Relationship between total extractable organic carbon and some parameters of soils from western Spain

Abstract

[EN] Different unit of soils from Western Spain were selected and some physico-chemical parameters analyzed. Samples of their soil horizons were submitted to humus fractionation and the total extraction of the humic substances of these horizons was calculated. A significant, inverse relationship between total extractable organic carbon (TEOC) and soil pH (R=-0.57, p <0.001.53 soil horizons) was found, which points to the importance of the exchangeable Ca2+ ib the insolubilization of humic substances. This relationship improved (R = - 0.76, p <0.001,38 soil horizons) when saline, sodic soils were excluded. Evidently, saline, sodic soils (soil pH >8.5) undergo an auto-extraction of humic substances that hampers this relationship. TEOC had also a significant, inverse relationship with the degree of base saturation and the clay content of soils. It is concluded that TEOC is strongly dependent, at least, on the soil pH; this fact indicates that the former is not a valid key parameter for soil quality. TEOC is also dependent on the clay content of the soil epipedons. The results also rejected the general idea that low humus extraction means a low degree of humification, at least in the Mediterranean region.