Saturday, 15 July 2006

Influence of Volcanic Parent Material on Soil Properties in Murcia Province (SE Spain).

Silvia Martínez-Martínez, Ángel Faz Cano, and Jose A. Acosta. Technical University of Cartagena, Area of Edafology and Agricultural Chemistry. Department of Agrarian Science and Technology, Paseo Alfonso XIII, nº 52, 30230, Cartagena. Murcia. Spain, Cartagena, Spain

Soils of volcanic regions, unique natural resources, are often fertile but also fragile resources. These soils have been extensively studied through the world despite only comprising 0.84% of the earth surface. The Region of Murcia presents a Mediterranean climate characterised by low rainfall, where the nature of the original material and the topography of the terrain have a strong influence on the development of the soil, besides these volcanic soils are susceptible to physical disturbance, such as landslides, erosion. So, in order to understand how the above factors have influenced in these soils was carried out the survey about the physical and physico-chemical properties of soils evolved from different volcanic materials (ophites, andesites and lamproitic type rocks) located in three different volcanic outcrops from Murcia (Southest Spain), Isla del Ciervo, Cabezo Mingote, and Cerro Volcanico de la Aljorra. In each hill, between thirteen and fourteen surface samples and one soil profile were taken. Firstly, soils were macromorphologically described and the analyses such as pH, electrical conductivity, organic matter, equivalent calcium carbonate, cation exchange capacity and size-particle analysis were used for the determination of the soils properties. The results show that the soils taken in the Cerro de la Aljorra, developed on lamproitic type rocks, and in the Cabezo Mingote, formed of ophites, are basic; however the surfaces samples taken in the Isla del Ciervo present pH heterogeneous values ranging from 6.5 to 7.8. None studied soil is saline, although the values varied from 95.5 to 585 microS/cm, due to samples location in the hills. Most soils developed on andesites did not prensent CaCO3 contents, only two samples registered percentages of 5.1 and 6.5, maybe caused by secundary recarbonatation. In the others volcanic areas, some surface samples did not have CaCO3 contents, and the rest of the samples presented values from 2.2 to 36.7 %. In the soils taken in the Cerro de la Aljorra and the Isla del Ciervo were not observed high differences in the results of the cation exchange capacity, being the mean value in the first volcanic area of 20.4 cmol/kg and in the second of 22.6 cmol/kg. The mean percentages of organic carbon were similar in the soils developed on lamproitic type rocks and on ophites, being of 1.6%; this value was lightly highest in the Isla del Ciervo (1.8%). In general, total nitrogen percentages were high (> 0.11%) in this last volcanic hill and in the Cabezo Mingote. In conclusion, the effect of the parent material and hill topography on soil properties has clearly been proved.

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