El sumidero de carbono de los suelos de Galicia

Resumo

In this study, the content and distribution of organic C in Galician soils and their rela-tionships with soil forming factors and soil processes has been established. Contents of organic C of Gali-cian soils range below detectable limits and 50%, and most of the values fall in the 6-9% range. The averageC storing capacity of forest soils is slightly above 200 t ha-1, with maximum values above 2000 t C ha-1. Thetotal organic C reservoir in Galician soils is estimated to be ~ 0.6 Pg C. Those conditions favouring organicC accumulation are: (i) altitude and precipitation (e.g., hill country soils), (ii) waterlogging conditions (e.g.,soils under suboxic conditions), and (iii) the chemical stabilization of organic matter through interactionswith soluble Al – mainly released during weathering of labile primary minerals. These interactions are es-pecially important during the formation of Andosols and aluminic soils (e.g., umbric horizons of Leptosols,Regosols and humic Cambisols). In Galicia, the former soils commonly develop from basic rocks, whereasthe latter do so from granitic and metamorphic rocks. Soils developed from sedimentary materials and thosederived from calcareous & ultrabasic rocks have the smallest organic C stocks of all the soil types studied.The amount of C stored in 1 cm depth of most surface horizons of Galician soils range between 5 and 8 t Cha-1cm-1. Exceptions are degraded and/or cultivated soils, in which this amount decreases to values below4 t C ha-1. The latter results raise the need to establish mechanisms for soil conservation against erosion andto promote pedogenesis processes that favour conditions of biostaxia. Anthropogenic activities, such as ti-lling, fire events and the subsequent erosion processes, have a negative effect in C stocks. Losses up to 70%have been detected, while a common value for C losses in agricultural soils is around 50%. Management ac-tivities favouring the increase of organic C stocks (e.g., supply of necromasa) have been described. A moresustainable agriculture and forest soil management techniques are proposed, and the restoration of degra-ded and contaminated land encouraged. As we learn from examining and studying natural mechanisms oforganic matter stabilization, we can apply this knowledge to reduce C emissions of soils management ofthe fermentable wastes and increase its sequestration in soils