Enhancing soil properties, soil-borne diseases control, and quality through selecting high C/N agricultural waste during reductive soil disinfestation for continuous tobacco cropping

The addition of organic matter is crucial for achieving successful reductive soil disinfestation (RSD) for flue-cured tobacco cultivation. However, the effects of diverse organic materials and their application rates on soil-borne disease control and yield enhancement remain poorly understood. To address this, field experiments were conducted at two sites. Two organic materials, G and D, were employed with varying application rates (CK, G/D0.8, G/D1.0, and G/D1.2). The results demonstrated that adding these organic materials enhanced soil physicochemical properties, including pH, alkaline nitrogen, available phosphorus, available potassium, organic matter, and the C/N ratio. Furthermore, the relative abundance of Phytophthora nicotianae and Fusarium spp., with associated soil-borne diseases, was significantly reduced. Particularly, the G1.2 treatment exhibited a remarkable reduction in the relative abundance of the two pathogenic bacteria by over 20% at both experimental sites. Moreover, this treatment contributed to a reduction in disease incidence by over 21% and severity by over 72%. Increasing the application rates of these organic materials also enhanced nutrient content, agronomic traits, and biomass accumulation of flue-cured tobacco plants, improving the chemical composition of tobacco leaves and economic outcomes in cured-tobacco leaves. Notably, the G1.2 treatment at both experimental sites significantly enhanced the economic indices of tobacco leaves, respectively increasing the yield and output value by 10.6 kg·ha−1 and 159.9 US$·ha−1. Overall, applying 15 t·ha−1 (G1.2 treatment) of solid organic material during RSD was the optimal choice for sterilization, elimination of harmful substances, and enhancement of the economic characteristics of flue-cured tobacco.