Abstract: We examined the effects of container size and medium formula with biochar addition on the growth of Betula alnoides seedlings with three superior clones of B. alnoides (FB4, FB4⁺ and FB01) grown under three container sizes (4.5 cm×8.0 cm, 6.0 cm×9.0 cm, 8.0 cm×12.0 cm, diameter and height) and six medium formulas (different ratios of yellow soil, composted bark, sawdust, charred bark and bamboo charcoal). The optimum container size and media formula were determined by comparing seedling growth and root morphology, with a comprehensive evaluation of seedling growth. The results showed that the media formula, container size, clone and their interactions had significant effects on root collar diameter, seedling height, leaf area, leaf number, biomass, and root morphology. When considering the growth performance of all clones among different media ratios under the same medium type, the optimal growth performance occurred in the medium 4, in which the root collar diameter, seedling height, biomass, branch number, leaf area, leaf number, root length, root surface area, root volume, average root diameter were 1.01-1.36, 1.11-1.62, 1.13-2.94, 1.05-3.94, 1.05-2.86, 1.03-2.44, 1.29-2.17, 1.29-2.20, 1.32-2.44 and 1.00-1.60 times higher than those of other media formulas, respectively. With the increases of container size, root collar diameter, seedling height, leaf area, leaf number, biomass and root morphological characteristics of all clone seedlings increased, indicating that larger container facilitated seedling growth. Principal component analysis was used to analyze the growth and root morphology indexes of B. alnoidesseedlings, the results from which showed that the leaf area, root surface area, average root diameter and survival rate were comprehensive evaluation indices of seedling quality. After further calculation of the comprehensive evaluation index, the combination of clone FB4⁺, container size 3 (8.0 cm×12.0 cm) and medium 4(74.625% yellow heart soil, 24.875% bark, and 0.5% bamboo charcoal) showed the largest comprehensive evaluation index (1.566), exhibiting the strongest effects on seedling growth performance.

Key words: whole field plastic mulching, fertilizer application, potato, seasonal water consumption, yield, water use efficiency.