Effects of Classification and Density Adjustment on the Morphological Attributes of Japanese Cedar (Cryptomeria japonica) Container Seedlings

Abstract

In this study, I investigated whether the sorting method of combining density adjustment and classification by height could produce Japanese cedar (Cryptomeria japonica) seedlings with a low H/D ratio (shoot height/basal diameter) and a low T/R ratio (shoot dry weight/root dry weight) after 1 year and if this could improve the yield rate (percentage of seedlings with shoot height ≥ 30 cm and basal diameter ≥ 3.5 mm to the number of cells used). Additionally, I examined the effects of sorting on the relationships between basal diameter and root dry weight, and the effects of topdressing applied to seedlings that were classified as short. I sowed in April 2019 and sorted the seedlings in August and September 2019, reducing the density according to the sorting classification. I measured the shoot height and basal diameter in November 2019, and measured shoot dry weight and root dry weight from March to June 2020. The sorting decreased both H/D and T/R ratios. The basal diameter could predict the root dry weight, but the predicted formulas differed depending on whether sorting was performed or not. During the seedling growth, sorting at least once improved the yield rate and sorting twice improved the percentage of seedlings yield and had a T/R ratio ＞ 100. The topdressing increased the T/R ratio but not the H/D ratio, and promoted shoot growth and let to an increased yield rate. These results confirmed the effectiveness of the sorting method in seedling production.