Soil quality and vegetation cover characteristics as influenced by diverse grazing regimes and soil disturbance histories in a semi-arid rangeland (Iran)

Abstract

This study investigates the soil functioning and regeneration processes in a semi-arid rangeland subject to an eleven-year conservation grazing (CG) program within the Gonbad paired watershed in Hamadan, Iran. Five distinct sites with varying rangeland vegetation cover were selected based on differences in grazing regimes and soil disturbance histories. These sites include: CG site with Astragalus-Artemisia vegetation (CG(A-A)); CG site with Astragalus-Bromus vegetation (CG(A-B)); CG site, easily accessible to grazing livestock, with Astragalus-Lactuca vegetation (CG(EA)); CG site with a history of past rainfed farming and Centaurea-Grasses vegetation (CG(PRF)); and free grazing (FG) site with Astragalus-Euphorbia vegetation. In addition, a long-term rainfed farming site (RF) was studied as the dominant land use. Rangeland management practices had a discernible impact on nearly all soil quality (SQ) indicators. However, due to their strong interdependence, only soil aggregate stability, carbohydrates, and phosphatase activity proved to be critical indicators representing soil functioning in the area. The general SQ index illustrated a decline in soil functioning at RF (58%), CG(PRF) (55%), FG (42%), and CG(EA) (22%) sites compared to sites classified as "good" (CG(A-A) and CG(A-B)). Total organic carbon and carbon stock were only recovered in well-restored sites, characterized by a predominance of shrubs and perennial grasses. Meanwhile, active carbon and carbohydrates revealed the positive effects of conservation grazing in moderately and poorly restored sites, characterized by a predominance of forbs and annual grasses. Our findings suggest that soil disturbance history and grazing accessibility are critical factors for successfully implementing conservation grazing management in the area.