CHARACTERISTICS OF THE ORGANIC-MATTER OF MEDITERRANEAN HIGH-MOUNTAIN SOILS

The organic matter from the A horizons of five soils developed under a shrubby cover and under pine groves in a Mediterranean high-mountain area has been studied. The characteristics of humic acids (HA) are com pared with those reported by other researchers in a variety of environ mental conditions. The organic matter from pine groves has a higher C/ N ratio, a greater content in fresh or little-transformed organic matt er, and a lower humic extract than that of shrublands. In general, the humic acids show a low humification index, with greater relative prop ortion of aliphatic chains and less condensed aromatic-type structure as the pH and base saturation diminish. The climatic extremes which ty pify these ecosystems, very cold winters and very dry summers, togethe r with the acidity and low base saturation of the soils, seem to be th e determining causes of the low-humification index. Felbeck's hypothes is of alteration of plant components appears to be the principal proce ss controlling the humic-acid evolution of the organic matter in these soils.