Investigation of some physical and chemical properties of soil in rangelands and abandoned drylands (Case study: Sanandaj rangelands)

 The growth of the population and the increase in food needs have caused humankind to turn to manipulating nature and converting natural lands into crops, especially rainfed agriculture, to provide the food they need. For various reasons, a large part of these lands is abandoned every year, which causes many changes in the physical and chemical properties of the soil. This research aimed to compare the most important physical and chemical characteristics of soil in two land uses, including rangeland and abandoned rainfed in Kurdistan province.

 This research was carried out in Kurdistan province. For this purpose, four regions, including Kilak, Salavat Abad, Sarab Qamish, and Mamukh, were selected in Sanandaj city. In each region, two neighboring rangelands and abandoned drylands were selected. Three 100-meter transects were established in each land use by random-systematic method, and soil samples were collected from 0-30 cm depth. Depending on the conditions and area of the region, 20 composite samples were taken in Kilak, 20 Salavat Abad, 14 Sarab Qamish, and 8 Mamukh. Half of the samples were collected in rangeland, and the other half in abandoned dryland. In the laboratory, soil physical and chemical factors, including acidity, electrical conductivity, absorbable potassium, percentage of soil organic carbon, total nitrogen, available phosphorus, soil texture, and bulk density, were measured by usual laboratory methods. A factorial experiment was conducted using a completely randomized design to analyze the data. The Duncan test was used to compare the means.

 The results showed no significant difference in the percentage of clay, silt, sand, and specific mass in the comparison of rangelands in four regions, the comparison of abandoned dryland in the four regions, and the comparison of abandoned dryland in each region. The comparison of the average acidity of abandoned rangeland and dryland did not show any significant difference in any region. Electrical conductivity in Kilak, Salavat Abad, and Sarab Qamish areas was higher than in dryland. However, only in Kilak was there a statistically significant difference. The electrical conductivity of rangeland soil was 143; in abandoned wetlands, it was 109.The comparison of abandoned rangelands and drylands in terms of total nitrogen and carbon numerical values showed that rangelands were more than abandoned drylands in all areas. This meant that nitrogen was 24%, 40%, and 42.8% higher in the Kilak, Sarab Qamish, and Mamukh regions. And statistically, their difference was significant. Also, the carbon difference between the rangeland and the dryland in Mamukh was statistically significant (1.47% in the rangeland and 0.74% in the dryland). There was a significant difference in the amount of phosphorus between the rangeland, 94 mg/kg, and the abandoned dryland, with 234 mg/kg only in the Mamukh region. Only in the Sarab Qamish area was soil potassium higher than in the rangeland by 24.7% in the abandoned dryland.Comparing rangelands and abandoned drylands in terms of the numerical amount of total nitrogen and carbon, it can be concluded that in all areas, the rangeland was more than the abandoned drylands, so that nitrogen in Kilak, Sarab-Qamish and Mamukh regions was 24, 40, respectively, and 42.8% more, their difference was statistically significant and also the carbon difference in Mamukh was statistically significant (rangeland 1.47% and dryland 0.74%). There was a significant difference in phosphorus between rangeland, 94 mg/kg, and abandoned dryland, 234 mg/kg only in the Mamukh area. There was a significant increase in soil potassium in abandoned drylands by 24.7% over rangeland soil in the Sarab-Qamish region.

 This research indicates that the change of land use from rangeland to dryland and then abandonment will change the soil's physical and chemical properties. After about 40 years since the drylands were abandoned, there has been an improvement in most of the physical and chemical factors investigated in this research. In this research, 40 years have been considered. It is suggested to consider different periods in the secondary sequence in future research. This will enable us to determine more precisely when the soil can improve. Also, similar research should be done in other ecological regions with different conditions so that the effect of climatic and topographical factors can be clearly defined.