Bioscience Methods 2026, Vol.17, No.1, 43-56 http://bioscipublisher.com/index.php/bm 48 fertilizer significantly decreases (Singh et al., 2017). This is consistent with field practice: excessive application of potassium fertilizer not only increases costs but also the excess potassium is difficult to be absorbed and utilized by the plants, resulting in a decrease in utilization rate (Shu et al., 2024). In terms of harvest index (Harvest Index, the proportion of root yield to biomass), sufficient potassium fertilizer can promote the allocation of dry matter to the roots, thereby increasing the harvest index (Gao et al., 2021). Under potassium deficiency conditions, the growth of the plant's aboveground and underground parts is unbalanced, and there may be a relative accumulation of stems and leaves while the distribution of roots is insufficient, resulting in a low harvest index; as potassium supply improves, more photosynthetic products are transported and stored in the roots, and the harvest index increases accordingly (Gao et al., 2021). Studies have reported that applying potassium fertilizer can increase the harvest index of sweet potatoes by approximately 10% or more compared to no potassium application, indicating that potassium effectively promotes the improvement of economic yield (Geng et al., 2024). However, when the potassium fertilizer reaches a high level, the increase in harvest index tends to level off, indicating that the dry matter distribution pattern of the plants has approached the optimal state (Shu et al., 2024). In summary, a reasonable potassium fertilizer application rate can achieve high fertilizer utilization efficiency and harvest index, achieving the best match between input and output; while too low or too high potassium application rates will reduce fertilizer utilization efficiency and are not conducive to the conversion of crop yield. 5 Effects of Different Potassium Fertilizer Dosages on Dry Matter Ratio and Starch Accumulation 5.1 Dynamic changes of dry matter ratio of potato tubers with growth stage/harvest stage The dry matter ratio of potato tubers is an important indicator for measuring the accumulation degree of nutrients (mainly starch and other solids) in the tubers, and it varies with the growth process and harvest period (Gao et al., 2021). In the early stage of tuber expansion, the tuber volume is small and the water content is high, so the dry matter ratio is often low; as the starch and other dry substances accumulate continuously in the later growth stage, the dry matter ratio of the tubers gradually increases and reaches the highest value close to the maturity harvest (Wu et al., 2024). The dry matter ratio of tubers in each treatment of this experiment showed a trend of increasing with the growth period, but the potassium fertilizer dosage affected the rate of its increase and the final level. Appropriate potassium application can accelerate the accumulation of dry matter in tubers in the middle and later growth stages, making the tubers reach a higher dry matter ratio at the harvest stage (Gao et al., 2021). However, insufficient potassium will limit the starch synthesis in the tubers, resulting in a slow increase in dry matter ratio and possibly remaining low at maturity (Sheng et al., 2023). Observations show that the dry matter ratio of potato tubers in the medium potassium application treatment is significantly higher than that in the no-knowledge treatment at the harvest stage, proving that adequate potassium nutrition is beneficial to increasing the final dry matter content (Geng et al., 2024). On the other hand, the dry matter ratio of potato tubers in the extreme over-application potassium treatment is close to or slightly lower than that of the appropriate treatment, indicating that excessive potassium cannot further increase the dry matter ratio (Geng et al., 2024). Thus, it can be seen that the dynamic changes of the dry matter ratio of potato tubers are dominated by the growth process and significantly influenced by the potassium fertilizer nutrition level. An appropriate potassium application strategy can promote the accumulation of dry matter such as starch in tubers at the appropriate time, thereby obtaining a higher and stable dry matter ratio at the maturity harvest. 5.2 Physiological explanation for dry matter formation: photosynthetic supply, catabolic transport and storage capacity The differences in dry matter accumulation in tubers caused by varying potassium fertilizer application rates can be explained from three aspects: photosynthetic supply, catabolic transport, and storage capacity (Gao et al., 2021). Firstly, potassium affects the supply of photosynthetic products. When potassium fertilizer is abundant, the photosynthetic efficiency of functional leaves of sweet potatoes increases, enabling the production of more organic assimilates (sugar and starch precursors), providing a continuous material basis for subsequent dry matter accumulation (Shu et al., 2024). Conversely, potassium deficiency leads to a decline in leaf photosynthetic performance, limited carbon assimilate synthesis, and a reduction in the available dry matter sources for the tubers
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