Optimal Nitrogen Fertilization for Two-Year-Old Korean Gin-seng (Panax ginseng C. A. Meyer) under shaded cultivation

Analysis showed a significant positive correlation between the steady-state net pho-tosynthetic rate (An) and N application, even in low-light conditions comparable to the forest floor (PPFD 200). The highest N level (8 g N m⁻²) yielded approximately 2.3 times the output of the 0 g N m⁻² plot. Shoot biomass and N/C accumulation also increased linearly with the fertilization rate, confirming that photosynthetic capacity is highly re-sponsive to nitrogen. Conversely, root dry weight gain decreased above 4 g N m⁻², and root N and C accumulation displayed a quadratic relationship, leveling off under high N ferti-lization conditions. This root behavior suggests an early saturation of root sink capaci-ty relative to the N-induced improvements in source capacity. Based on the balance be-tween the An‒N relationship and root carbon accumulation, the optimal N fertilization range for the 2-year-old stage is estimated to be 6–8 g N m⁻² (equivalent to 60–80 kg N ha⁻¹). This estimate is substantially lower than conventional high-concentration applications (20–30 g N m⁻²), which increase the risk of root quality deterioration and disease.
A combined solution is recommended to efficiently translocate assimilates to the roots. This involves the use of a 4 g N m⁻² basal fertilizer in conjunction with split appli-cations or foliar spraying to maintain assimilation capacity while preventing excessive N accumulation in the soil. Additionally, employing "root sink enhancement" management techniques, such as N:K = 1:2 fertilization or silicic acid spraying, is advised.