The Effect of Land Use Change on Some Physical and Chemical Properties of Soil in the Halshi Watershed, Kermanshah

Introduction
Land use change generally has a serious impact on the rate  Organic matter and other properties Physical and chemical soils.So that today, the study of the effects of land use change on soil characteristics in watersheds is one of the important and important topics for researchers. Pichakd, (2017)
Khatir Pasha et al. (2017) examined the effect of land use change on soil physical, chemical and biological characteristics in Qalaq forest of the city.The results showed that the physical, chemical and biological characteristics of the soil were significantly different between different uses and the dynamics of nitrogen could be affected by changes in forest uses.
Data and colleagues (2015) concluded by examining the characteristics of sodium soils and organic carbon components in various uses in northwestern India That's in all usesAs the depth increases,   bulk density, the amount of silt and clay, and the pH and electrical conductivity of the soil increase
The purpose of this study is to analyze the effect of land use change on the physical and chemical properties of soil in the Kermanshah Helshi watershed.
Methodology
The Halshi watershed is part of the Qarasu basin with an area of ​​about 7356.65 hectares, which is located 30 km southeast of Kermanshah..In this research, first, using topographic maps of the region and satellite images, the land use map of the region was prepared in three classes of agriculture, forest and rangeland.In the next step, based on land use maps, topography (slope, direction, height), geology, soil hydrology, land capability, erosion of soil sampling points in the study area in Arc GIS 9.3 software environment are specified and according to the conditions. Homogeneity and area of ​​each land use at a shallow depth of about 0-20 cm 38 soil samples including 18 samples in agricultural lands, 10 samples in rangeland lands and 10 samples in Forest lands  Accidentally harvested and the geographical characteristics of each soil sample were recorded by GPS. The soil samples were then transferred to the laboratory after drying in the open air and the physical and chemical properties were evaluated using one-way variance (ANOVA) and SAS software.
Discussion and results
According to the results of statistical analysis and the meanings obtained from clay, silt and sand ratio in the samples of soil tested, the type of soil texture in agricultural use is more than clay and loamy-clay type, rangeland lands with loamy texture and lands. It is a clay-silty forest,
Due to land use change, soil texture has changed from clay-silt in the forest to clay in agriculture.Reducing the stability of aggregate in agricultural use compared to two uses Rangelands and forests can be considered due to tillage operations and reduction of soil organic matter, which indicates unsustainable use in these lands.Average pH in agricultural use, Rangelands and forests show that these parameters do not change significantly in different uses and are the same.The existence of geological formations, especially lime and carbonates (karstic lime), and climatic conditions, physicochemical decomposition and material erosion, has increased and concentrated the amount of surface lime.The results show that forest use has the highest amount of organic carbon than both agricultural and rangeland use. The percentage of nitrogen in the surface layer in agricultural and rangeland use is lower than forest use, indicating that land use change from forest to agricultural reduces soil nitrogen.The average amount of potassium that can be absorbed by the surface layer of rangeland is higher than that of agriculture and forestry. But this difference was not statistically significantBased on the results of the Mean Comparison Test (ANOVA), it shows that land use change has led to changes in soil quality and some physical and organic carbon parameters of the soil.
Results
In general, the results of this study showed that conversion and change  Land, especially from Rangelands and forests to agriculture and consequently  Continuous cultivation on these lands leads to the destruction of some of the optimal physical and chemical properties of the soil.According to the results of this study, it can be concluded that land use change can reduce the appearent specific weieght in agricultural lands, increasing the amount of sand used. Rangelands, increasing the aggregate stability    and organic carbon soils in forest lands, reducing the amount of organic matter in arable land, increasing potassium Rangelands, increased phosphorus in arable land, increased organic carbon in the forest, increased electrical conductivity in agricultural use.The results of one-way analysis of variance (ANOVA) showed that the change in rangeland and forest use had the greatest impact on soil characteristics and the stability of aggregate  aggregate stability   and organic carbon in forest use made the most difference .Therefore, land use change, especially from Forest andRangelands To Agriculture affects soil properties and leads to soil degradation and reduction of nutrients.