Soil quality of an Iranian forest ecosystem after conversion to various types of land use

The impact of land-use change on parameters of the soil was evaluated in soil samples from arable land, orchard land, and grassland in West Azerbaijan, Iran, compared with their adjacent natural forestland, using some biological indices. Microbial biomass carbon (MBC); microbial basal respiration (BR); metabolic quotient (qCO2); substrate induced respiration (SIR); carbon availability index (CAI); the microbial quotient, i.e., the ratio of microbial carbon to soil organic carbon (C_mic/C_org); and soil organic carbon (SOC) were calculated in collected soil samples. Deforestation and long-term land use showed adverse effects on soil biological properties. The spatial distribution of MBC, BR, SIR, and SOC, followed the order: forestland > grassland > orchard land > arable land. SOC showed the highest decline by 67.7% in arable land, 43.6% in orchard land, and 36.3% in grassland, with an average reduction of 49.2% compared with forestland. Similarly, BR and MBC decreased by an average reduction of 41.3 and 34.8%, respectively, compared with forestland. By contrast, the qCO2 index, the CAI index, and the C_mic/C_org ratio were not affected significantly by land use, except from a significant raise of the C_mic/C_org ratio in the arable land. Land-use change exerted a remarkable negative influence on soil quality with several soil attributes affected due to cropping compared with adjacent grassland and forestland. At the field level, proper management practices that increase SOC in the soil, e.g., effective recycling of crop residues and manures, should be considered, when land is continuously cultivated.