Modification of transplanting substrates for promotion of rapid root development in early growing period of tobacco

Objective Low temperatures often cause delayed and poor root system development of the transplanted tobacco seedlings. We modified the transplanting substrates to creat good water and nutrient environment in the root zone of tobacco seedlings.

Methods Tobacco pot experiment method was used for the research. The basic transplanting substrate (JYC) was made of straw, coconut coir, and grass charcoal mixture in 3∶1∶1 (v/v). On the base of JYC, potassium humate, zeolite, and both of them were added for the modification treatments (denoted as JYCK, JYCZ, and JYCZK), and the growth soil was used as control (CK). Tobacco seedlings were planted inside the transplanting cups, in which different substrates were loaded, and the transplanting cups were placed into pots filled with soil. At 10, 30, and 50 days of transplantation, soil physicochemical indicators and tobacco biomass were monitored, and at 10 and 50 days the root morphology indices were measured.

Results Compared with CK, transplanting substrates significantly increased root biomass and the root-to-shoot ratio by 48.3%−62.1% and 80.4%−114.4%, increased root length and root forks number of tobacco by 45.9%−128.9% and 52.0%−174.3%, respectively. The nitrate nitrogen and dissolved organic carbon (DOC) content in the root zone of substrates were 62.9%−147.2% and 230.3%−399.8% higher than that in CK at 50 days of transplantation. A random forest model analysis demonstrated that the transplanting substrate, soil temperature, DOC content, root length, and root tips significantly influenced the tobacco shoot biomass. Correlation analysis and structural equation model analysis further revealed that the transplant substrates directly or indirectly impact on the accumulation of tobacco shoot biomass by maintaining good nutrient and environmental conditions in the root zone, and influencing the morphology of the root system, with JYCZK performed the best, and much better than the other substrates on the above beneficial effects.

Conclusions Modification of the conventional substrate with addition of potassium humate and vermiculite achieved significant promotion effect on the root development of the tobacco seedlings, due to improved nutrition supplying capacity, relative to the conventional substrate.