Assessing the effect of forest degradation in different slope positions on soil quality and evolution in west of Kurdistan Province

Soil quality is one of the most important factors to assess soil management. Therefore, recognition of all soil quality properties such as physical, chemical and biological is essential. Forest degradation and land use change effect on soil properties variability and led to decrease soil quality factors on soil quality. Moreover, soil characteristics also are related to slope position. The region of Marivan in Kurdistan province is one of the forested areas of Zagros which in recent decades, due to population growth and the increased need for food, has been threatened and some parts are now cultivated. The aim of this research is assessing the effect of forest degradation and slope position on soil quality and evolution in west of Kurdistan Province.
Eight soil profiles in different slope position (shoulder, back slope, foot slope and toe slope) of two adjacent hill slope, under land uses of cropland and forest (uniform condition) were dug and described. Moreover, in each land use three soil samples were taken from depth 0-20 cm in each slope position. Properties of soil texture, bulk density, particle density, fine sand, organic carbon, cation exchange capacity, field capacity moisture, permanent wilting point moisture, electrical conductivity, pH, carbonate calcium equivalent, total nitrogen, available phosphorous, available potash infiltration rate, microbial respiration rate, porosity, available moisture sodium adsorption ratio (SAR) and erodibility were measured and computed.
The results showed low slope positions (toe slope and foot slope) had higher contents of clay, organic carbon, available moisture, fine sand, silt, total nitrogen, available phosphorous, available potassium, CEC and microbial respiration rate and lower contents of electrical conductivity, soil erodibility, pH and SAR compared to high slope positions. Soils formed in low slope positions had higher depth and evolution compared to high slope positions. The results also showed two land uses (cropland and forest) in relation to bulk density, porosity, silt, clay, carbonate calcium equivalent, fine sand, pH, organic carbon, total nitrogen, microbial respiration rate, infiltration, soil erodibility and available moisture had significant difference and land use change of forest land to cropland has been led to degradation of Mollisols. Therefore, soil properties are dependent to slope position and land use kind and these factors have affected soil properties and evolution.
The results showed forest degradation has led to decrease of soil quality using significant decreasing of organic carbon, microbial respiration, total nitrogen, CEC, porosity, infiltration and available moisture and significant increasing of bulk density, pH, SAR, fine sand, soil erodibility, and silt. Forest degradation and land use change also due to cultivation led to decrease organic carbon content and soil structure degradation of Mollic horizon. Therefore, Mollic horizon has converted to Ochric horizon and Entisols and Inceptisols have formed in cropland land use. Moreover, the results showed different slope position effect on bulk density, sand, silt, clay, infiltration, erodibility, available water, pH, organic carbon, carbonate calcium equivalent, microbial respiration rate, nitrogen, phosphorous, CEC and potassium and have significant difference. These results show current management of studied land effect on soil quality and led to land degradation. Therefore, soil conservation of steep area using prevention of deforestation in Marivan forests and use of land based on their capability to conserve of soil and land quality is essential.