Long Term Enclosure Assessment on Stability of Soil Physical and Chemical Properties in Rangeland Ecosystems (Case Study: Khash County Rangelands)

This study aimed to investigate the effects of long-term (15-year) enclosure on the physical and chemical properties of soil in the arid and semi-arid rangelands of the Koteh region in Khash County. For this purpose, two sites were selected for comparison: an enclosed rangeland and a grazed rangeland with similar topography. Vegetation and soil samples were collected at two depths (0–15 cm and 15–30 cm), and parameters such as soil texture, pH, electrical conductivity, organic carbon, total nitrogen, phosphorus, potassium, and bulk density were measured. The results of data analysis showed that enclosure significantly increased canopy cover (32.3% vs. 10.9%), litter, and plant species diversity. At the 0–15 cm depth, organic carbon (0.48% vs. 0.24%) and total nitrogen (0.052% vs. 0.022%) were significantly higher in the enclosed area, while bulk density, available phosphorus, and potassium were higher in the grazed rangeland. At the 15–30 cm depth, organic carbon (0.33% vs. 0.23%) and total nitrogen were also higher in the enclosed area, with no observed differences in soil texture between the two sites. Additionally, pH and electrical conductivity values at both depths in the enclosed area were lower than or similar to those in the grazed rangeland, indicating a relative improvement in soil quality under long-term enclosure. These findings suggest that long-term enclosure can enhance the sustainability and ecological function of rangelands in arid and semi-arid environments by improving key soil indicators.




Introduction
Rangeland enclosure not only helps restore vegetation cover but also enhances the long-term sustainability and productivity of rangeland ecosystems by improving soil physical and chemical factors. Although ample evidence confirms the positive effects of enclosure, the results reported in some studies have been diverse and contradictory due to differences in climate, soil type, vegetation composition, and duration of enclosure. Considering the arid and semi-arid climatic conditions of the Koteh region in Khash County and the high vulnerability of its soils to overgrazing, a detailed study of the effects of long-term enclosure on the physical and chemical properties of the soil in this area is of great importance. Therefore, this study aims to scientifically assess the impact of enclosure on key soil indices in rangeland ecosystems in this region.
Materials and Methods
This study aimed to investigate the effect of long-term enclosure on the physical and chemical properties of soil in arid and semi-arid rangelands of Khash County. The Koteh rangeland was chosen as the enclosure site with a 15-year history of enclosure, and an adjacent rangeland with similar topographic conditions was chosen as the grazed site. Vegetation sampling was conducted in June by establishing six 100-meter transects at each site (three transects in the direction of the slope and three transects perpendicular to it) and sampling 10 one-meter plots in each transect using a random-systematic method. Data on canopy cover, litter, bare soil, and plant species were recorded. Soil sampling was performed from two depths of 0–15 and 15–30 cm at the beginning, middle, and end of the transects, and a total of 24 composite samples were prepared. Soil properties were measured, including texture, pH, electrical conductivity, total nitrogen, phosphorus, potassium, calcium, magnesium, sodium, organic carbon, and bulk density using standard methods. Data were analyzed using independent and paired t-tests in SPSS software. Correlation analysis was performed in R software.
Results and Discussion
The results showed that the vegetation of the area consisted of perennial and annual species with diverse growth forms. In the enclosure area, the canopy cover was significantly higher (32.3%) than in the grazed area (10.9%). More stable and diverse species were found in the enclosure area, and the amount of litter was also higher in this area (3.72%), indicating higher biological activity and reduced soil erosion. Regarding soil characteristics, the percentage of silt was higher in the grazed area, and the bulk density of the soil was also higher in the grazed area, indicating greater soil compaction due to livestock grazing. The amounts of organic carbon and total nitrogen at both depths (0–15 and 15–30 cm) in the enclosure area were significantly higher than in the grazed area, which could be due to the accumulation of plant residues, reduced erosion, increased biological activity, and improved microclimatic conditions. However, available phosphorus and potassium were higher in the grazed area. Also, soil acidity and electrical conductivity were lower in the enclosure area, indicating improved soil conditions. Soil texture composition was not significantly different at the depth of 15 to 30 cm, but bulk density and nutrients were still significantly different. These findings emphasize that livestock grazing management through enclosure improves vegetation cover and soil physical and chemical quality in semi-arid ecosystems.
Conclusion
According to the results of this study, long-term enclosure, as an effective management strategy, plays a significant role in restoring and improving the ecological conditions of arid and semi-arid rangelands. This method increases the percentage of vegetation cover and litter, preserves native and valuable rangeland species, and improves ecosystem dynamics. The decrease in soil bulk density indicates an improvement in the physical structure of the soil and a decrease in compaction caused by livestock grazing. From the perspective of chemical properties, a significant increase in organic carbon and total nitrogen, along with a decrease in acidity and electrical conductivity, indicates an improvement in soil quality and a strengthening of the nutrient cycle. Although the accumulation of phosphorus, potassium, and calcium in grazed areas was observed due to livestock waste, these elements are not stably stabilized and cannot replace the positive effects of enclosure. Therefore, it is recommended that enclosures be developed as a sustainable method in rangeland management and, along with continuous monitoring of soil and vegetation, help maintain and improve the health of the rangeland ecosystem.