Effect of Biochar, Azotobacter and Mycorrhizal Symbiosis on Yield, Nutrient Content and Phytochemical Properties of Flue-Cured Tobacco (Nicotiana Tabacum L.)

In tobacco, chemical fertilizers are used to achieve the desired yield like other crops. In recent years, with the aim of maintaining soil fertility, improving physical and chemical properties, and creating a balance in environmental factors, the use of biofertilizers and compounds such as biochar has been considered in line with the goals of sustainable agriculture. Biochar improves soil's physical and chemical properties, increases microbial activity, and provides microorganisms with carbon, energy, and mineral elements. The positive effects of using biochar with some beneficial microorganisms can be intensified. In some studies, the effect of biochar on the abundance of arbuscular mycorrhizal fungi and the positive effects of these in increasing yield have been reported. Mycorrhizal fungi can be considered a suitable solution to improve the plant's nutritional status by absorbing nutrients and more water, decomposing soil organic matter and improving the growth and development of host plants. Mycorrhizal fungi can increase water uptake by entering very small pores that even the plant roots cannot penetrate. Applying other useful soil organisms such as Azotobacter in tobacco fields due to its ability to dissolve phosphates and produce vitamins can improve plant growth and development. Considering that no research has been done in Iran on tobacco production without chemical fertilizers, in this study, the possibility of economic production of tobacco using biofertilizers and modifying compounds such as biochar is evaluated.

This experiment was carried out as a factorial based 3×2×2 on randomized complete block design including biochar (B) at three levels (0, 4, and 8 ton/ha), mycorrhiza (M), and Azotobacter (A) at two levels (without and with application) with four replications. The seedling roots of Azotobacter-containing treatments were inoculated ten days before transplanting. Also, mycorrhiza inoculum was mixed with the soil bed in a ratio of 1 to 10. The biochar was also distributed manually on the surface of the plots and mixed with field soil by a disc. The total weight of four picks of each experimental plot was calculated as fresh yield and after curing as dry plot yield. The leaf nitrogen content was measured by the Kjeldahl method, phosphorus was measured by spectrophotometer, and the amount of absorbable potassium was measured by reading potassium ions by flame photometer. Phillips and Hayman's (1970) method was used to calculate the mycorrhizal symbiosis of the root. The nicotine and sugar content was determined using the standard method Nos. 35 and 38 of the world organization of Corseta. 

Application of 4 ton/ha biochar increased fresh yield by 11%, cured yield by 12%, the leaf nitrogen, phosphorus, and potassium content by 13, 20, and 15%, respectively, and leaf nicotine and sugar content by 18 and 24% compared to zero level. The leaf nitrogen enhanced by increasing biochar consumption level. The highest amount of leaf nitrogen was obtained at the B8. The same trend was observed in leaf phosphorus content. But in terms of potassium content, the lowest amount was obtained at B0 with 2.6% and the highest at B4 with 3%. Application of mycorrhiza inoculum increased the fresh and dry yield by 6%. The positive results of this study in the simultaneous use of biochar and mycorrhiza and Azotobacter on the mycorrhizal symbiosis can be due to the positive effect of biochar in increasing the activity of other microorganisms such as mycorrhiza or reducing the negative effects of harmful chemical compounds in soil. In this study, although using Azotobacter increased the leaf yield, this increase was not significant. Also, the Azotobacter application had a positive and significant effect on nicotine content and increased it by 32%. The application of Azotobacter can be a desirable solution to increase tobacco nicotine content. 

Due to the lack of significant differences between 4 and 8 tons per hectare of biochar on the evaluated traits in terms of economic aspects, the use of 4 tons per hectare of biochar along with the use of mycorrhiza and Azotobacter to achieve acceptable yield while maintaining chemical quality in tobacco farms is recommended.