Combined Applications of Biochar and Straw Alter Nitrogen (N) Allocation in a Manure Amended soil–tobacco Continuum System: A Field N Tracing Experiment

Replacing mineral nitrogen (N) fertilizer with manure could enhance crop yield and mitigate the adverse environmental impacts. However, there has been little investigation into the impact of adding agricultural wastes, like straw and/or biochar, into manure on soil N supply, crop N utilization and subsequent yield and quality. Methods: This study delves into the effects of supplementing manure with biochar, straw, and their combinations on tobacco biomass, total N accumulation, manure-derived N fate, N use efficiency (NUE), agronomic characteristics and quality during various growth stages. Four treatments were included: manure only (M), manure plus biochar (MB), manure plus straw (MS), and manure plus both biochar and straw (MBS). Results: Our findings indicated that adding biochar enhanced manure-N supply and accumulation in the upper leaves, alongside a significant increase in leaf numbers and maximum leaf area of tobacco, compared to the manure treatment. The MS treatment also improved the manure-N allocation from the older organs to the young organs, while resulting in more N remained in the soil. The MBS treatment was found to be most efficacious in optimizing N assimilation and allocation. This suggests that the integrated application of biochar and straw with manure could be the most advantageous practice, without compromising yield and quality. Conclusion: Integrating biochar and straw with manure aligns soil N supply with tobacco N utilization, was conducive to the sustainable management of tobacco-planting soil.