Purpose Biogas slurry is increasingly used as crop fertilizer. Previous researches focused on the relationships between aboveground and root growth under biogas slurry application, with little attention to root exudates. The aims of this study were to investigate the influences of biogas slurry application on the quantity and composition of root exudates and their correlations with plant growth. Methods Four application levels of biogas slurry were performed according to total N of 0, 120, 240, and 480 kg ha(-1) (N0, N120, N240, and N480). The labile organic carbon (C), nitrogen (N), sugar and organic acids in root exudates were quantified at four growth stages (seedling, bolting, flowering, and ripening) of oilseed rape. Results Biogas slurry at N480 significantly increased plant height, branch height, branch number, pod number, pod length, and yield, but it had little influence on root morphology. Biogas slurry significantly decreased root C and N exudation at bolting. Organic acid exudation at bolting and flowering stages in N480 decreased by 44% and 81% compared to control, respectively. C, N exudation at bolting, organic acids at bolting and flowering stages were negatively linearly correlated with the application rate of biogas slurry. C, N, and organic acid exudation at bolting and flowering showed negatively correlations with inflorescence length, pod number and length. Conclusion Biogas slurry reduced root exudation rates and retained more C and N to improve reproductive growth, promoting the increase in yield. The results improve our understanding of the role of root exudates in plant development.
