Study on the Inhibitory Effect of the Aqueous Extract of a Botanical Mixture on Tobacco Black Shank and Its Influence on Soil Characteristics

Research was conducted to investigate the effects of an aqueous extract of a botanical mixture on soil characteristics and inhibition to black shank. The results showed that at the concentrations of 2.5, 5 and 10 mg/mL, the aqueous extract inhibited the growth of Phytophthora nicotianac and decreased disease incidence and disease index of black shank. The aqueous extract was able to improve cation exchange capacity and electrical conductivity of the soil, increase the contents of NH₄⁺, NO₃^-, available P and available K in the soil, while decreased the content of organic matter. At the concentration of 2.5, 5 and 10 mg/mL the aqueous extract increased activity of urease, sucrase, and acid phosphatase. At 2.5 mg/mL the aqueous extract increased amounts of fungus and actinomycetes in the soil. We thus concluded that the plant aqueous extract can inhibit growth of black shank, improve the transformation of available nutrients in soil and improve the soil environment eventually.