Inhibition of seed germination and seedling growth of Coix lacryma-jobi L. in leachate prepared from rhizosphere soil under different continuous cropping years and concentrations

Continuous planting of Coix lacryma-jobi L. has expanded, causing yield and quality drops. A key issue is autotoxicity due to unbalanced root-microbe interactions, but this is not well understood. In this study, we hypothesized that root exudates from C. lacryma-jobi impede seed germination and young plant growth, which is exacerbated in continuous cropping systems. Autotoxicity was simulated using rhizosphere soil leachate prepared from Xingren C. lacryma-jobi cultivated for different durations to investigate the effects on seed germination and young plant growth and explore the relationship between continuous cropping and autotoxicity. Four concentrations, 0.025 (C1), 0.050 (C2), 0.100 (C3), and 0.200 g/ml (C4), and three continuous cropping years, rotation (P0), continuous cropping for 4 years (P1), and continuous cropping for 6 years (P2), were set, with distilled water as the control, totaling 13 treatments. Seed germination and young plant growth tests were conducted. The results showed that the rhizosphere soil leachate significantly affected seed germination and young plant growth depending on continuous cropping years and leachate concentration. The inhibitory effect of P2 at C4 was the strongest. The synthesis effect (SE) of the rhizosphere soil leachate under different continuous cropping years and concentrations was P2 < P1 < P0, C1 < C2 < C3 < C4. The research results reveal key factors contributing to continuous cropping obstacles and provide a scientific basis for developing sustainable agricultural strategies. This will help increase crop yields in C. lacryma-jobi planting areas, improve soil health, and promote the development of more resilient agricultural systems.