Effects of Green Manure and Biochar on Soil Nutrients and Agronomic and Photosynthetic Characteristics of Flue-cured Tobacco

In order to explore the effects of green manure and biochar application on the physical and chemical properties of tobacco planting soil, agronomic traits and photosynthetic characteristics of flue-cured tobacco, four treatments were set up: no fertilization, conventional fertilization, conventional fertilization+33 750 kg/hm² green manure, and conventional fertilization+20 000 kg/hm² biochar. The results showed that: (1) Green manure and biochar significantly improved the physical and chemical properties of tobacco-planting soil. Compared with conventional fertilization, the soil hydrolytic nitrogen, available phosphorus and available potassium of green manure increased by 6.66%, 54.85% and 27.37%, respectively. The soil hydrolyzable nitrogen, available phosphorus and available potassium of biochar increased by 4.51%, 36.09% and 21.22%, respectively. (2) Compared with conventional fertilization, the treatment of the combined application of green manure and biochar significantly increased the plant height, stem circumference, leaf area and fresh mass of flue-cured tobacco at each growth stage. At the mature stage, the root activity of flue-cured tobacco treated with green manure was 120.42% higher than that of conventional fertilization treatment, the leaf area of tobacco plant increased by 68.52%, and the fresh weight of root increased by 66.73%. The root activity of flue-cured tobacco treated with biochar was 94.68% higher than that of conventional fertilization treatment, the leaf area of tobacco plant increased by 41.96%, and the fresh mass of root increased by 41.85%. (3) The photosynthetic capacity of tobacco leaves treated with a combined application of green manure and biochar was enhanced. Compared with conventional fertilization, the net photosynthetic rate, stomatal conductance and transpiration rate of green manure treatment increased by 128.02%, 158.29% and 50.39%, respectively, and the net photosynthetic rate, stomatal conductance and transpiration rate of biochar treatment increased by 44.86%, 64.74% and 32.04%, respectively. In summary, the application of green manure and biochar significantly increased soil nutrients and promoted the development of tobacco plants, and the effect of green manure was better than that of biochar. However, the effect of this measure on the quality of tobacco leaves needs further study.