The effects of soil disturbance due to land use change of forest lands to cultivated lands on biological soil quality indices of forest ecosystems of Northern Iran

Land use change of forest ecosystems in northern Iran changes the soil quality of Paresar (Gilan province) and Gorgan (Gorgan province) regions. In order to study changes in some biological soil quality indices due to land use change from forest to cultivated lands, composite soil samples from two depths (0-20 and 20-40 cm) were taken from Paresar and Gorgan regions and urease, alkaline and acid phosphatase, invertase and arylsulfatase enzymes activities besides some biological properties consisting of microbial biomass carbon and nitrogen, carbon and nitrogen mineralization and respiration due to substrate addition were measured. Results showed that land use change caused biomass carbon (44-82%), biomass nitrogen (30-200%) and their ratio (20-30%), carbon mineralization (11-67%), nitrogen mineralization (3-68%), respiration due to substrate (8-45%) and microbial enzymes activates to decrease in both regions (expect carbon and nitrogen mineralization in Paresar region). However, the metabolic coefficient (qCO2) in both regions increased due to land use change. Therefore, agricultural practices in forest lands cause oxygen availability to increase for soil microorganisms and this phenomenon stimulates the microbial activity and enhances organic matter decomposition and CO2-C emission from soil resulting in soil quality reduction. Also enhancement of carbon mineralization (microbial respiration), decreases soil organic matter concentration and reduces energy for microorganisms and this phenomenon caused soil microbial population to gradually decrease. According to the results it is recommended to reduce soil disturbance by using no-tillage or minimum tillage systems and planting perennial legumes can decrease greatly the harmful effects of cultivation.