Pedogenetic investigation of soil degradation on a deforested loess hillslope of Golestan Province, Northern Iran

Abstract

Genesis, mineralogy, and micromorphology of soils formed on a forest and adjacent cultivated loess hillslope were investigated to assess the effects of deforestation and hillslope position on soil properties and the intensity of soil degradation. The study revealed that deforestation caused a loss of soil organic carbon, a reduction of cation exchange capacity, and an increase in carbonates in the surface soil. The soils of the different slope positions of the forest land were Alfisols and Mollisols with well-developed argillic horizons. Speckled b-fabric of the argillic horizons and the crystallitic b-fabric of the underlying calcic horizon are evidence for a more stable landscape under forest ecosystem. Downward leaching caused decalcification of the upper horizons and clay movement in the profile. Formation of the mollic epipedon in the forest land confirms the accumulation of organic carbon and lower erosion in the surface soil. Soils of the adjacent cultivated area however, are less-developed, and classified as Inceptisols and Mollisols. Absence of the mollic epipedon in the shoulder, backslope and footslope positions, presence of the near surface calcic horizon and absence of argillic horizon in all slope positions are due to severe erosion. Absence of speckled b-fabric in all the slope positions of the deforested land is evidence that downward and surface movements of water have resulted in soil erosion and flooding. Higher smectite concentrations and occurrence of vermiculite in the forest area indicate favorable moisture availability. Pedology is an effective way of documenting the adverse effects of land use change especially in the hilly regions.