Resistance to Pulling Seedlings Out of the Nursery Container

An important issue in container nurseries is the production of seedlings of appropriate quality. These seedlings must meet specific biometric parameters and possess traits that ensure their suitability for later use in forest cultivation. One such traitis the ease of pulling the seedling out of the container cell, characterized by the pulling resistance. This resistance depends on many factors, including theseedling parameters, substrate, and container. In this work, a prototype measuring station was used to record seedling pull-out resistance as a function of their vertical displacement. Tests were conducted on 30 seedlings of each species: pine, beech, and oak. These were grown in polystyrene containers with cell volumes of 150 cm3 for pine (Pinus sylvestris L.) and 300 cm3 for beech (Fagus sylvatica L.) and oak (Quercus robur L.). Significant differences were observed in seedling extraction resistance between species, as well as between resistances associated with containers of different cell volumes. The maximum pull-out resistance of pine seedlingswas the lowest at 12.4 ± 8.58 N, followed by 22.5 ± 1.87 N for beech, and 33.5 ± 18.08 N for oak (extraction speed of 2.5 cm·s−1).Similarly, the total energy required to extract pine seedlings was 0.358 ± 0.196 J, compared to 0.502 ± 0.316 J for beech and 1.479 ± 0.774 J for oak. The pattern of pull-out resistance regardingvertical displacement was consistent across all species. A correlation was found between the maximum pull-out resistance and the total energy required to extract the seedlings, along with biometric parameters such as root collar diameter, shoot height, dry mass of seedling parts, root volume, the extent of root ball overgrowth, and the volumetric density of the substrate within the cell.These relationships should be considered when designing devices for the automatic extraction of seedlings from polystyrene containers.