Development of a soil quality index for characterizing effects of land-use changes on degradation and ecological restoration of rangeland soils in a semi-arid ecosystem

The aim of this research was to study the influence of land-use changes on degradation and ecological restoration of rangeland soils by quantifying 15 soil attributes and the subsequent development of a soil quality index (SQI). Soil properties were determined to establish a minimum data set (MDS) for the development of an overall weighted additive SQI. The soil attributes were measured on samples (0 to 15 and 15 to 30-cm depths) collected in undisturbed rangelands, cultivated rangelands, and restored rangelands following cultivation abandonment for 12 or 45 years in a semi-arid ecosystem, Central Iran. The selected MDS indicators consisted of the mean weight diameter (MWD), total nitrogen (TN), microbial respiration (MR), and alkaline phosphomonoesterase activity (ALP). Overall, soil aggregation, N content, microbial activity, and ALP activity were found to be the key indicators contributing considerably to the SQI of rangeland ecosystems. Soil MWD had the highest contribution (31%) to the estimated SQI values, followed by TN (27%), MR (22%), and ALP (21%). Results indicated a clear difference in soil quality among the common land uses with a significant decline of SQI after conversion of native rangelands (0.80) to croplands (0.53). Restored rangeland soils were characterized by a higher value of SQI (0.63-0.73) as compared with cultivated rangelands (0.53). This suggests a good recovery of soil capacity and functions after the abandonment of cropping activity in previously cultivated rangelands. Vegetation restoration and plant productivity appeared to be the major driver of improved soil quality of the abandoned croplands in these rangelands. Our SQI tool could be useful to determine the success of agricultural abandonment and ecological restoration of rangeland soils in the studied semi-arid environment.