Land use change effects on soil quality and biological fertility: A case study in northern Iran

The present work mainly focused to investigate the effects of land use change from natural forest (NF) to arable lands (AL), citrus gardens < 10 years old (CG < 10), citrus gardens > 10 years old (CG > 10) and paddy fields (PF) on soil physical, chemical, and biological properties in northern Iran. Moreover, soil fertility was mapped by ordinary kriging (OK) method based on the biological fertility index (BFI), which is based on soil organic matter (SOM), soil basal respiration (CbasR), cumulated soil respiration (CumR), microbial biomass carbon (Cmic), metabolic quotient (qCO2) and mineralization quotient (qM). The performance of OK was assessed by the relative root mean square error (RRMSE, %). Results indicated that land use change significantly influenced most soil properties. Soil organic carbon (SOC) and soil total nitrogen (TN) stocks decreased with land use changes compared to NF. In particular, SOC stocks decreases were lower in AL (29%) and higher in CG < 10 (48%) land uses. TN stocks ranged from 6.0 Mg ha−1 in CG > 10–11.0 Mg ha−1 in NF. BFI was higher in the NF (26 as average, range 24–29) compared to the other land uses (19–22 as average, range 13–26). The range was Good-High in NF and PF, Medium-High in the other land uses. Positive and negative correlations were found among the different soil parameters. OK method interpolated BFI and qCO2 with the lowest (13.69%) and highest (55.65%) RRMSE, respectively. We can conclude that mapping of the BFI is effective to indicate where to adopt a more sustainable management in the agricultural lands for improving soil quality and reducing soil degradation in these areas.