Ortiz, Roque (Univ. of Murcia, Departamento de Quimica Agricola, Geologia y Edafo, Murcia, MU, 30100, Spain; Phone: +34-968367443; Email: rortiz@um.es)

Organic Carbon Storage in Surface Soils from Murcia Province, Southeastern Spain in Relation to Land Use and Management

D.M. Carmona, A. Faz, R. Ortiz *

The Convention to Combat Desertification (CCD) is concerned that extensive areas, which have been rendered unsuitable for crop production due to land degradation and reduction in soil carbon stocks. Restoration could contribute to the proper placement of carbon in the geosphere and to food security. Restituting carbon to those lands would also contribute to reducing carbon in the atmosphere. Conservation strategies which sequester carbon include converting marginal lands to compatible land use systems, restoring degraded soils, and adopting best management practices. As a result, the agricultural soils and forestry sectors receive much recent attention because of their potential to store and retain carbon and thus reduce emissions to the atmosphere. The study area is located in Murcia, S.E. Spain. A systematic sampling was carried out for every 3 km, under the LUCDEME Project (Fight against desertification in Mediterranean area) which amounted to a total of 946 soil samples (0 to 25 cm deep) in a total area of 11,317 km². For this purpose, maps (1:50,000), as well as aerial photographs (1:20,000) were used. The soil samples obtained have the following uses: 1.-Dry trees, whose most representative species are almonds and olive trees, characterised by mostly lacking irrigation and also being found marginally (297 samples); 2.-Citrics, largely lemon and orange tree, appear mostly under localised irrigation (39 samples); 3.-Fruit trees, fundamentally, peach, apricot and plum tree and pip fruit trees, mostly the pear tree. Flood irrigation systems continue being the typical form of irrigation in most cases, although they are visibly replaced by drip irrigation (51 samples); 4. Horticultural species with drip irrigation intensive production high technology; among them the most typical species are broccoli and cauliflower, and onion(25 samples); 5.-The rest of the area destined to growing has been classified as extensive crops such as alfalfa and cereals (137 samples); 6.-Those areas occupied by forest land, with different level of degradation, such as pine (160 samples) and thyme fields (237 samples) are also considered. The main soil types in the area have been classified, according to WRB, as Regosols, Leptosols, Fluvisols, Calcisols, Gypsisols, Solonchaks and Kastanozems. The climate in Murcia province is semiarid Mediterranean, where maximum temperatures coincide with minimum rainfall levels. In relation to organic carbon contents the values were maximum in soils with forest (pine 4.7 kg m^-2 and thyme fields and shrubs 4.1 kg m^-2). Cultivated soils with fruit trees have the maximum content of carbon (3.5 kg m^-2), followed by horticultural species with drip irrigation (3.0 kg m^-2), extensive crops (2.6 kg m^-2), citrics (2.5 kg m^-2), and finally dry trees (2.0 kg m^-2). The maximum contents are related to the fact that those soils not only receive supplies from vegetable remains and chemicals fertilizers, but also organic fertilization. As a consequence, this must be the most appropriate management of soils in terms of soil quality and carbon sequestration.