Soil ecological stoichiometric characteristics of Medicago sativa land of mining area waste dumps

Planting of Medicago sativa has become the main ecological reconstruction model for the revegetation of waste dumps in semi-arid mining areas, owing to this plant’s strong adaptability and stress resistance. However, populations have been found to undergo premature declines during the restoration process. To determine whether M. sativa restoration in loess areas is restricted by a deficiency in soil nutrients, we selected sites that had undergone 2, 4, 6, and 10 years of restoration, along with newly dumped soil used as a control, and examined the C, N, and P contents and stoichiometric characteristics of the 0－60 cm soil layer. The results showed that the soil C, N, and P contents underwent inconsistent changes with a prolongation of the restoration period, with contents being highest after 10, 6, and 2 years, and lowest after 2, 4, and 10 years, respectively. Within the vertical soil profile, the soil C and N content generally showed a decreasing trend with soil depth. As M. sativa restoration proceeded, the C ꞉ N and C ꞉ P ratios showed a general “W”-shaped trend, whereas the N ꞉ P ratio showed a “V”-shaped trend. Both soil C ꞉ P and N ꞉ P ratios decreased with an increase an soil depth after 6 and 10 years. There was a very significant positive correlation between soil organic carbon and N and P contents (P < 0.01). Nutrients in soil of the mining area dumping ground were mainly closely related to soil organic carbon, whereas the total P content of soil was largely unaffected by other nutrients. In the semi-arid loess area, the mode of M. sativa restoration has a certain effect on restoring soil fertility. During the restoration process, plant growth is limited to varying extents by N and P deficiencies. Accordingly, to rectify this problem, we would recommend enhancing scientific fertilization management, or at least carrying out fertilization during the period between 4 to 6 years after commencing restoration.