Objectives Boron (B) deficiency affects the yield and quality of flue-cured tobacco. We propose an efficient B fertilizer technology for high-quality tobacco production using a response surface design model – the suitable combination of soil application and spraying of boron fertilizer in boron-deficient tobacco-growing soils.

Methods A field experiment was conducted with flue-cured tobacco variety Zhongchuan 208 as the study material, and borax was the source of boron fertilizer. Three factors and three levels of borax basal application rate (9 kg/hm², 12 kg/hm², and 15 kg/hm²), spraying concentration (0.10%, 0.25%, and 0.40%), and application period (60, 70, and 80 days after transplanting) were set, giving 16 treatments designed using software Box-Behnken. The appearance quality, chemical composition, and smoking quality of flue-cured tobacco leaves at the beginning of B2F grade were investigated. The effects of borax application rate, period, and concentration were compared using the response surface design model, and the optimal borax application method was proposed.

Results Compared with CK, under different levels of boron fertilizer treatment, the chemical composition score of tobacco leaves increased by 0.17%–11.70%, and the smoking score increased by 2.96%–10.26%. Similarly, the appearance structure, oil content, and aroma of tobacco leaves were improved. The application of boron fertilizer improved the comprehensive quality score of the upper leaves of flue-cured tobacco by 2.04%–8.40% compared with the control. The comprehensive quality score of the treatment combination with 12 kg/hm² of borax, spraying concentration of 0.25%, and the application period of 70 days after transplanting was the highest. The P-value of the response surface optimization design model based on the test results was <0.0001; the P-value of the model mismatch was >0.05, indicating that the model simulation effect was accurate and reliable. It was concluded that the upper leaves of flue-cured tobacco were affected by boron fertilizer in the order basal application rate > application period> spraying concentration. The interaction between boron fertilizer basal application rate and spraying concentration had the greatest influence on the quality score of the upper leaves of tobacco.

Conclusions Applying borax to boron deficient tobacco-growing soil could effectively improve flue-cured tobacco's appearance, smell, and comprehensive quality. According to the response surface analysis, it is best to apply 12.20 kg/hm² of borax combined with spraying at 0.26% and 67 days after transplanting.