Effect of the changing seedlings density of Quercus robur L. grown in nursery containers on their morphological traits and planting suitability

The density of seedlings in a nursery affects their growth parameters and subsequently their adaptation to the growth conditions of their planting sites. Density is especially important in the case of deciduous seedling species, such as pedunculate oak, as it significantly influences their size and leaf size during the production season. The research was conducted in 2015 and 2016 at the container nursery in Nedza (Rudy Raciborskie Forest District). The aim of the study was to investigate the effect of reduced density on the growth of pedunculate oak seedlings in Hiko V265 containers. Approximately three months after sowing in each container the seedlings were sorted into tall (TS) and short seedlings (SS). Subsequently, the TS seedlings were transferred to a new container until reaching 50% capacity. This provided double the growing space for the transplanted seedlings in the second half of the production season. Each year seedlings were analyzed at 14 dates in total in two-week intervals. During the first five dates one container was selected, and after sorting, two containers (one with TS and one with SS) were selected during the remaining nine dates. On each date seedling height, root collar diameter, the dry weight of the roots, shoots, leaves, and total seedlings were measured. Each seedling was assessed to deter- mine three indices of its breeding suitability including: sturdiness quotient (SQ), shoot-to-root ratio (S/R) and Dickson quality index (DQI). The study found that the SS seedlings that were retained in the container after sorting were on average characterized by a lower height and root collar diameter than the TS seedlings. However, by the end of the production season the SS seedlings reached the required quality class. Both the sorted seedling groups exhibited a com- parable sturdiness quotient and shoot-to-root ratio during the growth season, whereas only the TS seedlings had a higher Dickson quality index. Overall, the study results support the idea of reducing seedling density in a container during the production season by transferring the tallest seedlings to new containers. This procedure significantly increased the number of good-quality seedlings (by more than 100%) compared to the method without this process.