Spatial distribution of soil nutrients after the establishment of sand-fixing shrubs on sand dune

Caragana microphylla Lam., an indigenous leguminous shrub, was the dominant plant species to be used to control desertification in semi-arid Horqin Sandy Land. To elucidate the cover effect of Caragana microphylla planted for 25 years on spatial distribution of soil nutrients including C, N, P and K, soil samples were taken from four soil depths (0-5 cm, 5-10 cm, 10-20 cm, and 20-40 cm) and three slope positions (windward slope, top slope, and leeward slope). Soil nutrients under shrubs (US) and between shrubs (BS) were compared to investigate the enrichment effect of plantation. The results showed that soil nutrients except total K were significantly higher in surface soil (0-5 cm) than in deeper layer soil (P < 0.01). Significant differences were found in the contents of total organic carbon, total nitrogen, total phosphorus, and total K at different slopes. The contents of total organic carbon and total nitrogen were higher in US than in BS (P < 0.05), but pH was lower (P < 0.01). Our results indicated that the establishment of Caragana microphylla increased the accumulation of soil nutrients, and played an important role in restoring sand dune ecosystems.