The effect of land use change on chemical forms and availability of iron and manganese in arid and semi-arid region of southwestern Iran

Changing land use from rangeland and forest to agricultural land and orchard can greatly affect the characteristics and fertility of the soil, especially in arid and semi-arid regions. In this study, seven major land-use types in Kohgiluyeh-and-Boyer-Ahmad province of southwest Iran were selected; these land types were orchards (grape), forests, rangelands, and agricultural lands which cultivated corn, beans, and rainfed and irrigated wheat containing five soil orders, namely Entisols, Inceptisols, Mollisols, Alfisols, and Vertisols. The samples were collected from the soil depths of 0-30 cm. Based on the results, the highest average content of organic carbon (OC) was detected in the forest (3.3%). It may thus be stated that there is a balance in forest soils between the rapid decomposition of soil organic matter and the rapid accumulation of litter due to plantation and also an abundance of litter. In all soil samples, the highest percentage of Fe and Mn were found in the residual (Res) fraction and the lowest percentage in the exchangeable (Ex) fraction. The highest and lowest amounts of Fe and Mn carbonate (Car) form were associated with forest and rangeland land uses. Different land uses had an important influence on the amount of the Fe form bound to organic compounds. In this way, the maximum amount of this form belonged to forest use which contained the highest amount of organic matter; the lowest amount of organic matter was related to rangeland use.