CULTIVATION OF CONTAINERIZED SEEDLINGS IN SWEDEN - SYSTEMS FOR FROST PROTECTION AND METHODS TO DETECT ROOT INJURIES

In Sweden about 400 mill. containerized forest tree seedlings are produced in greenhouses each year. The change-over from bare root stock to containerized seedlings in Swedish forestry has involved extensive and rapid changes in methods of cultivation, handling and storage of seedlings in nurseries. Technical developments have in some cases not taken into account the biological restrictions. An example is the use of container types and storage systems which involve risks for overwintering injuries. Today, many nurseries store their seedlings out-doors on raised pallets during the winter. The paper presents a method involving a thermo-statically controlled soil heating system to protect seedlings against harmful temperatures on open land.

Apart from providing protection against frost, the heating system can be used to thaw frozen substrate in order to prevent seedlings from drying out during the spring. Technically it is possible to equip the heated bed with automatically controlled curtains for artificial night-length control or sunlight reduction. Further development could also involve a creation of an environment suitable for germination and growth of conifer seedlings.

As root damage frequently occurs when overwintering unprotected containerized seedlings, the need for reliable methods to detect injuries is of great value. Different methods have been tested and among these the following have been identified as methods of special interest for introduction in Swedish nurseries: RGC, Root Growth Capacity, - a growth test conducted in a standardized environment. TTC, Triphenyl Tetrazolium Chloride - the level of TTC-reduction indicates tissue vitality. REL, Root Electrolyte Leakage - the leakage of electrolytes from cells indicates injuries. The relevance of these methods has been tested at the Swedish University of Agricultural Sciences and results from these tests are presented.