Plant species identity drives soil legacies by affecting root morphology of maize but effects depend on phosphorus supply

Aims Soil biotic legacies of leys in grassland-crop rotation systems affect growth of subsequent crops and are garnering increasing attention. We studied how different grass and legume species grown in monoculture or mixture affect the growth of the subsequent maize crop and whether the legacy effects depend on external phosphorus inputs. Methods We collected microbial inoculum from a five-year experiment with nine leys, including monocultures of two grasses and two legumes, and five legume-grass mixtures in different ratios (3:7, 4:6, 5:5, 6:4, 7:3), and conducted a greenhouse experiment to explore the biotic legacy effects conditioned by these nine leys on maize growth at three P levels (0, 20, 50 mg kg ^− 1 ). Results Significant biotic legacies on biomass of maize were only observed at high P. The biotic legacies and P application interactively impacted root morphology. Maize growth in soil conditioned by alfalfa monoculture showed stronger legacy effects by enriching beneficial bacteria and reducing accumulation of pathogenic fungi than maize growth in soil from the orchard grass monoculture. However, the effects of other monocultures and mixtures did not differ significantly. Conclusion Legacy effects on plant growth were proven to be ley-specific and depended on P input. These findings stress that biotic legacy effects interacted with external nutrient input have a significant role in determining the performance of subsequent crops.