Effect of acid-modified biochar on the quality of flue-cured tobacco seedlings by replacing the grass char in the floating seedling substrate

To realize the sustainable utilization of tobacco conventional seedling substrate, this study used commercial peat substrate as a control. The effects of replacing the peat matrix with phosphoric acid modified rice husk biochar were evaluated under different emergence rates, botanical properties, leaf photosynthetic characteristics, root configurations, and leaf protective enzyme activities in tobacco seedlings. The results revealed that the tobacco seedlings grew well at all stages when the acid-modified biochar replaced 50% of the peat, with an emergence rate of 97.78%, which was 10.00 percentage points higher than that of the commercial matrix. The stem height, maximum leaf area, and biomass were significantly higher than those in the commercial matrix. The root configuration parameters (total root length, surface area, the total length of the fine root system, and medium root system were maximized following the replacement of the peat (40–70%), increasing by 93.92%, 59.66%, 110.52%, and 85.33%, respective, compared to the commercial peat matrix. In summary, acid-modified biochar has great potential as a substrate for tobacco floating seedling cultivation in place of peat. High-quality tobacco seedlings can be cultivated with less than 70% of peat replaced with acid-modified biochar.