The Effects of Livestock Grazing Intensity on Soil Physicochemical Properties in Moghan Rangelands

Introduction: Soil is one of the important components of rangeland ecosystems. Soil is the natural and dynamic layer of the earth that act as an important component of rangeland ecosystems for the human food
security and plants mechanical support which is the background for growth of them. Soil degradation decreases the potential of rangeland production; because soil is the primary factor for forage production in any rangelands with any kind of weather. Different grazing intensities change the chemical and physical properties of soil and plant composition of rangelands. It is important to know soil properties for the proper management of rangeland ecosystems. Therefore, this study was carried out with the objective of investigating the effects of grazing intensity on soil physical and chemical properties in Moghan rangelands using grazing gradient framework. Materials and Methods: Three villages of Tolklo, Kolash and Panjalo were selected as the representatives of grass-shrubland in Moghan rangelands, in Parsabad county, Ardabil province, northwest of Iran. Samples were collected from three grazing intensities and three distances from the center of villages, as the critical center. Three soil samples were taken at each distance of village (three replications) from 0 to 30 cm (main root activity areas) depth (27 samples). Soil parameters including pH, electrical conductivity, saturated water content, dissolved sodium, potassium, calcium, magnesium, exchangeable potassium, available phosphorus, calcium carbonate equivalent, organic carbon, particulate organic carbon, dispersible clay, total nitrogen, aggregate mean weight diameter and soil texture were measured. To identify the trend of changing soil parameters in different grazing intensities including light, moderate and heavy, weighted average was taken for each three samples, which were collected from the three-grazing intensity at each village. Data statistically analyzed by using the Two-way analysis of variance and using Duncan’s multiple range test. Results and Discussion The results of the soil data analysis showed that except dissolved sodium and potassium, lime and soil silt percentage, there was no significant statistical difference between measured values of soil properties in different grazing intensities in Moghan rangelands. The result of the mean comparison for soluble sodium and potassium, lime and soil silt percentage showed that with increase of grazing intensity, the values of soluble sodium decreased. In addition, at the nearby of critical center and with the increase of grazing intensity, the values of soluble potassium increased. However, its highest and lowest amount was observed at the heavy grazing intensity and moderate grazing intensity, respectively. The highest and lowest amount of lime were also observed at the heavy and light grazing intensity, respectively. In other words, in nearby to critical center and with the increase of grazing intensity the value of these parameters increased. The results of the data analysis for soil texture showed that in both areas with the light and moderate grazing intensity, soil texture class was silty clay loam, but in the areas with heavy grazing intensity, soil texture class had gradually changed from
silty clay loam to loamy texture. In other words, the soils had progressed to sandy soils, which is due to the change in their silty particles. With approaching to the critical center and with increase of grazing intensity the value of silt percentage decreased. The highest amounts of silt percentage were related to the light and moderate grazing intensities and its lowest amount was recorded in heavy grazing intensity. Results showed that the effects of heavy grazing on soil properties in the grazing gradient framework is detectable, and this framework can be sued for rangeland monitoring to detect the rangeland condition. Heavy grazing and overall utilization of rangelands have caused soil degradation in most rangelands of Iran. This study revealed that heavy grazing jeopardized the sustainability of the rangeland
ecosystem by creating unfavorable changes in soil and available minerals. Therefore, it recommended that soil parameters must be included in rangeland inventory and monitoring to use soil information for sustainable range management and, particularly in rangeland restoration and to select sustainable strategies for better and suitable management of these rangelands.