Changes in Soil Total and Microbial Biomass Nitrogen in Deforested and Eroded Areas in the Western Black Sea Region of Turkey

The microbial biomass in soil is an active and living constituent of organic matter. It is both a storage pool and a source of plant nutrients that can be used as required. In addition, each microbial indicator evaluates soil quality and health from different perspectives, which are not necessarily very different. This study was conducted to compare some physical, chemical, and biochemical characteristics of the soils of forest (SF) and deforested (SDE) areas located on the slopes of the Kirazlıköprü area, which was previously deforested due to dam construction in Bartın province in northwestern Turkey. Soil samples were taken from the topsoil surface (0–5 cm) to determine the microbial soil characteristics of the SF and SDE sites. The soil microbial biomass N (Nmic) was determined by chloroform fumigation extraction, and the Cmic/Nmic ratio and Nmic/Ntotal percentage were calculated using the original values. Total N, Nmic and Cmic/Nmic values are higher in the forest area. The lowest and highest total N (Ntotal) contents in the SF and SDE soils varied between 1.50 and 3.47 g kg−1 and 0.91 and 1.46 g kg−1, respectively. Similarly, the Nmic contents of the SF and SDE soils varied between 75.56 and 143.42 μg g−1 and 10.40 and 75.96 μg g−1, respectively. A statistical analysis revealed that the mean Ntotal and mean Nmic values differed (p < 0.05) in the SF and SDE soils. The mean Cmic/Nmic values in the SF and SDE soils were 8.79 (±1.65) and 5.64 (±1.09), respectively, and a statistical difference was found between the fields (p < 0.05). Our findings indicate that the soil microbial community structure varies according to the site. As a result, it can be concluded that deforestation and erosion due to dam construction in the area led to the removal of plant nutrients from the soil; deterioration in the amount and activity of microbial biomass; and, consequently, soil losses and degradation of soil quality.