Abstract: Agriculture in Portugal contributes for less than 10% of total greenhouse gas (GHGs) emissions, where 34% comes from methane (CH₄) from animal husbandry, 64% comes from nitrogen (N) oxides (NOx and N₂O) by the intensive use of mineral fertilizers, the incomplete nitrification and denitrification processes, the waterlogged rice fields, the addition of organic compounds to the soil, the drip fertigation, the N2 fixation by legumes, particularly, the pastures, and the sediments, by the alternate wetting and drying processes and the presence of soil organisms such as worms. Animal husbandry is the main responsible (71%) for total emission coming from agriculture, particularly the dairy cows housed. Methane emissions from animal housing are mainly caused by enteric fermentation. During storage and after spreading of farmyard manure in the soil substantial differences concerning ammonia (NH₃), N₂O and CH₄ emissions occur with composted and anaerobically stacked farmyard manure. The compost can emit more NH₃ than the anaerobically stacked farmyard manure. Ammonia is also released during the industrial production of mineral fertilizers and from senescent leaves. In agriculture, forests are the main responsible for CO₂ emission (4 Mt CO₂ equivalent year^-1) by the respiration process, and the double amount can be reached in presence of fires. However, forests have an important role on CO₂ capture during the photosynthetic process, by C accumulation in the plant biomass and soil organic matter. The Portuguese forest can sequester about 80 t CO₂ ha^-1 year^-1 and contributed to about 18% of C sequestration in 2010. The eucalyptus has a very efficient capacity to use water and nutrients and can accumulate C in the biomass and soil more efficiently than other plant species in temperate climate. Microbial activity is also responsible for CO₂ emission, particularly under soil disturbance. This is the case of pastures conversion to annual crops. On the other hand, if soil conservation practices have been used, such as for permanent pastures, CO₂ sequestration in the soil is appreciable. "Montado" is a Portuguese extensive farming system consisting of cork and holm-oak trees, several shrubs and biodiverse pastures. This is a very sustainable agricultural system where the biodiverse pasture consists of more than 20 species and include several legumes. They can sequester more than 4 t C ha^-1 year^-1, particularly in the soil since the crops are used for animal feeding (-4.5 t C km^-2 year^-1). Supposing an increase from 10 to 30 g organic matter kg^-1 soil, an accumulation of 33 t C ha^-1 in a 15 cm layer is expected, corresponding to a sequestration of the order of 128 t CO2 ha^-1. These data show that 200,000 ha of permanent pastures will largely meet the Kyoto Protocol Commitment (1997). About 80% of cultivated plants can be associated with mycorrhizal soil fungi. This symbiosis allows a better performance and health for most efficiently mycorrhized plants, particularly under biotic and abiotic stress, such as drought, high temperatures, saline soil and contaminants. These plants can capture more CO₂ from the atmosphere by the photosynthetic process, producing higher levels of photo assimilates which are exuded by the roots enriching the mycorrhizosphere and contributing for C sequestration.

Brief Biography of the Speaker:
Corina Carranca is a Researcher at INRB, I.P./INIA, at Oeiras (Portugal). She is a specialist in nitrogen cycling, namely nitrogen dynamics in soils and plant nutrition. She published ninety eight publications, including ten book chapters and thirty-three publications in national and international peer-review journals. She was a national representative of Portugal in the European Union for the Directive for Soil Conservation and Protection. She has been a referee of sixteen national and international journals and books and was included in two Editorial Boards of two international journals. She has been responsible for fifteen national research projects and cooperated in many others.