Effects of different vegetation on soil nutrients remediation degree in earth disposal site after 16a in mining area of Shanxi-Shaanxi-Inner Monglia adjacent region

Abstract: Shanxi-Shaanxi-Inner Monglia adjacent region is an important coal energy base, and also the most fragile ecological region in China. Recent years, the large-scale opencast mining has heavily destroyed the original landscape and ecosystem, and formed a large number of earth disposal sites. To guaranty the harmonious development of the local society, economy and ecosystem, the rapid artificial vegetation reconstruction in these sites is the key part of the local ecological restoration. To evaluate the effects of different vegetation measures in the process of land reclamation on the recovery of soil nutrient, the east earth disposal site in Heidaigou opencast coal mine located in Jungar Banner, Inner Mongolia was chosen as studying area, where the land reclamation was carried out with 7 different artificial vegetation configuration modes (Astragalus adsurgens, Stipa bungeana, Amorpha fruticosa, Robinia pseudoacacia, Hippophae rhamnoides, Poplar and Pinus sylvestris var mongolica Litv) since 1996. The recovery degrees of soil total nitrogen (TN), soil organic carbon (SOC), NO3--N and NH4+-N within 0-40 cm were studied by comparing with the nearby natural soil under 2 vegetation types (natural Stipa bungeana and natural Hippophae rhamnoides). The results showed that: 1) The content of TN, SOC, NO3--N and NH4+-N declined with the increase of the soil depth within 0-40 cm under different vegetation except the Pinus sylvestris var mongolica Litv and Astragalus adsurgens. 2) Within 0-40 cm, the contents of TN and SOC of 7 artificial vegetation types were significantly lower than the 2 natural vegetation types, and there was no significant difference between 7 artificial vegetation types and 2 natural vegetation types in NH4+-N within 0-10 and 20-40 cm. Seven vegetation types improved soil quality at different levels, and the remediation degree of Robinia pseudoacacia vegetation was better than other vegetation patterns. Average TN, SOC, NO3--N and NH4+-N within 40 cm soil depth were recovered to 44.15%, 44.65%, 85.33% and 93.77% of natural Stipa bungeana site and 56.85%, 54.82%, 84.66% and 105.70% of natural Hippophae rhamnoides site after nearly 16 years' recovery. And the remediation effects of Poplar and Pinus sylvestris var mongolica Litv were no more than 40% of the 2 natural vegetation types. The remediation effect of NH4+-N was relatively better under 7 vegetation patterns. Average NH4+-N within 40 cm soil depth was recovered to 79.50%-93.77% of natural Stipa bungeana site, and 89.47%-105.7% of natural Hippophae rhamnoides site. However, the remediation degree of TN, SOC, and NO3--N were relatively lower than NH4+-N. Average TN, SOC, and NO3--N within 40 cm soil depth had recovered to 24.70%-44.15%, 25.09%-44.65%, 47.25%-85.33% of natural Stipa bungeana site, and 33.52%-56.85%, 32.83%-54.82%, 47.18%-84.66% of natural Hippophae rhamnoides site. Although soil nutrients of 7 artificial vegetation modes in land reclamation area have not reach the natural level completely after 16 years' land reclamation, artificial vegetation is an effective measure to improve soil nutrients' recovery. Fabaceous plant vegetation (mainly Robinia pseudoacacia) was better than other vegetation patterns for soil nutrient recovery, so Robinia pseudoacacia, Hippophae rhamnoides and Stipa bungeana could be the suitable vegetation for the land reclamation in this area. The research has evaluated the soil nutrient remediation degree of different vegetation measures in the process of land reclamation and provided the theoretical basis for the vegetation measure selection during ecological restoration and land reclamation in the opencast coal mine area.