Bioscience Methods 2026, Vol.17, No.1, 43-56 http://bioscipublisher.com/index.php/bm 47 bring further significant yield increase; instead, it may cause a slight decline in yield gain due to nutrient imbalance (Shu et al., 2024). For example, a study investigated the potassium application effect within the range of 0 - 160 kg/ha, and found that the treatment of 80 kg K₂O/ha had the most significant increase in tuber yield, while 120 kg/ha and 80 kg/ha had similar yields, indicating that the yield increase effect decreases beyond the appropriate amount (Singh et al., 2017). Excessive potassium fertilizer may cause antagonistic absorption of other nutrients, leading to nutrient imbalance in the plant, thereby inhibiting further yield increase (Shu et al., 2024). Consistent with the yield trend, the commercial potato rate of sweet potatoes also rises first and then stabilizes with the potassium fertilizer dosage: Appropriate potassium application can increase the proportion of large tubers in the tubers, leading to an increase in the commercial potato rate; in extreme potassium deficiency, the proportion of small tubers is high, resulting in a low commercial rate; when the potassium fertilizer dosage is excessive, the commercial potato rate tends to stabilize or slightly decrease (Geng et al., 2024). In summary, rational application of potassium fertilizer is the key to increasing sweet potato yield and commercial potato rate, but blindly excessive application is difficult to continue increasing yield, and instead, it will reduce the input-output efficiency (Geng et al., 2024). 4.2 Response characteristics of root quantity, single potato weight and size grade distribution The application of potassium fertilizer not only affects the total yield of sweet potatoes but also alters the performance of yield components (Geng et al., 2024). Firstly, at different potassium application levels, the number of tubers per plant (root quantity) and the average weight of a single tuber show different response characteristics. The study observed that the effect of increasing potassium fertilizer on the number of tubers per plant is relatively limited, but it has a significant effect on the expansion and weight increase of individual tubers (Singh et al., 2017). Under low potassium conditions, due to insufficient nutrient supply, the development of sweet potato roots is hindered, and the weight of a single potato is significantly lower, and many small and thin tubers often appear (Liu et al., 2022). With adequate potassium supply, the expansion of roots is fully supported, and the average weight of a single potato significantly increases. In this experiment, the roots produced by the medium potassium application treatment are more coarse and plump, and the fresh weight of a single potato is significantly higher than that of the potassium-free treatment, while the number of roots does not increase significantly. The increase in yield mainly comes from the increase in the weight of a single potato. This is consistent with some research reports: after potassium application, the average size of sweet potato roots increases, while the change in the number of tubers per plant is not obvious, indicating that potassium mainly improves yield by promoting root expansion (Gao et al., 2021). Secondly, the potassium fertilizer level affects the size grade distribution of roots. When potassium is deficient, the tubers produced often have inconsistent sizes, with a high proportion of small tubers and poor shapes; moderate potassium application helps to improve the regularity of root specifications, with mostly medium and large tubers, reducing the occurrence of abnormal and small tubers, thereby increasing the proportion of commercial tubers in the yield (Geng et al., 2024). In summary, increasing potassium fertilizer input can optimize the yield composition of sweet potatoes - significantly increasing the weight of a single potato and the grade of commercial products, while the effect on the number of roots is relatively small. This further supports the conclusion that potassium is mainly responsible for improving the yield of sweet potatoes by enhancing root expansion and commercial quality. 4.3 Correlation between potassium fertilizer application rate and fertilizer utilization efficiency, and harvest index There are significant differences in fertilizer utilization efficiency and crop harvest index among different potassium fertilizer application rates (Geng et al., 2024). In terms of fertilizer utilization efficiency, moderate potassium application levels tend to achieve the highest potassium fertilizer utilization efficiency and yield increase benefits: appropriate potassium input not only meets the crop's needs but also avoids waste, maximizing the yield gain per unit of potassium fertilizer (Geng et al., 2024). In this experiment, the potassium agronomic efficiency (increase in yield per kilogram of potassium fertilizer) and potassium recovery rate of the appropriate potassium application treatment reached the highest. However, when potassium fertilizer is over-applied, due to the reduced marginal response of sweet potatoes to additional potassium, the yield increase benefit per unit
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