Environmental controls on physico-chemical properties of soils derived from andesite bedrock in northeastern Turkey

In the Eastern Black Sea Region of Turkey, significant climatic differences have occurred depending on the sea's effect and the mountains' position concerning the winds coming from the sea. These climatic differences, along with the slope position, aspect, slope, and bedrock characteristics, have led to the development of soils with different characteristics. In this study, 32 sites were sampled from pure oriental beech forests on andesite bedrock material in the Borçka and Akkuş regions to prove the effect of environmental factors on soil properties. Soil profiles were excavated in the sample plots and soil sampling was carried out according to genetic soil horizons. Two hundred seventy-five soil samples (128 undisturbed) were taken from the excavated soil profiles, and physiological soil depth (PSD), absolute soil depth (ASD), and humus forms were determined. In soil samples, soil pH (H₂O and KCl), soil organic matter (SOM), total exchangeable bases (TEB), field capacity (FC), wilting point (WP), sand, silt, and clay were analyzed. Bulk density (BD), available water capacity (AWC), and soil organic carbon (SOC) were calculated. Independent t-test results showed that the average values of selected soil properties differed by region. Significant correlations between soil properties were determined. Soil pH, SOM, SOC, TEB, BD values, and sand contents of very-humid and sunny Borçka region soils are lower than those of moist and shady Akkuş region soils. Especially, low soil pH and TEB values are most likely the results of leaching. The high amount of clay and AWC, excess of PSD and ASD, and low amount of SOC suggest that weathering conditions are more suitable in this region. Podsolized gray brown forest soils are dominant in the Borçka region, while gray brown forest soils are dominant in the Akkuş region. It should not be overlooked that due to the acidification of the soils of the research area, the nutrition-growth relations in forest ecosystems will deteriorate. For this reason, it is inevitable for forest managers to make necessary practices for the sustainability of ecosystem health.