Abstract: Clarifying the effects of fertilization on plant growth of rare earth tailings can provide theoretical support for ecological management and forage production of tailings abandoned land. We investigated the responses of yield and root growth of Pennisetum purpureum ×P. americana to fertilization in tailings. There were six fertilization treatments, including control (CK), biogas slurry group (T1), cattle manure group (T2), cattle manure + biogas slurry group (T3), earthworm casts group (T4), and earthworm casts + biogas slurry group (T5). We measured the agronomic character, fresh yield, root growth indices, and analyzed the effects of different fertilization treatments on aboveground and underground indicators. The results showed that fresh yield of Pennisetum purpureum ×P. americana increased by 4.57%-1066.11% after applying organic fertilizer, and the highest fresh yield was 83.26 t·hm^-2 under T5 treatment in the second year of planting. Plant height, tiller number and stem diameter of plants in T2, T3, T4, and T5 groups were boosted (P<0.05). The application of organic fertilizer significantly increased root length, numbers of root tips and crossings (P<0.05). Root length under T5 group was the greatest and the number of crossings was the highest, being 1.79 and 2.55 times of that of CK, respectively. Root biomass of individual plant in T5 group significantly increased to 2.52 g (P<0.05). After application of organic fertilizer, root length and the number of root tips of fine roots (0-0.5 mm diameter class) were significantly increased (P<0.05), and root architecture tended to be fishtail structure. Fresh yield was correlated with root length, root biomass and the length of 0-0.5 mm diameter root (P<0.01), and with the number of 0-0.5 mm diameter root tips and topological index P<0.05). In conclusion, organic fertilizer application can improve fresh yield of Pennisetum purpureum ×P. americana and promote root growth. The combination of earthworm manure and biogas slurry is the optimal fertilization treatment for phytoremediation of rare earth tailings by Pennisetum purpureum ×P. americana.

Key words: organic fertilizer, tailings reclamation, phytoremediation, Pennisetum purpureum ×P. americana, root index