Bioscience Methods 2026, Vol.17, No.1, 43-56 http://bioscipublisher.com/index.php/bm 51 6.3 Coupling relationship between sugar content, dry matter rate and starch content and quality evaluation indicators The sugar content, dry matter rate and starch content of sweet potato tubers are closely related and jointly determine the quality characteristics of the tubers (Gao et al., 2021). Generally, the higher the dry matter rate of sweet potato tubers, the higher the starch content, as starch is the main component of dry matter; at this time, the sugar content (especially free sugar) is relatively low (Sheng et al., 2023). Conversely, sweet potato tubers with high sugar content usually have lower dry matter and starch content, and have a more moist and less fibrous texture (Huang et al., 2025). Different uses of sweet potatoes have different preferences for these indicators: for fresh consumption types (such as baked sweet potatoes and steamed sweet potatoes), generally, a moderately high sugar content and acceptable dry matter content are desired to obtain a soft and sweet taste; while for processed starch sweet potatoes, high starch (high dry matter) output is pursued, with sugar content being secondary and not too high, to increase the flour yield and product quality (Geng et al., 2024). Therefore, when evaluating the quality of sweet potato tubers, it is necessary to consider both sugar content and dry matter (starch) indicators. This study found through correlation analysis that the quality indicators of sweet potato tubers are closely related to soil nutrient supply, and sufficient soil available potassium content can simultaneously improve yield and quality indicators such as sugar content, vitamins, etc. (Shu et al., 2024). This means that appropriate potassium application can achieve a balance between yield and quality. To quantitatively evaluate the differences in quality among different potassium application treatments, we constructed a comprehensive quality evaluation index, including the sugar content (total soluble sugar content), starch content and dry matter rate of the tubers, to reflect the overall edible and nutritional quality of the tubers (Geng et al., 2024). The comprehensive evaluation results show that the quality index of the treatment with moderate potassium application is the highest, indicating that under this treatment, the sugar content of the sweet potato tubers is appropriate, the starch content is sufficient, and the texture has a balance of softness and dryness. On the contrary, the quality index of the potassium fertilizer application treatments with too low or too high potassium is lower than that of the appropriate potassium application treatment (Geng et al., 2024). The former has poor quality due to insufficient accumulation of starch and sugar, while the latter may suffer from poor texture due to overly fine or dry tubers or a loss of flavor (Huang et al., 2025). Thus, by regulating the amount of potassium fertilizer application, the coupling relationship between sugar content and dry matter (starch) of sweet potato tubers can be coordinated, achieving the optimization of quality. In research and production, introducing evaluation indicators such as sugar-starch ratio and comprehensive quality index can help select the best potassium application scheme according to different usage requirements, ensuring simultaneous improvement of sweet potato yield and quality. 7 Case Study 7.1 Case background: the typical problem of high yield fluctuation and unstable sweetness in low-sodium potassium fields To further verify the above conclusion, this study selected a typical low-sodium potash-fertilization capacity field for case analysis (Geng et al., 2024). This field is located in a hilly area, with long-term low soil sodium potash content. During sweet potato cultivation, yield and quality problems frequently occur: during less favorable years, the root yield fluctuates significantly, and the rate of commercial sweet potatoes is low; at the same time, the sweetness of the sweet potato tubers is unstable, and in some years, the flavor of the sweet potatoes is weak, affecting the fresh eating taste. The investigation found that local growers are accustomed to applying large amounts of nitrogen fertilizer while neglecting potassium fertilizer input. This led to a long-term deficiency of potassium in the soil, coupled with the weak soil retention capacity (potassium is prone to leaching), and sweet potato production faced the dilemma of "too much fertilizer leads to unstable yield and poor flavor quality". The tested sweet potato varieties were local main-cultivated fresh-keeping varieties, and their high sugar content and moderate flouriness were the qualities favored by the market. However, on low-sodium potassium soil, this variety was unable to exert its expected yield potential and sweet aroma flavor, becoming a prominent problem restricting the industrial benefits (Gao et al., 2021). This case study was conducted to address this typical scenario, by scientifically applying potassium fertilization intervention, to explore feasible solutions for stabilizing the increase of sweet potato yield and root sweetness.
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