Le carbone dans les sols des zones sèches : des fonctions multiples indispensables

Le carbone organique des sols (COS) joue un rôle fondamental dans le comportement des sols et des agroécosystèmes. Augmenter sa teneur améliore la qualité et la fertilité des sols contribuant à la résilience et à la durabilité de l'agriculture et, donc, à la sécurité alimentaire des sociétés. De plus, les sols représentent le plus grand réservoir de carbone en interaction avec l'atmosphère. Les systèmes agricoles et forestiers qui réduisent les concentrations en carbone atmosphérique en le piégeant dans les biomasses et dans la matière organique du sol, sont des puits de carbone. La lutte contre la désertification permet de séquestrer du carbone dans les sols et donc d'atténuer le changement climatique, en plus de contribuer à une gestion agronomique durable. Depuis peu, les sols sont au coeur des débats internationaux, notamment dans le cadre des trois conventions internationales sur l'environnement. Elles ont des préoccupations liées entre elles, notamment dans les régions sèches : désertification, changement climatique et perte de biodiversité. Pourtant, des politiques concrètes concernant le carbone dans ces régions peinent à se mettre en place. Il manque notamment une meilleure prise en compte de l'impact des activités agricoles, pastorales et forestières sur le cycle du carbone. Dans l'actuel système des marchés du carbone, les secteurs agricoles et forestiers restent faibles face aux autres secteurs (industrie, etc.). De plus, ces marchés ne reconnaissent pas pleinement les activités qui favorisent la séquestration de carbone dans les sols agricoles, notamment dans les zones sèches. Les marchés se sont jusqu'à présent focalisés sur la vérification de la quantité de carbone séquestrée, alors qu'il serait beaucoup plus simple et vérifiable de promouvoir directement des pratiques reconnues comme « séquestrantes ». Un tel marché pourrait constituer un levier opérationnel beaucoup plus efficace pour modifier les pratiques agricoles et mettre en place une protection des sols des régions sèches

Assessing soil carbon stocks under pastures through orbital remote sensing

The growing demand of world food and energy supply increases the threat of global warming due to higher greenhouse gas emissions by agricultural activity. Therefore, it is widely admitted that agriculture must establish a new paradigm in terms of environmental sustainability that incorporate techniques for mitigation of greenhouse gas emissions. This article addresses to the scientific demand to estimate in a fast and inexpensive manner current and potential soil organic carbon (SOC) stocks in degraded pastures, using remote sensing techniques. Four pastures on sandy soils under Brazilian Cerrado vegetation in São Paulo state were chosen due to their SOC sequestration potential, which was characterized for the soil depth 0-50 cm. Subsequently, a linear regression analysis was performed between SOC and Leaf Area Index (LAI) measured in the field (LAIfield) and derived by satellite (LAIsatellite) as well as SOC and pasture reflectance in six spectra from 450 nm - 2350 nm, using the Enhanced Thematic Mapper (ETM+) sensor of satellite Landsat 7. A high correlation between SOC and LAIfield (R² = 0.9804) and LAIsatellite (R² = 0.9812) was verified. The suitability of satellite derived LAI for SOC determination leads to the assumption, that orbital remote sensing is a very promising SOC estimation technique from regional to global scale.CNP

Balanço ex-ante dos gases do efeito estufa nos programas de desenvolvimento na agricultura e em florestas

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.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