Resumen de El sòl
V. Ramón Vallejo Calzada, Pere Casals, Josep Lascurain i Golferichs, Núria Roca, Joan Romanyà Socoró, Pere Rovira, M. Teresa Sauras Yera
Soils are essential for life in terrestrial ecosystems: for plant life, by providingphysical support, water and nutrients, and for animal life, indirectly through the plantdependent food web and directly as the habitat for soil fauna. Soils are generatedthrough processes that take millennia to unfold. The build-up of artificial soils isfeasible only on a small scale and requires high investments (quarries, for instance).Therefore, policy-makers must consider soils to be an essential and non-renewableresource.Catalonia has been greatly affected by agriculture and other land uses for at leasttwo millennia so human-driven impacts are widespread. Soil pollution by organicchemicals and/or metals (mainly Cu, Pb, Sn and Zn) is common in old industrial areasand close to urban areas. The pollution due to poor agricultural practices affects largerareas – the excess of fertilizers, pesticides, and particularly slurries –, owing to theirleaching potential to groundwater. Nevertheless, the main threats to the soils ofCatalonia are from extensive land use changes, resulting in soil sealing – conversion ofagricultural lands into urban or industrial areas, and construction of roads and publicinfrastructures. We describe the example of the Llobregat delta, and the loss ofagricultural lands in favor of other uses (urban, infrastructure, industry) whicheventually represent an irreversible loss of prime farmland soils. This is a huge problemon a European scale and it should be addressed through soil protection policies.The abandonment of agriculture leads to the loss of agricultural soils and to theirconversion into other land uses (forests, grasslands, shrublands). Grasslands and forestsoils are richer in soil organic matter (SOM) than agricultural soils: thus, such aconversion entails a recovery of their natural fertility and increases carbonsequestration. The opposite path, i.e. the conversion of forest or grassland soils intoagricultural soils, is riskier, for it implies SOM losses and – due also to the operations ofdeforestation, often involving the use of heavy machinery – increased risks of soilerosion. Erosive processes can be also triggered by wildfires, even though they aretoday less severe than in the period of 1980-2000, owing to major efforts in prevention.The degradation of ancient man-made landscapes, particularly old agricultural terraces,strengthens these negative effects and the risk of desertification.Good agricultural practices are needed to maintain soil productivity in the longterm. SOM content in agricultural soils is low on the average, and it should beincreased. Irrigation increases both plant production and SOM levels. But the setting upof irrigation systems is costly in terms of carbon footprint, and their long-termsustainability in Catalonia – which is not particularly rich in water resources – should becarefully considered: the salinization of some areas could be an undesirable side effect.Conservation agriculture practices (less tillage or none at all, cover crops) are effectivein reducing soil erosion. A good management of organic amendments is needed, too:not all of them help to increase the SOM level and some (e.g., slurries) pose a risk ofgroundwater pollution.Climate change will worsen the aforementioned constraints. The projecteddecreases in precipitation and increases in temperature may lead to increased risks ofsoil erosion, soil fertility losses and, eventually, desertification. A proper managementof the soil as a global resource will be crucial to reduce damages to tolerable levels. TheEuropean directives for soil protection will be an important institutional framework tomaintain soils as a vital resource for feeding an increasing population and for supportingnatural ecosystems
