Effects of Different Potassium Fertilizers as Substitutes for Potassium Sulfate on Potassium Utilization, Yield, and Quality of Flue-cured Tobacco

Long-term excessive application of potassium sulfate can lead to soil nutrient imbalances, acidification, and low potassium fertilizer use efficiency. It can also hinder tobacco root growth and reduce leaf combustibility, ultimately affecting tobacco leaf quality. To identify suitable potassium fertilizers for tobacco production in the Fujian tobacco-growing region, a two-year field experiment was conducted in Nanping, Fujian province, from 2022 to 2023. Potassium sulfate, the locally conventionally used fertilizer, served as the control. The study examined the effects of four types of potassium fertilizers: potassium carbonate, potassium humate, and potassium silicate on soil properties, as well as the yield and quality of flue-cured tobacco. The results of the two-year experiment showed that: (1) In terms of soil properties, the potassium carbonate and potassium silicate treatments significantly increased soil pH by 0.06 to 0.08 units, while the potassium humate and potassium silicate treatments significantly reduced the available potassium content in the soil by 25.72% to 34.19%. The potassium carbonate treatment significantly reduced soil potassium dependency compared to the CK treatment, with reductions of 12.75% and 32.35% over the two years, respectively. (2) Regarding potassium absorption and utilization in flue-cured tobacco, the potassium carbonate treatment significantly increased the potassium content in the roots (by 11.23% to 25.55%), stems (by 4.16% to 39.31%), middle leaves (by 4.35% to 9.13%), and lower leaves (by 8.27% to 8.34%), which in turn significantly enhanced total potassium accumulation (by 14.64% to 47.77%). In both 2022 and 2023, the potassium carbonate treatment had the highest apparent utilization rate of potassium fertilizer, agronomic efficiency, and potassium partial productivity, which were significantly higher than the potassium sulfate treatment by 56.65% to 184.77%, 53.85% to 83.33%, and 3.73% to 6.40%, respectively. (3) A comprehensive quality evaluation of flue-cured tobacco using the fuzzy evaluation method indicated that the potassium carbonate and potassium humate treatments achieved superior sensory quality, with an overall quality higher than that of the potassium sulfate treatment. In summary, compared to other types of potassium fertilizers, potassium carbonate performed the best in alleviating soil acidification, increasing potassium content in tobacco, improving potassium fertilizer utilization, enhancing tobacco leaf quality, and boosting yield and income. It is recommended to apply potassium carbonate instead of conventional potassium sulfate fertilizer in tobacco fields with high sulfur content in the soil and tobacco leaves.