Effect of land-use changes on chemical and physical properties of soil in western Iran (Zagros oak forests)

The consequence of land-use change from forest to agriculture and other uses has become one of the world's greatest concerns. The soil, one of the most important components of forests and containing all the required plant nutrients as soluble ions, is highly impacted by these changes. Because vast areas of the Zagros forests in western Iran have changed in use during the last few decades, the present study investigated the effects of land-use changes of forest area to agriculture, orchard, and agroforestry on soil chemical and physical properties. Soil was sampled at four land-use areas: less-disturbed forest areas (control) and agricultural, orchard, and agroforestry areas. Among each of the two forest-use areas (agroforestry and orchard), we selected five trees with similar-sized crowns and sampled under each tree crown at 0-15 and > 15-30 cm depths. Five soil samples also were taken in agriculture area at each depth. The findings indicated that during land-use changes, soil sand particles decreased, and clay and silt particles of soil increased, resulting in a fine soil texture. Moreover, the amount of nitrogen (N), phosphorus (P), organic carbon (OC), and electrical conductivity (EC) of soil decreased at both depths due to the decrease in organic matter. Soil pH and magnesium (Mg) level rose during land-use change at both depths except at agricultural sites. Soil potassium (K) content decreased during agricultural use due to the elimination of tree cover. The level of K decreased only at the depth of 0-15 cm because of K dependency on parent materials. Generally, most soil nutrients were affected by plant removal in the conversion. Forest and agricultural soil are distinguishable by their properties, while land-uses such as agroforestry-orchard separated from the others. Soil nutrients were severely affected by the decrease and elimination of tree cover, plowing, and continuous harvesting, resulting in a decline in soil quality and fertility.