EDAFOLOGIA, Vol. 11 (3), pp. 279-293, 2004
CUANTIFICACIÓN DEL CARBONO ORGÁNICO DE LOS SUELOS DE PORTUGAL CONTINENTAL Y PARTICULARIDADES DE LOS SUE- LOS DEL NOROESTE Y SUR
MANUEL MADEIRA1, R. P. RICARDO1,2, A. CORREIA1, A. GARCEZ1, F. MON- TEIRO1, J. A. RAPOSO2, A. T. CONSTANTINO3 & J. M. DUARTE3
1Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa; 2Centro de Estu- dos de Pedologia do IICT, Tapada da Ajuda, 1349-017 Lisboa; 3Agroconsultores - En- genharia de Recursos Agrários Lda, Rua Sampaio Pina, 7, 1o D, 1070-248 Lisboa
The amount of soil organic C (kg m-2 ) in Portugal was assessed for the depth of 0-30 cm (surface organic C content), and values were correlated with the mean annual precipitation. In Northwest Por- tugal the estimation was done for both 0-30 (surface organic C content) and 0-100 cm (total organic C con- tent) depths, taking into account the Major Soil Groupings (FAO-Unesco), the mean annual precipitation (MAP) and the main land use/land cover systems. In Southern Portugal, the amounts of soil organic C down to 20 cm depth in areas which have been subjected to cereal crops were compared to those in oak woo- dlands either with natural understory or improved pastures, both beneath tree canopy and in the open The amount of organic C down to 30 cm depth, in soils of Portugal vary from 0,21 to 23,50 kg m-2. This amount is strongly correlated with mean annual rainfall (and with biomass productivity), increasing from semiarid to wet areas. In Northwest Portugal (wet climate), Regosols show the highest amount of organic C down to 30 cm depth whereas Anthrosols have the highest down 100 cm depth. In this region the variation of C in soil is mostly related to land use system, and the highest amount of organic C was observed in soils under shrubland. In Southern Portugal (dry climate) a strong increment of organic C was observed in soils with improved pasture, as compared to those subjected to cereal crops. This increment is enhanced in oak woodlands, especially in areas under tree crown, and carbon is mostly accumulated as non-humified orga- nic matter which show low C/N ratio.