EDAFOLOGIA, Vol. 11(2), pp. 119-135, 2004
MATERIA ORGÁNICA EN SUELOS DE BOSQUES SABINEROS (Juníperus thurífera L.)
J. GONZÁLEZ , M.A. CANDÁS
Departamento de Edafología. Facultad de Farmacia. Univ. Complutense Madrid
Soils under Spanish junipers (Juniperus thurifera L.) located in Arevalillo de Cega (calcareous material) and Pedraza (gneis), two villages in the east of the province of Segovia (Spain) were studied. The soils exhibited the following horizon sequence: O, Ah, C; O1, O2, Ah, C; and O, Ah1, Ah2, C. These ecosystems have borne strong human impacts through pasturage and agricultural practices; in both areas, trees play a prominent ecological role and constitute the principal ecosystem compartment as regards the carbon and nitrogen contents. We determined the characteristics (texture, pH, CEC, macronutrient concentration) of the soils developed on both type of lithological material, as well as the organic C and total N contents in tree leaves and organic (O) and organo–mineral (Ah) horizons. Organic matter was fractionated in order to determine the proportions of free C and N relative to the total C and N contents (91% and 89%, respectively) in the O horizons. These proportions were lower (53% and 54%, respectively) in the deeper Ah horizons.
Carbon from fulvic acids was found to prevail over that from humic acids in relation to total C, both increasing with increasing depth. The proportion of non-extractable humin (H2) exceeded that of extractable humin and, again, both increased with increasing depth. The proportion of inherited humin (H3) was always lower than that of insolubilized humin (H1 + H2) in relation to total C. The humus was of the calcic Mor- Moder type. The proportion of humic acids extracted by different agents in relation to bound C decreased in the following sequence: sodium hydroxide > pyrophosphate > tetraborate (with increasing polymerization) and hence increasing degree of humification.
The proportions of mineralized carbon and nitrogen relative to total C and N, and the degree of nitrification, were all higher in the Ah horizons of the soils developed on limestone than on those developed on gneiss. Also, the proportions of mineralization per day were higher for carbon than for nitrogen.
Keywords: Organic matter, mineralization, Spanish juniper (Juniperus thurifera L) woods.