word, behoort bulkdigtheidsbepalings egter verkieslik direk gedoen te word. Die voorgestelde modelle vir die bepaling van vertikale GOK verspreiding tot 1m gronddiepte sou die koste van grondkoolstof opnames in die studiegebied dramaties verlaag deur grondmetings tot die grondoppervlak te beperk. Grondmonsters sal in triplikaat per waarnemingspunt met 5cm diep silinders op die grondoppervlak geneem word vir ρb (bulkdigtheid) and Corg (organiese koolstof) bepalings. Die gemiddelde akkuraatheid van die genormaliseerde diepteverspreidingsmodel is hoog vir grasveld en woude/bosbou plantasies (R2 = 0.98), maar ietwat laer vir bewerkte landerye (R2 = 0.96) as gevolg van die vermenging van die ploeglaag tot op die diepte van bewerking. Koolstof voorraad tot 1m gronddiepte is bepaal deur middel van die integraal van die genormaliseerde eksponensiele verspreiding, vermenigvuldig met die waarde van Corg op die grondoppervlak en op ‘n volume basis uitgedruk as koolstofdigtheid (Cv, kg∙m-3). Die gevolglike voorraadopname is met gemete waardes vergelyk deur middel van ‘n stuksgewyse integrasie van die gemonsterde diepteinkremente om GOK voorraad per area (kg∙m-2) te lewer. Die gemiddelde geskatte fout van voorspelling was 1.2 (9%) en 3.7 kg∙m-2 (21.6%) in grasveld and plantasies onderskeidelik en 1.3 kg.m-2 (9.5%) in bewerkte landerye. Verdere verbetering van die modelle en ‘n verlaging in hierdie foute kan verkry word deur die grondtipe inligting as veranderlike in te bring en die funksies volgens grondtipe eerder as landsgebruik te groepeer. Resultate van hierdie werk is reeds aangebied tydens ‘n seminar by die department Grondkunde, Stellenbosch Universiteit (Ros Mesa et al., 2014), die gesamentlike kongres vir die Suid-Afrikaanse Verenigings vir Grondkunde, Hortologie, Onkruidwetenskap en Gewasproduksie (Rozanov et al. 2015), die Eerste Global Soil Map konferensie, Frankryk (Wiese et al, 2013), die 20ste Internasionale Grondkunde Kongres, Korea (Wiese et al. 2014) en is ingehandig vir publikasie in ‘n spesiale uitgawe van Geoderma wat, na aanleiding van die aanbieding by die 20ste Internasionale Grondkunde Kongres, Korea (Wiese et al., 2014), fokus op digitale grondkartering van grondorganiese koolstof.

Thesis (M.S.)--Michigan State University. Dept. of Plant Biology Ecology, Evolutionary Biology, and Behavior, 2008.
The direct goal of this thesis is determine the effect of expermental soil climate manipulatoins on carbon fluxes in an Alaskan rich fen and to assess the indirect influence of substrate quality on carbon mineralizaton rates in peat--From abstract. Title from PDF t.p. (viewed on July 29, 2009) Includes bibliographical references. Also issued in print.

Primarily, this thesis addresses the need for a cost and time efficient methodology to quantify both chemically and physically stabilized soil organic carbon (SOC) fractions. The time and cost saving would be gained if the need to physically and chemically separate soil samples to measure carbons of different fractions could be reduced. Some progress has been made by quantifying SOC using spectroscopy techniques (NIR and MIR) in place of combustion, which both give quantitative and qualitative (organic functional groups) measurement for SOC. What remains is to see if the comprehensive data that can be gained from the spectroscopic techniques can be used to quantify and characterize SOC in soil fractions while using minimal or no physical and/or fractionation pretreatments. Chapter 2 of this thesis is a comprehensive review of the literature focusing on soil C pools and significant aggregate theories currently developed. From the literature, it is apparent that soil aggregation is mediated by SOC and aggregate fractions of various sizes are stabilized by a range of SOC functional groups. At the same time SOC and aggregation models were being developed SOC pools were also being defined to populate soil carbon turnover models (e.g. Roth-C). Only recently, has research been undertaken which attempt to combine soil aggregation with soil C turnover models. A limitation to using these models is the time taken to separate aggregate and carbon fractions and the review of the literature indicates that using spectroscopic techniques may be a solution to this.

Soil organic carbon represents the largest constituent of the global C pool and carbon budgets are studied by researchers and modelers in C cycling, global climate change, and soil quality studies. Pedon and soil interpretation record databases are used with soil and ecological maps to estimate regional SOC even though these databases are rarely complete for surface litter and mineral subsurface horizons. The first main objective of the project is to improve the ability to produce soil organic carbon estimates from existing spatial soils datasets, such as STATSGO. All records in the STATSGO Layer table that were incomplete or appeared to be incorrectly filled with a null or zero value were considered invalid. Data sorting procedures and texture lookup tables were used to identify exiting correct (valid) data entries that were used to substitute invalid records. STATSGO soil property data were grouped by soil order, MLRA, layer number, and texture to produce replacement values for all invalid data used to calculate mass SOC. Grouping criteria was specific to each variable and was based on texture designations. The resulting filled and unfilled tables were used with procedures assuming Normal and Lognormal distribution of parameters in order to analyze variation of mass SOC estimates caused by using different computation techniques. We estimated mass SOC to 2 m in Maine and Minnesota using filled and unfilled STATSGO data tables. Up to 54% of the records in Maine and up to 80% of the records in Minnesota contained null or zero values (mostly in fields related to rock fragments) that were replaced. After filling, the database resulted in 1.5 times higher area-weighted SOC. SOC calculated using the Normal distribution assumption were 1.2 to 1.5 times higher than those using the Lognormal transformation. SOC maps using the filled tables had more logical geographic SOC distribution than those using unfilled tables. The USDA Forest Service collects and maintains detailed inventory data for the condition and trends of all forested lands in the United States. A wide range of researchers and landowners use the resulting Forest Inventory and Analysis (FIA) database for analytical and decision making tasks. FIA data is available to the public in transformed or aggregate format in order to ensure confidentiality of data suppliers. The second main objective of this project was to compute SOC (kg m-2) results by FIA forest type and forest type group for three depth categories (25 cm, 1 m, and 2 m) at a regional scale for the 48 contiguous United States. There were four sets of results derived from the filled STATSGO and FIA datasets for each depth class by region: (1) SOC computed by the Lognormal distribution approach for (1a) all soil orders, (1b) without Histosols; and (2) SOC computed by the Normal distribution approach for (2a) all soil orders, (2b) without Histosols. Two spatial forest cover datasets were relevant to this project, FIA and AVHRR. We investigated the effects of FIA inventory data masking for Maine and Minnesota, such as plot coordinates rounding to the nearest 100 arc-second, and the use of 1 km resolution satellite-derived forest cover classes from AVHRR data, on SOC estimates to 2 m by forest type group. SOC estimates by soil mapping unit were derived from fixed STATSGO database tables and were computed by the Lognormal distribution approach including all soil orders. The methods in this study can be used for a variety of ecological and resource inventory assessments and the automated procedures can be easily updated and improved for future uses. The procedures in this study point out areas that could benefit the most during future revisions of STATSGO. The resulting SOC maps are dynamic and can be rapidly redrawn using GIS whenever STATSGO spatial or tabular data undergo updating. Use of pedon data to define representative values for all properties in all STATSGO layers and correlation of STATSGO layers to soil horizons will lead to vast improvement of the STATSGO Layer table and promote its use for mass SOC estimation over large regions.
Master of Science

Doctor of Philosophy
Department of Agronomy
Charles W. Rice
Increasing atmospheric CO2 concentrations and other greenhouse gases have been linked to global climate change. Soil organic C (SOC) sequestration in both agricultural and native ecosystems is a plausible option to mitigate increasing atmospheric CO2 in the short term. Laboratory and field studies were conducted to (1) understand the influence of soil water content on the temperature response of SOC mineralization (2) investigate burn and nutrient amendment effects on biogeochemical properties of tallgrass prairie and (3) assess perennial and annual plant management practices on biophysical controls on SOC dynamics. The laboratory study was conducted using soils collected from an agricultural field, currently planted to corn (C4 crop), but previously planted to small grain (C3) crops. The changes in cultivated crops resulted in a δ¹³C isotopic signature that was useful in distinguishing older from younger soil derived CO2-C during SOC mineralization. Soils were incubated at 15, 25 and 35 oC, under soil water potentials of -1, -0.03 and -0.01 MPa. Soil water content influenced the effect of temperature on SOC mineralization. The impact of soil water on temperature effect on SOC mineralization was greater under wetter soil conditions. Both young and older SOC were temperature sensitive, but SOC loss depended on the magnitude of temperature change, soil water content and experiment duration. Microbial biomass was reduced with increasing soil water content. The first field experiment investigated burn and nutrient amendment effects on soil OC in a tallgrass prairie ecosystem. The main plots were burned (B) and unburned (UB) tallgrass prairie and split plots were nutrient amendments (N, P or N+P including controls). Vegetation was significantly altered by burning and nutrient amendment. Treatment effects on either TN or SOC were depth-specific with no impact at the cumulative 0-30 cm depth. The P amendment increased microbial biomass at 0-5 cm which was higher in unburned than burned. However, at 5-15 cm depth N amendment increased microbial biomass which was higher in burned than unburned. In conclusion, soil OC in both burned and unburned tallgrass prairie may have a similar trajectory however; the belowground dynamics of the burned and unburned tallgrass prairie are apparently different. Another field experiment assessed SOC dynamics under perennial and annual plant management practices. The main plots were grain sorghum (Sorghum bicolor) planted in no-tillage (NT) or continuous tillage (CT), and replanted native prairie grass, (Andropogon gerardii) (RP). The spit plots were phosphorus (+P) and control without P (-P). The P amendment was used to repress arbuscular mycorrhizal fungi (AMF), known to influence soil aggregation. The macroaggregate >250 µm, SOC and TN were higher in RP and NT than CT. The relative abundances of AMF and saprophytic fungi were greater with less soil disturbance in RP and NT than in CT. Therefore, less soil disturbance in RP and NT increased AMF and fungal biomasses. The higher relative abundances of AMF and fungi with less soil disturbance increased macroaggregate formation in RP and NT, which resulted in higher SOC sequestration in RP and NT than CT.