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The theories about plant nutrition and soil fertility varied widely from the antiquity to the middle of the nineteenth century, with major (Thaer A. 1809. Grundsatze der rationellen Landwirtschaft (1809-1812). Berlin (Germany): Realschulbuch Ed.) or minor (Liebig J. 1840. Die organische Chemie in ihrer Anwendung auf Agrikultur und Physiologie. Braunschweig (Germany): Vieweg) importance attributed to soil humus or soil organic matter (SOM). The importance assigned to humus over the past two centuries will be developed in this historical paper. Intensification of agriculture in the twentieth century permitted an important increase in cultivated plant yield of food, fiber, wood, and biofuel production, not only in the northern countries, but also in some southern countries (e.g., India and China) with the emergence of the Green Revolution. However, the question of organic restitutions and the maintenance (or increase) of the SOM stock was, at times, not taken into consideration; consequently, there was a general decrease in SOM stock for many tropical soils. It is now widely accepted by scientists that SOM depletion is one of the major factors leading to degradation of ecosystem services and loss of ecosystem resilience: new alternatives are now necessary for the maintenance and/or increase in plant productivity and production of environmental services by agriculture. Therefore, this paper will also present some recent research in different tropical countries with a focus on agroecological management of tropical soils.

Although much research has been carried out, there is still no consensus about the temperature dependence of CO2 emissions from soil organic carbon (SOC) decomposition. The temperature sensitivity of soil CO2 emissions varies with the time and the temperature levels used in laboratory experiments. Although combined models have been used to take account of the incubation time and temperature to describe the decomposition of SOC, the factors temperature and time in these models are still independent. These models were fitted to CO2 data obtained from parallel laboratory incubations. In this study, sequential incubations were carried out for 2 months at temperatures between 20 degrees C and 50 degrees C, assuming that (1) the sequence of temperature levels did not affect the soil CO2 emissions and (2) the CO2 emissions depended only on the temperature sum accumulated by the soil. A degree-day model, which is commonly used in agronomy, was applied to predict soil CO2 emission variations with time and temperature. The results showed that, for any sequence of temperature levels, the accumulation of degree-days explained the cumulative CO2 emissions during two months laboratory incubation over the 20-40 degrees C range, where 6% of SOC was emitted as CO2. However, at 50 degrees C, soil CO2 emissions were higher than predicted by the degree-day model. This underestimation of soil CO2 emissions lasted for one month after the soil had been at 50 degrees C. These results suggest that, for the range of incubation temperatures (20-40 degrees C) and time tested (56 days), or 2000 degree-days, (i) the degree-day model is valid only between 20 and 40 degrees C, (ii) the main determinant of soil temperature sensitivity is the amount of labile carbon rather than microbial adaptation of soil respiration to temperature. (C) 2012 Elsevier B.V. All rights reserved.

Countries should provide regularly national inventories of greenhouse gas emissions and sinks and, and for the agriculture and forestry sectors this comprise national estimates of soil organic carbon (C) stocks. Estimation of soil C stock requires soil bulk density (D-b) values. However, direct measurement of D-b is often lacking mainly for soils in arid and semi-arid conditions. Much effort has been made in finding alternative solution to predict D-b, either improving in situ determinations, either improving estimation procedures based on other soil properties. Regression models or pedotransfer functions (PTFs) based on easily measured soil properties constitute an adequate tool to assess D-b, since it needs a minimum data set of indicators. A forward stepwise multiple linear regression routine was used to predict D-b from physico-chemical soil properties. In this study, a soil database was organised from published and unpublished data from Tunisia. The database consisted of 238 soil profiles corresponding to 707 soil horizons from Tunisia. A general regression model fitted with all the data showed that CC, Clay, coarse-Sand and pH were the principal contributors to D-b prediction (R-2 = 0.55, standard error of prediction = 0.14). Additional models based on different set of variables are also provided providing alternative solutions for different levels of soil information. Predictions of the models were often improved when the data were partitioned into groups by soil depth (0-40 and 40-100 cm) and soil orders. This study also showed that CaCO3 might be an important predictor for deeper soil horizon. The proposed PTFs for Tunisia might be useful for a larger range of soil from arid and sub arid regions. (C) 2012 Elsevier Ltd. All rights reserved.

We studied the black carbon (BC) content of ca. 405 samples from French topsoil and artificial soil and carbonate mixtures. Our protocol involved three main steps: (i) decarbonation by HCl, (ii) elimination of non-pyrogenic organic carbon in a furnace at 375 °C, and (iii) quantification of residual carbon by CHN analysis. BC content increased for calcareous soils according to their carbonates content. Subsequent analyses confirmed the existence of a methodological artefact for BC determination only in calcareous soils. Decarbonation changes the thermal properties of organic matter, creating more recalcitrant carbon than in the initial sample. Higher CaCO3 and organic carbon content results in a more pronounced artefact. The reversal of the first two steps of the chemo-thermal oxidation method (i.e. thermal oxidation before soil decarbonation) eliminates this artefact. Overall, our results suggest that BC content may have been overestimated in a large number of studies on calcareous soils.

Restoration of atmospheric carbon in soils has principal many good effects. Arid lands cover more than 40 % of the global earth area, but only stock 16 % from the global carbon stock. It seems to be a suitable solution for this environmental issue, but still all variables controlling organic carbon in such kinds of soil, was ignored. This study aims to develop two models of organic carbon under clayey and sandy soils in semi-arid Mediterranean zones basing on physical and chemical soil properties. For establishing both models, structural equation modeling was used. For modeling organic carbon, two Tunisian soil databases composed from clayey and sandy soils made respectively, of 450 and 602 soil horizons were used. Using the two databases for all properties, the principal component analysis shows two components for clayey soil; (i) chemical properties and bulk density and (ii) physical properties. For the sandy soil it reveals two components; (i) chemical properties and (ii) physical properties. According to the derived components for each soil category, two models have been built. Structural equation modeling results show that clayey model has proved that organic carbon was controlled by chemical properties and bulk density more than physical properties and sandy model has proved that organic carbon was controlled by chemical properties more than physical properties. The root mean square errors of approximation were 0.079 and 0.050 for the clayey and sandy models, respectively. Then these two models were validated with two other databases from Tunisian dryland soils.

Geoderma ISI Document Delivery No.: 771EL Times Cited: 4 Cited Reference Count: 88 Razakamanarivo, Ramarson Herintsitohaina Grinand, Clovis Razafindrakoto, Marie Antoinette Bernoux, Martial Albrecht, Alain Departement de Soutien et de Formation des Communautes du Sud-Institution de Recherche pour le Developpement (DSF-IRD); French Government This study was funded by the "Departement de Soutien et de Formation des Communautes du Sud-Institution de Recherche pour le Developpement (DSF-IRD)" and the French Government within the framework of a PhD. We thank local people in the county of Sambaina for their profitable collaboration during field work and all our colleagues from the "Laboratoire des Radioisotopes (LRI)" and the "Ecole Superieure des Sciences Agronomiques-Departement Eaux&-Forets (ESSAgro-Forets)" at the University of Antananarivo and also the "Unite Mixte de Recherche Eco & Sols" of the Research Institute for the Development (IRD) for their technical supports and reliable scientific advices. Finally, I am gratefull to Saint-Andre Laurent and Jourdan Christoph for their help during upstreaming activities relatives to allometry equations. Elsevier science bv Amsterdam; International audience; Recent concerns about global warming have resulted in more concerted studies on quantification and modeling of carbon (C) storage in different ecosystems. The aim of this study was to assess and map the carbon stocks in above (ABG), below-ground (BLG) biomass and soil organic carbon contained in the 30 centimeter top-layer (SOC) in coppices of eucalyptus plantations in the central highlands of Madagascar in an area of 1590 ha. Relationships between C stock and various biophysical (stool or shoot stockings and ages, circumferences) and spatial (elevation, slope, and soil type) factors that may affect C storage within each pool were investigated. Three different modeling techniques were tested and compared for various factor sets: (i) simple linear regression (SLM), (ii) multiple linear (MLM) models and, (iii) boosted regression tree (BRT) models. Weights of the factors in the respective model were analyzed for the three pool-specific models that produced the highest accuracy measurement. A regional spatial prediction of carbon stocks was performed using spatial layers derived from a digital elevation model, remote sensing imagery and expert knowledge. Results showed that BRT had the best predictive capacity for C stocks compared with the linear regression models. Elevation and slope were found to be the most relevant predictors for modeling C stock in each pool, and mainly for the SOC. A factor representing circumferences of stools and their stocking (stools.ha(-1)) largely influenced BLG. Shoot circumference at breast height and shoot age were the best factors for ABG fitting. Accuracy assessment carried out using coefficient of determination (R-2) and ratio of standard deviation to prediction error (RPD) showed satisfactory results, with 0.74 and 1.95 for AGB, 0.85 and 2.59 for BLG, and 0.61 and 1.6 for SOC respectively. Application of the best fitted models with spatial explanatory factors allowed to map and estimate C contained within each pool : 32 +/- 13 Gg C for ABG, 67 +/- 15 Gg C for BLG and, 139 +/- 36 Gg C for SOC (1 Gg=10(9) g). A total of 238 +/- 40 Gg C was obtained for the entire study area by combining the three C maps. Despite their relatively low predictive quality, models and C maps produced herein provided relevant reference values of C storage under plantation ecosystems in Madagascar. This study contributed to the reducing of uncertainty related to C monitoring and baseline definition in managed terrestrial ecosystem.

A conversão de áreas nativas com o corte e queima de vegetação seguida do cultivo do solo resultam em mudanças na dinâmica da matéria orgânica do solo, com alterações nas emissões dos gases causadores de efeito estufa (GEE: CO2, CH4 e N2O) da biosfera para a atmosfera, que causam a elevação da temperatura média e, consequentemente, as mudanças climáticas globais. O objetivo deste estudo foi verificar as relações entre os fluxos de CO2, CH4 e N2O com a umidade, biomassa microbiana e as formas inorgânicas de N no solo com diferentes usos das terras no bioma Cerrado (Rio Verde, Goiás). O clima da região é do tipo Aw (Köppen-Geiger), e o solo foi classificado como Latossolo Vermelho distrófico caulinítico textura argilosa com vegetação original de Cerradão. O delineamento experimental foi inteiramente casualizado (DIC), com quatro tratamentos (áreas): vegetação nativa - Cerradão (CE); pastagem (PA) de braquiária, semeadura convencional (SC) de soja; e semeadura direta (SD) de milho sucedido por milheto. As emissões anuais de CO2 e N2O não mostraram diferenças significativas entre os tratamentos; isso ocorreu devido à elevada variação nos fluxos dos gases em decorrência da sazonalidade no clima, com as menores emissões observadas durante o inverno, devido à ausência da umidade do solo. A média na emissão de CO2 foi de 108,9 ± 85,6 mg m-2 h-1 , e para o N2O, de 13,5 ± 7,6 µg m-2 h-1. Os fluxos de CH4 apresentaram diferenças significativas somente para a pastagem, com emissão de 32 µg m-2 h-1 , enquanto nas demais áreas foram observados influxos entre 46 e 15 µg m-2 h-1 . Com os resultados das correlações, pode-se verificar que a umidade foi a variável do solo que apresentou maior correlação com o fluxo dos três gases de efeito estufa. O teor de N-NO3- e as emissões de CO2 mostraram correlações para todas as áreas. Quando consideradas as correlações para todos os tratamentos conjuntamente, verificou-se que os fluxos dos três gases apresentaram correlações significativas com os teores de C e N-microbiano. Contudo, a relação Cmicro:Nmicro não mostrou correlação significativa com o fluxo dos gases de efeito estufa. A pastagem foi a única situação em que os fluxos de CO2 e N2O apresentaram correlação com as quantidades de N-inorgânico. Os resultados sugerem que os fluxos dos GEE são dependentes do regime pluvial no bioma Cerrado, principalmente nas áreas cultivadas que recebem altas doses de fertilizantes para o aumento da produtividade. The conversion of native forests by cutting and burning into farming areas leads to alterations in the dynamics of soil organic matter, with changes in emissions of greenhouse gases (GHGs: CO2, CH4 and N2O) from the biosphere to the atmosphere. These cause an average temperature rise and, consequently, global climate change. The aim of this study was to examine relationships between the fluxes of CO2, CH4 and N2O with moisture, microbial biomass and inorganic N forms in soil with different land uses in the Cerrado biome (Rio Verde county, State of Goias - Brazil). The climate (Köppen-Geiger) was classified as Aw and the soil as Latossolo Vermelho distrófico caulinítico / a clayey kaolinitic Oxisol under original Cerrado (Brazilian savanna) vegetation. The experiment was arranged in a completely randomized design (CRD) with four treatments (areas): Native vegetation - Cerrado (CE); brachiaria pasture (PA); soybean in conventional tillage (SC) and no-tillage (NT) corn followed by millet. No significant differences in annual CO2 and N2O emissions were observed between treatments. This can be explained by the variability of gas fluxes due to climate seasonality, with lower emissions in the winter due to low soil moisture. Mean emissions of CO2 were 108.9 ± 85.6 mg m-2 h-1 , and of N2O 13.5 ± 7.6 mg m-2 h-1 . For CH4 significant differences in the fluxes were only observed in pasture (32 mg m-2 h-1 ), while in the other areas inflows between 46 and 15 mg m-2 h-1 were observed. The GHG fluxes showed close correlation with soil moisture. The N-NO3- emissions were significantly correlated with CO2-emissions in all areas. Considering all treatments together, the three GHG fluxes were correlated with the microbial C and N contents. However, the Cmicro: Nmicro ratio was not significantly correlated with the GHG flux. Only for pasture the CO2 and N2O fluxes were correlated with the content of soil inorganic-N. Results suggested that the GHG fluxes in the Cerrado are related to rainfall, mainly in farming areas treated with high fertilizer doses to increase productivity.

EX-ACT (EX-Ante Carbon-balance Tool) is a tool developed by the Food and Agriculture Organization of the United Nations (FAO). It provides ex-ante measurements of the mitigation impact of agriculture and forestry development projects, estimating net C balance from GHG emissions and Carbon (C) sequestration. EX-ACT is a land-based accounting system, measuring C stocks, stock changes per unit of land, and CH4 and N2O emissions expressed in t CO2-eq per hectare and year. The main output of the tool is an estimation of the C-balance associated with the adoption of improved land management options, as compared with a "business as usual" scenario. EX-ACT has been developed using primarily the IPCC 2006 Guidelines for National Greenhouse Gas Inventories, complemented by other existing methodologies and reviews of default coefficients. Default values for mitigation options in the agriculture sector are mostly from the 4th Assessment Report of IPCC (2007). Thus, EX-ACT allows for the carbonbalance appraisal of new investment programmes by ensuring an appropriate method available for donors and planning officers, project designers, and decision makers within agriculture and forestry sectors in developing countries. The tool can also help to identify the mitigation impacts of various investment project options, and thus provide an additional criterion for consideration in project selection. EX-ACT (Ex-Ante Carbon-balance Tool, ferramenta para o balanço ex-ante de Carbono) é desenvolvida pela Organização das Nações Unidas para Agricultura e Alimentação (FAO). Tem como finalidade de fornecer estimativas ex-ante do impacto de atenuação na agricultura e nos projetos de desenvolvimento florestal, estimando o saldo líquido das emissões dos gases do efeito estufa (GEE) e do seqüestro de carbono (C). EX-ACT é um sistema de contabilidade que considera o uso da terra, medindo estoques de C, mudanças do estoque por unidade de área, e emissões de CH4 e N2O expressos em CO2-eq por hectare e por ano. O resultado principal da ferramenta é uma estimativa do balanço de CO2-eq associados à adoção de opções de melhoria do manejo da terra, em comparação com um cenário chamado de "business as usual". EX-ACT foi desenvolvida usando principalmente as recomendações de 1996 para estabelecer os inventários nacionais de GEE (Guidelines for National Greenhouse Gas Inventories IPCC, 2006) complementada por outras metodologias existentes e coeficientes padrão especificos quando disponíveis. Os valores padrão para as opções de mitigação no setor agrícola são na sua maioria provenientes do 4º Relatório de Avaliação do IPCC (2007). Assim, EX-ACT estima o balanço de C dos novos programas de investimentos, garantindo um método adequado e disponível para financiadores e agentes de planejamento, projetistas, e governantes para os setores da agricultura e da silvicultura nos países em desenvolvimento. A ferramenta também pode ajudar a identificar os impactos de atenuação de opções possíveis em vários projetos de investimento, e assim fornecer um critério adicional para escolhê-las como parte dos projetos.

National inventories of anthropogenic greenhouse gas (GHG) emissions (implementation of the National Communications) are organized according to five main sectors, namely: Energy, Industrial Processes, Agriculture, Land-Use Change and Forestry (LUCF) and Waste. The objective of this study was to review and calculate the potential of greenhouse gas mitigation strategies in Brazil for the Agricultural and LUCF. The first step consisted in an analysis of Brazilian official and unofficial documents related to climate change and mitigation policies. Secondly, business as usual (BAU) and mitigation scenarios were elaborated for the 2010-2020 timeframe, and calculations of the corresponding associated GHG emissions and removals were performed. Additionally, two complementary approaches were used to point out and quantify the main mitigation options: a) following the IPCC 1996 guidelines and b) based on EX-ACT. Brazilian authorities announced that the country will target a reduction in its GHG between 36.1 and 38.9% from projected 2020 levels. This is a positive stand that should also be adopted by other developing countries. To reach this government goal, agriculture and livestock sectors must contribute with an emission reduction of 133 to 166 Mt CO2-eq. This seems to be reachable when confronted to our mitigation option values, which are in between the range of 178.3 to 445 Mt CO2-eq. Government investments on agriculture are necessary to minimize the efforts from the sectors to reach their targets. Inventários nacionais acerca de emissões de gases do efeito estufa (GEE) (refinamentos das Comunicações Nacionais) são organizadas de acordo com cinco principais setores, a saber: Energia, Processos Industriais, Agropecuária, Mudanças do Uso da Terra e Florestas e Tratamento de Resíduos. O objetivo dessa revisão foi calcular o potencial das estratégias de mitigação de GEE no Brasil para agropecuária e mudança de uso da terra e florestas. A primeira etapa consistiu na análise de documentos oficiais e não-oficiais do Brasil relacionados a mudanças climáticas e políticas de mitigação. O cenário atual, sem adoção de ações mitigadoras (BAU), e os cenários de mitigação foram elaborados para o período 2010-2020. Efetuaram-se os cálculos associados às emissões e remoções de GEE. Adicionalmente, duas estratégias foram utilizadas para destacar e quantificar as principais opções de mitigação: a) seguindo metodologia do IPCC 1996 e b) baseando-se no EX-ACT. Autoridades brasileiras anunciaram que o país buscará reduzir sua taxa de emissão de GEE em 36.1 a 38.9% em relação a 2020. Este é um posicionamento positivo que deve ser adotado por outros países em desenvolvimento. Para alcançar essa meta governamental, os setores agricultura e pecuária devem contribuir reduzindo a emissão em 133 a 166 Mt CO2-eq. Tal redução parece ser atingível quando confrontada com os valores do presente trabalho sobre opções de mitigação os quais estão entre 178,3 e 445 Mt CO2-eq. Investimentos governamentais nos setores agrícola, pecuária e silvicultura são necessários para minimizar os esforços para atingir as metas de redução de emissão pelos outros setores do país.

Correspondance: eric.scopel@cirad.fr; International audience; No-tillage mulch-based (NTM) cropping systems have been widely adopted by farmers in the Brazilian savanna region (Cerrado biome). We hypothesized that this new type of management should have a profound impact on soil organic carbon (SOC) at regional scale and consequently on climate change mitigation. The objective of this study was thus to quantify the SOC storage potential of NTM in the oxisols of the Cerrado using a synchronic approach that is based on a chronosequence of fields of different years under NTM. The study consisted of three phases: (1) a farm/cropping system survey to identify the main types of NTM systems to be chosen for the chronosequence; (2) a field survey to identify a homogeneous set of situations for the chronosequence and (3) the characterization of the chronosequence to assess the SOC storage potential. The main NTM system practiced by farmers is an annual succession of soybean (Glycine max) or maize (Zea mays) with another cereal crop. This cropping system covers 54% of the total cultivated area in the region. At the regional level, soil organic C concentrations from NTM fields were closely correlated with clay + silt content of the soil (r2 = 0.64). No significant correlation was observed (r2 = 0.07), however, between these two variables when we only considered the fields with a clay + silt content in the 500–700 g kg−1 range. The final chronosequence of NTM fields was therefore based on a subsample of eight fields, within this textural range. The SOC stocks in the 0–30 cm topsoil layer of these selected fields varied between 4.2 and 6.7 kg C m−2 and increased on average (r2 = 0.97) with 0.19 kg C m−2 year−1. After 12 years of NTM management, SOC stocks were no longer significantly different from the stocks under natural Cerrado vegetation (p < 0.05), whereas a 23-year-old conventionally tilled and cropped field showed SOC stocks that were about 30% below this level. Confirming our hypotheses, this study clearly illustrated the high potential of NTM systems in increasing SOC storage under tropical conditions, and how a synchronic approach may be used to assess efficiently such modification on farmers’ fields, identifying and excluding non desirable sources of heterogeneity (management, soils and climate).

International audience; The development of tree allometric equations is crucial to accurate forest carbon assessment. However, very few allometric equations exist for sub-Saharan Africa and as a result generalized allometric equations, often established for forests in other continents, are used by default. The objectives of this study were (1) to propose a sampling methodology and calculation procedures to assess biomass for tropical tree species of contrasted tree shapes in Africa, (2) to identify factors affecting within and between trees wood density, (3) to propose an allometric model that integrates these factors and (4) to evaluate the reliability of using generalized allometric equations in this type of forests. Models were developed to predict wood density and phytomass of the trees based on the harvesting of 42 trees from 16 species, representing three guild status in the wet evergreen forest of Boi Tano in Ghana. Results indicated that the wood density was highly influenced by the tree species, guild status, size of the tree and pith to bark distance. Dry mass of a tree was influenced by diameter at breast height, crown diameter and wood density. The wood density depends on the position of the wood within the tree and the guild status considered. The use of generalized allometric models in literature is limited by the specific climate zone, the consideration of tree height and species specific wood density. In considering those factors, using generalized allometric equations could result in an error of 3%. Further research should better consider the bigger trees and the influence of the topography and ecosystem history.

International audience; Biofuels are both a promising solution to global warming mitigation and a potential contributor to the problem. Several life cycle assessments of bioethanol have been conducted to address these questions. We performed a synthesis of the available data on Brazilian ethanol production focusing on greenhouse gas (GHG) emissions and carbon (C) sinks in the agricultural and industrial phases. Emissions of carbon dioxide (CO2) from fossil fuels, methane (CH4) and nitrous oxide (N2O) from sources commonly included in C footprints, such as fossil fuel usage, biomass burning, nitrogen fertilizer application, liming and litter decomposition were accounted for. In addition, black carbon (BC) emissions from burning biomass and soil C sequestration were included in the balance. Most of the annual emissions per hectare are in the agricultural phase, both in the burned system (2209 out of a total of 2398 kg C-eq), and in the unburned system (559 out of 748 kg C-eq). Although nitrogen fertilizer emissions are large, 111 kg C-eq ha-1 yr-1, the largest single source of emissions is biomass burning in the manual harvest system, with a large amount of both GHG (196 kg C-eq ha-1 yr-1). and BC (1536 kg C-eq ha-1 yr-1). Besides avoiding emissions from biomass burning, harvesting sugarcane mechanically without burning tends to increase soil C stocks, providing a C sink of 1500 kg C ha-1 yr-1 in the 30 cm layer. The data show a C output: input ratio of 1.4 for ethanol produced under the conventionally burned and manual harvest compared with 6.5 for the mechanized harvest without burning, signifying the importance of conservation agricultural systems in bioethanol feedstock production.

On the eve of the 15th climate negotiations conference in Copenhagen, the pressure to assess all climate mitigation options is mounting. In this study, a bio-physic model and a socio-economic model were designed and coupled to assess the carbon sequestration potential of agricultural intensification in Senegal. The biophysical model is a multiple linear regression, calibrated and tested on a dataset of long-term agricultural trials established in West Africa. The socio-economic model integrates both financial and environmental costs related to considered practice changes. Both models are spatially explicit and the resulting spatial patterns were computed and displayed over Senegal with a geographic information system. The national potential from large-scale intensification was assessed at 0.65-0.83 MtC. With regards to local-scaled intensification as local projects, the most profitable areas were identified in agricultural expansion regions (especially Casamance), while the areas that meet the current financial additionality criteria of the Clean Development Mechanism were located in the northern part of the Peanut Basin. Using the current relevant mode of carbon valuation (Certified Emission Reductions), environmental benefits are small compared to financial benefits. This picture is radically changed if "avoided deforestation", a likely consequence of agricultural intensification, is accounted for as the greenhouse gases sink capacity of projects increases by an average of a hundred-fold over Senegal.

Amsterdam; International audience; Changes in land use can result in either sources or sinks of atmospheric carbon (C), depending on management practices. In Brazil, significant changes in land use result from the conversion of native vegetation to pasture and agriculture, conversion of pasture to agriculture and, more recently, the conversion of pasture and agriculture to integrated crop-livestock systems (ICL). The ICL system proposes a diversity of activities that include the strategic incorporation of pastures to agriculture so as to benefit both. In agricultural areas, for example, the implementation of ICL requires the production of quality forage for animals between crops as well as the production of straw to facilitate the sustainability of the no-tillage (NT) management system. The objective of this study was to evaluate the modifications in soil C stocks resulting from the main processes involved in the changes of land use in Amazonia and Cerrado biomes. For comparison purposes, areas under native vegetation, pastures, crop succession and ID. under different edapho-climatic conditions in Amazonia and Cerrado biomes were evaluated. This study demonstrated that the conversion of native vegetation to pasture can cause the soil to function either as a source or a sink of atmospheric CO(2), depending on the land management applied. Non-degraded pasture under fertile soil showed a mean accumulation rate of 0.46 g ha(-1) year(-1). Carbon losses from pastures implemented in naturally low fertile soil ranged from 0.15 to 1.53 Mg ha(-1) year(-1), respectively, for non-degraded and degraded pasture. The conversion of native vegetation to agriculture in areas under the ICL system, even when cultivated under NT, resulted in C losses of 1.31 in six years and of 0.69 Mg ha(-1) in 21 years. The conversion of a non-degraded pasture to cropland (soybean/sorghum) released, in average, 1.44 Mg of C ha(-1)year(-1)to the atmosphere. The ICL system in agricultural areas has shown evidences that it always functions as a sink of C with accumulation rates ranging from 0.82 to 2.58 Mg ha(-1) year(-1). The ICL produces soil C accumulation and, as a consequence, reduces atmospheric CO(2) in areas formerly cultivated under crop succession. However, the magnitude of C accumulation in soil depends on factors such as the types of crops, the edapho-climatic conditions and the amount of time the area is under ICE

A região do Cerrado representa uma das maiores áreas cultivada do mundo. Os diferentes usos do solo empregados nesta região podem modificar efetivamente as quantidades de matéria orgânica e alterar a ciclagem dos nutrientes no solo. O objetivo deste estudo foi avaliar o efeito de diferentes sistemas de manejo nas relações entre o carbono total e os atributos químicos de um Latossolo Vermelho distrófico no Cerrado na região de Rio Verde, Estado de Goiás. As áreas estudadas foram cerradão, pastagem de baixa produtividade, plantio convencional de soja e plantio direto de soja com milho em sucessão. Os valores mais baixos no pH, cátions trocáveis, P-disponível e enxofre foram observados no Cerradão, contudo foram encontrados os maiores teores de C-total, que apresentaram correlação elevada com os teores de H+AL e a CTC potencial. Nas demais áreas, foram encontradas concentrações mais elevadas de cátions trocáveis, P-disponível e enxofre. Nas áreas onde não ocorreu o revolvimento do solo e a aplicação do corretivo e dos fertilizantes foi superficial, a estratificação dos teores de C-total promoveu a retenção dos elementos mais próximos à superfície, o que proporcionou correlações significativas com os atributos químicos do solo. The Brazilian savanna region (Cerrado) is one of the largest cultivated areas of the world. The different land uses in the region can effectively change the quantities of soil organic matter and the cycling of nutrients. The objective of this study was to evaluate the effect of different land use management systems on the relationship between soil organic carbon and the soil chemical attributes of a Red Latosol (Oxisol) under Cerrado in Rio Verde (Goiás state). The treatments studied were native vegetation (cerradão), low-productivity pasture, conventional tillage with soybean, and no-tillage with soybean and maize. The smallest values for pH, available P, K, Ca and Mg were observed for the Cerradão treatment, even if the relatively high C levels increased the potential soil cation exchange capacity. The pasture, conventional tillage and no-tillage treatments showed higher K, Ca, Mg, available P, and S concentrations in the soil. In the areas where soil tillage did not take place and lime and fertilizers were applied superficially, the stratification of the soil organic carbon provides the retention of the elements near to the surface, with significance correlations with the soil chemicals attributes.

Soil is a part of our daily lives by virtue of the role it plays in our environment, and by its position at the interface between the atmosphere, hydrosphere, biosphere and lithosphere. Consequently, soil appears in all the artistic fields, including comic strips and cartoons. Comic strips are scripted stories told in images. A comic strip is a means of communication that lies at the interface of graphic art, cinematographic art, and literature. From graphic art, it borrows the composition of the images, and the variations of shading and light, perspective and color. From cinematographic art, it borrows the script, the framing or the angles of sight, and the sequence of the images. From literature, it borrows the texts and the dialogues. Such stories in images appeared in Europe in the first half of the 19 century. Among the pioneers were “Histoire de M. Jabot” (Topffer 1833), “Max und Morizt” (Busch 1865) and “La famille Fenouillard” (Colomb 1889; pseudonym: “Christophe”). Primarily humorous, the comic strip became more serious in the United States, with “The Yellow Kid” (Outcault 1896) and “The Katzenjammer Kids” (Dirks 1897). Later, it moved to include fantasy themes, e.g., “Little Nemo in Slumberland” (McCay 1905). During the 1930s, American comic strips grew in popularity as daily features in newspapers, and Superman and Mickey Mouse (1934) became household names. The comic strip remained focused on the child audience for a long time. Its mission was to divert them. Since its birth, the comic strip has been evolving from its early, narrow focus on entertaining children with tales of humour and adventure, to more adult themes in the 1970s and 1980s. By the end of the 1990s, almost all literary styles had been explored (detective story, thriller, fiction, history, humour, heroic fantasy, etc.).

The African continent plays a growing role in the carbon (C) cycle. However, Africa is one of the weakest links in our understanding of the global carbon cycle particularly when considering the soil compartment. Most of the soil organic carbon (SOC) estimates concern the global size of the soil C reservoir without indication on its distribution, or if given, limited to the contribution of a large ecosystems or region. The aim of the study is i) to assess the original soil C stocks (SOC) of Africa for the different countries and Ecoregions, and ii) to compare SOC estimates from different soil properties databases and digital maps. Four recent global digital soil maps and five soil properties databases were used to estimate the SOC for different soil layers in Africa. Those databases hold between 1799 and 4043 soil profiles which are considered to represent the soil units showed on a 0.5 by 0.5 degree soil maps of Africa. SOC of Africa ranged 133 420–184 116 Tg for 0–100 cm soil layer. The most recent databases estimated 166 397 Tg C which corresponded to 9% of the global SOC stock and 68% of the terrestrial C pool of Africa. Average SOC ranges 0.4–8.2 kg m−2 at national scale and 1.53–6.61 kg m−2 for ecoregions. Using different soil database or spatial data leads to up to 30% of difference. These quantities indicate a great potential to develop sink activities through soil C sequestration activities.

Robust and accurate regional estimates of C storage in soils are currently an important research topic because of ongoing debate about human-induced changes in the terrestrial C cycle. Widely available geoprocessing tools were applied to estimate native soil organic C (SOC) stocks of Rio Grande do Sul state in southern Brazil to a depth of 30 cm from previously sampled soil pedons under undisturbed vegetation. The study used a statewide comprehensive soil survey comprising a small-scale soil map, a climate map, and a soil pedon database. Soil organic C stocks under native vegetation were calculated with two different approaches: the Tier 1 method of the Intergovernmental Panel on Climate Change (IPCC) and a refined method based on actual field measurements derived from soil profile data. Highest SOC stocks occurred in Neossolos Quartzarenico hidromorfico (Aquents), Organossolos Tiomorficos (Hemists), Latossolos Brunos (Udox), and Vertissolos Ebanicos (Uderts) soil classes. Before human use of soils, most C was stored in the Latossolos Vermelhos (Udox) and Neossolos Regoliticos (Orthents), which occupy a large area of Rio Grande do Sul. Generally, IPCC default reference SOC stocks compared well with SOC stocks calculated from soil pedons. The total SOC stock of Rio Grande do Sul was estimated at 1510.3 Tg C (5.8 kg C m(-2)) by the IPPC method and 1597.5 +/- 363.9 Tg C (7.4 +/- 1.9 kg C m(-2)) calculated from soil pedons. The SOC digital map and SOC database developed in this study provide crucial background information for state-level contemporary assessment of C stocks and soil C sequestration programs and initiatives.

International audience; While Carbon (C) sequestration an farmlands may contribute to mitigate CO2 concentrations in the atmosphere, greater agro-biodiversity may ensure longer term stability of C storage in fluctuating environments. This study was conducted in the highlands of western Kenya, a region with high potential for agroforestry, with the objectives of assessing current biodiversity and aboveground C stocks in perennial vegetation growing on farmland, and estimating C sequestration potential in aboveground C pools. Allometric models were developed to estimate aboveground biomass of trees and hedgerows, and an inventory of perennial vegetation was conducted in 35 farms in Vihiga and Siaya districts. Values of the Shannon index (H), used to evaluate biodiversity, ranged from 0.01 in woodlots through 0.4-0.6 in food crop plots, to 1.3-1.6 in homegardens. Eucalyptus saligna was the most frequent tree species found as individual trees (20%), in windrows (47%), and in woodlots (99%) in Vihiga and the most frequent in woodlots (96%) in Siaya. Trees represented the most important C pool in aboveground biomass of perennial plants growing on-farm, contributing to 81 and 55% of total aboveground farm C in Vihiga and Siaya, respectively, followed by hedgerows (13 and 39%, respectively) and permanent crop stands (5 and 6%, respectively). Most of the tree C was located in woodlots in Vihiga (61%) and in individual trees growing in or around food crop plots in Siaya (57%). The homegardens represented the second C pool in importance, with 25 and 33% of C stocks in Vihiga and Siaya, respectively. Considering the mean total aboveground C stocks observed, and taking the average farm sizes of Vihiga (0.6 ha) and Siaya (1.4 ha), an average farm would store 6.5 +/- 0.1 Mg C farm(-1) in Vihiga and 12.4 +/- 0.1 Mg C farm(-1) in Siaya. At both sites, the C sequestration potential in perennial aboveground biomass was estimated at ca. 16 Mg C ha(-1). With the current market price for carbon, the implementation of Clean Development Mechanism Afforestation/Reforestation (CDM A/R) projects seems unfeasible, due to the large number of small farms (between 140 and 300) necessary to achieve a critical land area able to compensate the concomitant minimum transaction costs. Higher financial compensation for C sequestration projects that encourage biodiversity would allow clearer win-win scenarios for smallholder farmers. Thus, a better valuation of ecosystem, services should encourage C sequestration together with on-farm biodiversity when promoting CDM A/R projects. (C) 2008 Elsevier B.V. All rights reserved. [References: 40]

International audience; Soil bulk density values are needed to convert organic carbon content to mass of organic carbon per unit area. However, field sampling and measurement of soil bulk density are labour-intensive, costly and tedious. Near-infrared reflectance spectroscopy (NIRS) is a physically non-destructive, rapid, reproducible and low-cost method that characterizes materials according to their reflectance in the near-infrared spectral region. The aim of this paper was to investigate the ability of NIRS to predict soil bulk density and to compare its performance with published pedotransfer functions. The study was carried out on a dataset of 1184 soil samples originating from a reforestation area in the Brazilian Amazon basin, and conventional soil bulk density values were obtained with metallic "core cylinders". The results indicate that the modified partial least squares regression used on spectral data is an alternative method for soil bulk density predictions to the published pedotransfer functions tested in this study. The NIRS method presented the closest-to-zero accuracy error (-0.002 g cm-3) and the lowest prediction error (0.13 g cm-3) and the coefficient of variation of the validation sets ranged from 8.1 to 8.9% of the mean reference values. Nevertheless, further research is required to assess the limits and specificities of the NIRS method, but it may have advantages for soil bulk density predictions, especially in environments such as the Amazon forest.

This paper serves two purposes: it provides a summarized scientific history of carbon sequestration in relation to the soil-plant system and gives a commentary on organic wastes and SOC sequestration. The concept of soil organic carbon (SOC) sequestration has its roots in: (i) the experimental work of Lundegardh, particularly his in situ measurements of CO2 fluxes at the soil-plant interface (1924, 1927, 1930); (ii) the first estimates of SOC stocks at the global level made by Waksman [Waksman, S.A., 1938. Humus. Origin, Chemical Composition and Importance in Nature, second ed. revised. Williams and Wilkins, Baltimore, p. 526] and Rubey [Rubey, W.W., 1951. Geologic history of sea water. Bulletin of the Geological Society of America 62, 1111–1148]; (iii) the need for models dealing with soil organic matter (SOM) or SOC dynamics beginning with a conceptual SOM model by De Saussure (1780–1796) followed by the mathematical models of Jenny [Jenny, H., 1941. Factors of Soil Formation: a System of Quantitative Pedology. Dover Publications, New York, p. 288], Henin and Dupuis [Henin, S., Dupuis, M., 1945. Essai de bilan de la matiere organique. Annales d’Agronomie 15, 17–29] and more recently the RothC [Jenkinson, D.S., Rayner, J.H., 1977. The turnover of soil organic matter in some of the Rothamsted classical experiments. Soil Science 123 (5), 298–305] and Century [Parton, W.J., Schimel, D.S., Cole, C.V., Ojima, D.S., 1987. Analysis of factors controlling soil organic matter levels in great plains grasslands. Soil Science Society of America Journal 51 (5), 1173–1179] models. The establishment of a soil C sequestration balance is not straightforward and depends greatly on the origin and the composition of organic matter that is to be returned to the system. Wastes, which are important sources of organic carbon for soils, are taken as an example. For these organic materials the following factors have to be considered: the presence or absence of fossil C, the potential of direct and indirect emissions of non-CO2 greenhouse gases (CH4 and N2O) following application and the agro-system which is being used as a comparative reference.

The intensive land use invariably has several negative effects on the environment and crop production if conservative practices are not adopted. Reduction in soil organic matter (SOM) quantity means gas emission (mainly CO2, CH4, N2O) to the atmosphere and increased global warming. Soil sustainability is also affected, since remaining SOM quality changes. Alterations can be verified, for example, by soil desegregation and changes in structure. The consequences are erosion, reduction in nutrient availability for the plants and lower water retention capacity. These and other factors reflect negatively on crop productivity and sustainability of the soil-plant-atmosphere system. Conversely, adoption of "best management practices", such as conservation tillage, can partly reverse the process - they are aimed at increasing the input of organic matter to the soil and/or decreasing the rates at which soil organic matter decomposes. O uso intensivo da terra invariavelmente causa efeitos negativos ao ambiente e produção agrícola se práticas conservativas não forem adotadas. Redução na quantidade de matéria orgânica do solo significa emissão de gases (principalmente CO2, CH4, N2O) para a atmosfera e aumento do aquecimento global. A sustentabilidade do solo é também afetada, uma vez que a qualidade da matéria orgânica remanescente muda. Alterações podem ser verificadas, por exemplo, pela desagregação do solo e mudança na sua estrutura. As consequências são erosão, redução na disponibilidade de nutrientes para as plantas e baixa capacidade de retenção de água no solo. Estes e outros fatores refletem negativamente na produtivade das culturas e sustentabilidade do sistema solo-planta-atmosfera. Ao contrário, a adoção de boas práticas de manejo, tal como o sistema plantio direto, pode parcialmente reverter o processo, uma vez que objetiva o aumento das entradas de material orgânico no solo e/ou diminuição das taxas de decomposição da matéria orgânica do solo.

Correspondance: a.metay@istom.net; International audience; The management and enhancement of soil organic carbon (SOC) is very important for agriculture (fertility) as well as for the environment (carbon (C) sequestration). Consequently, changes in soil management may alter SOC content. No-tillage (NT) practices are potential ways to increase SOC. We studied the SOC from agricultural soils in the Cerrados in Central Brazil. We compared two different tillage systems: conservation agriculture with no-tillage under cover crops (NT) and disc tillage (DT) for 5 years in a context of rainfed rice production. The soil is a dark red Oxisol with high clay content (about 40%). The objectives of the study were: (i) to evaluate the short-term (5 years) impact of tillage systems on SOC stocks in an Oxisol and (ii) to better understand the dynamics of SOC in different fractions of this soil. We first studied the initial situation in 1998, and compared it to the 2003 situation. NT with cover crop (Crotalaria) was found to increase the storage of C in the topsoil layer (0-10 cm) compared to DT. The difference observed for the 0-10 cm layer under NT in comparison with DT represented C enrichment under no-tillage amounting to 0.35 Mg C ha(-1) year(-1) and corresponding to less than 10% of cover crops residues returned to the soil. A particle-size fractionation of soil organic matter (SOM) showed that differences in total SOC between NT and DT mainly affected the 0-2 mu m fraction and, to a smaller extent the 2-20 mu m fraction.This specific enrichment of SOC in the silt and clay fraction was attributed to (i) the storage of a water soluble C in the field and (ii) the effect of soil biota and especially fauna activity. The mean residence time of carbon associated with the fine fractions being rather long, it might be assumed that the preferential storage in fine fractions resulted in a long-term carbon storage. This study suggests a positive short-term effect of a no-tillage system on C sequestration in an Oxisol

Currently we have little understanding of the impacts of land use change on soil C stocks in the Brazilian Amazon. Such information is needed to determine impacts on the global C cycle and the sustainability of agricultural systems that are replacing native forest. The aim of this study was to predict soil carbon stocks and changes in the Brazilian Amazon during the period between 2000 and 2030, using the GEFSOC soil carbon (C) modelling system. In order to do so, we devised current and future land use scenarios for the Brazilian Amazon, taking into account: (i) deforestation rates from the past three decades, (ii) census data on land use from 1940 to 2000, including the expansion and intensification of agriculture in the region, (iii) available information on management practices, primarily related to well managed pasture versus degraded pasture and conventional systems versus no-tillage systems for soybean ( Glycine max ) and (iv) FAO predictions on agricultural land use and land use changes for the years 2015 and 2030. The land use scenarios were integrated with spatially explicit soils data (SOTER database), climate, potential natural vegetation and land management units using the recently developed GEFSOC soil C modelling system. Results are presented in map, table and graph form for the entire Brazilian Amazon for the current situation (1990 and 2000) and the future (2015 and 2030). Results include soil organic C (SOC) stocks and SOC stock change rates estimated by three methods: (i) the Century ecosystem model, (ii) the Rothamsted C model and (iii) the intergovernmental panel on climate change (IPCC) method for assessing soil C at regional scale. In addition, we show estimated values of above and belowground biomass for native vegetation, pasture and soybean. The results on regional SOC stocks compare reasonably well with those based on mapping approaches. The GEFSOC system provided a means of efficiently handling complex interactions among biotic-edapho-climatic conditions (>363,000 combinations) in a very large area (∼500 Mha) such as the Brazilian Amazon. All of the methods used showed a decline in SOC stock for the period studied; Century and RothC simulated values for 2030 being about 7% lower than those in 1990. Values from Century and RothC (30,430 and 25,000 Tg for the 0–20 cm layer for the Brazilian Amazon region were higher than those obtained from the IPCC system (23,400 Tg in the 0–30 cm layer). Finally, our results can help understand the major biogeochemical cycles that influence soil fertility and help devise management strategies that enhance the sustainability of these areas and thus slow further deforestation.

Correspondance: L. Chapuis-Lardy, fax: 1261 (0) 20 22 369 82, e-mail: lydie.lardy@ird.fr; International audience; Soils are the main sources of the greenhouse gas nitrous oxide (N2O). The N2O emission at the soil surface is the result of production and consumption processes. So far, research has concentrated on net N2O production. However, in the literature, there are numerous reports of net negative fluxes of N2O, (i.e. fluxes from the atmosphere to the soil). Such fluxes are frequent and substantial and cannot simply be dismissed as experimental noise. Net N2O consumption has been measured under various conditions from the tropics to temperate areas, in natural and agricultural systems. Low mineral N and large moisture contents have sometimes been found to favour N2O consumption. This fits in with denitrification as the responsible process, reducing N2O to N2. However, it has also been reported that nitrifiers consume N2O in nitrifier denitrification. A contribution of various processes could explain the wide range of conditions found to allow N2O consumption, ranging from low to high temperatures, wet to dry soils, and fertilized to unfertilized plots. Generally, conditions interfering with N2O diffusion in the soil seem to enhance N2O consumption. However, the factors regulating N2O consumption are not yet well understood and merit further study. Frequent literature reports of net N2O consumption suggest that a soil sink could help account for the current imbalance in estimated global budgets of N2O. Therefore, a systematic investigation into N2O consumption is necessary. This should concentrate on the organisms, reactions, and environmental factors involved

Soil organic carbon (SOC) plays a vital role in ecosystem function, determining soil fertility, water holding capacity and susceptibility to land degradation. In addition, SOC is related to atmospheric CO, levels with soils having the potential for C release or sequestration, depending on land use, land management and climate. The United Nations Convention on Climate Change and its Kyoto Protocol, and other United Nations Conventions to Combat Desertification and on Biodiversity all recognize the importance of SOC and point to the need for quantification of SOC stocks and changes. An understanding of SOC stocks and changes at the national and regional scale is necessary to further our understanding of the global C cycle, to assess the responses of terrestrial ecosystems to climate change and to aid policy makers in making land use/management decisions. Several studies have considered SOC stocks at the plot scale, but these are site specific and of limited value in making inferences about larger areas. Some studies have used empirical methods to estimate SOC stocks and changes at the regional scale, but such studies are limited in their ability to project future changes, and most have been carried out using temperate data sets. The computational method outlined by the Intergovernmental Panel on Climate Change (IPCC) has been used to estimate SOC stock changes at the regional scale in several studies, including a recent study considering five contrasting eco regions. This 'one step' approach fails to account for the dynamic manner in which SOC changes are likely to occur following changes in land use and land management. A dynamic modelling approach allows estimates to be made in a manner that accounts for the underlying processes leading to SOC change. Ecosystem models, designed for site scale applications can be linked to spatial databases, giving spatially explicit results that allow geographic areas of change in SOC stocks to be identified. Some studies have used variations on this approach to estimate SOC stock changes at the sub-national and national scale for areas of the USA and Europe and at the watershed scale for areas of Mexico and Cuba. However, a need remained for a national and regional scale, spatially explicit system that is generically applicable and can be applied to as wide a range of soil types, climates and land uses as possible. The Global Environment Facility Soil Organic Carbon (GEFSOC) Modelling System was developed in response to this need. The GEFSOC system allows estimates of SOC stocks and changes to be made for diverse conditions, providing essential information for countries wishing to take part in an emerging C market, and bringing us closer to an understanding of the future role of soils in the global C cycle. (C) 2007 Elsevier B.V. All rights reserved.

Land use and land cover changes in the Brazilian Amazon have major implications for regional and global carbon (C) cycling. Cattle pasture represents the largest single use (about 70%) of this once-forested land in most of the region. The main objective of this study was to evaluate the accuracy of the RothC and Century models at estimating soil organic C (SOC) changes under forest-to-pasture conditions in the Brazilian Amazon. We used data from 11 site-specific 'forest to pasture' chronosequences with the Century Ecosystem Model (Century 4.0) and the Rothamsted C Model (RothC 26.3). The models predicted that forest clearance and conversion to well managed pasture would cause an initial decline in soil C stocks (0-20 cm depth), followed in the majority of cases by a slow rise to levels exceeding those under native forest. One exception to this pattern was a chronosequence in Suia-Missu, which is under degraded pasture. In three other chronosequences the recovery of soil C under pasture appeared to be only to about the same level as under the previous forest. Statistical tests were applied to determine levels of agreement between simulated SOC stocks and observed stocks for all the sites within the 11 chronosequences. The models also provided reasonable estimates (coefficient of correlation = 0.8) of the microbial biomass C in the 0-10 cm soil layer for three chronosequences, when compared with available measured data. The Century model adequately predicted the magnitude and the overall trend in delta C-13 for the six chronosequences where measured 813 C data were available. This study gave independent tests of model performance, as no adjustments were made to the models to generate outputs. Our results suggest that modelling techniques can be successfully used for monitoring soil C stocks and changes, allowing both the identification of current patterns in the soil and the projection of future conditions. Results were used and discussed not only to evaluate soil C dynamics but also to indicate soil C sequestration opportunities for the Brazilian Amazon region. Moreover, modelling studies in these 'forest to pasture' systems have important applications, for example, the calculation of CO, emissions from land use change in national greenhouse gas inventories. (0 2007 Elsevier B.V. All rights reserved.

The GEFSOC soil carbon modelling system was built to provide interdisciplinary teams of scientists, natural resource managers and policy analysts (who have the appropriate computing skills) with the necessary tools to conduct regional-scale soil carbon (C) inventories. It allows users to assess the effects of land use change on soil organic C (SOC) stocks, soil fertility and the potential for soil C sequestration. The tool was developed in conjunction with case-studies of land use and management impacts on SOC in Brazil, Jordan, Kenya and India, which represent a diversity of land use and land management patterns and are countries where sustaining soil organic matter and fertility for food security is an on-going problem. The tool was designed to run using two common desktop computers, connected via a local area network. It utilizes open-source software that is freely available. All new software and user interfaces developed for the tool are available in an open source environment allowing users to examine system details, suggest improvements or write additional modules to interface with the system. The tool incorporates three widely used models for estimating soil C dynamics: (1) the Century ecosystem model; (2) the RothC soil C decomposition model; and (3) the Intergovernmental Panel on Climate Change (IPCC) method for assessing soil C at regional scales. The tool interacts with a Soil and Terrain Digital Database (SOTER) built for the specific country or region the user intends to model. A demonstration of the tool and results from an assessment of land use change in a sample region of North America are presented.

Establishing pasture on cultivated tropical Vertisols can increase soil organic carbon (SOC), but it is not known whether this increase results solely from enhanced inputs or also from suppressed mineralization. We measured CO2 emissions from a Vertisol under market gardening, and under "young" and "old" Digitaria decumbens pastures. Emissions of CO2-C increased in pastures, compared to market gardening, but relative SOC mineralization (CO2-C/SOC) decreased, implying the protection of SOC against mineralization with pasture establishment.

International audience; Soils represent a large carbon pool, approximately 1500 Gt, which is equivalent to almost three times the quantity stored in terrestrial biomass and twice the amount stored in the atmosphere. Any modification of land use or land management can induce variations in soil carbon stocks, even in agricultural systems that are perceived to be in a steady state. Tillage practices often induce soil aerobic conditions that are favourable to microbial activity and may lead to a degradation of soil structure. As a result, mineralisation of soil organic matter increases in the long term. The adoption of no-tillage systems and the maintenance of a permanent vegetation cover using Direct seeding Mulch-based Cropping system or DMC, may increase carbon levels in the topsoil. In Brazil, no-tillage practices (mainly DMC), were introduced approximately 30 years ago in the south in the Paraná state, primarily as a means of reducing erosion. Subsequently, research has begun to study the management of the crop waste products and their effects on soil fertility, either in terms of phosphorus management, as a means of controlling soil acidity, or determining how manures can be applied in a more localised manner. The spread of no-till in Brazil has involved a large amount of extension work. The area under no-tillage is still increasing in the centre and north of the country and currently occupies ca. 20 million hectares, covering a diversity of environmental conditions, cropping systems and management practices. Most studies of Brazilian soils give rates of carbon storage in the top 40 cm of the soil of 0.4 to 1.7 t C ha-1 per year, with the highest rates in the Cerrado region. However, caution must be taken when analysing DMC systems in terms of carbon sequestration. Comparisons should include changes in trace gas fluxes and should not be limited to a consideration of carbon storage in the soil alone if the full implications for global warming are to be assessed.

International audience; Soil organic matter (SOM) contributes significantly to the chemical, physical and biological ecosystem functions of soil. It influences on plant growth, thus contributing to agricultural production, and performs environmentally valuable services such as carbon sequestration, regulation of the water cycle and detoxification of pollutants. Identification of the functions and services provided by SOM has a long and tumultuous history of scientific discoveries and struggles against false assumptions. This work reports the major steps of this history, with emphasis on two services secured by SOM: (1) the role of SOM in plant production and its connection to soil fertility and thence to the sustainability of cropping and farming systems; and (2) the recognition and assessment of the contribution of SOM to climate-change regulation. Finally, the work explores how SOM, as a multifunctional resource, may be allocated an economic value as a way of promoting its conservation.

The study area was defined as 6°-square portion of the Brazilian Amazon, from longitudes 60–66° West and latitudes 8–14° South. This region corresponds to ∼334,000 km2 of the western Brazilian Amazon, that is 6.7% of the Brazilian Amazon basin. A database was constructed from soil profile information reported in published and unpublished soil surveys. Bulk density (BD) values were derived from multiple regressions with other available parameters. Two digitised soil maps were considered: a 1:5,000,000 soil map and 1:1,000,000 soil map of the region that was digitised for the purpose of this study. Individual C stock for each profile was calculated by two procedures. The first and classical procedure consists in summing C densities by horizon, determined as a product of BD, C concentration, and horizon thickness. The second calculation used a double exponential model of organic C vertical distribution in soils: (C(X) − C2)/(C1 – C2)=(e−b X − e−b X2)/(e−b X1 − e−b X2), where X and C(X) are the depth and the C content, X1 and C1 the depth and the C content of a fixed upper position, and X2 and C2 for a fixed deeper position. Regional C estimates were derived using different map approaches or geostatistical interpolations. Geostatistical interpolations were run not only on the individual C stock, but also on the parameters of the vertical model separately. Two types of validation were conducted, an “internal” validation known as “jackknifing” and an external validation with preserved data (about 10%). The regional stock was obtained multiplying the carbon content of each taxonomic unit by its area. This calculation leads to similar results using the soil map either at 1:5,000,000 scale or at 1:1,000,000. Regional stocks (0–100 cm) ranged between 2100 Tg using median values, and 2300 Tg, using means, and exhibit an associated error (based on SD) of 900 Tg. Variographic analysis showed that carbon stocks exhibit a spatial structure at the regional scale. However the high nugget effect reveals that about half of the spatial variability may appear within distances less than a few tens of kilometres. Results of the fitting of the experimental semivariogram for the top metre showed the same pattern with a nugget effect of 4.70 (kg C m−2)2 and a sill value of 4.26 (kg C m−2)2, but the range is reduced to 513 km. Geostatistical interpolations run either on the C stocks values or independently on each parameters of the vertical model led to similar results.

Land-use change for human settlement and agricultural purposes, especially pasture establishment, has caused major impacts on the Amazon Basin's environment. Development of strategies for reformation and restoration of already degraded pastures constitutes the main goal of the authors' research work. For some of this work, a homogeneous area of land in terms of soil characteristics was selected at Nova Vida ranch in Rondônia state to conduct a multidisciplinary experiment, which included agronomic, environmental and economic analyses. Since July 2001, the authors have monitored five treatments: control, herbicide, tillage, no-till rice and no-till soybean, arranged in four blocks. Early results on carbon and nitrogen stocks, nitrogen mineralization, trace-gas fluxes, dissolved organic carbon and microbial biomass are briefly presented.

This paper shows the geographic distribution in Germany of iron (Fe), nickel (Ni) and lead (Pb) analyzed in mosses in 1995/96 and compares it with the results of the 1990/91 pilot study within a European moss-monitoring programme. Other elements (As, Cd, Cr, Cu, Ti, V, Zn) are compared on basis of the overall element medians for Germany of the 1990/91 and 1995/96 survey. Samples of Pleurozium schreberi, Scleropodium purum, Hypnum cupressiforme and Hylocomium splendens were taken at a total of 1026 sites. In the 1995/96 monitoring campaign, 95% of the original sites of the 1990/91 study were resampled. The results from 1995/96 display local elevated values and many cases of areas affected by known sources of heavy-metal emissions. The industrialized and urban regions of Germany are shown up clearly by the 1995/96 moss-monitoring results: the Ruhr area, parts of Saarland and Baden-Württemberg, as well as areas in eastern Germany. Relatively low values for many elements were found in large areas of Lower Saxony and Bavaria. A comparison of the results of the 1990/91 and 1995/96 moss-monitoring programmes shows a fall in the concentration of the presented elements (except cadmium, copper and zinc) over the relevant period. Especially in the former GDR, chromium (Cr), iron (Fe), titanium (Ti) and vanadium (V) decreased significantly. This is, firstly, a reflection of the closure of and/or technological improvements to large power plants; secondly it is due to the fact that lignite has given way to other fuels. Vanadium (V) and nickel (Ni), typical constituents of crude oil, also show a decrease in the western part and thus document changes in the type of fuel consumed. The significant fall in lead concentration in 1995/96 as compared to 1990/91 in what used to be East and West Germany probably results from the increasing use of lead-free petrol. A comparison of the median values for 1990/91 and 1995/96 in mosses to the rate of emission of heavy metals in Germany for 1990 and 1995 shows similar trends in the case of elements such as arsenic (As), chromium (Cr), nickel (Ni), and lead (Pb). The comparison of the medians of the elements analyzed for 19 European countries indicates for most of the elements a general tendency to lower values in 1995, except for Lithuania, Netherlands, Portugal, Italy and United Kingdom.

The main objective of the study was to investigate soil carbon and nitrogen stocks in five soil types within a 63-ha Amazon degraded pasture area using the Century model and to combine this information with soil C and N spatial variability at Nova Vida ranch in the western Brazilian Amazon. Samples for soil chemical, physical, and biological analyses were collected at eight different georreferenced points in each of five studied soil types. Century was used to simulate soil C and N contents in the 0- to 20-cm layer in each soil type within a 63-ha degraded pasture area. Century accurately simulated the level of total soil C and N for the five soil types, but it was not successful in predicting seasonal variations in microbial biomass C. The influence of soil texture and hydrological process affecting the ability of soils to accumulate soil organic matter were discussed. Scenarios for soil C and N stocks with varying pasture management were examined through a period of 40 years after deforestation. In conclusion, modeling and geostatistical techniques can be used for measuring and monitoring soil C and N stocks. Modeling provides a flexible and powerful way to assess how different scenarios for pasture management and land use change can affect soil C and N dynamics, but it is important to highlight that even the best models (as Century is) need to be used with caution for Kyoto Protocol projects at plot scale and that benchmark sites are needed to augment model predictions.

[1] This paper presents a first estimation of net CO2 fluxes from liming of agricultural soils in Brazil for the period 1990–2000. The calculation was based on the methodology proposed by the IPCC, but separately conducted for the five administrative Brazilian regions. The summarized annual CO2 emission for Brazil varied from 4.9 to 9.4 Tg CO2 yr−1 with a mean CO2 emission of about 7.2 Tg CO2 yr−1. The South, Southeast and Center region accounted for a least 92% of total emission. Neglecting the emissions from organic soils, the CO2 fluxes from soils (reported under the category 5-D in the National Inventories of Greenhouse Gas Emission) amounted an updated value of around 51.9 Tg CO2 yr−1 for the period 1975–1995. Uncertainties, projection and other correlated fluxes related with liming are briefly discussed.

Carbon dioxide and methane integrate biogeochemical cycles of C and constitute, together with nitrous oxide, the main trace gases responsible for the greenhouse effect. Increasing interest in the global consequences of climate change has prompted the global scientific community to deepen their studies about the global C stocks and the interrelations among its different compartments. As main compartments, soils and phytomass (living and nonliving) have received special attention. Many authors proposed a quantification of C stored in soils and proposed to study their role as both a source and sink of carbon (Post et al. 1982, Eswaran et al. 1993, Sombroek et al. 1993, Batjes 1996). The world’s mineral soils are estimated to contain about 1500 Pg C (Post et al. 1982, Eswaran et al. 1993, Batjes 1996), while the biomass of plants is estimated to be comprised between 560 and 835 Pg C (Whittaker and Likens 1975, Bouwman 1990). Tropical forests account for between 20 and 25% of the world terrestrial C (Brown and Lugo 1982, Dixon et al. 1994). The Amazon contains the largest expanse of native tropical ecosystems and has a direct influence on global biogeochemical cycles, especially the C cycle. The C stored in phytomass is of importance because of its quantity and its potential to be released easily. Carbon in soil is proved to be important because soil organic carbon (SOC) is intimately involved in virtually all biological processes, and organic matter (OM), even when present in small amounts, is an extremely important soil constituent. Two Brazilian soil classes, Latossolos and Podzólicos, make up 73% of the total area of the Legal Amazon Basin of Brazil (Prado 1996, Jacomine and Camargo 1996). More precisely, only three dystrofic soil types, Podzólico Vermelho Amarelo (Acrisol), Latossolo Amarelo (xanthic Ferralsol), and Latossolo Vermelho Amarelo (orthic Ferralsol) cover approximately 60% of the total, and are therefore of prime interest. The remainder is distributed between 13 additional classes. Only 6, however, represent more than one percent, and only 2 of which are more than 5%: Plintossolos (Inceptisols, Oxisols, and Alfisols) and Gleissolos (Entisols and Inceptisols).

In spodosols of Gascony (France), conversion of maritime pine stands into maize cropping leads to an incorporation of maize organic matter, which changed the isotopic (δ13C) and phenolic signature in A and L horizons of soil. Hydrolysis of phenol lignin in forests and cultivated soils showed the predominance of vanillic units under forest and the early but moderate incorporation of cinnamic acids. Incorporation of syringic units appeared higher, related to a large maize production of stable syringic phenols. Syringic units represented a long-term marker of maize inputs in soils, whereas vanillic units revealed the degradation of forest organic matter.

Because soils are both a source and a sink for atmospheric CO2, there is an increasing need to characterize the spatial distribution of soil C pools. Large amounts of organic carbon (OC) accumulate in hydric bottom-lands soils. In the Armorican Massif (Western France) where these soils represent 20%

Soil maps analysis to identify the role of the tectonic regime on saprolite permeability regional distribution. For applied geology, e.g., geotechnics or hydrogeology, it is of prime interest to know the spatial distribution of the saprolite permeability. This study focuses on the role of the tectonic regime on saprolite permeability regional distribution. Comparison of data concerning the uplift regime and soil organisation data from several pedological maps of the Armorican Massif (France) showed that blocks in relative uplift were characterized by a low proportion of hydromorphic soils, whereas a higher proportion marked blocks in relative downlift. Such differences can be related to the denudation regime, which affects the saprolite permeability.

Amostras de terra de áreas desmatadas há 4, 10 e 15 anos e utilizadas como pastagem e uma floresta nativa na região de Paragominas-PA, foram analisadas quanto à constituição isotópica e teor de carbono (C) e nitrogênio (N) com o objetivo de quantificar os estoques de C e N e as alterações devidas a mudanças do uso da terra. O conteúdo de C e N aumentaram ao longo do tempo de uso do solo como pastagem. Após 4 e 15 anos de cultivo o conteúdo de C aumentou 0,28 e 0,86 kg.m-2 na camada superficial 0-30 cm do solo; a pastagem de 10 anos ficou estável (diminuição de 0,02 kg.m-2) em relação à mata natural para a camada 0-30 cm, mas diminuiu de 0,15 na camada 0-10 cm. Na camada superficial 0-30 cm, a matéria orgânica da área sob mata natural é composta por 2,6 kg.m-2 de C estável e 2,1 kg.m-2 de C biodegradável, sendo que após 10 e 15 anos de pastagem o C biodegradável representou 1,3 e 1,0 kg.m-2, correspondendo a 27,7% e 21,3% do C original da floresta e o carbono estável representou 2,6 kg.m-2. Pode-se supor que os processos biológicos do solo ficam quase exclusivamente na dependência do C introduzido pela pastagem, uma vez que metade do estoque do C está na forma estável e que o C biodegradável remanescente da floresta mineraliza rapidamente. Soil samples from sites 4, 10 and 15 year-old pastures and one reference native forest, from Paragominas-Pará (Brazil), were used to determine the carbon (C) and nitrogen (N) contents and the natural abundance of ¹³C isotope, with the objective of quantifying the C and N budgets during replacement of the forest by pastures. With pasture establishment, C and N contents were increased. After 4 and 15 years of pasture, the C content increased to 0.28 kg.m-2 and 0.86 kg.m-2 respectively in the 0-30 cm soil layer. The 10 year pasture remained stable (0.02 kg.m-2 decreased) in relation to the natural forest, but decreased by 0.15 kg.m-2 in the 0-10 cm layer. In the 0-30 cm layer, organic matter in the natural forest site was 2.6 kg.m-2 stable C and 2.1 kg.m-2 biodegradable C. After 10 and 15 years under pasture, biodegradable C represented 1.3 kg.m-2 and 1.0 kg.m-2, corresponding to 27.7% and 21.3% of the original forest C, while the stable C represented 2.6 kg.m-2.

The results of this study provide the first baseline for predicting Db from soil properties for soils across the Amazon basin. Bulk density values are needed to convert nutrient content and organic carbon (OC) content to weight of nutrient and OC per unit area ; unfortunately, common field methods to measure Db are limited with regard to reliable, complete, and uniform soil data. Much effort has been made in finding alternative solutions to predict Db from soil properties. We hypothesized that Db could be reliably estimated by multiple regression of OC, soil textural properties, and some chemical properties. Using the data of 323 soil horizons from the Brazilian Amazon basin, a stepwise multiple regression (SMR) procedure was developed to predict Db from other soil properties. Multiple regression relationships were obtained for all the data, which were also partitioned by layer and then by main soil order : latossolos (oxisols, 62 horizons) and podzolicos (alfisols and ultisols, 212 horizons). The SMR on all the data showed that clay content is the best predictor of Db, accounting for 37% of the variation. Adding OC content increased the explained variance up to nearly 50%. Predictions of the models were improved when the data were partitioned by order and by horizon type. In the case of latossolos (oxisols), the use of OC and clay content as predictors increased the percentage of explained variation, reaching 71% using all layers and 79% for A horizons. The results of this study will provide a basis for estimating OC stocks in the Amazon basin. (Résumé d'auteur)

Oxisols have great ecological significance in tropical soils because they are the dominant soil type of the Brazilian Amazon ecosystem, comprising more than 40% of its total. To estimate carbon (C) stocks and changes requires knowledge of the vertical distribution of C in profiles. The objective of this study was to determine if specific patterns occur in C profiles of Oxisols in the Western Brazilian Amazon so that total C storage can be assessed down to any given depth by simple models with low input data requirements. Two models, a power-based model and an exponential-based model, were tested using nonlinear regression analysis on a soil database made up of 129 Oxisol profiles corresponding to 519 soil horizons. These models, as judged by the coefficient of determination (R 2 ) value, explained more than 55% of the total variance for all of the horizons, whether or not segregated by taxonomic unit. The models were then tested with individual profiles. The power model exhibited a tendency to overestimate C stocks when integration was done for the 0-20-cm and the 0-100-cm layers. Results from the exponential model were better than those from the power model. The R 2 values were greater than 0.82, and the associated standard error was reduced. In a validation procedure, the mean error (ME) was close to zero for the exponential model, with a systematic ME of only 0.06 kg C.m -2 for the 0-100-cm layer.