Impacts of biochar and <italic>Trichoderma</italic> enriched bio-organic fertilizer on nitrogen using efficiency, yields and product values of flue-cured tobacco in reddish paddy fields

<bold>Objective</bold> This study aims to explore the optimal application amount of biochar and Trichoderma bio-organic fertilizer under the ‘rice-tobacco’ rotation mode in red soil area，thus providing a new path for promoting early growth and rapid development of flue-cured tobacco and increasing production value and resource efficiency. <bold>Method</bold> A field trial was conducted to investigate the optimal application rates of biochar（B）and Trichoderma enriched bio-organic fertilizer（OF）in the rice-tobacco rotation system of reddish paddy fields.The interactive effects of different application rates （0 kg/hm²，low dose（750 kg/hm²）and high dose（1 500 kg/hm²），respectively） of B and OF on the dry matter accumulation（DMA），root volume，ratio of root to shoot，partial factor productivity from chemical N fertilizer（PFP <italic>_N</italic> ），yield and the economic benefits of FCT plants were investigated. <bold>Result</bold> The interaction between B and OF significantly affected the growth，N using efficiency，yield and economic benefits of FCT.Compared with no B（B₀），applying B can increased root volume（6.6%－54.0%），DMA（2.3%－15.3%），ratio of root to shoot（8.0%－44.4%），PFP <italic>_N</italic> （3.1%－6.0%），and economic benefits（1.6%－8.3%）of FCT，respectively.The practice of applying 750 kg/hm² of biochar achieved the optimal effect.Moreover，compared with no OF（OF₀），applying 750 kg/hm² of OF significantly increased the root volume（3.5%－23.2%），DMA（5.3%－18.3%），ratio of root to shoot （8.7%－13.0%），yield（5.2%），and PFP <italic>_N</italic> （19.6%－35.5%）of FCT.However，the application of high dose of OF significantly reduced DMA by 6.01% and root volume by 7.0%－10.4% at the later growth stage of FCT.In addition，compared with no B and OF（B₀OF₀），the practices of combining B and OF replaced not onlymineral N fertilizer（15%），but also the DMA，root volume，ratio of root to shoot，yields，economic values and PFP <italic>_N</italic> of FCT exhibit varying degrees of improvements. <bold>Conclusion</bold> Therefore，the application of biochar and Trichoderma bio-organic fertilizer can not only effectively promote the dry matter accumulation and root growth of flue-cured tobacco plants，but also effectively improve the yield，average price and product value of flue-cured tobacco and the partial productivity of nitrogen fertilizer，which has important theoretical and practical application value for promoting the green production of flue-cured tobacco in red soil paddy fields.