Regulated effects of preceding crop on soil property and cultivating seedlings for Angelica sinensis on cultivated farmland

The traditional nursery approach for Angelica sinensis (Oliv.) Diels seedlings in wild alpine meadow causes serious soil erosion. In order to reveal how preceding crop regulates the soil property and affects the subsequent nursery outcome of A. sinensis seedlings, A. sinensis seedlings were cultivated in cultivated farmland with different preceding crops in Zhuoni County, Gansu Province. This region is a geo-authentic habitat for the medical plant. The soil characteristics and seedling yield were measured at the seedling cultivated stage, taking fallow as the control. The rotation crops had significant effects on soil characteristics in the subsequent field of A. sinensis seedlings. Compared with the fallow field, soil conductivity in fields with potato (Solanum tuberosum L.), oil rape (Brassica campestris L.), and broad bean (Vicia faba L.) as preceding crops was significantly decreased. The soil pH was significantly increased, while the soil pH and conductivity in highland barley (Hordeum vulgare var. nudum Hook. f.) field were both decreased. Rotation with crop significantly increased soil cation and decreased anion contents. The K⁺ content in fields with different preceding crops was arranged as highland barley > broad beans > oilseed rape > potato > fallow. Na⁺ was arranged as potato > highland barley > broad bean > rape and fallow. Cl^- was ranked as fallow > potato > highland barley > oil rape > broad bean. As the soil layer deepened, compactness increased and porosity decreased, while the water content varies with the soil layer and the preceding crop. Loose soil with high water content in 0-15 cm layer of soil was beneficial to seedling survival. Seedling numbers and yield were all significantly negatively correlated with soil conductivity and Cl^- content. The seedling yield was positively significantly related to pH and K⁺ content, but was negatively significantly related to bulk density in the 5-10 cm soil layer. Seedling numbers were significantly positively correlated with total porosity in 0-5 cm soil. The ranking of seedling yield under each preceding crop was consistent with the comprehensive assessment index, and the index ranked as broad bean (0.986) > oilseed rape (0.682) > highland barley (0.668) > potato (0.297) > fallow (0.159). Therefore, optimal preceding crop could adequately optimize soil environment in which A. sinensis seedlings rely on. Concerning acquisition strategies, improving soil property, enriching nutrient ions, promoting growth and seedling surviving, broad bean stubble was markedly superior in regulation.