Ginseng Cultivation and Soil Analysis

The sample sites were in Wendeng Dist., the Wehai City of Shandong Province, one of China's main American ginseng-producing regions. In the first year of the study, 7.5 metric tons of organic fertilizer (with an organic matter content >80%) were applied per hectare. In the following years, increasing amounts of compound fertilizer were applied per hectare: 150–200 kg in the second year, 300–400 kg in the third year, and 450–600 kg in the fourth year. The compound fertilizer used had a nitrogen, phosphorus, and potassium content >16%. This region has a northern temperate marine monsoon climate and receives an annual precipitation of ~762 mm. The plow layer in the plantation consists of gray-brown soil. In 2017, it was decided to directly sow American ginseng for 1 to 4 years in adjacent charmilles of Xishuipo Village, Dashuipo Town (122°14′07″E, 37°10′48″N, marked as Site I). For each ginseng age, four sampling points (replicates) of about 10 m² were chosen and marked for subsequent sampling.
During the spring (late May), summer (late July), and autumn (late September), at each sampling location, half-row ginsengs (6–10 individuals) were collected, and the rhizosphere soil of these ginsengs was thoroughly mixed. Some amounts of soil was stored at −80°C for DNA extraction, while the rest was air-dried for chemical analysis. The ginseng from each site collected in the summer and autumn was cleaned to calculate the disease index (DI). In the summer (July 20th) and autumn (September 20th) of 2018, the experiment was repeated in Liujiatuan Village of Zetou Town (121°51′44″E, 37°03′14″N, referred to as Site II), another town of Wendeng District. In total, 80 = 4 replications × 4 ages × [3 seasons (of 2017, Site I) + 2 seasons (of 2018, Site II)] soil samples were obtained (Supplementary Table S1).