Effects of spraying potassium fertilizer with surfactant on wettability, physiology and quality indexes of flue-cured tobacco

The 'K326' flue-cured tobacco variety was used to investigate the improvement of potassium fertilizer utilization and quality of tobacco leaf under combined application of surfactant and potassium fertilizer. While in the study the contact angle method was used to determine critical surface tension of tobacco leaf, the study critical micelle concentrations of surfactants of sucrose fatty acid ester, tea saponin and washing powder were measured by using surface tension method. By spraying water and potassium fertilizer as the control, the 3 surfactants were added to potassium fertilizer in the field spraying test. In the experiment, CK was the control involving water, CK1 was the control involving potassium fertilizer, T1 was the treatment involving potassium fertilizer plus sucrose fatty acid ester, T2 was the treatment involving potassium fertilizer plus tea saponin, and T3 was the treatment involving potassium fertilizer plus washing powder. The potassium content, antioxidant enzymes activities and plastid pigments contents of tobacco leaves in 5 treatments in different times were measured, and the chemical constituents of flue-cured tobacco leaf were determined. The effects of spraying potassium fertilizer with surfactant on the wettability, physiology and quality indexes of flue-cured tobacco leaf were determined. The results indicated that:1) critical surface tension of tobacco leaf was 30.41 mN·m^-1 indicating lower wettability of tobacco leaf. The critical micelle concentrations (CMC) of sucrose fatty acid ester and tea saponin were 1 000 mg·L^-1 and 5 000 mg·L^-1, with corresponding surface tensions of 32.64 mN·m^-1 and 40.33 mN·m^-1, respectively. When washing powder concentration was 2 000 mg·L^-1, its surface tension (30.30 mN·m^-1) was close to the critical surface tension of tobacco leaf. Under the addition of surfactant, the surface tension of potassium fertilizer solution decreased significantly while the wettability increased. 2) Surfactants promoted the absorption of potassium in tobacco leaf. Potassium contents under T1 and T2 treatments were higher than under CK1 during the growth period of tobacco. Application of potassium fertilizer with surfactant increased the activities of SOD and POD and decreased MDA content in tobacco leaf. This increased antioxidant capacity of tobacco leaf and reduced membrane lipid peroxidation. Also after the addition of surfactant, chlorophyll and carotenoid contents of tobacco leaf increased at the peak function stage. This enhanced photosynthesis of tobacco leaf which in turn was conducive for the synthesis and accumulation of photosynthetic products. 3) With the addition of surfactant, the contents of total nitrogen and nicotine decreased, while those of potassium, total sugar and reducing sugar increased in flue-cured tobacco leaf. The chemical constituents were more harmonious and the quality of tobacco leaf better. In summary, the addition of sucrose fatty acid ester had the best effect in terms of improving wettability of tobacco leaf, absorption of potassium fertilizer, physiology of tobacco and quality of tobacco leaf.