Response of soil quality indicators and their spatial variability to land degradation in central Iran

Abstract

Studying land degradation through a soil quality approach, which reveals soil functioning within the ecosystem, is necessary for sustainable management of land resources. This investigation was conducted to understand the changes of soil functions, resulting from exploitive management, using some soil quality indicators and their statistical and geostatistical measures. Undisturbed and disturbed sites were identified in each of two study areas, including an oak forest and a semiarid rangeland in central Iran. Soil organic carbon (OC), total nitrogen (TN), microbial respiration (MR), aggregate stability (AS), and hydraulic properties of the sites were determined. Statistical comparisons of frequency distribution functions of OC and MR revealed that these functions are normal in protected forest, while in the disturbed forest distributions deviate from normality. In the rangeland sites, the results were exactly the opposite. Spatial variability of the two variables in forest sites demonstrated pure nugget and spherical pattern in protected and disturbed sites, respectively. As for the rangeland ecosystem, pure nugget pattern was observed for both sites. According to our findings, protection of rangeland has resulted in higher OC and MR with no effect on the amount of TN and infiltration rate. The negative effect of this management system was a decrease in aggregate stability due to the formation of crust as a result of complete grazing exclusion. By contrast, improvement in all soil quality indicators in protected forest indicated the success of conservative management in this region.