Effects of Long Term Grazing Exclusion on Some Soil Physicochemical Characteristics and Sustainability

Heavy livestock grazing is a severe threat to soil quality in the rangelands, particularly in the semiarid regions. However, grazing exclusion is the effective and low cost management measure combating improper grazing impact. The purpose of this study was to investigate the effects of grazing exclusion on soil physicochemical properties in Dalahoo Rangeland, Kermanshah, Iran, and was carried out during 2016-2019. For this purpose, two linear transects were performed in exclosure (Ex) and grazed (Gr) sites. In each transect, 12 sampling points were selected with 250 m interval and soil samples were taken from topsoil and repeated annually. The results of this study revealed that the respective value of soil organic carbon (SOC) in Ex and Gr was 1.10 and 1.09 %, showing no significant differences between them in the first year. However, in the fifth year, SOC was enhanced to 3.70% in Ex, which was significantly higher compared to Gr (p <0.05) and 5.5 times higher than the first year. The bulk density (BD) in the Ex and Gr soil in the first year was 1.56 and 1.57 gcm-3, respectively. Over five year time, the BD of Ex significantly decreased to 1.266 gcm-3, while there was no significant change in Gr site. Furthermore, the respective ratio of coarse soil aggregate (CSA) with > 1 mm diameter in Ex and Gr was, respectively, 9.18% and 8.09% in the first year, while it was, respectively, 30.29% and 6.90% in the fifth year, which was significantly higher in Ex (p<0.05) and indicated 3.3 times improvement through exclosure measure. Finally, the limitation class for soil quality in the Ex was changed from high (1st year) to no limitation (5th year), while Gr site, which was in “high limitation class” in the first year, showed no change during five year. This study demonstrates that five years grazing exclusion significantly improved soil quality.