Abstract: With Artemisia sacrorum community on old field in a loess hilly region as the control, we investigated the characteristics of A. sacrorum community under artificial restoration and natural restoration after returning farmland and the effects of artificial restoration and natural restoration on soil organic matter and aggregates. The results showed that: (1) After about 20 years restoration, species number and diversity of A. sacrorum community had no significant differences between artificial restoration and natural restoration, but they were lower than those of A. sacrorum community in old field. (2) The content of soil organic matter in artificial restoration (29.68 g·kg^-1) was similar to that of old field (29.25 g·kg^-1), but significantly higher than that of natural restoration (14.34 g·kg^-1). (3) Soil aggregate indicators (water-stable large aggregates, mean weight diameter and geometric mean diameter) were all in the order as old field > artificial restoration > natural restoration. (4) Soil organic matter and aggregate indicators were positively correlated with species diversity, total number of species, the number of Compositae species, and the number of Gramineae species. In summary, after 20 years restoration, artificial restoration accelerated the improvement of aggregates and organic matter. However, taking the old field as a reference, natural restoration could result in a richer species composition and higher species diversity, and have positive effects on soil aggregates with the extension of restoration duration.

Key words: species diversity, species composition, soil property, loess hilly region.