Abstract: A field experiment was conducted to examine the effects of different rates of chemical fertilizer nitrogen substitution by biogas slurry on rice growth (development progress, plant height dynamic, population dynamic, and dry matter accumulation dynamic), yield, quality, and heavy metal content. The results showed that when the amount of nitrogen input was same, rice growth indices and yield first increased and then decreased with increasing rates of chemical fertilizer nitrogen substitution by biogas slurry, with rice growth indices and yield under the treatment with 70% chemical fertilizer nitrogen substitution by biogas slurry (70%Nbs) being the highest. Biogas slurry could improve rice quality. With the increases of the proportion of biogas slurry application, the contents of Cu, Zn, Pb and As in grains increased slightly, while the contents of Cd and Cr in grains decreased slightly. The contents of heavy metals in grains of all treatments were lower than the critical levels of contaminants in foods (GB 2762-2005). Compared with the treatment of chemical fertilizer application alone (Ncf), the rice growth indices in the treatment with 100% chemical fertilizer nitrogen substitution by biogas slurry (100%Nbs) decreased, with a risk of yield reduction. The treatment with 200% chemical fertilizer nitrogen substitution by biogas slurry (200%Nbs) could lead to rice lodging and yield reduction and increase the risk of secondary pollution, due to the prolonged growth duration and the increased basal internode length. Therefore, the optimal proportion of chemical fertilizer nitrogen substitution by biogas slurry was 70%, with the biogas slurry application level of 278.56×10³ kg·hm^-2.

Key words: multi-response permutation procedure, indicator species analysis, secondary forest, leaf area index, forest regeneration