Optimal Nitrogen Fertilization for Two-Year-Old Korean Gin-seng (Panax ginseng C. A. Meyer) under shaded cultivation
Description
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.
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During the cultivation period, SPAD values were measured five times (June 19, July 20, August 20, September 23, and October 20) using a SPAD meter (SPAD-502Plus, Konica Minolta, Tokyo, Japan). Leaf area was measured four times (July 20, August 20, September 23, and October 20). Leaf area estimation Individual leaf area was estimated non-destructively using the linear dimensions of the central leaflet, following the regression models described by Parmenter and Littlejohn [18]. For each plant, the length (L) and width (W) of the central leaflet on the compound leaves were measured. First, the area of the central leaflet (Acentral) was calculated as 0.6144 * L * W. Based on the consistent relative area ratios among the five leaflets of Panax ginseng (marginal: intermediate: central = 0.2 : 0.8 : 1.0), the theoretical total area for a single palmately compound leaf corresponds to 3.0 times the central leaflet area (3.0 * Acentral). The actual area of the compound leaf was then determined by multiply-ing this theoretical sum by the regression coefficient 1.0048. Since the 2-year-old plants used in this study possessed two compound leaves, the total leaf area per plant was ob-tained by doubling the estimated area of the single compound leaf. Photosynthetic rate measurements were conducted on July 20 using an LI-6800 portable open-system photosynthesis and transpiration measurement device (LI-COR, Lincoln, NE, USA). Light response curves were created by setting four levels of Photosyn-thetic Photon Flux Density (PPFD): 0, 50, 100, and 200 µmol m⁻² s⁻¹. The steady-state net photosynthetic rate (An) measured at a PPFD of 200 µmol m⁻² s⁻¹ served as the representa-tive value for regression analysis against the fertilization rate. The final harvest survey was conducted on November 4. All plants in each plot were excavated and separated into shoot (above-ground) and root (underground) parts. Shoots were oven-dried at 80°C for 48 hours before measuring dry weight. Roots were carefully cleaned of soil prior to fresh weight measurement and were then divided into main and lateral roots, with root length and maximum root diameter measured using calipers. After measurement of these traits, roots were oven-dried in a manner similar to the shoots to determine dry weight.
Institutions
- Shimane UniversityShimane, Matsue